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Production Engineering Thesis
2020-03-16
Quality Analysis in Production and
Operation of Transformers: the Case of
Tatek Transformer Factory
Girmay, Hailemariam
http://hdl.handle.net/123456789/10428
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BAHIR DAR UNIVERSITY
BAHIR DAR INSTITUTE OF TECHNOLOGY
SCHOOL OF RESEARCH AND GRADUATE STUDIES
FACULTY OF MECHANICAL AND INDUSTRIAL ENGINEERING
Thesis on: - Quality Analysis in Production and Operation of
Transformers: the Case of Tatek Transformer Factory
By:- Hailemariam Girmay
A thesis Submitted to Bahir Dar Institute of Technology
Presented in partial Fulfillment of the Requirements for the Degree of Masters of Science
in Production Engineering and Management in the (Industrial Engineering Stream)
Advisor. Dr. Ing. Ephrem Gidey
Bahir Dar, Ethiopia
Dec-2018
ii
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Declaration
I hereby declare that the work which is being presented in this thesis entitled
―Quality Analysis in Production and Operation of transformers: in the case of Tatek-
Transformer factory.‖ is original work of mine, has not been presented for a degree in
any other university and all the resources or materials used for this thesis have been duly
acknowledged.
Hailemariam Girmay Date
This is to certify that the above declaration made by the candidate is correct to the best of
my knowledge.
Dr.Ing. Ephrem Gidey Date (Advisor)
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
ACKNOWLEDGEMENT
First and foremost, thanks to my friends and colleagues of Ethiopian Electric Utility
(EEU) for giving me the strength, ability and patience to start and complete this
research study.
Next, I would like to thank my advisor Dr. Ephrem Gidey for his follow up,
forwarding crucial documents and comment during process guidance and
insightful comments through this thesis and throughout my time here.
I would also wish to thank my friend Kassa, in charge of Energy portfolio and logistic
head in EEU for his encouragement, supporting me by providing software and
relevant documents with respect to this research and throughout the course of the
study.
Special thanks goes again to EEU staffs for providing me with the necessary
resources and materials. Thanks to Mr. Tesfaye Alemayehu and Mengstu Aseres,
both form Quality Assurance and Quality control team, Abadi Gebrehiwot from
Energy Management, Demeke Tsehay and Kasaye heads of wire business
(Distribution) EAAR and SAAR respectively. I would also like to thank Mrs.
Sirgut Mitiku, in charge of EHS, Health and Quality department executive
secretary for preparing and arranging and editing my document in every stage
ofthis thesis process.
Thanks are also due to my family and friends who have always been by my side to
support and encourage me and for bearing with me.
Hailemariam Girmay
Dec-2018, Addis Ababa
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Contents
TABLE OF CONTENTS
Page ACKNOWLEDGEMENT i
Table of Content ii
List of Figures iv
List of Tables v
ACRONYMS vi
Abstract vii
CHAPTER ONE ............................................................................................................................. 1
1.INTRODUCTION ....................................................................................................................... 1
1.1 BACKGROUND OF THE STUDY................................................................................................. 2
1.2. STATEMENT OF THE PROBLEM ............................................................................................... 3
1.3. OBJECTIVES OF THE STUDY.................................................................................................... 3
1.3.1 General objective ............................................................................................................ 3
1.3.2 Specific Objectives ......................................................................................................... 3
1.4 SCOPE AND LIMITATIONS OF THE STUDY ................................................................................ 4
1.5 SIGNIFICANCE OF THE STUDY .................................................................................................. 4
2.0 LITERATURE REVIEW ......................................................................................................... 6
2.1.2. LOAD CHECKING................................................................................................................. 8
2.1.3. Protection system Failure................................................................................................... 9
2.1.4 SHORT CIRCUIT EXPOSURE ............................................................................................... 10
2.1.5. Un balanced loading and earth fault protection 11
2.1.6 Installation components and work man ship quality 12
2.1.7 Preventive maintenance schedule and consistency replacement of aged
transformers 12
2.1.8 RISK MITIGATION PLAN AND PREVENTION MECHANISM .........................................
2.1.9 Job quality Controlling procedure
............ 13
14
2.3 Testing in Distribution Transformers 16
2.3.1 Manufacturing quality 17
2.3.2 Quality Production Certification 17
2.3.3 Routine Test 17
2.3.3.1 Separate Source Test
19
2.3.3 2. Induced over voltage test 20
2.3.3 3. Measurement of the no load loss and no load current 20
2.3.3. 4. Measurement of the winding resistance 20
ii
2.3.3.5 Measurement of the load loss and impedance voltage
20
2.3.3. 6. Measurement of voltage ratio and vector grouping 20
2.3.3.7. Measurement of the insulation resistance 20
3. RESEARCH METHODOLOGY.............................................................................................. 25
3.1 Research Design 23
3. 2 Data Collection 28
3.3 Research analysis 29
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
4. DATA COLLECTION AND ANALYSIS ............................................................................... 30
4.1 DATA COLLECTION ............................................................................................................. 30
4.2. Pareto Analysis for the supplied transformers 42
4.3. Primary Data form site 55
4.3.2. EEU's central region 55
4.3.3. EEU's North Addis Ababa 56
4.3.4. EEU's West Addis Ababa Region 58
4.3.5. Site investigation is east Addis Ababa region of the utility 60
4.4. Summary findings on site 62
4.5. Operation proceduie 63
CHAPTER FIVE
5. CONCLUSION AND RECOMMENDATION ................................................................... 64
5.1 Conclusion .............................................................................................................................. 64
5.2 Recommendations:……………………………………………………………………….… 65
REFERENCE
Annex
iii
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
List of Figures
Fig 2.1 index age of transformers--------------------------------------------------------------------------16
Fig: 2.2. Literature of Cause and effect diagram-------------------------------------------------------23
Fig: 2.3. Standard graph of Pareto------------------------------------------------------------------------24
Fig 4.2: Insulation resistance test in MV and LV ------------------------------------------------------31
Fig 4.3 Test between MV and Ground-------------------------------------------------------------------32
Fig 4.4: Test between LV and Ground-------------------------------------------------------------------32
Fig 4.5. Winding resistance test---------------------------------------------------------------------------33
Fig 4.6: Voltage ratio test---------------------------------------------------------------------------------34
Fig 4.7: No load loss and no load current test----------------------------------------------------------36
Fig 4.8: Load test impedance voltage--------------------------------------------------------------------37
Fig 4.9: Separated source power frequency test-------------------------------------------------------38
Fig 4.10: Induced over voltage with stand test---------------------------------------------------------38
Figure:-4.11 SPSS result of pareto chart of failed transformers KVA------------------------------43
Figure. 4.12 Progress of failure transformer based on year -----------------------------------------43
Fig 4.13 Total supplied and failed transformers ------------------------------------------------------45
Fig 4.14 Annual Failure progress -----------------------------------------------------------------------46
Fig 4.15 Failure rate states based on kVAs-------------------------------------------------------------47
Fig4:16 SPSS result of Failure reasons pareto chart-------------------------------------------------49
Fig4:17 Failure reasons in Quantity --------------------------------------------------------------------50
Fig 4:18 Percentage of as per the types and kinds of reasons ---------------------------------------51
Fig 4:19 Cause and Effect Diagram for Transformer failing ---------------------------------------53
Fig 4: 20 Age of METEC-EPEI's transformers -------------------------------------------------------54
Fig 4.21፡- Transformer without any protection--------------------------------------------------------57
Fig4.22 ፡- Transformer with pillar (Proper installations)---------------------------------------------58
Fig 4;23፡- Cable without sheath and cause for transformer failed and power interruption-------60
Fig 5: 1 Recommendation replacing HRC fuse with Pole mount circuit breaker -----------------67
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
List of Tables
Table: 2.1 The standard capacity value. ------------------------------------------------------------------10
Table 2.2 cable current carrying capacities-------------------------------------------------------------11
Table: 2.3. Example of Pareto data sheet ---------------------------------------------------------------23
Table:- 4.1 Routine test samples from 13/02/2010 E.C. to 23/05/2010 E.C ------------------------30
Table 4.1 Supplied Transformers Data collection-------------------------------------------------------41
Table:- 4.2 Pareto table for Addressing issues based KVA on priority------------------------------42
Table 4.3 Secondary Data of supplied VS failed transformers of 3 Historical years collected
from EEU's Procurement Department and Transformer workshop of EEU.-------------44
Table 4.4 Comparison of Annual failure rate of transformers-----------------------------------------45
Table. 4.5 Type of Transformers Failure status -------------------------------------------------------46
Table 4:6 Failed transformer failures based on kind of the fault.-------------------------------------48
Table:-4.7 Pareto table for causes of failure reasons---------------------------------------------------48
Table 4:8 Failure reasons of Distribution transformers in percentage ------------------------------50
Table 4:9 Age of the failed Transformers ---------------------------------------------------------------54
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
ACRONYMS
EEU Ethiopian Electric Utility
EEP Ethiopian Electric Power
EPEI Ethiopian power engineering industry
HV High Voltage
MV Medium Voltage
LV Low voltage
IEC International electro-mechanical Commission
SPSS Statically Package for Social Science
LPF Lighting proof fuse
RCA Root cause analysis
IEEE Institute of Electrical Electronics Engineering
ANSI American National Standard institution
JIS Japanese industrial Standard
BS British Standard
HRC High Rupturing Capacity
EAAR Eastern Addis Ababa Region
SAAR Southern Addis Ababa Region
PMCB Pole mounted Circuit Breaker
PLW Procurement Logistic & warehouse
DVDF Double Voltage Double Frequency
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Abstract
Analysis Quality in Production and Operation is a systematic standard based management
approach which targets customer satisfaction by applying product inspection on process of
production before use and on the operation during utilizing the specific product. The main
purpose of this research is to analyze Quality transformers in production and Operations in using
Transformers manufactured in Ethiopia by Tatek Transformer factory. The research covers only
transformer type of distribution oil immersed. Protection methods are considered and also there
is detailed analysis about distribution transformers in the testing, inspection and operational
failure reasons.
The Quality analysis in production and operation of distribution transformer analysis resulted
Primary data for testing and inspection within the factory, secondary data collected from the
EEU's maintenance center and site observation within the distribution network. The scientific
approach to analysis these collected data are IEC standard parameters, Pareto and cause and
effect analysis.
The study addresses 20, 940, 22 transformers are deemed in sampling for testing within the
premises of the factory the transformers, secondary data collected from EEU’s maintenance
and site observations respectively. The voltage level and the capacity in kVAs deemed for
this study are 15 and 33KVs and form 25-1250kVAs. I have received the report of 940 from
the four regions of Addis Ababa, and this secondary data reveals that, among the reasons
reported the issue of overload, lightening and unbalanced loading and earthlings fault were from
the worst to the least in terms of reason.
Over all, this study finalized and concludes that the failure rate is 9.6%, this show very high and
beyond the expectation to be. Failure rate 0.05% is the accepted rate. The manufacturer share for
damaging of transformer is 20.11% this is assured this much of transformers are found damage
before energized to the existing distribution network. This is also can happened because of
missing design test, there is no operational manual on how to loading and. The other 79.89%
share for the failing of transformer is on the Utility side; this is also because of not using
protection devices, unbalanced load, over current, improper usage of ratings and phase balance.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
CHAPTER ONE
1. INTRODUCTION
In today’s world it has become increasingly important for companies to be able to compete
on a global competitive market through producing quality and reliable products. Companies
are no longer just competing for business within their own local markets, but with
companies that reach far across the globe. [9] For companies to be able to compete on this
level they must strive to produce their products more quality and meet the expected
standards effectively and more efficiently than ever before and then other companies
engaged in the same business [10]. International electro-mechanical Commission (IEC)
Standards has been becoming increasingly popular for the competitions of standard
products [11. The same quality of using the good product is required by utility companies.
Most utility companies including EEU have to adopted best practices in installation,
operation and maintenance that have to be taken to harvest the best out of the good
transformers they purchased.[11]
Therefore, as there has to be a dynamic value adding quality production process in
manufacturers to settle their being ever market leading manufacturing companies, there
should be a best figure in using and caring for their assets and being reliable service
provider for the customers, who spend much of its expenses for expansion and
modernization than being busy in a daily replacement of failed transformers in addition to
securing its financial capability to be best place for its employees, too.
