Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
The magnitude of fault current depends upon
Total impedance up to faults
Voltage at the fault
Load current being supplied before occurrence of fault
Both (a) and (b)
Both (a) and (b)
The magnitude of a fault current in a power system is determined by the ratio of the pre-fault voltage at the fault point to the total Thevenin impedance of the network up to the point of the fault ┬╖ Ohm's Law for circuits is the fundamental principle applied here, where IfaultтАЛ=ZthтАЛVfтАЛтАЛ.
The magnitude of a fault current in a power system is determined by the ratio of the pre-fault voltage at the fault point to the total Thevenin impedance of the network up to the point of the fault ┬╖ Ohm's Law for circuits is the fundamental principle applied here, where IfaultтАЛ=ZthтАЛVfтАЛтАЛ.
IfтАЛ=ZthтАЛVfтАЛтАЛ тАФ Fundamental relation for fault current calculation
ZthтАЛ=ZsourceтАЛ+ZlineтАЛ тАФ Total impedance from source to fault
When a short circuit occurs, the impedance of the path drops drastically ┬╖ According to I=ZVтАЛ, since the system voltage V remains relatively constant (governed by the source) and the impedance Z suddenly reduces to the impedance of the transmission lines and transformers up to the fault point, the resulting current spikes to a high value.
Fault current is primarily limited by the system impedance.
The pre-fault load current is generally neglected in fault analysis because it is insignificant compared to the magnitude of the fault current.
Voltage at the fault point depends on the distance from the source.
Simplified analysis using Thevenin equivalent circuits.
Provides worst-case scenarios for circuit breaker rating selection.
Assumes steady-state conditions ignoring sub-transient components.
Does not account for non-linear fault impedance in basic calculations.
Relay coordination studies.
Selecting rupturing capacity of circuit breakers.
Power system stability analysis.
Option C is incorrect because the load current is typically negligible (often < 5%) compared to the fault current, making it practically irrelevant for fault calculation.
The magnitude of the fault current determines the mechanical and thermal stress on electrical components during a fault.
D is correct тАФ The fault current magnitude is governed by the ratio of the source voltage to the total series impedance at the fault location, making both the voltage and impedance critical factors.
Always remember that in fault analysis, the pre-fault load current is ignored to simplify calculations, whereas the internal impedance of the system is the dominant limiting factor.