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Line Start Permanent Magnet Motors
The search for new structures of electrical machines is determined by obtaining energy efficient and reliable drives. Construction of motors having an efficiency greater than the efficiency of currently used energy-saving induction motor requires the use of modern materials in their structures, in particular permanent magnets. In addition, the motors should be adapted to variable operating mode of driven machines eg. Fans and pumps, which allow a step or continuous speed control that allows for energy efficiency. Reliability of motors should not be less and operation no worse than for induction motors, which means the simplest possible design for sought new structures of machines.
Construction of synchronous motors excited by permanent magnets
The construction of the mechanical system and the stator is identical to the induction motor. The difference in the construction of the rotor arises from the need to place the permanent magnets. Since it is assumed that this type of motors should be run DOL, their start-up is carried out by generating the asynchronous torque. This torque is produced by the squirrel-cage winding arranged in a rotor as in the induction motor.
The arrangement of permanent magnets in the rotor has an impact on their use (inducing sufficiently large electromotive force impacting the power factor), harmonics in the magnetic field (THD value) and the value of tapped torque.
Figures 1, 2 shows graphs of power factor, efficiency, and the current drawn from the network as a function of synchronous permanent magnet motor load. These plots were compared with the corresponding graphs of induction motor.
Based on a comparison of characteristics of the induction motor and permanent magnet synchronous motor it can be concluded that usage of LSPM allows for:
• compensation of reactive power drawn from the network (increased power factor)
• practically constant power factor over load range
• increased efficiency,
• practically constant efficiency over load range
• reduction of rated current drawn from the network (from 177.5 to 156.4 A A).

A model of a prototype of LSPM motor designed for driving modernized main pump of mine dewatering system is presented. The motor has a rated power of 1600 kW at 1500 rpm.

Fig. 1. Power factor as a function of the load of the induction motor and permanent magnet motor Fig. 2. The characteristics of efficiency and the stator current as a function of the load of the induction motor and permanent magnet motor

Reduction of magnetizing current improves the power factor and reduces the current drawn from the mains. Based on the experience it can be said that such motors can be built in the full range of power ratings - from small machines to very large. It should be emphasized that the operating parameters (cosφ and η) are constant in a very large range of load changes. Moreover permanent magnet motors meet the requirements of Class IE-4 standards of the International Electrotechnical Commission IEC 60034.

Installed drive systems are operational and energy savings depend on a set schedule of extraction of raw materials, which determines time of motors operation. Registered power consumption indicates that savings on energy consumption as a result of use of energy efficient motors are significant. This combined with high power of installed motors gives a significant reduction in operating costs.

Lengths of power lines within the site vary but are significant: from 1 500 to 5 000 m. Therefore reduction of electricity flow losses (due to increase of  power factor and reduction of current) is often higher than reduction of losses in the motor resulting from increased efficiency.


In recent months, EMIT produced LSPMSM with power of 200kW (10kV) and 1600kW (6 kV).


For more information please contact us



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