Routine maintenance and inspection for power transformers

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Safety Precautions

• A work permit must be issued and the qualified maintenance staff should carry the suitable safety category, 
• Safety fence (rope) with caution marks surrounding the work area,
• Transformer isolation and proper grounding is rquired
• Wear your safety helmet

Tools and Equipment

• Complete tool set
• Digital DC voltmeter
• Blower or vacuume cleaner
• PVC ladder, brushes, megger 5000v/9000 vdc

Work to be Carried Out

1. Check oil leaks,
2. Check oil level in main tank, and bushings,
3. Read and record the max oil temperature,
4. Read and record the max winding temperature,
5. Check all cooling fans for correct operation, and unusual noises,
6. Check the transformer control cabinet for door seal, clean by blower with moderate pressure.
7. Check the tap changer control cabinet ( if any ) for door seal, clean by blower with moderate pressure.
8. Check the Silicagel breather,
9. Clean all porcelain surfaces of all bushings insulators,
10. Clean the neutral current transformer,
11. Clean the neutral earth disconnect switch blades,
12. Lubricate the neutral earth disconnected switch bearing points,
13. Check all bolted connections for tightness,
14. Measure the insulation resistance for each winding to ground to other winding and for core to ground
15. Measure the winding turns ratio. R60/R15 > 1.2   every year 
16. Measure the winding resistance using megger 5000/9000 Vdc  every year
17. Check the pressure relief device,
18. Check the temperature gauges indicator,
19. Check all protection devices,
20. Read and record the leakage current monitor test on the lightening arrestor,
21. Check the Deluge system, transformer protection by water spray.
22. Measure the insulation oil breakdown voltage test.     every year.
23. Operate the tap changer from up to down off load (in case of step down transformer) and change the oil every year in case of  the transformer works at full load and every 2 years if at half load.
24. Check the gas in the oil and treatment if necessary taking an oil sample 
25. As required perform Power Transformer tests

Maintenance Record Data Sheet

Works to be Carried out	Test Result
Any oil leaks (if yes give location)	Yes        No
Oil level in main tank	OK       low      add
Oil level in bushings	OK       low      add
Max oil temperature	oC
Max winding temperature	oC
All cooling fans operational (if "on" indicate no. of fan)	Yes    No
Cooling fans noise (if "yes" indicate no. of fan)	Yes    No
Transformer control cabinet cleaned and inspected	OK
Tap changer control cabinet cleaned and inspected	OK
Silicagel breather	OK            Change
All porcelain surfaces of all bushings insulators cleaned	OK
Neutral earth disconnect switch blades cleaned	OK
Neutral earth disconnected switch bearing points lubricated	OK
Neutral CT cleaned	OK
All bolted connections checked for tightness	OK
Insulating oil breakdown voltage test  average kv   every year	kv,  air gap       mm
Turns ratio value for winding   R60/R15 > 1.2   every year	OK            Not
Winding resistance using megger 5000/9000 Vdc  every year	OK            Not
Pressure relief device,	OK            Not
Temperature gauges indicator	OK            Not
Record the leakage current monitor test on the lightening arrestor
(Deluge system) transformer protection by water spray	Yes       No
Check the tap changer (if any in case of step down transformer) and change the oil                                   every year	OK            Not
Take oil sample for gas analysis and treatment if necessary	OK            Not