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Parallel Motor Connection

Created by: nickasaurous at: 9/21/2012 3:50 AM (2 Replies)

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9/21/2012 3:50 AM	Rate (0)
nickasaurous Posts: 4 Rating: (1)	Hi all, I have a coulple of general questions regarding the parallel connection of motors. First of all, I've had a look through a few manuals and couldn't find too much on the subject - but perhaps I didn't look hard enough. If anyone knows of any material I should read please let me know! :) Basically I was looking at some drawings (pic attached) of an existing installation (long travel on a coal stacker) and found a few things I thought interesting. The drive was supplying seven motors in parallel; each motor had its own circuit breaker and overload, each placed between the drive and the motor. I was wondering if this is good practice? And if not, what is good practice? Obviously if a motor has a fault, you want the motor protection to trip and isolate that motor. But putting a circuit breaker after the drive could cause damage to the IGBT's yes? I'm assuming it was done the way it was done to minimise downtime, such that the faulty motor will trip and won't bring down the other motors. And with that motor out of the circuit, the rest of the motors could still push the stacker i.e. to have built in redundancy. Also, how would you perform a motor ID on a parallel connection? Would you do it just as a normal ID, and ID all motors in parallel? I was thinking, that if this was the case and one or two motors tripped, the ID parameters would have to be redone? My personal thinking (which might be terrible) is that it would be better to have indiviaual protection relays on each motor, all connected to an external trip on the drive. With decoupling plugs on each motor to allow isolation of each motor in the event of a fault. Assuming the motor ID is done with all motors in parallel, you could probably setup different motor data sets and switch to a different one in case of a fault. Any experience with this type of setup would be great. Thanks! Nick Attachment parallel.jpg (675 Downloads)
nickasaurous Posts: 4 Rating: (1)
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9/21/2012 7:10 AM	Rate (0)
Marcjan Platinum Member Joined: 4/22/2010 Last visit: 11/18/2024 Posts: 5697 Rating: (715)	Hello, I think this might answer some of the questions: Will a MICROMASTER 4 drive more than one motor? Regards, Marcjan
	Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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9/23/2012 12:26 AM	Rate (0)
Graeme Platinum Member Joined: 6/4/2008 Last visit: 12/10/2024 Posts: 1511 Rating: (327)	nickasaurous Hi all, I have a coulple of general questions regarding the parallel connection of motors. First of all, I've had a look through a few manuals and couldn't find too much on the subject - but perhaps I didn't look hard enough. If anyone knows of any material I should read please let me know! :) Basically I was looking at some drawings (pic attached) of an existing installation (long travel on a coal stacker) and found a few things I thought interesting. The drive was supplying seven motors in parallel; each motor had its own circuit breaker and overload, each placed between the drive and the motor. I was wondering if this is good practice? And if not, what is good practice? Obviously if a motor has a fault, you want the motor protection to trip and isolate that motor. But putting a circuit breaker after the drive could cause damage to the IGBT's yes? Absolutely correct, yes this is a risk. Normally, it is expected that local motor "Isolators" are opened OFF-LOAD. However, in the event of using Motor Overloads/contactors, it is not always possible to do so, some applications I have seen use a leading (early break) contact on the overload/contactor which feeds a fault input on the drive and disables the pulses immediately. I have also seen safety systems that utilise a double output contactor system in line with the motor. Once a drive output was COMPLETELY destroyed by a loose contactor coil supply cable, so your concerns are valid. nickasaurous I'm assuming it was done the way it was done to minimise downtime, such that the faulty motor will trip and won't bring down the other motors. And with that motor out of the circuit, the rest of the motors could still push the stacker i.e. to have built in redundancy. Also, how would you perform a motor ID on a parallel connection? Would you do it just as a normal ID, and ID all motors in parallel? I was thinking, that if this was the case and one or two motors tripped, the ID parameters would have to be redone? My personal thinking (which might be terrible) is that it would be better to have indiviaual protection relays on each motor, all connected to an external trip on the drive. With decoupling plugs on each motor to allow isolation of each motor in the event of a fault. Assuming the motor ID is done with all motors in parallel, you could probably setup different motor data sets and switch to a different one in case of a fault. Nick Yes, individual protection is a must, however, any reconfiguration (motor out for a PM, or replacements) should really be done stationary. There are not many systems where it is not possible for a system to be stopped to protect a life/motor/cable, and then the operators/engineers can quickly switch it out/switch in the redundancy and restart whilst the problematic items can then be looked at. However, some drives will withstand having their outputs switched on-load (There are no guarantees). If the system was running in V/F for example, the drive just carries on as normal, surprisingly, the current probably would not change by much as the fewer motors would probably require a little more current to drive the load. I have used multiple motor data sets and created various configurations before (Mostly for redundancy), whilst your current configuration (MDS) is active, you run the Motor ID and store the results in that MDS. So when the configuration changes, you then have the optimised data for the connected motors. I hope I was not waffling too much. Regards, Graeme

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