Line Relay Settings. 1

[SauravWest]

Dear Sirs,

Could you please suggest me what types of relay settings are necessary for 33 kV, 11 kV lines?

We have transformer diff relay for our 6/8 MVA transformer. But if a line breaks, what relay should operate?

Regards,

 

[RRaghunath]

Present day, multi-function relays have a protection element called 'Broken conductor protection'.
This is based on measurement of (I2/I1) and is reliable in detecting any line break.

 

[Mbrooke]

In general terms if the line radial you would use 50/51, if the 33kv is run normally closed past the supply substation 21 and differential is typical.

 

[bacon4life]

RRaghunath- Do many utilities actually use negative sequence elements on distribution lines? I had the impression that negative sequence settings on distribution feeders had to be set pretty high to avoid tripping on:
1)unbalanced loads
2)faults on the low side of delta/wye transformers
3)unbalanced flows from tying feeders using single phase switches
4)unbalanced flows from tying feeders using gang operated switches because the timing difference between phases can be several cycles

 

[RRaghunath]

bacon4life, Yes, setting I2/I1 to detect broken conductor in overhead distribution lines is popular. Considering the points you made, the protection is always time delayed 5sec typically) to prevent unwanted trip.
Many of the clients prefer to wire it only for alarm to alert the operator.