Circuit breaker interrupting

[electrics]

Hi, I wonder if there flows a current from wye to earth on a xformer as the phase currents are interrupted sequentially because of their phase differences, namely firstly first phase interrupts and 2 phase remains and this means an unsymmetrical case and afterwards second phase is interrupted and one phase remains and all the current flows from neutral connector , is this scenario makes sense?

 

[electrics]

is this an absurd question? are all these currents interrupted at the same time? I dont think so...what do you say?

 

[mcclary's electrical]

Hi, I wonder if there flows a current from wye to earth on a xformer as the phase currents are interrupted sequentially because of their phase differences, namely firstly first phase interrupts and 2 phase remains and this means an unsymmetrical case and afterwards second phase is interrupted and one phase remains and all the current flows from neutral connector , is this scenario makes sense?

I suppose what you are saying would be possible if there were big differences in opening times, but all phases are opened simultaneously, thus eleminating that problem

 

[ron]

All three phases are on a common "linkage". They open essentially at the same time or you would be tripping GF all the time.

There are some types of transfer switches (some static types) that open one phase at a time, so there is always the fear of GF trip.

 

[SG-1]

All three breaker poles would be opened at the same time.

The current magnitude interrupted for each phase would be different for each pole. The arc may not extinguish in each pole until the zero crossing.

Welcome to the Forum !

 

[hurk27]

primary: possible
secondary: never

but why would such a switch ever be used, as it would cause problems on GF detection and loss phase conditions on motors and phase detectors, and would be a NEC violation to the intent of all phases opening simultaneously requirement?

or are we talking about the effect of the current being placed upon the neutral at the zero crossing of one phase in the rotational relationship to the other phases, which the answer would be no, as the neutral would still be in a balanced phase relationship with the other two phases otherwise there would always be current upon the neutral balanced or not.

 

[electrics]

as a rule if all three current are not interrupted (not enough that poles are opened but currents must be zero ) simulatenously it is sure that neutral current will occur..isnt it rational?

 

[electrics]

since this duration (current occurence on neutral) is very short,perhaps GF device wont sense it, is this scenario good? in fact all poles could be opened at the same time but it is unreasonable to think that there would be no current on the neutral .
Think once since one of the phases will be interrupted as final phase to keep the current flowing this current will flow out of neutral passing through phase-neutral-point -neutral-and phase again, this will cause GF trip if long enough, all this is fiction,maybe true?

 

[hurk27]

since this duration (current occurrence on neutral) is very short,perhaps GF device wont sense it, is this scenario good? in fact all poles could be opened at the same time but it is unreasonable to think that there would be no current on the neutral .
Think once since one of the phases will be interrupted as final phase to keep the current flowing this current will flow out of neutral passing through phase-neutral-point -neutral-and phase again, this will cause GF trip if long enough, all this is fiction,maybe true?

sure if you interrupt 1 or 2 of the 3 phases, for more then a cycle, you will have neutral current, but as far as current being on the neutral and tripping a GF device it would not since it monitors the grounding after the service main bonding jumper and would not care about neutral current, if it did it would trip anytime the neutral had current. if you had lost 1 or 2 of the phases ahead of the GF detection device it still wouldn't trip as a GF device does not monitor up stream from the detection point, so I'm not sure what you asking?

A GF device on the primary side of a transformer will not detect an GF on the secondary side as it will only produce a line to line current on the primary side,

 

[electrics]

okey you are right since any ground fault is not of question here, but what I am trying to understand is if there is a real case like I mentioned above, theoretically is it possible that since all the currents are not interrupted at the same time (not poles but currents, poles are opened at the same time always it is sure)a current will show up on the neutral definitely. All the question is thisi, by the way thank you for your mild answers...