The SX440 is a half-wave phase-controlled thyristor type
Automatic Voltage Regulator (AVR) and forms part of the
excitation system for a brushless generator.
In addition to regulating the generator voltage, the AVR
circuitry includes underspeed and sensing loss protection to
ensure safe, reliable control of the generator. 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 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%.
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 underspeed protection
of the excitation system, by reducing the output voltage
proportionally with speed below a presettable threshold.
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 push-on wire link selection.
Overvoltage caused by open circuit sensing terminals are
avoided by sensing loss detection circuitry which reduces the
generator terminal voltage to a safe fixed level.
Provision is made for the connection of a remote voltage
trimmer, allowing the user fine control of the generator's