DER2 digital regulator instruction manual - rev. 02 - pag. 27
4. Underspeed
4.1 Description
For speeds lower than a programmable threshold, the machine voltage is no longer constant, but is
regulated proportionately with the frequency at a ratio, which is also programmable, as shown in figure 10a e
10b. The intervention threshold depends upon:
the status of jumper 50/60 (terminals 25 and 26) if enabled from the Settings/UFLO&LAMS Menu.
the status of the 50/60 setting in the Settings/UFLO&LAMS Menu
the position of the Hz trimmer if enabled from the Settings/Potentiometers Menu
the value entered at parameter P[21] (ref. Settings/UFLO&LAMS menu or area Transmit/Receive of
Settings/Advanced menu).
Activation of the function with voltage proportionate to the frequency is signalled by activation of alarm 6
(visible from the DER2 Terminal control panel and due to a change in the flashing indicator light).
Parameter P[21](equivalent to the Hz trimmer) sets the Underspeed protection intervention threshold; if this
is set on 26214, the protection cuts in at 48 Hz (if the 50/60 jumper and 50/60 flag in the Settings/
UFLO&LAM menu are not present) or at 57,5 Hz (if the 50/60 jumper is enabled or the 50/60 flag is active in
the Settings/UFLO&LAM Menu). Values between 0 and 26214 proportionately lower the threshold,
respectively to 40 Hz and 48 Hz; values between 26214 and 32767 proportionately raise the threshold,
respectively to 50 Hz and 60 Hz.
Once the underspeed protection has intervened, the frequency is proportionately reduced, as indicated in
figure 11a and 11b.
3.2 Calibration with a supervision unit
To calibrate the overload protection, when the machine is cold, perform the following procedure:
1) turn the AMP trimmer fully clockwise (if enabled from the Settings/Potentiometers menu) or write 32676
in location 22
2) feed the alternator an overload having cosphi = 0.8 or cosphi = 0 respectively equal to 125% or 110% of
the nominal load
3) read the value displayed at location 45 2 minutes after overload application
4) if the AMP trimmer is enabled turn it anti-clockwise until the value read at location 55
becomes equal to the
value read at point 3 (location 45); the operation is simplified a lot by using the DxR terminal software
which provides, in the lower part of the main window, a graphic representation of the time evolution of loca-
tions 45 (“real excitation”, red line) and 55 (“excitation threshold” - yellow line): the intervention threshold
must be calibrated so that the yellow line should intersect the red line when, from the application of the
overload, the time specified at point 3 has passed.
5) if the AMP trimmer is not enabled, write the value read at point 3 (location 45) in location 22.
6) Alarm 5 should set off (visible both on the main panel of the DxR Terminal and through a change in the
LED flash) and the voltage should start to decrease
7) If the load is removed, alarm 5 disappears after a few seconds and the generator voltage goes back to the
nominal value.
3.3 Calibration without a supervision unit
NB: this calibration can be performed only if the AMP trimmer was previously enabled.
To calibrate the overload protection, perform the following procedure:
1) turn the AMP trimmer fully clockwise
2) feed the alternator an overload having cos phi = 0.8 or cos phi = 0 respectively equal to 125% or 110% of
the nominal load
3) after two minutes slowly turn the AMP trimmer anti-clockwise until you get a reduction of the generator's
voltage value and the activation of alarm 5 (visible through a change in the LED flash)
4) Calibrate the AMP trimmer so as to get an output voltage value of 97% of the nominal value: alarm 5 is still
active.
5) If the load is removed, alarm 5 disappears after a few seconds and the generator voltage goes back to the
nominal value.
NOTES: If the machine is used in single phase or voltages different to the ones set by the pro-
ducer, a recalibration of the overexcitation protection might be necessary.
If it is not possible to apply the prescribed overload, the overexcitation condition may be simulat-
ed by adequately increasing the regulated voltage so as to get an excitation current equivalent to
the overload current.
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