MAINTENANCE PROCEDURE FOR SUBSTATIONS AND SWITCHGEAR
GENERAL
The maintenance of the switchgear and electrical equipment can be carried out safely and efficiently through the following steps.
1. Understanding the job
2. Availing the permit to work
3. Organizing for the work
4. Availing the shut-down
5. Maintenance work6. Closing the work
7. Normalizing power status
8. Returning the permit
9. Record results.
1.) Understanding the job:
a) The Supervisory staff must have a clear idea about the job to be carried out in detail and stepwise. They should have a fair idea of this job to their subordinates.
SUBSTATIONS RM01 TO RM13 MIANTENANCE OF 11 K. V./ 3.3K.V. TRANSFORMER
After obtaining the work permit, check the tag number on the VCB Panel.
Request M-20 staff to trip and earth 11K.V. connected feeder with copy of the work permit.
M-20 staff will place earthing truck in place of drawn out 11KV breaker.
Confirm that M20 staff makes this earthing truck “ON” and then lock it using your own lock and carry the key with you.
While going back to your substation confirm that the transformer under maintenance has no humming noise.
Check again the YCB panel; it should be in off position. This confirms the operational status of the inter-trip with M-20 feeder.
Rack-out the YCB
Open the cubicles, holds both handle and lift the latch and with sufficient force, draw-out the breaker and the breaker can be drawn-out to its Test/Rack-out position. At the correct position, the latch shall come back down to its position.
Switch off the control supply and disconnect the control cable plugs. Remove stopper strip in front of the VCB by unscrewing the nuts. Pressing two knobs to their handle hooks, draw-out breaker completely out of panel.
Earth the cable side of the incomer.
Insert the earthing handle in its position, push the latch and operate.
Identification of the job includes knowing location of the equipment, its function along with its general characteristics such as voltage level, capacity, duty etc.
Alternate arrangement should be considered and must be provided for continuity of power supply before starting to avail shut down on the equipment.
Availing Permit to Work
Permit to work must be availed.
1.1.1. By a person competent to receive it.
1.1.2. From a person competent to issue it.
1.1.3. For a valid assigned and approved work.
1.1.4. After having explained to Operation staff details of steps of the work to be done.
1.1.5. With due intimation and signature of the KNPC.
Engineer in case the work involves switching operation of any UPS system.
In case the work involves probability of annunciation / alarm to any department other than operation, i.e. Fire Station then such department should be informed accordingly about the work prior to taking up such work.
Permit to work must be readily available / displayed at the site of work to the inspecting authorities.
Organizing the work
Caution Notice duly filled in and signed must be prominently displayed at the equipment control panel under work and half portion of Caution Notice should be displayed at the equipment.
Staff for the maintenance work should be nominated and informed accordingly.
Equipment for work must be identified by at least two senior supervisor staff for its correctness before starting any work.
Cordon-off the correct equipment with caution tape around.
Inter-relation between the equipment under maintenance and that related to it by Power-flow or process logic must be clearly understood by the person authorized to work. In case of any doubt, seniors must be consulted till satisfactory clarification.
Availing shut-down
Check the prevailing status of the Power-flow before starting any work, its total load in case of parallel Operations of the Transformers and the status of the Bus-tie.
Just before availing shut down, inform Operations staff (and Fire Station if required) about your steps of operation and theirs expected alarms and changes in Power – flow.
Switch – off the circuit Breaker after confirming the tag number, this operation should be done by the authorized person who avail the work permit and in the presence of the area engineer.
Rack-out the circuit Breaker.
Earth the circuit as per manufacturer procedure and using the proper tools.
MAINTENANCE WORK
Allocate the job to certain staff whom should be only allowed to be present at he site.
Carry out the required maintenance for the equipment as per the CMMS and the manufacturer recommendations.
Closing Down Maintenance Work.
Remove cordon-tape around the equipment (if applicable).
Clean the site.
Declare to your staff that the work is completed.
