OPX300K2 05/12
7
Performance and Function
EXCITATION SYSTEM
The excitation system of the PX-300K Series genera tor uses
an Automatic Voltage Regulator (AVR) which uses a portion
of the output power to supply controlled DC power to the
exciter fi eld (EX) as show in Figure 2. When DC power is
supplied to the exciter fi eld, output from the exciter armature
is rectifi ed by a 3-phase bridge rotary rectifi er (Si) and
supplied to the main fi eld coils. See Figure 2.
AUTOMATIC VOLTAGE REGULATOR (AVR)
The PX-300K2 Series generators use a DST-100-2FAK
AVR. This is a compact voltage regulator for generators
with an output up to 50kW. The AVR can be used in 120V
single phase applications and is installed inside the generator
junction box.
The AVR obtains sensing input from the main stator coils
and compares the rectifi ed value of the sensing voltage with
the reference voltage produced inside the AVR. Input power
is obtained from the main stator.
Rectifi ed output power to the exciter fi eld is controlled by
switching a transistor on and off. This AVR will control
terminal voltage even if the input sine wave is distorted.
Figure 2: PX-300K2 Block Diagram
AVR:
Automatic Voltage
Regulator
EX:
Exciter
Si:
Rotating
Rectifi er
Figure 4: For 60 Hz
Figure 3: For 50 Hz
UNDER SPEED PROTECTION
A frequency sensing circuit is built into the AVR.
When the generator speed drops to 90% of rated
speed this circuit protects the AVR by reducing
the voltage in proportion to the decrease in engine
speed. In addition, when the generator is hit with a
rapid overload, this circuit will lower the voltage to
protect the engine. See Figures 3 & 4.
ROTARY RECTIFIER AND SURGE
SUPPRESSOR
The rotary rectifi er assembly, consisting of six
diodes, functions as a 3-phase full wave rectifi er for
the output of the exciter armature and supplies this
to the main fi eld. To protect the diodes from large,
instanta neous voltage surges, surge absorbers are
provided as part of the rotating rectifi er assembly.
