How do you calculate short circuit current for buses on a single line diagram?

To determine the fault current at any point in the system, first draw a one-linediagram showing all of the sources of short-circuit current feeding into the fault, aswell as the impedances of the circuit components.To begin the study, the system components, including those of the utility system,are represented as impedances in the diagram.The impedance tables include three-phase and single-phase transformers, cable,and busway. These tables can be used if information from the manufacturers is notreadily available.It must be understood that short circuit calculations are performed withoutcurrent-limiting devices in the system. Calculations are done as though thesedevices are replaced with copper bars, to determine the maximum “available”short-circuit current. This is necessary to project how the system and the currentlimitingdevices will perform.Also, multiple current-limiting devices do not operate in series to produce a“compounding” current-limiting effect. The downstream, or load side, fuse willoperate alone under a short circuit condition if properly coordinated.The application of the point-to-point method permits the determination of availableshort-circuit currents with a reasonable degree of accuracy at various points foreither3Ø or1Ø electrical distribution systems. This method can assume unlimitedprimary short-circuit current (infinite bus) or it can be used with limited primaryavailable current.

S(sc( =S rated /Zp.u

CALCULATED ON THE BASE OF THE REACTANCE OF THE SYSTEM.

General Comments on Short Circuit Calculations Sources of short-circuit current that are normally taken under consideration include: - Utility Generation - Local Generation - Synchronous Motors - Induction Motors - Alternate Power Sources Short circuit calculations should be done at all critical points in the system.
These would include: - Service Entrance - Transfer Switches - Panel Boards - Load Centers - Motor Control Centers - Disconnects - Motor Starters - Motor Starters

I would explain this in a simpler way as below.

 

Short circuit current is calculated based on the simple Ohm's Law.  We need to know :

System Voltage, Voltage at the point where we need to calculate the short circuit rating, Imedance of the different components in the system incuding Cables/busbar, any switching devices, internal imepedances...

 

There are different ways to calculate the impedance (Z) of the system.  You can apply a random lesser ac voltage at the point where you need to calculate short circuit current and measure the current taken by the system.  Impedance = Voltage applied / Current taken by system.

 

Short circuit  rating at the bus bar point = Voltage / Impedance calculated.

Calculation will be based on current load that circuit diagram will carry,analysis it to mesh node then you will know the result

What I'm looking to find out is the methodology employed.

reading each of the circuit part one by one and to know the damage one that is shorting the voltage.

Essentially we can analyze and compute for the short circuit current by pointing to the path of closed circuit with lowest resistance and considering involved components in the circuit.

No need to calculate where any short circuit, Its understood it will be infinity.

It depends on the phase of the circuit i.e., three phase or single phase, then that would determine the calculation you would use.