Normalizing the system.
Remove the circuit earthing as per the approved procedure after checking he tag number.
Rack – in the circuit breaker as per the approved procedure.
Returning permit to work.
Inform Operation staff that the work is completed.
Operate the earthing handle downward using sufficient force. The earthing switch will operate making the incoming cable earthed.
Observe and check correctness of indications i.e. VCB OFF condition Earth Switch ON condition.
Lock the cubical compartment.
Maintenance of the transformer.
Allocate this job to certain staff whom will be only allowed to enter the transformer yard.
Clean externally the body of transformer starting from the top downwards, watching for any damage, oil leakage etc.
Open up primary and secondary side cable box covers. Open also the neutral C.T. Box cover and clean them all.
Check for any spark – pitting or looseness of connections and if so, rectify.
Check and clean all earthing connections and refit them.
Check the condition of the silica gel and, if necessary, replace it along with necessary oil quantity.
Clean and check the control panel for the cooling system of the transformer for manual operation of the fans.
Megger the transformer as under:
1. Making earthing truck at M-20 S/S “OFF”.
2. Switch “OFF” the 3.3KV side earthing switch.
3. Megger 11 KV to transformer body and note down results.
4. Measure insulation resistance values’ of primary and secondary
5. Sign in column no.9 for having completed the work. See that all copies have this signature.
6. Confirm that operators signature is obtained on all three copies for having agreed that the work has been completed.
7. Take away your copy of the permit to work.
Recording the results
1. Record the job done in the substation log book
2. Make entries in the history card file about the maintenance work done and sign it.
For primary to earth and primary to secondary use 5KV megger.
For secondary to earth use 2.5KV megger.
Close the terminal boxes and ensure no tools, materials left inside.
Take transformer oil (testing of dielectric strength and acidity) samples.
Position the lifting trolley of potential transformer near the P.T. cubicle. Lift the latching pin on P.T. handle on both sides, pull out outward. Lock it in trolley. Remove control plug pins. Pull out and place it on floor.
Position the same trolley near lightning arrestor cubicle. Lift the locking pins on L.A. handles, pull outward. Lock it in trolley and pull out.
Clean P.T & L.A., tighten connection, and check for abnormality. Measure insulation resistance values (2.5 KV megger).
Rack – in P.T. & L.A. following same procedure.
Clean VCB, lubricate all moving parts, and check for manual operation, clearance of contacts. Measure contact resistance and insulation values of poles.
Insert VCB in test position. Replace stopper flap in its original position. Connect control plug pins to VCB and switch on control supply.
Carry out functional tests.
a) Inter trip
b) Buchholzs relay trip alarm
c) Winding temperature and oil level alarms.
Closing down maintenance work.
1. Remove cordoning-off tape around the transformer.
2. Confirm that transformer yard has danger warning signs in their proper place.
3. Clean the transformer yard.
4. Ask everybody to go out of transformer yard and lock the yard from outside.
5. Calibrate the measuring and protecting instruments with KNPC approval and record results.
6. Declare orally to all that the work is completed.
Normalizing the system
1. Return the key and open lock of earthing truck in M-20 S/S.
2. Request M-20 S/S staff to remove earthing truck and insert 11 KV VCB in service position.
3. Request M – 20 staff to make concerned 11 KV feeders VCB ON.
4. Check the humming noise of this transformer is audible.
5. Checks from the panel that correct values o voltage are available.
6. Close 3.3KV breaker of the transformer.
7. Check the load shared by this transformer with previous values and that of the other transformer.
Returning permit to work
Inform operation staff that the work is completed.
Sign in column no.9 for having completed the work. See that all 3 copies have this signature.
Confirm that operator’s signature is obtained on all three copies for having agreed that the work has been completed.
Take away your copy of the permit to work.
Recording the Results
Make entries in the history card file about the maintenance work done, sign it.
Obtain oil sample results and study them. Also enter this result in the history file.
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