ABB ACH550-UH User Manual page 175

ACH550-UH User's Manual
Group 81: PFA CONTROL
This group defines a Pump-Fan Alternation (PFA) mode of operation. The major
features of PFA control are:
• The ACH550 controls the motor of pump no. 1, varying the motor speed to control
the pump capacity. This motor is the speed regulated motor.
• Direct line connections power the motor of pump no. 2 and pump no.3, etc. The
ACH550 switches pump no. 2 (and then pump no. 3, etc.) on and off as needed.
These motors are auxiliary motors.
• The ACH550 PID control uses two signals: a process reference and an actual
value feedback. The PID controller adjusts the speed (frequency) of the first
pump such that the actual value follows the process reference.
• When demand (defined by the process reference) exceeds the first motor's
capacity (user defined as a frequency limit), the PFA control automatically starts
an auxiliary pump. The PFA also reduces the speed of the first pump to account
for the auxiliary pump's addition to total output. Then, as before, the PID controller
adjusts the speed (frequency) of the first pump such that the actual value follows
the process reference. If demand continues to increase, PFA adds additional
auxiliary pumps, using the same process.
• When demand drops, such that the first pump speed falls below a minimum limit
(user defined by a frequency limit), the PFA control automatically stops an
auxiliary pump. The PFA also increases the speed of the first pump to account for
the auxiliary pump's missing output.
• An Interlock function (when enabled) identifies off-line (out of service) motors, and
the PFA control skips to the next available motor in the sequence.
• An Autochange function (when enabled and with the appropriate switchgear)
equalizes duty time between the pump motors. Autochange periodically
increments the position of each motor in the rotation – the speed regulated motor
becomes the last auxiliary motor, the first auxiliary motor becomes the speed
regulated motor, etc.
Code Description
8103 REFERENCE STEP 1
Sets a percentage value that is added to the process reference.
• Applies only when at least one auxiliary (constant speed) motor is running.
• Default value is 0%.
Example: An ACH550 operates three parallel pumps that maintain water pressure in a pipe.
• 4011
INTERNAL SETPNT
• The speed regulated pump operates alone at low water consumption levels.
• As water consumption increases, first one constant speed pump operates, then, the second.
• As flow increases, the pressure at the output end of the pipe drops relative to the pressure measured at the input
end. As auxiliary motors step in to increase the flow, the adjustments below correct the reference to more closely
match the output pressure.
• When the first auxiliary pump operates, increase the reference with parameter 8103
• When two auxiliary pumps operate, increase the reference with parameter 8103
8104
REFERENCE STEP
• When three auxiliary pumps operate, increase the reference with parameter 8103
8104
REFERENCE STEP
Group 81: PFA Control
Range
0.0...100.0%
sets a constant pressure reference that controls the pressure in the pipe.
2.
2 + parameter 8105
REFERENCE STEP
Resolution Default
0.1% 0.0%
REFERENCE STEP
REFERENCE STEP
REFERENCE STEP
3.
1-171
S
1.
1 + parameter
1 + parameter
Parameters