Vector Group Test Conditions: ELECTRICAL ENGINEERING MATERIALS

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Three-phase transformers contain Vector groups. Ensuring Vector group by doing a Vector group test is necessary before taking the transformers into operation. Here we are going to discuss the Vector group test procedure and conditions for different vector groups in detail.

The vector group test is one of the transformer tests.

Firstly, we discuss the vector group test procedure and then the conditions to check the vector groups.

Transformer Vector Group Test Procedure:

Voltage Ratio Measurement:

For doing a Vector group test measurement of voltages between various windings is necessary. Voltage ratio measurement is carried out by use of the potentiometric method.

2. Checking Winding Polarity:

Winding polarity is important since reversing the connections across a set of windings affects the phase shift between primary and secondary.

Vector groups identify the winding connections and polarities of the primary and secondary. From a vector group, one can determine the phase shift between primary and secondary.

3. Obtaining the Phasor Diagram:

The measured values of the individual voltages are entered on a phasor diagram, from which the correct polarity and vector group can be determined.

Following are the steps to obtain the phasor diagram of a transformer.

By doing Voltage ratio measurements, the voltage measured between the various terminals will be indicative to ensure the phase shift.
The two voltages which are to be compared must be in phase and have the same orientation. This is achieved by ensuring that the high and low-voltage terminals are correctly connected.
Testing Engineer should derive at least three conditions to compare, add and or equate the particular set of voltages measured. These conditions should be in such a way as to ensure the phase shift and phase sequence.
Usually, 1U and 2u are connected but it is not necessarily to be so, Testing Engineer can choose by his/her own choice and the conditions shall be derived accordingly.
If the derived conditions are satisfied the vector shall be confirmed.

Vector Group Test Conditions:

Following are the various Vector groups of a three-phase transformer and the conditions to be satisfied to confirm the vector group.

1. YNyn0 Vector Group

Connect 1U and 2u
Keep the neutral floating
Apply 3Φ Voltage on the HV side (Voltage may be applied in either of the winding preferably in the HV side as it is safe).