Single Pump Control (Pfc) - ABB ACQ580 Firmware Manual

Program features 63
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Single pump control (PFC)

The Single pump control (PFC) is used in pump systems consisting of one drive and
multiple pumps. The drive controls the speed of one of the pumps and in addition
connects (and disconnects) the other pumps directly to the supply network through
contactors.
The PFC control logic switches auxiliary motors on and off as required by the
capacity changes of the process. In a pump application for example, the drive
controls the motor of the first pump, varying the motor speed to control the output of
the pump. This pump is the speed regulated pump. When the demand (represented
by the process PID reference) exceeds the capacity of the first pump (a user defined
speed/frequency limit), the PFC logic automatically starts an auxiliary pump. The
logic also reduces the speed of the first pump, controlled by the drive, to account for
the addition to the total system output by the auxiliary pump. Then, as before, the PID
controller adjusts the speed/frequency of the first pump in such a way that the system
output meets the process needs. If the demand continues to increase, the PFC logic
adds further auxiliary pumps, in a similar manner as just described.
As the demand drops, making the speed of the first pump fall below a minimum limit
(user defined as a speed/frequency limit), the PFC logic automatically stops an
auxiliary pump. The PFC logic also increases the speed of the drive controlled pump
to account for the missing output of the stopped auxiliary pump.
The Single pump control (PFC) is supported in external control location EXT2 only.
Autochange
Automatic rotation of the start order, or Autochange functionality, serves two main
purposes in many PFC type setups. One is to keep the run times of the pumps equal
over time to even their wear. The other is to prevent any pump from standing still for
too long, which would clog up the unit. In some cases it is desirable to rotate the start
order only when all units are stopped, for example to minimize the impact on the
process.
The Autochange can also be triggered by the Timed function (see page 72).
Interlock
There is an option to define interlock signals for each motor in the PFC system. When
the interlock signal of a motor is Available, the motor participates in the PFC starting
sequence. If the signal is Interlocked, the motor is excluded. This feature can be used
for informing the PFC logic that a motor is not available (for example due to
maintenance or manual direct-on-line starting).