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# Transformer Riddle No.25 – Partial Discharge In Cast Resin Transformers

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• #320
Shane Alfonso

Is there any link between Odd Harmonics causing Partial Discharge in Medium/High Voltage ( in this case 15 KV ) Cast Resin Current Transfomers , Voltage Transfomers or Power Transformers.

Is there any link between Odd Harmonics causing Partial Discharge in Medium/High Voltage ( in this case 15 KV ) Cast Resin Current Transfomers , Voltage Transfomers or Power Transformers.

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• #1620
Hamid

In partial discharge phenomenon; because the grading material is non-linear it is expected that the current in the grading is significantly non-sinusoidal, containing higher harmonics as well as the fundamental component. Since the material can reasonably be taken to have properties independent of the polarity of the voltage, the current waveform must have positive and negative parts that are simply negations of each other. According to basic Fourier analysis in this situation (equalizing of positive and negative portion of periodic variation signal) the odd harmonics are therefore the only expected components of the harmonic spectrum, and this was confirmed by the measurements.

#1636
R K Mohapatra

Partial dischage is a claer cut function of Voltage Stress in insulation . The harmonics have a single point major effect , that it makes the waveshape PEAKY which can cause additional voltage stress in the insulation causing increase in Partiual Discharge . This pheniomena is not so relevent to power transformer . The phenomena could be more pertinent in Dry type trasformer because the insulation system ( epoxy casting or resin impregnation )of the Dry type trfr are normally not free from voids . The breakdown voltage across the voids can be easily crossed with minor increase in volatge stress causing more PD .

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