Transformers

How do transformers work?

A transformer is a simple and efficient device made up of coiled wire wrapped around an iron core. It is used to convert electric power from one voltage level to another. Some transformers increase voltage while others lower it. The iron core in the transformer acts as a magnetic link between the input coil and the output coil. Electric current from the input coil creates a magnetic field in the core, which in turn produces a voltage on the output coil. The iron core concentrates the magnetic field inside the coils and increases the efficiency of the transformer.

All transformers, ranging from very large ones in power system substations, medium size pole-top or pad-mounted ones commonly found in our neighbourhoods to small ones in radios, televisions and cordless appliances (with battery chargers), use magnetic fields to perform this function.

How strong are fields from transformers?

In order to improve its efficiency, a transformer is designed and built so that as much as possible of the magnetic field generated to change voltage stays within its iron core. With power system transformers, a high level of efficiency is especially critical, since they operate 24 hours a day. Modem power transformers use coaxial-type high voltage (HV) and low voltage (LV) coils or "windings" which are wound closely together around an iron core. With this design, a high degree of "cancellation" occurs and 99% of the magnetic field stays within the core and windings of the transformer.

Regardless of efforts taken, magnetic fields can be found close to any power system transformer. However, these fields drop off quickly as distance increases from the transformer source so that levels at the fenced boundary of the outdoor or indoor transformer stations are generally comparable to magnetic field levels found in typical homes. The majority of the fields associated with transformer stations are from the power lines going in and out of the station, and from the "buswork" within the station.

Similarly, normal background field levels can be found at a distance of two meters or less from neighbourhood pad-mounted transformers and underneath distribution pole-top transformers.

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