VT - Phase Checking

[mikelangel78]

Hello everyone,

I'm testing a 220kV Voltage Transformer with a CPC100 Omicron device.

One of the test that i've to perform is the phase checking. I've a three-phase VT of a bank of three single phase VTs.

I'll do a primary injection and measure the voltage between phases and neutral in the secondary side, at a marshalling box. These three-phase VT have a tertiary winding (broken delta configuration), and the voltage between the neutral and phase of this winding must be measure.

I've made some calculations (see the attached file) and i'll be very happy if someone could confirm my calculations.

Thank you in advanced,

 

[Kiribanda]

mikelangel78,
Your calculation is technically correct. You can check only the voltage ratio (NTR) of the VTs and not the full zero seq voltage across the broken DELTA during a ground fault. Under un-faulted conditions the voltage on each leg shall be 100V whereas under single phase to grond fault conditions on 220kV side,the MAXIMUM possible voltage across the broken DELTA terminals (two wires) shall be 3x100V=300V. Therefore, your 59N relay shall be adjusted considering this 300V thresohld. That is all. During commissioing, we normally confirm only the NTR by voltage injection and nothing else.