Voltage Transformer Testing - Secondary Phase-Angle

[mikelangel78]

Hello

Testing a HV Voltage Transformer, using a OMICRON equipment (that must be connected to earth) I must inject in the primary side a test voltage, and I want to check the phase-angle in the secondary of the VT. Why the phase-angle should be near zero volts?

Thank you in advanced

 

[davidbeach]

Something's not quite right, an angle can't be measured in volts.

 

[mikelangel78]

Yes, sorry, you're right...my mistake "0º"

 

[davidbeach]

One wouldn't expect a phase angle change across a VT. It would make protection much more difficult if the VT had anything other than a 0 degree phase shift.

 

[scottf]

The secondary output of a VT has a given accuracy class rating. The accuracy class is defined by a limit to the ratio error and phase angle error of the secondary voltage versus the primary voltage.

The phase angle error is expressed in minutes.

Same thing for CTs.

Now, depending on the voltage rating of the VT and the applied voltage used in the test set, you may not get a very accurate reading if the VT is fully excited. For example, if you energize a 230 kV VT with a 10V test set, the ratio and phase angle error listed is likely going to be off from what it would be if energized at the rated 230 kV/sqrt3.