Inverter / motor question.

Discussion in 'General Electronics Chat' started by Dyslexicbloke, Feb 21, 2011.

  1. Dyslexicbloke

    Thread Starter Well-Known Member

    Sep 4, 2010
    Hi guys this is probably a bit basic but I am out of my comfort zone here.
    I have a small 3 phase motor that drives the guide vanes of a water turbine. The motor is rated 220 / 380v and the inverter output is 220v


    I was expecting the motor to be permanently star connected to the inverter and looking at the plate it suggests that I would need 380-415 from the inverter to do that.

    I ahve attached the motor rating plate and some inverter info.

    Am I just missing something or do I have an odd inverter or motor ..
    I expected both to be general purpose standard stuff.:confused:

    Feel free to tell me If I'm being daft, I should probably know this :eek:
    Thanks Al
  2. SgtWookie


    Jul 17, 2007
    At 50Hz, the motor is rated for 230v operation wired in a delta configuration, or 400v if in a wye configuration. Note the voltage increases at 60Hz operation.

    You know the difference between delta and wye configuration, right?

    You should set up your converter to output 50Hz. If your output frequency is significantly lower than that, you may wind up overheating the motor.
  3. kkazem

    Active Member

    Jul 23, 2009
    I design Inverters for a living and have a few thoughts for you:

    a) The inverter output frequency isn't all that important as long as you don't overheat the motor. This depends on the following factors working together: Output Voltage, Output Frequency, 3-Phase connection (delta or Wye), ambient temperature, and the torque loading on the motor. Unless your application demands the motor run at an input frequency of 50 Hz, you can use 60 Hz, 400 Hz, 1KHz, 20KHz, etc. It's a bit more complicated that I'm making it sound, but the output frequency isn't that important so long as it's not so low or so high that the motor overheats from the core losses. To start, 50Hz or 60 Hz would be your best bets. You can change it from there as your application needs dictate.

    b) In the datasheet, notice that the 3-phase input voltage is rated at the same lower end voltage (380V) at 50 vs 60 Hz, but at 60 Hz, the input can go up to 460 VAC, while at 50 Hz, it can only take 415 VAC.

    c) It really doesn't matter whether your input or inverter output is wired for delta or for wye. What's important is that the voltage going to the input is in the correct range and the same is true for the inverter output. If it requires delta, use that. If it requires wye, use that. Remember, Vline-to-line WYE is SQRT(3) * Vline-to-line Delta. SQRT(3) = 1.7320508 (Approximately). Conversely, Vline-to-line Delta = Vline-to-line WYE / SQRT(3). And of course, at the same time, if you change from delta to wye and the voltage goes up by 1.7320508; the line current = the Phase Current. While in a WYE circuit, the line current is the Phase Current /(1.7320508).

    c) Try to keep the output frequency in the range of 45 Hz to 400 Hz to keep the motor core from overheating. Remember, you can adjust the output voltage of the inverter to control speed. If you lower the inverter output frequency, you can keep the motor within safe temperature limits by reducing the inverter output voltage to keep the volt-seconds per period on the low-frequency end below the core saturation range and on the high inverter output frequency, reducing the inverter output voltage will keep the maximum flux density that the motor sees low enough to keep the core losses due to high frequency in a safe enough range for the motor.

    I hope all this helps.

    Kamran Kazem
  4. Dyslexicbloke

    Thread Starter Well-Known Member

    Sep 4, 2010
    Yes that helps a great deal .... Thanks guys
    I have always thought in star / delta as in starters and was a little unsure as to weather the motor would start at all if it was delta wired.
    The inverter is single phsase input and the motor will never be heavily loaded because it is running a worm drive.