Machine Parts

Temperature rise in a transformer is the temperature of the windings and insulation above the existing ambient or surrounding temperature.

Voltage regulation in transformers is the difference between the no load voltage and the full load voltage. This is usually expressed in terms of percentage.  For example: A transformer delivers 100 volts at no load and the voltage drops to 95 volts at full load, the regulation would be 5%. ACME dry type distribution transformers generally have regulation from 2% to 4%, depending on the size and the application for which they are used. 

Transformers can be used at frequencies above 60 Hz up through 400 Hz with  no limitations provided nameplate voltages are not exceeded. However, 60 Hz transformers will have less voltage regulation at 400 Hz than 60 Hz.

Primary and Secondary Terminations are provided on ACME Dry Type Transformers as follows: No lugs-lead type connection on:  •0-25 KVA single phase •0-15 KVA three phase •Bus-bar terminations (drilled to NEMA standards) •37 1/2-250 KVA single phase •25-500 KVA three phase

1. Determine primary voltage and frequency.  2. Determine secondary voltage required.  3. Determine the capacity required in volt-amperes. This is done by multiplying the load current (amperes) by the load voltage (volts) for single phase. For example: if the load is 40 amperes, such as a motor, and the secondary voltage is 240 volts, then 240 x 40 equals 9600 VA A 10 KVA (10,000 volt-amperes) transformer is required. ALWAYS SELECT THE TRANSFORMER LARGER THAN THE AC TUAL LOAD. This is done for safety purposes and allows for expansion, in case more load is added at a later date. For 3 phase KVA, multiply rated volts x load amps x 1.73 (square root of 3) then divide by 1000.  4. Determine whether taps are required. Taps are usually specified on larger transformers.  5. Use the selection charts in the Acme catalog. 

No. Phase converters or phase shifting devices such as reactors and capacitors are required to convert single phase power to three phase. 

Yes. Any single phase transformer can be used on a three phase source by connecting the primary leads to any two wires of a three phase system, regardless of whether the source is three phase 3-wire or three phase 4- wire. The transformer output will be single phase. 

Dry type Distribution transformers can be reverse connected without a loss of KVA rating, but there are certain limitations. Transformers rated 1 KVA and larger single phase, 15 KVA and larger three phase can be reverse connected without any adverse affects or loss in KVA capacity. The reason for this limitation in KVA size is, the turns ratio is the same as the voltage ratio.  Example: A transformer with a 480 volt input, 240 volt output - can have the output connected to a 240 volt source and thereby become the primary or input to the transformer, then the original 480 volt primary winding will become the output or 480 volt secondary. On transformers rated below 1 KVA single phase there is a turns ratio compensation on the low voltage winding. This means the low voltage winding has a greater voltage than the nameplate voltage indicates at no load.  For example, a small single phase transformer having a nameplate voltage of 480 volts primary and 240 volts se

Single phase transformers can be used in parallel only when their impedances and voltages are equal. If unequal voltages are used, a circulating current exists in the closed network between the two transformers which will cause excess heating and result in a shorter life of the transformer. In addition, impedance values of each transformer must be within 7.5% of each other. For example: Transformer A has an impedance of 4%, transformer B which is to be parallel to A must have an impedance between the limits of 3.7% and 4.3%. When paralleling three phase transformers the same precautions must be observed as listed above, plus the angular displacement and phasing between the two transformers must be identical. 

ACME transformers rated below 1 KVA can be used on 50 Hz service. Transformers 1 KVA and larger, rated at 60 Hz, should not be used on 50 Hz service due to the higher losses and resultant heat rise. Special designs are required for this service. However, any 50 Hz transformer will operate on a 60 Hz service.