Thursday, 14 August 2014

John Guthrie, Energy Efficiency Manager, ABB writes: Selecting variable-speed drives (VSDs) is all about getting the rating correct and making sure it matches the motor, right?

Well, up to a point, yes. But there are also some other vital considerations that don’t always get the attention they deserve. These five drive selection tips will help you ensure you get exactly the right drive for the job.

1. Does the drive have the correct enclosure and environmental ratings?
The right enclosure is all important. Do you need to specify Ingress Protection (IP), NEMA, UL Type enclosures? Match the needs of the application with the right enclosure, either with a stand-alone VSD with the proper enclosure rating, or putting the VSD inside another enclosure.  And don’t forget - the VSD must also give the required current at the application’s altitude and ambient temperature.

2. Does it offer the features needed to meet the application’s demands?
The VSD must have software features that match the application’s requirements. Hardware, such as inputs and outputs, feedback and communications, are all vital to perform the application. Need tight process control? Then a sensorless vector or flux vector variable frequency drive may be needed - these allow a high level of accuracy when controlling speed, torque and positioning.

3. Does the drive have the motor control performance demanded?
The VSD must give the necessary torque at the required speeds to match the requirements of the application. Consider Direct Torque Control or DTC. This control method gives VSDs an excellent torque response and as well as induction machines, it can control synchronous machines such as wound rotor, permanent magnet and reluctance motors.

4. Do you need a simple keypad, no keypad or full text assisted keypad?
The user must be able to control the VSD in the way they need. This could mean several things – he may need to alter a few parameters, choose from a menu of production recipes or alter times of operations to suit usage patterns. Choose the VSD that offers the right input method for the job.

5. Does the drive have the correct level of safety?
The old saying is ‘safety first’ and the VSD you choose could be responsible for safety in your system. Be careful how you chose the safety functions since a safety function may be inappropriate. For example, safe torque off (STO) would not be used as the only safety function for a crane hoist.

Bearing these tips in mind when planning your next application will help you get the most appropriate drive for your needs, keeping capital costs and operating expenses to a minimum.

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