A PQ Case Study · Case study 40 Distribution Network Voltage related power quality issues in a...

Case study 40 Distribution Network Voltage related power quality issues in a food and beverage industry

A PQ Case Study

APQI (C) Copyright 2014 (December 2014) All Rights Reserved 1

A PQ Case Study CS 40 FNB 14

Distribution Network Voltage related power quality issues

in a food and beverage industry


A PQ Case Study


40 Abstract: Power quality issues generated from

incoming grid are one of the prevalent

problems of power quality. Any

disturbance on the grid in the form of

huge load variation will affect entire grid.

Voltage dips, sags, swells, under voltage

and interruptions are still quite common

in Indian grid.

Digital electronics, computers and other

microprocessor based equipment are

more sensitive to power line disturbances

than other electrical equipment

depending on the quality of their power

supply and how they are interconnected.

The circuits in electronic equipment

operate on direct current (DC) power. The

source is an internal DC power supply

which converts, or rectifies, the AC power

supplied by the utility to the various DC

voltage levels required. Variations in the

AC power supply can therefore cause

power quality anomalies in computers

and power electronic components.

If there are heavy loads connected on the

same grid as of a sensitive process driven

manufacturing facility, any variation in the

heavy load at the grid will cause voltage

disturbances at the manufacturing facility.

In modern and state of the art automatic

food processing industries, any

disturbance in supply voltage parameter

in the form of voltage dip, sag, swell or

interruption can result in stoppage of the

manufacturing process.

The Case study below presents problems

faced by a beverage facility due to above

mentioned reasons. The power quality

issues were generated due to traction

load connected on the same grid as of the

industry. The case study also analyses

monetary loss due to each event of

voltage disturbance and mitigation

measure adopted by the industry.


A PQ Case Study


Introduction Voltage related power quality issues are quite common and faced by most of the industries

in some way or other. Most of the time these voltage related power quality issues are not

taken seriously by concerned distribution companies and industries continue to pay a price

for these problems. Voltage sags/swell/interruptions are few voltage related power quality

issues that can have severe financial impact on industries. These events are time bound and

adversity of the events also depends on duration of each event. Information Technology

Industry Council (ITIC) developed a graph known as ITIC curve that provides a guideline for

safe operating limit of electronic equipment in case of there are any voltage variation.

Voltage Sag/Swells:

Voltage Sags are brief reductions in voltage, typically lasting from a cycle to a second or so,

or tens of milliseconds to hundreds of milliseconds. Voltage swells are brief increases in

voltage over the same time range. If reduction or increase in voltage lasts for longer

duration of time, then the phenomenon is known as under voltage or over voltage.

Voltage sags are caused by abrupt increases in loads such as short circuits or faults, motors

starting, or electric heaters turning on, or they are caused by abrupt increases in source

impedance, typically caused by a loose connection. Voltage swells are almost always caused

by an abrupt reduction in load on a circuit with a poor or damaged voltage regulator,

although they can also be caused by a damaged or loose neutral connection.

Fig-1 shows a typical voltage waveform related to sag.

Fig.1 Voltage waveform during sag event


A PQ Case Study


Electronic or any sensitive equipments are affected most due to voltage sags and are prone

to malfunction or failure during the event of sag.

Voltage Interruptions:

A voltage interruption is a large decrease in RMS voltage to less than a small percentile of

the nominal voltage, or a complete loss of voltage.

Voltage interruptions may come from accidents like faults and component malfunctions, or

from scheduled downtime. Short voltage interruptions are typically the result of a

malfunction of a switching device or a deliberate or inadvertent operation of a fuse, circuit

breaker, or re-closer in response to faults and disturbances. Long interruptions are usually

the result of scheduled/unscheduled downtime, where part of an electrical power system is

disconnected in order to perform maintenance or repairs. Figure 2 shows voltage waveform

for an interruption event.

