Special Electrical Machines

Special Electrical Machines

1. Special electrical machines Prepared by, A.Johny Renoald M . E., Ph.D.,

2. Electrical machine A electrical machine consumes electrical energy to do a specific work or it convert electrical energy to other forms like mechanical energy, light energy, heat etc.,

3. Special Electrical Machines Types Permanent Magnet DC Motor 1. PM synchronous motor 2. PM brushless DC motor Reluctance motors 1 . Synchronous reluctance 2 . Switched Reluctance Stepping motors 1. Single stack multi-machine 2. Multi stack multi-machine

4. Permanent magnet DC Motors

5. PMSM Depending on how magnets are attached to the rotor, PMSM motors can be classified into Two types: Surface PMSM ( SPMSM ) and interior PMSM ( IPMSM ). Permanent Magnet Synchronous Motor, PMSM is a kind of synchronous motor in which permanent magnet is used as rotor to create field poles. No field winding is wound on the rotor.

6. Advent of Switching power transistor and SCR in 1950’s replaced the mechanical commutator with electrical commutator in the form of inverter. PMSM

7. The main advantage when compared with the conventional synchronous machine is the elimination of the field coil, dc supply, and slip rings; hence, lower loss and a less complex motor. PMSM

8. INTRODUCTION A permanent magnet synchronous motor is also called as brushless permanent magnet sine wave motor . A sine wave motor has a Sinusoidal or quasi-sinusoidal distribution of magnetic flux in the air gap. 2. Sinusoidal or quasi-sinusoidal current wave forms. 3. Quasi-sinusoidal distribution of stator conductors (i.e.) short-pitched and distributed or concentric stator windings.

9. Construction The basic construction of PMSM is same as that of synchronous motor . The only difference lies with the rotor. Unlike synchronous motor, there is no filed winding on the rotor of PMSM . Field poles are created by using permanent magnet. These Permanent magnets are made up of high permeability and high coercivity materials like Samarium-Cobalt and Neodium-Iron-Boron. Neodium-Iron-Boron is mostly used due to its ease of availability and cost effectiveness. Theses permanent magnets are mounted on the rotor core.

10. Working principle The working principle of permanent magnet synchronous motor is same as that of synchronous motor. When three phase winding of stator is energized from 3 phase supply, rotating magnetic field is set up in the air gap. At  synchronous speed , the rotor field poles locks with the rotating magnetic field to produce torque and hence rotor continues to rotate. As we know that  synchronous motors are not self starting , PMSM needs to be started somehow. Since there is no winding on the rotor, induction windings for starting is not applicable for such motors and therefore variable frequency power supply for this purpose.

11. Application: Permanent Magnet Synchronous Motor can be used as an alternative for  servo drives . It is widely used in various industrial application viz. robotics,  traction, aerospace etc.

12. EMF and Torque equation

13. Torque equation in PMSM

14. PMSM phasor diagram

15. Power controllers

16. Application in railway traction