SX440 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 +/-0.5%.
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 push-on link selection.
Provision is made for the connection of a remote voltage trimmer, allowing the user fine control of the generator's output.

Technical specification

INPUT
Voltage: 170-250V ac max
Frequency: 50-60 Hz nominal
Phase: 1
Wire: 2

OUTPUT
Voltage: Max 90V dc at 207V ac input
Current: Continuous 4 A dc
Transient: 6 A for 10 secs
Field Resistance: 15 ohms minimum
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REGULATION: (See Note 1) +/-1.0%

THERMAL DRIFT
(after 10 min)
1% for 40º C change in AVR ambient

TYPICAL SYSTEM RESPONSE
AVR response: 20 ms
Filed current to 90%: 80 ms
Machine Volts to 97%: 300 ms

EXTERNAL VOLTAGE ADJUSTMENT(see note 2)
+/-8% with 1 k ohm 1 watt trimmer

UNDER FREQUENCY PROTECTION
Set point (see note 3): 95% Hz
Slope: 170% down to 30 Hz

UNIT POWER DISSIPATION
12 watts maximum

BUILD UP VOLTAGE
3.5 Vac @ AVR terminals

ACCESSORY INPUT
+/- 1V = +/- 13% change in output volts

QUADRATURE DROOP SENSITIVITY
Maximum sensitivity (10 Ohm Burden)
0.07A for 5% droop @ 0p. F.

ENVIRONMENTAL
Vibration 20 -100 Hz 50mm/sec
100Hz -2kHz 3.3g
Operating temperature: -40º C to +70º C
Relative Humidity: 0-60º C 95%
Storage temperature: -55º Cto +80º C