Every circuit breaker/interrupter type in PSI service shares roughly 80-90% of the same checklist item names across Monthly, Half-Yearly, and Yearly schedules — porcelain insulator condition, counter reading, mechanism box, control circuit, local/remote switch operation, interlocking, earth connections, and so on. What genuinely differs between types is a small set of precise numeric specifications: gas/air pressure, IR values, timing, contact resistance, and coil parameters. This chapter states the common checklist ONCE, then gives the complete type-specific numeric reference as tables — this is both more useful and far less repetitive than reading the same 16-item checklist nine times with two words changed.
- Safety precautions BEFORE any CB/interrupter maintenance: switch off all auxiliary supplies; ensure the circuit/interrupter is in the OPEN condition; ensure the circuit/interrupter and sequential isolators are FULLY OPEN; discharge the spring.
Common Checklist — Monthly Schedule
- Surface of porcelain pole insulator unit: check for damages, flash mark, chipping — replace if required; clean with dry cotton cloth.
- Counter reading: check operation and record before/after maintenance — must function properly.
- Mechanism box: open cover, check/clean for condensation/rainwater, gasket, dust, hinges — apply weather sealant per Annexure V.
- Heater, thermostat & lamp: check function — thermostat setting should be 25-30°C.
- Control circuit: check/record operating voltage; wiring/connections should have proper lugs and ferrule numbers in the terminal box.
- Local/Remote switch operation and function: breaker should open/close correctly on the selected position.
- Position of indicator: check alignment and any missing indicator.
- Earth connections & foundation bolts: check and tighten if found loose.
- Condenser Tripping Device (CTD) for CB, and Anti-Pumping Device (APD) for BM (Bus-coupler/Bay Module): check for proper function — attend if defective.
- Interlocking with isolator: check the function.
- Main terminal (for SF6/gas types): check for discoloration, overheated/rusted nuts, bolts, washers — replace if required.
- Shock observer/absorber (for vacuum, oil, and some SF6 types): check for oil leakage — repair or replace if necessary.
| CB/Interrupter Type | Make/Type | Monthly-Schedule Gas/Distinguishing Pressure |
|---|---|---|
| 25kV Vacuum CB/Interrupter | ALIND VSE/5/20, BHEL PVTB/PVTI, ABB FSK-II | N/A (vacuum — no gas fill) |
| 132kV SF6 CB | 120 SFM-32B, CGL | 7.0 kg/cm² at 20°C |
| 25kV SF6 CB (GCB) | 50 SFGP-20A, CGL | 5.0 kg/cm² at 20°C |
| 132/25kV SF6 CB — 70-SFM-32A variant | CGL | 5.0 kg/cm² at 20°C |
| 132/25kV SF6 CB — 120-SFM-32A variant | CGL | 6.0 kg/cm² at 20°C |
| 220kV SF6 CB | ELF SL-4-1, ABB | 7.0 bar at 20°C |
| 25kV SF6 Double Pole CB/Interrupter | EDF SK-1-1(S) / EDF SK-1-1, ABB | 7.0 bar at 20°C |
| 25kV SF6 Interrupter (Single/Double Pole) | 30 SFGP-25A / 25 SFGP-25A, CGL | 5.0 kg/cm² at 20°C |
| 25kV Minimum Oil Interrupter | HPGE7/9A, ALIND | N/A (oil type — BDV tested instead) |
| 25kV SF6 Single Pole CB | LTB 72.5D1, ABB | 7.0 bar at 20°C |
The 132/25kV SF6 CB (air-blast/pneumatic assisted type) also has monthly air-pressure alarm/cutout thresholds that differ between its two sub-variants: 70-SFM-32A — alarm ON 13.2±0.3 kg/cm², alarm OFF 14.2±0.3 kg/cm², cutout ON 12.00±0.3 kg/cm², cutout OFF 13.00±0.3 kg/cm²; 120-SFM-32A — alarm ON 13.5±0.3 kg/cm², alarm OFF 14.5±0.3 kg/cm², cutout ON 13.00±0.3 kg/cm², cutout OFF 14.00±0.3 kg/cm². Compressor governor settings: 70-SFM-32A ON 14.5±0.3/OFF 15.5±0.3 kg/cm²; 120-SFM-32A ON 14.8±0.3/OFF 15.8±0.3 kg/cm². The 220kV SF6 CB's compressor oil is specifically Servo-150.
