Understanding the Causes of Heat Generation in Specialized VFDs and Solutions

Variable Frequency Drives (VFDs) are vital components in various industries, delivering precise control over electric motors. While VFDs offer numerous advantages, one common issue is heat generation, which can affect their performance and lifespan.

1. VFD and Motor-Related Issues:

Over time, the motor can experience issues like inadequate insulation, blocked bearings, or wear and tear, which result in higher current and increased heat generation. Likewise, complications such as wear and tear in the coupling between the motor and the load, unbalanced three-phase operation, or loose motor fixtures can lead to unusual noise and the generation of excess heat.

In some instances, aging VFD components, mismatched vector parameters with the motor, excessively configured torque enhancements, or excessively short acceleration and deceleration times can cause both the motor and the VFD to generate heat.

The connecting cables between the motor and the VFD should be kept to a reasonable length to avoid signal degradation and waveform distortion. When longer cables are necessary, specialized VFD cables and reactors should be used for proper signal management.

Certain applications that require rapid braking call for the selection of appropriate braking resistors and braking units based on the required braking power.

2. Prolonged Operation at Low Frequencies:

Designing the motor to operate below 8Hz should be generally avoided. Even with vector-controlled VFDs, it is crucial to steer clear of such usage. Working at low frequencies results in distorted waveforms, substantial deviation from sine waves, poor motor performance, and significant torque reduction leading to heat generation. Adjusting the gear ratio and increasing the VFD’s output frequency can help address this issue.

If extended operation at low frequencies is unavoidable, specialized VFD motors or forced cooling, including air and water cooling, can be used to lower the temperature.

3. Optimize Operating Environment:

In the past, economic constraints led many small factories to forgo the creation of dedicated control rooms, and even when control rooms were available, air conditioning was not installed. Nowadays, with improved economic conditions, it is entirely feasible to house VFDs and related equipment in controlled environments with air conditioning. This optimizes VFD temperatures, minimizes heat generation, extends lifespan, and reduces susceptibility to dust, thus presenting a worthwhile investment.

4. Ensure Correct Sizing:

The motor is the heart of the equipment and serves as the power source for nearly all loads. In the process of equipment selection and design, factors like the torque and power required by the load need to be carefully considered to choose the right motor power and torque. Undersizing the motor can cause it to operate in an overloaded state, leading to excessive heat generation.

Similarly, if the VFD’s specifications are undersized, it will be subjected to continuous current higher than its rated capacity, causing excessive heat and potential burnout. Choosing the correct sizes for both the motor and VFD is non-negotiable, and timely adjustments are essential, as continuing to operate an undersized system can lead to disruptions in production or even incidents like explosions or fires due to heating issues.

5. Equipment and Load Problems:

Mechanical equipment or loads may encounter anomalies such as damaged transmission gears or bearings, leading to increased resistance and subsequently higher motor output and potential motor lockup. In severe cases, motor stalling may occur, resulting in significantly increased current. Although most VFDs are equipped with overload and overcurrent protection to trigger alarms and shutdown, some situations may reach critical thresholds, or the VFD’s protection parameters might not be set correctly, causing unusual heat generation. In these situations, it is necessary to address the issues from the mechanical equipment and load perspectives.

For example, in cases where VFDs control liquid pumps or air blowers, a clogged pipeline or bends in the system can result in increased resistance, causing excessive current in both the motor and the VFD. It is essential to maintain and clean these systems promptly.