This study in particular is concerned to investigate if the frequency of failing transformers
in Addis Ababa is related to the poor quality transformers manufacturing of distribution
power transformer in Ethiopia by Ethiopian power engineering industry (EPEI) by
evaluating their product against standard quality(IEC standard 600076-1, 3, 5, 8&10.), by
conducting tests and inspections within the factory.[11]
Of course, there are believed to be more operational factors which this study is
going to reveal their level of impact in affecting their best performance desired and then
transformer is analyzed accordingly.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 1
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
1.1 Background of the Study
All across the globe, countries and corporations are facing pressure from world leaders to
produce and manage power with greater quality of transformers. In today’s world it has
become increasingly important for companies to be able to compete on a global competitive
market considering the quality product. Companies are no longer just competing for
business within their own local markets, but with companies that reach far across the globe.
[Sarah Kahn 2014] states that in the electrical equipment industry, ―globalization has
increased in this industry due largely to the following: increased international trade; foreign
takeovers of companies and joint ventures; growing global demand for industry products,
particularly in the Asia-Pacific region; the off shoring of manufacturing operations to low-
wage cost countries by industry firms; and the outsourcing of production to third parties in
low-wage cost countries.
There are several reasons studying the level of good transformer production in terms of
quality assurance during manufacturing and also insuring the good utilization working
practice in securing all type of protection and programmed servicing that the transformer
deserves during its service time.
Primary reason is, the rate of transformer failure per year in Ethiopia is large and the major
recent year supplier is EPEI and hence the root cause should be investigated to limit the rate
by taking appropriate data collected from the total supplied and number of transformers
failed during service providing within three consecutive years.
As it is clear known from the history of industrial revolution, the supply of huge amount of
energy at a very reliable and quality service is mandatory to support industrial
transformation. As part of this, making study on quality on the most electrical equipment of
which is distribution transformers is crucial.
Finally, it is clear that the cost of replacement shall be kept minimum as the country is in a
situation of vast electrification which needs a financial capability to do it by itself. This is
also what has to be addressed to minimize the replacement finance, time and human
devotion cost together with all other resource it consumes.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
1.2 Statement of the problem
The major customers of the transformers of EEU and its technical staffs usually report that
transformers supplied by EPEI were not tested properly, do not comply with standards,
some parts are not fixed properly during loading and uploading, there is no output while
energizing and one phase or two-phase line is/ are missing. Besides, some private
customers are buying transformers from overseas due to the fact that the local transformers
are not of good quality. The transformer maintenance team of EEU has reported 142
transformers were damaged from 2015 to 2017 (2008-2009E.C).To sum up, EEU stated
that the one of the main reasons for power interruption is failure of transformers. On the
other hand, the manufacturer stated that "transformers are being manufactured following
the IEC standards; the problem is not because of supply of poor quality transformers but
due to EEU’s failure in installing standard protective devices, not properly erecting and not
managing the load properly". The problem already exists, power supply is continuously
being interrupted and transformer are failing and in some cases damaged.
Therefore, this study intends investigate the quality of transformers starting from the
manufacturing process up to the operation on site in such away to indentify the root cause
of severe transformers failures and to develop and forward scientific improvement
approaches.
1.3. Objectives of the study
1.3.1 General objective
The main objective of this study is to analyze quality in production based on the IEC
standards and operation failure reasons for the transformers supplied by EPEI. so as to
come up with alternative scientific transformer operational performance improvement
approaches.
1.3.2 Specific Objectives
1. To analyze transformer production process based on the IEC standards.
2. To examine which type of quality problem belong to the utility company and which
one belong to the manufacturer or EPEI.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
3. To analyze the root cause of transformer failure
4. To develop transformer quality improvement scheme
1.4 Scope and Limitations of the study
This study exclusively focuses on Production and operation failure reasons on the
distribution transformers manufactured locally in Ethiopia by Ethiopian power Industry
Engineering (EPEI). Primary sample is taken from the factory for testing within the
factory from five production batch based on the contract signed between EEU and
EEPI. The research also covered 940 transformers which failed within three
consecutive years and were reported to EEU's maintenance department. Additionally,
some data was taken from site observation within Addis Ababa region to ensure that
the data from EEU's maintenance department reflects the realities on operation site.
The scope of this study for operation standard is mainly focused on transformers which
are installed by EEU's and are pole mounted distribution transformers and rated from
25 to 1250kVA of both 15and 33kV lines. In addition, the limitation of this study was
getting similar study done before.
1.5 Significance of the study
The share of in this theoretical knowledge of the study is such that the quality problems of
locally produced and operated transformers would be new contributions to the body of
knowledge in the area of quality of transformers. In addition, the findings would be an
important factors for the improvement of currently applied operational standards.
The findings of this research is to identify the present problems and its causes so that
provide remedy solutions and reported to the manufacturers for adhere to the international
best practices in the field. This thesis also got supportive to conduct further research to
meet the standards and operation serving on transformers. EEU and EPEI would also
benefit from this research when the findings and recommendation are put in to action. EEU
would be benefited from saving frequent interruptions, high cost for maintaining
transformers, rework to reenergize the transformer, customer and higher public
representative resentment. Customers and stakeholders also benefited from this research
power would not interrupted frequently, damaging materials or house hold used through
power supply, researchers, government, lecturers and students would also benefited from
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 4
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
for further study, calling and encourage of local and foreign investors, performing their
daily task without wastage of time and being power interruption would be a reason
respectively
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Overview to Transformer
Transformer is an electricity distribution network element which is used in transmission,
distribution systems and it is used to raise the voltage level of the generated power in to a
transmittable voltage at generation stations and reduce it in to a user friendly voltage levels
at substations and distribution lines, so that the generated energy can be used for different
purposes ranging from domestic up to medium and large industries. Based on the reason
they are fixed anywhere in the network they are classified in to two as step up and step
down transformers. [14]
The step down transformers is used for electric power distribution and sub transmission
extensions to reduce the voltage form High voltage in to distribution level and sub
transmission voltage levels. And named as Generation-transmission station transformers
and Substation -distribution transformer and distribution customer transformers. There are
several types of transformer used in the distribution system such as single phase
transformer, three phase transformer, pole mounted transformer, pad mounted transformer,
and underground transformer.[1, 12, 14]
Even though they all work based on a common principle of electromagnetic induction
joining their primary and secondary winding through a common ferromagnetic metal core,
the size of Distribution transformers are generally small compared to sub transmission and
big substation transformers. This is due to power demanded to be supplied from these
transformers and the insulation against their relatively lower voltage and the heat rejection
capacity of the oil needed to keep the insulation safe live longer, is smaller than the sub
transmission and substation transformers.[13]
Distribution transformers are commonly called by their power supply capacity and level of
their medium voltage, accordingly EEU uses distribution transformer named as 25kVA-
1250AkVA, in regard to voltage ratings.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2.2 Standard of Distribution Transformer in Operation
To minimize the risk of failure of transformers during operation utility companies develop
and follows a document known as code of practice and operation and maintenance manual
derived from other countries experience and manufacturers caution and product name
plates. And EEU has this type of document which I have used as a reference and short
listed issues which are relevant to this thesis
It is a document that includes sets of rules and regulations during performing transformer
related works like transporting loading and unloading installing and commissioning as well
as schedules and frequencies of regular preventive maintenances on the transformers so that
the transformer can deliver the desired service for the customer.
For this thesis we only focus on the operational transformers these includes
1. Lists of types ( lightening, overload, unbalance and dropout fuses) and rating of
protection devices for each KVA size of transformers in 15 and 33 KV voltage
labels
2. Installation components and work man ship quality.
3. Loading quality( load checking)
4. Preventive maintenance schedule and consistency replacement of aged transformers
5. Commissioning and job quality approval.
2.1.0. Failure reasons on distribution network
Lightening arrestor are used to protect the transformers against damage resulted from
lightening stroke. And the standard lightening protection system installation is stated in the
manual to include
Three lightening arrestors, bare copper wire with diameter of 35 sq mm and two earth rods
made of two options copper 2m or galvanized iron 3m length .
The connection has to be using factory accessories supplied with the lightening arrestor for
connecting the three arrestors with the line and the earth wire at the pole top and welding
with the earth rod and the dawn comer of the earth wire.[18]
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2.1.1 Overload and over current protection
There are two points where stated at the operation manual that should be provided over load
and over current protections these are Dropout fuse at the MV side and HRC fuses at the
LV side of the transformer terminals. Dropout fuses are intended to prevent upcoming
current trying to pass through the transformer and HRC uses are intended to prevent excess
current demand to be drawn out of the transformers.
Loading history this is the historical data recorded daily, hourly, monthly and annually by
station operators or any automation. Data sources includes the date ,time of hour of
occurrence ,the type of situation of interest( Load, Overload, short circuit, earth unbalance,
surge etc) and the magnitude or value of the issue. [7]
Beyond the above instantaneous values daily, monthly and annual values and frequency of
occurrence and much aggregate information is there so that using this recording of loading
history will to measure the time of hit by high load, lightening stroke, growth rate of the
load demand and hence determine the action that should be taken like upgrading,
rehabilitation, or select the type of detail test that should be done to a particular transformer
than suggesting all type of tests while investigating a claim of failure to transformers.
Since this is much practically an daily experiences is done in substation and transmission
system operation departments including EEP but it is expected to be done twice a year in
distribution transformers based on the inspection schedule. [1]
2.1.2. Load checking
This is removing unplanned work order issuing and unconsciously loading the transformer
over the rated standard and it also is a means of simple manually performing of loading
history data of case 5 above.
It has a number of a advantages including carefully adding new demands so that the
transformers are not overloaded, The rate of request is used to put an estimated date of up
grading or putting additional transformers nearby as rescue measure and risk mitigation
plan [1,18]. Dropout fuse and HRC have specific value defined as the capacity or rating of
the protection which varies with respect to the capacity of each transformers. They limit the
maximum current that should pass through the transformers while the transformer remains
safe.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2.1.3. Protection system Failure
The main function of the protection system is to protect the transformer from faults by first
detecting the fault and then resolving it as fast as possible.
So the failure of protection system means allowing the danger system to pass through the
transformers and looking forward to see the burn of transformers and blown out. If it
cannot fix the fault, it isolates it so that it may not damage the transformer. Protection
systems include the Buchholz protection, pressure relief valve circuitry, surge protection
and Sudden Pressure Relays, LV HRC fuse and circuit breakers.
The Surge protector protects the transformer from over voltage by allowing specific
magnitude of voltage to go to transformer and for the rest alternate route is found.This
means they are like diodes reverse biased ,they only will act as a shorted to ground line
provision (an easy way for current to pass) than passing through relatively higher
impedance terminal of the transformer connection.
Failure in surge protection causes high voltage to pass to the windings which becomes
damaged because of its effects as listed above. [5].
Moisture, heat and corrosion are the main reasons of the failure of surge protection as it
causes overheating and short circuit in it.
There are different protection systems and installation architectures that can be adopted
from world class standards in utility installation and protection system manufacturers like
ABB circuit breakers for over load and over current protection corresponding to the
designed levels of protection of transformers. Anything beyond this value is going to be
isolated from the transformer, Siemens HRC FUSES, BREAKERS and Schneider
electronics arrestors and Dropout Fuses are the most common protection devices
manufacturers [6]
To investigate health index and failure cause and modes of failure of transformers the
following issues are very important parameters together with the above [4]
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2.1.4 Short circuit exposure
This is the level of exposure of the transformer to the stated conditions of 1 and 2 above
and also the dawn stream network installation qualities to seem are going to create short
circuit sooner or later [11].
This means that any weak points at the transformer out let cable, and Distribution box
connections and opened to the rain and dust also poor LV and MV network are supposed to
be exposure to short circuit. The exposure will raise its risk to highest level when they are
not equipped with protection system.
KVA
MV (D.O fuse
element in
ampere.)
LV (HRC fuse total
sum in ampere.)
50KVA 10 60
100KVA 15 120
200KVA 20 240
315KVA 35 380
630KVA 55 750
Table 2.1 The standard capacity value is specified as follows
Above 630KVA transforms protection against over load and over current is made using
MV and LV switchgear of 75A for 800kVA MV side by 1000A LV side while up to 110A
for 1250KVA MV side and 1500A LV side
The installation of these protection devices as stated on the manual shall consider the
following qualities.
