Steven • Lenze-AC Tech: Follow these tips to get the most out of your drives:

• Always verify the motor full load amperage (FLA) rating and choose a drive with an equal or higher amperage rating.

• Evaluate the environment in which the drive will be located and choose an appropriate enclosure.

• Bigger is not always better — especially in torque control applications. Drives that are drastically oversized can have poor response in torque-control applications because here, the torque set point is only utilizing a small portion of overall torque resolution.

• Choose a drive that offers the right level of features for the application. Drives that offer a staggering range of features also typically introduce a staggering level of complexity. Look for drives that are feature-rich, but also userfriendly. A good benchmark for usability is the user manual. If the manual is several hundred pages long, then the drive is likely to be complex and commissioning could be arduous.

• Where productivity is paramount (in other words, you want quick commissioning or to be able to quickly replace drives in the event of failure) choose a drive with removable programmable memory. This allows drive preprogramming for fast installation and commissioning. It also allows transport of configurations and parameter settings from an old drive to a new drive in the event of failure. This is especially productive for OEMs needing to duplicate drive settings in every new machine they build. It can save many hours of programming time and eliminate human errors that are possible when programming by hand.

Rick • Baldor: Match the FLA of the motor to the drive. Do not oversize the drive unless the application requires it. Also, make sure to match the type of application (constant or variable torque) to the drive rating. Next, check the overload requirements of the application. Many drives allow for 150% current in the standard case — 50% overload for a full minute. If only 10% overload is required, then a normal-duty drive will work.

Be sure to check application torque performance requirements (both steady state and dynamic) and select the appropriate drive — either V/Hz, sensorless vector, full vector, servo, and so on. Don’t forget to consider the application’s environmental requirements. If a higher enclosure integrity is required (such as NEMA 12/IP55 or NEMA 4X/ IP66), some drives can provide this out of the box while others will have to be “enclosed” in a separate host enclosure to obtain these levels.

Avoiding drive disasters

What’s the worst that can happen if a motor or drive is not specifi ed or installed correctly?

Len • Bodine: As with other advanced speed control systems, initial setup of the drive and motor parameters is critical. Most inverters accept a 50/60 Hz line input. However, aside from this input capability, an internal setting for the motor frequency is often required as well. If this setting is not made, the motor or gearmotor overheats and can even burn out. Ac inverter-duty motor windings are often designed for either 50 Hz line (for most of Europe), or 60 Hz line (in North America); the inverter (ASD) needs to be con gured for the motor.

Steven • Lenze-AC Tech: The worst that can happen is a failure to the drive power section. This can happen in two situations: if line power applied to the drive is higher than the drive rating (i.e. 600 Vac line power is applied to a 240 Vacrated drive), or if the drive is miswired such that input line power is connected to the output terminals. Unfortunately, both of these scenarios are fairly common and are usually due to haste in installation. This is why drives manufacturers urge users to read and understand all the ratings and installation procedures before attempting to wire or commission the drive.

Another worst-case scenario occurs when load requirements exceed the rating of the drive and/or motor. Often, older speed-control technology such as variable-ratio belts or older dc drive systems are replaced with new drives. These are great applications for new ac drive technology, but care must be taken when sizing and selecting the ac motors and drives here. Designers must identify load speed and torque requirements and choose the appropriate drive and motor (and possibly gearing) to accommodate these.

For example, if the selected drive and/ motor cannot produce the torque needed, then the application may never perform to expected levels. There is also a high risk of overload. All drives have built-in protection for overload conditions, so there is no danger of damaging the drive; the danger is having a machine or process that cannot operate to its full potential, or possibly not at all.

Rick • Baldor: Here are a few of the mishaps that can happen with drives: The drive will not function in the application (in other words, will not start, will not run, shuts down, and so on); the drive functions, but the quality of the product being manufactured is not high enough (here, the wrong type of drive/motor is probably selected); the application appears to work, but experiences nuisance trips that impact productivity; the drive works, but only after advanced manual tuning efforts. The drive should run properly out-of-the-box after executing an autotuning routine.

Shad • Leeson: The worst scenario is loss of productivity or damage to equipment. Example: A customer uses one of our inverters on a machine that de-ices airplanes at an airport. The equipment was working just  ne when the temperature outside was above freezing. However, when the temperature dropped below freezing, the motor either wouldn’t start or wouldn’t operate properly. In the hangar, everything seemed to work  ne. After receiving a phone call from the upset operator, we determined that the inverter was acting up due to cold temperatures, as ambient temperature fell below the inverter’s recommended speci cation. We recommended that they install a heater by the inverter’s power board and this solved the problem.