CONTENTS
Chapter Description Page No.
Foreword iii
Preface iv
Contents v
Correction Slip viii
1 INTRODUCTION 01
1.1 EQUIPMENT IN DISTRIBUTION SUB-STATION 02
1.1.1 Distribution Transformer 02
1.1.2 Circuit Breaker 05
1.1.3 Lightning Arrester 05
1.1.4 Air Break (AB) Switch 06
1.1.5 Insulator 06
1.1.6 Bus Bar Arrangement 06
1.1.7 Capacitor Bank 06
1.1.8 Earthing 06
1.1.9 Fencing Arrangement 06
1.1.10 Distribution Panel Board 06
1.2 GRAVEL/CRUSHED ROCK 07
1.2.1 Advantages of Crushed Rock Used as a Surface Layer 07
2 MAINTENANCE
2.1 DAILY SCHEDULE 08
2.2 MONTHLY SCHEDULE 09
2.3 QUARTERLY SCHEDULE 09
2.4 HALF YEARLY SCHEDULE 10
2.5 YEARLY SCHEDULE 11
2.6 5 YEARLY SCHEDULE 12
2.7 TIPS FOR IMPROVING MAINTENANCE 12
2.7.1 Transformer 12
2.7.2 Circuit Breakers 16
2.7.3 Air Break Switch/ Isolators 16
2.8 MAINTENANCE PROFORMA 17
2.8.1 Daily Maintenance Proforma 17
2.8.2 Monthly Maintenance Proforma 18
2.8.3 Quarterly Maintenance Proforma 19
2.8.4 Half Yearly Maintenance Proforma 20
2.8.5 Yearly Maintenance Proforma 21
2.8.6 5 Yearly Maintenance Proforma
TROUBLE SHOOTING 23
3.1 AN APPROACH TO EQUIPMENT FAILURE INVESTIGATION
3.1.1 On Failure Aspects 23
3.1.2 On Maintenance Aspects 23
3.1.3 About Staff 23
3.1.4 About Material 23
3.1.5 About Testing 24
3.1.6 General Points 24
3.1.7 Any other Findings not covered in the above
3.2 CAUSES OF FAILURES AND THEIR REMEDIES
3.2.1 Common Failures of Transformer 24
3.3 INVESTIGATION INTO CAUSES OF FAILURES OF TRANSFORMER 27
3.3.1 Failure due to Lightening Discharge or Over Voltages 27
3.3.2 Sustain Overloads 27
3.3.3 Inter-turn short, Inter-layer short, or Inter coils short 28
3.3.4 Dead Short-circuit 28
3.3.5 Buchholz Relay Tripping 28
3.3.6 Internal Flashover 28
3.4 DO’s & DON'Ts 28
3.4.1 Do’s 28
3.4.2 Don’ts 29
4 EARTHING
4.1 PURPOSE OF SUBSTATION EARTHING SYSTEM
MAXIMUM PERMISSIBLE RESISTANCE OF EARTHING SYSTEM 30
4.3 TOUCH VOLTAGE (E - TOUCH) 30
4.4 STEP VOLTAGE (E - STEP) 31
4.5 EARTHING SYSTEM IN SUB STATION 31
4.5.1 Earth Mat or Grid 31
4.5.2 Construction of Earth Mat 31
4.5.3 Earth Mat in a Sub-Station 32
4.6 LOCATION OF EARTH ELECTRODE 32
4.6.1 Pipe Electrode 32
4.7 EARTHING OF VARIOUS EQUIPMENT IN THE SUB-STATION 32
4.7.1 Isolators and switches 32
4.7.2 Lightning Arrestors 32
4.7.3 Circuit Breakers 33
4.7.4 Transformers 33
4.7.5 Current Transformers and Potential Transformers 34
4.7.6 Other Equipments 34
4.7.7 Fences 34
4.7.8 Ground Wire
4.7.9 Cables and Supports 35
4.7.10 Panels and Cubicles 35
4.8 DISTRIBUTION TRANSFORMER STRUCTURE EATHING 35
4.9 TESTING OF EARTHING SYSTEM 37
4.9.1 Measurement of Earth Electrode Resistance
4.9.2 Details of Earth Tester (Hand Driven) 38
4.10 MAINTENANCE FREE EARTHING 39
4.10.1 Earth Resistance 39
4.10.2 Applications 39
5 GENERAL 40
5.1 ELECTRICAL ENERGY BASICS 40
5.2 POWER FACTOR 42
5.2.1 Principal Causes of Low Power Factor 42
5.2.2 Effect of Power Factor to Consumer 43
5.2.3 Power Factor Calculation 43
5.3 ECONOMICS OF POWER FACTOR IMPROVEMENT 43
5.4 USE OF CAPACITORS 44
5.5 WHAT IS ENERGY CONSERVATION 45
5.6 PERMIT TO WORK 45
5.7 COMMON SAFETY PRECAUTION 45
5.8 ILLUMINATION SYSTEM IN SUB-STATION 46
5.8.1 Yard Illumination 46
5.8.2 Emergency Lighting system in sub-station 46
5.9 FIRE FIGHTING ARRANGEMENT 46
5.10 LIST OF SUPPORTING AND OTHER AUXILIARY ITEMS AT
SUB-STATION 47
5.11 INSTRUCTIONS FOR RESTORATION OF PERSON
SUFFERING FROM ELECTRIC SHOCK 47
ANNEXURE – A
TESTING OF TRANSFORMER OIL
48
ANNEXURE – B
CONDITION MONITORING OF TRANSFORMER BY
DISSOLVED GAS ANALYSIS 50
ANNEXURE – C
INFRARED THERMAL IMAGING CAMERA
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