How to Design an Industrial Transformer

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Transformers are critical parts of energy-distribution systems throughout the industrial sector. They ensure the right amount of power reaches the load relative to the full capacity of the supply infrastructure

Industrial transformers have a significant impact on electricity-distribution performance and meeting process needs. An improperly built or sized transformer will compromise the effectiveness and success of your operations and threaten regulatory compliance.

Here's what to know about industrial transformer design, including essential sizing and component-selection considerations.

Decision-makers must decide between the two main categories of industrial transformers: dry-type transformers and liquid-filled transformers. The factors that impact this decision include location, environment, targeted cost outlay, and the existing configuration of the electrical system.

The latter type has some disadvantages despite its higher power loads. Dry-type transformers need more robust insurance coverage and ventilation systems, but their ability for on-site installation is a big advantage.

Another critical step is determining what kind of core your transformer will require. This occurs in two stages.

Here are some core selection guidelines based on operational frequencies:

Some core types need a bobbin while others do not — check with your component manufacturers to be sure about your application's specific requirements.

According to Texas Instruments, an acceptable temperature rise for an industrial transformer is somewhere on the order of 40-50 °C. This would result in an internal temperature of 100 °C at a maximum. Note that larger cores reduce temperature-rise rates within transformers. Managing temperature effectively is another step in managing power losses and ensuring satisfactory efficiency.

Optimizing the size of your new or replacement industrial transformer is critical for realizing acceptable energy costs over time. Decision-makers must ensure the transformer has appropriate demand and connected loads ratings. The connected load, measured in kVA (kilovolt-amperes), is always larger than the demand load, but the latter must match the engineering team's understanding of operational needs.

The best way to optimize transformer size is to use historical data. Under NEC guidelines 220.87, engineers can use one year of accumulated peak-load data to optimize their new transformer. If this information isn't available, NEC also allows the use of 30-day metered peak-load data. Both methods require matching intervals of heating and cooling requirement data — one year or 30 days, respectively.

Cost isn't the only variable impacted by sizing. Transformers that are right-sized — compared to being too large — reduce the impacts of energy hazards and the risk of arc flashes.

Industrial transformers are further subdivided between single-phase and three-phase. Single-phase transformers have a primary and secondary winding component, while three-phase models need three primary and three secondary windings.

You won't need to concern yourself with the winding type in a single-phase transformer. However, achieving the desired performance of a three-phase transformer involves selecting the correct primary and secondary windings. These include star (wye), delta (mesh) and interconnected (zig-zag) windings.

Choose carefully — some tradeoffs and advantages are associated with various pairings of winding types. For example, a star-delta connection configuration is better for transferring unbalanced loads and is more frequently associated with step-down transformers. Star-star arrangements have their own advantages, like needing fewer wound turns around the core.

You should familiarize yourself with the formulas used to determine the amount of winding you need to accommodate the transformer's capabilities. A transformer with a 12-volt, 2-Amp output with a 120-volt input should use this formula. The 110 is there to add a 10% increase in power input to offset power losses in the system:

Remember to prioritize high-quality materials and craftsmanship, no matter what else you decide during the transformer design process. There are several undesirable effects of improper configuration and low-quality build materials:

A well-built transformer should deliver reliable performance over a lifetime of 25-40 years. Inferior products will have a shorter service life — beginning with higher ongoing maintenance costs and culminating with a transformer that fails before its time.

The U.S. Department of Energy continuously busies itself with revising its standards for industrial transformer design, often with input from the public. It's wise to familiarize yourself with these compliance requirements and protect yourself from unnecessary power loss.

Industrial transformer design begins with determining the needs of the operation and the basic parameters. These are the most important characteristics you’ll need to nail down before work begins:

The primary voltage is provided on the input side of the transformer. The secondary voltage is what's put out by the transformer. The supply voltage and required output must match the transformer's capabilities — for example, 415 V of input and 240 V of output.

You can determine the kVA rating during your transformer selection or construction process using the following formulas:

The operational frequency of the transformer must be listed and rated for compatibility and compliance purposes.

The nameplate should also include these details:

Each of these distinguishing factors must be inscribed on the transformer's nameplate. Subsequent inspection of the transformer will reveal the contents of the nameplate and avoid misunderstandings during component selection or installation.

The construction sector is undergoing several significant changes, including new priorities in green building and resilient material selection. One thing that will never change is the need for electrical engineers and building managers who understand what goes into industrial transformer design and component selection. All industries are preparing for digital transformation to achieve greater output and improved harmony with the planet, and reliable power distribution infrastructure is critical for that.

The built environment requires higher-than-ever tolerances and greater prioritization of efficiency. Paying attention here will yield dividends over time in terms of operational stability and a consistent power supply.

Image Credit: Wang An Qi / Shuttestock.com