Fig.2 Voltage waveform during short interruption event

CBEMA/ITIC Curve:

In the 1970s, Computer and Business Equipment Manufacturers' Association (CBEMA)

developed one of the most frequently employed power acceptability curves as a guideline

for the organization's members' design of their power supplies. Basically, the CBEMA curve

was originally derived to describe the tolerance of mainframe computer business equipment

to the magnitude and duration of voltage variations on the power system. It eventually

became a standard design target for sensitive equipment to be applied on the power system


A PQ Case Study


and a common format for reporting power quality variation data. It was later renamed as

Information Technology Industry Council (ITIC) curve. Fig 3 shows ITIC curve defining safe

zone for operation of electronic equipments.

A change in voltage causes a decrease or an increase in the amount of energy supplied to

components in an electrical power system, which leads to an amount of energy that is

different from the amount required for normal operations. A decrease in energy during a

voltage dip can cause equipment to reset or shut down and cause mechanical devices, such

as motors, to stall or overheat. An increase in voltage during a voltage swell can cause

immediate or long-term breakdown of components because of overheating.

Because the voltage level during a voltage interruption rapidly decays to zero, or to almost

zero, no energy is transferred to components in an electrical power system when there are

voltage interruptions. A voltage interruption therefore can cause the complete shutdown of

equipment and also can lead to damage. The curve has change in nominal change in voltage

(percentage) on Y axis and duration of the event on X axis in cycles and seconds.

Fig – 3 ITIC Curve

Voltage related events like voltage sags, swells or interruption can cause damage to

electronic equipments, resulting in loss of production and time for a continuous plant.


A PQ Case Study


Background

Coca Cola is one of the leading beverage manufacturing companies in the world. Since its

inception in the year 1892, the company grew over the years to become leader in non

alcoholic beverages. Over the years it adopted best available manufacturing processes and

now its plants across the globe have most modern and automated manufacturing lines.

Hindustan Coca Cola Beaverages Pvt. Ltd (HCCB) Plant in Khurda Industrial Estate in one of

the largest and key bottling facilities in CBO with 2400bpm+ manufacturing capacity,

supported by 6 lines. Existing capacity includes 600bpm of Sparkling RGB, 600bpm of Juice

RGB, 720bpm (including 600bpm high speed line) of sparkling PET, 400ppm of Juice

Tetrapak and 75bpm retail Water. For the last few years, Khurda Industrial estate has been

experiencing poor quality of incoming power from Odisha State Electricity Board and all

major industries (including HCCB) in this estate have been impacted badly due to this issue.

It has become more significant for HCCB with addition of high speed PET, juice RGB and

Tetra capacities.

Current substation at Khurda industrial estate is connected to 220Kv grid from Menthsal

(about 25 kmtrs away from Khurda) through an incoming feeder near Khurda town.

Menthsal Grid is also connected to a railway feeder. There are frequent voltage drops and

unscheduled power cuts at Khurda substation due to distribution issues from this grid. This

gets further aggravated, with railway feeder also getting connected to this supply due to

frequent distribution issues. We have done various audits like Power quality audit, Energy

audit to find the actual root cause of the problem. With power quality getting deteriorated,

all major industries in Khurda has started working on to find a solution for the same.

The plant was facing problem of stoppage of production line causing loss of productivity.

The problems were mainly due to interruptions in power supply and under voltage events.

Apart from this, plant was also facing problems due to over voltage particularly failure of

electronic cards.

After each power supply interruption, there was some time required to resume

productivity. Time required to resume productivity after resumption of power varies from

10-15 minute. Table – 1 shows monetary loss plant was facing due to each event of supply

interruption.


A PQ Case Study


Sl No Line

Line running time after

power resume in mins

Production Capacity per hour (No of

cases per hour)

Load factor

Actual Cases Lost

Monetary Loss in Rs per event

1 Krones 15 1500 80% 300 3168

2 Maaza 12 1500 80% 240 2534.4

3 RGB 10 1500 80% 200 2112

4 Kinley 10 300 80% 40 422.4

5 PET-140

15 933 80% 187 1970.496

Total Loss 10207

Table – 1 Monetary loss due to power supply interruption

Table – 2 shows number of events of power supply interruptions in each month.

