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When a motor starter is to be replaced by a 3-phase 415V~ VFD, can the existing motor be used without changing its winding configuration (star/delta)?

The motors are from different manufacturer

  • earlier was 37 kw, 415 v , star connection and

  • now 37 kw , 415 v , Delta connected.

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  • \$\begingroup\$ Is the new motor the same manufacturer and model as the old motor? New motor and old motor are identical? \$\endgroup\$
    – mkeith
    Aug 7, 2020 at 5:46
  • \$\begingroup\$ motors are from different manufacturer earlier was 37 kw, 415 v , star connection and now 37 kw , 415 v , Delta connected. \$\endgroup\$
    – Ambuj Nema
    Aug 7, 2020 at 7:15
  • \$\begingroup\$ You need a better description of the winding arrangements. It is almost certain that the new motor is NOT a 415V delta connected motor BUT is really a 230V delta or 415V star connected motor. ie the correct voltage depends on the configuration. This information IS ALWAYS available from the manufacturer for any motor worth buying. || Some VFDs will allow 415V or eg 220V operation but many don't. If it is a 415V only VFD then you MUST use a 415V motor for full utilisation of the VFD. It is LIKELY that the new motor when connected in STAR configuration will work. BUT you must ask the manufacturer \$\endgroup\$
    – Russell McMahon
    Aug 7, 2020 at 12:13
  • \$\begingroup\$ if motor connection is changed from detla to star its kw rating may derated so instead of 37 kw it will deliver only 13 kw .isn't it? \$\endgroup\$
    – Ambuj Nema
    Aug 8, 2020 at 4:57
  • \$\begingroup\$ What is the input voltage to the VFD? 415V line-to-line or 415V line-to-neutral? \$\endgroup\$
    – mkeith
    Aug 12, 2020 at 5:05

1 Answer 1

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When a motor starter is to be replaced by a 3-phase 415V~ VFD, can the existing motor be used without changing its winding configuration (star/delta)?

Yes. VFDs have the same nominal output voltage as input voltage. If you have a 415V supply, you buy a 415V input - 415V output VFD. You connect the VFD for 414V operation. It makes no difference whether the motor was originally connected star or delta, it must be connected for 415V operation. When you disconnect and reconnect the motor, you must get that correct. Just as if you were to change from a star-delta starter to a direct-on-line starter.

The only exception is the connection of the motor for operation above the original frequency, for example 87 Hz rather than 50 Hz. However that is a different and more complex question.

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