Pump And Fan Cascade Control - Honeywell NXL Series Applications Manual

Page 56 (68)

4.11 Pump and Fan Cascade Control

The P ump and F an C ascade control can be used to control one variable speed drive and up to 3
auxiliary drives. The PID controller of the frequency converter controls the speed of the variable
speed drive and gives control signals to start and stop the auxiliary drives to control the total flow.
In addition to the eight parameter groups provided as standard, a parameter group for multi-pump
and fan control functions is available.
As already its name tells, the Pump and Fan Cascade control is used to control the operation of
pumps and fans. The application utilizes external contactors for switching between the motors
connected to the frequency converter. The autochange feature provides the capability of changing
the starting order of the auxiliary drives.
4.11.1 Short description of PFC function and essential parameters
Automatic changing between drives (Autochange & Interlockings selection, P2.10.4)
The automatic change of starting and stopping order is activated and applied to either the auxiliary
drives only or the auxiliary drives and the drive controlled by the frequency converter depending
on the setting of parameter 2.10.4.
The Autochange function allows the starting and stopping order of drives controlled by the pump
and fan automatics to be changed at desired intervals. The drive controlled by frequency
converter can also be included in the automatic changing and locking sequence (par 2.10.4). The
Autochange function makes it possible to equalize the run times of the motors and to prevent e.g.
pump stalls due to too long running breaks.
•
Apply the Autochange function with parameter2.10.4, Autochange .
•
The autochange takes place when the time set with parameter 2.10.5 Autochange interval,
has expired and the capacity used is below the level defined with parameter 2.10.7,
Autochange frequency limit .
•
The running drives are stopped and re-started according to the new order.
•
External contactors controlled through the relay outputs of the frequency converter connect
the drives to the frequency converter or to the mains. If the motor controlled by the frequency
converter is included in the autochange sequence, it is always controlled through the relay
output activated first. The other relays activated later control the auxiliary drives
This parameter is used to activate the interlock inputs (Values 3 & 4). The interlocking signals
come from the motor switches. The signals (functions) are connected to digital inputs which are
programmed as interlock inputs using the corresponding parameters. The pump and fan control
automatics only control the motors with active interlock data.
•
If the interlock of an auxiliary drive is inactivated and another unused auxiliary drive available, the latter
will be put to use without stopping the frequency converter.
•
If the interlock of the controlled drive is inactivated, all motors will be stopped and re-started with the
new set-up.
4
Description of parameters
Honeywell