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The hidden gems inside an AC drive

Dismissing variable speed drives (VSD) as nothing more than motor controllers is to miss the huge cost-saving potential built within the product

Panels containing pump system control gear are used extensively throughout the water industry. Within these panels are VSDs and a host of additional components including thermostats used for controlling cabinet fans to save standby losses, timer relays, contactors and door-mounted HMIs.

The panel may include a moving iron meter indicating amps or volts instead of true process values such as water flow rates. And it might include a mini PLC for decision-making or for controlling the system to behave at different times of the day, or to monitor variables in the field, against which decisions are made.

Yet all these components, and more, are often not needed as they are already built within the VSD.
You don’t need the thermostat (saving around £200) as the drive will tell you when its own fans are running, thereby switching on cabinet cooling fans automatically.

Timer relays (saving around £180) are not required as the drive has a real-time clock, from which timers can be set to either start or stop an application running, depending on operating conditions.
You no longer need the contactor as the drive has built-in safe torque off (STO); a SIL 3 PL e stop function that is safer than contactors.

Using the drive’s fieldbus means you can utilise un-used drive I/O to gather telemetry onto the fieldbus system, without having to purchase additional remote I/O stations.

The VSD removes the need for external HMI displays to be cut into the door of cabinets. Today’s VSD keypad offers 21 variables, displayed via graphs, charts and meter readings that speak the language of any application.

There is no need for any analogue meters as the keypad has a view that looks like an analogue moving iron meter, scaled and labelled in the correct customer units.

The keypad negates the need for cabinet furniture such as start/stop buttons, as these can be programmed into the keypad. Costs are saved as the sheet metal worker no longer needs to cut holes for an external HMI.

Text editing means that if you are pumping water, for instance, you don’t need to read the motor’s speed in rpm but rather the actual flow rate in litres per second with scaling factors.

The VSD can be customised to present the language of the application or industry and change warnings and trips into plain, simple language.

This eliminates the need to connect an HMI to Modbus, saving substantial costs. It also simplifies technical support as the language of the customer is one the drives engineer can easily relate too. An OEM using this facility can now dispatch a true customer-ready drive package.

Users need to ask: What are they doing with the VSD? Why install a host of additional components in the panel when they are already contained in the drive? Why struggle to manage the cabinet cost, when understanding what’s inside the drive could save up to 50 per cent of the cost of cabinet components?


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