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Minimum Oil Circuit Breaker

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JYOTI MAKE : TQFQ 150.12 TYPE

Weekly Maintenance :

20 F-01 W Checking of Oil Level in Each Pole :
  • Do as described in Sub para 20 C-01 W
20 F-02 W Checking of Visible Oil Leaks :
  • Do as described in Sub para 20 C-02 W
20 F-03 W Checking of Silica Jel Breather for Colour Change :
  • Do as described in Sub para 20 C-03 W

Quarterly Maintenance :

20 F-04 Y Checking of Heater Functions :
  • Open the mechanism door and check the operation of heater. Replace the damaged/defective heater.
20 F-05 Y Visual Inspection Of Breaker And Operating Mechanism :
  • Interrupters and insulators in the breaker are to be examined of excessive dust collection on insulators
  • Oil level in each circuit breaker pole be checked and it should be in the middle mark 200C of the oil level glass. If less then add fresh oil.
  • Reading of the pressure gauge be observed. The pressure gauge (20) with pump stopped should show a pressure of approx. 335 atm.
  • The oil level with accumulator charged should be with in the range of the red mark on the oil level indicator.
  • Check for leakage on the high and low pressure joints.
  • Check dielectric strength of oil.
Tipping Based Maintenance:
  • Record no. of Trappings if any and identify the pole which has cleared the short circuit fault current.
  • If fault are occurring in one particular phase, shorter trip base overhauling may be necessary.
Following maintenance work is to be carried out after :-
  5 interruptions at rated interrupting current.
  Or 10 interruptions at 50% rated interrupting current.
  Or 500 interruptions at rated current (1250 A)
20 F-06 T Checking of Dielectric Strength Of Oil :
  • Condition of oil may be checked after about 7 interruptions of partial short circuit current. Minimum permissible withstand value of oil in service should not be found below 30 kV for one minute at 4 mm gap, however preferable value should be 50 kV, for one minute. Oil be filtered or replaced to achieve value 50 kV for one minute.
20 F-07 T Checking of Contact Burning :
  • Contact fingers (17), the arcing finger (38) and the moving contact arcing tip (37). are to be replaced if the wear has reached the maximum permissible limit as shown in Fig. 11 of Operate Manual. Contact fingers (17) should be replaced if burning extends to the length of safe tungsten tip. Contact arcing tip (37) is to be replaced if the burning is maximum up to 20 mm distance. For assembly of contact tips and fingers etc see the Op. manual. If burning in not much then file off the burn mark.
20 F-08 T Checking of Extinguishing Chamber :
  • Whenever the contacts are inspected, the Quenching chamber should also be checked, In the quenching chamber (41), cover disc. arcing blocks (92) and intermediate section (93) are to be replaced when worn out to the maximum permissible degree as shown in fig. (12) of Op. manual safe distance should be minimum 2.5 mm.
20 F-09 T
  • all gaskets, removed during dismantling of the breaker, should be examined and if necessary be replaced.

Yearly Maintenance :

20 F-10 Y Carryout maintenance work as given under sub-paras of quarterly maintenance.
20 F-11 Y Cleaning and Lubrications :
  • Clean the mechanism and insulators with non fluffy cloth and lubricate the parts.
20 F-12 Y Checking of Dielectric Strength of Oil :
  • Do as described in 20 F-06 T
20 F-13 Y Checking/Tightening of Foundation ................. All Hardware in Breaker and Mechanism :
  • Check the foundation, structure bolts and all fixing screws/bolts in the mechanism.
20 F-14 Y Checking/Tightening of all Electrical Terminal Connections :-
  • Check all the auxiliary contacts. Clean dirty contacts with fine emery cloth and oil slightly with hydraulic of transformer oil.
  • check each wire by slightly pulling out at the terminal block and observe for oxide coating/broken strands whenever loose jointing between terminal and wire is found.
  • Tighten the terminal connections properly after removing oxide coating, if any In addition to loose terminals, tightening of all terminal connections in general is essential.
20 F-15 Y Checking of Collector Motors :
  • Check the conditions of collector and bushing in case of collector motors.
20 F-16 Y Checking of Collector Motors :
  • Check pre-charging pressure of accumulator with eh operating mechanism functioning satisfactorily. A provisional inspection with the built in pressure gauge will be sufficient.
  • With accumulator fully charged, check indication of pressure gauge with nominal value of 335 atm. With deviating pressure indication, continue checking with precision instrument in accordance with para 9 of Op. manual.
  • If built in gauge shows the correct pressure, empty accumulator, with pump switched off, by repeated closing and tripping operations.
  • check zero position of the gauge.
  • Switch no motor pump for some revolutions until the pressure is stabilized.
  • Wait for some minutes for temperature alignment of accumulator.
  • Read the pressure on gauge and compare with nominal value of 200 kg/ Cm2 at150C.
  • If the pre charging pressure is correct, charge accumulator again fully.
20 F-17 Y Checking of Tripping Coil At 50% D.C. Voltage :
  • Check whether tripping coil operates of 50% of its rated voltage. If not then check the coil and remove the defect.
20 F-18 Y Measurement of Contact Resistance :
  • Measure and compare contact resistance with initial values.

Maintenance After 5 Years of Service :

20 F-19 F Resistance measurement of contact in current path, to be done.
20 F-20 F Measurement of closing time and operating time of the breaker be done.