PLucas
Member
Hi All, especially DickDV
As I have seen a number of motor related questions posted recently, so I thought that I would have a go.
Here is the problem, we have 1 Siemens VFD powering 4 motors, speed feedback to the drive is taken from a pulse encoder mounted on the shaft of 1 motor. The motors run at 1485rpm full load. The motors via a 19.8 – 1 ratio gearbox drive the wheels of the crane. A new wheel size is 630mm diameter and the crane is designed to run at 150M/min. Now then by my calculations each wheel will run at 75 (ish) rpm.
So, the motor with the speed feedback signal has a full size wheel and is happily running at 1485 rpm, 1 of the wheels has worn by, say, 2mm diameter so the wheel size is now 628mm, now with the motor running at 1485 rpm then this wheel will still turn at 75 rpm. But over the distance of 150M the wheel will need to turn 76 times, (1 more revolution than the other 3 wheels). I assume that this smaller wheel will be dragged by the other wheels thus forcing it to run that little bit faster, then, via the gearbox the motor will also run that little bit faster and bring the motor speed up to practically sync speed (76*19.8=1504rpm), at which time that motor will not have any torque, so it will be quite happy being pulled along by the other wheels (I think).
Now then, can someone shed some light on to what detrimental effect this will have on the following (if any):
1. Current of this particular motor
2. Current of the other 3 motors
3. DC link voltage in the drive
4. Anything else you can think of
Unfortunately when I served my apprentiship, I worked for British Rail where they used only DC motors for traction etc so I did not take too much notice of AC machines. Now I have to work with AC motors the old grey matter gets a bit clogged up. Any help would be gratefully appreciated.
Paul
As I have seen a number of motor related questions posted recently, so I thought that I would have a go.
Here is the problem, we have 1 Siemens VFD powering 4 motors, speed feedback to the drive is taken from a pulse encoder mounted on the shaft of 1 motor. The motors run at 1485rpm full load. The motors via a 19.8 – 1 ratio gearbox drive the wheels of the crane. A new wheel size is 630mm diameter and the crane is designed to run at 150M/min. Now then by my calculations each wheel will run at 75 (ish) rpm.
So, the motor with the speed feedback signal has a full size wheel and is happily running at 1485 rpm, 1 of the wheels has worn by, say, 2mm diameter so the wheel size is now 628mm, now with the motor running at 1485 rpm then this wheel will still turn at 75 rpm. But over the distance of 150M the wheel will need to turn 76 times, (1 more revolution than the other 3 wheels). I assume that this smaller wheel will be dragged by the other wheels thus forcing it to run that little bit faster, then, via the gearbox the motor will also run that little bit faster and bring the motor speed up to practically sync speed (76*19.8=1504rpm), at which time that motor will not have any torque, so it will be quite happy being pulled along by the other wheels (I think).
Now then, can someone shed some light on to what detrimental effect this will have on the following (if any):
1. Current of this particular motor
2. Current of the other 3 motors
3. DC link voltage in the drive
4. Anything else you can think of
Unfortunately when I served my apprentiship, I worked for British Rail where they used only DC motors for traction etc so I did not take too much notice of AC machines. Now I have to work with AC motors the old grey matter gets a bit clogged up. Any help would be gratefully appreciated.
Paul