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How to Choose a Transformer

How to Choose a Transformer

When choosing a transformer, there are two primary concerns: the load and the application. Several factors must be evaluated carefully while making the choice, to ensure that the needs of both primary concerns are met.

To use a clich?, it is typically a ‘no-brainer’ to choose smaller transformers. A unit with a kVA rating that is larger from the anticipated load can quickly be picked up. But if you are selecting a large unit for an electrical utility system, to be part of a large distribution network, you are typically making a much larger investment; thus the evaluation process is much more detailed and elaborate. With over 90 years of experience in this industry, Pacific Crest Transformers has put together a quick checklist to help you make your choice judiciously.

Top Questions

There are three major questions that influence your choice:

  • Does the chosen unit have enough capacity to handle the expected load, as well as a certain amount of overload?
  • Can the capacity of the unit be augmented to keep up with possible increase in load?
  • What is the life expectancy of the unit? What are the initial, installation, operational, and maintenance costs?

Evaluation Factors

The cost and capacity of the transformer typically relate to a set of evaluation factors:

1. Application of the Unit

Transformer requirements clearly change based on the application.

For example: in the steel industry, a large amount of uninterrupted power is required for the functioning of metallurgical and other processes. Thus, load losses should be minimized – which means a particular type of transformer construction that minimizes copper losses is better suited. In wind energy applications, output power varies a great extent at different instances; transformers used here should be able to withstand surges without failure. In smelting, power transformers that can supply constant, correct energy are vital; in the automotive industry, good short-term overload capacity is a necessary attribute. Textile industries, using motors of various voltage specifications, will need intermittent or tap-changing transformers; the horticulture industry requires high-performance units that suit variable loading applications with accurate voltage.

These examples serve to underline that type of load (amplitude, duration, and the extent of non-linear and linear loads) and placement are key considerations. If standard parameters do not serve your specific application, then working with a manufacturer that can customize the operating characteristics, size and other attributes to your needs will be necessary. Pacific Crest regularly builds custom transformers for unique applications.

2. Insulation Type (Liquid-Filled or Dry Type)

While there is still debate on the relative advantages of the available types of transformers, there are some performance characteristics that have been accepted:

  • Liquid-filled transformers are more efficient, have greater overload capability and longer life expectancy.
  • Liquid-filled units are better at reducing hot-spot coil temperatures, but have higher risk of flammability than dry types.
  • Unlike dry type units, liquid-filled transformers sometimes require containment troughs to guard against fluid leaks.

Dry type units are usually used for lower ratings (the changeover point being 500kVA to 2.5MVA). Placement is also a crucial consideration here; will the unit be indoors serving an office building/apartment, or outdoors serving an industrial load? Higher-capacity transformers, used outdoors, are almost always liquid-filled; lower capacity, indoor units are typically dry types. Dry types typically come in enclosures with louvers, or sealed; varnish, vacuum pressure impregnated (VPI) varnish, epoxy resin or cast resin are the different types of insulation used.

3. Choice of Winding Material

Transformers use copper or aluminum for windings, with aluminum-wound units typically being more cost-effective. Copper-wound transformers, however, are smaller – copper is a better conductor – and copper contributes to greater mechanical strength of the coil. It is important to work with a manufacturer that has the capability and experience to work with either material to suit your specific requirement.

Read more on how to choose a transformer

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