Frequency inverters run remote pumps from SWER supplies

Lenze SMV frequency inverters are providing the means for isolated rural communities in the Australian outback to save both water and energy at the same time. The SMV, supplied through Lenze's Australian distributor FCR, is at the heart of an innovative pumping system that matches the delivery of water to demand, rather than running the pump at full pressure irrespective of demand - which was the previous default operating mode. The new system overcomes the problems of operating on a SWER (Single Wire Earth Return) system, which is common in remote areas of Australia and other large countries.

With a SWER mains supply there is only a single supply cable, typically strung on poles above ground. In this case the supply is 480V AC. The return path for the power is literally the earth, that is soil, and this creates effectively a 480V single-phase supply. Previously special pump motors were used to suit the supply, adding to the installation costs. This fixed-speed motor/pump combination would be sized for the maximum flow corresponding to most of the community taps on at once, so every time a single tap is opened, full power was used to maintain pressure. As the starting currents for the motor can be 200-800 per cent of rated current depending on motor load, this would cause lights to dim and other household appliances to be adversely affected.

Lenze's alternative is to use a three-phase SMV sensorless vector drive connected for single-phase input. The inverter requires derating, as the input rating with single-phase current needs to be about twice the output current (allowing for a root-3 conversion plus a service factor). One immediate gains is that a standard three-phase motor can be used. In addition, the soft starting nature of the drive ends the problem of dimming lights. However, the biggest benefit is that by using the inverter's PID input, the pump can run to match demand by maintaining system pressure. The pump speed is varied and energy savings above 50 per cent can be achieved.

65 per cent saving in energy

The first customers for this new pump concept are situated in the regional areas of Northern Victoria and southern New South Wales. Adrian Villanti of FCR states: "On the strength of these two successes, we reckon that there is great potential for this system In addition to the savings in water usage, the reduction in energy usage is considerable, helping to ensure fast payback for the SMV-based pumping system. To put these savings in context, we were running a 2.2kW motor the pump of the latest application. At rated speed the motor uses all the 2.2kW of power. We measured it from the SMV's power usage parameter. When the motor was running at reduced speed, the speed required to maintain pressure flow requirements were measuring just 0.75kW of power usage." This represents a 65 per cent saving in the power required.

In addition to its water and energy saving benefits, the IP65-rated SMV also saves money on the installation, as a secondary control enclosure is not required. Even though the drive is usually installed in a shed or sheltered from the weather, there is still a need to protect the electronics from moisture, wildlife and other contaminants. The IP65 rating on the SMV delivers this protection and, for additional long-term reliability, a polycarbonate casing is supplied that does not degrade from the UV rays in sunlight. Furthermore, consistent operation is assured even if there are major fluctuations in the supply voltage because the SMV accepts inputs from 320 to 528V AC.

SWER supplies are common in many remote parts of the world including Australia, Canada, Brazil, Africa and parts of the USA. The robust Lenze SMV inverters with wide voltage tolerance provide an energy-saving alternative to direct-on-line pump systems. Installation costs are low and standard motors can be used. A steady water pressure avoids problems with pulsing and leakage, and the amount of energy saved is large, typically more than 50 per cent.

Follow the link for more information about the SMV frequency inverters..