Capacitor Bank (TI/MI/00026 Rev. 2)
- Quarterly: check porcelain insulator for damages/flash marks/chipping, clean/replace; check dielectric leakage/seepage — minor seepage attended with M-seal (fast-drying compound), study extent for major leakage and attend/replace; check and remove birdcages in/around the substation to avoid bird electrocution; check for abnormal temperature rise of capacitor units, find reason and rectify.
- Half-Yearly (additional): check/release excessive tension on connections; check/clean rust/corrosion marks on metallic parts with cleaning agent; check/measure/record current and voltage variation for AT LEAST 24 HOURS.
| Yearly Test | Standard Value |
|---|---|
| Tan Delta (dielectric loss angle), standard shearing bridge | Not more than 0.0005 |
| Capacitance value change (digital multimeter, to 1 decimal) | Beyond 6% change → replace the capacitor |
| Temperature rise over 24 hrs (suitable thermometer on capacitor can) | Should NOT rise more than 15°C above ambient temperature |
| Protective relays & setting | Working satisfactory — check/record functioning |
| NCT relay setting | Per RDSO guidelines — examine if changed |
| Fasteners & connectors | Tighten if loose |
Exam Focus — Capacitor Bank's Three Real Failure-Predicting Numbers
Three genuinely distinct, precise thresholds worth keeping separate: Tan Delta ≤0.0005 (a much tighter tolerance than the power transformer's 0.007 — don't transpose the two); capacitance drift >6% is the replace-trigger; temperature rise >15°C above ambient is the third, unrelated warning sign. Each measures a different failure mode (dielectric loss, internal element failure, and thermal stress respectively) — a capacitor bank could fail any ONE of these three checks independently of the others.
Series Reactor (Oil Type)
- Monthly: check porcelain insulator for damages/flash marks/chipping, clean/replace; check reactor tank/cover plate for damages/oil leakage-seepage, find reason and rectify; top up oil level to mark with new oil if required (BDV more than 40kV of oil); check silica gel colour (reactivate/replace if pink), top up breather oil cup; check/tighten bushing connection bolts/nuts, replace if rusty/overheated; check/tighten earthing connections; check/tighten terminal connector & bus-bar connector bolts/nuts (top and bottom), replace if rusty/overheated; check Buchholz Relay for gas collection — send for DGA per RDSO guideline if gas collected (Annex 2.04, ACTM Vol II Part I).
- Half-Yearly (additional): insulation resistance of winding-to-earth (with ambient temperature also recorded), 2.5kV megger — MINIMUM 200 M OHMS.
- Yearly (additional): oil condition check (BDV, colour, sludge) — CENTRIFUGE the oil if necessary; painting (epoxy + polyurethane per RDSO spec ETI/PSI/118 [10/93], A&C slip no.8) if tank colour faded/rusted.
Series Reactor (Dry Type)
- Monthly: check porcelain insulator for damages/flash marks/chipping, clean/replace; check/tighten bushing connection bolts/nuts, replace if rusty/overheated; check/tighten earthing connections, replace rusty/overheated bolts/nuts; check/tighten terminal connector & bus-bar connector bolts/nuts (top and bottom), replace if rusty/overheated; check coil visually for warmth — find reason and attend if warm.
- Half-Yearly and Yearly (additional): insulation resistance of winding-to-earth (ambient temp recorded), 2.5kV megger — MINIMUM 200 M OHMS; painting if faded (epoxy + polyurethane per ETI/PSI/118 [10/93]); check/tighten earthing connections; check/tighten terminal connector & bus-bar bolts/nuts; check coil for warmth.
Exam Focus — Oil vs Dry Type Series Reactor, What's Different
Both types share the SAME winding-to-earth IR threshold (min 200 MΩ, 2.5kV megger). What's genuinely different: Oil type has Buchholz relay gas monitoring, oil BDV/sludge checks, and centrifuging as a yearly maintenance action — none of which apply to Dry type at all, since there's no oil. This maps directly to how power/auxiliary transformers also split into oil-cooled vs other cooling — the same 'no oil, no oil-related checks' logic applies across PSI equipment generally.
Control and Relay Panel
- Monthly: clean accumulated dust externally & internally with dry cloth; check all indicating/recording instruments working normally; check/clean outer terminals of relay for abnormality; check/tighten cable connections if loose; check/clean terminal board/cable damage with dry cotton cloth, attend damaged cable; check all fuses for proper rating/overheating, replace if necessary; check/tighten earthing connections; check doors/hinges for intactness and free movement; check/plug holes to avoid moisture/insect entry.
- Half-Yearly (additional): check all indication/recording instruments for healthiness, replace if defective; check/clean outer terminals of relay (intact); check/replace door gasket & hinges for damages; check/tighten all connections if loose.
- Yearly (additional): check/record operation of ALL relays — working satisfactory; conduct relay testing by testing instrument and record, compare as per setting; check/clean all contactors, push buttons, switches for burnt/carbonised/corroded marks, replace if defective; check/record voltage between +ve to Earth and -ve to Earth — take action if variance observed.