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UNDER FREQUENCY KNEE ADJUSTMENT
AVR BL4-U incorporates an underspeed protection circuit (UF) which gives a volts/Hz characteristic
when the alternator speed falls below a presettable threshold known as the "knee" point.
The UF knee adjustment is preset at factory at the 47Hz on a 50Hz system or 57Hz on a 60Hz
system. Selection of 50 / 60Hz can be made using the Switch 1.
Figure 3, shows the curves for voltage variation as a function of frequency variation.
For nominal frequency operation, UF is disabled. When rotation decreases (e.g. when shutting
down), excitation decreases, reducing the output voltage of the alternator.
The pre-set "knee" point can be altered, by UF trimpot, according to the needs of each application.
Under frequency “knee”: a) 50 Hz system, b) 60 Hz system
PROTECTION FUSE
The fuse is used to limit the input supply current in order to protect the alternator field.
AVR BL4-U regulator possesses a rectifier that controls the field voltage of the alternator.
For the maximum field voltage, the supplied current at input Aux N is half of the field current, and
the maximum current of the fuse should be a little more than half of the current supplied by the
regulator. The fuse must be: Fast action, 5x20 mm, 3,15A/250V.
TRIMPOTS
Trim pot functions
V = Voltage adjustments;
ST = Stability adjustments;
UF = UF “knee” adjustments.
Trim pot adjustments
V = Turning clockwise, increases voltage;
ST = Turning clockwise, speeds up response;
UF = Turning clockwise, increases the UF protection limit.
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