O/H Open Delta Unique Configuration
O/H Open Delta Unique Configuration
(OP)
At a neighboring utility we discovered a very unique connection on a three phase O/H bank. The coneection was open wye-open delta one two single bushing pots. The secondary had 480v L-L with one leg split to get 240v. The oddity came where the one leg was slipt was get 240, the utility also claimed that configuration would give them 120v. They called it an "A-frame" configuration. Has anyone heard of this and possible have a wiring diagram or vector diagram to explain where the 120V comes from?
Thanks!
Thanks!






RE: O/H Open Delta Unique Configuration
It has been discussed in this forum. If I have time later to locate it I will.
respectfully
RE: O/H Open Delta Unique Configuration
RE: O/H Open Delta Unique Configuration
RE: O/H Open Delta Unique Configuration
In the instance at hand, are you sure that the "A frame" connection is not another name for a four wire center-tapped delta connection?
This connection is most common with 120:240 volt transformers which give 240 volt 3 phase delta and 120:240 volts from the center tapped transformer.
respectfully
RE: O/H Open Delta Unique Configuration
If anyone knows a way to post a diagram I have this drawn out.
Thanks!
RE: O/H Open Delta Unique Configuration
RE: O/H Open Delta Unique Configuration
This configuration will give 240 volts three phase and 120:240 volts single phase if 120:240V transformers are used. This is a common connection.
While it is possible to add a third transformer in crossbar configuration to construct an "Open delta" inside an "Open Delta" it is not a common connection, and iot requires three transformers, not two as originally stated.
respectfully
RE: O/H Open Delta Unique Configuration
Thanks!
RE: O/H Open Delta Unique Configuration
You will have to see the connections to determine if the 240 volt three phase system is open delta, closed delta, or broken delta.
Two 240:240 volt transformers may be used as an open delta autotransformer bank to derive 480 volts 3 phase from a 240 volt 3 phase syetm. This sounds similar, (not the same, but similar).
respectfully