Fault level Vs Switchgear Capacity
Fault level Vs Switchgear Capacity
(OP)
I have the next situation:
In a substation (115 kV system) I found a fault level of 43 kA (symmetrical value) in the busbar, and the switchgears in this substation are 40 kA (symmetrical).
The 43 kA are the result of a vectorial sum of the contributions of the derived circuits conected to this substation, but in a fault after a switchgear, the fault current that will flow through this switchgear will be less than the total fault current in the busbar and less than 40 kA.
Can I assume that this switchgear will withstand the fault?
Any reference about this issue, will be appreciate!
FernandoM
In a substation (115 kV system) I found a fault level of 43 kA (symmetrical value) in the busbar, and the switchgears in this substation are 40 kA (symmetrical).
The 43 kA are the result of a vectorial sum of the contributions of the derived circuits conected to this substation, but in a fault after a switchgear, the fault current that will flow through this switchgear will be less than the total fault current in the busbar and less than 40 kA.
Can I assume that this switchgear will withstand the fault?
Any reference about this issue, will be appreciate!
FernandoM






RE: Fault level Vs Switchgear Capacity
RE: Fault level Vs Switchgear Capacity
You have to consider the x/r ratio that the switchgear interrupting rating is based on.
RE: Fault level Vs Switchgear Capacity
The next size of the switchgear will be 63kA, which is available for rated continuous current 2000A (rms). It is not advised to assume any higher than rated values to be withstand since the switchgear is not tested for such values, and it may explode for untested values. Some designers and engineers are leaving certain design margin to 40kA or 63kA.
RE: Fault level Vs Switchgear Capacity
Appear unclear to me how the 43 kA fault was found. Perhaps someone could be able to help if you could please clarify the following:
1- Describe briefly the one line diagram with sources and components (transf, gen, TL, etc).
2- Available max. fault current and X/R ratio at the substation incoming/outgoing TL.
3- Confirm 40kA sym. is the lowest interrupting rating of the substation components (breaker, sw, etc.)
and bus withstands SC capacity based on clearance, insulator mech. strength, bus conf, etc.
RE: Fault level Vs Switchgear Capacity
The rated values of your switchgear must be:
Icw > Ik"
Ipk, Icm > ip for the busbar, cabinets and all devices such as short circuit breakers.
In case of a short circuit in one of the connected sub stations, the short circuit will be less than the max. value that you have given. But in case of a short circuit in your main switchgear, you will have the full short circuit. If it is above the design value of the switchgear you might have a problem. In this case, you cannot assume that the switchgear will withstand the short circuit.
RE: Fault level Vs Switchgear Capacity