Isolating or autotransformer: which do I need?

Isolating or autotransformer: which do I need?
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Isolating transformers and autotransformers are both used to convert voltage. So what is the difference and when is each type used?

Of course there is a fundamental difference in their design. In an isolating transformer the primary and secondary windings are fully electrically separated by means of a basic isolation. In an autotransformer, by contrast, the primary and secondary windings are partly common.

Isolating transformer

Because of the insulation between the windings, the risks on the secondary side of an isolating transformer are limited in the event of inadvertent simultaneous contact with earth and one of the live parts. Also, unlike an autotransformer, it can also accept an earthing system or a neutral conductor system .

An IT network can be achieved by not earthing the secondary side, without a connection between earth and the secondary, but with a connection between earth and the primary supplying current network. Because of the high level of assurance regarding operating reliability and safety, this system is often used with complex production processes and in rooms for medical use or with an elevated risk of explosion. Conversely, the neutral terminal on the secondary side can be earthed. This results in a network with a clean earth, which is essential for charging stations or HVAC installations.

IN SUMMARY: An isolating transformer can convert incoming and outgoing voltages, create a neutral conductor and adapt network systems. It is also safe and reliable in operation. Because more copper is required it will be larger and more expensive than an autotransformer.

Autotransformer

An autotransformer also has a secondary winding but this is realised by means of a branch off the primary winding. The voltage in the secondary winding is dependent on the position of the branch that runs off the primary winding.

IN SUMMARY: An autotransformer contains less copper and is therefore smaller and cheaper, with a higher efficiency than an isolating transformer. Step-down transformation is not recommended; it is less safe and the neutral conductor cannot be earthed.

Like to know more about the differences between isolating transformers and autotransformers? Download our white paper here . Still have questions? Please do not hesitate to contact us !

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