Product category:
Industrial Drives/Controls
News Release from: ABB Automation Tech (Drives and Motors) | Subject: Comp-AC AC drives
Edited by the Engineeringtalk Editorial
Team on 22 March 2000
Comp-AC drives now suitable for pump/fan
control
A Pump and Fan Control (PFC) macro - which enables a single drive to control up to four motors - is now supplied as standard with ABB's Comp-AC drives for 2.2-37 kW (380-480 V).
A Pump and Fan Control (PFC) macro - which enables a single drive to control up to four motors - is now supplied as standard with ABB's Comp-AC drives for 2.2-37 kW (380-480 V) The combination of PFC macro and PID controller makes these drives a cost-effective solution for many applications using closed-loop control
This article was originally published on Engineeringtalk on 22 Mar 2000 at 8.00am (UK)
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Water supplies, chemical processes and air conditioning are typical applications where closed-loop control is utilised.
The task of the control system is often to maintain a stable pressure or rate of flow while the usage level varies.
This is generally achieved by using a drive with PID control: the drive takes a reference signal (setpoint) and an actual signal (feedback), and automatically matches the actual signal to the reference by adjusting the motor speed.
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Using the PFC macro, ABB's Comp-AC(tm) drives can control loads such as a pump (or fan, or compressor) station with one to four parallel pumps.
One motor is speed regulated and the others are on/off controlled.
In a water supply system using four pumps, for example, only the first (speed regulated) pump is run when consumption is low.
As consumption increases, the second (constant speed) pump is connected direct on line.
If demand continues to grow, the third, and then the fourth, pumps are also connected direct on line and operate at constant speed.
When consumption falls, the pumps are stopped one by one in the reverse order.
At all times the PID controller seeks to match the process actual value with the reference by adjusting the speed of the first pump.
The frequency limits at which the individual motors are activated are user programmable.
To utilise the PFC macro, contactors are used in addition to the drive to minimise the number of drives required and therefore save cost.
As one drive can control up to four motors, this solution is cost effective and has a shorter payback time, and it also helps to save space.
Other advantages include energy savings and easier maintenance, as individual pumps can be 'locked' by means of a digital signal for servicing purposes.
Furthermore, smoother pressure control means less noise in the pipes and less pipe damage due to abrupt pressure changes.
The PFC macro supplied with ABB's Comp-AC(tm) drives also includes an 'autochange' feature.
This alters the sequence in which the motors are operated, so that all equipment has an equal duty time, improving the operating lifetime of the motors.
The autochange switching interval is user-programmable.
The Comp-AC(tm) drives with PFC macro are supplied for 3-phase (380-480 V) operation in the range 2.2-37 kW.
ABB also supplies Comp-AC(tm) drives for 1- and 3-phase (200-240 V) operation in the 0.37-2.2 kW range.
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