Operating Alternators or AC Generators in Parallel

Pointers for Operating Alternators in Parallel:
1) If the load of a single generator becomes too large that its rating is exceeded, it is necessary to add another generator in parallel to increase the power available from the power station. Before attempting to connect AC generator in parallel, the following conditions must be met:

Three Phase Synchronous Motor

Figure 1: Cutaway view of  an eight pole, 2000 horsepower synchronous motor.

Introduction:
The synchronous motor is one type of three phase AC motor which operates at a constant speed from no-load to full-load.  It is similar in construction to a three phase AC generator but it has a revolving field which must be separately excited from a direct current source.  By changing the DC field excitation current, the power factor of this type of motor can be varied over a side range of lagging and leading values.  This motor is used in many industry applications because of its fixed speed from no-load to full-load, its high efficiency and to initial cost. It is also used to improve the power factor of three phase AC industrial circuits.

Polyphase Induction Motors

Figure 1: A typical three phase motor.

                                                     

Shaded Pole Induction Motor

Shaded-Pole Induction Motor

Figure 1: Cutaway view of a totally enclosed fan-cooled shaded-pole induction motor

A shaded-pole motor maybe defined as a single-phase induction motor provided with an auxiliary short-circuited winding or windings displaced in magnetic position from the main winding.

Shaded-pole induction motors are used in a wide variety of applications requiring an induction motor of 1/2 horsepower or less, even down to less than 1 mhp. It is simple in construction, low in cost, and extremely rugged and reliable - like a polyphase induction motor. Its torque characteristics and applications are similar to those of a permanent-split capacitor motor, except that it has a lower efficiency and a lower power factor. It is used in extremely wide variety of applications: home appliances, such as rotisseries, fans of all kinds such as those most commonly found in homes such as home electric fans, humidifiers, slide projectors; small business machines such as photocopy machines; vending machines, advertising displays, etc.

Electrical Control Circuit Schematic Diagram of Two-Value Capacitor Motor

TWO-VALUE CAPACITOR MOTOR

Figure 1: An autotransformer consisting of a coil of wire wound on a laminated core. The coil is tapped at several points to obtain different voltages