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# Basic principles and operation of a transformer

## Vector groups & neutral earthing

Three configurations in which three phase windings of the transformer are usually connected are delta, a star or an interconnected star (zig-zag). The configurations (winding arrangements) are shown in Figure 1 below.

How the vectors are grouped and how the phase relationship nomenclature is used are defined as follows:

• Capital letters for primary winding vector group designation
• Small letters for secondary winding group designation
• D or d represents a primary or a secondary delta winding
• Y or y represents a primary or secondary star winding
• Z or z represents a primary or secondary interconnected star winding
• N or n indicates primary or secondary winding with an earth connection to the star point
Numbers represent phase relationship between the primary and the secondary windings.

The secondary to primary voltage displacement angles are given in accordance with the position of the â€śhandsâ€ť on a clock relative to the mid-day or twelve oâ€™clock position.

This means: 1 is -30Â°, 3 is -90Â°, 11 is +30Â° and so on.

Example on defining Dy1 vector grouping is given in Figure 1 In this case, it isÂ noticeable that the secondary star voltage is at the one oâ€™clock position, meaningÂ that it is lagging the primary delta voltage vector by 30Â°.

In Figure 2 below, there is another example of defining Dyn5 vector grouping.

It is clearÂ that the secondary star voltage is at the 5 oâ€™clock position, meaning that it isÂ lagging the primary delta voltage vector by 5 Ă— 30Â° = 150Â°.

Mostly the system designers are the one to decide which vector groupingÂ arrangement is required for each voltage level in the network, though there areÂ many factors influencing the decision.

Important aspects from userâ€™s point of viewÂ are:

1. Vector displacement between the systems connected to each winding of theÂ transformer and ability to achieve parallel operation
2. Provision of a neutral earth point or points, where the neutral is referred toÂ earth either directly or through an impedance
3. The practicality of transformer design and cost associated with insulationÂ requirements
4. The Z winding reduces voltage unbalance in systems where the load is notÂ equally distributed between phases and permits neutral current loading with inherently low zero-sequence impedance. Therefore, it is often used forÂ earthing transformers.
 Title: Basic principles and operation of a transformer (Seminar paper for course Distribution and industrial networks) – Andrea Ljubljanac Format: PDF Size: 1.0 MB Pages: 28 Download: Right here | Video Courses | Membership | Download Updates

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### One Comment

1. Rajendra Prasad Thapliyal
Sep 22, 2020

information are good for general knowledge.

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