Open-delta connection

[marchar]

I have VTs of A, b, and C phases to be connected open-delta. The ratios are 115/3 for both A & B phases and 115 for C phase. What will be the effect and what can I do?

 

[waross]

When rated primary voltages are applied, you will have 115V - 3V = 112 Volts across the BROKEN delta. What do you want to do??

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[marchar]

(1)If I want to connect a Resistor across the open-delta, what will be the safe value?
(2) It was to be used for 64N protection

 

[davidbeach]

Again, open delta is two transformers, no resistor, while broken delta is three transformers of exactly the same ratio with a resistor across the broken corner.

 

[waross]

marchar: Where in the world are you located?
In North America an open delta is as davidbeach has described; two transformers used for delivery of three phase power for generally small loads.
In Europe an open delta is three transformers in delta with one corner of the delta open. This connection is called a broken delta in north America. For this connection you must start with three transformers with equal ratios. It is not a good idea to mix 115 Volt transformers with 3 Volt transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[marchar]

Thanks very much. I am in Ghana which is in the Western part of Africa.
It is not a good idea, but if it happen, what will be the effect? 115/root3 for A & B phases and 115 for C phase

 

[davidbeach]

It won't work, for balanced system voltages you'll have a large standing voltage across the resistor instead of zero. The "right" system problem could actually push the voltage to zero. The output would be entirely worthless for protection purposes.

 

[marchar]

Thanks very much David for your appreciative contribution. My sincere regards from Ghana