L3UnbalancedFaults.pdf - University of Sydney School of Electrical Information Engineering ELEC 5204 Power Systems Analysis Protection 3 Unbalanced

L3UnbalancedFaults.pdf - University of Sydney School of...

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University of SydneySchool of Electrical & Information EngineeringELEC 5204 - Power Systems Analysis & Protection3. Unbalanced Fault Analysis 1
The three sequence networks allow analysis of unbalanced faultsUsing 3 phase voltages and 3 phase currents at point of fault (i.e., the boundary conditions), we can derive the sequence network connections and hence equations for different fault typesConnecting up Sequence Networks to Analyse Unbalanced Faults 2
• VA= 0• IB= IC= 0 ‘A’ phase to Earth FaultIAVAIBICVBVC3
Current Analysis• IB= IC= 0• IA= IFTherefore the three sequence currents are equal‘A’ phase to Earth Fault3I3IIII3I3aIIaII3I3IaaIIIFCBA0AFCB2A2AFC2BA1A=++==++==++=4
Voltage Analysis:• VA = 0• VA= VA1+ VA2+ VA0= 0Therefore the sum of the three sequence voltages is zero‘A’ phase to Earth Fault5
The sequence networks can be connected in series‘A’ phase to Earth FaultZ1N1E1F1(N1)V1I1Z2N2F2(N2)V2I2Z0N0F0(N0)V0I06
Example : Phase to Earth FaultSOURCELINEF132 kV2000 MVAZS1 = 8.7ZS0 = 8.7A - GFAULTZL1= 10ZL0= 35Total impedance = 81.1I1 = I2 = I0 = 132000 = 940 Amps3 x 81.1IF = IA = I1 + I2 + I0 = 3I0 = 2820 AmpsIF8.710I1F1N18.710I2F2N28.735I0F0N07
Example : Phase to Earth FaultSOURCELINEF132 kV2000 MVAZS1 = 8.7ZS0 = 8.7A - GFAULTZL1= 10ZL0= 35IFpu1712.87.8puZpu1712.87.8puZ712.82000132Z0S1S2BASE====pu017.4712.835puZpu148.1712.810puZ0L1L====Alternatively using the Per Unit MethodOn a 2000MVA, 132kV Base 8
Example : Phase to Earth FaultSOURCELINEF132 kV2000 MVAZS1 = 8.7ZS0 = 8.7A - GFAULTZL1= 10ZL0= 35IF11.148I1F1N111.148I2F2N214.017I0F0N0E=1pukA808.2I3IA936kA748.8107.0IkA748.8kV1323MVA2000Ipu107.0

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