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The Basics of Delta-Wye Transformers

Dec 1, 2000 12:00 PM, By C. Sankaran

Find more articles on: Transformers

The electrical configuration of the delta-wye transformer makes it the most popular transformer connection in the world.

When it comes to making proper transformer connections, more industry professionals choose the delta-wye connection than any other 3-phase transformer connection in power distribution. Why is it so popular? You can use the secondary to provide a neutral point for supplying line-to-neutral power to serve single-phase loads and ground the neutral point for safety reasons.

The delta primary serves several useful functions. If the transformer secondary supplies large amounts of unbalanced loads, the delta primary winding provides you with a better current balance for the primary source. How can you be sure which transformer is right for your particular application? Let's look at your options.

Dry-type and liquid-filled transformers. Transformers fall into one of two categories - dry-type or liquid-filled units. In dry-type transformers, the most common cooling medium is air (some sealed dry-type transformers use nitrogen for cooling). You typically use them indoors and up to a maximum-rated voltage of 34.5kV.

You use liquid-filled transformers in medium- and high-voltage applications - especially outdoors. The liquid makes an excellent cooling medium. Now let's look at a typical transformer makeup.

Core and winding characteristics. A transformer winding and its magnetic core are the two most vital parts required for voltage transformation. The core consists of thin laminations of silicon steel, which help reduce eddy current losses. Eddy currents are induced in the core structure as a result of exposing the core to an alternating magnetic field.

Copper and aluminum are common materials used for transformer windings. Aluminum is a lighter metal, but has a higher resistivity than copper. Copper-wound transformer coils are more mechanically rigid than aluminum-wound coils, which help increase the transformer's reliability when subjected to an external fault.

Harmonics. Third harmonic currents are common in facilities that house computer, communication, and data processing loads. Ideally, the delta primary windings should trap the third harmonic current in the closed delta winding; however, a low level of third harmonic current still passes to the primary lines. The figure shows a delta-wye transformer connection where the third harmonic currents remain trapped in the primary delta winding.

Although deciding which transformer connection is right for you may seem like an easy task, take time to research your options before you buy.

 

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