I am working at oil pump station plant as electrical technician, I have 4 years experience in the field, and I face a problem which you can help me with. I appreciate any kind of information that will help me.
First of all, I was assigned to repair our plant fence lights. We have huge area of fence lights and at the switchgear room, we have 4 circuit breakers 480 VAC from main substation feeding 9 loads. It's our fence light divided in several loops including some area lighting.
My job is to clear a short circuit on isolated fence lighting loop. After finding shorted connection terminal in lighting pole, I clear this issue and return that loop in service, but when I was checking the voltage
Phase to phase I got 460 to 470 VAC, and I got 270 phase to ground which is good, because I don’t have neutral in the circuit. So I started to energize second breaker while I am checking voltage at breaker number 1 I found (unbalanced voltage) phase to ground I got
A-G = 418
B-G = 170
C-G = 200
Then I switch off second breaker, and I got normal voltage, then I start third one, found again unplanned voltage
A-G = 600
B-G = 190
C-G = 70
I started all 4 breaker one by one and I check them. Each one working alone is balanced, but when any 2 of 4 breakers working together, I got unbalanced voltage.
Note : all breaker running together (phase to phase voltage readings are 480 VAC) which is good and our transformer in each lighting pool needed that amount of voltage.
The breakers are not tripped and all lights working fine because it gets 2 phase 480 power. But I still don’t understand if this issue will affect our lighting systems or what?
Also the current reading for each phase is different in all 4 breakers. I am really thankful if you reach this point in my long explanation.
I hope you can help me.