MOTORS AND INVERTERS: ALL WRAPPED UP

Dave Wilson saw all the major vendors demonstrate integrated motor/inverter packages at this year’s Hannover Fair

At the Hannover Fair, a plethora of vendors, including ABB, Siemens, Danfoss and Brook Hansen, Rockwell Automation and Leroy Somer, all demonstrated or discussed integrated motor drive units.

The rationale for the new breed of motor /inverter combination is simple: they allow a complete variable speed motor unit to be installed as simply as a standard motor. The user simply needs to install the motor, connect it up to a power supply and it is ready for operation.

In terms of inventory, the integral motor can also replace all the standard motors in its size group. Motors can be used in different ranges simply by changing the settings.

The integral motor may be an ideal solution for ventilation applications that call for the permanent monitoring of air flow, pressure or volume. Air conditioning systems for residential properties and office buildings, roof ventilators and hot air stoves are just a few of the applications for which they are suited.

Pump, fans and compressors have traditionally been adapted by manufacturers in terms of size and performance to suit existing standard motors with constant speeds and standardised outputs. Now, however, the designer has the opportunity to design a product from scratch with a variable speed alternative.

The integral motor provides an alternative to throttle, gear or drive belt regulation of the motor output. Compared to applications where output is throttled to vary the output from a constant speed motor, for example, a variable speed motor can save energy. For instance, a fan running at half its speed only consumes a quarter of the energy it does at full speed. In addition, throttling devices are noisy, while the new motor/drives are apparently not.

Because motor speed is controlled by a stand-alone frequency converter, the need for cabling, inverter control rooms, ventilation equipment and shielded cables between the inverter and motor are eliminated. This allows for simpler installation and commissioning. No special installation is required for the converter.

What is more, because there is no need for an expensive screened cable between the inverter and the motor, the amount of electrical noise that the package as a whole generates is minimised. Many of the packages include an RFI filter to meet the CE requirements.

All of the units that have presently been announced, with the exception of the ABB unit, have placed the inverter on top of the motor. ABB chose to mount its inverter on the back, citing the fact that as heat from an operating motor rises, particularly when shut down after heavy loads, it would adversely affect the frequency converter if it was located on the top of the motor.

Rather than building the inverter as an integral part of the motor, Rockwell Automation have chosen a modular approach that allows the inverter section, developed by Reliance Electric, to be separated from the motor easily. Rockwell says that this approach allows an easier mix and match capability between the inverter and the motor itself.

Because less than 5% of the motors shipped in the world presently are variable speed, it would appear that the new inverter/motor drive combinations have got plenty of opportunity to make inroads into the market.

Figure 1: Danfoss and Brook Hansen have joined forces to produce this integrated motor/drive unit

Figure 2: The Siemens Combimaster variable speed drives are rated from 1.5kW to 7.5kW

Figure 3: The constant speed motor can be easily replaced by the variable speed motor with integrated inverter

{{Table 1: All the new inverter/drive combinations at a glance

Manufacturer Power range Telephone Enter

Brook Hansen/Danfoss 0.55kW to 4kW (01484) 422150 500ABB 0.75kW to 7.5kW 0161-445 5555 501Siemens 1.5kW to 7.5kW 0161-446 5424 502Rockwell Automation 0.75kW to 4kW (01908) 838800 503LeRoy Somer 0.75kW to 2.2kW 0181-756 7000 504}}