3 Phase Motors & Drives

Table of Contents
Task 1 (P3) 2
Task 2 (P3) 5
Task 3 (P4) 6
Task 4 (P5) 8
Task 5 (M3) 13
Task 6 (M3) 15
Task 7 (M3) 16
Task 8 (M3) 17
Task 9 (M3) 17
Bibliography 19

Task 1 (P3)

A Synchronous Motor is three-phase AC motors which run at synchronous speed, without slip. The constructions are similar to induction motors apart from the design of the rotor and the ability to self-start.
The stator is made of a frame of cast steel which supports the core of low Silicon steel rings, these are used due to its high permeability and ability to reduce hysteresis, which decreases the efficiency of the motor by converting magnetic energy into thermal energy.
The steel is also laminated to reduce eddy currents which also improve efficiency.
The conductive coils in the stator are layered either in mono or poly configuration, this means it either has a slot to itself or it shares a slot with another coil (see Fig.1.).
Between each layer of conductor, there must be an insulator. This is usually made from Mylar, which is a type of polyester film.
To prevent the coils from coming out of the slots under magnetic force, there are wedges placed at the end as a cap.
When an external AC current is passed through the windings (coils) in the stator, it creates a rotating magnetic field which runs at synchronous speed, which is 50Hz in the UK.

(http://electrical-engineering-portal.com/synchronous-motor-construction, 10.2.15)

FIGURE 1 - Ten-pole Salient synchronous motor showing rotor (top half) and stator construction (bottom half).

When an electromagnet is present in this rotating magnetic field, the electromagnet is magnetically locked with the rotating magnetic field and rotates with same speed of rotating field; at synchronous speed.

The rotor of a synchronous motor is constructed in two different varieties; Salient pole and cylindrical.  
Both types of rotor use 2 brushes and 2 slip rings and operate using DC current.

fig.14. – The above...