FAQs

Our recommendation is that you buy a purpose-built step-up transformer instead of reverse feeding when possible.

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Learn more about reverse feeding transformers in this article

Autotransformers are often employed as a cost-effective substitute for 3-phase general purpose distribution transformers for adjusting supply voltage for particular load requirements, provided that isolation from the supply line is not necessary.

Below are some examples of autotransformer applications, and installation considerations.

Voltage Adjustments for Stand Alone Equipment

• Autotransformers are ideal for voltage adjustment for commercial and industrial machines. They provide an efficient, low cost way of serving the proper voltage to motors and compressors, lathes, CNC machines and other industrial equipment requiring a step up or down from a building’s service voltage. Their smaller profile is often half the size of a standard two winding transformer, which makes for a discreet installation.

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If you are unsure if an autotransformer is compatible with a particular piece of equipment, we recommend contacting the equipment manufacturer. However, as a general rule, this issue goes beyond the scope of an equipment manufacturers’ specifications since it is largely dependent on the existing electrical system configuration, where the equipment is installed, and local code requirements.

One hard and fast rule around autotransformer use, is that if the machine requires a neutral, and your system does not have one, an isolation transformer is required to create that neutral. Autotransformers do not create their own neutrals.

When a transformer is first energized, there is no magnetic flux in the core, so a large current must flow through the primary winding to create the initial magnetic flux. This current can be several times the transformer's rated current, which means special precautions must be taken to manage it.

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If your primary concern is lead time, repair is almost always quicker than buying a new unit—and this is especially true given the current supply chain crisis.

However, replacing the damaged unit with a reconditioned one can sometimes be just as fast or faster than repairing or replacing with a brand new unit. If an available reconditioned unit matches the dimensions of the unit in need of repair, you can sell the failing one and replace it with the reconditioned one. Maddox has thousands of reconditioned, ready-to-ship transformers in stock for most common voltage configurations. These are typically available with a warranty comparable or identical to the warranties of newly manufactured units.

The DGA has long been the most reliable and accurate method for determining the internal health of oil-filled transformers. The analysis requires drawing an oil sample from the unit, extracting the gasses from the sample, and analyzing the gasses through gas chromatography. The results of the chromatography tell the lab about different problems that may be arising inside the transformer. Some modern transformers have gauges on them that read levels of dissolved gasses in the oil in real time. But usually, the oil must be drawn and sent to a lab.