Hi Jim ! Thanks for the amazing video !! Can you help me out on something ?? I have a 10 hp a 30 hp and a 60 hp motor. All of these are in a crane. They all work on 240v. I need to calculate the ohms of the resistors to add in order to get a 50% speed. Can you help me on this calculation ??
Probably the best help we can provide are two links : www.postglover.com/wp-content/uploads/downloads/2014/04/MC105-07_Wound_Rotor_Mtr_Res_Te_Sht.pdf i-gard.com/site/assets/files/1120/resistor_control_of_wound_rotor_motors.pdf
Thanks Jim this is an old bridge crane controlled by large drum switches. im converting it to a pendant control from the floor instead of cab control. the bridge is a 15hp WRM. if i were to keep the resistors in the rotor circuit, wouldnt that give me good torque and be easier on my vfd? just bouncing some thoughts of you. thanks
The VFD is connected to the stator. You have to use many other parts that breakdown and cause the rotor winding to fail permanently if not maintained. Brushes Sliprings Brush older and springs The VFD wouldn’t see anything . Jim
Thanks Jim, There is this 4100kW wound rotor that usually have burnt pigtail (middle) on all the 18 carbon brushes of the slip ring after few weeks of operation. We have changed the LRS solution, the carbon brushes and also improve on the compartment cooling. What else can contribute to this?
It appears that one ring is burning. Most likely there is a short in that ring's connected phase. Only the LR is starting. My suspicion would be either the brush rigging has a fault or there is a rotor short. Hope this info is helpful and hope your investigation finds the problem.
if you were to replace a drum controller with a pendant control and use pendant to energize a vfd. would setting the resistance of the rotor curcuit at half way would that be a happy medium?
No. Adding resistance to the rotor effects torque. You want to remove all the resistors when using the VFD. The rotor becomes an induction rotor. Changing the frequency will change the torque and the speed. The down side is the original design has a very low starting amperage or code letter. This made it good for lower starting current than the induction motor. Now you can use motor horsepower with the same power supply. - Jim Hudspeth - Technical Trainer
Clear in-depth explanation. Thanks for the video please continue!
You are very welcome. Thank YOU for investing your valuable time.
Very interesting! Thank you for sharing.
Thanks for investing your time
Hi Jim ! Thanks for the amazing video !! Can you help me out on something ?? I have a 10 hp a 30 hp and a 60 hp motor. All of these are in a crane. They all work on 240v. I need to calculate the ohms of the resistors to add in order to get a 50% speed. Can you help me on this calculation ??
Probably the best help we can provide are two links :
www.postglover.com/wp-content/uploads/downloads/2014/04/MC105-07_Wound_Rotor_Mtr_Res_Te_Sht.pdf
i-gard.com/site/assets/files/1120/resistor_control_of_wound_rotor_motors.pdf
Thanks Jim
this is an old bridge crane controlled by large drum switches. im converting it to a pendant control from the floor instead of cab control. the bridge is a 15hp WRM. if i were to keep the resistors in the rotor circuit, wouldnt that give me good torque and be easier on my vfd? just bouncing some thoughts of you. thanks
The VFD is connected to the stator. You have to use many other parts that breakdown and cause the rotor winding to fail permanently if not maintained.
Brushes
Sliprings
Brush older and springs
The VFD wouldn’t see anything .
Jim
Thanks Jim, There is this 4100kW wound rotor that usually have burnt pigtail (middle) on all the 18 carbon brushes of the slip ring after few weeks of operation. We have changed the LRS solution, the carbon brushes and also improve on the compartment cooling. What else can contribute to this?
It appears that one ring is burning. Most likely there is a short in that ring's connected phase. Only the LR is starting. My suspicion would be either the brush rigging has a fault or there is a rotor short. Hope this info is helpful and hope your investigation finds the problem.
if you were to replace a drum controller with a pendant control and use pendant to energize a vfd. would setting the resistance of the rotor curcuit at half way would that be a happy medium?
No. Adding resistance to the rotor effects torque. You want to remove all the resistors when using the VFD.
The rotor becomes an induction rotor. Changing the frequency will change the torque and the speed.
The down side is the original design has a very low starting amperage or code letter. This made it good for lower starting current than the induction motor.
Now you can use motor horsepower with the same power supply.
- Jim Hudspeth - Technical Trainer