CURRENT RELAY OPERATION TO GFCI IN STARTER
CURRENT RELAY OPERATION TO GFCI IN STARTER
(OP)
hello to all
Before than other thing,please excuse my english, i hope somebody can help to me in this cuestion.
Some time ago i see in a old starter for winding rotor motor ( by resistances ), a system that i think is to provide protection to the motor for unbalanced current and/or ground fault. This consist in the 3 main cables of primary ( 4,160 V )in starter, pass together trough CT of ratio 9/0.5 amp, conected to a current relay in series with the coil ( secundary of CT ).
This is a Westinghouse design in 1968 or around.
Im interesting in the theory of operation of this system, and i'm thinking about to make a similar system to protect small transformers ( 45 to 500 kva ), it is right???
I hope anybody can ilustrate me.
Thanks a lot .
Alfredo Corona
Mexico
Before than other thing,please excuse my english, i hope somebody can help to me in this cuestion.
Some time ago i see in a old starter for winding rotor motor ( by resistances ), a system that i think is to provide protection to the motor for unbalanced current and/or ground fault. This consist in the 3 main cables of primary ( 4,160 V )in starter, pass together trough CT of ratio 9/0.5 amp, conected to a current relay in series with the coil ( secundary of CT ).
This is a Westinghouse design in 1968 or around.
Im interesting in the theory of operation of this system, and i'm thinking about to make a similar system to protect small transformers ( 45 to 500 kva ), it is right???
I hope anybody can ilustrate me.
Thanks a lot .
Alfredo Corona
Mexico





RE: CURRENT RELAY OPERATION TO GFCI IN STARTER
RE: CURRENT RELAY OPERATION TO GFCI IN STARTER
To add to DanDel’s comments freddycor, no. Zero-sequence overcurrent tripping cannot protect a transformer by itself. Per-phase overcurrent relaying is also needed for adequate protection of transformers.
RE: CURRENT RELAY OPERATION TO GFCI IN STARTER
Just now Im thinking about it, because here in this area is in the coast and very wet conditions that many substations in 34.5 KV have trouble with contamination of insulators and is some common that they having loose of one phase, and burn some threephasic motors/loads. ( Subestations that no receive apropiate maintenance periodicially ).
Im talking about TRs from 45 to 500 KVA with no protection more than the monopolar fuse in primary, and main breaker in secundary.
I hope somebody have an idea if is possible to apply this system or something simmilar, to provide aditional protection considering the actual conditions of operation descrited above.
Thanks a lot for your time and energy !!!!
Alfredo Corona
Mexico
RE: CURRENT RELAY OPERATION TO GFCI IN STARTER
RE: CURRENT RELAY OPERATION TO GFCI IN STARTER
If you want to protect the transformers you will need more than GF protection. If you want to protect the motors against single phasing as a result of fuses blowing then what you propose will work. You have to be careful that you do not try to interupt the circuit (contactor or starter for motor) in the event of a short circuit. That task belongs to the circuit breaker. Measuring voltage (vectors) is more common for detecting single phase conditions than measuring the GF current, with attention given to so called 'regenerated voltages'.
It will be interesting to see what amplitudes of current are flowing to ground as a result of moisture.
You could use this info to find the trend and make decisions on rising GF current.
RE: CURRENT RELAY OPERATION TO GFCI IN STARTER
thanh you very much for your responses. I hope more people have some experience in this case ( if somebody have a system simmilar in operation please let me know yours results/recomendations ).
Thanks in advance.
Alfredo Corona
Mexico
RE: CURRENT RELAY OPERATION TO GFCI IN STARTER