SX421 AUTOMATIC VOLTAGE
REGULATOR (AVR)
SPECIFICATION, INSTALLATION AND ADJUSTMENTS
GENERAL DESCRIPTION
The SX421 is a three phase sensed 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 a number of protective 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 and exciter field
windings to provide closed loop control of the output voltage
with load regulation in the order of +/-0.5% RMS.
The AVR senses the output voltage from the main stator
windings and in response to this controls the power fed to the
exciter field and hence the main field to maintain output
voltage within the specified limits, compensating for load,
speed, temperature, and power factor of the generator.
Overvoltages caused by open circuit sensing terminals or
short circuit power device are avoided by overvoltage
detection circuitry which provides circuit breaker trip signals
for circuit isolation. (see note 1).
A frequency measuring circuit continually monitors the
generator output and provides underspeed protection of the
excitation system by reducing the generator output voltage
proportionally with speed below a presettable threshold. A
further enhancement of this feature is an adjustable V/Hz
slope, to improve frequency recovery time on turbo-charged
engines.
Provision is made for the connection of a remote voltage
trimmer, allowing the user fine control of the generator output.
Accessories are available for this AVR. Please refer to factory
for further details.
TECHNICAL SPECIFICATION
SENSING INPUT
Voltage
170-250 V ac max
Frequency
50-60 Hz nominal
Phase
3
Wire
3
OUTPUT
Voltage
max 90 V dc at 207 V ac input
Current
Continuous 4 A dc
Transient 6 A for 10 seconds
Field Resistance
15
Ω
minimum
REGULATION
(See Note 2) +/- 0.5% RMS
THERMAL DRIFT
(after 10 min)
0.5% for 40°C change in AVR ambient
TYPICAL SYSTEM RESPONSE
Field current to 90% 80ms
Machine Volts to 97% 300ms
EXTERNAL VOLTAGE ADJUSTMENT
+/- 6% with 1 K
Ω
trimmer
UNDER FREQUENCY PROTECTION
Set Point (See Note 3)
95% Hz
Slope
100-300% down to 30 Hz
UNIT POWER DISSIPATION
20 watts maximum
BUILD UP VOLTAGE
3.5 V ac @ AVR terminals
ACCESSORY INPUT
+/- 1V = +/- 5% change in output
volts @ 415 V
QUADRATURE DROOP
Maximum sensitivity (10
Ω
Burden)
0.22A for 5% droop @ 0p.f.
OVER VOLTAGE PROTECTION
Set Point
300 V dc
Time Delay (fixed)
1 second
Circuit Breaker Trip Coil Voltage
12-30 V dc
C/B Trip Coil Resistance
25-40
Ω
ENVIRONMENTAL
Vibration
20-100 Hz
50mm/sec
100 Hz-2 kHz
3.3g
Relative Humidity
0-60°C
95%
Operating Temperature
-40°C to + 70°C
Storage Temperature
-55°C + 80°C
NOTES
1.
A miniature circuit breaker must be fitted to use the Overvoltage
Protection feature.
2.
With 4% engine governing.
3.
Factory set, semi-sealed, jumper selectable.
