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Power transformer energization

Power transformer energization

We have commissioned and tested a power transformer 63MVA, 132/33kV, but because of the delay of executing the 132kV source cable we didn't energize the transformer, it's now about one year since our testing, what tests can be done before energize the transformer? Keeping in mind we have done all recommended tests one year ago.
Please advice.
Thanks in advanced.

RE: Power transformer energization

You must check the BDV and water content of oil in main tank and OLTC chamber. Check the power factor of each winding insulation and LV bushing. Operate the tap changer from one end to other.

RE: Power transformer energization

Not to be an ass, but you should explain the BDV. It's spelled to much like a BVD.

RE: Power transformer energization


"Why not the best?"
Jimmy Carter

RE: Power transformer energization

Commissioning activities recommended by the factory of the transformer (Prior to HV power energization)
a- Measurements
• Electric strength of the oil (IEC test): minimum value 60kV,
• Winding insulation resistance to ground: at 20°C, The insulation resistance should reach a value of some hundreds MΩ for windings up to 72.5 kV, and some thousands MΩ for windings owning higher rated voltage.

b- Checks
Before energizing the transformer all the following checks must be done:
• Visible check of general installation and proper fastening of all components,
• Proper earthing of tank,
• Oil level in the conservator according to ambient temperature,
• Condition of oil preservation system (air bag),
• Oil level in the bushings,
• Color of hygroscopic salts inside air drier(s),
• Good operation of Buchholz relay alarm and tripping circuits,
• Minimum setting of max. current relays, taking into account the inrush current,
• Correct operation of main circuit breakers and relevant control circuits,
• Correct operation of pressure relief valve(s),
• Proper operation of alarm and tripping circuits relevant to protective devices, like temperature indicators (oil thermometer, winding temperature indicator, if any, etc.) and oil filling in the relevant pockets,
• Correct operation of control and protective circuits of on load tap changer, if any;
• "Open" position of interception valves on piping connecting tank and conservator, as well as tank and cooling plant,
• Vent of all bushings and piping running below the oil level in the conservator, so as to avoid that air or gas is trapped inside and be sure that all cavities are filled with oil,
• Absence of foreign bodies on the transformer, particularly on the cover,
• Cleanness of bushing porcelains,
• Proper setting of arcing horns on bushings,if any,
• Grounding caps fitted on bushings provided with taps for power factor measurement,
• Current transformers mounted on bushings: short circuit on secondary side or proper connection and earthing,
• Proper connection to overhead lines or cables and effective grounding of terminals to be earthed permanently (e.g. neutral ends),
• Removal of all earthing connections put for safety during erection,
• Verify the painting of the main unit and of all equipment, retouch the parts eventually deteriorated during transport or erection Before energizing it is important also to check that the unit is connected correctly for the relevant voltage. Only the connections shown on the rating plate are allowed.
If possible the unit should be energized by applying increasing voltage according to the following
• 50% of rated voltage is applied all at once and maintained for few minutes,
• The voltage is slowly increased up to 75% of rated value and maintained for few minutes,
• The voltage is slowly increased up to 100% of rated value. Opening and closing of the line circuit breakers should be performed before putting the unit under load.

Thanks to everyone tryied to help.

RE: Power transformer energization

I think it is fair to say you could skip some of the tests, but not all of them. A year is a long time. Has anyone "borrowed" parts from it. Is the earthing intact, or has it been stolen? Were the cubicle heaters energised? Has someone left the CT's shorted? Personally I would re-run some of the basic inspections, checks and tests, but a lot depends on the context. Can you guarantee that nobody has touched the transformner over the year it's been sitting there?


RE: Power transformer energization

Since so much time has passed since installation, a full set of field Acceptance tests should be performed per the NETA ATS spec, including Insulation Resistance/PI/DA, Doble PF (including all bushings), Turns ratio on all taps, and fluid DGA & screening. Also SFA (Sweep Frequency Analysis), especially if it was performed in the factory and when it was first onsite. Also, full inspections and tests of all accessories.

RE: Power transformer energization

Tan δ test would give a good indication of the healthiness if the previous test result is available for comparison.

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