Multispeed motors are available in two basic versions: 1) Consequent pole, and 2) separate winding. A separate winding motor has a winding for each speed while a consequent pole motor has a winding for every two speeds (three speed motors have two windings). The motor connections (and thus the types of controllers) for two speed starters are exemplified by the schematic diagrams shown below. Note that consequent pole two speed controllers involve a 5-pole and a 3-pole starter while separate winding controllers have two 3-pole starters.
The type of motor must be verified prior to ordering. Field modification of starters to match the motor
may not be possible.
Separate winding motors are usually chosen when flexibility is important, since the speeds of a consequent pole motor are usually limited to a 2/1 ratio; a broad range of speeds can be obtained on a separate winding motor.
Both consequent pole and separate winding motors are available in three types: 1) Constant horsepower, 2) Constant torque, and 3) Variable torque. Typical applications for these different types of motors are shown below.
Note: For detailed information involving the technical aspects of flexibility of the starters used in the multispeed controllers, see Classes 8702, 8736 and 8810 application data.
General. Some applications require special relays to control the speed change and/or starting of the motor. The descriptions below cover the four common relay schemes for these applications.
Form R1 Compelling Relay. This relay requires the motor to be started at low speed before any higher speed can be selected. This arrangement ensures that the motor will always start the load at low speed. The stop button must be pressed before it is possible to change from a higher to a lower speed. (Not available with
Form R2.)
Form R2 Accelerating Relay/Timer. With
Form R2 accelerating relays, the ultimate speed is determined by the button which is pressed, but the starter will start the motor at low speed and automatically accelerate it through successive steps until the selected speed is reached. Definite time intervals must elapse between each speed change. Individual adjustable timing relays are provided for each interval. The stop button must be pressed before it is possible to change from a higher to a lower speed. (Not available with
Form R1.)
Form R3 Decelerating Relay/Timer. This is similar in action to
Form R2 accelerating relays, except that they function to prevent immediate transfer from a higher to a lower speed. A definite time interval, preset on the timer, must elapse between each speed change.
Form R10 Antiplugging Relays/Timers. This form imposes a time delay when transferring from the forward to the reverse direction or reverse to forward, for
reversing multispeed starters. This provides up to a 60 second delay in the transfer of the direction of the motor, and can help prevent damage which could result from plugging.
Overload Relay Modification. Form Y81 (Low Speed)—
For NEMA size 3 and 4, when the low speed full load current
does not appear on the appropriate thermal unit selection tables, include
Form Y81 (Low Speed) (No Charge for this form). This form modifies the overload relay block to accept Type B thermal units. Consult your nearest Square D/Schneider Electric sales office for assistance on thermal unit selection.
