How can slip be optimized for different applications and industries that use VFDs?

1 Why slip matters

Slip is not necessarily a bad thing. In fact, it is essential for the induction motor to generate torque and operate. However, too much or too little slip can cause problems, such as overheating, vibration, noise, reduced power factor, and increased energy consumption. Therefore, it is important to choose the right VFD and motor combination that can match the slip to the load requirements and operating conditions of the application.

2 How to measure slip

Slip can be measured by comparing the synchronous speed and the actual speed of the motor. The synchronous speed is determined by the frequency of the power supply and the number of poles in the motor. The actual speed is measured by a tachometer or a speed sensor. The slip can be calculated as a percentage or a ratio of the difference between the two speeds and the synchronous speed. For example, if the synchronous speed is 1800 RPM and the actual speed is 1740 RPM, the slip is 60 RPM or 3.33%.

3 How to adjust slip

Slip can be adjusted by changing the frequency or the voltage of the VFD output. Increasing the frequency will increase the synchronous speed and decrease the slip, while decreasing the frequency will decrease the synchronous speed and increase the slip. Increasing the voltage will increase the torque and decrease the slip, while decreasing the voltage will decrease the torque and increase the slip. However, there are limits to how much the frequency and voltage can be changed without damaging the motor or the VFD.

4 How to optimize slip for different applications

Different applications and industries have different slip requirements depending on the type and characteristics of the load, such as constant or variable torque, steady or dynamic speed, and high or low inertia. For example, pumps and fans are constant torque loads that require low slip and high efficiency. Conveyors and compressors are variable torque loads that require moderate slip and variable speed. Crushers and mixers are high inertia loads that require high slip and high torque. Therefore, it is essential to select the appropriate VFD and motor parameters that can optimize the slip for each application.

5 How to monitor and troubleshoot slip

Slip, a crucial aspect of VFD operation, can significantly impact the performance and efficiency of electric motors. To monitor slip, one can use a VFD display, a multimeter, a tachometer, or a speed sensor. The VFD display shows frequency, voltage, current, power, and speed of the output; a multimeter can measure voltage and current of the input and output; and a tachometer or speed sensor can measure the motor's actual speed. By comparing these values, one can detect any deviations or anomalies from the expected range. Common causes of excessive or insufficient slip include incorrect VFD settings such as frequency, voltage, acceleration/deceleration/ramp time; loose/damaged wiring/connectors/terminals; faulty/worn-out motor components like bearings/windings/rotor bars; overloaded/underloaded motor/VFD; and environmental factors such as temperature/humidity/dust/vibration. To troubleshoot these problems, one should check and adjust VFD settings, inspect and repair wiring and motor components, reduce or increase load, and improve ventilation and cooling of the motor and VFD. By understanding how to measure, adjust, optimize, monitor and troubleshoot slip, you can improve your VFD skills and bolster applications that use VFDs.

6 Here’s what else to consider

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