Transformer Insulation Resistance

[sjt1956]

In thread238-219928 dating back to 2008 MVP prc stated that, with respect to the formula CE/Sqrt(KVA), for dry type transformers C=16 when measured without guard (that's if I've read it correctly). Could someone please provide an explanation of how the figure of 16 is arrived at when the initial figure is 30 given an ambient of 20degC.

Many thanks.

 

[prc]

When measurement is made without guard, there will be leakage currents and IR will be less. I took the constants 30 & 16 from TMG book. I think they were arrived at from actual test values. These are all quite old data. I shall give here latest C for vacuum cast epoxy resin transformers after a few days.

 

[sjt1956]

Thanks for this response, it makes sense. When considering dry type transformers I am also including open style, non-cast resin units. I will be very interested to hear your thoughts and could you please give some detail on the TMG book - I don't recognise this. Much appreciated.