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I've got an old Soviet 4kW motor, made in 1983. The dilemma is that the nameplate info states a Y-connection/380v/8.7amps and I want to run it on delta using my VFD which produces 3ph 220v. All my other motors are rated for both 220v delta & 380v star and I've never had a situation like this, so I was wondering what are the dangers of running a motor on delta if that's not specified?

Thank you in advance.

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  • \$\begingroup\$ probably the soviets had no need to use the motor in that configuration, so they didn't put it on the boilerplate. \$\endgroup\$ – Jasen Apr 29 '18 at 9:04
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    \$\begingroup\$ Are you sure about your inverter? I guess it's 220V L-N and 380V L-L, not vice versa. The motor seems to be a 660V/380V type from your description. \$\endgroup\$ – Janka Apr 29 '18 at 9:11
  • \$\begingroup\$ The VFD produces 3ph 220 line-to-line voltage out of a 1ph 220v L-N from the mains. The only voltage that's specified on the plate is 380v Y-connected. \$\endgroup\$ – Ivan P. Apr 29 '18 at 9:35
  • \$\begingroup\$ @IvanP.: That sounds right. The input is rectified to give a DC bus of \$ \sqrt 2 V_{IN} \$. This determines the max line-line output of \$ \frac {1}{\sqrt 2} V_{BUS} \$. With single phase in you can get the same voltage but phase-phase on the output. \$\endgroup\$ – Transistor Apr 29 '18 at 9:35
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    \$\begingroup\$ Then, your inverter is a 220V/130V type. I don't see how this matches either 380V/220V nor 660V/380V motors. \$\endgroup\$ – Janka Apr 29 '18 at 9:45
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If the motor has six leads brought to the terminal box and you can reconnect the motor to delta, it should run properly with 220 volts. If the proper leads are not available for reconnection the motor to delta, you can not run the motor at full speed with the VFD. You could connect the motor to the VFD with the motor wye connected, but you would need to configure the VFD to output 58% of rated frequency at rated voltage. Operated that way, the motor will produce rated torque for rated current, but can not operate at rated speed except at reduced torque.

At reduced speed, the motor will not move enough air over or through itself for proper cooling. That may prevent continuous operation at full torque particularly at low speeds. In addition, the insulation in an old motor may be less tolerant of operating at a higher temperature and less tolerant of the voltage transients caused by the VFDs PWM waveform. The voltage transient problem can be mitigated somewhat by locating the VFD near the motor so that the motor cable is short. There are also transient limiting motor lead inductors or filters for that.

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    \$\begingroup\$ Yes, there are six leads at the terminal box. I tested it and it works fine on delta. Seems like @Jasen was right that they had no need to use it on 220v and did not put that on the plate. Thank you all for the quick responses! \$\endgroup\$ – Ivan P. Apr 30 '18 at 20:51

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