ABB RET 670
ABB RET 670
(OP)
Hi guys, we have this new relay, ABB RET 670 differential + ref. The relay has three sets of current sensing terminals for differential protection. But in our switchyard configuration, there must be four sets (1-low side of transformer, 3-high side of transformer). Since there are only 3 sets of terminals available on the relay, is it okay to parallel 2 sets of CTs in 1 terminal of the relay? Thanks!





RE: ABB RET 670
RE: ABB RET 670
Paralleling CT inputs can work, but it can also leave you without sufficient restraint current if current can enter on one of the paralleled CTs and leave on the other during an external fault.
RE: ABB RET 670
The CTs are identical. Same class, ratio, model and maker.
David,
Please elaborate further. Thanks!
RE: ABB RET 670