Fault Current Limiter (FLC) and Breaker size upgrade

[Hameedulla-Ekhlas]

Greeting all,

I was reading one topic regarding to Fault current limiter. It had explained the advantages of fault current limiter as below


1-a larger transformer can be used to meet increased demand on a bus without breaker upgrades
2-a large, low impedance transformer can be used to maintain voltage regulation at the new power level
3- I2t damage to the transformer is limited

My question is regarding to point number one. It says if we upgrade the transformer for larger demand load in a bus we dont need to upgrade the breaker size. On other hand have read that fault current limiter comes in function only during a fault.
Now during steady state or normal operation if we upgrade the transformer for larger demand load and we dont upgrade the breaker size for larger demand load
This makes me confused, since this breaker may not have load current capacity, will it not trip?

 

[zog]

Greeting all,

I was reading one topic regarding to Fault current limiter. It had explained the advantages of fault current limiter as below


1-a larger transformer can be used to meet increased demand on a bus without breaker upgrades
2-a large, low impedance transformer can be used to maintain voltage regulation at the new power level
3- I2t damage to the transformer is limited

My question is regarding to point number one. It says if we upgrade the transformer for larger demand load in a bus we dont need to upgrade the breaker size. On other hand have read that fault current limiter comes in function only during a fault.
Now during steady state or normal operation if we upgrade the transformer for larger demand load and we dont upgrade the breaker size for larger demand load
This makes me confused, since this breaker may not have load current capacity, will it not trip?

It is refering to upgrading the breaker to one with a higher interuption rating, not frame size.

 

[weressl]

Greeting all,

I was reading one topic regarding to Fault current limiter. It had explained the advantages of fault current limiter as below


1-a larger transformer can be used to meet increased demand on a bus without breaker upgrades
2-a large, low impedance transformer can be used to maintain voltage regulation at the new power level
3- I2t damage to the transformer is limited

My question is regarding to point number one. It says if we upgrade the transformer for larger demand load in a bus we dont need to upgrade the breaker size. On other hand have read that fault current limiter comes in function only during a fault.
Now during steady state or normal operation if we upgrade the transformer for larger demand load and we dont upgrade the breaker size for larger demand load
This makes me confused, since this breaker may not have load current capacity, will it not trip?

Hmmmm...it appears to me that you think that this forum is an online college course. We are soon start charging you....

 

[Hameedulla-Ekhlas]

The best way of education is discussion. :grin: I really appreciate your all explaination.

 

[jim dungar]

This makes me confused, since this breaker may not have load current capacity, will it not trip?

I agree with Zog about the interrupting rating. but, I also agree with you that the statement may be confusing.

This is a true example at an existing facility, with an adequately sized transformer and (1) breaker. Due to a recent transformer failure and future growth requirements, the facility plans for the replacement transformer to be larger and have lower losses. A second breaker will eventually be added to as part of the future growth.

A fault current limiting device might allow the existing main breaker and switchgear to accommodate the expected increased fault current.

 

[Hameedulla-Ekhlas]

I agree with Zog about the interrupting rating. but, I also agree with you that the statement may be confusing.

This is a true example at an existing facility, with an adequately sized transformer and (1) breaker. Due to a recent transformer failure and future growth requirements, the facility plans for the replacement transformer to be larger and have lower losses. A second breaker will eventually be added to as part of the future growth.

A fault current limiting device might allow the existing main breaker and switchgear to accommodate the expected increased fault current.

Yeah, it confused me only on normal operation. Since FCL only comes in operation during a fault situation. But it does not make any affect on normal operation. If the load increases and we uprgrade the transformer size to larger capacity and if we dont change the breaker. It will trip during normal operation.

I am using digsilent power factory software for short circuit analysis. We know each breaker has kA capacity too. I have faced sometimes to change the main breaker size due to kA capacity eventhough it has no problem in steady state or normal operation.

But point number which was mentioned in topic was something confused me.

 

[bob]

A fault current limiting device might allow the existing main breaker and switchgear to accommodate the expected increased fault current.

Jim
Would this not require series rated components? The statement seems to indicate the current limiter would allow the existing breaker to remain in place even though the AIC rating was too low.

 

[jim dungar]

Jim
Would this not require series rated components? The statement seems to indicate the current limiter would allow the existing breaker to remain in place even though the AIC rating was too low.

It all depends on what is there.

If the current limiting device is a 'fusible element' and the down stream device is bus bars or ANSI breakers, then a 'listed' series rating may not be required.

If the device is a 'fusible element' and the downstream device is a UL489 listed breaker then series ratings are almost always required.

 

[bwyllie]

what is the difference between an ANSI rated circuit breaker and a UL489 listed breaker and how would one identify these breakers as such?

 

[jim dungar]

what is the difference between an ANSI rated circuit breaker and a UL489 listed breaker and how would one identify these breakers as such?

Quick and dirty.

If it is a molded case breaker (maybe 90% of breakers) it is UL489.
If it is a power circuit breaker, insulated case - it is a toss up.
If it is a drawout style/iron frame power circuit breaker it is likely ANSI.
When in doubt post the catalog number and manufacturer.