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Buck - Boost Transformers

Terms & Definitions:
Buck-Boost transformers are single phase, four winding transformers designed for two purposes. The first purpose is as a low voltage isolation transformer for use on 12, 16, 24, 32, or 48 colt circuits. When used as low voltage transformers, Buck-Boost transformers have capacities of .050 kVA to 5.0 kVA. Their second, and more important use, is as a "Buck-Boost" transformer. Buck-Boost means that these transformers are used to buk (lower) ro boost (increase) line voltage to match required load voltage.

Buck-Boost transformers are used to correct consistently low or high voltage conditions, where the voltage difference ranges from approximately 5% to 27%. Variation of the input voltage is passed through to the output side of the transformer in the same percentage. This concept is important because the question is frequently asked if Buck-Boost transformers will stabilize variable voltages. They will not!

Buck-Boost transformers are simple and straigt forward to specify, size and connect. Buck-Boost connections are achieved by interconnecting the 8 copper lead wires supplied with each transformer in accordance with the cahrtts contained in this section. In addition eah transformer shipped from the factory is equipped with a simialar chard to assure ease of use at the installations site.

The most common applications for these transformers are boosting 208 volt lines to 230 or 240 volts, and vice-versa. These applications include both single and three phase lines and are particularly common in HVAC applications for airconditioning appliances.

Additionally, Buck-Boost transformers are very well suited to motor loads, boosting 240 to 277 for lighting loads and many applications where nominal voltage is above or below 120 volts. Their use should be considered where supply line voltage is found to be consistently avobe or below desired nominal values of load voltage.

Single Phase Applications:
Single phase applications require the purchase of one transformer. Download charts onpages 53-55 for specifying and sizing single phase applications.

Three Phase Applications:
Three phase applications require banking either 2 or 3 Buck-Boost transfromers. Download charts on pages 56-58 for specifying and sizing three phase applications.

Preconnected Three Phase Applications:
Series ODY Autotransformers provide an ecinomical, factory preconnected installation for transfroming three phase lines from 208 to 240, or 240 to 208. This series banks 2 Buck-Boost transformers into one assembly for mounting and one assembly for connecting. Simply bring in three wires on the line side and take out three wires on the load side. Download page 52 for additional information.

Dongan Buck-Boost Transformer Sizing Table 1
Dongan Buck-Boost Transformer Sizing Table 2

Spec-Tech Industrial Electric is a stocking distributor of electrical automation products and parts. We carry Dongan products to satisfy a full range of industrial factory and process applications.

Updated on April, 18th 2018

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