Month Unscheduled Power cut Unbalanced Voltage Total No of Occurrences

No. of Occurrences No. of Occurrences

January'14 10 9 19

February'14 17 8 25

March'14 45 42 87

April'14 68 51 119

Table – 2 Power supply interruptions in each month

From above table it can be seen that from January to April 2014, number of under voltage

and unscheduled power supply interruptions were 250. With cost of each event being INR

10,207.00, plant lost around INR 2,551,750.00 during January – April 2014. Apart from loss

in productivity, plant also spent more money for operating DG set due to each event. This

increased energy cost along with GHG emission. From June 2014 onward Electrical energy

generated from DG set was 60% of total electrical energy usage. With average electricity

consumption of 9 lakh units per month, 5.4 lakh units were generated using DG set. With

average cost of electricity generation using DG set is around INR 17 per kWh and for grid

power cost of electrical energy being INR 8.5 per kWh, differential energy cost of DG set and

grid power is INR 8.5 per kWh. Plant is spending INR 4.5 Million per month additionally


A PQ Case Study


towards electrical energy. With this trend, annual additional cost of electricity will be INR 55

Million due to furnace oil utilisation. In four months, production loss was around INR 2.5

Million. Extrapolating this, annual loss would be around INR 7.5 Million due to loss in

productivity. Total monetary loss incurred by the plant due to power supply interruptions

would be 62.5 Million INR per year.

In addition to cost, utilization of furnace oil will lead to release of additional 180 tonnes of

CO2eq to the atmosphere annually.

The increased use of DG is not due to non availability of power but due to poor quality of

supply power. With poor quality of supply, which is not desirable for the equipments, plant

is forced to use DG set despite availability of power. This has not only increased operating

cost of the plant but also carbon emission from plant.

CORRECTIVE ACTIONS BY PLANT: This being a frequent and quite common problem with regular occurrence, plant took

various measures like automatic switch over system for DG sets during power failure,

forward and reverse synchronisation system, and SCADA system.

SCADA system helped the operation team to monitor the voltage profile more closely. After

installation of SCADA system, plant team could identify cause of malfunctioning of various

sensitive equipments. After monitoring of the voltage profile at SCADA, it came to the

knowledge of the plant team that there are voltage dips in the system. Voltage drops to as

low as 15-20 Volts on the LT side for couple of mili seconds. During the events of voltage

dips, sensitive equipments do malfunction or drop out.

Synchronisation with Grid – forward and reverse process helped the operation team to

transfer power from switch over either to grid or to DG sets without interrupting the

production lines. During forward synchronization, DG's are switched on half an hour before

schedule power interruption. Before scheduled power interruptions, load is switched over

to DG sets. During reverse synchronization DG sets are kept running even after power from

the grid resumes. Once the system is synchronized, then load is transferred from DG set to

grid power without any disturbance to the manufacturing process. However,


A PQ Case Study


synchronisation system helped only during the scheduled power interruptions. For un-

scheduled power interruptions, synchronization system was of little help.

In order to find more reliable solution during the un-scheduled power interruptions and

voltage variations, plant team carried out a detailed power quality study to find reason of

voltage variations and possible solution to mitigate the problem.

Summary of PQ Audit: The plant carried out a detailed power quality audit to find root cause of the problem.

Measurements were carried out at all critical locations and logged for longer duration of

time to record number of events and duration of each event.

The plant receives electrical power from state electricity Distribution Company from a

shared grid with railway traction. Fig-4 shows representative single line diagram of electrical

power supply to Coca Cola plant.

Fig – 4 Representative single line diagram of electrical power supply

As seen in the single line diagram, Coca Cola and other food processing industries in this

industry zone are connected to the 33 kV grid which is shared by traction load. Traction

substation is located at around 15 km from the plant. Traction load receives main power


A PQ Case Study


from a dedicated traction supply feeder. During maintenance or any breakdown on the

traction feeder, power for the traction load is drawn from the industrial feeder as shown in

figure 4.

Fig 5 shows simplified single line diagram of the plant. The facility is getting 33 kV supply

from Central Electricity Supply Utility of Odisha (CESU). Contract demand is 4000 kVA with a

billing demand of 5628 kVA. The 33kV is stepped down to 440 V through one 2 MVA and

one 3.15 MVA transformer. In addition to supply from grid, the facility has 6 numbers of DG

sets and operated during scheduled/un-scheduled power cuts. Out of these 6 DG sets, 3 DG

are 1250 kVA, and rest 3 are 750 kVA, 500 kVA and 250 kVA rating.

