Generac Power Systems 55, 75, 65 manual A Simple Ac Generator, A More Sophisticated Ac Generator

Section 1

GENERATOR FUNDAMENTALS

A SIMPLE AC GENERATOR

Figure 1-4 shows a very simple AC Generator. The generator consists of a rotating magnetic field called a ROTOR and a stationary coil of wire called a STA- TOR. The ROTOR is a permanent magnet which con- sists of a SOUTH magnetic pole and a NORTH mag- netic pole.

As the MOTOR turns, its magnetic field cuts across the stationary STATOR. A voltage is induced Into the STATOR windings. When the magnet's NORTH pole passes the STATOR, current flows in one direction. Current flows in the opposite direction when the mag- net's SOUTH pole passes the STATOR. This con- stant reversal of current flow results in an alternating current (AC) waveform that can be diagrammed as shown in Figure 1-5.

The ROTOR may be a 2-pole type having a single NORTH and a single SOUTH magnetic pole. Some ROTORS are 4-pole type with two SOUTH and two NORTH magnetic poles. The following apply:

1.The 2-pole ROTOR must be turned at 3600 rpm to produce an AC frequency of 60 Hertz, or at 3000 rpm to deliver an AC fre- quency of 50 Hertz.

2.The 4-pole ROTOR must operate at 1800 rpm to deliver a 60 Hertz AC frequency or at 1500 rpm to deliver a 50 Hertz AC frequency.

Figure 1-5. – Alternating Current Sine Wave

A MORE SOPHISTICATED AC GENERATOR

Figure 1-6 represents a more sophisticated genera- tor. A regulated direct current is delivered into the ROTOR windings via carbon BRUSHES AND SLIP RINGS. This results in the creation of a regulated magnetic field around the ROTOR. As a result, a reg- ulated voltage is induced into the STATOR. Regulated current delivered to the ROTOR is called “EXCITATION” current.

		Figure 1-6. – A More Sophisticated Generator
	See Figure 1-7 (next page). The revolving magnetic
	field (ROTOR) is driven by the engine at a constant
	speed. This constant speed is maintained by a
	mechanical engine governor. Units with a 2-pole rotor
	require an operating speed of 3600 rpm to deliver a
Figure 1-4. – A Simple AC Generator	60 Hertz AC output. Engine governors are set to
	maintain approximately 3720 rpm when no electrical
	loads are connected to the generator.

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