MA327 AUTOMATIC VOLTAGE
REGULATOR (AVR)
SPECIFICATION, INSTALLATION AND ADJUSTMENTS
General description
The MA327 is a three phase full wave, pulse width modulated
type automatic voltage regulator (AVR) and forms part of the
excitation system for a brushless generator.
Excitation power is derived from a three-phase permanent
magnet generator (PMG), to isolate the AVR control circuits
from the effects of non-linear loads and to reduce radio
frequency interference on the generator terminals. Sustained
generator short circuit current is another feature of the PMG
system.
The AVR senses the voltage on the main generator winding
and controls the power fed to the exciter stator and hence the
main rotor to maintain the generator output voltage within the
specified limits, compensating for load, speed, temperature
and power factor of the generator. Three-phase root mean
squared (RMS) sensing is employed for superior voltage
regulation.
Soft start circuitry is included to provide a smooth controlled
build up of generator output voltage.
A frequency measuring circuit continually monitors the speed
of the generator and provides under-speed protection of the
excitation system by reducing the generator output voltage
proportionally with speed below an adjustable threshold. A
further enhancement of this feature is an adjustable volts per
Hertz slope to improve engine recovery time on turbo charged
engines.
Protection circuitry is included which cuts off the excitation
power in event of over-voltage.
Excitation limiting is a standard feature allowing control over
the amount of short circuit current flowing during short circuits
of the generator output.
Uncontrolled over-excitation is limited to a safe period by
internal shutdown of the AVR output device. This condition
remains latched until the generator has stopped.
For complete protection, a miniature circuit breaker option is
available, providing circuit isolation in the event of a short
circuit AVR power output device.
Provision is made for the connection of a remote voltage
trimmer allowing the user fine control of the g
enerators
output.
Technical specification
Sensing input
Voltage
170-250 Vac max
Frequency
50-60 Hz nominal
Phase
1 or 3
Wire
2 or 3
Power input
(PMG
)
Voltage
140-220 Vac max
Frequency
100-120 Hz nominal
Phase
3
Wire
3
Output
(limited by PMG output
)
Voltage
max 180 V dc (1800 rpm)
Current
continuous 6 A
Intermittent
12 A for 10 secs
Resistance
15 ohms minimum
Regulation
(4% engine governing)
+/- 0.5% RMS
Thermal drift
0.015%V per degree centigrade
change in AVR ambient
Soft start ramp time
0.5 - 4 seconds
Typical system response
(AVR and generator)
Exciter current to 97%
300 ms
External voltage adjustment
+/-5% with 5 k ohm 1 watt trimmer
Under frequency protection
Set point
97% Hz
Slope
100-300% down to 25 Hz
Max. Dwell
10 % V/ Sec. recovery
Unit power dissipation
30 watts max
Accessory input
+/-1 volt input = +/- 5% generator volts
Quadrature droop sensitivity
0.04 Amps for 5% droop @ pf
Excitation limit
Setting range
50 - 100%
Over excitation protection
Setting range
60-90 V dc
Time delay
inverse time
< setting = infinity
>25 % setting = 10 seconds max
Over-volts protection
Setting range
250-350 volts
Time delay
1 second fixed
Circuit breaker trip coil voltage 10 to 60 V dc
Circuit breaker trip coil resistance 50 to 100 ohms
Environmental
Vibration 5-10Hz 1mm
pk
10-100Hz 50mm/sec
RMS
100Hz-300Hz 4.4g
pk
Relative humidity 0-70c
95%
Operating temperature
-40 to +70c
Storage temperature
-55 to +80c
Fuse rating
10 Amps 1.25ins. quick-blow ceramic CSA UL approved
Accessories are available for this AVR.
