Swichgear high impedance differential relay settings

[rockman7892]

I am looking for some guidelines for setting an ABB 87B high impedance differential relay used for bus differential protection on 13.2kV switchgear. Differential zone is between main breaker and feeder breakers when switchgear is fed from utility and between generator tie-breaker and feeder breakers when fed from generator source.

From what I understand the relay elements have an impedance associated with them that corrospond to a voltage when the differential current is passed acorss them. The only setting on the relay is a volage setting and there is no time delay or slope element.

From what I read in the relay manual you should set the voltage setting as low as possible however it should be set high enough so that the relay should not misoperate due to CT saturation for fault outside of the differential zone. From what I saw it suggested that you use the CT impedqance along with CT wiring impedance between furthest set of CT's as well as max fault current avaliable just outside differential zone to set the relay?

I was curious to see what suggestions others had for setting these differential relays in this bus differential application or any other resources that may help.

One additional question I had was related to a reverse power (ANSI device 32) setting on the switchgear main breaker. I'm assuming that this setting is used on main breaker when the switchgear is being fed from the generator source. Any suggestions or standards for this reverse power setting on a main breaker?

Thanks for the help.

 

[rockman7892]

I have been looking into information on the main breaker reverse power relay trying to determine any requiremnts for its setting. From the looks of it, the setting will be there to prevent backfeeding the utility when a downsteram generator is operating with the main breaker closed, or if a tie breaker from another utility source is closed with the main breaker closed. Either of these cases I suspect could feed into a fault on the utility system.

Is there any guideline from the utility on what to set these reverse power relays to at the POCC? From some exapmle settings I have looked at I have seen between 15-20% rated power of the main service.

 

[DTR2011]

GE had a very popular EM relay called the PVD, which did essentially the same function as the 87B from ABB Allentown. You may want to check the manual for that, as well as SEL and others (Alstom MFAC) for more specific application guidelines. Some manufacturers use a LOR in the scheme to short out the cts, while others use metrosils (voltage clamping device), to protect the cts from overvoltage.

You may also have to check with the local utility as far as the 32 relay. They likely have paralleling agreement which does not permit any transfer of power to them and your setting may have to be quite sensitive to prevent this.