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Wye-delta transform

The Wye-delta transform is used in induction motor and drives. It is related to Three phase theory (or polyphase systems).

Table of contents
1 Configurations
2 Wye connection
3 Delta connection
4 Terminology
5 See also


Two different configurations:

Wye windings - low speed, high-voltage [standard]
Delta winding - high speed, low-voltage

Wye/Delta selection can be used like a gear for the motor speed. Switching “on-the-fly" starts in the Wye winding and changes to Delta winding where performance can be improved.

Wye connection

To minimise the number of electrical connections to a generator, one end of each winding is connected to a common point called the 'neutral' or 'star' point. The other end of each winding has its own connection. This results in four connections to the generator: one neutral and three phases. This has the advantage that the neutral wire can be made thinner than the phase wires, therefore saving weight and cost. In some systems the neutral wire is omitted and the return currents are allowed to flow through the ground.

  . N
 / \\
/   \\

Delta connection

When the generator is connected with three wires, with each wire attached to opposite ends of two adjacent windings, a delta connection is formed.

  / \\

Delta connections can be ungrounded, which was once common. Today, there are some corner-grounded delta systems, where point A is grounded, and some midpoint-grounded delta systems, where a point on the winding midway between A and C is grounded, and a few zigzag-grounded systems that derive a neutral for grounding purposes using a zigzag transformer.


United States   United Kingdom
Wye or YStar

See also

single phase electric power
alternating-current electric power
polyphase systems