Multi-Function Numerical Relay for 11 kV Capacitor Banks

try siemens siprotec relays or areva P127 /P130 relays

There are a number of different relays avaiable, Siemens, Schneider, Areva, ABB, Schwiezter etc.

You need to design your protection system first & get the relays to suit.

Try the IEEE Guide for the Protection of Shunt Capacitor Banks (IEEE C37.99-2000) it is a very good giude for this purpose.

There are some tricks to be aware of - out of balance for un-grounded systems is needed but make sure you have loss of phase, under & overvoltage protection up stream as well. Be carefull of the circuit breaker or contactor you use to open & close as most on the market have clearance problems at the terminals due to capbank overvoltages. Make sure the terminals are well insulated or you will not have long to wait to have a BBQ & then replace the capbank.

Also if you Google Capacitor bank protection you get a lot of good reading material.

good luck

You have to be very specific in your design to select the relays as if it is a 3.2MW 11KV motor is distributed by

1. individual transformers then your protection will be such that Numerical 87 relay will have the protection function, for capacitor unbalance u have to install Areva P120 unbalance relay or equiv.

2. individual breakers only then your Main relay 50/51/27/59 will do the main protection, P120 unbalance only to be added.

As you have to put interlock for the Motor breaker with the capacitor bank breaker, so its better Numerical relays are selected on both ends for easy communication.

could you tell what for a 3.2 MW IM is used?

For driving a HP Nitrogen Compressor In the Oxygen Plant.The 11 kV VCB feeder for the Motor is provided with Siemens Make protection relay type 7SK804 & 7UM621 to meet all types of protection requirement for the motor.

I need to know the Make & Model No. of suitable Numerical relay for the 900 kVAR Cap. Bank which has to be operated in conjunction with the said motor with required interlocking.The Vendor has offered a Siemens Make Motor Protection relay type 7SJ621 for the Cap. Feeder.

Hope, I am clear now.

The siemens relay 7SJ621 is meeting all the protection requirements, you also have Areva Micom P127 which is also a multi functional protection relay covering all the protection functions required.

Thanks a lot Mr.Amarnath.SN.

However ,I could not find any mention about capacitor protection in the relevant catalogue of 7SJ621 allthough it talks about line,motor & transformer protection.

Capacitor Bank Protection requires

Over Current(50/51) & earth fault (50N/51N)

Under/Over Voltage(27/59)

Negative Phase sequence Protection (46)

Thermal Overload (49)

These are the main required, which are available in the 7SSJ621 and Micom P127 relays. The relays can be chosed based on our requirements, if they meet our requirements we can use them when the manufacturer's also agrees with our applications.