Fig – 5 Simplified plant SLD

During the power quality audit, measurements were carried out at following points.

Sr. Number Measurement Point

1 33 kV main HT incomer

2 2000 kVA transformer – LT side

3 3150 kVA transformer – LT side

4 Krone UPS

Table – 3 Measurement points

In addition to above major locations, measurements were carried out at all load end MCC’s,

UPS and servo stabilizer. One of the UPS at Krone line was studied in detail.

Section below shows analysis of measurements at above locations.


A PQ Case Study


33 kV main HT incomer:

Voltage Profile:

Measurements were carried out at 33 kV main incomer. Figure – 6 shows voltage profile at

the 33 kV incomer.

Fig – 6 Voltage profile at 33 kV main incomer

From the figure – 6 it can be seen that maximum voltage at HT incomer is 34.2 kV where as

minimum voltage at the incomer is 26.7 kV. As per Indian Electricity rules 2005 in the case

of high voltage (33kV), voltage variation should not be more than 6 per cent on the higher

side or by more than 9 per cent on the lower side. Voltage is dropping by 19% from 33 kV to

26.7 kV which is not acceptable as per Indian Electricity Rules.

Total Harmonics Distortions:

Figure – 7 shows total harmonic distortion at the 33 kV incoming feeder.

Fig – 7 Total Harmonic distortions at 33 kV incomer


A PQ Case Study


Total voltage harmonic distortion at the 33 kV incomer were found to be within limit (5% as

specified by IEEE-519) at a maximum value of 4.3% but current harmonics were found to be

at a maximum value of 22.7% which is above acceptable limits of 15% as specified by IEEE-

519. At 33 kV feeders, voltage variation and current harmonics were found to be major

areas of concern.

Transformer – 2000 kVA & 3150 kVA:

Voltage Profile:

Measurements were carried out on LT side of 2000 and 3150 kVA transformer to record

voltage profile. Fig 8 & 9 shows voltage profile on LT side of the 2000 and 3150 kVA

transformer.

Fig – 8 Voltage profile at 2000 kVA transformer LT side

Fig – 9 Voltage profile at 3150 kVA transformer LT side

For 2000 kVA transformer the voltage varies from 203V to 252.3V whereas for 3150 kVA

transformer the voltage variation is from 199.3V to 266V. The voltage variation is more than


A PQ Case Study


specified limit of Indian Electricity Rule. As per IE rule, in the case of low or medium voltage,

voltage variation should not be more than 6 per cent. The variation on LT side of the system

is due to voltage variation from grid at 33 kV. As the voltage variation on HT side is around

19% on the lower side, OLTC being a dynamic system is associated with time delay will not

able to response to sudden drop in voltage.

Total Harmonic Distortion:

Figure 10 and 11 shows total harmonic distortion at 2000 and 3150 kVA transformers on

their LT side.

Fig – 10 THD at 2000 kVA transformer

Fig – 11 THD at 3150 kVA transformer

The voltage harmonics at 2000 kVA transformer are varying from 2.2 to 5.6%. As per IEEE

519 standard, the voltage harmonic limit is 5%. Current Harmonics varies from 5.3 to 26.7%

which is above the limit.


A PQ Case Study


The voltage harmonics are varying from 1.2 to 6.1%. As per IEEE 519 standard, the voltage

harmonic limit is 5%. Current Harmonics varies from 6.4 to 49% which is above the limit. As

per IEEE 519 standard, the current harmonic limit is 8%.

Above measurement result shows that there could be problem for the equipments installed

at the plant due to current harmonics and voltage variations. However, further analysis was

carried out to find if voltage variations are safe or unsafe for electronic components at the

plant.

As per the IEC 61000-4-30 standard for the power quality, the power quality analyzer

connected at the LT incomer of 2000 kVA Transformer – 1, 3150 kVA Transformer – 2 &

1600 KVA Servo Stabilizer output side which is under the transformer – 2. The following

parameters set in the meter to capture any deviations.

Nominal Voltage : 240Volts (L-N) 415Volts (L-L)

Voltage upper limit : 110%

Voltage lower limit : 90%

Nominal frequency : 50Hz

Recorded events of voltage variations were plotted against ITIC curve.

