Open Delta connections; V-V connections

In electrical Systems we have seen Single phase and three phase transformer, Single phase Transformers have single winding and three phase transformers have three windings. These windings are connected in connections such as star-delta, delta-delta, star-star connections. There is another connection known as open delta connections, which consist of two windings of transformers.

Open delta connections are done when one winding of Transformer get faulty so as to continue the operation of Transformer but at reduced load.

Open delta connections are as shown below:-

There are only two windings on both Transformer primary and secondary sides.

Open delta connections are often known as V-V Connection Transformers. Open delta connections are usually used to cater small loads.

Power Delivered by Open Delta connected Transformer:-

Power delivered by open delta connections in comparison to 3-winding Transformers is about 57.7% of power delivered by Three winding Transformers.

Calculations for the same as shown below:-

From Figure above you can see that:-

In case of delta connections ILine = √3 X IPhase

And in Open delta connections ILine =  IPhase

Power delivered by Transformer in VA for Delta connection will be = 3 VL X IPhase

In case of open delta connection power delivered by Transformers in VA will be= √3 X VL X IPhase

Power delivered by open delta connected Transformer= √3 X VL X IPhase

Power delivered by Delta connected Transformer                 3 VL X IPhase

Now from both Power’s we get; Power output of open Delta connections is 57.7% of Power delivered by delta connected power Transformer.

Advantages of Open delta connections:-

Open delta Transformer connections have following advantages:-

1.       These are used where Three phase power load is lower as cost of 3-winding Transformer is very higher.

2.       When Delta-delta connected transformer one winding get burnt than open delta connections will restore supply but with reduced load.

Disadvantages of Open Delta connections:-

With open delta connections power factor of the system get reduced to 86.6%. When load connected at Open delta Transformer is having power factor 1 , then system power factor for open delta connection s will be 0.866.,But when there are delta connected Transformer is connected to that load then system power factor will be 1 means that of load.