Factors to Consider When Selecting a Transformer

9 May 2023

There are several factors to consider when determining the characteristics of a transformer. The most suitable transformer should be chosen by taking these factors into account. The key factors to consider include:

Voltage Ratio, Value, and Connection Method

Voltage value, ratio, and connection method are critical factors to consider both for initial supply and future modifications. In many small-scale commercial projects, a secondary voltage of 208Y / 120V is often required, primarily due to the significant load being comprised of small household appliances and lighting. Higher voltages may be preferred when there is a need for extensive lighting.

Insulation Temperature Ratings

The average conductor, measured with resistance, should consider temperature rise up to 40°C. Transformers with low conductor losses have lower temperature rises. Properly selected insulation temperature ratings result in longer-lasting and more efficient transformers.

Noise Levels

Transformer noise can be disturbing in settings where silence is required, such as commercial buildings, conference rooms, or office spaces. Controlling transformer noise can be achieved by placing transformers in separate rooms or using soundproofing measures.

Harmonic Load Content

Certain transformer types can fail due to high harmonic emissions or nonlinear loads. Therefore, transformers should be designed to withstand harmonic currents and the magnetic fields they produce.

Effects of Transformer Failures

Transformer failures are not common but can have significant consequences in buildings with limited backup conditions. Therefore, specific provisions should be in place to effectively deal with failure modes.

Voltage Taps

Taps are used to adjust the ratio between turns. The selected tap and maximum no-load voltage conditions should be compatible.

Kilovolt-Ampere (kVA) Rating

Both three-phase and single-phase transformers have power and regulation requirements, and they must comply with IEEE General Requirements for Liquid-Immersed Power Transformers. Neglecting these requirements can lead to safety and cost issues.

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