WHEN TO USE DISTRIBUTED DRIVES – AND WHEN NOT TO

Power electronics used to be situated at a distance from the machine in a control cabinet. Now, however, inverters are often mounted near the motor, and integrated units combining drive mechanics and electronics open up new possibilities.

Drive control units installed centrally or in the field offer their respective advantages and disadvantages, all depending on the application conditions. In mixed environments, it is important that users do not have to learn different operating procedures.

Moving drive electronics from the control cabinet to the machine can reap considerable economic advantages over centrally installed power electronics. The components have a 20 to 30% higher purchase price, but that is outweighed by up to 40% lower engineering costs, up to 60% savings during installation and commissioning, and maintenance costs reduced by up to 50%. Over the product lifecycle, the savings typically amount to about 30%, depending on the size and type of application.

Facilities with many drives used to require centrally installed freq - uency inverters in control cabinets (the drives, of course, were installed near the machine or application).

And since the control cabinet with the drive electronics was the starting point for cabling all motors or geared motors in the field, star wiring was the automatic result.

Materials handling facilities in particular, such as loading zones in high-bay warehouses and belt or roller conveyors, benefit from integrated drive solutions not requiring long motor cables and large numbers of control cabinets.

INTEGRATED UNITS

Integrated drive units can be completely wired and tested before installation, reducing design comm - issioning time. Any remaining control cabinets are much smaller and cooler and easier to standardise.

Shielded motor cables are either not required at all (with direct motor mounting), or very short (with wall mounting near the motor).

Integrated drive units in the field are also easily accessible for service personnel and diagnostics can be performed directly at the site. Due to pluggable connections, many units can even be exchanged without an electrician.

When connecting remote geared motors with a centrally situated control cabinet, the maximum motor cable lengths must not be exceeded. Shielded cables might be obligatory. Long motor cables necessitate motor chokes. Alongside the power lines, a number of other wiring lines including signal cables for motor brakes, temperature sensors, incremental encoders, and other components must be laid - and all these diverse components need to be made compatible.

But despite the obvious drawbacks, there is often no way around centrally installed control cabinet inverters. In extreme environmental conditions, the electronic drive technology must be somewhere safe and enclosed in a robust housing. Drives installed too close to each other, especially those above 22kW, make using distributed inverters difficult, since the temperature can quickly rise above their limit. Series machines that are shipped in one piece, will keep on profiting from centralised drive technology as the most costefficient solution.Certain applications require cabinet inverters to be accessed and operated along with the controller.

In all such cases, even large drive components such as motor chokes or mains filters can be integrated in control cabinets without problems.

In distributed systems, on the other hand, space for all kinds of optional equipment (such as I/O and circuit breakers) is considerably limited.