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Transformer Riddle No.88 - Stary loss of the transformer
Dear Sir,

In one of our 50MVA, 132 kV class transformers tested recently, stray losses are coming around 100kW more than the calculated although all other losses are with in the limites.

Can anybody tell me what could be the reason for such high stray losses.


Regards
Sreelatha
Author : Sreelatha - From: India
 
#1
Wed, October 24th, 2012 - 17:19
Generally the leakage fluxes of power transformer having their paths partly in the metal components of the transformer cause extra eddy current and hysteresis losses (known as stray losses) which reduce the efficiency of the transformer. The stray losses in the tank and core clamp are usually 15%-%30 of transformer copper losses (Ri2). In modern transformer this stray losses is controlled using the electromagnetic shield around the windings. For more information you can refer to:
Olivares JC, Cañedo J, Moreno P, Driesen J, Escarela R, Palanivasagam S (2002) Experimental study to reduce the distribution-transformers stray losses using electromagnetic shields. Electric Power Systems Research 63(1)
 
Author : Hamid - From: Iran
 
#2
Wed, October 24th, 2012 - 17:49
Generally the leakage fluxes of power transformer having their paths partly in the metal components of the transformer cause extra eddy current and hysteresis losses (known as stray losses) which reduce the efficiency of the transformer. The stray losses in the tank and core clamp are usually 15%-%30 of transformer copper losses (Ri2). In modern transformer this stray losses is controlled using the electromagnetic shield around the windings. For more information you can refer to:
Olivares JC, Cañedo J, Moreno P, Driesen J, Escarela R, Palanivasagam S (2002) Experimental study to reduce the distribution-transformers stray losses using electromagnetic shields. Electric Power Systems Research 63(1)

The electromagnetic shield can be affected and bended due to short circuit stress.The precise magnitude of the short-circuit forces depends very much upon the leakage flux pattern, and the leakage flux pattern also determines such important parameters as the leakage reactance and the magnitude of the stray losses. Manufacturers nowadays have computer programmes based on finite element analysis which enable them to accurately determine the leakage flux throughout the windings. Therefor after each sever short circuit, some shield deflection is possible and the extera leakage flux and stray losses is expected. 
Author : Hamid - From: Iran
 
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