SEL351S Watts & Vars

[SG-1]

I have a SEL 351S Protective Relay & a Bank of electro-mechanical Panel meters. At Unity PF both the relay & meters read nearly the same.
When I shifted the voltage 120 degrees by moving:
A-Phase Voltage to the relays B-Phase Input

B-Phase Voltage to the relays C-Phase Input

C-Phase Voltage to the relays A-Phase Input

I am at a loss trying to reconcile the relays numbers with the bank of meters. By my thinking this voltage shift should be into LEAD as indicated by the PF Meter sketch. I do not understand how the Watts & Vars add up to be greater than the Watts at Unity. At .5 PF I would expect that the watts & Vars would be equal.


Looks like the Varmeter may have a wiring issue, that is yet unresolved because it is reading low. The electro-mechanical panel meters use 2 currents A & C for measurements. The low reading on A-phase current is a test set anomaly.

 

[ptonsparky]

Did you move the CTs as well?

 

[mach531]

I would expect watts and vars to be equal at 0.7pf or cos(45).

Also, it looks like your sequence is ACB....what is your PHROT setting in the relay?


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[SG-1]

Did you move the CTs as well?

CT connections did not change.

Understand this is a test to get the PF Meter to read something besides Unity & The VARMeter to read something besides zero.

 

[SG-1]

I would expect watts and vars to be equal at 0.7pf or cos(45).

Also, it looks like your sequence is ACB....what is your PHROT setting in the relay?


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Relay is set for ABC (default) Phase sequence is CABCABCABC which is still A-B-C.

 

[SG-1]

Thanks mach531

I made the attached chart & see that I have exceeded the limits of the electro-mechanical PF meter. It reads Unity at the 12 o'clock position & only goes to .5 in either direction + or- 60 degrees. The .5 LAG or LEAD would be 60 degrees. I am now thinking the 120 degree shift is driving the indicator all the way around to the opposite .5 reading & hence the SEL -.5 LAG reading (120 degrees). How to prove ? I think a 360 degree diagram of a electro-mechanical PF meter might help.


This is probably the issue with the VAR Panel meter too. How to prove ??