Does LSIG replace Relay 50/51/51G functions?

[tumbleweed1]

Few questions:
1) If a main or feeder breaker has LSIG functionality, does this remove the need to have 50/51/51G protection in an external solid state relay?
2) If so, is one more desirable over another? Obviously SS is more flexible but breaker LSIG would be more “custom” as it is provided by MFR for their specific product
3) Can one simply incorporate the exact LSIG curves from a manufacturer into a programmable SS relay and forget about an electronic trip unit on the breaker itself?

Cheers!

 

[collies99]

LSIG trip module has both phase time, phase instantaneous, ground time and ground instantaneous element.

you do not need any other protective relaying, and low voltage protection does not need any other with the exception of zero sequence CT or neutral CT which may be incorporated into your LSIG trip unit depending on make and model and protection requirements.

All functions should be detailed in the unit operating instruction manual.

 

[rcw retired EE]

Adding an external relay to a low voltage breaker adding curent transformers, external trip inputs and possibly a control power supply to the switchgear. (The LSIG unit is typically self-powered from the breaker's integral CT circuts and only uses external power to run a display). The breaker price will not be much less if you delete the LSIG trip unit. The deduct will defintely be less than the cost of CT's and external trips.

Why not just stay with the normal design?

If you need special protection features, such as directional overcurrent, reverse power, or voltage restrained overcurrent, an external relay might make sense.

I am working on a project that has external relays as you suggest on the Mains & Ties for several 480V substations and it is causing a lot of problems. Coordination and controls would have been much easier if we had just used the integral trip units.