SFT QUESTIONS Flashcards
Test prod checks
- Check in date for testing
- Correct prods for the switchgear
- No loose parts, general condition ok
- Check clean and contacts are good
What must you do to the test prod and why
Wipe with a lint free cloth before and after to prevent contamination from oil/dirt
HV insulations tests on overhead line
High leakage to earth may occur due to dirty/damp insulators
Normal 11kV test voltage and duration
18kV DC for 5 minutes less than 1mA leakage
What is a good HV test result
- Steady leakage of less than 1mA.
- If the test is unsatisfactory discuss with system controller
18kV = New cables
15kV <= 20 years old
13kV > 20 years old
Distribution ground mount transformer testing (prior to energising)
1000V DC IR test with winding to earth/tank in turn for HV and LV windings
Secondary switchgear
- Close switch, test between phases and each phase to earth 1000V DC/100MOhm
- Switch open test across each phase contacts
11kV GMT TX
- LV winding IR 1000V DC test with HV winding/tank grounded
- HV winding IR 1000V DC test with LV winding/tank grounded
- Test between HV/LV winding
11kV PMT tests
- LV winding IR 1000V DC test to earth
- HV winding IR 1000V DC test to earth
- Test between HV/LV winding
- Between Neutral and earth
5 Continuity between HV winding phases and LV winding phases/neutral
100MOHMs
Colour cartridge for armoured cables up to 80mm diameter/plain lead/covered sheath
Green
Heavy Charge for Steel Armoured Cables with a diameter between 80-150mm.
Red
Light Charge for all aluminium
corrugated sheathed cables up to
300mm² including
small plain lead cables.
Silver
Extra Light Charge for small XLPE
polymeric type cables without any solid
outer metallised sheath.
Yellow
Procedure for spiking pot ended cables
- Issue SFT/Carry out risk assessment for PE cable/Identify other cables/confirm with plan
- Spike cable whilst on phone to control
- Insulation test the cables to confirm the cores have been spiked
- Use spiking gun as short and IED cable at point of work (signal on one side but not the the other)
Misfire procedure
- Do not touch anything and inform control
- Wait 3 minutes
- Set safety catch to correct safe position
- Undo breech cap 1 turn, lift extractor to remove cartridge
- Remove breech cap and lift out cartridge
Methods of checking phasing
- Cold phasing (end to end before and after)
- Testing against and LV backfeed
- VT/Pfisterer on secondary side
- Use of HV phasing sticks or phasing pods across switch or spouts
HV belted cable
L1, L2 to -ve L3 - earth, test set to earth then swap after 5 minutes on cores
XLPE cable testing connections
All cores together for 5 minutes
4 exceptions to spiking cables at point of work
- Traced visually to a CME
- Gas/Oil/Submarine cables
- Sheath repairs
- Pot ended cables
Preparing ends for testing
Under immediate supervision of an SAP
If you cannot get a clear signal on a cable ID
Switchout and ID all other cables
If you cannot get a good signal on the point of work
Put in test prods, short 2 cores together and remove CME
ID a HV cable connected to a transformer
- Connect cable IDer to LV windings and close remote HV earth switch
- Insert C carriage to fuse switch and use TX windings as a remote short
Who records and retains the details of the issue and cancellation of each SFT
Control engineer or SAP if under NOP2, 3 or 4
What can you do to avoid X-rays from vacuum switchgear
Stand clear of 3 m whilst switchgear is being tested
