capacitanceelectrostaticmeasurementshieldtransformer
I want to measure which is the effect of the connection of the electrostatic shield (between primary and secondary) to ground (or to neutral) in reducing the interwinding capacitance in my transformer.
How I can simply measure with a multimeter or a LCR the new reduced capacitance between primary and secondary (or the delta interwinding capacitance by using a floating shield or a "grounded" shield)?
If you are sure there is not a ground fault (i. e. current flowing through the ground wire), then all current flowing through one leg must also flow through the other. Therefore, it is sufficient to measure only one leg.
If you are not sure about ground current and don't have a GFCI on the circuit, you would need an additional current transformer, either on the ground wire or the other leg.
I have done this before.
Make the 132kV winding of the 3W transformer be un-earthed wye.
Insert a "node bus" at 132kV.
At the node bus, model a shunt impedance (if PSS/E will let you do such a thing - maybe it's called a 'constant admittance'.)
Make the shunt impedance have infinite positive sequence impedance, and 30 ohm zero sequence resistance, such that the phase to ground fault current is 2,540 amps. Note 2,540 A = 132kV / sqrt(3) / 30 ohms. (If you get a funny number, try using Z0 = 1/3rd of 30 ohms, or 3 times 30 ohms - funny things happen with 3 × I0.)
I have to run now, please comment if anything requires further explanation.
Best Answer
One way that I can think of would be to connect the LCR meter to the shield and to one of the primary or secondary terminals with all other ports on primary and secondary open.
One thing that may get in the way of a capacitance measurement like this is inductance, so try and minimize wire length to the transformer. This would give a rough idea of what the capacitance is.