Let's calculate the following: The maximum power of an open delta transformer connection, the new line voltages of the open delta transformer,  ‎Three Phase Sample PE · ‎Open Delta KCL · ‎Open Delta Phase and Line. An open Delta Transformer is a conventional three phase transformer The transformer load is split across the three input phases but in a ration, so while. An open delta transformer is a three phase transformer that only has two primary and secondary windings, with one side of the delta phase diagram “open”.


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The line-to-line voltages will all be equal, for example V.

  • What is an Open Delta transformer? 3 phase open delta ratings
  • What is an Open Delta Transformer
  • What is an Open Delta Transformer

With respect to the line-to-neutral voltages, however, one will be larger by a factor of 1. For example, open delta transformer three-phase, volt system will have line voltage of V, V and V.

KVA transformed by each transformer is: This means the total instantaneous power transformed by each transformer forming a open delta system is only Open delta transformer does open delta transformer compare with regular three phase transformers?

The ratio of kVA between open delta and regular three-phase transformer is This means an open delta transformer will only be able to deliver Alternate way of stating the same is that if a delta-delta transformer is converted to open-delta transformer, then the new transformer will only be able to supply How to size open delta transformer for a given load?

Open delta connection for voltage metering applications Application of open delta connection for providing power to customers is getting rarer these days.

Voltage Disturbance

Due to the inherent voltage unbalance issues, new connections using open delta is not common. The advantage provided by open delta connection for metering at MV is that only two voltage Transformers VT are required.

VTs are expensive at open delta transformer voltages and hence open delta connection provides an economical way to gather voltage data. Below is a schematic of open delta connection as applied in medium voltage metering circuits.

Open delta transformer the primaries of VT are not grounded the VT is less prone for ferroresonance damage. This connection is well suited for application in ungrounded delta system voltage metering.

On both the primary and secondary there are only two windings. Even in this configuration, it is still possible to transform a three phase voltage.

Open Delta Transformer Connection

Open Delta Transformer Open delta transforms are not the commonly used. Typically they would be used for small loads where cost open delta transformer important. Since the active power output in watts is equals the apparent power rating of a transformer in volt-amps during maximum power conditions, we can check our work by adding up the power ratings of each individual single-phase transformer used to make the three open delta transformer transformer: So far so good, this is the easy stuff.


Go back to top 6. This results in an open delta transformer configuration that looks like this: Go back to top 7. So far, nothing has changed for the delta A-phase and C-phase voltage, but we are not so sure about the delta B phase voltage just yet: We will use a positive polarity reference at B and a negative open delta transformer reference at C, just like what the line would see prior to the winding failure.

Open Delta Transformer – Voltage Disturbance

Starting from the B to C connection we have negative A-phase delta voltage followed by the negative C-phase delta voltage from the A to Open delta transformer connection.

The magnitude of the voltage across the missing winding has neither increased or decreased in value, it is equal to the previous magnitude of the same balanced phase voltage.

The angle of the voltage across the missing winding has also neither increased or decreased in value. It is still equal to the angle of the voltage that was there prior to the winding failure.

The surprising finding is that the connected three phase system sees no difference in the supply voltage with the missing winding! The open delta phase voltages are identical to the three phase delta voltages prior to the winding being removed: The resulting open delta phase voltage phasor diagram is identical to the previous delta phase voltage phasor diagram with all three windings in service: