TRANSFORMER VECTOR GROUP.pdf

TRANSFORMER VECTOR GROUP

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TRANSFORMER - VECTOR GROUP
Amala Joseph J | Testing & Commissioning Engineer | Aura Engineering LLC


HOW TO DETERMINE THE VECTOR GROUP OF A T RANSFORMER
WITHOUT NAMEPLATE DE TAILS

A transformer vector group is a classification system that describes the phase shift
between the primary and secondary voltages of a transformer. The vector group is determined
by the way the transformer windings are connected.
Determining the vector group of a transformer is crucial to ensure its compliance with
customer specifications. This information holds significant importance, particularly when,
 Transformers operate in parallel : Transformer vector groups are important
because they must be ma tched when connecting transformers in parallel.
Transformers with different vector groups cannot be connected in parallel because this
would cause circulating currents to flow.
 and implementing differential protection schemes : Accurate knowledge of the
phase shift is essential for proper settings in the protection relay to avoid false trips
during normal operation.
The vector group test is performed before commissioning the transformer. To find the
vector group, follow these steps.
1. Isolate the transformer : Ensure the transformer is disconnected from the power
source.
2. Short circuit HV R-phase and LV R-phase: You can select any combination if you
have a good understanding of the vector diagram.
3. Apply 415V AC to the HV side: Connect a 415V AC source to the HV side of the
transformer, minimizing high voltage risks.
4. Measure voltages in all combinat ions: Measure voltages for all possible
combinations, as outlined in the table below.
Table: Measured Voltages

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5. Compare the readings : Compare with the following conditions; if they match, you
have determined the vector group of the transformer:

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HOW TO CREATE A VECT OR GRAPH

Ever wondered where these graphs come from, what these conditions mean, or how
to draw them yourself? Let's explore how to draw a vector graph independently.
Consider a transformer with the vector group DYn11, where "D" represents delta connection
on the HV side, "Yn" signifies star with neutral connection on the LV side, and "11" implies a
+30 degree phase shift.
Where,
 HV: High Voltage
 LV: Low Voltage

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For reference:


DECODING DYN11:
"HV" is a delta connection, so you can represent it like this:

Diagram: Delta Connection
"LV" is a star connection, so you can draw it smaller due to its lower voltage:

Diagram: Star Connection

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"DYn11" indicates an 11 o'clock position, equivalent to a +30 degree phase shift, which
you can represent like this:

Diagram: +30 Degree Phase Shift | Final vector diagram of DYn11 tran sformer

ENSURING THE VECTOR GROUP:
To confirm the vector group of the transformer, short-circuit the HV and LV R-phase,
effectively connecting R and r. The diagram will look like this:
R-r Short-circuited

Diagram: Vector Diagram Resulting from R-r Phase Short Circuit

Diagram: Resultant Vector Diagram with Conditions

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From the above drawing, these conditions apply:
1. Voltage between R and Y = Voltage between R and n + Voltage between Y and n.
2. Voltage between B and y is greater than Voltage between B and b.
3. Voltage between Y and b is approximately equal to Voltage between Y and y

If these conditions match the measured voltages, the transformer is identified as DYn11.

TESTING CONNECTION D IAGRAM FOR DYN11 TRA NSFORMER:

Diagram: Testing Connection for DYn11 Transformer

Thank you for reading.

FOR ADDITIONAL INFOR MATION:
The outcome of short-circuiting the HV Y-phase and LV Y-phase is depicted in the
following resultant vector diagram (in the case of Y-y short circuit).


Diagram: Vector Diagram Resulting from Y-y Phase Short Circuit