Query on High-Impedance Bus Differential Relay Operation
Query on High-Impedance Bus Differential Relay Operation
(OP)
Dear All,
Good day!!! Hope everyone doing well now.
I have a query regarding the effect of power cable shield ground which is covered by the high-impedance bus differential relay with a window type CT as current analog input.
Our bus is having 6 distribution feeders each with breaker and power cable length to about 10meters as take off and distributed through overhead lines. The zone of the bus protection is covered by window type CTs which is partially extended to the power cable length. The power cable shield is being grounded only at one, near the bus, and the other end (towards overhead line) left hang.
My question is, does will affect the operation of the relay when external faults (fault at overhead line) occur? Considering our power cable shield is grounded that way.
Please advise.
Thanks & Regards,
GRAEE
Good day!!! Hope everyone doing well now.
I have a query regarding the effect of power cable shield ground which is covered by the high-impedance bus differential relay with a window type CT as current analog input.
Our bus is having 6 distribution feeders each with breaker and power cable length to about 10meters as take off and distributed through overhead lines. The zone of the bus protection is covered by window type CTs which is partially extended to the power cable length. The power cable shield is being grounded only at one, near the bus, and the other end (towards overhead line) left hang.
My question is, does will affect the operation of the relay when external faults (fault at overhead line) occur? Considering our power cable shield is grounded that way.
Please advise.
Thanks & Regards,
GRAEE






RE: Query on High-Impedance Bus Differential Relay Operation
RE: Query on High-Impedance Bus Differential Relay Operation
Regards
Marmite
RE: Query on High-Impedance Bus Differential Relay Operation
Thanks for the enlightenment.
The cable shield ground is connected above the CT but only in one end, the other end is not grounded. As explained by davidbeach, we expect no return current for external fault.
Regards,
GRAEE
RE: Query on High-Impedance Bus Differential Relay Operation
Regards
Marmite
RE: Query on High-Impedance Bus Differential Relay Operation
We're using single core unarmoured XLPE Insulated PVC Oversheathed Cable and this cable is lay down on the trench.
What's the best practice?..Is it to connect one end of cable shield above the CT and brought back out through the window type CT and connect to ground? Or we left both ends of cable shield floating and ungrounded?
Regards,
GRAEE
RE: Query on High-Impedance Bus Differential Relay Operation
RE: Query on High-Impedance Bus Differential Relay Operation
If you don't want to trip the bus differential on a cable fault, route the shield ground back through the CT.
RE: Query on High-Impedance Bus Differential Relay Operation
Ok, we have to route back out the shield to the CT window.
I have another query on bus differential relay performance where it covers the whole length of the cable. The shield is within/between the zone of the bus differential and one end of the shield is grounded. Would that also affect the operation of the relay?
Thanks
RE: Query on High-Impedance Bus Differential Relay Operation