Fuse cut-outs on transmission lines tripping the feeder

[viking684]

Hello everyone!

I am trying to figure out why a burnt fuse cut-out on our transmission lines tripped the feeder. There are other fuses along the line and an over current relay at the feeder. A transient fault caused the fuse to burn out which caused a short that tripped the whole feeder. What could it be? What should we do to rectify this problem?

 

[waross]

The feeder breaker may have tripped while the fuse was clearing.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[viking684]

Thanks Bill for the response.

Do you have any suggestions on how to rectify the problem?

 

[dpc]

You should review the coordination between the upstream relaying and the fuses downstream. Changes to the relay settings could improve the coordination. You might also make sure the correct size fuses are being used, not just the sizes the linemen had in their rig that day.

 

[desrod]

Viking, you wrote: "A transient fault caused the fuse to burn out which caused a short that tripped the whole feeder."

If there was no other fuse between the feeder breaker and the fault, it is expected that the breaker will clear the fault. If there was one, then as suggested by dpc, you should review your protection coordination to get better selectivity.

I am also curious at which voltage you are working. I very seldom associate fuses with transmission but my background is with networks in North America.

 

[jghrist]

A transient fault caused the fuse to burn out which caused a short that tripped the whole feeder.

Did the fuse cutout fail causing a short or did the cutout fuse blow because of a short? How did you determine that a transient fault caused the fuse to burn?

 

[bacon4life]

The utility could be using a fuse saving scheme.

 

[viking684]

Hello everyone,

Thanks for your replies. Anyhow here is a little more info:

We use a nominal voltage of 13.2 kV. When the feeder tripped, our linemen traced the line to see what caused it to tripped and they found a burnt fuse and a dead bird on the ground. So, they assumed the bird caused fault. Anyhow, there are other fuses downstream from the line before the feeder breaker and none of those fuses stopped the feeder from tripping. I agree we need to check the protection coordination. There is a lot of information that I need to compile from the utility. I am an Electrical Engineering student and I am interning at our local Utility Company, so any help is greatly appreciated.

 

[jghrist]

Have you compared the total clearing curve of the fuse with the relay time-current characteristic curve?

 

[viking684]

JGHRIST,

We are currently working on that as well as collecting data from the feeder relays and fuse ratings on the lines. We use fuse link type T fuses on our overhead lines as well as some expulsion type and current limiting fuses for some of our LVS switches. Thanks!

 

[Mbrooke]

Type Ts are slow blow fuses, hence they are usually intended to be used in conjunction with reclosing

 

[Mbrooke]

....

Normally it is desirable to use a fuse saving scheme in that the reclosing protective device has a fast curve or 2, where the instantaneous "magnetic" trip is low along with the long time delay "thermal curve". The next closing attempts have a delayed curve intended to blow the fuse if the fault is right after it. Fuse saving schemes are the best for bare wire construction or where many trees/rodents/lightning is present.

Fuse saving isn't always used, either always or only enabled during weather related conditions through DSCADA.


How is the feeder grounded? Wye or Delta system?