Expulsion Type Fuses Vs Current Limiting? 1

[majesus]

I'm trying to figure out why you would choose an expulsion type fuse vs Current limiting. I was reading the MV Fuse PDF found here:

http://www.ferrazshawmut.com/en/pdf/edupack/GB108_ANSI37_American_medium_voltage_fuses.pdf

On page 5 it gives a neat little comparison table between the two technology. My guess would be generally speaking: if current limitation is not required, then choose an expulsion type fuse due to cost only?

 

[dpc]

Take a visit to the S&C website,

http://www.sandc.com

to learn all the virtues of expulsion fuses.

Time-current characteristics of expulsion fuses can provide much better transformer primary protection compared with CLF. They are generally easier to coordinate with, both upstream and downstream.

Expulsion fuse characteristics are supposed to be more stable over time, especially after exposure to through faults.

 

[magoo2]

The flip side to using expulsion fuses is that things go boom! Current limiting fuses provide energy limiting so that transformers, capacitors and other equipment don't experience 'disruptive discharges' when they fail, which is a fancy way of saying they don't blow up.

A lot of work was done in US the 70s on cover blowing related to internal faults on pole type transformers. The general conclusion was that pressure buildup with internal faults was sufficient to result in to cover blowing and pressure relief devices were not fast enough. CLF's reduced the fault energy so that cover blowing did not occur.

On balance, the CLF is a more expensive fuse, but it does reduce the energy delivered when various faults, including cable faults, occur.

 

[dpc]

magoo2,

Sorry, I don't really agree with all that. "Things" don't go boom, the FUSE goes boom. (Capacitor fusing is a separate topic by itself really.) At the high end of the fuse's fault current range, the CLF will clear a fault perhaps one cycle faster than an expulsion fuse. For lower values of fault current, the expulsion fuse is often faster. The CLF is only current-limiting for very high values of fault current.

CLFs do have some advantages:

Silent, non-venting operation
Higher interrupting capability (in many cases)

 

[RRaghunath]

I was told the range available in expulsion type is limited to transformers rated 500kVA.
The name suggests that the fuses are for outdoor installation only (another limitation).

 

[davidbeach]

Expulsion type fuses go way beyond 500kVA, and with mufflers can be used indoors.

 

[saladhawks]

Another issue to consider when using C-L fuses is the arc voltage that is produced when the fuse operates in the C-L range. This arc voltage can be much higher than the system voltage and needs to be considered when specifying arresters.

 

[majesus]

"Take a visit to the S&C website,

http://www.sandc.com

to learn all the virtues of expulsion fuses." Quote from DPC

Thanks DPC, will check it out.

 

[majesus]

FYI:

"Current-limiting fuses are very good at clearing high-current faults. They have a much harder time with low-current faults or overloads. For a lowlevel fault, the fusible element will not melt, but it will get very hot and can melt the fuse hardware resulting in failure. This is why the most common CLF application is as a backup in series with an expulsion fuse."

pg 413 of ELECTRIC POWER Distribution Handbook by
T.A. Short (2004 by CRC Press LLC)

 

[magoo2]

We use the backup CLFs for our pole type transformers. Prior to doing that, we had a fairly large number of covers blowing. That's the boom that I was referring to earlier, not the operation of the expulsion fuse. It was a safety hazard both to our own people and to the public.

The assumption was that we had a high current internal fault in the transformer. Since we've used them, we don't have disruptive failures of distribution transformers any more. I think our assumption was correct.

 

[RRaghunath]

Thought this will be an interesting info for some:

The Expulsion type fuses are available upto 8kA fault rating (Source - Bussmann).