WEG AVR-A-OPT-03 Installation, Operation And Maintenance Manual page 13

5 BLOCK DIAGRAM
Referency
1
- Only on AVR-A-OPT-03/C version.
Operation is based in the comparison of the RMS sensing voltage with the reference voltage, adjusted by the sum of the
voltage adjustment trimpots and the external potentiometer. The error is processed by the sensing grid, and this value
determines the firing angle of the thyristor which can vary from 0 to 180, controlling in this way the output voltage of the
generator. With zero degree firing angle, we get zero volt on the rectifier output, and with a firing angle of 180 degrees, we
get the maximum output allowed by the half wave rectifier.
Generation starts through the residual voltage. After the voltage has reached approximately 10% of the rated value, the
regulator controls the voltage of the alternatorcausing the voltage to increase in approximately 1 second, until it reaches
rated voltage. From this moment on, the control grid will maintain constant output voltage of the alternatorwithin the
adjusted value.
Sensing Voltage
AlternatorVoltage
U/F Adjust
Alternator Frequency
On Figure 5.2 the control diagram of the AVR-A-OPT-03 voltage regulator is shown. The control is similar to ST1A, shown
by IEEE applied to systems where the rectifier is fed from the alternatoroutput (Type ST - Static Excitation Systems)
directly, through auxiliary coils or per transformer.
Automatic Voltage
Increase
Current limiter
Sensing
Figure 5.1: Voltage regulator block diagram
Error
Signal
Figure 5.2: Control diagram of AVR-A-OPT-03
Excitation Field
Power Stage
Field Voltage
Rectifier
Analog Voltage Regulator AVR-A-OPT-03
www.weg.net
AlternatorOutput
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