pajce
Electrical
- Jan 18, 2007
- 40
Hi all,
I have recloser installed downstream of Transformer Station. LDC I work for have guidlines for calculating relay settings , but I can't seem to find guidlines for revising of the relay (in the Station) settings when we introduce recloser downstream. This is not coordination question, my question is: how do I calculate setting for 50b and 50Nb elements? Without recloser we have criteria that 3ph fault current at the feeder end is devided by 2 and this would be Pick Up for 50b relay in the TS. It also need to be higher then 2 x max load on the distribution feeder. This devision by 2 gives margin for inaccuracy of CT etc and for fault resistance. (is fault resistance always purely resistive?)
For 50Nb we have criteria that TS relay Pick Up need to be less then 20% of phase-ground fault at the feeder end, and also need to be higher then 2 x unbalance on the feeder.
Now, my question is : is there any guidline what happens when we introduce recloser downstream of this relay in order not to disturbe Customer with A/R 's, normally 50b and 50Nb settings need to be revised, as zone of protection (feeder end) is now place where recloser is installed???
How do we cater for fault resistance there? Is it fair to say that fault resistance on 27.6 and 44 kV is 4 OHMs?
Thanks for any feedback on this number of questions
I have recloser installed downstream of Transformer Station. LDC I work for have guidlines for calculating relay settings , but I can't seem to find guidlines for revising of the relay (in the Station) settings when we introduce recloser downstream. This is not coordination question, my question is: how do I calculate setting for 50b and 50Nb elements? Without recloser we have criteria that 3ph fault current at the feeder end is devided by 2 and this would be Pick Up for 50b relay in the TS. It also need to be higher then 2 x max load on the distribution feeder. This devision by 2 gives margin for inaccuracy of CT etc and for fault resistance. (is fault resistance always purely resistive?)
For 50Nb we have criteria that TS relay Pick Up need to be less then 20% of phase-ground fault at the feeder end, and also need to be higher then 2 x unbalance on the feeder.
Now, my question is : is there any guidline what happens when we introduce recloser downstream of this relay in order not to disturbe Customer with A/R 's, normally 50b and 50Nb settings need to be revised, as zone of protection (feeder end) is now place where recloser is installed???
How do we cater for fault resistance there? Is it fair to say that fault resistance on 27.6 and 44 kV is 4 OHMs?
Thanks for any feedback on this number of questions