Figure 12 and 13 shows analysis of under voltage and over voltage event with ITIC curve at

transformer 2000 kVA and 3150 kVA respectively.

Fig – 12 Sags and over voltage events on ITIC curve 2000 kVA transformer

Over voltage events

Under voltage events


A PQ Case Study


Fig – 12 Sags and over voltage events on ITIC curve 3150 kVA transformer

In addition to transformers, measurements were carried out on output side of servo

stabilizer for sag, over voltage & interruption events and are recorded during the study. The

detail of the same are given below in figure 13.

Fig – 13 Sags and over voltage events on ITIC curve – 1600 kVA Servo stabilizer

From the measurement and analysis of the voltage variation, sags, over voltage and

interruptions, it was evident that voltage fluctuations, over voltages, voltage sags and

interruptions due to un-scheduled power cuts were main reason for the failure of critical

components in the plant. Even servo stabilizer was not able to control the issues and there

was variation in the output voltage of the servo stabilizer.

Over voltage events


Interruptions due

to power cuts

Over voltage events


Interruptions due

to power cuts


A PQ Case Study


The plant also have few number of UPS installed which were installed along with installation

of the line as part of project. Some of the sections at the Krone line were provided with UPS

at the design stage. Measurements were carried out at the installed UPS output for voltage

profile. Figure – 14 shows voltage profile at the output of UPS.

Fig – 14 Voltage, current and power profile at UPS

It can be seen that there is negligible variation in voltage profile at the output of UPS. Even

though there are variation in the supply voltage more than 10 %, there is negligible (0.1%)

variation in voltage profile at the output of the UPS.

Problem definition and mitigation:

As seen from Figure – 4, Coca Cola plant receives its supply from 132 kV grid and stepped

down to 33 kV at utility sub-station. The same 33 kV grid also supplies to traction load

during maintenance or breakdown at dedicated grid of traction. When traction load is on

the industry grid of 33 kV and electrical rail is comes in operation, there are frequent

changes in the operating condition. The load varies from starting, accelerating, idle running

and braking. Due to frequent change in load and various trains operating at a given time,

there is huge load variation on the grid. Due to sudden change in high loads, voltage across

the grid and downstream of the grid gets affected. The variation in voltage and interruptions

at downstream of the grid will affect all industries connected on the same grid.

As the problem is generated from outside the boundary limit of the plant, the plant

requested state electricity DISCOM to separate traction load from industrial supply. Plant is

Voltage – 396 to 397

Volts


A PQ Case Study


losing around INR 62.5 Million per year due to higher energy cost and loss in productivity. In

addition to monetary loss, around 180 tonnes of additional green house gas is being

released to atmosphere due to use of diesel in DG sets.

As the issue is with distribution system, mitigation at distribution needs to be carried out. As

is understood, serious PQ issues occur when the industry is fed from Narendrapur, 150 km

away over a 132 kV single ckt line, through two levels of transformation. The short ckt level

at Khurda 33kV bus is very low causing high variations in voltage for small increase or

decrease in load. When the feed is from the Chandaka grid the situation is better but the

reliability of supply from Chandaka is poor because of disturbances at Meramundli and

other upstream grid s/s.

The other major PQ issue arises when traction load is supplied from 33 kV industry feeder

and the loaded phase experiences serious under voltage and rapid variations. Traction load

does introduce 2nd 3rd and 5th harmonics and under un favorable conditions this could cause

voltage amplification. An SVC with ‘Load balancing control’ can balance out the voltage

supply but can be an expensive solution.

As mentioned in the case study short time severe voltage dips are being recorded by SCADA.

This could be due to flash faults in nearby grid, discharges across weak insulators, lightning

arrester operation nearby, or loose earth connections. This may not be a serious problem ,

but if it is causing tripping/ load dropping, the protection settings have to be adjusted and

reason for these 2ms duration dips identified. We should also see if these are reflected in

the recordings taken upstream and downstream.

