VFD insights

• The proliferation of modern power electronics and advanced internet of things monitoring solutions have changed the concept of how motors are managed and controlled.
• A manufacturing plant’s electricity use can be reduced by using VFDs.

The U.S. Department of Energy reports that 26% of the country’s total retail sales electricity usage comes from the industrial sector. Approximately 60% of that electricity consumption within an industrial facility is used by electric motors, representing a cost center for consumers and a significant portion of total national energy usage.

Electricity billing for large industrial customers typically consists of two parts: demand (peak kilowatts or energy per second averaged over a 15-minute window) and energy consumption (kilowatt-hour). Variable frequency drives (VFDs) for motors can help reduce both power and energy charges.

Equipment such as pumps — which use electric motors — are started and stopped using relatively simple contactor starters in many plants. On startup, the motor draws between 6 and 8 times its rated full load amperage, depending on the motor type. This can cause voltage sag in the supply bus and contribute to high peak demanding loading and motor overheating on multiple starts.

In the past, a commonly used method of inrush mitigation involved installing soft starters, which reduced the inrush current by around 30%. However, contemporary VFD technology has decreased in size and increased in efficiency to the point where it is becoming competitive with soft starters in cost.

Moreover, using a ramped approach, VFDs with advanced control schemes such as vector control can vary torque and speed to a motor, softening the mechanical stresses on the motor and load, reducing mechanical fatigue and lengthening the equipment’s lifetime.

Modern VFDs come equipped with advanced algorithms designed to optimize energy usage according to load demands. These algorithms dynamically adjust operational settings such as voltage and frequency, aligning them with the load requirements to minimize energy consumption.

Figure 1: An electrical engineer reviewing a start/stop switch for a variable frequency drive. Courtesy: Hedgehog Technologies

This marks a significant departure from older VFD models that operated on fixed or less flexible parameters. Unlike older VFDs, which often had efficiencies below 85%, certain manufacturers now boast efficiencies reaching up to 98% at full load. This advancement is particularly noteworthy given the constraints of previous transistor technologies, where a compromise was necessary between low-voltage fast switching and higher-voltage slower operations.

Additionally, it’s increasingly common to find VFDs integrated with sophisticated regenerative braking capabilities, enabling them to capture and repurpose energy otherwise lost during deceleration or braking. This feature proves particularly advantageous in applications characterized by frequent start-stop cycles.

Furthermore, contemporary VFDs boast improved designs and components aimed at reducing electrical harmonics, thereby enhancing power quality and mitigating inefficiencies.

Monitor and control energy use with VFDs

Many larger motors involved in process control are accompanied by a suite of encoders, temperature sensors and vibration transmitters. Recent generations of VFDs offer onboard input/output (I/O) and modular expansions to the power electronics controller, enabling them to function as remote I/O for associated instrumentation.

Specifically, this allows any communication network-linked drive installed remotely from a distribution center to marshal control information into internet protocol or other communications protocols. By minimizing cabling, this approach reduces and simplifies material and installation costs while also reducing cable tray fill, which can be at a premium in older plants.

Figure 2: Reviewing new motor monitoring instrumentation. Courtesy: Hedgehog Technologies

High-bandwidth networking of drives offers additional benefits beyond the reduction of physical installation. Real-time monitoring of motor parameters such as current, temperature, and vibration can identify problems before they start to negatively affect the process.

In a plant environment, unexpected downtime means lost production and is a significant cause of stress for production staff. Detailed data collection over time can identify trends and predict possible future failures before they happen. A common use of this technique would be to identify motors experiencing increased temperature, indicating internal issues or a buildup of contaminants on the motor itself.

Should a spontaneous fault occur, an accurate picture of the conditions leading to the fault can heavily aid in root cause analysis. As machine learning and artificial intelligence evolve, they will become a commonly used tool in the arsenal of preventative maintenance and control, reducing time lost to unexpected outages.

Enhancing motor control

The evolution of VFDs and the integration of advanced internet of things monitoring technologies have significantly modernized motor management in industrial settings. Contemporary VFDs enhance motor control through precise torque and speed adjustments, extending equipment life and reducing mechanical stress. They also improve energy efficiency dramatically, with capabilities such as regenerative braking and high-efficiency operational modes contributing to substantial reductions in energy consumption and electrical costs.

Figure 3: Electrical engineer doing final inspection on a motor control center for variable frequency drive bank. Courtesy: Hedgehog Technologies

Additionally, onboard data acquisition and sophisticated monitoring tools enable proactive maintenance strategies, reducing downtime and anticipating failures before they occur. This paradigm shift in motor management boosts operational efficiency and supports a sustainable industrial environment by optimizing energy use and minimizing waste.

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