Drives cut cost of compressed air

Avelair Compressors has switched to the new Unidrive SP for its variable-speed range, designed to save energy - typically over 30% compared with fixed speed alternatives.

Avelair Compressors has switched to the new Unidrive SP, from Control Techniques, for its variable-speed range, designed to save energy - typically over 30% compared with fixed speed alternatives.

"The choice of Unidrive SP, with its integral PLC, has enabled us to offer a more compact, more efficient and more price-competitive product", says Managing Director, Brian Wood, "and the user is assured of optimum efficiency at all times, with the compressor constantly matching output to demand".

Avelair Compressors of Bury-St-Edmunds, is a fast-growing manufacturer of rotary-screw compressors, with both standard products and with the capability to design and build systems to order.

The VSD variable speed range has been offered for two years, using a market-leading inverter drive coupled to a PLC, "but the need for a separate drive and PLC, plus the associated costs of the complex wiring were making the build costs expensive", explains Technical Director, Tim Shepherd, "with the necessity to add PLC modules and almost every unit requiring a new layout for the control cubicle, all of which added costs.

"We had all of the drives companies calling on us and were able to analyse what each could offer to meet our needs".

"Control Techniques was the only company that came back with a solution that offered us real cost-savings whilst meeting our specification".

"Now, with the Unidrive SP, we have been able to standardise on layout to a large extent and, by using the plug-in applications/PLC module, we've been able to eliminate the need for a separate PLC completely, whilst retaining all of the flexibility and functionality we had before".

Unidrive SP models from 11 to 35kW span the standard Avelair VSD range and each is supplied complete with an SM applications module that incorporates a powerful, fully programmable PLC.

It was Mark Dunn of local company Trax Circuits who undertook the programming of the Unidrive SP drives and their onboard PLCs.

"Although this was a first for me, I found the process very straightforward and logical using Control Techniques' software tools - CT-Soft for programming the drive and SYPT Lite for the PLC - both excellent programs - and the transition worked flawlessly".

The PLC is responsible for the complex procedures involved in starting up and closing down the VSD compressor to meet safety requirements as well as monitoring of line pressure, control faults (sticky solenoid valve or broken coupling for example) and the cooling fan as well as integrating the fault conditions from the drive itself to produce a visual warning of system or control faults and a 2000-hour service indication.

When starting, the compressor motor is accelerated to minimum speed, the cooling fan is started, and the inlet solenoid valve remains closed while the control system checks for fault conditions.

After 30 seconds, if the compressor internal pressure is above 1bar, the system goes into running mode.

In running mode, the compressor motor speed is controlled by the Unidrive SP in closed-loop speed control using its internal PID loop to maintain the set pressure.

If the compressor runs at minimum speed (ie no air required) for more than 5 minutes, the system automatically goes into idle mode to save energy.

Unidrive SP, the universal drive from Control Techniques, launched last year, is software configurable to five user-selectable operating modes.

With connectivity to most industry-standard networks and accepting 14 position-feedback protocols, Unidrive SP continues to be developed as a "solutions platform" with new features and software being added to give enhanced integration flexibility, functionality and communications.

The drive is packed with features including secure disable for safe machine maintenance, an optional LCD keypad that provides comprehensive on-board help and set-up "wizards", a Universal feedback interface option for synchronising and positioning applications and 48V operation for setup and lift rescue applications.

The Avelair range of VSD compressors can operate as stand-alone units or work in conjunction with fixed-speed units that provide the base-load required, with the variable speed unit providing additional air as demand requires.

"This saves energy in two ways", explains Brian Wood.

"Firstly, obviously the air system only provides as much air as is required".

"But, with fixed speed systems, the air pressure is usually set just above the required pressure - for example if 8bar is needed, the compressors are set to provide 9bar - to give a margin".

"With a system that includes a VSD compressor, the pressures would be set at 8bar - a further reduction of waste energy across the system".

"We are a small company, but growing rapidly", says Brian Wood, "with much of our success coming from our emphasis on customer service".

"We need to be certain that, with the sophisticated electronics that are needed for our VSD range, we can get support both during development and in the field".

"Control Techniques has demonstrated a good understanding of our needs and we have been impressed with the concept of the Unidrive SP".

"The plug-in PLC has saved space, eliminated considerable wiring, removed a potential source of failure and cut costs all in one go".

"We like other features too such as the through-hole mounting so that heat is dissipated from the cooling fins at the back of the panel".

"This means that the panel can be sealed against dirty environments and there's no problem of overheating through blocked filters".

"The small size of the drive has allowed us to reduce the size of the control cubicles on most of the units too and control panel layouts have been standardised".

"It's all so much simpler - a very elegant solution all round".

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