Interruption records are alarming, as much as 60 times in some months! Auto changeover of

supply through RMUs could be a solution, provided an alternate supply was available. Not

having an alternate dedicated feeder clearly shows a gap in planning. Such an industry

complex having a load of about 18 to 20 MW should have alternate supplies from two

equally reliable HV circuits with auto change over. In this case the alternate stand-by

sources from Puri and Narendrapur are very weak and unreliable.

It is understood from CESU that at Arugul where IIT Bhubaneswar is coming up, a 3*40 MVA

station is under commissioning and a 20 MVA transformer is already commissioned.


A PQ Case Study


Apparently the industries , can draw power from there, by drawing a 12 km feeder. It

probably needs to convince CESU that CESU should plan to supply the 20 and odd MW load

to industry complex from the new S/S from their own resources.

The other alternative is when a sub station ATRI gets commissioned by OPTCL and Khurda

gets strengthened by a connection from Mendhasal which is a stronger bus. The down

stream connections from the ATRI bus are not frozen and the Industry consortium can try

for the connection. One of the above two alternatives has to be sorted out with the

CESU/OPTCL authorities. The traction load must have a separate connection from a voltage

level one or two steps higher and the supply feeder to Traction should be provided with an

SVC with load balancing features. All this needs to be checked through a system study to

ensure that voltage sags and O/V , stay within permissible limits , that the system recovers

from faults fast without load dropping, and voltage unbalance with Traction load is within

limit.

To handle frequent interruptions due to faults a study may be done to have sectionalizers

and autoreclosures installed as a reliability enhancement measure.

As of now, In order to protect its failures and loss of productivity, based on the power

quality study and its finding, the plant team has decided to install two numbers of UPS each

of 600 kVA at critical locations to avoid breakdown arising due to voltage variations and un-

scheduled power interruptions.

The present case is an example of ‘how poor quality power supply’ can affect a running

industry and be counterproductive to industrial growth . In some states special Electronic

zones (SEZs) have been created by Industry consortiums to ensure quality power and

uninterrupted production.


A PQ Case Study


About the authors:

Mr. Sampath Arul:

Mr. Sampath Arul is a Graduate in BE Electrical Engineering with 16yrs of Industrial experience. Presently, working in Maintenance in Hindustan Coca –Cola Khurda. Had successfully completed various Kaizen Projects on Energy saving like Lob/Kwh and DG efficiency improvement from

2.82units/lit to 3.5units/lit

Prof. A. K. Tripathy – Expert Review

Prof. A. K. Tripathy is presently Advisor (research) at Silicon Institute of Technology Bhubaneswar Odisha.

Professor A. K. Tripathy is a graduate in Electrical Engineering from NIT Rourkela and M.Tech from I.I.S c Bangalore. He started his career in SAIL as a maintenance engineer between 1972 and 1976 before he joined BHEL in 1976 in its consultancy division. Till 2004 Prof. Tripathy was in BHEL and Chief of Transmission and Distribution of BHEL. He

was involved in several high technology projects in the area of HVDC, FACTS, UHV Transmission, Substation design, industrial consultancy and power system analysis. In 2004 he was awarded BHEL’s Anusandhan award and in 2005 , the P.M.Ahluwalia award for outstanding contribution to Power sector.

He was Director General of Central Power research institute (CPRI) Bangalore between 2004 and 2008. During this period he was chairman of ETDC-40 committee of Bureau of Indian standards and also headed the Transformer standards committee.

Prof. Tripathy during his 42 years of experience in industry and academics has contributed immensely to the area of Power Electronics application, Energy Conservation and Power Quality improvement, with focus on system analysis, design, equipment standardization, and testing. At present he is listed as an adjunct professor with NIT Rourkela, is a member of State advisory Committee of OERC, a consultant with OPTCL and a Board member of CESU Odisha.

He is a Steering Committee member of National Mission on Power Electronics projects, Department of electronics and IT Govt. of India.

Prof Tripathy is a Fellow of Indian National Academy of Engineering, a Fellow of Institution of Engineers, a senior member of IEEE, and a life fellow of ISTE.

Disclaimer: The sole responsibility for the content of this document lies with the authors. It does not represent the opinion of

the Asia Power Quality Initiative and ICA network. APQI and ICA network are not responsible for any use that may be made

of the information contained therein.

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