Troubleshooting series: Suboptimal load profile

It’s 2:49 pm, and this morning you went live with Motors@Work’s condition-monitoring service. You received a flurry of power-quality related notifications shortly after go-live. Now, your phone dings with a new notification: “Motors@Work detects Compressor #1 operating at 38% load; consider downsizing.”

Many of our customers receive this alert a few hours into our condition-monitoring service. This alert probably generates the most questions: “Why do I need to know my motor is running well within its operating range?”

Certainly, a low load falls well within the motor’s rated range. Yet because this motor is operating well within range, most of our clients are unaware of the additional costs associated with operating oversized motors.

Here’s how Motors@Work can help you identify, troubleshoot, and resolve load-profile issues that otherwise would have gone undetected without our timely condition-monitoring alerts.

Over the next quarter, you gather some more load-profile data on this motor. Its load never exceeds 50%, and most commonly falls between 28% and 40% of its rated range.

As shown in the figure below, motor efficiency falls off sharply at low loads — anything below 50% — meaning an increased percentage of the power you purchase goes to waste. That waste adds up, often making it economical to downsize the motor — or, at a minimum, install a variable speed drive.

When operating in this range, this 25-year-old, 150-Hp motor’s efficiency falls to 86.1% to 87.9%, far below its 93.4% nominal efficiency.

Motors@Work calculates that this motor’s weighted-average load over the past three months equals 32.4%, and at that point its efficiency is 86.5%. That means of the 42 kilowatts drawn when operating at this load, 5.66 kilowatts goes to waste, at a cost of $5,296 per year.

You review Motors@Work’s downsize recommendations and use its Motor Evaluation tool to create a detailed business case for downsizing. Replacing this 150-Hp motor with a $6,225, 75-Hp motor would reduce your energy expense by $3,770 per year, paying for itself within two years.

Armed with this data, you meet with the engineers who designed the plant and specified the equipment for Compressor #1, and find that the entire compressor system was designed to handle three-times the production that the plant has ever seen.

The engineers put together a business case for installing a drive, and ultimately decide to specify a slightly more expensive 75 Hp motor with integrated variable frequency drive that will pay for itself with energy savings in 25 months.

Motors@Work’s continuous, near-real-time condition monitoring algorithms watch for energy-dollar-consuming load profiles and send out content-rich alerts that facilitate troubleshooting — so you can operate your motor-driven systems at their lowest energy cost.

How will condition monitoring benefit your organization? Email Nicole at to learn more.

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