Maintenance of Electrical General Services Substation


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 
 

Maintenance of Electrical General Services Substation

The maintenance of an Electrical General Services Substation (GSS) is a critical activity to ensure reliable operation, enhance equipment lifespan, and maintain safety standards. A GSS typically handles the distribution of medium to low-voltage power for commercial, industrial, and residential areas, supporting auxiliary systems like lighting, HVAC, and control systems.

Proper maintenance minimizes the risk of equipment failure, ensures regulatory compliance, and promotes efficient energy distribution.

Types of Maintenance

  1. Preventive Maintenance:

    • Scheduled inspections and servicing to prevent unexpected failures.
    • Includes cleaning, lubrication, and functional testing of equipment.

  2. Predictive Maintenance:

    • Uses condition monitoring techniques to predict potential failures.
    • Includes thermal imaging, vibration analysis, and partial discharge monitoring.

  3. Corrective Maintenance:

    • Reactive repairs or replacements to address faults or breakdowns.
    • Focuses on restoring normal operation promptly.

  4. Condition-Based Maintenance:

    • Maintenance activities based on real-time data from monitoring systems.
    • Helps in optimizing maintenance schedules and reducing downtime.

Key Components and Maintenance Activities

  1. Transformers:

    • Inspection:
      • Check for oil leaks, physical damage, and overheating.
      • Inspect bushings, connections, and cooling systems.
    • Testing:
      • Perform insulation resistance, winding resistance, and oil dielectric strength tests.
    • Maintenance:
      • Clean radiators and replace deteriorated oil.
      • Tighten connections and repair leaks.

  2. Switchgear (MV/LV):

    • Inspection:
      • Check for loose connections, corrosion, and physical wear.
      • Inspect insulation and busbars for damage.
    • Testing:
      • Conduct insulation resistance tests and contact resistance measurements.
      • Perform functional tests for circuit breakers and relays.
    • Maintenance:
      • Clean and lubricate moving parts.
      • Replace worn-out contacts and update relay settings as needed.

  3. Cables and Busbars:

    • Inspection:
      • Check for insulation degradation, cuts, and moisture ingress.
      • Inspect termination points for signs of overheating.
    • Testing:
      • Conduct partial discharge testing and cable fault location.
    • Maintenance:
      • Replace damaged cables or joints.
      • Clean and tighten busbar connections.

  4. Protection Relays:

    • Inspection:
      • Verify proper relay settings and connections.
    • Testing:
      • Perform relay functional tests to confirm operation under fault conditions.
    • Maintenance:
      • Update firmware or software if applicable.
      • Replace faulty relays.

  5. Batteries and Chargers:

    • Inspection:
      • Check for corrosion on terminals and electrolyte levels.
      • Verify the charging system's functionality.
    • Testing:
      • Measure battery voltage, capacity, and impedance.
    • Maintenance:
      • Replace deteriorated batteries and clean terminals.
      • Adjust charging rates as necessary.

  6. Earthing and Lightning Protection:

    • Inspection:
      • Check earthing connections and rods for corrosion or damage.
      • Inspect lightning arrestors for physical and operational integrity.
    • Testing:
      • Measure earth resistance using an earth tester.
    • Maintenance:
      • Replace corroded earthing rods and repair damaged connections.

  7. Auxiliary Systems:

    • Inspection:
      • Check HVAC systems, lighting, and control panels for functionality.
    • Maintenance:
      • Clean air filters, replace faulty lighting, and repair control systems as required.

Maintenance Schedule

  • Daily:

    • Visual inspections of critical equipment.
    • Monitor operational parameters like temperature, load, and voltage.

  • Monthly:

    • Inspect transformers, switchgear, and protection systems.
    • Test alarms, annunciators, and control systems.

  • Quarterly:

    • Perform comprehensive tests on relays, batteries, and circuit breakers.
    • Clean and inspect all components.

  • Yearly:

    • Conduct detailed testing of insulation, oil analysis, and thermographic scans.
    • Replace worn-out parts and recalibrate equipment.

Tools and Equipment for Maintenance

  • Multimeters, insulation resistance testers, and thermal cameras.
  • Circuit breaker testers, relay test kits, and oil testing equipment.
  • Earth resistance testers and partial discharge monitors.

Safety Measures

  1. Personal Protective Equipment (PPE):
    • Insulated gloves, face shields, and flame-resistant clothing.
  2. Lockout/Tagout (LOTO):
    • Ensure equipment is de-energized before maintenance.
  3. Environmental Safety:
    • Proper disposal of waste oil, insulation materials, and batteries.
  4. Emergency Procedures:
    • Establish protocols for fire, electrical shocks, and other emergencies.

Benefits of Regular Maintenance

  • Enhanced Reliability: Reduces downtime and service interruptions.
  • Cost Savings: Minimizes costly repairs and extends equipment life.
  • Safety: Ensures a safe working environment and compliance with safety standards.
  • Efficiency: Optimizes energy distribution and reduces losses.

Conclusion

The maintenance of Electrical General Services Substations is essential for ensuring uninterrupted power distribution and operational safety. A structured maintenance program, combined with advanced testing techniques and adherence to safety protocols, ensures that substations operate efficiently and meet the demands of modern electrical networks.


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