
slip ring motors and vfd's
#1
Posted 17 September 2002 - 04:57 PM
#2
Posted 17 September 2002 - 07:36 PM
Welcome to the forums.
Yes, a slip ring motor can be used with a vfd, and because when under VFD control, the slip ring motor will never be operated under high slip, you just short out the rotor circuit. i.e. dispose of the secondary starter circuit completely. You can short out at the out put of the brushes, but you still need to maintain the brushes, or you can short out on the rotor itself and remove the brushes. You can not leave the rotor circuit open circuit though.
The only thing to be careful of is, you may have problems if you use a fancy sensorless vector drive due to motor characteristics that are different from the norm.
Best regards,
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
#3
Posted 19 September 2002 - 08:11 AM
charles ray;
The other trap is to ensure that the current delivering capability (overload) of the drive is sufficient for the motor you are connecting to it. For this you will need the motor curves.
#4
Posted 20 September 2002 - 03:53 AM
Assuming you agree with marke's comment above;
"....and because when under VFD control, the slip ring motor will never be operated under high slip...."
....and I do, how can overload capacity become a trap?
VSD manufacturers only have to provide overload capacity to allow for the mis-setting of a VSD (ie insufficient accel time), or for the use of otherwise undersized motors, resulting in 'slip' and overload currents.
Applications requiring in excess of motor FLA (assuming the motor is sized correctly) are surely rare. In fact, I can't think of one, and all commisioned jobs I have been involved in have never required an 'overload capacity'.
Perhaps your experience is different?
Cheers!
BigMax;b;
#5
Posted 20 September 2002 - 04:39 AM
A WRM is generally used because of the high starting torque that can be achieved (up to 250% FLT). This is the ONLY reason I suggested looking at the drive overload capability. If it is an exsiting application (as this one sounds like), a WRM may have been used because of high starting torque requirement with little running torque. A good example of this type of load would be a loaded rock crusher. The drive must be capable of delivering the current demmanded by the motor/load.
Do you agree?
#6
Posted 20 September 2002 - 05:38 AM
Yep, good point! Seems that driving WRMs with VSDs under some circumstances may require some caution.
It all sounds a bit 'messy' to me though. I like everything to be simple;b;
"If I don't understand it, it must be BS"
Quote by unknown author.
Cheers!
BigMax
#7
Posted 21 September 2002 - 02:26 AM
Best regards
Mark Empson | administrator
Skype Contact = markempson | phone +64 274 363 067
LMPForum | Power Factor | L M Photonics Ltd | Empson family | Advanced Motor Control Ltd | Pressure Transducers | Smart Relay | GSM Control | Mark Empson Website | AuCom | Soft Starters
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