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Phase displacement of 60 degree during Fault

Phase displacement of 60 degree during Fault

(OP)
1. In the event of a ground fault in one phase in ungrounded systems, the phase-to-ground voltage in the remaining two phases is now equal to the phase-to-phase voltage with a displacement of 60 degrees.

2. Similarly, In the case of star connected motor or capacitor, on complete short circuit of one of the phase winding results in the remaining two phases attaining phase-to-phase voltage with a displacement of 60 degrees.

I can understand the unfaulted phases attaining the phase to phase voltage but I couldn't understand the phase displacement of 60 degrees.

Thank you.

RE: Phase displacement of 60 degree during Fault

Some of the discussion in this previous thread should shed some light.

Regards
mgtrp

RE: Phase displacement of 60 degree during Fault



This image is how i had it explained to me that helped me understand this. Remember that the generator is trying to maintain the same potential difference between poles. So if one pole is shorted during a ground fault you get the effect of sliding all three over.

Clay

Pardon my quick sketch isn't so good but i'm a visual person.

RE: Phase displacement of 60 degree during Fault

2
During a SLG fault on an ungrounded system, the ground point shifts from the neutral to the faulted phase. If you look at the diagram below, no current (I1,I2,I0) can flow for the fault since the zero sequence network provides no return path. The voltages on the ungrounded system ,however, will change as the result of the fault and this can be seen by transferring the sequence network voltages at H ,in the diagram below, from the sequence domain to the phasor domain. The voltages below at point H are V(positive) = E1G, V(negative) = 0, and V(zero) = -E1G. If these voltages are transferred from the sequence domain to the phase domain, the ground has shifted to the faulted phase and the line-to-neutral voltage on the other phases has increased to the line-to-line voltages and the angle between the two line-to-ground phasors has reduced from 120 to 60 degrees . No negative sequence voltage developed to change the line-to-line voltages (open circuit sequence network) ,which are unaffected by zero sequence.


Unintended ungrounded system situation that happens on our system.






Varying amount of zero sequence voltage.



Sequence network for an SLG fault.





Voltages on an ungrounded system with a SLG fault.


RE: Phase displacement of 60 degree during Fault

Hamburger:
Impressively extensive answer! Interesting there is no V2. Had to talk myself into recognizing that. Guess I am so used to thinking of all the negative sequence voltage you get during SLG fault on a solidly grounded system.

RE: Phase displacement of 60 degree during Fault

JensenDrive,

I had that locked and loaded from one of my wikia pages that I put together a couple years ago.

http://powerprotection.wikia.com/wiki/Analyzing_Fa...

The GIFS were put together using Alex Eachern's Power Quality Teaching Toy. It is what I use to get a visual idea of how sequence domain relates to the phasor domain and oscillography. It is worth playing with to get an idea how the two domains relate to each other.

http://www.powerstandards.com/PQTeachingToyIndex.p...

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