25kV Bus Fault clearing time

[Sn00ze]

Hi,

Just curious (if anyone knows) what are typical clearing times for a 25kV bus fault from the protections?

zone1 and zone2?

Does adding an NGR change this? (Assuming Zone 2 will come upstream form the TX prot)

Does the choice of having a high impedance vs low impedance relay affect these?

EDIT: Sorry forgot to add, im in Canada, AB., also mainly (but not only) interested in Phase to ground or phase to phase to ground or 3-phase to ground.

Thanks.

 

[Mbrooke]

If you want fast fault clearing, (under 5 cycles) a dedicated bus differential scheme is the way to go. Low impedance vs high impedance does not matter much when set correctly in my experience.

 

[marks1080]

For a bus dont worry about zone 1 and zone 2. Use differential as Mbrooke suggests. Bus blocking is gaining popularity at that voltage level, but personally i would stay with differential.

NGR won't have any impact.

Decent differential protection with a decent breaker will give you sub-5 cycle clearing time.

Whether or not to use a high-impedance differential set up depends if fault levels are high enough such that a close in (but out-of-zone) fault doesn't saturate the Bus CTs, which would cause an over-trip of the Bus.