unbalanced current and Zero sequance component

[hossam77]

if there are 3 line (3 phase power system)passing through a ring transformer (core balanced CT) and feeding unbalanced delta load. Does the core balanced CT get an output (secondary winding) related to this imbalanced current?.
or it will only get an output in the case of earth leakage?.

 

[Marke]

Hello hossam77

Provided that the supply to the load is a three wire system (no neutral) there will be no output from the CT. All the current going to the load passes through the CT and all the current returning also passed through the CT so the filed cancel out. If there was a neutral connected to the load, the answer would be different.
Best regards,

Mark Empson

http://www.lmphotonics.com

 

[rbulsara]

only in case of earth leakage..

marke: even if there is a neutral, it should pass through the CT window and CT secondary will not read any current. ..(and of course the earthing wire should be out side of the CT to detect the earth leakage)

 

[Marke]

Hello rbulsara

Yes I agree, provided that the neutral does pass through the CT as well, there will be no reading.
Best regards,

Mark Empson

http://www.lmphotonics.com

 

[hossam77]

first .. thank u all
i have one more question ...
for the unbalanced line currents ... the magnetude of the current will be different also their summation is zero ..
** so the phase shift angle between the line currents will not be the same (120), isn't it? **

 

[Marke]

Hello hossman77

Yes that is correct. With a three wire system, as the current magnitudes change, their apparent phase shift also changes.
Take the exteme and connect across two phases only, the two currents are 180 degrees out of phase.

Best regards,

Mark Empson

http://www.lmphotonics.com