Use appropriate connectors and cable lugs, avoid lose connection, use appropriate cable
sizes (diameters as per the designed transformers capacity) and cable types.
The appropriateness of the cables and connector accessories are specified as follows.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
cable current carrying capacities
Table 2.2 cable current carrying capacities
2.1.5 . Un balanced loading and earth fault protection
The quality of connecting customer loads is determined by the equality of current passing
through each of the three windings and zero current through the neutral earthed wire. This
is done by evenly distributing customer connections throughout the routine operation of
EEU, any un balanced load will result in circulating current within the transformer if it is
not provided with neutral wire connected to the ground it will cause damage on one of the
windings and hence appropriate neutral grounding must be provided on LV side of the star
connected distribution transformer. The standard neutral grounding is stated as follows.[18]
The loading quality of DT states about the maximum amount of 80% of load that a given
transformer must be loaded and the maximum unbalanced loading that should be taken as
tolerable if higher correction action should be taken or the transformer will sooner or later
get damaged. [18]
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
The Operational manual regulation says 85% of the transformer rating shall correspond to
the load of the customer, during design stage and found unsafe if 100% and above so that
transformer capacity upgrading and/or additional transformer erecting or load shifting to the
nearby transformers are suggested as remedial actions. And 10% unbalance between the
phase currents is the maximum unbalance current and suggests load balancing tasks to be
launched if higher than 10% .[18]
It must have 2 earth rods buried 5mt apart and one neutral line from the transformer neutral
terminal is drawn and connected to the 2 earth rods before 5mt. the connection between the
neutral wire and transformer must be using factory supplied connector and the earth wire
and rod shall be welding. And no lose connection shall be observed.
2.1.6 Installation components and work man ship quality
The installation accessories and work man ship qualities are stated as
Use standard connectors and joints and creeping hand tools and dynamometer to fix
them
Avoid lose connections and missed connections
Avoid under sized wiring and overrated protection devices
Avoid uncovered terminals at the LV distribution boxes and clean any metal scraps
on the work bench. .[18]
2.1.7 Preventive maintenance schedule and consistency replacement of aged
transformers
It provides a time bounded consistent technical inspection followed by preventive
maintenance as per the investigations and suggestions during inspection
EEU has a checklist annexed with the operational manual which includes the following
important preventive measure insights. These are
Cooling oil level
Oil leakage, dust and other external maters accumulation on surface of the
transformers
LV distribution box physical condition remarks
HRC fuse rating recording column for each out going LV lines
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Line and Phase voltages measurement recording at three different loading hours
(normal, peak, off peak hours)
Phase and neutral current measurement recording at corresponding voltage
measurement recording hours
Pole support strength and uprightness remarks
Potential short circuit wiring and clearance remarks
Neutral earth and lightening protection system continuity remarks
Availability and connection of dropout fuse and arrestors remarks
Lists of recommendations on correction actions that should be approved and
commenced officially. [18]
2.1.8 Risk mitigation plan and prevention mechanism
Since transformer is a valuable asset of Utility companies it must be provided necessary
operational risk mitigation plans which should be routinely assessed and any indication of
possible occurrence of failure reason must be cleared. These activities includes, many
utility companies adopted the following specific strategies to address the predominant
causes and consequences of failure: [5]
preventive maintenance; contingency planning;standardisationprescriptive technical
specifications, quality control measures, failure point awareness and environmental.
They mean a regular at least twice a year before summer and just after summer
transformers have to be paid a visit and seen for any problem defect or need of service it
requires and must be followed by a corrective action, doing this will significantly reduce
the number of transformers failed per year.
And also during installation and weather fit and range of operations expected to meet
should be there conditioned to the local area of application, and so should be standard range
of protection devices equivalent to the standardized technical specification un like to
buying same type for a country like us with all type of world weather existence should
require higher expertise in designing specific prescription of transformers. In addition to
this quality control measures ,failure point awareness shall always be recorded and known
to further studies and understand the trend of failure and propose the solution in designing a
change in risk mitigation plan,[5,12]
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
To optimize the cost effectiveness of the preventive maintenance the task could be arranged
based on the priority number generated from the site inspection data and calculated as in
equation: PN = Severity * Occurrence * Detection [1]
The transformer core is made up of laminated sheets of Ferro magnetic material used to
provide a controlled path to guide the magnetic flux generated in the primary voltage side
of the transformer to the secondary coil so that most of the flux generated is passed through
the secondary side, too. This is meant there is minimum loss of energy during voltage
transformation, that’s why we call the capacity of the transformer ideally constant. The
core is generally not a solid bar of steel, rather a construction of many thin laminated steel
sheets or layers. This construction is used to help eliminate and reduce heating loss and
heating effects. By providing a kind of obstruction intentionally created on the eddy current
Path so that the cause of the heat is limited. It is a mechanism of voltage regulation. This
allows for variable turn ratios to be selected in discrete steps so that the voltage level of the
user is kept standard. Transformers with this mechanism obtain this variable turn ratio by
connecting to a number of access points known as taps along either the primary or
secondary winding. [12,13]
2.1.9 . Job quality Controlling procedure
This is all about sort of work flows and sequences as well as approval and corrective or
rejection and authorizing work progress based on the approved design.
EEU has a procedure that specifies sequences of procedures and delegations of power for
each department related to transformer installation and new customer connection on
existing transformers and stated as follows. .[18]
A) New transformers installation
1. New transformer installation shall pass through planning and design department to
decide the KVA size of the transformer, wiring sizes and sets of protection devices
and all lists of materials the job requires based on the Customers request
information.
2. Following the approval of the work authorization the customer is made to pay the
cost of material lists
3. The issue is then forwarded to the technician teams to commence the installation
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
4. After the team declares completion of the transformer installation the overall work
is evaluated in reference with the design and planning design before energizing.
This stage includes correction or rework if need be.
5. Following the approval of energizing he transformer is left for service.[18]
B) Customer connection request from existing transformer
EEU customer service policy and procedure regulates the following sequences of tasks
before authorizing the connection.\
1. The technician is sent to the customers’ address of service request and transformer
to conduct the following inspection and material cost estimation.
1.1.Transformer KVA size
1.2.HRC fuse size
1.3.LV cable and conductor size
1.4.The voltage and current measurement recording at different loading hours of
each out going LV feeders.
1.5.The distance of the customer service request from the transformer and distance
of meter point from the existing LV line that passes by his address.
2. The data is then received by office engineers and verify the existing transformer can
accommodate the new request immediately or after some network augmentation.
3. Lists of materials for the service and for network improvement are listed and made
the customer aware of to pay
4. After the customer pays the issue is handed over to working teams to commence the
connection.
5. The overall installation work is checked for safety and energized and declared the
job is completed.
The above controlling procedures are supposed to be strictly followed by respective offices
and task forces so that the transformers are provided with all protection devices at deserved
installation quality as well as avoid unconsciously introducing new demands to existing
transformers and potential risks of transformer damage. .[18]
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2.2.0. Age of transformers
Transformers are going to be called aged when they are found to be 20 or more under
service network for distribution transformers and 40-50 year for power transformers.
The first 2 are much related to the occurrence of the nature failure source and the last
except 8 are operational works that has to be done before the occurrence of failure
indications. Even though 3-8 are important in determining thehealth index oftransformers
as stated by [1] early age transformers show a relatively small in risk index but the
dispertion of the result as shown below indicates bad shaped and conclude that age alone
should not be taken as a measure of health index. [11]
In regard to transformer age , MR. Brian Sparling, Jacques Aubin supported their study in
titled by ―Determination of Health Index for Aging Transformers in View of Substation
Asset Optimization‖ which was published GE engineering presented to techcon in 2010 by
stating ―some interesting data has been published on its relationship to Heath Index. As in
the figure below, presented by, Hydro-Quebec, at Cigre 2008. It characterizes the
classification of health condition versus age for 2300 transformers 49 kV to 765kV. The
health condition is expressed here as a risk index leading to new a transformer in excellent
condition scoring near a zero value and aged units in bad shape score up to 45 on a scale 0-
64. Obviously, there is an upward trend, as transformer conditions tend to degrade with
time. However, there is a large dispersion of results indicating that age alone cannot be used
to assess 9 transformer conditions and should not be assigned an important weight in Health
Index determination.‖
Fig 2.1 index age of transformers
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Which means that the risk level of early age transformers is lower than the aged ones;
especially there is a sudden raise in risk index to a bad level after 20 years. But the
distribution of the population is so dispersed that it shall be considered as not a critical
measure of being a reason of raising factor for failure rate [1,11,12]
2.3 Testing in Distribution Transformers
2.3.1 Manufacturing quality
The quality of transformer as any product depends on the raw material quality, raw
material handling, production process and product handling qualities.
In view of the above parameters there are internationa standards that has to be tested and
passed as an indication of following good production process quality. The quality of the
product is blieved to be an indication of fulfilment of the above critical issues. Had it not
been the case it is impossible to get an acceptaable product specification test results. To
insure this there are many tesing s that has to be done and its result has to be seen, they
include the following [10]
2.3.2 Quality Production Certification
The common transformer standard used as the reference in Ethiopia is based on
International Electro technical Commission (IEC). However, there are also other standard
that being used like American National Standard Institutes (ANSI) or Japanese Industry
Standard (JIS) and British Standard (BS). Fit for use in Ethiopia network system. The test
can be categorized as routine test, type test and special test.[10] Ethiopia and other utility
always required Short Circuit Testing Liaison (STL) members to witness and to verify the
test during customer witness testing process.[7]
2.3.3 Routine Test
Routine test is required to be performed on every transformer produced by the manufacturer
mainly within the manufacturer’s premises. Test under routine test are namely ratio test,
winding resistance, insulation resistance, separate source voltage withstand test, induced
over potential, no load loss and load loss, short circuit impedance test. Manufacturers are
required to supply the transformer within the required losses and impedances values at all
time. [7,10]
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2.3.4 Type Test
Design test or the common named as‖ type test ― is a test which required to be done only
once for every new design made by the manufacturer by third authorized body. It is
intended to check the design characteristics. The test can be said much more destructive if
compared to the routine test. The tests are temperature rise test and impulse voltage test.
Temperature rise test is a test in which a transformer is put under full load and the
temperature of the windings and the oil are monitored as per design values. This test need
long hours and mostly take about 12 to 24 hours to perform. Impulse test is a dielectric test
in which it has to be tested to insure the transformer capability and to withstand high
voltages transient especially during lightning, switching and during fault. The transformer
needs to reduce the voltages within specific duration to the IEC standard. All of these tests
cannot be performed in Malaysia (Ethiopia)using facilities from the manufacturers high
voltage laboratory.[10,7]
2.3.5 Special Test
Special test is a test specially required by utility to be performed on a new design
transformer, like type test category. This test is conducted in the presence of the purchaser
or its representative as specified in the tender. Test fall under this category are short circuit
test, noise level test and zero sequence impedance test. Short circuit test which is a
destructive test cannot be performed in Ethiopia since the testing facility is not available.
Testing is done to test the transformer ability to withstand both thermal and dynamic effects
during short circuit. Thermal ability is demonstrated by calculation while dynamic ability is
proven through actual physical testing. Most of the time the test is performed with STL
members like CESI of Italy, KEMA of Holland, ASTA of Australia, etc. For transformer
certification and acceptance with utility in Ethiopia it is a must for the manufacturers to
pass the physical short circuit test. There are also other special test required like partial
discharge test and harmonic test but these tests only limited to special distribution
transformer used for example in oil and gas industry, factory, etc [7, 10,13]. Most of the
time EEU use IEC standards for transformers and same time IEC and Bs for other items.
Tenders given out by utility or private sectors will mostly refer to IEC standard or else
stated otherwise.
