System fault levels

[Audun]

What does "fault make", and "fault break" represent when indicated for a systems fault levels. I'm only used to transient and subtransient short circuit currents.
For a breaker I know what make and break levels indicate, but I have never before seen it used for system levels.


Audun

 

[wbd]

Off the top of my head, I would say that those terms are being used to refer to what the breakers should be capable of making and breaking. Perhaps, if you can elaborate further on the context those terms are being used in, it would help clarify things.

wbd

 

[busbar]

To add to wbd's query, is the subject low-, medium- {or high-}voltage breakers; ANSI or IEC?

 

[Audun]

The levels is indicated in a technical project description.

2.0 Electrical supply system and tolerances
.....
...
2.3 Fault levels

* 13.8 kV System - Fault make, 1.5kA, Fault break 1.0 kA
* 440 V System - Fault make, 25 kA , Fault Break 1.7 kA

As you can see, it is not in a breaker spec, but maybe that is what it is intended to be?
It should be IEC. (but to my eyes it is not..)

Audun

 

[Audun]

I think I will interpret as follws.
Fault make: Subtransient short circuit current.
Fault break: Transient short circuit current.

If anybody thinks this is wrong, please let me know.

Audun

 

[RRaghunath]

You can refer Thread 238-15838 in the same forum. The subject has been discussed in detail. Further, there are some more threads on the subjects and key word search should help.

 

[nag400]

May be this will help

Breaking Current : Highest value of short-circuit which a circuit breaker is capable of breaking under specified conditions of recovery voltage and power frequency recovery voltage. It is expressed by two values
1. RMS value of the ac component at the instant of contact seperation given by = Iac/ sqrt(2)
2. The percentage dc component at the instant of contact seperation, given by (Iac x 100 )/ Iac
unit kA
Making current : Rates short circuit making current ( Peak Value) It may so happen that circuit breaker may close on existing fault. In such cases the current increase to the maximum of the peak of first current loop. The CB should be able to close without hesisation as contact touch.
The making current should be at least 2.5 times the rms value of the ac component of rated breaking current

Rated making current Im = 1.8 x sqrt(2) x rated short circuit breaking current
= 2.5 x rated short circuit breaking current (peak)
unit : kA Peak

 

[nag400]

May be this will help

Breaking Current : Highest value of short-circuit which a circuit breaker is capable of breaking under specified conditions of recovery voltage and power frequency recovery voltage. It is expressed by two values
1. RMS value of the ac component at the instant of contact seperation given by = Iac/ sqrt(2)
2. The percentage dc component at the instant of contact seperation, given by (Iac x 100 )/ Iac
unit kA
Making current : Rates short circuit making current ( Peak Value) It may so happen that circuit breaker may close on existing fault. In such cases the current increase to the maximum of the peak of first current loop. The CB should be able to close without hesisation as contact touch.
The making current should be at least 2.5 times the rms value of the ac component of rated breaking current

Rated making current Im = 1.8 x sqrt(2) x rated short circuit breaking current
= 2.5 x rated short circuit breaking current (peak)
unit : kA Peak
- nag400