Buck-Boost Transformers

A Buck-Boost Transformer is used to provide an economical method of correcting a lower or higher voltage to a voltage rating more suitable for efficient operation of electrical equipment.

Buck-Boost Transformers are small KVA, single phase, 600 volt class insulating transformers with dual primary and dual secondary windings and are usually connected as autotransformers by utilizing one unit for single phase applications and either two or three units banked for three phase operation. They are primarily used for motor operation and should not be used for motor control circuits, to correct fluctuating line voltage or to obtain a neutral on a delta system. These applications require transformers especially designed for these specific applications.

Note: When installation is to be made on a grounded system, consideration must be given to the resulting voltage. Thus, on a 208 grounded wye/120 system the voltage can be boosted to 240 volts but the voltage to ground will be 139 volts. If 240/120 volts with a mid-point ground is needed, a standard two-winding transformer must be used.

The following formulas can be used to calculate specific requirements.

For Single Phase:

LOAD KVA =
Load Voltage x Full Load Amps
1000

For Three Phase:

LOAD KVA =
Line Load Voltage x 1.73 x
Full Load Amps
1000

The following information is necessary for selecting a buck-boost transformer.

Line Voltage – The voltage that you want to buck (decrease) or boost (increase). This can be found by measuring the supply line voltage with a voltmeter.Load Voltage -The voltage at which your equipment is designed to operate. This is listed on the nameplate of the load equipment.

Load Amps or Load KVA – You do not need to know both-one or the other is sufficient for selection purposes. This information usually can be found on the nameplate of the equipment that you want to operate.

Frequency – The supply line frequency must be the same as the frequency of the equipment to be operated-Micron Buck-Boost Transformers operate at 60 Hz only.

Phase – The supply line should be the same as the equipment to be operated-either single or three phase.

Transformer Interconnection

For three phase applications, interconnections of transformers should be made in a junction box. Two or three transformers may be used depending on an open delta (2) or wye (3) connection.

Note: For 1 phase connections and 3 phase open delta connections, inputs and outputs may be reversed. KVA capacity remains constant.

To order, call 1-800-664-4660.

View Buck-Boost FAQs.