MV Fuse Lifetime

[anggapra]

Hi All,

Is it possible for MV Fuse to have expiry date? I mean if one fuse surpassed it's expiry date/lifetime then it won't work properly.
Anybody have technical reference related this issue?

Thanks
Angga

 

[RRaghunath]

Fuses are supposed to be good enough for 20 years as a minimum if these are stored properly or used as recommended. This is like any other electrical equipment.
Some of the parameters that can reduce the life of fuses:
+ Exposure to bad weather while in storage
+ Frequent overloading while in service
+ Exposure to higher temperatures than rated
As such there is no expiry date indicated for fuses to my knowledge. However, it is recommended to replace all three fuses when one of them blows due to fault downstream.
This is about HRC fuses. Drop-out or Expulsion type fuses are exposed to weather and tend to become open circuited while in service due to adverse weather conditions they are exposed to.

 

[anggapra]

Thanks Raghunath for the explanation,

is it possible to test the fuse's curve using primary injector?
Recently in my plant, there was transformer's fault that protected by Fuses. The fuses didn't trip, later the upstream protection (circuit breaker) cleared the fault.
I want to make sure fuse tripping time at fault current (from relay event record).

 

[davidbeach]

Testing fuses is somewhat pointless. You'll know how that particular fuse operated, but you'll still have to rely on the manufacturer's curves for the one you replace it with.

What type of fuse? Some age more gracefully than others, and the environment does make a difference. For some a moist environment doesn't matter, for others it will totally mess up the fuse. What's your load profile like? A fuse that stays comfortably warm all the time will far out last one that thermal cycles on a regular basis. Any time you're thermal cycling electrical equipment of any type that can breath at all you're running a water pump, moving water into the equipment. Small amount, slowly accumulated, perhaps, but water none the less.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[anggapra]

thanks David, I agree with you that it's somewhat pointless. I just want to make sure that the existing fuse can't work properly.

The fuses are BUSSMAN HRC fuse, 17.5SFMSJ80A, protecting 500 kVA 13.8/2.4 kV transformer. The fuses were oversized, but it should have trip before upstream protection.
Load current prior fault were very low and stay low almost all the time. The load was only 1 ESP motor, approximately 1 amps @13.8 kV. The fault current detected by upstream relay were: 272/1154/242/677 (ia/ib/ic/in)

 

[RRaghunath]

As per Bussmann catalog, the 17.5SFMSJ80A fuse has minimum breaking current rating as 270A.
This means the fuse can safely interrupt a fault current of 270A and beyond.
If the current stays between 80A and 270A for sufficiently long period, it is possible that the fuse suffers thermal / physical damage.

 

[jghrist]

Was there neutral overcurrent protection upstream? This could have tripped with 677 A neutral current before the fuses blew on phase current.

 

[anggapra]

RRagunath, I think the load never went between 80A and 270A. But the fuse probably used for another transformer before.

jghrist, yes, upstream protection (50N) cleared the fault.

 

[stevenal]

Sounds like the system worked as designed. Fuses can only respond to phase current, not residual; and attempting coordination with a 50 element will always leave gaps. Good coordination software might be helpful in analyzing this.

 

[anggapra]

Stevenal, i've checked using Easy Power. Below the coordination for SLG fault at TR's HV.
The simulated fault current quite similar with the actual one.