I'm trying to solve some puzzles around the electronics of an amusement ride. It's basicly an old carousel with a wave-like pattern (3 tops/downs along the circle) that i'm restoring. (So that you know the application) I've been researching some while now and would like to have answers instead of doubting myself over and over, spending too much time on it when I can just ask.
I've got a 3 phase slip ring (wound rotor) motor with the following plate:
- HP: 2
- V st. 220 / 380
- A st. 5.9 / 3.4
- V rot. 53
- A rot. 19
- RPM: 1385
- Freq.: 50 Hz
(ofcourse I'm in Western Europa and using the 230V now)
I found out that I could make this a normal ac motor by shorting the slip rings (just connecting them together) so that I can use a VFD and connect it in delta. (Please correct me if i'm wrong on anything)
1) Is just shorting it ok? I read something about putting little resistors between? Why would that be better?
2) Do I need a dv/dt filter? (it sounds like overkill to me?) The length of the cable from vfd to the motor will be max 10 meters.
3) Risk here is that the insulation could fail. How do I measure this and what values should I get? (ofcourse all of them giving the same value)
4) Now the plate gives me that it's actually a 1.3kW motor. Now to select an VFD I assumed I would need a 1,5kW VFD. But I got told that I would need a 2,2kW VFD due to that it is a slip ring motor, is this true? And what ac motor should i buy when i decide to replace the old one? Would 1,5kW VFD still be sufficient?
5) Would a VFD with built-in brake unit (resistor) of 50% nominal current be good enough?
6) If I calculate the slip % it is 1500 - 1385 = 115, thus slip = 115/1500 * 100 = 7,67%. In this article they say this is a high slip motor and therefor I should use sensorless vector instead of a V/F VFD?
7) I don't know how I came up with this info, but somewhere I read I should ground the rotor in some special case. I was shocked and now i'm just becoming insecure. Am I true that this is weird? And you should just ground the stator.
8) Some company told me I should use a linear curve instead of an S-curve in my application. I thought the S-curve was the way to go.. So which is it and why?
If anyone can answer one or more of these questions, please do so. Even if you're not sure, just give your opinion so that I can see how many people think what. Thanks a lot!