OT: V/F controled motor problem

[allscott]

Injection braking.

http://resource.controleng.com/article/CA6318574.html

The OP stated he is using a Eurotherm (now SSD) 650 drive. This drive like most these days has a provision for injection braking. This drive is limited to 600 seconds IB, not a full time solution.

The problem is that injection braking causes alot of heat. You can turn down the braking current to not heat up the motor, however as you do that its effectiveness as a brake diminishes as well.

The Marathon motors mentioned are excellent. The black max and blue max can both be run all day at 0 speed producing full torque and not overheat. If you wanted the motor to be an electric brake you would hook it up in flux vector control and tell it to run at 0 HZ as opposed to telling it to stop.

 

[milldrone]

If you wanted the motor to be an electric brake you would hook it up in flux vector control and tell it to run at 0 HZ as opposed to telling it to stop.

Allscott, in that instance would you A. use a preset speed of zero or B. use an analog zero? or C. profibus or modbus comms.

It seems you might be setting yourself up for creep between a digital to analog and then from analog to digital conversion. As kamenges mentioned.

So has DC injection changed in the last couple of years? Because I'm remembering a motor that used DC injection and while it was being injected I could turn the shaft by hand, albiet slowly. This same motor could slow very quickly using the injection. The motor was just placed on a workbench, and tested right there. The injection was turned on at about 500 rpm and the motor flew off the table. Like I said I could turn it by hand but the faster I tried to turn it while the DC injection was on the more resistance I could feel in the shaft. It was almost effortless to turn it at about a 1/4 revolution a minute.

 

[bguinn]

I have used the DC injection on a AB PowerFlex 700 on a 5 hp Marathon BlueMax motor at 75% FLC for 2 or more days at a time, with no ill effects.

I looked at the manual for an SSD 650 drive it looks like setting p9 to DC injection will do what you are looking for.

If power is killed the DC injection will not be on, and I doubt that it will be available till the drive is put thru a run stop cycle again.

 

[allscott]

Allscott, in that instance would you A. use a preset speed of zero or B. use an analog zero? or C. profibus or modbus comms.

It seems you might be setting yourself up for creep between a digital to analog and then from analog to digital conversion. As kamenges mentioned.

So has DC injection changed in the last couple of years?

Of course it depends on the application. As you know with an analog signal 0 does not equal 0.000000. So if you rely on an analog 0 signal the motor will creep.

I prefer a bus for many reasons but have done this with analog. The SSD drives I have been working with lately use block programming and have a nice minimal speed block you can use to clamp the reference to 0. You can use a PLC to turn on a DI in the drive as well.

As far as using DC injection braking to hold a motor shaft, I'll have to say that I have never tried to do this because I don't think it will really work that well and it will be terribly inneficient for whatever you can get out of it.

Under normal operation you have two rotating magnetic fields (rotor and stator) the rotor field is chasing the stator (that's the way I think about it anyways). Injection braking works because you are introducing a constant field on the stator that is at odds with the rotating field of the rotor. The effectiveness of the actual braking action diminishes as the the rotor speed slows. Once at a stop you have 2 out of 3 stator windings energized and a round piece of copper sitting on bearings (rotor).

There will definately be a force on the motor shaft. However, it will not be controlled and the holding force is questionable at best.

Yes with a TENV motor designed to run at 0 speed you can pump 100% current through it and not burn it up, however you will never get alot of torque out of it with injection breaking (you will generate lots of heat though).

Way back to the start of this thread. The OP seemed to think that with a motor and a drive, when the drive stopped it should lock the shaft, which is wrong. When a drive stops it simply stops trying to turn the motor (shuts the power off). A motor by itself turns quite easily.

Brake motors are designed to lock the shaft of a motor when it doesn't have power. If you don't want the motor to move when it isn't supposed to then turn the brake on!!

DICKDV WHERE ARE YOU! I'm a tech, not drives application Engineer. I need an expert back up. Maybe I will learn something.

 

[Krcedinac]

Is there a significant number of total operating hour differences between the two "identical" machines? The reason I'm asking this is because I once had two identical machines that used worm gear drives. The machine that was new had very good "self braking" action in the gearbox. The machine that had lots of run time had almost no "self braking" action from the gearbox.

The both motor+gearbox are on the same unit but on different postions. They have the same load but the first one has more start-stops. We also have two more older units with the same motors and gearboxes but the inverter is SSD 605 and we do not have this kind of problems with them. This new one has this problem from the beggining

IF it were mine I would set the brake even during STOP command to VFD.
ASSUMING the motor is not restarted for several minutes even though this is frequent restarting of motor it should cool enough given several minutes before restart.

I do not think I would rely on motor gearbox (using STOP command) to hold the load - UNLESS you have independent cooling to motor.

The motor has independent cooling... fan works all the time. The brake power supply is connceted to the fan power supply

The motor has 20-22 start - slowdown(first cam)- stop(second cam) cycles in one minute.I do not know if this is a good idea in this case.
Also the load that is moved by the motor is not constant.It depends on the number of the toilet paper logs that are in the accumulator.

Way back to the start of this thread. The OP seemed to think that with a motor and a drive, when the drive stopped it should lock the shaft, which is wrong. When a drive stops it simply stops trying to turn the motor (shuts the power off). A motor by itself turns quite easily.

Brake motors are designed to lock the shaft of a motor when it doesn't have power. If you don't want the motor to move when it isn't supposed to then turn the brake on!!