The routine test held consists of several types of tests;
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2.3.3.1. Separate source test
2.3.3.2. Induced over voltage test
2.3.3.3. Measurement of the no load loss and no load current
2.3.3.4. Measurement of the winding resistance
2.3.3.5 Measurement of the load loss and impedance voltage
2.3.3 6. Measurement of voltage ratio and vector grouping
2.3.3.7. Measurement of the insulation resistance
2.3.3.8 Separate Source Test
This test is important in testing the insulation and clearance of the HV/LV coil to
core/earth and HV coil to LV coil by using a single-phase test transformer. The test value
for HV is 15Kv33kV while for LV is 400kV: The values used to test are usually higher to
check the ability to withstand. This test is carried out for 60 sec and no short circuit
between HV to LV and other parts [10]. The calibration is performed on test circuit. The
factor Ku is calculated. The wiring is connected as per test circuit. Voltage is applied at 1.8
of rated voltage for 30 seconds. Then it would be reduced to 1.3 of rated voltage for 3
minutes. The discharge value is recorded in the report during 3 minutes period. Charge is
recorded at 90,150 and 210 seconds. The value obtained must be below 10pC.
Testing of any electrical equipment indicates the extent to which the equipment is able to
comply with a customer’s requirements. In this paper testing of distribution transformer is
considered. Manufacturers test thousands of distribution transformers at worldwide
locations each week. The primary incentive is to make sure the transformers meet
manufacturing specifications .Tests are part of a manufacturer’s internal quality assurance
program .A manufacture’s own criteria have to be fulfilled in addition to requirements
specified by customers and applicable standards, Besides, equipment of testing machineries
should calibrated within six to one year period and design test should also performed within
five years base time.. [10,13]
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2.3.3 2. Induced over voltage test
This is to test the insulation between turns of the winding (HV and LV). Three phases line
fed to the LV terminals of the transformer. Twice of rated voltage is fed at frequency of 125
Hz (433Vx2=866V –feed on LV side). Duration of this test is 48 seconds and no short
circuit between turns [10,13]. Here for Ethiopia context (400Vx2=800V –feed on LV side)
2.3.3 3. Measurement of the no load loss and no load current
The transformer is energized with rated voltage, normally feed from the LV side and the no
load loss is directly from megger Power analyzer meter. Through this test the result must be
guaranteed value. Tolerance for No Load Loss (Po) is +15% [10].
By using the DC power supply (current is controlled), the phase to phase is measured on
HV and LV side. The resistance value is determined by calculating V/I formula.
Approximately 10% of the rated current is applied on HV side and 15amp current on LV
side [7.10].
2.3.3. 4. Measurement of the winding resistance
By using the DC power supply (current is controlled), the phase to phase is measured on
HV and LV side. The resistance value is determined by calculating V/I formula.
Approximately 10% of the rated current is applied on HV side and 15amp current on LV
side [10,13].
2.3.3.5 Measurement of the load loss and impedance voltage
The LV side is short circuited; feed on HV side with 50% of the3 rated current. Losses (PL)
and impedance (ez) which determined at ambient temperature shall be corrected to
temperature 120°C by calculation. The tolerance for Load Loss (PL) is +15% and
Impedance voltage (ez) is +/- 10% [10].
2.3.3. 6. Measurement of voltage ratio and vector grouping
All connection is connected to ratio measuring device. Ratio value must not exceed the
guaranteed ratio value. The tolerance of the ratio is +/- 0.5% on the principal tap [10].
2.3.3.7. Measurement of the insulation resistance
Meggar tester is used at 2.5kV DC. The value obtained must be above 1kΩ/V [10].
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
In addition to the above, a case study was made by C. Ndungu, J.Nderu, L. Ngoo, P. Hinga
in Kenya to verify root causes of higher failure rate of Distribution transformers and
verified the following based on the local observation they made in 2017 [1] They recall
from [2] that Standard acceptable annual failure rate of transformer is 1-2% and referred
from [ 3, 4, 5 and 6] that life span of transformers larger than 100KVA is 35 while less than
100 KVA are 25 year and stated ―It is important to note that, average life expectancy of the
transformers is directly proportional to the average life of insulating materials. On steady
state power supply, harmonics and variations in frequency are the main factors that
accelerated aging of insulation materials and hence premature failure of distribution
transformers‖ and the phenomenon and their effect are Operational miss uses like poor
protection system, replacing the damaged transformer without being sure of clearing the
root cause and not performing preventive maintenances like tree trimming, sagging and
phase to phase clearance [19]
In my thesis I come up with the failure rate of transformers is 9.6% which similarly is going
to be considered high failure rate as compared to 1-2 % standard and average age of
transformers failed is less than 3 years excluding those which fail before giving any service
which is far beyond the standard life expectancy 35 for >=100KVA and 25 years for
<100KVA transformers. But I have also investigated that there is a20% initial condition
failure that EEU has to address with the manufacturer. Sever operational miss use were also
observed in Addis Ababa regions. The unbalanced loading, overloading of transformers,
totally missing of any of protection devises, and almost abandoned regular inspection and
preventive maintenances were among worsening situations towards aggravating failure rate
I observed during my survey. And hence I can say that the survival of transformers only
depends on the probability of fault occurrences. Also found similar to Kenya that EEU
transformers always get replaced after damage without insuring the root cause investigation
and clearing is done. Especially poor protection system and poor installation workmanship
resulted from negligence of cru management were among my observation that has to be
reviewed by EEU.
International journal of engineering science and research technology also has released a
publication work done by Tarini Dewangan , Miss Pragya Patel from Dr. C. V. Raman
institute of science and technology department of electrical engineering in May, 2017 on
premature distribution transformer failure prevention[25] And come up with the results of
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
their assessment as Electrical disturbances, Overloading 29.43%, Lightings Strike 17.32%,
Loose Electrical Connections, High Resistance 7.3%, Maintenance Issues, Oil
Contamination 5.91%, Moisture Ingress 4.03%, Line Surge, Other Issues 3.25% and further
recommend the failure results can be significantly reduced by doing corrective measures
against the following lists of major contributors of raising the failure rate of
transformers[25]
1) Poor earthing system, 2. Absent of lightening Arresters, 3. overloading of a transformer,
4 Lightning Surges, 5 Line Surges/External Short Circuit 6.Thief on apparatus, 7.
Consumers wrong connection 8. Poor Workmanship-Manufacturer. 9. Deterioration of
Insulation. 10. Moisture.11. Inadequate Maintenance,12 Sabotage, Malicious Mischief and
13. Loose Connection
I have used the above recommendations to be included in my check list to verify that EEU
is using them as transformer failure risk mitigation plans during my site survey and found
EEU has only included them in his code of practice and operation and maintenance
procedure but none of them were practiced as a result transformer failure is found as Due to
lightening strike 25.21%, Due to overload and over current 25.64%, due to unbalanced
loading and earth fault 29.04%, Initial condition failure 20.11% and hence in addition to the
recommendations stated in[25] I shall recommend Utility companies must develop a
procedure and continuously perform factory testing followed by on delivering tests as well
as pre commissioning tests. Last but not least EEU has to refresh its distribution team on
its’ own operational and maintenance manual that I believe has included most of cares that
should be given to transformers throughout the life time of transformers.
2.4. Cause and effect chart.
Is a tool for describing Quality of products can be Best described in production industries to
improve their products quality and production process improvements using assessment on
one or all of the following major parameters ,which have a relation with the product and
process. These are Man power, Material, Management, Machinery, Method and
Measurement. [26]
And I have used this resource I.e. cause and effect chart from the resources on the
references by optimizing the parameters that fits my investigation parameters.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Manpower
Material Machine
Effect
Method Measurement
Management
2.5. Pareto chart
Fig: 2.2. Literature of Cause and effect diagram
Pareto analysis have been used as a means of describing root causes of poor product quality
and production process by prioritizing issues in to 80 to 20 weighted percentage
contribution of effects. And as a result I have used the tool from the resource described as a
reference
Mr. Aschner have presented an example to demonstrate the purpose of pareto in priority
indexing and benefit of pareto analysis in optimization of addressing the effects of variables
Table: 2.3. Example of Pareto data sheet
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 23
Dent Scratch Hole Others Crack Stain Gap
Defects 104 42 20 14 10 6 4
Qu
an
tity
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
The result of the above table came as in the following bar graph He described the result
as,‖The quality will be improved as longer as the bar chart if we work on the defects stated
as Dent‖
120
100
80
60
40
20
0
Fig: 2.3. Standard graph of Pareto
I have used the method by optimizing the prepared my own parameters table and
values of my investigation results to show the priority of addressing the causes of failure of
transformer and also which transformer KVA sizes accounts for the major raise of failure
rate of transformers .
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
CHAPTER THREE
3. RESEARCH METHODOLOGY
3.1 Research Design
The study of this thesis focuses on analyzing Quality in production and operation,
inspection and testing of transformers within the Tatek transformers factory. It also
includes analyzing the secondary data from EEU's maintenance department damaged
transformers within two consecutive years. The analysis uses graphs presentations and
samples of pcs of transformer taken from site visit on the installed and already serving
transformers. As per the EEU and EPEI contract agreement signed on Feb, 2014 5%
samples from are batch of production exclusively set aside for testing and inspection
within the company to be analyzed with respect to the parameters of IEC 60076
standards. Investigations on transformers being observed on site and checked all
standard installation and accessories installed. Analysis done based on the required
observation and standards. For the transformers failed on operation, 940pcs reported
as failed during serving and analyzed using excel and different graphs software.
The excel and different graphs in this work begins with identifying modes of failures,
age, over load, unbalanced phases, during special events like holidays and
protective devices. Revealing underlying causes of the failure modes and
proposing appropriate remedial measures. In this respect, the excel and different
graphs study forms the background to focus on recurring failures or components
that have most significance for the reliability of transformers.
The work presented in this study is done based on IEC tasting and inspection parameters,
pareto and effect and cause and effect analysis. The Pareto anal ysis is belong to
anal ysis identify the most severe transformers, recurring and hard to detect
failures according to EEU maintenance staff opinion. In this case the staff opinion
serves to emphasize in finding remedial measures and keep the focus of the work on
failures that have strong link with the reliability of power transformers instead of
acting upon each failure regardless of their relevance. The testing and inspection
have been executed as per the IEC 60076 standards are describe based on routine
test within the factory and design test by third authorized high equipment testing center.
Routine test: test to be carried out on each job within the factory premises
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
1. Measuring of the winding Resistance
Procedures: - Use Digital multi meter to measure winding resistance,
Then, connect the two terminal ends of the meter in between the two terminal ends of R and
S, R and T, and S and T phases of the primary side windings. See the diagram of Fig 4
attached here with. The expected magnitude of winding resistance varies and depends on
the design, cross-sectional area of the winding wire, number of turns of the winding,
resistivity of the winding wire, and so on even though transformers do have the same
voltage level and KVA. Note that this happens not only for the primary windings but also
for the secondary windings. Besides, consider that the higher the KVA the lower resistance
value and vise versa. It is because
Resistance (R) = Resistivity*length
Cross-Sectional Area
From the mathematical expression, since the lower KVA transformers’ have lower cross
sectional area it implies to have the higher resistance value. Therefore the expected
measuring resistance value to be is higher than that of the transformer with the higher rated
KVA.
Similarly, repeat this procedure to measure the secondary side winding resistance. The
expected measuring resistance value to be is in milliohm.
2. Measuring of insulation Resistance
Procedures: -use the Megger of 5KV rating measuring instrument.
To get measure between MV and LV connect the two output terminals ends of the megger
to MV and LV terminals respectively. It is strongly recommended the measured value to be
nearly infinity to get the most best insulation level which assures long service life of the
transformer during operation. The supply voltage must be 5KV. See the diagram of Fig 4.1
attached here with.
3. Separate source voltage withstand test
Procedure: - Shunt the primary side and connect to the supply voltage of 38KV or 70KV
for one minute while the secondary side must be shunt with its neutral and be connected
with the ground (earthling). The expected result from this test is to withstand this over
voltage. Shunt the secondary side and connect to the supply voltage of 3KV or 8KV for one
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
minute while the primary side must be shunt and connected with the ground (earthling).
The expected result from this test is to withstand this over voltage.
4. Induced over voltage withstand (DVDF)
Procedure: -Supply the voltage for one minute to the secondary side windings of the
transformer at its double rate voltage level and double rate frequency setting the primary
side windings open. The expected result from this test is to with stand this over voltage.
5. Measurement of voltage
Procedures: - Supply the rated voltage to the primary side of the transformer when
secondary side windings are at open condition. Then, the displayed voltage ratio readings
from the meter in the laboratory must be the same as the calculated above.
