Winding Temperature

Normaly the insulation class for a transformer is 'A' accordingly:

Maximum sustained operating temperature is 90 deg C, but the life span would be cut down to half if operated at 97 deg C and the life is cut down to about 50 days if operated at 150 deg C.

Formula: T = 7.2 X 10 ^{4 _e -0.09 ø}

Where life of insulating material in years is T and ø is the temperature to which the material can be continuously subjected.

BASICALLY YOU HAVE TO SEE THE DESIGN PARAMETERS.

UNLESS OTHERWISE SPECIFIED FOR A TRANSFORMER WITH NAPTHENIC BASED OIL AS PER IEC-60296 THE MAXIMUM OPERATING TEMPERATURE IS 100DEGc FOR OIL AND 105dEGC FOR WINDING.

SO YOU CAN SAFELY OPERATE THE TRANSFORMER WITH OIL AT MAX 90dEGC AND WINDING AT 95dEGC .

BUT IF YOU CONTINUOUSLY OPERATE AT A HIGHER TEMPERATURES YOU WILL PROPORTIONATELY REDUCE THE LIFE OF TRANSFORMER.

CHECK THE DESIGN -SOME FURNACE TRANSFORMERS ARE ALLOWED TO OPERATE AT A HIGHER RATING FOR A SHORTER DURATION ALSO.

APART FROM THAT FOR GETTING MAXIMUM HEAT AT A FASTER TIME YOU MUST OPERATE AT A HIGHER OPERATING VOLTAGE AND USE A CAPACITOR BANK/SVC UNIT TO GET A HIGHER CURRENT ,AND IF YOU ARE ABLE TO OPERATE AT AN HOURLY AVERAGE VOLATGE 11.5 KV,YOU WILL GET OPTIMIZED HEAT AND ALSO NOTE THIS IS NOT GOING TO HARM THE EQUIPMENTS ALSO KEEP THE TEMPERATURE WITHIN LIMIT AS 11KV SYSTEM IS DESIGNED FOR 12KV-Um.

I agreed with Mr. Bhattacharya, Normally the winding temperature alarm / trip contacts set within 90 to 95 deg C. You can operate the TX upto 90 deg C temperature.

The aging of insulation decreases, if we run longer time in hot condition / peak load.

CAN Y SPECIFIED ON WHCH TAP IT GOING TO HIGH TEMPERATUR ?

& IT IS ON LINE TAPE OR OFF LINE TAPE CAN U SPECIFIED ? WE R KNOWING THAT SOME TIMES TAP IS NOT FIXED PROPERLEY OR ERODE OF TEP NIP BECAUSE THAT ALSO IT WILL EXEED THE TEMPERATUR DUE TO CONTINUOUS HEATING OF CONTACT MATERIAL . ALSO THERE IS ONE OF THE POSSIBILTY THAT PERTICULAR TAPE LOOSE CONTACT INSIDE SO CAN U VERIFIED THIS MATTER ALSO?

Hi,

When designing transformer the temperature calculated at higher tap position only. The amount of temp. produced by onload tap cahngers is considering at the time of design and decided the oil & temperature rise. The data available in TX Name plate.

Normally winding / oil temp. is 50 / 45 deg C with out Ambient temp. If we consider ambient temp. 45 deg C, the winding / top oil rise goes to 95 / 90 deg C.

If TX insulation class A i.e 105 deg C.

If we run the TX in peak temp's the insulation starts aging fastly.

The temp. rise deponds on the following:

1. Loose contacts on tap switch, LV & HV connections etc

2. Improper oil circulation due to sluge in oil, uneven installation of TX etc

I hope this helps some extent.

Regards,

Hanumanthu