Power Line

The majority of textbooks disregard open circuits when presenting unbalance faults in a power system. Almost always, only short-circuit faults are considered.

In the following circuit diagrams, it is assumed that the lines were opened between points X & Y.


Va1 = Line to neutral voltage
I1F = Positive sequence fault current
I2F = Negative sequence fault current
I0F = Zero sequence fault current
Z1 = Positive sequence impedance
Z2 = Negative sequence impedance
Z0 = Zero sequence impedance

1 Line Open Fault

2 Lines Open Fault

2 Lines Open Fault

It is noticeable that the 2 lines open fault network sequence diagram is similar to the 1 line to ground fault. The only difference is the polarity of connection. The resulting formula however will be the same.

Electrical Transmission & Distribution Reference Book - Westinghouse Electric


  • A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia, and Professional Electrical Engineer (PEE 2574 - 1st Place April 1991) - Philippines with extensive experience in concept selection, front-end engineering, HV & LV detail design, construction, and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and wastewater pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).


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