open delta Vs broken delta

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mivey

Senior Member
Not the same.

Open delta is a delta bank with two transformers.

Broken delta is referring to unbalanced voltages (the three voltage vectors do not sum to zero).
 

mivey

Senior Member
Two different words. Same set up, but the broken one is created by default. I assuming this is just a question about English?
It is not the same setup.

A broken delta is used to measure 3Vo (the sum of the delta voltages) for a ground relay.
 

jumper

Senior Member
It is not the same setup.

A broken delta is used to measure 3Vo (the sum of the delta voltages) for a ground relay.
I was not trying to answer any technical question, I was trying to answer an English one. The word "open" can get confusing for some people at times when dealing in electrical.

Open delta- two xformrs, not broken.
Closed delta- 3 xformrs, one is " open", so now you have 2, broken.

Open can mean broken, as in an open in a wire, or it can mean off, as in a breaker that is in the open position.

This is what I was trying to say in regards to OP.
 

Hameedulla-Ekhlas

Senior Member
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ok thanks guys and one more question

broken delta is used most of the time for protection and ground fault
Zigzag transformer is also used for protection and ground fault.

what is the difference usage between these two.
 

SG-1

Senior Member
Broken Delta Protection

Broken Delta Protection

Here is a schematic for the broken delta side. I still see this arrangement used several times a year. I have never seen a zig-zag transformer used for this. Since it is used to derive a neutral, then I would think you could detect zero sequence current. I will look some more in this same book.

The difference I see is that open delta ( for PTs ) uses 2 transformers, broken delta ( for PTs ) uses 3 transformers as shown.
 

mivey

Senior Member
The use of a zig-zag transformer is discussed as a means of low reactance grounding, not protection. A delta-wye transformer is shown as a form of low resistance grounding.
Once you have the zig-zag, you can use it to measure ground currents. The broken delta just for protection schemes.
 

mivey

Senior Member
The broken delta is used on ungrounded systems.

Using the zig-zag would ground the system, so other types of protection schemes would be used.
Yes, the broken delta is for ungrounded systems.

If the system is grounded with a zig-zag transformer, zero sequence current only will flow through its grounding point (often with a resistor or reactor added in series to limit ground fault current). An over-current relay can be added to the grounding point of the zig-zag.
 

72.5kv

Senior Member
Broken Delta voltage is used on distance protection scheme to protect against transmission line ground faults
 

mivey

Senior Member
Broken Delta voltage is used on distance protection scheme to protect against transmission line ground faults
It is tied to the SBMTT relay (SomebodyBetterManTheTelephones) and the CYB relay (if you don't know this one, you are in trouble already). :grin:
 
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