6. Measurement of no load loss and Current
Procedures: - supply the rated voltage to the primary side winding setting the secondary
side open. Then, induced voltage is created on the secondary side windings so that due to
magnetic current created in the iron core which results No-Load loss is displayed on the
meter which is associated to its no-load current. The displayed value of No-load loss must
be precisely the same as the calculated value.
7. Measurement of load loss and Impedance (efficiency & Regulation)
Procedures:- supply the current source to the primary side winding until the supplied
current reaches the rated current setting the secondary side short circuit Then, due to this
current load loss is created and displayed on the meter which is associated to its impedance
voltage.
Type test: This type of test is carried out during design test up to destructive and is given
by authorized and third body. For transformer the following Design test (Type test)
executed.
1. All type tests,
2. Lighting Impulse test, and
3. Temperature test
Special test: This test measures the ability of the transformers to withstand the mechanical
and thermal stress caused by the external short circuit.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
1. Additional Impulse test
2. Measurement of Zero phase sequence impedance test
3. Measurement of acoustic noise level
4. Measurement of Harmonic of the no load current, and
5. Magnetic balance test. sense sampling
3. 2 Data Collection
The sampling data is considered as the whole sampling damaged and reported to EEU's
maintenance center. Primary and secondary data were collected from Ethiopian
power engineering transformer factory located at Tatek and from Ethiopian Electric
utility Addis Ababa regions and transformer workshop maintenance of the utility.
Primary data was collected from the factory and EEU’s Addis Ababa’s wire
business heads during site visit and Secondary data was collected from EEU’s
maintenance department. Secondary data collection began by selecting 940 transformers
which were given for maintenance from four of the Addis Ababa regions and use the
details of their history card as secondary data source and the information in the history
card were filtered to include the following points for our analysis
1. Duration of transformer failed
2. Evaluating the service life of the failed transformer
3. Cause for failure
4. Over loading
5. Unbalanced connection and Protection
The detailed secondary data is attached as annex and the table below shows the
summarized and rearranged form which is made ready for software analysis and added
special event during the date of failure like, holiday, peak hour, and rainy seasons. Data is
collected Five percent from each patch following the contract agreement between
EEU and EEPI taken for the quality analysis through testing, data collection on the
site for failure on the history of failed transformers within 2015-2018 (2008-2010 E.C)
collected for the purpose evaluating the hypothesis and recommendation purpose of
the study.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
3.3 Research analysis
The study data was analyzed based on the data collected from the factory, EEU's
maintenance center and site observations. Accordingly, the factory data is analyzed
based on the IEC standards of transformer testing and inspection whereas the data from
the maintenance centers of EEU is analyzed using the Pareto and cause and effect analysis.
For the data collected from the EEU's maintenance center it is analyzed by applying the
Pareto analysis and for the data collected from the site it analyzed based on the cause and
effect analysis.
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
CHAPTER 4
4. Data Collection and Analysis
4.1 Data collection from the factory:- The following table is primary data taken
during testing as per the IEC 60076 standards, these data are routine test or factory test
performed within Tatek Transformer factory. The methods, procedures and expected values
are mentioned under the table
NO
ITEM Description METEC
(Serial No.)
KVA
Customer Product
Year
Date (E.C)
1 New .prd(15kv/0.4 2502936 25 EEU 2010E.C 13/2/2010
2 New .prd(15kv/0.4 20002724 200 EEU 2010E.C 13/2/2010
3 New .prd(33kv/0.4 2502538 25 EEU 2010E.C 13/2/2010
4 New .prd(33kv/0.4 2502596 25 EEU 2010E.C 13/2/2010
5 New .prd(33kv/0.4 2502597 25 EEU 2010E.C 13/2/2010
6 New .prd(33kv/0.4 20001913 200 EEU 2010E.C 13/2/2010
7 New .prd(15kv/0.4 5001822 50 EEU 2010E.C 4/3/2010
8 New .prd(15kv/0.4 31503247 315 EEU 2010E.C 4/3/2010
9 New .prd(33kv/0.4 2502718 25 EEU 2010E.C 4/3/2010
10 New .prd(33kv/0.4 2502721 25 EEU 2010E.C 4/3/2010
11 New .prd(33kv/0.4 10001778 100 EEU 2010E.C 4/3/2010
12 New .prd(33kv/0.4 10001783 100 EEU 2010E.C 14/3/2010
13 New .prd(33kv/0.4 80000227 800 EEU 2010E.C 14/3/2010
14 New .prd(15kv/0.4 63001111 630 EEU 2010E.C 9/4/2010
15 New prd. (33kv/0.4 80000243 800 EEU 2010E.C 26/04/2010
16 New prd. (33kv/0.4 10001850 100 EEU 2010E.C 4/5/2010
17 New prd. (33kv/0.4 80000251 800 EEU 2010E.C 4/5/2010
18 New prd. (33kv/0.4 20001952 200 EEU 2010E.C 16/05/2010
19 New prd. (33kv/0.4 10001854 100 EEU 2010E.C 23/05/2010
20 New prd. (33kv/0.4 20001970 200 EEU 2010E.C 23/05/2010
Table:- 4.1 Routine test samples from 13/02/2010 E.C. to 23/05/2010 E.C.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 30
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Testing type and Methodology of Distribution transformers based on the IEC
standard
1. Insulation Resistance Test: -the above data are tested based on the following the
IEC standards; this activity is performed to know the insulation level in between
MV to Ground, LV to Ground, and LV to MV. The magnitude of the measuring
value is in Giga Ohm. When the magnitude of the insulation approaches to infinity
it indicates that the transformer insulation level is very efficient and reliable so that
the durability during service giving is very high. The measuring instrument to
measure insulation resistance is known as MEGGER.
Fig 4.2: Insulation resistance test in MV and LV
Expected Measuring Value = Infinity
To measure between MV and ground connect the two output terminals ends of the megger
to MV terminals and body of the transformer respectively. It is strongly r000ecommended
the measured value to be nearly infinity to get the most best insulation level which assures
long service life of the transformer during operation. The supply voltage better to be 5KV.
See the diagram of Fig 4.2 attached here with.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 31
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Fig 4.3 Test between MV and Ground
Expected Measuring Value = Infinity
To measure between LV and ground connect the two output terminals ends of the megger
to LV terminals and body of the transformer respectively. It is strongly recommended the
measured value to be nearly infinity to get the mostbest insulation level which assures long
service life of the transformer during operation. The supply voltage better to be 2.5KV -
5KV. See the diagram of Fig 4.3 attached here with.
Fig 4.4: Test between LV and Ground
Expected Measuring Value = Infinity
2. Winding Resistance test: - this test helps to identify whether the windings of each
phase for both MV and LV are equal. It means those MV windings of each phases
(R, S, T) are exactly equal with each other. Besides, those LV windings of each
phases are also equal with each other.
It can be expressed mathematically as:
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 32
Therefore,
Tap Position Voltage Level Voltage Ratio Calculated Result
5 15,750 15,750/220 71.59
4 15,375 15,375/220 69.89
3 15,000 15,000/220 68.18
2 14,625 14,625/220 66.48
1 14,250 14,250/220 64.77
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
RT + XLT , Rሰ+ XLሰ , RR+ XLR for MV side
Rተ+ XLተ , Rሰ+ XLሰ , Rr + XLr for LV side
Fig 4.5. Winding resistance test
Expected Measuring Value = Lower KVA, Higher Resistance
Higher KVA, Lower Resistance
3. Voltage Ratio Test: -it is the turn ratio of the medium voltage at different tap position
with the RMS voltage of 220vwhich is induced voltage of phase to neutral from the
secondary side.
For instance, for 15KV distribution transformer the voltage ratio mathematically expressed
as the following.
VR = Voltage level of primary side
220
Note that Transformer has +5% tolerance from its rated voltage level.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 33
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Hence, when 15KV transformer is being tested in the Laboratory the displayed result of
voltage ratio must be the same as the calculated value as shown above.
Fig 4.6: Voltage ratio test
Expected Measuring Value = 68.0105 - 75.1695
66.3955 - 73.3845
64.771 – 71.589
63.156 – 69.804
61.5315 – 68.0085
4. Vector Group Verification test: - Three phase transformer windings can be connected
several ways. For example, for 0 degree phase shift Dy0, Dd0, Yy0, for 30 degree phase
shift Yz1, Dy1, for 150 degree phase shift Yd5, Dy5, Yz5, and so on. The determination of
vector group of transformers is very crucial before connecting two or more transformers in
parallel. So, Vector Group Verification test: is an approach to identify the phase shift
(angle) difference between the primary windings and secondary windings introduced due to
that particular configuration of transformer winding connection.
If two transformers of different vector groups are connected in parallel then phase
difference exist between the secondary side windings of the transformer and large
circulating current flows between the two transformers which is very detrimental. The
Procedure and diagram is the same as Fig 4.6
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 34
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Expected Measuring Value = Depends on the connection type of MV &
LV windings.
5. No-Load loss and No-Load Current Test: - it helps to know the power dissipated or
consumed by the secondary side windings at open circuit condition when the primary side
windings are energized or supplied the rated voltage. The power consumed is from the iron
core where magnetic current is created and is known as Iron loss (I2R).
It is recommended that the iron loss to be consumed by the Iron core is not to exceed 1.5%
of the rated load current.
Therefore, when transformer is checked or tested in the laboratory the expected No-load
current must not exceed as described above.
This explanation can be expressed mathematically as shown below.
For example, for 100KVA transformer with voltage rating of 15KV,
Let the displayed reading of the
No-Load loss from the Wattmeter be: 281.51 watts
No-Load current from the Ammeter be: 1.02 Amps
Therefore, when calculating the no-load current in terms of percentage, it shows:
1.02A*100% = 0.71%
144.34A
Then the result shows that this transformer comply or satisfied the recommended value
which is <1.5%.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 35
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Fig 4.7: No load loss and no load current test
Expected Measuring Value for different ratings:
–100kVA: Po: 380W, – 160kVA: Po: 480W,
– 250kVA: Po: 750W, – 315kVA: Po: 1050W,
– 400kVA: Po: 1320W, – 500kVA: Po: 1630W, Pt(+70°C) : 5960W
Where:
– Po: the Losses without load
6. Load loss and Impedance Voltage Test: -it is also useful to know the power dissipated
or consumed by the primary side windings during being energized or supplied the rated
current at short circuit condition of the secondary side windings. The power consumed is
from the primary winding which is known as copper loss.
For example, for 100KVA transformer with voltage rating of 15KV,
Supply the current source to the primary windings until it reaches its rated current which is
3.84Amps.
Then, the displayed reading of the
Load loss from the primary wattmeter is 1282.76 watts
Displayed voltage from the voltmeter is 601.35Volts
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 36
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Therefore, when calculating the impedance Voltage in terms of percentage it shows:
Impedance Voltage = .601.35*100% = 4.01%
15,000V
Then the result shows that this transformer complies or satisfied the recommended value.
Fig 4.8: Load test impedance voltage
Expected Measuring Value for different ratings:
–100kVA: Pt(+70°C) : 1800W – 160kVA: Pt(+70°C) : 2550W
– 250kVA: Pt(+70°C) : 3120W – 315kVA: Pt(+70°C) : 4050W
– 400kVA: Pt(+70°C) : 5000W – 500kVA: Pt(+70°C) : 5960W
Where: – Pt(+70°C) : the losses with ful load at ‖ +70°C ―
7. Separate Source Power Frequency withstand test: -The main purpose of this test is to
assure the insulation level of each windings of both the primary and secondary sides to be
ok when both the primary and secondary side windings inject the high voltage of 38KV and
3KV or 70KV and 8KV for one minute for both primary and secondary respectively.
Therefore, if both primary and secondary side windings with stand the given voltage the
transformer is said to be in a reliable condition of insulation so that can give service in
operation.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 37
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Fig 4.9: Separated source power frequency test
Expected Measuring Value: With stand the given voltage with in a given period of time;
that is one minute.
8. Induced Over voltage withstand test: - The secondary side of the transformer will be
supplied 800V which is double voltage of the rated voltage at 100HZ frequency which is
double from its rated frequency keeping the primary side open. That is this test is known as
Double Voltage Double Frequency Test.(DVDF).
Fig 4.10: Induced over voltage with stand test
Expected measured value for different ratings: With stand the given voltage and frequency
within a given period time; that is 1 minute.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 38
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Summary of tests and inspections performed within the factory.