Half-Yearly Additions — IR/Insulation Testing
At Half-Yearly, in addition to everything in Monthly, every CB/interrupter type gets real insulation-resistance (IR) testing of the pole unit (breaker open: Top-Bottom, Top-Earth, Bottom-Earth; breaker closed: continuity + Top/Bottom-Earth) using a 2.5/5.0kV megger, PLUS IR testing of control circuit-to-ground with a 500V megger (uniformly >2MΩ across all types). The pole-unit IR threshold itself varies dramatically by type — this is a key distinguishing, testable fact:
| CB/Interrupter Type | Pole-Unit IR Threshold (Half-Yearly) |
|---|---|
| 25kV Vacuum CB/Interrupter | More than 5000 MΩ |
| 132kV SF6 CB | More than 1500 MΩ |
| 25kV SF6 CB (GCB) | More than 10,000 MΩ |
| 132/25kV SF6 CB (both variants) | More than 1500 MΩ |
| 220kV SF6 CB | More than 2000 MΩ |
| 25kV SF6 Double Pole CB/Interrupter | More than 2000 MΩ |
| 25kV SF6 Interrupter — 30 SFGP-25A | More than 10,000 MΩ |
| 25kV SF6 Interrupter — 25 SFGP-25A | More than 500 MΩ |
| 25kV Minimum Oil Interrupter | More than 1000 MΩ |
| 25kV SF6 Single Pole CB | More than 2000 MΩ |
- 132kV SF6 CB additionally gets closing/trip coil parameter checks: Voltage 110V DC±10%, Resistance 32Ω, IR Value 2MΩ (both coils identical spec). Charging time of closing spring: 15 sec.
- 25kV SF6 CB (GCB) additionally: tripping trigger & roller gap = 0.3 to 0.7mm; spring charging motor checks (commutator, brushes, tension, lubrication).
- 132/25kV SF6 CB additionally: consumption of air to open the breaker — drop should be LESS than 1.2 kg/cm² per operation.
- 220kV SF6 CB additionally: compressor governor setting ON 19.5 bar/OFF 20.5 bar; air pressure drop maximum 1.0 bar per operation; air pressure charging time LESS than 75 minutes for a 200-litre air reservoir (0 bar to 20.5 bar).
- 25kV SF6 Double Pole CB/Interrupter and Single Pole CB additionally: charging time of spring at nominal tension NOT MORE THAN 15 sec.
- 25kV Minimum Oil Interrupter additionally: oil sample BDV test (before and after monsoon) — MINIMUM 40kV; if BDV low or excessive carbon present, replace oil.
Yearly Additions — Timing, Contact Resistance & Coil Parameters
Yearly is where CBs get their full dynamic performance characterization: closing/opening TIMING (measured with a timer, in milliseconds), CONTACT RESISTANCE (measured with a contact resistance meter, in micro-ohms), and closing/trip coil electrical parameters (voltage, resistance/power, IR value).
| Type/Make | Closing Time | Opening Time | Contact Resistance |
|---|---|---|---|
| 25kV Vacuum CB — ALIND (BEL VAC bottle), CB | < 150 ms | < 65 ms | < 50 µΩ |
| 25kV Vacuum BM — ALIND | < 120 ms | < 80 ms | < 50 µΩ |
| 25kV Vacuum BM — BHEL | < 120 ms | < 80 ms | < 80 µΩ |
| 25kV Vacuum CB/BM — ABB | < 65 ms | < 45 ms | < 50 µΩ |
| 132kV SF6 CB (120 SFM-32B) | < 130 ms | < 32 ms | < 50 µΩ |
| 25kV SF6 CB (GCB, 50 SFGP-20A) | < 100 ms | < 43 ms | < 50 µΩ |
| 132/25kV SF6 CB (70-SFM-32A) | < 100 ms | < 30 ms | < 50 µΩ |
| 132/25kV SF6 CB (120-SFM-32A) | < 100 ms | < 30 ms | < 50 µΩ |
| 220kV SF6 CB (ELF SL-4-1) | < 130 ms | < 35 ms | < 51 µΩ at 20°C |
