DER2 digital regulator instruction manual - rev. 02 - pag. 26
As you can see in figure 9, when the estimated temperature (represented by the continuous line) reaches the
threshold value, the reduction of excitation current (and consequent drop in voltage generated) brings about
the stabilisation of the temperature near a limit value.
Curve Description
L[45] (alt1, I=In) : value read at location L[45] with a certain alternator
(1)
L[45] (alt2, I=In) : value read at location L[45] with a second alternator of a different type
(1)
L[45] (alt2, I>In) : value read at location L[45] with the second alternator during overloading
(2)
T[45] (alt1, I=In) : value that would be read at location L[45]with the first alternator, without protection
(1)
T[45] (alt2, I=In) : value that would be read at location L[45] with the second alternator, without protection
(1)
T[45] (alt2, I>In) : value that would be read at location L[45] with the second alternator during overloading,
without protection
(2)
.
L[55]=12970 : Represents the value of the current limit set using the AMP trimmer or the P[22] parameter for
the first alternator
L[55]=21617 : Represents the value of the current limit set using the AMP trimmer ot the P[22] parameter for
the second alternator
3. EXCITATION OVERCURRENT
3.1 Description
The DER2 regulator is equipped with an excitation (main rotor) winding temperature estimator. An estimate
of the temperature (in relative values) is available in real time (and it can be read) in location 45; in the lower
part of the main window of the DxR terminal software there is a graphic representation of location 45. The
progress of the temperature is of the exponential type (see figure 9).
Through parameter P[22] or the AMP trimmer, it is possible to define a limit (which involves intervention of
alarm 5) to the excitation voltage and therefore to the temperature.
The function of this alarm is not only to signal an excessive temperature, but it also has an active function in
reducing the cause. In fact, an adjustment ring takes control of the voltage generated when the threshold
set is exceeded: This reduces the voltage to the point of reducing the excitation current by a value
compatible with the ability of thermal dissipation of the machine. The stability of the regulation in case of
overexcitation alarm, if necessary, may be adapted to the application by varying the value of parameter 28.
For an increased protection of the electrical machine, the excitation overcurrent protection was extended to
the whole speed interval (frequency) of the alternator, particularly for the lower frequencies, to a preset
threshold (56.7Hz with the jumper inserted between the 25 and 26 terminals of connector CN1, if enabled,
or, otherwise, if the 50/60, 49Hz setting is enabled) the protection intervenes with an effective threshold
(relative to the one set through the AMP trimmer or parameter 22) reduced proportionally to the frequency.
The extent of this reduction depends on parameter 29 which is by default set to an adequate value for the
standard alternators, used in three-phase in nominal voltage.
An increment of the value of P[29] determines a bigger reduction of the intervention threshold, based on the
frequency reduction, a decrease of the value of P[29] determines a smaller reduction of the intervention
threshold.
fig. 10
0
5000
10000
15000
20000
25000
30000
0
10
20
Location 45
time [sec]
L45(alt1,
I=In)
L45(alt2,
I=In)
L45(alt2,
I>In)
T45(alt1,
I=In)
T45(alt2,
I=In)
T45(alt2,
I>In)
L[55]=12970
L[55]=21617
WARNING:
If the magnetic gain of the alternator is high, unstable events may occur when the pro-
tections intervenes, therefore it is necessary to adjust parameter 28 (usually by reducing its value).
W
hen the alternator works with reduced load and speed, overheating, which is dangerous to the integrity of
the machine, might occur, if the overcurrent protection threshold is not sufficiently reduced when reducing the
frequency.
(1) Nominal load and 90% of nominal frequency
(2) with load greater than the nominal one
