?Application of Autotransformers

[AJ2002]

Has anyone had any experience with applying an autotransformer for a step-down application 460 V 60hz to 220 V three phase 1000 kVA?

The kVA required will be decreased by 48%. I now typically you would like to see a closer voltage ratio for an autotran. application.

Does anyone have a good source of information for this type of application?

Thank You.

 

[busbar]

Try American Electrician's Handbook. Nota Bene—the voltage relationships on the 460V system may cause problems for the 220V equipment. Proceed carefully.

 

[busbar]

Pardon, but the question sounds perfectly academic, as though for second-year power-option EE homework. It’s best for later if you can do your own brain stretching, as apposed to not reasoning the problem out for yourself, or trick a teaching assistant in to fill up a chalkboard with sketches and calculations along with insisting you sit through detailed recording of lab-notebook observations with a 3ø powerstat and doorbell transformers.

An aside—a practical approach may be to apply a pair of commercially available 240:240 units in open delta, but they must have a full 480V rating based on Art. 450-4 limitations. Don’t forget to allow for root3/2 derating of an O-D arrangement, which partly negates the desirability of an autotransformer arrangement. The low-side voltage will be closer to 230V, unless the units have componentiationalized FCAN taps.

Take time to understand the potentially assorted characteristics of the 460V source and how they could very well cause trouble powering the “220V” stuff. (Consider what the “usual” 220V load might expect.)

1 megavoltampere at “220 volts” is a fairly staggering load from a classical “copper-economy” standpoint.