Speed control in asyncronous wound rotor
Speed control in asyncronous wound rotor
(OP)
Does anybody knows if exist some solid-state device that replace the large multi-stage bank resistor that is normally used in wound rotors in order to start and control the speed?
Thanks in advance
Thanks in advance





RE: Speed control in asyncronous wound rotor
http://www.thomasregister.com
and type Starters: Motor under Product or Service, which will return 133 companies to approach to
RE: Speed control in asyncronous wound rotor
If your load increases torque as speed increases, then you can control speed.
As for solid state rotor controllers, I wouldn't be much help on that. Every such motor I've encountered has had its rotor resistance fixed at the minimum value and an inverter added for speed control.
RE: Speed control in asyncronous wound rotor
"Venditori de oleum-vipera non vigere excordis populi"
RE: Speed control in asyncronous wound rotor
I think the one that have better understood what I'm looking for is jraef.
What I want to do is to replace the resistor bank for some solid state device that simulate exactly its behavior.
I've never seen such a device.
Have you?
RE: Speed control in asyncronous wound rotor
I have a known load to move.
With the rotor slip rings short circuited I get a certain speed called "n1".
If I add resistance using a resistance bank, then I will get another speed called "n2" where n2<n1.
My problem is that this practice is not an energy effective solution because of the energy wasting in resistance bank.
What I'm looking for is some solid state device that use less energy in order to get the same effect as the resistance bank.
RE: Speed control in asyncronous wound rotor
RE: Speed control in asyncronous wound rotor
RE: Speed control in asyncronous wound rotor
http://www.flomatch.com/
The problem is that the cost is fairly close to that of a standard off-the-shelf VFD, hence the tendancy for users to just go with something less unique.
"Venditori de oleum-vipera non vigere excordis populi"
RE: Speed control in asyncronous wound rotor
RE: Speed control in asyncronous wound rotor
RE: Speed control in asyncronous wound rotor
It seems to me that this is going to be a wrong application.
Wound rotor induction motors are used where you need to reduce the starting current or/and where you need to have a higher starting torque. As you are also aware, the motor is started with the full resistor in the rotor circuit and then it is gradually reduced to "ZERO" when the motor attains its no-load speed and then it is loaded to its full load speed.
As such the rotor resistor is never and should not be used to "control the speed" and should never be kept in rotor circuit which will result considerable heat loss.
If you regulate the speed then at that speed it may NOT develop enough torque to get the desired flow.
Therefore my understanding is using a wound rotor motor as a variable speed drive is a wrong application.
Thanks!
Kiribanda
RE: Speed control in asyncronous wound rotor
You are right about how it works, but your statement about it not being suitable for speed control flies in the face of almost 100 years of people doing that exact application successfully!
Flomatcher is named that because that is exactly what they do; use wound rotor motors and liquid rheostats to control the speed of pump motors in order to match the flow to the application requirements. And Flomatcher did not invent this idea nor have an exclusive on it. Before the advent of Inverter drives, this was the premier "high tech" method of controlling motor speed. Ski lifts are another major application world-wide that used WRIM controls as speed control. Technically you are right that it does not directly control speed as we understand it now, i.e. frequency control. However if you can modulate output torque into a given load, without burning up the induction motor, you will in EFFECT be controlling speed. That is of course exactly what a WRIM and controller do.
"Venditori de oleum-vipera non vigere excordis populi"
RE: Speed control in asyncronous wound rotor
RE: Speed control in asyncronous wound rotor
RE: Speed control in asyncronous wound rotor
Why not consider starting the motor on the existing resistors, cut out all the resistors to bring the motor to full speed and then use the VFD on stator to control the speed?
You will be relacing the existing main contactor/controller with VFD and some messing around with rotor controls.
Risky method (or one needing a good rotor analaysis) would be to short out the resistor completely and even start the motor on VFD. Success of this will depend how much starting torue is required and produced.