For confirming the specifications and performances of a transformer it has to go through
numbers of testing procedures. Some tests are done at manufacturer premises before
delivering the transformer. Mainly two types of transformer testing are done at
manufacturer premises- type test of transformer and routine test of transformer as per IEC
standard mentioned above
In EPEI Transformer factory case all testes of routine test performed as per the IEC 60076
standards recommendation. But, the following type testesnever performed and tests type or
prototype tests have high impact for failure in operation.
1. Dielectric tests of transformer, 2 Vector Group Verification
3. Vector Group Verification, 4 Temperature Rise test,
4. Impulse test of a transformer, 5. Tests on on-load tap-changer, and
6. Vacuum tests on tank and radiators.
The Dielectric test of transformer is generally performed in two different steps, likewise,
separate source voltage withstand test and induced voltage withstand test of transformer,
which we have discussed one by one below. This dielectric test is intended to check the
ability of main insulation to earth and between winding. If the insulation of the active parts
of the transformer with the earth is weak the transformer fails to operate.
The Vector Group of transformer is an essential property for successful parallel operation
of transformers. Hence every transformer must undergo through vector group test of
transformer at factory site for ensuring the customer specified vector group of transformer.
The phase sequence or the order in which the phases reach their maximum positive
voltages, must be identical for two paralleled transformers. Otherwise, during the cycle,
each pair of phases will be short circuited. Therefore, it is very difficult to use two
transformers in parallel without knowing the vector group.
Temperature rise test of Transformer is included in type test of transformer. In this test
we check whether the temperature rising limit of transformer winding and oil as per
specification or not. Here the test is allowed to be continued until the top oil temperature
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 39
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
rise does not vary more than 1oC per hour for four consecutive hours. The least reading is
taken as final temperature rise of the oil. This test is very useful mainly to determine and
know the transformer heat effect at peak load. It means, during operation at peak load there
will be heat developed in the windings, oil, and the tank. Therefore, if heat developed
without limit the transformer tends to be malfunction. Thereby, it is strongly recommended
the developed heat has to be at steady state condition.
Impulse test of a transformer: - Lighting is a common phenomenon in transmission lines
because of their tall height. This lightning stroke on the line conductor causes impulse
voltage. The terminal equipment of transmission line such as Power Transformer then
experiences this lightning impulse voltages. Again during all kind of online switching
operation in the system, there will be switching impulses occur in the network. The
magnitude of the switching impulses is about 3.5 times the system voltage.
Insulation is one of the most important constituents of a transformer. Any weakness in the
insulation may cause failure of transformer. To ensure the effectiveness of the insulation
system of a transformer, it must confirms the dielectric test. But the power frequency
withstand test alone cannot be adequate to demonstrate the dielectric strength of a
transformer. That is why impulse test of transformer performed on it. Both lightning
impulse test and switching impulse test are included in this category of testing. Hence,
this test is very helpful to determine how the insulation of the transformer withstand the
incoming high voltage at instant time. If it withstands the transformer is at good condition
for operation; if not it fails.
On-load tap changer testing: - The tap changer allow ratio to be increased or decreased by
fractions of a percent. Any of the ratio changes involve a mechanical movement of a
contact from one position to another. It is this contact that needs to be checked by way of its
resistance. The contact may go bad for a number of reasons.
1. Misaligned when manufactured causing insufficient surface contact. Full load
current overheats contact surface causing it to burn.
2. Current passing through contact exceeds full load rating.
3. Tap changing operation not "Make before break" creating internal arcing of contact
surface.
Tap changers are divided into two types; On-load (OLTC) and Off-load/de-energized
(DECT). The OLTC allows selection of ratio change while the transformer is in service.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 40
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
This means that the ratio of a transformer can be changed while power (current) is still
passing through it. Thereby, to protect the transformer not to be burnt due to those bad
reasons listed above it is recommended to perform on-load tap changer testing.
Vacuum tests on tank and radiators: - This test is mainly useful for the transformers
which are oil immersed type. When manufacturing the tank and its radiator if the welding
process is poor the oil of the transformer will be leaked so that it causes the minimum level
of oil in the tank, this in turn causes also the burning of the active parts of the transformer
which is the malfunction of the transformer. To protect this phenomena Vacuum tests on
tank and radiators has to be performed. All in all, these testing are very crucial and which
are determining the quality of transformer and insure the performance of transformers in
operation. Besides, insuring these test through other testing company is witnessing
transformer products being reliable and leads to compute international bid. EPEI's
transformer factory located in Tatek doesn't execute these test which is during the design or
Prototype of new products. Finally, these tests should tested for official confirmation being
the supplying locally manufacturing are reliable and Met the IEC standard. Meanwhile, not
testing during design test by other body leads for failure reasons in operation since they are
able to withstand operational effects, same phase are missing before energized due to poor
handling and the manufacturer didn't have operational manual for how to how to transport,
installed, maintained and out operate.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 41
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
4.2 Pareto analysis for the supplied transformers
SNo
Rating of
Transformer
2015
2016
2017
Total
Quantity
1 25KVA 368 1153 797 2318
2 50KVA 312 509 278 1,099
3 100KVA 412 412 742 1,566
4 200KVA 314 559 598 1,471
5 315 KVA 723 820 952 2,495
6 400KVA 38 59 30 127
7 500KVA 25 45 40 110
8 630KVA 42 118 184 344
9 800KVA 26 40 46 112
10 1250KVA 73 6 70 149
Total 2333 3721 3737 9791
Table 4.1 Supplied Transformers Data collection
Rating of
Transformer
Count
Percentage
Cumulative
Percentage
25KVA 68.00 7.23 7.23
50KVA 135.00 14.36 21.60
100KVA 260.00 27.66 49.26
200KVA
215.00
22.87
72.13
315 KVA 217.00 23.09 95.21
400KVA 4.00 0.43 95.64
500KVA 1.00 0.11 95.74
630KVA 36.00 3.83 99.57
800KVA
2.00
0.21
99.79
1250KVA 2.00 0.21 100.00
Table:- 4.2 Pareto table for Addressing issues based KVA on priority
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 42
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Figure:-4.11 SPSS result of pareto chart of failed transformers KVA
The above pareto chart indicates that transformer sizes ranging from 25KVA up to
315KVA accounts for the 80% of the failed transformers and addressing issues related to
these sizes will bring about a significant percentage reduction on transformer failure.
The above table 4.1 indicates the delivering of transformers from the METEC significantly
increased from 2015 to 2016 and kept as more as it was in 2016 even in 2017. This is
depicted as in the following graph.
4000
3000
2000
1000
0
Qty 2015GC 2016GC 2017GC
Qty
Figure. 4.12 Progress of failure transformer based on year
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 43
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Secondary Data of supplied VS failed transformers of 3 Historical years collected from
EEU's Procurement Department and Transformer workshop of EEU.
2015Gc 2016Gc 2017Gc Total Rating of
Transformer
Failure
rate
Supplied Failed Supplied Failed Supplied Failed Supplied Failed
25KVA 368 1 1153 12 797 55 2318 68 2.933563
50KVA 312 12 509 49 278 74 1099 135 12.28389
100KVA 412 22 412 98 742 140 1566 260 16.60281
200KVA 314 23 559 71 598 121 1471 215 14.61591
315 KVA 723 16 820 67 952 134 2495 217 8.697395
400KVA 38 0 59 0 30 4 127 4 3.149606
500KVA 25 0 45 0 40 1 110 1 0.909091
630KVA 42 4 118 14 184 18 344 36 10.46512
800KVA 26 0 40 2 46 0 112 2 1.785714
1250KVA 73 0 6 2 70 0 149 2 1.342282
Total 2333 78 3721 315 3737 547 9791 940
Table 4.3 Secondary Data of supplied VS failed transformers of 3 Historical years
collected from EEU's Procurement Department and Transformer workshop of EEU.
Pareto Analysis: The most frequently failed types of transformers are the 100,200, and
315kVAs. This, shows 74% percentage of failure is occurring by the 30% types of
transformers. From the above table we have observed that the numbers of transformers
failed increased from year to year since 2015. And also they were 315, 100,and 200 and
50KVA transformers which were most frequently failing transformers respectively. And
these are the transformers sizes which appear in public service except 25kva which is used
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 44
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
in ethio telecom towers. To have a clear insight how the failure of transformers and supply
are figured let us look at the following graph.
Total Supplied Vs Failed transformers
2500
2000
1500
1000
500
0
Purchased Failled
Fig 4.13 Total supplied and failed transformers
As it is indicted within the graph above, the most supplied type of the transformer is the
315kVA and the next one is also 25kVAs. The most failed is also 100kVA and 315kVA
respectively. It shows 100 and 315kVAs are most demanded transformers which mostly
requested and connected to the private and public customer loads. Besides, these types of
transformers are found being missed operational distribution standards and some of them
also connected over its capacity expected to be.
Comparison of Annual failure rate of transformers
Research covered years annual failure rate
2015G.C 3.34
2016G.C 8.46
2017G.C 14.63
Table 4.4 Comparison of Annual failure rate of transformers
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 45
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
The table above and the graph bellow show that there is no progress in reducing the failure
rate of transformers from year to year, Ruther it increased by 5.12% from 2015 to 2016 and
by 6.17% from 2016 to 2017. And the issue still remains a problem that EEU should
concern.
Annual failure Progress
20
15
10
annual failure rate
5
0
2015G.C 2016G.C 2017G.C
Fig 4.14 Annual Failure progress
The Supply demand Of EEU is increasing from year to year at almost same rate after 2016
and doesn’t seem to reduce for several years even up to this year, But the per unit failure
rate of failure of transformers should have to reduce by performing a selective intervention
on either the quality control document revision or /and operational misuse.
To made some selective criteria let us analyze the data found in the above table further up
to which type of transformers do have a per unit supply rate of failure. I.e. The ratio of
failure to purchase during these three years
Type of Transformers Failure status
KVA Failure rate
25KVA 2.933563417
50KVA 12.28389445
100KVA 16.60280971
200KVA 14.61590755
315 KVA 8.69739479
400KVA 3.149606299
500KVA 0.909090909
630KVA 10.46511628
800KVA 1.785714286
1250KVA 1.342281879
Table 4.5 Type of Transformers Failure status
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 46
%fa
ilure
rat
e o
ver
the
3 y
era
s p
eri
od
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
18
16
14
12
10
8
6
4 Failure rate
2
0
KVA
Fig 4.15 Failure rate states based on kVAs
From the above figure we can observe that the 100KVA transformers are the highest
percentage of failure in reference to the amount of 100KVA transformers supplied similarly
200,50,630,315 are the next sequentially having failure rate of next to 100KVA. This
means 16+ out of the 100 100KVA transformers fail within three years, and 14+ out of
100,200KVA transformers fail within three years 12+ out of 100 50KVA transformers fail
within three years etc. these rates are very high as compared to the ever increasing cost and
demand of transformers for new expansion
Causes of failed transformers reported analysis
I had a secondary data of the transformers failed within these three years and they include
in their history card when they return them to the work shop. And the data is filtered and
organized as in the following table. unlike the fault by the manufacturers the secondary data
collected from the Maintenance center of EEU summarized as the fault happened are due
to:-
1. Get installing without having protective device s like lightning arrestors, dropout fuses
and HRC fuses.
2. Unbalancing and grounding earthing and
3. Overloading
4. Failed to connect before connected to the existing network
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 47
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Failed transformer failures based on kind of the fault
Total failure reason for 33 and 15KV
KVA
Lightening
Unbalanced
Earth
Overload
Failed before
energized
Total
25KVA 13 15 25 15 68
50KVA 36 35 40 24 135
100KVA 70 66 73 51 260
200KVA 73 46 54 42 215
315 KVA 43 56 70 48 217
400KVA 0 3 1 0 4
500KVA 0 0 1 0 1
630KVA 2 16 9 9 36
800KVA 0 2 0 0 2
1250KVA 0 2 0 0 2
Total 237 241 273 189 940
Table 4:6 Failed transformer failures based on kind of the fault.
