ARC FLASH LINE SIDE PROTECTION 1

[SRA007]

I am trying to protect the line side of the switchboard, I tried to change the setting of HV really above the transformer but it seems to cause instability. Does any one know any thing practically or theoretically how to protect the line between the switchgear and transformer.

 

[davidbeach]

The best way is to make it be part of the transformer differential zone.

 

[dpc]

Using differential relaying is probably the best approach, but sometimes it is not possible to get the CTs where they would need to go on existing equipment.

Other options might be use of "maintenance mode" settings on the primary relay, or installing CTs and relays on the LV side of the transformer and using these relays to trip the primary breaker.

 

[cranky108]

We used a hot line work mode for feeder exits, which basically turned on the 50P1, and 50G1 elements.

For source side we try to include in the differential zone of the transformer.

 

[EddyWirbelstrom]

Another solution is to install arc sensors / relay in the LV incomer cubicle. When the sensors detect an arc ( especially on line-side terminals ) and a high current is also detected, an intertrip signal is sent to the HV breaker supplying the transformer and clearing the fault in approx. 0.1 sec. Arc detection sensors could be installed to along the MCC main bus and droppers.

 

[jghrist]

What do you mean by changing the HV settings causing instability?

 

[SRA007]

I am using 12X inrush current of transformer, if i change more setting of the Relay there is a chance that it will trip while re energising.

 

[cranky108]

I believe he is talking about an arc-flash relay, which uses an arc sensor in combonation with an over current detector.

Given, if installed wrong it could misoperate for an inrush event.
Better to install with over currents on X bushings of transformer to avoid inrush. But you would still trip high side breaker.