2018.01 / a
7
Electric Power Generation
Installation and maintenance
R121
AVRs
5657 en -
The AVR builds up the generator voltage
from its residual voltage to rated voltage.
When the generator is loaded, the sensed
voltage decreases and generates an error
signal, which is required in order for the
closed loop system to work.
Depending upon the value of the amplified
voltage, the ramp intersects the amplified
voltage at a point which is early or late in the
half-cycle.
At this intersection point, a starting pulse is
produced to trigger the power device.
Only qualified personnel should replace/
work on the AVR.
Do not increase the voltage beyond the
rated voltage.
5 - AVR SETTINGS
5.1 - V - Voltage
This function is provided for setting the
voltage up to ±10% of rated voltage by
means of a single-turn potentiometer. Turn
the potentiometer clockwise to increase the
voltage and vice versa, once the rated
speed has been reached.
External voltage setting up to ±15% of rated
voltage with 2K potentiometer on terminals
R1 and R2.
5.2 - UF - Under frequency knee
point setting
This function is provided to protect the AC
generator from sustained low speed
operation through a potentiometer. The
AVR will reduce the voltage in proportion
with the speed below the defined value.
The procedure for setting the UF
potentiometer is as follows:
First select 50 Hz/60 Hz mode on the AVR.
Run the generator at 48.5 Hz for a 50 Hz
system (or 58.5 Hz for a 60 Hz system). Turn
the UF potentiometer until the UF LED
blinks. The potentiometer position at which
the UF LED blinks is the correct UF
potentiometer setting.
The factory default setting is 48.5 Hz.
5.3 - S
This function is provided to stop voltage
hunting by means of a potentiometer. Turn
clockwise to increase stability (to stop
oscillation). Turning too far clockwise will
result in a sluggish response and possibly
also oscillations.
The factory default setting is slightly
higher than critical damping.
6 - AVR CONTROLS
No.
Control
Function
Direction
1
V
Sets the generator output
voltage
Turn clockwise to increase output voltage
2
S
Stops voltage hunting
Turn clockwise to increase stability
3
UF
Sets the Under frequency
knee point
Turn anticlockwise to reduce the knee point
4
50 Hz/60 Hz
selection
Selects 50 Hz mode or 60 Hz
mode of operation
60 Hz operation is selected when kept open
Caution: Whenever the R121 AVR is used with low voltage 110 VAC generator (parallel
connection) for the first time, the AVR should be started with Voltage pot V in the minimum
position (fully anticlockwise). The R121 AVR can generate high voltage because the
voltage range is from 110 VAC to 270 VAC.
