Three Phase Auto Transformer

The three phase auto transformer has only one winding per phase part, common to both primary and secondary circuits. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. It can be designed to “step-up” or “step-down” voltages and works on the magnetic induction principle. A transformer has no moving parts and is a completely static solid state device, which insures, under normal operating conditions, a long and trouble-free life. It consists, in its simplest form, of two or more coils of insulated wire wound on a laminated steel core. When voltage is introduced to one coil, called the primary, it magnetizes the iron core. A voltage is then induced in the other coil, called the secondary or output coil. The change of voltage (or voltage ratio) between the primary and secondary depends on the turn ratio of the two coils.

Using an auto-transformer is an economical and compact means of connecting electrical equipment to a power supply or a different voltage. Part of the winding is common to both primary and secondary circuits so there is no isolation between the two. This may be acceptable on some power transformers. Typical applications include motor loads of industrial machinery, electric heating, air conditioners etc. It performs the same function as an isolation transformer of the same KVA and voltage rating without the isolation feature. Auto transformers may be used in either step-up or step-down configurations. All terminals are clearly identified and easy to connect. Transformer terminations rated below 330A are supplied with suitable hardware and lugs for cable connection. Terminations above 330A are supplied with termination pads and are generally quieter than the equivalent isolation transformers. Low regulation is typically less than 3%.