Published: 11/29/2005
| Question: | Can a contactor be installed between a drive and motor to start and stop the motor? |
| Answer: | Leaving the drive running while opening or closing an output contactor is not recommended.
If an output contactor is opened while the drive is running, inductive collapse of the motor field may cause undesirable currents thru the drive output transistors. In addition, the motor current sensing circuit will detect an unusual output condition, As a result, one of the following two conditions may occur:
1.) A drive fault such as short circuit or ground fault
2.) Potential damage to the output transistors.
If an output contactor is closed while the drive is running, the motor will attempt to pull locked rotor current. (see Figure 1, typical NEMA B Torque/Speed plot)
AC drives are typically not designed to supply motor locked rotor current. The drives fault circuitry will typically trip on an overcurrent condition.Therefore using an output contactor on an AC drive to start and stop the motor is not recommended.
Steps to prevent AC drive damage while controlling motor start/stop by output contactor:
CAUTION: ALWAYS ENSURE THE OUTPUT MOTOR CONTACTOR IS CLOSED BEFORE STARTING THE DRIVE
- Connect an normally open auxilary contact from the motor contactor to the drive run/stop digital input.
- Enable the drive coast -to-stop function .
(This will use the drives own internal logic to immediatly turn off the output transistors when stopped, this leaves the motor coasting)
- Enable the drives Speed Search function, Rotating Start function or Catch a spinning motor function.
(This will allow the drive to restart smoothly into a coasting motor if the contactor was just previously opened)
- Enable the drives Dynamic Braking at Start Function.
(This will allow the drive to stop the motor before the run command is sent, preventing damage caused by starting an already rotating motor. See Figure 3 example from GPD506/P5 technical manual.)
SEQUENCE OF OPERATION:
- When the motor contactor is closed the auxilary contact will start the AC drive immediatly.
- When the motor contactor is opened, the aux contact will cause the drives output to shut off instantly. (motor coasts)
- If the motor is restarted right away, the drives Speed Search function will catch the motor at the present coasting speed.
If this cannot be avoided, then the setup of Example 2 is preferred, using an auxillary contact to trip the drives external fault circuit.
Figure 1: Typical NEMA B motor Torque/Speed plot.
NOTE: This example is provided for the GPD506/P5 , RUN switch connection points will vary with other Yaskawa drives.
Figure 3
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Product Information:
| Product Group: | Inverters/Drives |
| Product: | P5 GPD506 Drive, P5 Drive 600 Volt |
| Applications: | |
| Category: | Starting/Stopping |
Other Information:
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Please read and understand the product instruction manual before installing, servicing or operating Yaskawa products. FAQ content and illustrations are provided as technical advice to augment the information in manual, not superceed it. It is not possible to give detailed instructions for all types of installation or support activities. The information described in the FAQs are subject to change without notice to improve the product or FAQ. Yaskawa assumes no responsibility for errors or omissions or damages resulting from the use of the information contained in any FAQ.
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