| 25kV SF6 D/P CB/Interrupter (EDF SK-1-1) | < 60 ms | < 35 ms | < 42 µΩ at 20°C |
| 25kV SF6 Interrupter (30 SFGP-25A) | < 100 ms | < 50 ms | < 50 µΩ |
| 25kV SF6 Interrupter (25 SFGP-25A) | < 100 ms | < 60 ms | < 50 µΩ |
| 25kV Minimum Oil Interrupter (HPGE7/9A) | < 120 ms | < 80 ms | < 50 µΩ |
| 25kV SF6 Single Pole CB (LTB 72.5D1) | < 65 ms | < 45 ms | < 42 µΩ at 20°C |
| Type | Closing/Trip Coil Voltage | Coil Resistance/Power | Coil IR Value |
|---|---|---|---|
| 25kV SF6 CB (GCB) | 110V DC ±10% | 22.28 Ω | 2 MΩ |
| 132/25kV SF6 CB | — | — | — |
| 220kV SF6 CB | 110V DC ±10% | 20.07 Ω | 2 MΩ |
| 25kV SF6 D/P CB/Interrupter — closing coil | 110V DC ±10% | 500 W | 2 MΩ |
| 25kV SF6 D/P CB/Interrupter — spring charging motor | 110V DC ±10% | 750 W | 2 MΩ |
| 25kV SF6 Interrupter (both variants) | 110V DC ±10% | 22.28 Ω | 2 MΩ |
| 25kV Minimum Oil Interrupter | 110V DC ±10% | 15 Ω | 2 MΩ |
| 25kV SF6 Single Pole CB — closing/trip coil | 110V DC ±10% | 500 W | 2 MΩ |
| 25kV SF6 Single Pole CB — spring charging motor | 110V DC ±10% | 735 W | 2 MΩ |
| 220kV SF6 CB — compressor motor | 110V DC ±10% | 2 HP, 16.5 A | 2 MΩ |
- 132kV SF6 CB yearly gas pressure settings: Normal 7.0 kg/cm², Alarm 6.5 kg/cm², Lockout 6.0 kg/cm². Dimensional tolerances (mm): stroke of moving core of trip coil 2.8-3.2, gap between trip-coil plunger and trip trigger 1.0-1.4, difference between stroke and gap (trip side) 1.6-2.4, stroke of moving core of closing coil 4.5-5.5, gap between anti-pumping lever and closing trigger 2.0-3.0, difference (closing side) 2.5-3.5, gap between anti-pumping lever and anti-pumping pin 1.0-2.0, gap between anti-pumping lever and closing trigger 2.3-3.0, stroke of spring operating mechanism 100mm±3mm, gap between roller and cam 1.4mm±3mm.
- 25kV SF6 CB (GCB) yearly gas pressure: Normal 5.0 kg/cm², Alarm 4.5 kg/cm², Lockout 4.0 kg/cm².
- 132/25kV SF6 CB yearly settings — 70-SFM-32A: air pressure alarm 13.2/trip 12.0 kg/cm², gas pressure normal/alarm/lockout 5.0/4.5/4.0 kgf/cm². 120-SFM-32A: air pressure alarm 13.5/trip 13.0 kg/cm², gas pressure normal/alarm/lockout 6.0/5.5/5.0 kgf/cm². Air pressure charging time LESS than 20 minutes (0 to 15 kg/cm², 70-litre reservoir). Tripping mechanism clearances: ST (solenoid magnet stroke, armature-core) 2.0-2.4mm, GT (plunger-trigger) 0.5-0.9mm, combined 1.5-1.7mm. Closing mechanism: SC 4.5-5.5mm, anti-pumping pin-to-latch clearance 'p' 1-2mm. Pole/mechanism setting: operating mechanism over-stroke 6±1mm, interrupter stroke 180+2/-5mm with wipe 36±2mm, operating mechanism stroke 40+1/-3mm.
- 220kV SF6 CB yearly: gas pressure normal/alarm/lockout 7.0/6.2/6.0 bar; air pressure normal/alarm/lockout 20.5/18.0/17.0 bar.
- 25kV SF6 D/P and Interrupter (both) and Single Pole CB yearly gas pressure: Normal 7.0 bar (D/P & Single Pole) or 5.0 kg/cm² (Interrupters 30/25 SFGP), Alarm 6.2 bar / 4.5 kg/cm², Lockout 6.0 bar / 4.0 kg/cm² respectively.
- 25kV Minimum Oil Interrupter yearly: linear stroke of closing spring 108mm, tripping spring 138mm; travel of moving contact rod 275±2.5mm.