Medium power transformer routine maintenance
The following periodic tests and inspections are recommended for routine maintenance of the medium power substation transformer.
8 Recommended Periodic Inspections of a Substation Transformer (photo credit: gridsense.com)- Gauge readings
- Cooling fans
- Control wiring
- Paint finish
- Fluid dielectric test
- Bushing and surge arrester insulators
- Bushing terminals
- Gaskets
1. Gauge readings
One month after initial energization and annually thereafter
Gauge readings, ambient temperature, and kvA load should be measured and recorded. Any abnormal reading suggests that further diagnostic testing or inspection should be done. If pressure/vacuum gauge and/or fluid level gauge readings suggest a possible tank leak, perform a pressure test according to instructions (15 Pre-energization Tests and Checklist).
Tank leaks must be repaired immediately to prevent serious damage to the transformer and danger to life.
2. Cooling fans (annual)
Check the cooling fans (if any) by setting the fan “auto/manual” control switch to the “manual” position. The fans should rotate at full speed within approximately five seconds. The fans should rotate smoothly with minimal vibration.
3. Control wiring (annual)
Control wiring should be checked to insure that wire insulation is in good condition. The control cabinet and associated conduit should be inspected to ensure that weather seals are intact.
Control power supply voltage should be checked and compared to the voltage stated on the wiring diagram.
4. Paint finish (annual)
Inspect the paint finish for damage or weathering that exposes the primer coat or bare metal. Repair any paint damage that might be found.
5. Fluid dielectric test (annual)
Sample the insulating fluid as described below. The dielectric strength of the insulating fluid should measure at least 26 kV.
Sampling of Insulating Fluid //
Transformers are filled with insulating fluid, which provides electrical insulation within the transformer tank and transfers heat generated in the coils to the tank wall and radiators.
The fluid is either:
- Conventional transformer oil (mineral oil),
- Envirotemp® FR3 fluid, or
- Silicone fluid.
It is also recommended that a fluid sample be drawn annually and tested for dielectric strength. Samples should be drawn from the bottom of the tank. Use proper sampling procedures to prevent erroneous test results. Dielectric strength should measure 26 kv minimum.
6. Bushing and surge arrester insulators (annual)
Bushing and surge arrester insulators should be clean. If the surfaces are excessively dirty, they should be cleaned while the transformer is not energized.
7. Bushing terminals
One month after initial energization and annually thereafter
If the transformer is energized and under load, measure bushing terminal temperatures using an infrared scanner. Excessive bushing terminal temperature indicates a loose or dirty connection. If the transformer is not energized, use a torque measuring device to make sure terminal connections are tight.
8. Check the gaskets
Visually check all gaskets for cracking or other signs of deterioration. Replace as necessary.
Do not reuse old gaskets. Six months after replacing a gasket, check and retighten if necessary.
Reference // Instructions Installation, Operation, and Maintenance of Medium Power Substation Transformers – Howard Industries // Substation Transformer Division
Related electrical guides & articles
Edvard Csanyi
Hi, I'm an electrical engineer, programmer and founder of EEP - Electrical Engineering Portal. I worked twelve years at Schneider Electric in the position of technical support for low- and medium-voltage projects and the design of busbar trunking systems.I'm highly specialized in the design of LV/MV switchgear and low-voltage, high-power busbar trunking (<6300A) in substations, commercial buildings and industry facilities. I'm also a professional in AutoCAD programming.
Profile: Edvard Csanyi
Need an inspection of a substation transformer. Can you do this? Or tell me who can?
Please send to me softcopy
i appreciate your efforts , many thanks for you.
Substation maintenance very simply explained. ✌
Thanks for your splendid explanation. I’m a substation guy and interested in detail information regarding control and protection systems for substation.
Thanks again for all the good information and I look forward to receiving more.
Very educative information.Thank you
I like this sharing it was really wonderful. but one question, what are the critical parts of power transformer of 33kVA and above?
Thanks for sharing such a wonderful information and it’s was really helpful.
Thank for useful topic. I have a question about bushing. How can we check the bushing oil pressure?
Thanks a lot it helpful but for Extra High power transformer and shunt reactor is the same or there are more than 8 points above.
Thanks for sharing such a nice informations. I have a question:
What’s the standard and process of recoloring the power transformers?
(how Changing the pervious color, fleece or sandblast the previous color to achieve the standard thickness of new color.)
Edvard , thank you very much for your information , periodic inspections are important to keep in mind the preventive maintenance of distribution transformers.
I think when it comes to oil transformers , one of the most important points for a preventive maintenance is the periodic review of the oil.
plz send me 11/.440 kv transformer testing prosses
Am any Electrical Engineer i will like to work with you
Thank you for your valuable topic and illustration. I would always prefer for all testing wither transformers or switchgear or any kind of test a “check list”. This would useful in case if you forget some thing specially if you work on maintenance programs.
All very well to have such important information available so that interested parties can read and
make use of such info that which most probably they have or have not heard of before, please do take heed and do the necessary inspections you will never be sorry.
Dear Edvard Csanyi,
Please send details testing and commissioning of the 220 KV GIS sytem with protection and control
Edvard:
This 8 Recommended Periodic Inspections of a Substation Transformer is a good summary.
Thanks for all the good information,
Alexis B. Rodriguez