Reason
Count
Percentage
Cumulative
percentage
Lightening 237 25.21 25.21
Unbalanced earth 241 25.64 50.85
Overload 273 29.04 79.89
Initial condition 189 20.11 100.00
Table:-4.7 Pareto table for causes of failure reasons
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 48
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Fig4:16 SPSS result of Failure reasons pareto chart
From the above pareto chart we can see that Lightening, unbalanced earth and overloading
of the transformers accounts for 80% of failure reasons reported, and hence if we prepare
and work on mitigation plans on these issues we can achieve a significant improvement on
failures. To address the cause and effects related to our site survey and observations we
have put as in the following cause and effect chart.
The above table 4.5 shows there are 940 transformers various KVA sizes of METEC
origins failed within these three years and as depicted in the graph below most frequently
failed transformer types were 100KVA, 315KVA, 200KVA, and 50KVA transformers.
And the most reason reported as being the reason of failure is overload and unbalanced
loading followed by Lightening and initial condition problems. This means that
transformers capacity upgrade and additional transformers installation are required as a
relief of existing transformers. Furthermore the load balancing and customer network
reconfiguration are needed and also lightening protection system has to be reviewed and
correction action has to be made before every summer season.
But the failure during commissioning which is thought to have been factory error are also
seen to be significantly more in number. The relative impact shall have a significant
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 49
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
difference between other three reasons and factory error; however, they are viewed as
equally significant issues as in the next topic.
1000 900 800 700 600 500 400 300 200
0
Lightening
Unbalanced Earth
Overload
Failed before energized
Total
Fig4:17 Failure reasons in Quantity
Percentage of failure reasons as a measures of prioritizing issues
To further develop the relative strength of the issues of the four reasons reported let us see
the following summary and graphs
Failure reasons of Distribution transformers within the percentage
KVA
Lightening
Unbalanced
Earth
Overload
Failed
before
energized
25KVA 19.11765 22.05882 36.76471 22.05882
50KVA 26.66667 25.92593 29.62963 17.77778
100KVA 26.92308 25.38462 28.07692 19.61538
200KVA 33.95349 21.39535 25.11628 19.53488
315 KVA 19.81567 25.80645 32.25806 22.11982
400KVA 0 75 25 0
500KVA 0 0 100 0
630KVA 5.555556 44.44444 25 25
800KVA 0 100 0 0
1250KVA 0 100 0 0
Total average 25.21277 25.6383 29.04255 20.10638
Table 4:8 Failure reasons of Distribution transformers in percentage
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 50
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
From the table above and the graph bellow we can see that Overload accounts for 29+ % of
the failure of transformers and unbalanced loading 25.36+ % followed by 25.21% of
lightening and 20.10 % of initial condition failure.
Percentage failure of each transfomer KVA by each reason
100%
80%
60%
40%
20%
0%
Lightening Unbalanced Earth Overload Failed before energized
Fig 4:-18 Percentage of as per the types and kinds of reasons
As we can see the failure of unbalanced loading and lightening are only 5% higher than the
factory error, which means the quality of the product is seriously questionable that EEU has
to review. As we can see the failure of unbalanced loading and lightening are only 5%
higher than the factory error, which means the quality of the product is seriously
questionable that EEU has to review.
The lightening impact is seen to be significant on 200KVA and 100KVA transformers
followed by 315KVA, 50KVA and 25KVA. In this case we can also see that big size
transformers are seen to be less affected for some reason that we are going to verify it on
site investigation information.
The unbalanced load is seen to affect more of the 100KVA transformer followed by
315KVA, 200KVA and 50KVA. And we can see there is a much far less impact of
unbalanced load on big size transformers also.
When we observe the overload impact it is seen to affect most of the 315KVA transformers
followed by 100KVA, 200KVA and 50KVA transformers, similarly the big size
transformers are much less affected by overload.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 51
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
The failure of transformers during commissioning ,which means failure due to initial
conditions of the transformers were also severely observed on the 100,200,315 and 50KVA
transformers respectively followed by 25 and 630KVA transformers. This amount of
transformer failure due to initial condition is significant that must be closely investigated
especially for a company which is suffering from material shortage and financial
challenges.
Finally in 15KV transformers we can summarize that the overall failure reasons reported
have much impact on those transformers which are less than 400KVA size and greater than
50KVA.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 52
Po
or P
rocess Ex
Pro
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Cause Effect
Man Power Material Machine
Control
Supervised
Negligence
Protection device missed
Overrated
Miss use
Direct connection
Improper modification
& Re Use
Missed Testing
Procedure
Preventive
Maintenance
Construction
Improper stock
laming
Failed
transformers
O.P Manepment
Managemen
Sample quality
controle controle
PLW based on
only 5% sample
Poor imitation
quality Load checking Commissioning
Method Measurement
Fig 4.19 Cause and Effect Diagram for transformer failing
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 53
A
vera
ge s
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Age of the failed transformers
As per the literature review transformers may fail due to aging but only after 20+ years of
service. and the guarantee period is 5+ years; But in case of METEC transformers they are
all failing almost before 3 years of service to reveal this let us see the following
KVA
Average
25KVA 1.50
50KVA 1.98
100KVA 1.76
200KVA 2.43
315KVA 1.26
400KVA 2.00
500KVA 0.50
630KVA 1.32
800KVA 0.50
1250KVA 1.00
Table 4:9- Age of the failed Transformers
Excluding the failure of transformers on initial condition the earliest age failure is within
0.5 years and the oldest service year is 2.43 years this generally means transformers from
METEC are under age and within warranty period that EEU could have claimed however
their warranty period agreement is stated as one year which clearly is in need of revision.
3.00
2.50
2.00 1.50
1.00
0.50
0.00
Average
Transformer KVA
Fig 4: 20 Age of METEC-EPEI's transformers
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 54
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
For this thesis we have make use of two data sources as secondary data source which
includes number of received and purchased transformers from METEC categorized by
voltage levels and KVA size from the year 2015 up to 2017 as in the following table
Table 4.1 number 15KV and 33KV transformers inspected and purchased from METEC
since 2015 up to 2017.
4.3 Primary collected from site observation on the EEU distribution
network
I have made site observations on four of Addis Ababa regions of EEU and focusing
on the following issues
Are the transformer stations equipped enough to protect the transformers
Is the installation quality good enough to enable the protection devices’ operation
Do the regions make due care to the transformers during operation
Do the construction team conduct a site test prior to energizing the transformers
4.3.1 The protection devices and their installation status
The survey is made based on the check list I have stated at the literature review and I
come up with the following results
4.3.2 EEU’s Central Region
Debrezeit No. 1 Kebele 12:- 315KVA transformer is installed without lightning
arrestor and drop out fuse on the primary side; however, there is fuse box on the secondary
side with three HRC fuses rated 400A.
Debrezeit No. 1 Kebele 12 mwmhiranSefer:- 50KVA transformer is installed without
lightning arrestor and drop out fuse on the primary side, besides, there is no fuse connected
on the secondary side which is out going line to the customer.
Debrezeit No. 1 Kebele 12 Addis Sefer:- 315 kVA transformer is installed without
lightning arrestor and drop out fuse on the primary side, besides, there is no fuse connected
on the secondary side which is out going line to the customer and another outgoing has only
two phases with HRC fuses 200A and 300A rating.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 55
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Debrezeit No. 1 Bale Godana- 315 kVA transformer is installed without lightning arrestor
and drop out fuse on the primary side, besides, there is no fuse connected on the secondary
side which is out going line to the customer and another outgoing has HRC fuses with
300A, 300A, and 300A rating.
Debrezeit No. 1 end of No.60 Bus station:-315 kVA transformer is installed without
lightning arrestor and drop out fuse on the primary side, besides, it has three independent
out goings in which two of them in each box with 300A, 300A, 300A HRC fuse rating and
the other one has only two fuses with rating of each 200A and one phase is connected
directly.
Debrezeit No. 2 near bishoftu cliff፡- 315 kVA transformer is installed without lightning
arrestor and drop out fuse on the primary side, besides, it has three independent out goings
in which two of them are connected directly and the other one has two fuses with rating of
each 200A and one phase is with 400A rating.
Debrezeit No. 2 tajima bridge bajaj station:- 315 kVA transformer is installed without
lightning arrestor and drop out fuse on the primary side, besides, it has three independent
out goings which are connected directly and always causes for the transformer to be
burned.
4.3.3 EEU's North Addis Ababa Region
According to the information given from regional wire business head the place where
frequent power interruption occurs is Holleta District. It is because the main reasons are:
1. The substation is saturated with its peak load.This case had been informed with
official letter written on the date 02/13/2007 with reference No.054/HSC/08 to
regional head. Even though it is informed the region do not discontinue to connect
the new line for the new customers.
2. Besides, in Holleta almost all transformers are connected without any protection so
that this case also informed to regional wire business head with official letter
written on the date 10/08/2008 but no action has taken place till now instead the
activity to connect the new line to the new customers still is ongoing.
During surveillance of transformers within the Holleta district the Quality office
observed the followings:
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 56
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Mehal Ketema 44:- Near Birhan Bank 630 kVA transformer is installed without lightning
arrestor and drop out fuse on the primary side, besides, the outgoing of the secondary side
is connected directly.
Fig 4.21፡- Transformer without any protection
1. AddisuGebeya 315 kVA transformer is installed without lightning arrestor and drop
out fuse on the primary side, besides, the outgoing of the secondary side is
connected directly.
2. In front of Gottera School: - 200 kVA transformer is installed without lightning
arrestor and drop out fuse on the primary side, besides, the outgoing of the
secondary side is connected directly.
3. DandiBoru Flower Farm: - 100kVA transformer is installed without lightning
arrestor and drop out fuse on the primary side, besides, it has burnt three times.
4. Kaf Rose Flower Farm: - 315 kVA transformers is installed without lightning
arrestor and drop out fuse on the primary side, besides, it has burnt two times.
5. Yewel Stone Crusher፡ 100kVA transformer is installed without lightning arrestor
and drop out fuse on the primary side, besides, it has burnt once.
6. Holleta Farm: - 630 kVA transformers is installed without lightning arrestor and
drop out fuse on the primary side, besides, it has burnt once.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 57
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
4.3.4 EEU's West Addis Ababa Region
When comparing with the rest of the region this region relatively uses protection devices
for the installed transformers; besides, the outgoing of the secondary side is installed with
pillar and its outgoing cable is Copper Cable.
Fig4.22 ፡- Transformer with pillar (Proper installations)
In this region at different sites, researcher has observed the followings; the surveyed sites
are those who are in frequent power interruption:
1. FM Surrounding:- 630kVA transformer is installed without lightning arrestor but has
drop out fuse on the primary side, besides, it has four out goings with two boxes each
with two by 250A and one by 350A rated foses..
2. SIlte Sefer:-630 kVA transformer is installed with lightning arrestor and drop out fuse on
the primary side, besides, it has four out goings with four boxes each with
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 58
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
(400A,300A,315A), (400A,355A,315A), (400A,300A,350A), (300A,300A,3A) fuse
ratings.
3. Zenebe work ZelekeTejBete:- 315 kVA transformer is installed with lightning arrestor but
without drop out fuse on the primary side, besides, it has three out goings with three
boxes each with (315A,315A,350A), (315A,315A,350A), (350A,350A,350A), fuse
ratings.
4. Mekanisa Amigo Caffe Near safe children፡-100 kVA transformer is installed without
lightning arrestor and drop out fuse on the primary side, besides, it has one out going
with one box each with (250A, 250A, 300A) fuse ratings.
5. On the way to Jemo at Mekanisa፡- the MV line which is installed to supply water pump,
when energized the pin insulator is bursting so that the region is in frightened to
reconnect the line. Therefore, still the line is not reconnected.
6. Yemane (Wedi) Condominium: - the insulation sheath of the cable which comes to the
fuse box is worn out so that it is very dangerous and hazardous. ፡
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 59
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Fig 4;23፡- Cable without sheath and cause for transformer failed and power
interruption
4.3.5 Site investigation in East Addis Ababa Region of the utility
During the face to face discussion with technical distribution line staffs of the region named
Ato Biru and Ato Tesfahun the following constraints can be noticed:
Wooden poles are not impregnated very well.
In distribution line where chain insulator has to be used, pin insulator are using
instead at dead end and T-off position.
Using jumper is not in proper situation.
cable lag which is made of brass is not compatible with secondary side stud which
is made of copper. This incompatibility causes wear out the studs.
