adccommunitymod (AutomationDirect) asked a question.
Created Date: November 28,2007
Created By: bmaderazo
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I have two 3phase AC motors that need to run synchronously. There's two options I have thought of and I was wondering if anyone had a better idea. 1. Buy a 2HP drive and drive both 1HP motors from that single drive. If one is ahead of the other, drop out a phase for a short period of time (ms), allowing the other to catch up. 2. Use 2 drives, one master and one slave. Send the same speed signal to both drives and use a PID loop on the slave drive to "chase " the master. I 've tried the first option and it seems to work, though I'm worried about damaging the motor. The second option seems to be the best. Is there any other option besides the expensive servo system? Thanks for any suggestions.
Created Date: November 28,2007
Created by: milldrone
bmaderazo,
I have two 3phase AC motors that need to run synchronously
This needs better definition as to the degree of sync. How much error is tolerable? Do the motor shafts need to be "in time " with each other (like an "electronic gearbox ")? Or is a 1/2 revolution in 100 revolutions good enough? Is there any room for "sag " or "tension " between the motors like a "dancing idler "?
Vaughn
Created Date: November 28,2007
Created by: bmaderazo
1 rev / 200 revs sounds reasonable.
My main concern is that the two motors will have different loads. Though the single drive will keep the two motors synced within a reasonable tolerance with equal loads, will this remain true for different loads on each motor?
Created Date: November 28,2007
Created by: bmaderazo
Also if they do become grossly out of sync, would it be alright to drop a motor phase possibly or the entire motor to allow the other motor to catch up?
Created Date: November 28,2007
Created by: Tech Guy
To me dropping a phase would seem to put a lot of strain on the IGBT's of the drive shortening the life of both the motor and the drive. Also using this method, the drive is unable to provide adequate protection for the motors.
I'd go with two drives and sync them in a master/slave setup. The advantage here is the drives are able to provide protection for the motors as well as keeping the motors synced.
To answer your last question, dropping a motor on or off line on a vfd while running isn't a good idea. It might not cause the IGBT's to fail the first time or the second, but it is guaranteed to kill them eventually.
Created Date: November 28,2007
Created by: milldrone
bmaderazo,
Though the single drive will keep the two motors synced within a reasonable tolerance with equal loads, will this remain true for different loads on each motor
Presuming you are using two identical 1750 rpm motors. The motors could be within 45 to 48 revolutions after only 1800 revolutions and still be not overloaded if they are connected to the same supply.
I'm curious how do you know you are out of sync now? You indicate you are having some success now by "dropping a phase ". By the way I'm with Tech guy on this potentially bad practice.
To get any where near the 1 revolution in 200 you indicated was OK. My gut feel you will need a encoder feed back system and two drives.
Another presumption: If using 1750 rpm motors any speed below 200 rpm is not do able.
Vaughn
Created Date: November 29,2007
Created by: Tech Guy
Another presumption: If using 1750 rpm motors any speed below 200 rpm is not do able.
I would think if you have a motor with a high enough turn down ratio such as a Marathon Blue Max (2000:1 turn down ratio) it could work.
Created Date: November 29,2007
Created by: bmaderazo
Sorry for the confusion. I haven't attempted dropping a phase. I 've attempted using two motors on one VFD.
In my project, there will be two separate pedastols. Each motor will drive one pedastol. A distance sensor will measure how much the pedastols are "out of sync " for the lack of better terms. I would use this to feed into the PID or to determine when to drop out a phase. Though since dropping a phase/motor will damage the drive, I will be going with the PID. Thanks for the help.
Created Date: December 08,2007
Created by: milldrone
Tech Guy,
I'm curious because I have an upcoming project that begs for a high turn down ratio. The blue max motors seem to be from 40 hp up.
The black max motors are in a hp range that will work for my project. The black max motors are advertised as being Constant torque operation from 0 to base speed on vector drive
The durapluse drives are advertised as being Sensorless vector control with optional encoder feed back card for better speed control
Does this mean that we cannot get full vector control from a durapulse?
What I need to do is give the drive a run command and zero speed also. So that the motor will resist shaft movement for about 10 seconds.
Vaughn
Created Date: January 07,2008
Created by: APplas
What type of speed signal do you use? You may try a Introloc Syncronizer or Yaskawa MP940 Module. Also if using SureServo, it can follow a encoder counts from the Master drive.
Created Date: February 17,2012
Created by: PopaB
ernb@supanet.com
You do not say purpose or size of drives. Two slip-ring motors can be synchronised by connecting the slip rings via individual buffer resistors that must always be left in circuit. Else synchronising torque can damage shafts and gearboxes.
I have used this system on long span crane drives, doing away with cross-shafting.
It is an extension of the old selsyn system.
HTH