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Air Insulated and Gas Insulated Substation

A

Seminar Report

Submitted in Partial Fulfillment of the Requirements for the Degree

Of

Bachelor of Technology

In

Electrical Engineering

Submitted By:

Pathik Patel (13BEE079)

Rajkumar Patel (13BEE081)

Under Guidance of:

Prof. C.R.Mehta

Department of Electrical Engineering

Institute of Technology, Nirma University

Ahmedabad – 382481

April 2015

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ACKNOWLEDGEMENT

It is our proud privilege and duty to acknowledge the kind of help and guidance received from

several people in preparation of this report. It would not have been possible to prepare this report

in this form without their valuable help, cooperation and guidance.

First and foremost, our sincere gratitude to our guide, Prof. C. R.Mehta, Department of

Electrical Engineering, Institute of Technology, Nirma University for guiding us in

investigations for this seminar. Our numerous discussions with his were extremely helpful.

We express our sincere gratitude to Prof. Sarika S Kanojia, Department of Electrical

Engineering, Institute of Technology, Nirma University for her valuable suggestions and

guidance throughout the period of this seminar.

The seminar on “Air Insulated and Gas Insulated Substation” was very helpful to us in giving

the necessary background information and inspiration in choosing this topic for the seminar. Our

sincere thanks to Prof. Gaurang Buch and Prof. Sukanta Sahoo Seminar Coordinator for

having supported the work related to this project.

Last but not least, our classmates who made valuable comment suggestions on this proposal

which gave us an inspiration to improve our work. We thank all the people for their help directly

and indirectly to complete our work.

Special Thanks to Microsoft Office 2007.

Place: Ahmedabad Raj Patel

Pathik Patel

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ABSTRACT

Reliable and economical power transmission and distribution are key functions for the future

electric power supply. Air insulated Substation requires more space and more danger to faults.

So, Gas insulated switchgear is used in industrial areas to fulfill high-energy demands by space

saving design with a minimum of cost. Only SF6 insulated switchgear is able to fulfill these

requirements. SF6 switchgear installed in Canada in a 550 kV substation with 100 kA as the

highest breaking capacity ever achieved in one of the steps of development since then.

Consistent research and development and innovative energy led to the third generation of

nowadays compact and overall optimized switchgear. The advantages of gas-insulated

switchgear are its compact design and the modular system. The standardized modular structure is

made to match the various customers specifications and allows to realize almost all substation

configurations in compliance to them.

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LIST OF FIGURES

1) Fig.1.1 (A) Air Insulated Substation

2) Fig.1.1 (B) Gas Insulated Substation

3) Fig.1.2 (A) Pole Mounted Substation

4) Fig.1.2 (B) Traction Substation

5) Fig. 1.3 ELECTRICAL DISTRIBUTION NETWORK

6) Fig. 2.1.4 Protective Relays

7) Fig. 2.1.6 (a) Pin Type Insulator

8) Fig. 2.1.6 (b) Suspension Disc Insulator

9) Fig. 2.1.6 (c) Strain type Insulator

10)Fig. 2.1.7 Lightning Arrestor

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NOMENCLATURE/ABBREVIATIONS

1) AIS - Air Insulated Substation

2) GIS – Gas Insulated Substation

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TABLE OF CONTENTS

ACKNOWLEDGEMENT (2) ABSTRACT (3) LIST OF FIGURES (4) NOMENCLATURE/ABBREVIATIONS (5) TABLE OF CONTENTS (6)

CHAPTER 1: INTRODUCTION (8)

1.1 INTRODUCTION TO SUBSTATION

1.2 TYPES OF SUBSTATION

1.3 BLOCK DIAGRAMS OF ELECTRICAL

DISTRIBUTION NETWORK

1.4 SITE SELECTION FOR SUBSTATION

CHAPTER 2: SUBSTATION EQUIPMENTS (13)

CHAPTER 3: COMPARISION OF AIS AND GIS (18)

CHAPTER 4: CONCLUSION AND FUTURE SCOPE (21)

REFERENCES (22)

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CHAPTER 1: INTRODUCTION

1.1 INTRODUCTION TO SUBSTATION

What is a Substation??

A Substation is a part of an electrical generation, transmission, and distribution system.

Substations transform voltage from high to low, or the reverse, or perform any of several

other important functions.

Between the generating station and consumer, electric power may flow through several

substations at different voltage levels.

Globally economy and population continues to grow, results, rise in electrical power

requirements. For this purpose, substation equipment has to be made more efficient and reliable

to cope up with increase in demand, specially adapting current power distribution and

transmission system.

Air insulated Substation:-

An electric power substation that has the busbars and equipment terminations generally open to a

ir and utilizes insulation properties ofambient air for insulation to ground.

Gas insulated Substation:-

A Gas insulated substation (GIS) is a high voltage substation in which the major

structures are contained in a sealed environment with sulfur hexafluoride gas as the

insulating medium.

All the equipments are placed inside SF6 modules filled with SF6 gas.

GIS technology originated in Japan, where there was a need to develop technology to

make substations as compact as possible.

Gas Insulated Substations are high voltage Substations that are compact, requiring little

maintenance when compared to air-insulated conventional Substations.

