Instruction manual

Cascade Controller Option
Operation
modes
■ Standard Cascade Control Mode
In standard cascade control, the AFD with the Cascade
Controller option card installed controls a variable
speed motor and is used to stage additional constant
speed motors on and off. By varying the speed of
the initial motor, variable speed control is provided
for the system. This maintains constant pressure
while eliminating pressure surges, resulting in reduced
system stress and quieter operation.
The motors can be of equal or differing sizes. The
controller offers a selection of eight pre-defined pump
combinations. Selections allow mixing pumps of
100%, 200% and 300% capacity. This provides a
dynamic capacity range of 9 to 1. The AFDs internal
PID controller directs the cascade option card based
upon the feedback signal. The cascade controller
will continue operation of the constant speed motors
to meet demand should the drive trip.
D
e-stage Timer
A de-stage timer takes effect in standard control when
the drive runs continuously at minimum speed with
one or more constant speed motors running. Since a
variable speed pump at minimum speed adds no or
very limited flow to the system, it is advisable to stop
a constant speed motor and allow the drive to provide
the required flow. The de-stage timer is programmable
to avoid frequent staging of the constant speed motors.
When the master drive is the only one running, the
drive’s sleep mode can discontinue system operation
when not needed while staying ready to start on
demand. Variable speed control with fixed speed
motors optimizes energy consumption and avoids
damaging a pump running at near no flow condition
L
evel Control
With level control, multiple pumps can be used
to keep a constant level in applications such as a
buffer tank. Typically, a water level sensor provides a
feedback signal for the AFDs built-in PID controller.
Precise level control is maintained in response to
the system setpoint. With a cascade controller,
additional fixed speed pumps will be staged on or
off, as required, to maintain level control.
Level Control in Standard
Cascade Control Mode
■ Lead Pump Alternation
The function makes it possible to cycle the AFD
between the pumps in the system (max. 4 pumps).
In this way the use of all the pumps can be averaged
out and there is no risk that a pump gets stuck due
to corrosion and lack of operation. This reduces
maintenance, increased reliability and increases lifetime
of the system. The changeover of the AFD from one
pump to the other is controlled by means of a timer, so
that it is possible to set the desired time interval between
a change. Only 100% capacity pumps can be used.
MG.60.I5.22 - VLT is a registered Danfoss trademark
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