Emerson TRE Ex e Transformers Buyer's Guide

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Transformers
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3. If the load is expressed in wattage, either utilize the
formula below to convert to kVA or refer to the
equipment nameplate to obtain amperage
requirement.
4. If the load is a motor and expressed in horsepower,
refer to the motor horsepower charts on the
next page.
Some sizes may require an optional weather shield
(order separately) for outdoor use.
Always size the transformer
to the load requirements.
kVA (1Ø) =
Volts x Amps
1000
kVA (3Ø) =
Volts x Amps x 1.732
1000
Selection Steps
A. Use the following steps below to manually select
a transformer.
B. Findtheelectricalloadrequirements.Theseare:
1. Load operating voltage.
2. Load frequency (expressed in Hz).
3. Determine load size - usually expressed in kVA,
amperage or horsepower.
4. Is the load designed to operate on single phase
or three phase power?
This information is available from the equipment
manufacturer and is typically listed on the nameplate
of the equipment.
C. Know the supply voltage conditions:
1. Available source voltage.
2. Available source frequency (a transformer will not
change frequency. The frequency of the supply
voltage and the needed load voltage must be equal).
3. Number of phases on power source.
D. Determine the transformer kVA rating:
1. If the load is expressed in kVA, select the appropriate
transformer from the following selection charts (make
sure the selected transformer’s kVA rating is equal to
or greater than the required load kVA).
2. If the load is expressed in amperage, use either
the appropriate kVA formula listed below or the
appropriate sizing chart on the next page.
kVA =
Wattage
(1000 x Power Factor of the load)