Back to Basics

There are four features that the customer will generally specify when looking into an adjustable frequency drive. These are:

Let’s take a brief look at each feature.

Bypass

Adding a bypass to the AF drive allows the motor to be transferred via a set of contactors to the utility line, to allow maintenance to be done on the drive.

There are two bypass types available:

Line Reactor

The customer may specify a line reactor for the application.

Get all the pertinent information from the customer and from the product catalog. Then, refer to the section on impedance (earlier in this module) to determine whether a line reactor is needed for the customer’s application.

Control Signal

The customer may specify a control signal type or types for the application.

Determine the customer’s requirements and decide whether analog or digital inputs and outputs are more appropriate.

Output Filter

When the cable length for an application exceeds the acceptable length in the product catalog, you will need to add an output filter (also called a “dv/dt” filter) to the circuit. The output filter will reduce the Voltage Transients before they can damage the motor.

The customer may specify the need for an output filter if the cable length is excessive, but may not be aware of this requirement. In any case, you should verify whether an output filter is needed for the customer’s application.