Course Overview

Substations using SF6 Gas insulated switchgear (GIS) are preferred for voltage ratings of 110 kV and above. In such a situation, the various equipment like circuit breakers, bus bars, isolators, load break switches, current transformers, voltage transformers, earthing switches etc. are housed in metal enclosed modules filled with SF6 gas. The SF6 gas provides phase to ground insulation and arc quenching medium. As the dielectric strength of SF6 gas is higher than the air, the clearances required are smaller.

Hence, the overall size of each equipment and the complete substation is reduced to about 10% of conventional air insulated substations. As a rule GIS are installed indoor. However outdoor GIS have also been installed earlier. The various modules of GIS are factory assembled and are filled with SF6 gas at a predefined pressure. Thereafter they are taken to site for final assembly. Such substations are compact and can be installed conveniently on any floor of a multi – storied building or in an underground substation. As the units are factory assembled, the installation time is substantially reduced.

Such installation are preferred in cosmopolitan cities, industrial townships, etc. where cost of land is very high and higher cost of SF6 insulated switch gear (GIS) is justified by saving due to reduction in floor area requirement. They are also preferred in heavily polluted areas where dust, chemical fumes and salt layers can cause frequent flashovers in conventional outdoor air-insulated substations. The GIS has monitoring system. The gas density in each compartment is monitored. If pressured drops slightly, the gas is automatically tapped up. With further gas leakage, the low-pressure alarm is sounded or automatic tripping or lock out occurs. By this method we can save the space required for the substation to build up. This means that gas-insulated substation can be built in any metropolitan city.

Course Objectives

By the end of the course, participants will:

• Understand the function of an electrical switchgear

• Understand the difference of GIS And AIS

• Understand the principles of SF6 and the procedures for gas handling

• Know the main working principles

• Know the design and function

• Be familiar with construction of the GIS and its components

• Understand the functionality of the components

• Perform GIS maintenance and testing

Who Should Attend

Design and planning personnel, engineering and application personnel, operation and maintenance personnel, consultants from electricity supply industry, all electrical engineers working in substations.

Course Content

Module (01) Gas Insulated Sub-station/Switchgear (GIS)

1.1 Introduction

1.2 What is the substation?

1.3 Substation component

1.4 The difference between AIS & GIS

1.5 Single Line Diagram

1.6 Bay Information

1.7 Classification of GIS

1.8 Design Consideration

1.9 Components/Modules

1.10 Bus bar

1.11 Disconnectors (Isolators)

1.12 Circuit Breaker

1.13 Current Transformer

1.14 Earth Switch

1.15 Accessories

1.16 Properties of SF6

1.17 Constructional Aspects of GIS

1.17.1 Enclosure

1.17.2 Seals and Gaskets

1.17.3 Gas Circuit

1.17.4 Expansion Joints

1.17.5 Current Transfer and Plug-in-Joints

1.17.6 Support Structure

1.18 Installation and Maintenance of GIS

1.19 Lifecycle Cost of GIS

1.20 Conclusion

Module (02) High Voltage Circuit Breaker 

2.1     Introduction

2.1.1 Classification of Circuit Breakers

2.1.2 Classification by Voltage

2.1.3 Classification by Location

2.1.4 Classification by External Design

2.1.5 Arcing Process

2.2 Classification by Interrupting Media

2.2.1 Development of Single-Pressure Puffer Breakers

2.2.2 First Generation SF6 Circuit Breakers

2.2.3   Second Generation SF6 Circuit Breakers

2.2.4   Third Generation SF6 Circuit Breakers

2.2.5   Design Features of Puffer Circuit Breaker

2.3     Operating Mechanisms for Circuit Breakers

2.3.1 Spring Mechanism

2.3.2   Pneumatic Mechanism

2.3.3 Hydraulic Mechanism

2.3.4   SF6 Gas Dynamic Mechanism

2.3.5 Motor-driven Mechanisms

2.3.6 Comparison of Operating Mechanisms

2.4     System Requirements of Circuit Breakers

2.4.1 Circuit Breaker Faults

Module (03) SF6 Gas Handling

3.1   Why SF6? Analysis of Fundamental Properties and Comparison with Air and Other Gases

3.2   Reaction with Electric Arc and Decomposition Products

3.3   Humidity and Acidity

3.4   Factors Affecting the P.

3.5   Environmental Aspects

3.6   Recovery of SF6 Gas

3.7   Gas handling

3.8   Tests of SF6 Gas

Module (04) Operation and Maintenance of GIS

4.1 Maintenance of GIS

4.2 Maintenance of Circuit breakers

4.3 Maintenance of CT and VT

4.4 International Standards

4.5 Tests of Circuit breakers

4.6 Maintenance of Circuit breaker mechanism

4.7 Maintenance and Testing of Surge arresters

4.8 Overall Maintenance of GIS

4.8 Cases Study of GIS Faults

Module (05) GIS Testing and Commissioning

5.1 GIS Type Tests

5.2 Mechanical Checks and Visual Inspections

5.3 Electrical Tests

5.4 Dielectric tests on the main circuit

5.5 Tests on auxiliary and control circuits

5.6 Measurement of the resistance of the main circuit

5.7 Tightness test

5.7 Visual inspection & design check, schemes & interlocks check, LCC tests, gas pressure switch test

5.8 Tests on auxiliary circuits, equipment and interlocks in the control mechanism.

5.9 Mechanical operation tests

5.10 Perform all electrical tests on GIS components (CB, E/S & D/S) as per manufacturers

5.11 HV tests

5.12 Timing tests for all equipment (CB, E/S & D/S)

5.13 Accuracy and Interpretation of test results and of test reports