2018.01 / g
4
Electric Power Generation
Installation and maintenance
R150
AVRs
5384 en -
1 - GENERAL DESCRIPTION
The R150 automatic voltage regulator
(AVR) is a compact, high-performance
encapsulated unit. It incorporates the latest
technology and efficient components to
achieve a high degree of miniaturisation
when applied to a 3-phase and 1-phase AC
brushless generator, within its input and
output limits. The unit offers excellent
reliability.
The AVR provides DC excitation to the
exciter field of a brushless generator to keep
the voltage within the approximate operating
limits from NO-LOAD to FULL LOAD.
The typical recovery time in the event of
sudden loading is around 0.5 sec. to recover
98% of the rated voltage. Transient
performance such as voltage dip and
recovery time is mainly determined by the
generator and exciter design parameters.
Optimum AVR performance can be obtained
by keeping full-load excitation to around
60 VDC.
The generator uses a true average sensing
circuit, dV/dt snubber and special filter
circuits to manage NON-LINEAR loads
such as battery chargers, DC motors, etc.
Voltage regulation is only guaranteed for
linear loads. Severely distorting NON-
LINEAR loads can cause regulation
problems.
Each AVR is tested prior to dispatch as part
of a quality plan, for standard voltage and
frequency.
The R150 AVR is provided with two
accessory input terminals A1 and A2.
Injecting ± 4.5 VDC into these terminals will
change the generator voltage by ± 10%.
The AVR allows a shunt power supply from
the generator output voltage.
A soft-start circuit is included which provides
smooth control of the build-up of generator
output voltage.
A frequency roll-off circuit continuously
monitors the generator underspeed
protection by reducing the generator output
voltage in proportion with the speed below a
threshold.
The AVR has the facility for droop CT
connection, which is required for equal
KVAR load sharing during parallel operation.
2 - OPERATION OF THE AVR
The AVR is powered by the line-to-neutral
terminal of the AC generator, with 277 VAC
rms at 50 Hz or 60 Hz. The sensing voltage,
which is the regulated voltage, is based on
line-to-line (for 3-phase) and line-to-neutral
(for 1-phase). The AVR forms an important
part of the closed loop system comprising
the generator field, generator armature and
the AVR.
The AVR first builds up the generator voltage
from its residual levels. When the generator
is loaded, the sensed voltage decreases
and generates an error voltage, which is
required in order for the closed loop system
to work.
The AVR contains a high gain amplifier,
ramp and a pedestal circuit. Depending
upon the value of the amplifier voltage
(either high or low) the ramp intersects the
amplified voltage at a point, which is either
early or late in the half-cycle. At this
intersection point a starting pulse is
produced to trigger the power device.
When the power device is triggered early in
the half-cycle, more voltage is transmitted to
the field and when triggered late in the half-
cycle, less voltage is transmitted to the field.
In order to reduce the generator voltage at
low speed, a signal inversely proportional
to the speed is generated as an extra input.
At higher speeds the voltage decreases at a
faster rate than in proportion with the speed.
The R150 AVR has two additional terminals
A1 and A2. These inputs can be used to
connect an external control signal from
controllers such as APFC, Auto
Synchronizer, etc.
It is important that the DC power supply
should be electrically isolated from the line
terminals.
