LT Breaker Tripping

check your Ir and Tr settings....can you tell us what settings are in your breaker...Is there connected any external protection relay with your breaker,like CBCT+ELR or any other...???

You dont know how to calculate the short circuit current, and now advising about tripping!!!.....GA

beta harami pan chor dy,,I know u very well..masseera Industrial switchgear engineer:)

Hello Aseer,

Thanks for you reply. Herewith I mention settings. Ir =1, Isd=1.5,

Ir(s) = 0.5 (I am not sure whether it is Ir(s) or tr(s))

Regards

Kiran

I wonder about a ground fault somewhere--the motor drawing normal current, but maybe a chafed cable somewhere shorting (or arcing) to the crane frame and/or ground.

I agree with Tornado, there might be some leakage, that is to be checked in Cable or some other place which is creating a huge current.

1. Check your relay setting along with CT Ratio.

2. Check for load shedding scheme, if any.

3. Check for malfunctioning of relay.

4. Ensure cable leakage current through IR value.

When you report that the breaker is tripping under a 600A load, are you measuring the load on all legs, or just one leg? It's possible you have a high leg somewhere and just haven't measured it yet.

Possible Solution:

Some breakers operate on range settings, Please check if this breaker has such functionality. If it has then adjust the range to the available load.

If this breaker does not operate on range settings then be sure there is no short circuit anywhere. Thanks.

I agree with LAA Lucke, deenergize equipment and inspect breaker contact points if black and visible signs of arcing are present you'll need to replace said breaker unless you can take it apart and clean contacts with a burnishing tool

check the rating of you contactors, the sizes of your circuit breakers and the size of the cables. check specifically the size of wire in the breakers and ensure it is standard and equivalent to the load; you also have to do sensitivity check in calibrating the breaker.