Power distribution: Do you need a Wye or Delta transformer?

Energy management: Larson Electronics compares Wye and Delta wiring configurations, as well as provides an overview of the pros and cons of the connections in relation to power distribution applications.

Apr 16th, 2018
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Power distribution: Three-phase transformers are configured or wired differently, allowing businesses to make full use of their power distribution systems. The units are equipped with three windings on the primary and secondary side. How the connections are setup on each side essentially determines its configuration.

This article compares Wye and Delta wiring configurations, as well as provides an overview of the pros and cons of the connections in relation to power distribution applications.

Wye vs. Delta Connections

Starting with Wye, the connection consists of a total of five wires: (3) hot, (1) ground and (1) neutral. The configuration closely resembles a letter Y, with the neutral component connected at the middle, which is also where all the lines converge. It is at this point wherein the voltages are all equal.

It is important to point out that the phase and line current are also considered to be equal. Multiplying the phase voltage by 1.732 (or square root of 3) will result in arriving at the voltage present between any of the two lines. In a Wye system, 120V can be measured from any hot wire to neutral. Additionally, 208V is measured from hot wire to hot wire. This is also the same for Delta configurations.

By comparison, a Delta circuit inside a transformer appears as a triangle with equal sides, resulting in a closed path. In most cases, such wiring configurations do not have a neutral and is present on the secondary side of the transformer. The three phases are connected at every meeting point on the triangle. Moreover, a Delta system is equipped with four wires: (3) hot and (1) ground.

Which One Do I Need?

Transformer connections do not have to take on the same wiring configurations on the primary and secondary side, i.e., Wye-Wye (Yy) or Delta-Delta (Dd). The units can also be wired Delta-Wye (Dy) or Wye-Delta (Yd), depending on the requirements of the business. Each configuration comes with their own respective benefits and use:

• Delta-Wye: Delta-Wye transformers are commonly found in industrial facilities. From an economical perspective, this setup is advantageous, since Delta configurations are associated with lesser amps (and less heat generation). Because of this, less insulation on the primary side is required. Smaller wiring on the primary coils can be utilized. On the secondary side, a neutral is provided.
• Wye-Delta: A Wye-Delta connection is found in three-wire transformer applications requiring a neutral and service of loads the secondary side. This type of configuration may promote harmonic disturbances. Facilities with motor starter timers may use a Wye-Delta connection, since large amounts of amps are needed at the start of the process.
• Wye-Wye: A Wye-wye connection is suitable for transformer applications that do not need a neutral on the primary side. The three-wire configuration can be used on three-phase and single-phase circuits. In the event one of the transformers fails prematurely or gets damaged, the entire system could become compromised.
• Delta-Delta: A Delta-Delta configuration is recommended for projects that does not need a neutral on the secondary side. Though one can be provided, which is called a high leg. This type of wiring may also be beneficial for operations that require a minor single-phase component. Should one of the three transformer components fail, the other two can continue to function at a lower output.

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