Electrician Talk banner
1 - 15 of 15 Posts

·
Registered
Joined
·
11,762 Posts
If its 3 separate transformers were used to make a bank a loss of say primary B phase would cause the secondary C phase to remain normal, it would read 120 volts to neutral, but A and B phase on the secondary would read about 60 volts assuming the load is balanced.


A 3 phase bank made of a conjoined core ie 3 4 and 5 leg cores would probably behave differently from induced inductance crossing over that would normally be cancelling. Anyone know better the effects in that case?
 

·
Donuts > Fried Eggs
Joined
·
17,042 Posts
If they're a common core, it's almost certainly gonna result in a L-L or L-G fault and take down the entire transformer.

If this is a ganged group of transformers, you can remove the faulted can and run open-Y:eek:pen-Δ. You end up getting the same voltages, but your capacity is reduced by 58% because you no longer have all three phases of your Δ to contribute current, so you're limited to single-phase winding capacity.

EDIT: Nuts, I just realized you asked Δ:Y. If you lost any phase in that configuration, you'd basically go offline, because you can't support a 3 phase load on an open Y. They could, however continue to run single phase at reduced capacity.
 

·
Registered
Joined
·
44 Posts
Discussion Starter · #6 ·
If they're a common core, it's almost certainly gonna result in a L-L or L-G fault and take down the entire transformer.

Today i saw a Δ:Y transformer with a blown fuse on the primary side. All the loads connected to the secondary are L-N loads. every thing that was supplied by the transformer was not running smoothly, clearly voltage fluctuation, all the lights where dimming and brightening. but the transformer was still running even though the fault wasn't repaired at that time. I wasn't there to witness the repair.


The transformer is a common core type
 

·
Donuts > Fried Eggs
Joined
·
17,042 Posts
It's hard to say what was happening there, because a blown fuse on the primary doesn't necessarily mean that there was a transformer winding fault, it just means you're missing a phase, and I'm not sure how a closed Δ:Y would behave if it single-phased.

Was there a phase dead on the wye side or was everything still running, just acting strangely?
 

·
Registered
Joined
·
11,762 Posts
Today i saw a Δ:Y transformer with a blown fuse on the primary side. All the loads connected to the secondary are L-N loads. every thing that was supplied by the transformer was not running smoothly, clearly voltage fluctuation, all the lights where dimming and brightening. but the transformer was still running even though the fault wasn't repaired at that time. I wasn't there to witness the repair.


The transformer is a common core type
Could be anything. How do you know the primary was Delta wye, some pole pigs and 3 phase pad mounts are Ygr Ygr. Just asking. :) 1/3 of those single phase loads should have been working right, the other 2/3 would have essentially been fed by 2 primaries in series. But, being a common core, Im not exactly sure what would happen.


There is form Mike holt, the guys on there are brilliant and usually go into great detail on the theories behind electrical power.
 

·
Registered
Joined
·
44 Posts
Discussion Starter · #9 ·
It's hard to say what was happening there, because a blown fuse on the primary doesn't necessarily mean that there was a transformer winding fault, it just means you're missing a phase, and I'm not sure how a closed Δ:Y would behave if it single-phased.

Was there a phase dead on the wye side or was everything still running, just acting strangely?
I am not sure if there was a dead phase on the secondary. But as far as i know is that the blown fuse was caused by an overload.
 

·
Registered
Joined
·
11,762 Posts

Attachments

1 - 15 of 15 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top