POWER SYSTEM FAULT ANALYSIS

POWER SYSTEM FAULT ANALYSIS   : 

POWER SYSTEM FAULT ANALYSIS Engr. Jerny D. Catibayan EE- Faculty Member

Fault Analysis : 

Fault Analysis Analysis types power flow - evaluate normal operating conditions fault analysis - evaluate abnormal operating conditions Fault types: balanced faults Three-phase unbalanced faults single-line to ground and double-line to ground line-to-line faults Results used for: specifying ratings for circuit breakers and fuses protective relay settings specifying the impedance of transformers and generators

Slide 3: 

Magnitude of fault currents depend on: the impedance of the network the internal impedances of the generators the resistance of the fault (arc resistance) Network impedances are governed by transmission line impedances transformer connections and impedances grounding connections and resistances Generator behavior is divided into three periods sub-transient period, lasting for the first few cycles transient period, covering a relatively longer time steady state period

Fault Studies : 

Fault Studies Sub-transient period, XG = Xd " determine the interrupting capacity of HV circuit breakers determine the operation timing of the protective relay system for high-voltage networks Transient period, XG = Xd ’ determine the interrupting capacity of MV circuit breakers determine the operation timing of the protective relay system for medium-voltage networks transient stability studies

Fault Representation : 

Fault Representation A fault represents a structural network change equivalent to the addition of an impedance at the place of the fault if the fault impedance is zero, the fault is referred to as a bolted fault or solid fault

First order method : 

First order method the faulted network can be solved conveniently by Thévenin’s method network resistances are neglected generators are modelled as an emf behind the sub-transient or transient reactance shunt capacitances are neglected system is considered as having no-load

Short Circuit Capacity (SCC) : 

Short Circuit Capacity (SCC) Measures the electrical strength of the bus Stated in MVA Determines the dimension of bus bars and the interrupting capacity of circuit breakers

Thévenin’s Method : 

Thévenin’s Method The fault is simulated by switching a fault impedance at the faulted bus The change in the network voltages is equivalent to adding the pre-fault bus voltage with all other sources short circuited

examples: 

examples

Slide 11: 

Determine the minimum rupturing capacity of the circuit breaker as shown, if a three- phase symmetrical fault occurs at point P.