So I must suppose that in something is wrong with the gear box from the begining and that it`s friction force is not enough to keep the load stedy and let say that break is not an option.
Is the motor going to hold its stop position in the Sensorless Vec mode (not Closed Loop because it is not an option with SSD 650V)?
I will also talk with the desingers of the system about DC injection option...

Thank you all for answering.

 

[rsdoran]

Way back to the start of this thread. The OP seemed to think that with a motor and a drive, when the drive stopped it should lock the shaft, which is wrong. When a drive stops it simply stops trying to turn the motor (shuts the power off). A motor by itself turns quite easily.

The OP thought correct, some drives can do that. Its known as zero speed full torque, a stop command does not necessarily shut the power off. In this case you should not be able to turn the motor shaft by hand.

 

[allscott]

Ok if your going to set up the drive in sensorless vector then injection braking is out (it just doesn't work in SV), also with the duty cycle you are talking about the motors wouldn't take the heat.

This drive has a stop delay feature you can use to hold the shaft between cycles. It will only hold the shaft for 30 seconds though. Or you can tell the drive to go 0 HZ instead of telling it to stop. How well this will work in SV is hard to say, you'd have to try it, again with SV your mileage will vary.

If this doesn't work for you there are 2 other options.

1. Use the brake on the back of the motor which you seem hesitant to want to do. Is there a reason for that? It is really quite common?

2. Upgrade your drive to a 690+ and control in closed loop Flux vector. This route requires an encoder.

 

[milldrone]

tell the drive to go 0 HZ instead of telling it to stop. How well this will work in SV is hard to say, you'd have to try it, again with SV your mileage will vary.

If this were my problem, this is what I would try before spending any money.

 

[rsdoran]

Hello everybody,

I know it may not be a question for this forum but I have to post it. Inverter is SSD (Eurotherm) 650V, controls 1.10kW 5.04A motor which is connected to the gearbox. When it gets stop command from PLC (rising edge of the cam), stops in the right position but if the machine is stopped for some period of time it can not hold it`s possition. Eventualy after some time (15-20m) it moves for 25-30 degrees and cam together with it causing the alarm. I must say that there is some load that the motor has to hold in that position. There is one more motor with the same inverter working in the practicaly same conditions but it holds its position while stoped.
I am 99% sure that it is not mechanical (gear box) problem.
Is there some suggestions what to do or what to check?

Regards

In the original post he stated he had a similar machine using the same inverter but it holds the load.

I would see what differences there are, if any, between the machines.

He is telling you what he has and y'all are telling him what he should have. I am taking it that he did not build the machine and that it has probably worked for some time; SO it may be time to see what has changed,,,,NOT what can be changed.

 

[allscott]

In the original post he stated he had a similar machine using the same inverter but it holds the load.

I would see what differences there are, if any, between the machines.

He is telling you what he has and y'all are telling him what he should have. I am taking it that he did not build the machine and that it has probably worked for some time; SO it may be time to see what has changed,,,,NOT what can be changed.

A few posts back we started to come to the conclusion that the motors on this installation as well as his others weren't actually holding the load, just friction in the mechanicals keeping things from moving.

At least that is what I got out of the discussion.

 

[milldrone]

Ron, This is what Allscott is refering to, post #20

The both motor+gearbox are on the same unit but on different postions. They have the same load but the first one has more start-stops. We also have two more older units with the same motors and gearboxes but the inverter is SSD 605 and we do not have this kind of problems with them. This new one has this problem from the beggining

 

[rsdoran]

I missed that post, so went back and read it all again.

I am lost and confused, so this one is all y'alls.

Hopefully the problem(s) and solution(s) will be found and provided here.

 

[Krcedinac]

He is telling you what he has and y'all are telling him what he should have. I am taking it that he did not build the machine and that it has probably worked for some time; SO it may be time to see what has changed,,,,NOT what can be changed.

This is exactly the case. When I was first called to solve the problem they had 20 alarms during one shift - stopping the whole line. After adjusting the cams and motor ramps they had no more alarms during the production. After that I was not called again but I saw in the alarms log "load not in phase" again and was very confused. Than I saw that the alarm occures when the whole line is stoped i.e. when the motor has to be stoped and to hold cam position... So, this is not a problem any more but I am very interested in resolving this situation because of myself. Since it is not stoping the production any more I am not in position to stop 24/7 line to do some tests or modify (motor brake for example).I will have to wait for opportunity to do that. In the mean time I am trying to do all that can be done while machine is working.

This is what the supplyer of the machine stated in his las email (lines in red):
I discussed our problem with some people on the forums and with SSD representative here in Serbia.


It is pointles to change the control mode because we do not have the problem when the motor is running, we have problem when 650V has stop command (0V on DIN1). In V/F and also in Sensorless Vec control mode the motor is free to rotate when stoped, NO. In sensorless vector mode the motor is not free to rotate ! Magnetising current (approx 60% of the max) is supplied by the DC BUS Output Station even without speed reference when drive is enabled ! This current maintains the motor in its position. It is clearly not a brushless motor which has max torque @ zero speed, but it is quite a good torque value (a good percentage – dependant on motor). We make use of sensorless vector mode on newer machine.

So, when and if I get a chance I will do the autotune procedure and swich the control mode to SV to see it it is going to give any results.
One more time thank you all for your suggestions and oppinions.

Regards