How to Choose the Best Transformer

Transformers have been around for almost two hundred years. The technology began with the discovery of electromagnetic induction by the English scientist Michael Faraday in the 1830s. (Other scientists probably discovered it around the same time, as well.) Induction is the phenomenon in which a changing magnetic field (magnetic flux) creates a current in a nearby wire. An electrical transformer uses this phenomenon to convert one voltage to another. Since the 1800s, inventors have been making better and better transformers. Today, transformers are crucial components of our electronics as well as our electrical grids.

When choosing a transformer, the top concern is picking the right one for your application. Small transformers come in a variety of sizes and configurations and are suited for electronics or other devices. Large transformers, on the other hand, are capable of connecting you (your building, your campus, etc.) to the power grid. Let’s review some of the considerations when choosing a transformer.

What Is the Right Transformer for the Job?

No matter the size of the transformer, a few factors are key in determining which the best fit is. Understanding these factors—and weighing which are the most important to your project—will ensure long-term success, safety, and savings.


Protection from the elements: Transformers that require enclosures offer many options that meet NEMA (National Electrical Manufacturers Association) standards. Many transformers come with NEMA 3R rated enclosures, along with weather shields. (NEMA 4 enclosures are often available, too, and offer even higher levels of protection against elements like dust and moisture.) Because large transformers often sit outside, these high standards for protection are critical.

Transformers also offer a variety of cooling options to ensure optimal performance and long lifespans. Units are often ventilated or even outfitted with forced-air cooling. Oil or water cooling are also available. Transformers that are used indoors often have cooling systems filled with non-flammable dielectric fluids rather than oil, as an extra safety measure.

An example of these safety measures is seen on the Jefferson Electric Three-Phase Ventilated transformer (rated from 15 to 2,500 KVA). It has insulation rated to 220°C and a temperature rise of 150°C. This transformer is a good fit for all general loads, including lighting, industrial, and commercial uses.

Flexibility: Manufacturers such as Jefferson Electric or Hammond Manufacturing offer electrical transformers in a wide array of sizes and capabilities. Whether it’s a small transformer to fix a guitar amp or a 3-ton, 1000 kVA transformer to power your building, there are many options available and affordable on the market. The top factor for choosing a transformer is likely the voltage rating. The Jefferson Electric Three-Phase Ventilated transformer mentioned above comes in no fewer than 27 voltage options, from 15 to 2,500 KVA.

A huge variety of enclosures is possible, too. Housing dimensions for these large transformers vary from the size of a suitcase to that of a small car. These units can be mounted in a number of ways. Wall brackets are an option for transformers up to 75 kVA. Beyond that, transformers become very heavy, and a floor or concrete pad mount is likely necessary. Drip pans, pole-mounting brackets, and other hardware are also available.

Applications involving facilities with critical needs, such as hospitals or data centers, might require special transformers. Units such as drive isolation transformers or harmonic-mitigating transformers are appropriate for these situations. These units guarantee steady electrical supply in all circumstances. Other specialized transformers are suited for non-linear loads that occur in some buildings, such as offices that use large amounts of modern office equipment.

Efficiency: Today’s transformers are much more efficient than their early ancestors. Manufacturers have had decades to fine tune their designs, and many transformers today are nearly 99% efficient.

Small energy losses can occur in a couple of ways inside a transformer. Energy can be lost in the windings—the coils of metal wire—as well as in the transformer’s metal cores. Sometimes the energy is lost to resistance in the metal, resulting in unwanted heat. Other times, parts of the magnetic field are not fully converted into energy. However, advanced designs have rendered these losses minimal. Different designs include core, shell, concentric, and sandwich configurations of the windings and cores.

In short, the higher the quality of the metals, the more efficient the transformer will be. High-quality windings—either aluminum or copper, usually—and the best steel cores ensure minimal losses.

Seismic protection:Sometimes a transformer needs to be “seismic qualified” for a specific project or region. Critical facilities like hospitals, government facilities, or fire or police stations often fall into this category. In these situations, transformers must be guaranteed to work after seismic events like earthquakes.

Fortunately, many transformers have been built to this high standard and have undergone independent, third-party testing to gain the seismic qualification (the ICC-ES AC156 qualification). These units meet the International Building Code (2015 IBC), as well as the California Building Code (2016 CBC). Units can still be either floor-mounted or wall-mounted.

These seismic qualified transformers can be found in a wide variety of sizes and voltage ratings. For example, Jefferson Electric offers both wall-mounted and floor-mounted transformers in either single or three-phase encapsulated or ventilated models. These seismic qualified units guarantee legal compliance in applications or regions that require it. The seismic protection also offers an additional layer of protection even when not legally mandated.

Quality: Looking for high quality in a transformer ensures that you get a unit which performs at the highest level, runs efficiently, and lasts as long as possible. Duralec-provided transformers, for example, are best in class and offer top performance. High-quality metals in the windings and cores promise efficiency and minimal load losses. Good venting and cooling tools keep transformers running smoothly and add to their long lifespans.

A high-quality transformer will operate more quietly, as well. Some transformers produce a steady humming sound. This is the result of components expanding and contracting with the magnetic field. A transformer with higher-quality materials, however, will be quieter. Its better build quality will also lead to less long-term vibration and noise.

To explore the many electrical transformers on the market, reach out to a Duralec expert today.


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