Paralleling of CBCTs

Do i understand you correctly, are both cables from the same source, feeding the same load ?

In such a case, the CBCT should encompass both cables (both are 3φ+N i hope?). Earth fault protection is achieved.

However, if the sources are NOT the same (mains/generator for example), then also, only one source is feeding the load is it not? So the same CBCT will still work, since only one cable will be carrying current at any point in time.

They are 2RX3.5CX300sqmm cable from the same source to the same feeder.The CBCT we have cant accommodate both the cables ,as one can imagine the size of the cables......Is it advisable to parallel them to the earth fault relay CDG14?

I would advise you to go for three CTs in the busbar and residually connect the ELR.

Nice to see you back sir! Isn't connection will trip on unbalance also???The connection plan we have won't work?pls opine soon..........

To provide for unbalance only you do have plug settings in the relay. Don't you? If you still want to have sensitive earthfault protection, you may go for a neutral CT too and connect it too in the residual circuit. Now, the relay wouldn't trip for unbalance, which would be offset by the neutral CT.

Won't the scheme we are going to implement work?Pls reply.Is it not practical to connect cbct in parallel?We have no other option for time being.

Assume that in one of the cables there is an earth leakage and its CBCT gives an output. Now, if the other cable is healthy, its CBCT will act as a burden to the faulty cable's CBCT and the output of this CBCT(F) will circulate thro the output winding of the CBCT (H) and there will be current division. The earth leakage relay may not receive the current for proper operation and thus protection is compromised.

Though a rare occurrence the above scenario cannot be ignored.

But, I have seen rectangular window type CBCTs for encircling larger cross sectional areas. In the past, I have even encircled bus bars in Unitised Sub-stations with such rectangular CBCTs.

Electrical Expert65

cbct (supply side)+ elr (1 phase n neutral or earth)........elr should be linked to a shunt trip release (MX) Linked to mccb (load side)

Hi

Why can't u treat these two cable as two separate feeders and arrange protection.

RajuS