Overview fault current calculation
Short Circuit calculation/fault current calculation in designing High Voltage system is important to determine the fault current at Main Switchboard (MSB) and also could be considered to calculate all the way up to Distribution Board (DB). Normally, I just calculate the fault current up to MSB only and the remaining downstream I just estimated according to standard condition.
To calculate the fault current we need to know the fault current at provider side. For Malaysia is Tenaga Nasional Berhad (TNB).
The calculation above has been developed using two (2) way of calculation which will provide the same result. 1) using resistance (ohm) and per unit (p.u). If we could see the above overview, there is two (2) section which is at the left side is using resistance calculation and the right side using per unit (p.u) calculation.
This calculation also could be used to determine the selection of the cable size for the High Voltahge (HV) cable and the conductor could be copper or aluminium. The calculation is based on the IEC standard. There is also complicated software that develops by ABB that could be used to determine the fault current and cable size. But that software also could be used to determine the selection of the breaker/switchgear/etc but as usual since that the software develop by the ABB so all the protection are based on the ABB protection devices.
I have been using this application / calculation for my Hotel and service apartment project in Shah Alam.
Result of the fault current calculation.
The calculations that develop above also include the selection of the busduct and cable for the Low Voltage (LV) section.
The preset criteria that I develop for the above calculation based on my current project which is as follows:-
First section: Provider HV Switchgear section (TNB)
Second Section: Owner HV Switchgear section
Third Section: Transformer section
Fourth Section: LV Main Switchboard section