22-08-2012, 01:15 PM
SX440 AUTOMATIC VOLTAGE REGULATOR (AVR)
AUTOMATIC VOLTAGE REGULATOR.sx440.pdf (Size: 47.56 KB / Downloads: 101)
General description
SX440 is a half-wave phase-controlled thyristor type
Automatic Voltage Regulator (AVR) and forms part of the
excitation system for a brush-less generator.
In addition to regulating the generator voltage, the AVR
circuitry includes under-speed and sensing loss
protection features. Excitation power is derived directly
from the generator terminals.
Positive voltage build up from residual levels is ensured
by the use of efficient semiconductors in the power
circuitry of the AVR.
The AVR is linked with the main stator windings and the
exciter field windings to provide closed loop control of the
output voltage with load regulation of +/- 1.0%.
In addition to being powered from the main stator, the
AVR also derives a sample voltage from the output
windings for voltage control purposes. In response to this
sample voltage, the AVR controls the power fed to the
exciter field, and hence the main field, to maintain the
machine output voltage within the specified limits,
compensating for load, speed, temperature and power
factor of the generator.
A frequency measuring circuit continually monitors the
generator output and provides output under-speed
protection of the excitation system, by reducing the output
voltage proportionally with speed below a pre-settable
threshold. A manual adjustment is provided for factory
setting of the under frequency roll off point, (UFRO). This
can easily be changed to 50 or 60 Hz in the field by pushon
link selection.
Provision is made for the connection of a remote voltage
trimmer, allowing the user fine control of the generator's
output.
An analogue input is provided allowing connection to a
Newage Power Factor controller or other external devices
with compatible output.
The main functions of the AVR are:
Potential Divider and Rectifier takes a proportion of the
generator output voltage and attenuates it. The potential
divider is adjustable by the AVR Volts potentiometer and
external hand trimmer (when fitted). The output from the
droop CT is also added to this signal. An isolating
transformer is included allowing connection to various
winding configurations. A rectifier converts the a.c. input
signal into d.c. for further processing.
The Sensing Loss Detector is an electronic changeover
switch, which normally connects the Amplifier (Amp) to
the Voltage Sensing input and automatically changes
over to the Power input when the normal sensing voltage
is lost.
The DC Mixer adds the Analogue input signal the
Sensing signal.
The Amplifier (Amp) compares the sensing voltage to the
Reference Voltage and amplifies the difference (error) to
provide a controlling signal for the power devices. The
Ramp Generator and Level Detector and Driver infinitely
control the conduction period of the Power Control
Devices and hence provides the excitation system with
the required power to maintain the generator voltage
within specified limits.
ADJUSTMENT OF AVR CONTROLS
VOLTAGE ADJUSTMENT
The generator output voltage is set at the factory, but can
be altered by careful adjustment of the VOLTS control on
the AVR board, or by the external hand trimmer if fitted.
Terminals 1 and 2 on the AVR will be fitted with a shorting
link if no hand trimmer is required.
CAUTION Do not increase the voltage above the rated
generator voltage. If in doubt, refer to the rating plate
mounted on the generator case.
CAUTION Do not ground any of the hand trimmer
terminals as these could be above earth potential. Failure
to observe this could cause equipment damage.