Guardian Technologies 4270 manual Simple AC Generator, 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.

CURRENTVOLTAGE

(+)

0 180 360

(-)

ONE CYCLE

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.

STATOR

ROTOR

MAGNETIC FIELD

Figure 1-4. – A Simple AC Generator

OUTPUT
		120 V		STATOR STATOR
	240 V
AC	120 V
CURRENT
			BRUSHES
DC
				SLIP
				RINGS

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 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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