Our ABB 3750kVA 11kV/3.3kV class F dry-type transformers are suffering from overheating under no load condition. They are also very noisy. Insulation barrier between secondary windings and iron core have been added at site prior to energization. Ever since we have been experiencing overheating and tripping under no load due to over temperature set to trip at 140 degC. Please justify
The case you described is quite an unusual one, but not entirely unheard of. The fact that you reference both overheating at no load and excessive noise points to possible circulating currents in the transformer core. These currents are most commonly created by system voltage harmonics causing potential differences inside the core laminations. A system harmonic analysis would be recommended to determine the proper means of resolution.
We can definitely support in such an analysis.
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