89
CASCADE CONNECTION
4.6.2
Par 148 = 1
In this mode the system manages the cascade so that the min-
imum number of modules is on.
The first difference in relation to mode 0 refers to the logic with
which the modulation of Depending modules within the cas-
cade is managed.
In fact, while each thermal module modulates with its own PID
in mode 0, no more than two Depending modules modulate
with the same criteria in mode 1, while the remaining modules
operate at maximum power. The diagram is represented in the
following figure:
Managing
Managing
PID
PID
100%
100% 100%
100% 100% 100%
PID
PID
PID
PID
PID
PID
PID
Managing
Managing
Managing
Practically speaking, if more than two thermal modules are on,
only two thermal modules are controlled via PID, while the oth-
ers receive a signal to move to maximum power.
The second difference refers to the start-up/shutdown rules of
the individual modules.
In any case, the start-up and shutdown rules are managed ac-
cording to the indications shown in the previous graph. The dif-
ference is that it is also possible to have start-ups/shutdowns of
the Depending modules in the "balancing" zone.
This additional start-up criteria (valid in the balancing band
only) ensures that a module is started-up when any one of
the two modules controlled by a PID adjustment has reached
a threshold power (Par 82) once a specific wait time defined by
Par 75 has elapsed.
Similarly (still within the balancing band), a module is shut-
down if both modules controlled by a PID adjustment have
reached a percentage of power which is below the minimum
power threshold (Par 83) once a specific wait time defined by
Par 75 has elapsed.
4.6.3
Par 148 = 2
In this mode the system manages the cascade so that the max-
imum number of modules is on.
This mode is similar to mode 0 apart from the start-up and
shutdown rules.
In this case the rules based on the information illustrated by the
previous graph are still valid, with the following differences (in
any case, always applicable to the "balancing" band only):
To add an additional depending module, the managing module
evaluates whether the sum of the power (calculated on the ba-
sis of the fan speed) of all the active thermal modules is greater
than the product between the number of the active depend-
ing modules increased by one and the minimum power value
(Par 152) increased by a hysteresis value (defined by Par 153). [
Σ
(
P1,P2,…Pn) > (n+1) * (Par 152) + (Par 153)].
To shutdown a depending access, the managing module eval-
uates whether the sum of the power (calculated on the basis of
the fan speed) of all the active thermal modules is less than the
product between the number of the active depending modules
and the minimum power value (Par 152). [
Σ
( P1,P2,…Pn) < (n) *
(Par 152)].
9
We must consider that the percentage of power varies from
a minimum of 1% and a maximum of 100% and therefore,
the parameter values 152 and 153 are not to be taken as the
percentage of absolute power.
