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Minimum Oil Circuit Breaker : Bhel Make HLD Type

Weekly Maintenance :

20 D-01 W Checking of Oil Level in Each Pole:
  • Check and ensure that the indicating button of the oil float is approximately at the middle of the oil level indicator glass.
20 D-02 W

Checking of Visible Oil Leakage :

  • Do as described in sub para 20 C-02 W
20 D-03 W Checking of Silica Gel Breather for Color Change :
  • Check silica gel color whether blue or not.
    Recondition/replace silica gel if found pale plunk.

Quarterly Maintenance:

20 D-04 Q Checking of Heater Function :
  • Do as described in Sub-Para 20 C-04Q.
20 D-05 Q Visual Inspection of Breaker and Operating Mechanism :
  • Do as described in Sub-Para  23C-05 Q.
20 D-06 Q Checking of Breaker Operation and Removal of Coatings Developed on Current Carrying Parts of the Breaker, Remains for Long Time in the Closed Position :
  • Do as described in Sub-Para 23 C-06Q.
20 D-07 Q Checking of Oil Leaking From Oil Dash Pot in Operating Mechanism :
  • In the closed position the oil surface should not be more than 15 mm below the edge of the filling hole.
  • Do as described in in Sub para 20 C-07 Q
20 D-08 Q Checking of Gas Vent :
  • Ensure vent pipe is free of obstructions like insects, wasp, rusting etc. The vent pipe is be checked with the help of thin rod to remove obstructions.
20 D-09 Q Lubrication :
  • Check whether gears, latches and springs etc. are properly lubricated. Do, if not
20 D-10 Q Cleaning of The Breaker :
  • Clean the circuit breaker with non fluffy cloth with special attention to porcelain insulators. Cotton waste is unsuitable not recommended.
20 D-11 Q Checking of Dielectric Strength of Oil :
  • Do as described in sub para 20 C-08 T.
NOTE : The circuit breaker should be overhauled regularly, the first time after one year operation and there after every third year unless operational experience motivates other periods.
Tripping Based Maintenance :
  • Record no. of short circuit tripping if any and identify the pole which has cleared the short circuit fault current.
  • Following maintenance work is to be carried out after 3 tripping at rated short circuit current or 8 tripping at 50%breaking capacity or 400 tripping at rated normal current. If faults are occurring in one particular phase, shorter trip based overhauling may be necessary.
20 D-12 T Checking of Dielectric Strength of Oil :
  • Do as described in 20 C-08 T.
20 D-13 T Checking of Plug Contacts Burning :
  • Contact plugs are to be examined for burning :
    Check contact measurement as described in the manual. If burning is very slight, removing of burn heads and polishing the surface insufficient. Replace the tips and arcing ring when burning is heavy. The degree of burning of the plug contact should be checked when the circuit breaker is in closed position. Correct measurement of distances as per BHEL manual reference no. BHE/IM/SEG/005/5000/3.79'a1' to 'a2' from the ruler DA-10 to the plug contact DA-13 and the surface DA-12 is to be done. If the degree of burning approaches the value given for used tip, remove the plug contact from the interrupter for more careful measurement of the contact tip.
Dimensions at a1 and a2 in mm.
new tip  a1 – a2 = 50 mm.
used tip a1 – a2 = 56 mm.
20 D-14 T Checking of Extinguishing Chamber :
  • Do as described in 20 C-10 T and see the manual. It is important that the chamber is kept free from contamination and that contacts and insulating parts are not burnt/damaged. Valve and piston should not be sluggish or hindered in their movement.

Yearly Maintenance :

20 D-15 Y Do as described in sub para 20 D- 12 T 2008 T P 37
20 D-16 Y -do- 20 D- 13 T   P 43
20 D-17 Y -do- 20 D- 14 T   P 43
20 D-18 Y Cleaning and Lubrication :
  • Do as described in sub para 20 C-12 Y
20 D-19 Y Checking/Tightening of All Electrical Terminal Connections :-
  • Do as described in sub para 20 C-15 Y
20 D-20 Y Checking/Tightening of All Electrical Terminal Connections :- -
  • Do as described in sub para 20 C-15 Y
20 D-21 Y Checking Of Auxiliary Switch :
  • Do as described in sub para 20 C-16 Y
20 D-22 Y Checking Of Limit Switches And Friction Clutch :
  • Do as described in sub para 20 C-17 Y
20 D-23 Y Checking Of Spring Charging Motor :
  • Do as described in sub para 20 C-18 Y
20 D-24 Y Checking Of Tripping Of Trip Coil At 50% Dc Rated Voltage :
  • Do as described in sub para 20 C-19 Y
20 D-25 Y Checking Of Contact Resistance :
  • Do as described in sub para 20 C-10 Y

Maintenance After Every Third Year :

20 D-26 TR

Overhaul the circuit breaker by carrying out the maintenance works listed under sub paras of yearly maintenance. Testing of the breaker for the following functions be also done every third year :
20 D-27 TR Leakage In Shaft Oil Seal : :
  • If any oil leakage around the operating shaftDR-5 occurs, remove and inspect the sealing unit. Leakage may also arise if the shaft is lubricated excessively, causing the grease to lift up the edge of the sealing ring from operating shaft.
  • For dismantling and mounting the sealing device consult manual.
20 D-28 TR

Overhauling Of Extinguishing Chamber :

  • Extinguishing chamber should be overhauled regularly in accordance with the instructions given for the circuit breaker. Check the movement of piston and valves in each case. Ensure also that all contact surface are free from coating so that the contact resistance is kept as low as possible. For comprehensive overhauling, see the Maintenance manual.
20 D-29 TR Speed Measurement :
  • Opening and closing speeds of moving contact in each pole be measured as described in manual and compare with test certificate values ( initial values.)
20 D-30 TR Resistance Measurement Of Contacts In Current Path :
  • Contact resistance of each breaking unit as described in the manual should be measured after every overhaul.
20 D-31 TR Measurement Of Closing Time & Opening Time Of The Breakers :
  • Operating time of the breaker, after every overhaul need to be measured with the help of a synchronous clock as described in manual.
Maintenance After 15 To 20 Years Of Service :
  • Dismantle the breaker completely and re-assemble. Replace the worn out components. Check timings Operating speeds, contact travel. Avail services of BHEL, if needed.
Lubrications :
  • lubricate the circuit breaker regularly. The two nipples DI-1 and DI-2 should be lubricated with grease E. Nipple DI-2 should be lubricated generously so that the grease fills up the bearing space and prevents ingress of water. Nipple DI-1, on the other hand, should be lubricated sparingly as excessive grease may cause oil leakage.
  • Lubricate other sliding surfaces and bearings with oil B.
  • As a protection against rust, all the untreated steel surfaces exposed to the atmosphere, should be coated with a thin coating grease.