Wye-Delta issues

Status
Not open for further replies.
B

Basra123

Member
Re: Wye-Delta issues

Rattus,
thanks! what about when you lose one transformer, not the center-tapped, completely with no remaining connections to the other 2 transformers? isn't that an open wye - open Delta and hence there is no changes in the secondary voltages? or it is still a single phase, no neutral, with the same voltages magnitudes as discussed earlier, with case of a blown fuse?
 
R

rattus

Senior Member
Re: Wye-Delta issues

Basra,

It might look like an open delta, but it would not behave as you suggest.

With an open neutral, the loss of one transformer leaves us with only a single phase which results in zero volts across the secondary of that transformer providing that the loads are equal across the remaining transformers. Otherwise, the secondary voltages would not cancel.
 
B

Basra123

Member
Re: Wye-Delta issues

Rattus,

Here is a nother scenario where one primary winding is shorted, not to ground, and our 3 phase wye-delta bank. as before the wye is not grounded. the voltages on the scondary now:
415,415, and 415*1.732=718. Do you agree?
 
R

rattus

Senior Member
Re: Wye-Delta issues

Basra, I think this would happen:

If primary A shorts, then line voltage appears across primaries B & C. This tends to increase all secondary voltages by 1.732.

BUT, the reflected short of A shorts out the delta and everything burns up. Also, increasing the primary voltage this much would likely cause the iron to saturate and the primary currents would increase for that reason.

Anyone see a different scenario?
 
R

rattus

Senior Member
Re: Wye-Delta issues

Originally posted by Basra123:
Rattus,

Why the short of A will shorts out the delta especially if short isn't to ground?
Click to expand...
Basra, the transformer is bidirectional. The shorted primary is reflected to the secondary. In effect the secondary is also shorted.
 
B

Basra123

Member
Re: Wye-Delta issues

Here is another question: someone was connecting steel pipes (for sewer) in the middle of the road. The distribution line 13.8kv is running along side the road. The worker says that as he apporaches one section, to connect the next section of the pipe, about 1" away from it he draws an arc? What is causing this Arc?
 
Status
Not open for further replies.
Top