3300 / 440V TRANSFORMER MAINTENANCE PROCEDURE

HTCB – VCB (TOSHIBA MAKE)                        LTCB – ACB (TOSHIBA MAKE)

1.      Obtain work permit from operations for the required transformer with proper tag number.

2.      Check all the parameters on both HV/LV side and both LV & HV are closed. Check both transformers are in service.

3.      Prepare caution notice/permit to work and display it on HV & LV panels.

4.      Switch off LV side breaker (ACB), and then switch off HV side breaker (ACB) of current tag number. Make sure that there is no power interruption.

5.      Open the HT breaker panel. Lift the latch pin upward on both the handles pull the breaker outward from service position to test position.

6.      Switch off control supply and remove control plugs and the front o ‘CB’. Remove the stopper plate, pull the  VCB outside breaker compartment

7.      Open LV (ACB) breaker panel.

8.      Lift the flapper (Middle of breaker – right hand side) upward and insert rack out/in handle into the slot.

9.      Rotate the handle anti-clockwise till it reaches disconnected position. Pull the ACB outward after lifting the stopper levers on both sides of ACB

10.  Position the trolley carrier and move it inside, below the lifting pins or both sides of ACB. Lift the trolley upward will it carries breaker. Pull the trolley outside and place the breaker on floor.

11.  Release charged spring by manually operating on/off of VCB and ACB.

12.  Put the earthing hand le of 3.3 KV side earthing switch compartment which is above VCB cubicle.

13.  Slide the stopper plate towards right hand side, lift earthing leaver and release the stopper plate.

14.  Remove the castle key from ACB, insert in the earthing breaker operate the key to release the locking pin.

15.  Insert the rack-in handle to the slot (right side) and turn it clockwise if it reaches service position.

16.  Remove handle and switch on control supply of earthing switch.

17.  Close panel door and turn earthing switch on. Observe earthing indication.\provide barrier caution tape on both sides of transformer of correct tag number.

18.  Clean whole transformer. Open LV & HV side terminal boxes. Inspect and tighten terminations hi-speed bushings.

19.  Clean and tighten all earthing connections.

20.  Measure insulation resistance of primary and secondary windings with earth and between windings. For HT winding use 2.5KV megger. For LV winding use 500V megger. Remove LT side neutral link before meggering.

21.  Close the terminal boxes. Check inert gas pressure. Take transformer oil for testing.

22.  Clean, check and inspect VCB and ACB for looseness and any abnormality. Apply petroleum jelly for finger contacts. Megger insulation resistance values of terminals. Measure contact resistance of poles.

23.  Check manual operations of ACB and VCB.

24.  Insert VCB in breaker compartment up to test position. Put back the stopper flap in position. Make sure breaker is off plug in control pin plugs and switch on control supply.

25.  Rack out earthing breaker to disconnected position on LV side. Take out the castle key.

26.  Insert the ACB using trolley and rack – in by turning rack – in handle clockwise to service position.

27.  Perform functional test by operating protective devices.

28.  Push both breakers to service position. Switch on HT breaker. Observe voltage.

29.  Close LT breaker. Observe voltage and current on both HT & LT sides.

30.  Remove caution tags and cancel permit.

31.  Enter rack – in / rack – out details in substation log book.

32.  Record all readings and values in history cards.

33.  Send oil samples for testing acidity and dielectric strength.