AC vari drive motor
AC vari drive motor
(OP)
Motor has mind of its own!! I have a Toshiba 3 phase induction motor, (480 VAC, 0.75 Kw, 4 pole, 1.5 Amps) being driven by a Toshiba VFA5 480V inverter, that randomly accelerates to max speed without any noticable change in current, voltage, frequency, etc. It is driving the customer and I silly! Does anyone know why this would happen?
Thanks,
Casey
Thanks,
Casey





RE: AC vari drive motor
There must be a change in the frequency for the motor to change speed (speed = 120 x Frequency / number of poles).
If the speed reference is from an analog signal, I would suggest that you check what the signal level is at the VSD.
Also, the VSD may be going into a "current limiting mode", where the VSD will try to limit the current to the motor. This is done when the current limit threshold is reached, the drive does not accelerate (and sometimes decelerates) until the current is below the current limit setting.
RE: AC vari drive motor
Is the display changing the reported frequency and the motor is running at some constant speed or it the motor shaft rotation changing and the drives LED display remaining constant.
Voltage, frequency and current are all tied pretty close so if one is really changing at least one of the others should as well
RE: AC vari drive motor
This inverter and motor are used in a machine that polishes the surface of silicon wafers before any circuits are laid down. Wafers are arranged under 'heads' in a cloverleaf pattern with this particular motor driving a center hub that rotates the 'heads'. Each 'head' has an applied downforce of between 45kg to 150kg.
The machine has been installed and operating normally for more than one year before this problem arose. I have monitored the voltage at the outputs from the inverter, the voltage is steady at 480 VAC. I monitored the freq using a Fluke DMM, and never saw the frequency change. I monitored the current from the LED display on the inverter, and this also held steady.
By "randomaly accelerates to max speed etc." I mean that the motor takes off at full speed (98rpm) about once or twice during a 12 hr shift. I have measured the rpm using a digital photo tachometer. I have seen the motor 'take off' while monitoring voltage, current, frequency, and they all read normal, as if the motor is running normally. After shutting down the machine and re-starting everything is good for the next several hours. I know that a motor will usually slow down or stop if anything in the loop goes bad, but what would make a motor ramp up to full speed??
RE: AC vari drive motor
RE: AC vari drive motor
you said this drive is fine for almost one year..
do you have any record of the parameters?
toshiba drives are quite reliable so why don't you
try to go over the parameters again..and
analyze them one by one...or compare them with
another identical machines..
dydt
RE: AC vari drive motor
RE: AC vari drive motor
RE: AC vari drive motor
Is the PID control set to the on position? This is what I suspect is causing your problem. With this drive if the feedback signal is lost it interpets the loss of signal as an infinte error and responds by immediately ramping to the programmed frequency limit and staying there. This most often occurs when the sensor providing feedback is powered from the drive's terminal block and has its own ground. (The common positions on the terminal block are floating and should never be connected to earth)
Other thoughts
Which state is the true torque control in. This is the "Open Loop vector control".
Have any long lead filters been added to the system or have any other sources of impedence been added to the output side.
Typically the A5/G3 performs best when the open loop vector is in the on position.
If you are unable solve the problem I would suggest contacing the Toshiba US Tech support. The A5 is an LED keypad version of the G3 sold in the US and operate more or less the same
RE: AC vari drive motor
RE: AC vari drive motor
RE: AC vari drive motor
RE: AC vari drive motor
CMiller, once the problem is solved be sure and post the solution. The suspense is killing me
tmahan