Fuses as back up protection?

[Mbrooke]

Normally the loss of distribution feeders from stuck breakers or relays failures is mitigated by a double breaker-double buss or a breaker and a half scheme.

Smaller/ older substations are single breaker single buss, so if one breaker fails the entire buss is lost as well as all outgoing feeders. Is it possible, or practical, to add power fuses in series with the breakers to avoid such a contingency?

 

[cranky108]

If the fuse can be coordinated.

I don't find this possible at higher fault currents.

 

[dpc]

It would also complicate any reclosing sequence quite a bit.

 

[cranky108]

Suck it up and change your reclosing sequence.

 

[wroggent]

Also may interfere with proper operation of any directional relaying?

 

[Mbrooke]

Thanks.

S&C power fuses will be used, so reclosing could be easier to coordinate since these are not standard fuse links.

http://www.sandc.com/products/fusing-outdoor-distribution/sm-power-fuse.asp

 

[jghrist]

You are essentially putting in one more series overcurrent device to coordinate. The fuse will have to be slower than the feeder overcurrent relay and faster than the backup (main bus breaker?) overcurrent relay. It is often difficult to coordinate overcurrent relays without adding an extra device. If you use a fast bus scheme (zone interlocking) for bus protection, the fuse won't act fast enough to prevent a bus trip.

 

[Mbrooke]

I might go with zone interlocking or transfer trip type logic. Worse come to worse I can set the transformer secondary buss feed breaker to a higher inverse time current curve level.


The other option, and Im not sure how to get it to work is motorized air breaks... Basically is a feeder breaker fails to trip, the main buss breaker will trip. The effected circuit will sectionalize via air breaks and once having done so the main buss breaker will reclose. However, from a relaying standpoint I have little idea how to go about it as the distribution level.