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1.2 TYPES OF SUBSTATION

Classification Based on Configuration, e.g.:

1) Conventional Air Insulated outdoor substation,

2) SF-6 Gas Insulated Substation,

3) Composite Substations having combination of above two.

Classification Based on Voltage levels, e.g.:

A.C. Substation: EHV, HV, MV, LV; HVDC Substation.

Classification Based on Outdoor or Indoor:

Outdoor Substation is Under Open Sky.

Indoor Substation is inside the building or in ground.

Pole mounted Substation:-

Fig.1.1 (A) Air Insulated

Substation

Fig.1.1 (B) Gas Insulated Substation

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Pole mounted substation are mainly distribution substation constructed on two pole

Traction Substation:-

Electrified Railways use distributed and Transmission Substation.

For DC trains, Rectifier (Mercury) based Substation.

For AC trains, Rotary converters are used.

Fig. 1.2 (A) Pole mounted Substation

Fig. 1.2 (B) Traction Substation

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1.3 BLOCK DIAGRAMS OF ELECTRICAL DISTRIBUTION NETWORK

Fig. 1.3 ELECTRICAL

DISTRIBUTION NETWORK

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1.2 SITE SELECTION:-

It should be located at the centre of gravity of load.

It should involve minimum capital cost.

It should provide safe and reliable arrangement.

There should be space for future expansion.

There should be enough space for accessing incoming and outgoing lines.

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CHAPTER 2 SUBSTAION EQUIPMENTS

2.1 Equipments used in Substation

The major equipments and accessories that may be used in substation:--

1. Bus bar,

2. Circuit Breakers,

3. Isolators,

4. Protective Relays,

5. Transformers,

6. Insulators,

7. Lightning Arrester,

8. Current Transformers,

9. Potential Transformer,

10. Control room.

2.1.1 Bus Bar:-

The bus is a line in which the incoming feeders come into and get into the instruments for

further step up or step down.

Various Incoming and outgoing circuits are connected to Bus Bars.

There may be double line in the bus so that if any fault occurs in the one the other can

still have the current and the supply will not stop.

The Cross Section of the bus bar is to be decided as follows :

1) It should be able to carry the current without any heating so that maximum temperature

doesn’t exceed 700C.

2) The current capacity generally adopted as 200 amp/mm2.

3) Corona must not be formed at normal operating voltage. To prevent corona hollow bus

bar is also used.

4) Mechanical force ∝ current I2 ∝ 1/ Spacing between two conductors

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2.1.2 Circuit Breakers

Circuit breaker is used for switching during normal and abnormal conditions.

It is used to interrupt short circuit currents and connected in series with circuit.

There are many types of circuit breakers.

1) Air blast circuit breaker

2) Oil circuit breaker

3) SF-6 circuit breaker

2.1.3 Isolators

Mainly Used when repairing and maintenance of substation has to be carried out.

Operated on No load as circuit breakers are used for On Load.

2.1.4 Protective Relays

Employed to give protection to the equipments against abnormal conditions and faults in

the power system.

Isolates the faulty element from the system with the help of circuit breakers.

Fig. 2.1.4 Protective Relays

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2.1.5 Transformers:

There are three transformers in the incoming feeders so that the three lines are step down

at the same time.

At the generation, it will be step-up transformer and at the distribution end, there will be

step-down transformer.

Transformer tanks up to 25 MVA capacity are generally oil filled.

And those of higher capacity are transported with N2 gas filled in transformer tank to

avoid the ingress of moisture.

2.1.6 Insulators:

There are mainly three types of insulator used as overhead insulator likewise

1. Pin Insulator

2. Suspension Insulator

3. Strain Insulator

Insulators serve two purposes

o They Support conductors (Bus Bar),

o Confine the current to the conductors.

Most Commonly used material for manufacture of insulator is porcelain.

Fig. 2.1.6 (a) Pin Type Insulator Fig. 2.1.6 (b) Suspension Disc Insulator

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2.1.7 Lightning Arrestors:-

Lightening arrestors are the instrument that are used in the incoming feeders so that to

prevent the high voltage entering the main station.

This is done by MOV Disk which is fast acting electronic switch.

If some lightening occurs the arrestors pull the lightening and ground it to the earth.

In any substation the main important is of protection which is firstly done by these

lightening arrestors.

Fig. 2.1.6(c) Strain Type Insulator

Fig. 2.1.7 Lightning Arrestor

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2.1.8 Current Transformer:-

A current transformers step down the current and this is used for metering purpose.

The relays which detects abnormal conditions by monitoring system currents which

supplied from the outputs of CTs.

2.1.9 Potential Transformer:-

There are two main parts in it

o Measurement

o Protection

The main use of this transformer is to measure the voltage through the bus.

This is done so as to get the detail information of the voltage passing through the bus to

the instrument.

2.1.10 Control Room:-

For controlling entire Substation.

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CHAPTER 3 – COMPARISION OF AIS AND GIS

3.1 Limitations of Air insulated substation:-

More Space is required.

Outdoor switch yards are more danger to faults as it is located in outside atmosphere

which has some influence from pollution, saline environment and other environmental

factors.

