Selecting the supply transformer
￭ Basic guidelines
1. Define the apparent power of the transformer:
• if the drive is equipped with a diode supply unit, or a regenerative supply unit, use
this equation:
S
N
(kVA) = 1.32 × sum of the motor shaft powers (kW)
• if the drive is equipped with an IGBT supply unit, use this equation:
S
N
(kVA) = 1.16 × sum of the motor shaft powers (kW)
2. Define the nominal voltage for the transformer secondary winding according to the
nominal input voltage of the drive. See the supply unit hardware manual.
3. Make sure that the transformer complies with the electrical power network specification
of the drive. See the appropriate drive or supply unit hardware manual for:
• nominal input voltage, allowed voltage variation and imbalance
• nominal frequency and allowed variation
• short-circuit withstand strength (IEC), or short-circuit current protection (UL or CSA)
• etc.
4. Consider the additional notes below.
5. Contact the transformer manufacturer for more information on the transformer selection.
Electrical planning guidelines 15
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