480V Open Delta

[Designer69]

In the past through various posts in this site I learned that in an open delta connected system if you lose a phase, the breaker does not trip and the remaining 2 phases continue operating.

well come to find out the term "lose a phase" has many possibilities. If one of the phases gets grounded out, is it true that system continues functioning, current between phases remains the same but something wacky happens to the voltage?

someone said if you "lose a phase" the full current will jsut travel through the remaining 2 phases. Did he mean if one of the phases shorts or something?

Thanks

 

[Smart $]

In the past through various posts in this site I learned that in an open delta connected system if you lose a phase, the breaker does not trip and the remaining 2 phases continue operating.

well come to find out the term "lose a phase" has many possibilities. If one of the phases gets grounded out, is it true that system continues functioning, current between phases remains the same but something wacky happens to the voltage?

It's more like several possibilities than many.

First thing to determine is if you or someone means they lost a winding or a line. If a three winding secondary and one winding is lost (open) the system operates as an "open delta" with reduced power output and voltage regulation.

As for a line getting grounded by way of a fault, an ungrounded system or on a grounded system in which the fault occurs on a grounded conductor, yes the system will continue to operate depending on the ground fault protection (GFP) scheme. Regardless of continuing to operate on one ground-fault condition, the GFP is to disconnect the faulting load(s) upon a second fault on a different line.

someone said if you "lose a phase" the full current will jsut travel through the remaining 2 phases. Did he mean if one of the phases shorts or something?

I believe he is referring to an open winding of a true delta secondary. The other two windings [attempt to] pick up the entire load.

 

[bob]

in the past through various posts in this site i learned that in an open delta connected system if you lose a phase, the breaker does not trip and the remaining 2 phases continue operating.

Well come to find out the term "lose a phase" has many possibilities. If one of the phases gets grounded out, is it true that system continues functioning, current between phases remains the same but something wacky happens to the voltage?

Someone said if you "lose a phase" the full current will jsut travel through the remaining 2 phases. Did he mean if one of the phases shorts or something?

Thanks

Attached is a dwg from the Bussman site. If you click on the dwg you will see on the left the normal operating currents for this load. The dwg on the right shows a contactor open and removes phase A and caused a single phase situation. Assuming 240 volts, this leaves coils AB and AC in series and 120 voltage across coil AB and AC. Voltage across coil BC is 240 volts. The currents in AC is now double its normal amount which usually will cause damage to the unit. I hope this sheds some light on the subject.