Deposition of saline particles on insulators can cause insulator failures. They are also

vulnerable to direct lightning strikes and other external events such as heavy winds, rains

and cyclones.

Low reliability.

Regular maintenance is required.

3.2 Advantages of GIS:-

A GIS has many advantages over a conventional substation, including a space saving and

flexible design, less field construction work resulting in quicker installation time, reduced

maintenance, higher reliability and safety, and excellent seismic withstand characteristics.

Aesthetics of GIS are far superior to that of a conventional substation, due to its substantially

smaller size. A GIS can even be installed in a building, if desired. When all of these advantages

are taken into consideration, a GIS is a cost effective alternative to a conventional substation that

offers many benefits to the end user.

Special Features Enhanced insulating properties and reduced long-term operational costs by means of sealed

metal enclosure filled with SF6 gas.

Reliability Extensive experience in designing optimum phase and feeder spacing dimensions according to

site conditions enable compact dimensions that reduce space requirements to less than 20%

of conventional air insulated substations.

Compact Design Ensured personal safety by earthed enclosure, numerous

interlocks and lockout devices. Increased stability during earthquakes with a low center of

gravity.

Maintenance

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Virtual elimination of long-term maintenance costs and contamination of critical components by

means of SF6 gas-filled metal enclosures, automatic monitoring of operating mechanisms and

SF6 gas system.

Efficient Installation Assembly at factory and shipment in one complete bay dramatically reduces installation time and

customer’s costs.

Environmental Minimized operation noise levels allow installation in urban and sub-urban indoor substations.

Elimination of radio interference problems and individual painting of enclosures with the

color of customer choice.

Space Saving:- SF6 switchgear installations take up only 10% of the space required for the conventional

installations.

Economical Initial high investment is required for installation but the cost can be comparable for the less

maintenance, reliable, safe operation against conventional substation. Ability to interrupt out-of-

phase.

Compatibility It is incombustible, non toxic, colorless and chemically inert.

Low Weight Due to aluminum enclosure, corresponds to low cost foundations and buildings.

The dielectric strength of SF6 gas at atmospheric pressure is approximately three times that of

air.

It has arc-quenching properties 3 to 4 times better than air at equal pressure.

Ability to interrupt short-line faults.

Overvoltage is kept to a minimum.

Minimum gas leakage (less than 0.1% per year).

The use of SF6 gas as an insulating medium in switchgear reduces the clearance distance

between active and non-active parts of a switchgear facilitating the following advantages of gas

insulated applications compared to air insulated applications:

● Less space requirements – especially in congested city areas.

● Less sensitivity to pollution, as well as salt, sand or even large amounts of snow

● Less operation & maintenance costs

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Disadvantages with Air Insulated Substations:- a) It requires huge amount of area.

b) Cost is higher compared to Air Insulated Substation or conventional substation.

Maintenance cost is more.

c) Normally this type of substations are indoor type and requires separate building. Each

and every component of substation is exposed to air and pollution.

d) Maintaining Cleanliness is very important. Dust or moisture inside the compartment

causes the flash overs so frequent flashovers and breakdown occurs.

e) When fault occurs internally, the outage period will be very long. The damage effect will

also be severe.

f) Installation time is also more.

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CHAPTER 4 CONCLUSION AND FUTURE SCOPE

4.1 Conclusion

GIS are necessary for EHV&UHV and some important areas to be studied include more

conservative designs better particle control & improved gas handling & decomposition product

management techniques. Achieving & maintaining high levels of availability requires a more

integrated approach to quality control by both users and manufactures.

4.2 Future Scope related to development of GIS

Compact design of switchgear by using three phase switchgear in the same enclosure.

Use of Vacuum circuit breaker cells in the medium high voltage GIS and fewer breaks

per pole in high voltage circuit breakers.

Optimization of GIS design to allow easier maintenance by reducing access points.

Smart GIS – Integration of Electronic CT’s and PT’s.

Another important problem facing the industry is to develop strategies to effectively use

older equipment. Even today, spare parts are not easily available for the older design of GIS.

A completely satisfactory solution for the management of spare parts is yet to be found. A

compromise solution will be a reasonable and rational stocking of spare parts by both the

utilities and manufacturers. Also, a solution has to be found for fitting the new switchgear

into old installations with minimum readjustment work.

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REFERENCES

1) http://www.prnewswire.com/news-releases/global-gas-insulated-switchgear-gis-transmission-

-distribution-manufacturing--processing-infrastructure--transportation-and-power-generation-

market---trends-and-forecasts-to-2019-789339884.html

2) ELECTRICAL POWER SYSTEMS: Concept, Theory and Practice, By SUBIR RAY

3) http://www.cea.nic.in/reports/regulation/grid_standards_reg.pdf

4) http://www.spml.co.in/mediaroom/2014/Electrical-Monitor-April-2014.pdf

5) Comparison of Gas Insulated Substation over Air Insulated Substation by M.Bilal Latif,

Department of Electrical Engineering, Superior University, Lahore, Pakistan.

6) GAS INSULATED SUBSTATIONS BY M.S.NAIDU.