Using Fuses and Fuse boxes which are not comply the quality standards.
When using ABC cables termination is not performed as per standard and extra
length of ABC cables will be coiled in th line which causes stress. On the top of
this, frequently interrupted line with different sites are deemed.
1. The Transformer with rating of 315KVA at Gerji surrounding:
Installed without lightning and drop out fuse.
Has two out goings with two fuse boxes each with (315A, 350A, 300A) and
(350A, 300A, 300A) fuse ratings respectively.
The two outgoing lines are connected with ABC cables instead of using
Copper cables.
Silicagel of the transformer do not change properly during deterioration.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 60
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
The transformer is erected very near to the rasident’s fence within about 20
cm gap.
2. The Transformer with rating of 315KVA at Gerji condominium surrounding:
Installed with lightning and drop out fuse.
Has three out goings with three fuse boxes each with (300A, 350A, 250A)
(250A, 300A, 300A) and (400A, 315A, 350A) fuse ratings respectively.
The three outgoing lines are connected with ABC cables instead of using
Copper cables.
Silica gel of the transformer do not change properly during deterioration.
3. The Transformer with rating of 315KVA at Gerji wetader area and surrounding:
Installed with lightning Arrestor but without drop out fuse.
Has three out goings with three fuse boxes each with (400A, 400A, 350A)
(315A, 300A, 300A) (250A, 250A, 250A) fuse ratings respectively.
The three outgoing lines and primary side lines are connected with ABC
cables instead of using Copper cables.
Silica gel of the transformer do not change properly during deterioration.
The transformer is erected very near to the resident’s fence within about 20
cm gap.
4. The Transformer with rating of 315KVA at Gerji sun shine condominium
surrounding:
Installed with lightning Arrestor and drop out fuse.
Has three out goings with three fuse boxes each with (250A, 350A, 400A)
(300A, 300A, 250A) and (400A 350A 315A) fuse ratings respectively.
The two outgoing lines are connected with ABC cables instead of using
Copper cables.
During celebration of Ethiopian New Year 2010 it is obviously observed since the day
before the eve power interruption has occurred and transformers are burnt at different sites.
Here are the followings:
1. On the date 04/03/2009 at Legetafo CCD real state compound 315 KVA
transformer with serial No. 77388 burnt because of over load and chaned by the
other transformer with serial No. 03217 but again burnt this transformer.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 61
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
2. On the date 04/03/2009 at Kottebe Mesalemia surrounding 315 KVA transformers
with serial No. 28855 burnt because of over load.
3. On the date 05/03/2009 E.C Ayat Quter 1 condominium Block 24 surrounding 200
KVA transformers with serial No. 01344 burnt because of over load.
4. On the date 01/01/2010 Goroselasie 315 KVA transformer with serial No. 01094
burnt because of over load.
5. On the date 02/01/2010 Legetafo Mamitie Real State surrounding 200 KVA
transformer with serial No.032072 burnt because of over load.
Section switch is used partially to disconnect the line from the net work. However,
in EEU case most of section switches are shunted so that do not give the required service.
To show the evidence, the place at Gerji surrounding the two section switches are shunted
because the contact point of the section switch is copper where as the conductor which has
to be connected with the section would be aluminum, this improper connection results
incompatible with each other.
In this region the places where difficulties of frequent power interruption occur always at
Bole Lemi Industry Park. The line of this site is installed with double line using AAC
cables. These double lines rest on a single pin insulators using cross arm. It is because
during the time of construction of the lines there was scarce resource of cross arm.
Therefore, till the interview conducted no action has taken place to get rid of this problem
From the above site observations we can summarize the investigation as follows
Even though it is not mature enough to generalize that site conditions I surveyed is major
issue of raising failure rate of transformers between these years due to the my small sample
size and the coincidence year I observed and the historical data I used, however it indicates
the survival of the transformers I observed depends only on the withstanding tolerance of
the transformers and on the frequency of occurrences of various faults as well as magnitude
of the fault current.
4.4 Summary of Findings on site
I found there are some transformers connected without protection, poor installation,
unbalanced load and overloads. The standard protection devices for distribution
transformers are:- HRC Fuses rated according the load and capacity of transformers,
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 62
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
dropout fuse for over current protection, Lightening arrestors for protection against
lightening stroke and grounding system for unbalanced current relief during excess
unbalanced current circulation occurrences and providing an information for protection
devices to act before the transformer gets damaged. Besides,
There are transformer protection devices installed but they are much more than the
standard operating capacity of the transformer so that they bypass the over load and
over current demand of the load,
There are also transformers which have non uniform size of protection devise and also
partially availability of devices. This also causes a partial or total damage to
transformers due to the bypassed fault on one of the phase windings and also on one
side of the LV network depending on the direction of fault.
There are bad installations which may adhere the desired functionalities of
protective devise among them are
Manual splicing and Using ABC cables instead of standard connectors and
underground cables
Improper earthling system installation and wiring connections
Leaving the HRC fuse terminals open to weather human access, so that it
may cause improper functioning and bypass the undesired current flow.
4.5 Operation procedure
The EEU operation manual states that the transformers installation shall pass a number of
sequences of tasks that has to be performed before energizing.
One of them is the transformer must be tested without load at the completed transformer
station before energizing referred as ―pre commissioning step.‖ in the reference document
However for different reasons ,especially the non availability of proper testing equipment’s
like MEGGER and Earth test Meters‖ site testing is not carried out this time. There for
even though it is clear that transformer damaged when energized without load side
installation being connected suggests initial condition failure, it is hard for EEU to claim
the supplier and hence take the risk towards itself.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 63
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
CHAPTER FIVE
5. Conclusion and Recommendation
5.1 Conclusions
Even though the factory testing conducted shows there is a confirming mechanism of
quality product before it is delivered to customer there are still missing very crucial tests
which should performed by third authenticated body during the design phase(Proto type/
test type) there are also high contribution in failing in operation and looked at its results so
the result of the statistical significance analysis of the failed transformers and the site
observation of the network and transformer preventive maintenance practice it shows I have
enough evidence to conclude the following generalizations. The failure rate is 9.6% this
shows it out of expected manufacturing quality error.
Almost all failed transformers are get failed early age. The expected average service life of
transformers are 40 year based on the literature review sates .Besides, the 20.11% failure of
transformers failed at initial condition before connected to the existing distribution network.
This suggests that those transformers supplied by METEC between these years missed are
missing standard quality of production. The missing quality aspects are because of not
conducted designed test, recommending only 5% for routine test for sampling and there is
no operational manual which suppose how to loading, uploading, transporting, packaging,
and operating and maintain.
The failure percentage of failure rate are increasing from year to year and EEU has
to act up on any measures that should be taken to improve on the failure of
transformers
The other 79.89% failure share is because of failures on the operation missing of
operational standards during installations. Based on the secondary data collected from the
maintenance center and site observation, transformers on operations are found get
damaging because of missing protective devices like lighting arrestor and dropout out
fuses, unbalanced load connection and overload connection 25.21%,25.64% and 29.04%
respectively.
The site observations tells leads as, EEU should provide appropriate protection devices ,
should also work based on the EEU's O&M manual.
From the above conclusions I would like to pass the following recommendations and
operational model to minimize their effect and reduce their risk level.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 64
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
5.2 Recommendations:
The missed designed testing items must be full filled to verify if the manufacture is
producing quality and standard transformers following the recommended IEC 60076
The missed testing schedules at the factory and additional quality control revision has
to be done on new basis by conducting a mutual study of their products
Agreement has to be reached to include random checking of production process to
verify the consistency of quality production process agreed.
EEU must follow its own operation procedure and start claiming the supplier if it
verifies poor transformers before energizing and burning it.
EEU shall schedule and sustain transformer stations inspection and preventive
maintenances to minimize the loss of transformers at early age trough suggested
inspection investigations correction action and insure reliable customer services.
EPEI should provide operational manual to EEU which supports how to installed,
operate, transport and maintenance.
EEU should test the transformer by megger before energized in the network and should
also check the customer load and standard protection proved or not.
The protection system of transformers must be insured as any unhealthy conditions
could occur any time, and it is also the company’s valuable asset. EEU shall avoid
creating the issues and eradicate the issues by performing a regular inspection of the
transformer stations as well as provide the required standard protection at least to the
above Known cause of fault occurrences and keep them serve for long period of time.
As a matter of fact EEU has its own standard protection and installation procedure of
transformer installation the problem is not following that standard rating and
installation as well as knowingly or un knowingly adding additional load to the
transformers. This is because a customer has also a technical obligation to keep the
safety of the transformers to prevent them from uncontrolled wrong power signal.
Which by default will destroy the transformers?
The problem I found during site observation is related to the un availability of some
protection resources will force them to install without protection. So I recommend the
work shall stay paned until appropriate materials are delivered. And by doing so it will
lead the technicians accept as if they are doing legally the right thing to install them
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 65
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
wrongly. If it is not resolved earlier it will lead to being a bad operational practice
adopted by all its technicians.
The operational issues
These include the regular visiting of the transformer stations and looking any of the
preventive maintenance recommended and conducting the preventive maintenance it
deserves. EEU has in principle adopted many years ago but left over these days. It must
have started to neglect it the operational procedure someday in the past and it becomes
totally forgotten as being operational excellence to provide a service at a desired pre
specified design and construction standard and new connection service. Since we have seen
that not all transformers have got failed at equal period, as long as we made some
correction action at least as per the standard of EEU itself twice a year we could have
rescue those which fail in less than 10 years. And also check the load on the transformers
before new request is additionally connecting to it. By doing this we can minimize the raise
of the overload failure reason and failure of transformers due to overload. This means an
operational quality control model must be there to sustain the good operational and
maintenance best practices. As a result I propose the following Model for operational
control system.
EEU must see itself by conducting a separate study on how much is it loosing due to its
own failure to meet the operational standards so that it can make awareness appraisal prior
to taking administrative and legal measures over the sources of failure.
EEU should use PMCB in place of HRC fuse for monitoring the load management.
Applying this, EEU would be benefited from installing improper fuse rate,
frequently interruption, damaging transformers, repeatedly buying fuses. Protection
is vital part of electrical power systems. The secondary of low voltage distribution
transformers of EEU are protected using fuse. However, pole mounted circuit
breaker (PMCB) [5]; unlike the conventional protection, would help network
operators to have a better protection mechanism of their transformers against short
circuit and overloading while enhancing reliability, saving investment cost and
transformer sizing forecast.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 66
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
Fig 5: 1 Recommendation replacing HRC fuse with Pole mount circuit breaker
The PMCB presented here is designed and manufactured by Schneider Electric. It is based
on the thermal image technology. Its tripping unit is composed of 3 thermistors which heat
proportionally to the windings of the transformer (joule effect). The system is continuously
watching the critical transformer heating point of 120 complying by the IEC 60076-7
above which the transformer is in danger. Hence, unlike the conventional protection; fuse,
it does not act depending on the amount of current only. It rather checks if the thermal
effect of it. If the current flowing through is not in an amount and duration that crosses the
thermal limit of the transformer, it does not interrupt the operation i.e. advanced reliability.
Furthermore, it has got a 24 hours clock that indicates the period accumulation the load gets
above 85% of the transformer’s nominal load. Each time the load exceeds 85%, the clock
hand turns and registers all these periods. When the sum of the periods reaches 24 hours,
the PMCB will trip or signal a red flag depending on your PMCB managing choice.
Investing in such a unit will help in curbing several costs. The multiple costs; but not
limited to, that one can get rid of are:
Replacement of conventional protection (Material + Labor + Logistics)
Storage Costs (fuses)
This unit is in use in several countries such as Kenya. A pilot case is running in Ethiopia as
well.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 67
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
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Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
[26] Julia Mortal, Quality tools, presentation Revision number 80, 17-feb-2005* presented
by M. Aschner a 22 years as quality professional, Certified Quality Engineer Certified SW
Quality Engineer, RAB trained auditor, ASQ LI Section Chairman & programs coordinator.
[27] Richard Koch*The 80/20,Principle, The Secret of Achieving More with Less,
published by Nicholas Brealey Publishing Limited in 1998.
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 70
Quality analysis in Production and Operation of Transformers: in the case of Tatek transformer factory
BY HAILEMARIAM GIRMAY BI T-BDU,2018 Page 70
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