Blue Bird Coachworks 450 LXi, Owner'S Manual

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4-2 Generator
450 LXi Owner Manual
~ 4-2-8 ~
Rev. “C”
4-2.4 Principles of Operation
The exciter pole pieces contain residual magnetism, setting up lines of force across the air gap to the exciter armature. When
the exciter armature begins to rotate a voltage is induced and current fl ow is initiated in the exciter armature AC windings.
This voltage is fed to the rotating rectifi er assembly, rectifi ed and fed to the alternator fi eld coils. This DC voltage is suffi cient
to magnetize the laminated alternator fi eld which will set up lines of force across the air gap to the alternator stator. As the
generator rotor rotates a voltage will be induced and current will fl ow in the alternator stator windings and to the output circuit.
A static type voltage regulator is connected to the generator output. The regulator will rectify part of the output voltage to
provide a DC voltage to the exciter fi eld coils. This will increase the density of the lines of force in the exciter, increasing the
voltage induced into the exciter armature windings, and therefore to the rotating rectifi ers.
The rotating rectifi er output will be increased, which will increase the alternator fi eld strength and the generator output will
build up to its rated voltage.
Adjustment of the generator output to the rated voltage level is accomplished by controlling the current fed to the exciter fi eld
coils.
Regulation is automatic with the static type voltage regulator. An additional voltage adjustment range is provided if desired by
operating the voltage adjust rheostat.
ROTATING FIELD ASSEMBLY (ROTOR)
- The rotating fi eld assembly consists basically of four members; the shaft
assembly, the core assembly, fi eld coil damper windings and balance lugs to provide a high degree of static and dynamic
balance. The exciter rotor and rotating rectifi er-hub assembly are separate units which are heat shrunk onto the generator
shaft.
CORE ASSEMBLY -
The core assembly consists of one piece electrical steel laminations which are stacked on the shaft
assembly.
FIELD COIL -
Field coils of heavily insulated wire are “wet” wound directly onto the poles. Field coil leads are brought out to
the rectifi er assembly for connection to the source of DC excitation voltage.
GENERATOR SHAFT -
The generator shaft is made of forged high strength steel, which is turned to close tolerances and
then ground to a closer tolerance.
GENERAL DESCRIPTION -
The revolving fi eld type generators have a DC fi eld revolving within a stationary AC winding
called the stator. AC power is distributed from the generator through leads connected to the stator windings. There are no
sliding contacts between the AC winding and the load, therefore, great amounts of power may be drawn from this generator.
VOLTAGE CONNECTIONS
-
The generator may be connected at the terminal board to deliver 120/240 volts to a 3 wire
grounded neutral system, or 120 volts only to a 2 wire distribution system. If any equipment requires 240 volts, then the
120/240 volt connection must be used. If all equipment requires 120 volts, then the 120 volt connection is preferred even
if two lines leave the switch box. The two lines at the input to the switch box are both connected to the ungrounded 120
volt lines from the generator. The 120 volt connection enables the EVR to hold the voltage very close the 115 or 120 volts
(as initially adjusted) regardless of the power distribution among the different distribution lines. The 120 volt connection is
recommended if all the electrical load requires only 115 or 120 volts.
Although the 120/240 volt connection may also be used when all load requires only 120 volts, it should be pointed out
that this connection the 240 volt is regulated and the lightly loaded phase will deliver a high line-to-neutral voltage and the
heavily loaded phase will deliver a low line-to-neutral voltage. The heavily loaded line may have such a low voltage that air
conditioning will have more diffi culty in starting, and long starting time may over-load generator and trip circuit breakers.