Part winding motors are similar in construction to standard squirrel cage motors. However, part winding motors have two identical windings that may be connected to the power supply in sequence to produce reduced starting current and reduced starting torque. These motor windings are intended to operate in parallel. Because only half of the windings are connected to the supply lines at startup, the method is described as part winding. (Many, but not all, dual-voltage, 230/460-volt motors are suitable for part winding starting at 230 volts.) By bringing out leads from each winding, the motor manufacturer enables the windings to be connected in parallel, external to the motor, with the starter.
Part winding starters are sometimes used on motors would for dual voltage operation, such as a 230/460 V motor. These motors have two sets of windings connected in series for high-voltage operation. When used on the lower voltage, they can be started by first energizing only one winding, limiting starting current and torque to approximately one-half of full the voltage values. The second winding is then connected normally, once the motor nears operating speed about 2 s later.
Part winding starters are designed to be used with squirrel cage motors having two separate and parallel stator windings. In the part winding motor, these windings may be Y connected or delta connected, depending on the motor design.
Part winding starters are not suitable for use with delta-wound and dual-voltage motors.
Part winding motors are used to drive centrifugal loads such as fans, blowers, or centrifugal pumps. They are also used for other loads where a reduced starting torque is necessary.
This type of motor is also used where the full voltage starting current will produce objectionable voltage drops in the distribution feeders or where power company restrictions require a reduced starting current. Using a part winding starter to start a motor does not necessarily reduce the maximum starting current. Instead, incremental starting is obtained. Neither one of the two windings has the thermal capacity to operate alone for more than a few seconds. Therefore, unless the motor accelerates to practically full speed on the one winding, the TOTAL cur rent drawn may approach that of line voltage starting.
This type of starting has many applications in air-conditioning systems. This is due to the increased capacity built into these systems and the necessity of limiting both the current and torque on starting.
– Industrial electronics web. “Part Winding Motor Starters–AC Reduced Voltage Starters”. 20 Mei 2014. http://www.industrial-electronics.com/Motor_Control_5-28.html
– Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 246.