Detection of CT secondary open circuit on a running system 3

[sramesh]

Good day

We had a failure of CT in a 6.6KV Motor feeder panel due to one secondary CT wiring connection was loose/Open in the terminal block. Is there any kind of online detection system or relay to detect the open circuit in the CT Secondary circuit. We are using SEPAM 2000 relay for the Protection purpose and I could not find any feature in this relay to detect if any one PHASE current is not available. Since I am doing the study to recommend a solution to avoid CT failures in future, your expert advice is appreciated.
Best regards and Have a great day

 

[slavag]

Hi.
I don't know this relay.
You can check few optioms ( 99%, Im sure, this relay is included one of the options) All are same, only other naming.
1. CT supervision
2. Curennt supervision
3. Current condition monitoring
4. Broken phase detection
etc.
More or less this functionality is base on the simple principal: (Imax-Imin)/Imax, from time to time ( depend on relay type) used Iavg.

In few type relays it's used as protection in case of loss of primary phase, in few in additional to protection function, used additional function: current supervision function for alarm.
But I never see some special CT open circuit online monitoring. You can't separate. what happened: open CT circut, CT fault or loss of primary phase.
In special application like to 87B ( BBP) used term CT open circuit supervission/detect for avoid maoperation of BBP.
But it's build on the diff current level

Hope it help.
Best Regards.
Slava

 

[sramesh]

Thank you very much for the quick reply and suggestion, CT supervision will suit to solve our problem. Is there any stand alone CT supervision/monitoring relay from a reputed manufaturers available in the market or you have experienced with for Motor /transformer feeders?

Thanks again
Best regards
Ramesh

 

[Marmite]

It would probably be easier to change the relay for one with the CT supervision functionality built in. If you want to stick with Schneider, have a look at the Sepam 40 series. Areva Micom P226 might also be suitable.
Regards
Marmite

 

[sramesh]

Thank you verymuch and I will consider the option of changing the relay with in built CT supervision.

Regards
Ramesh

 

[tinfoil]

Is this a wye connected CT arrangement?

If you have a way to compare the vector sum of the three phase currents (i.e the residual current) with a MEASURED neutral current, then you could also alarm if the difference is too great, as this is sometimes caused by loss of input from one of the 3 + 1 CT circuits.

 

[slavag]

Hi
Sramesh, Im fully agree with Marmite and tinfoil.
What Marmire saied, all newer relays are included this option.
Good Luck.
Slava

 

[davidbeach]

You can also build CT supervision in logic, the presence of negative sequence current without negative sequence voltage will indicate a CT problem.

 

[sramesh]

Good day to you
Thanks David for the valuable suggestion, I will discuss with Schneider Electric on the possibility of modifying the logic of the existing SEPAM 2000 relay,which will avoid buying new relays.

Thanks again and Have a great day

 

[glendale]

As a temporary measure you could select the 46 function on the SEPAM with a low setting and the time function set to definite minimum 0.1 seconds. This would at least detect unballanced CT inputs. Not ideal but would add a degree of confidence.

 

[slavag]

46 function is good option, as David and glendale wrote, but not 0.1sec. OP saied about transfromer and motor protection, In time of start or inrush, 46 will pick-up all the time.
David, you recommned build invert logic of 60 functionality .
Best Regards.
Slava