Motors and Drives

Davidson Water Gets Pumped Up on Motor Management

Advanced Energy experience has shown that with good motor management policies in place, motor failure rates can be reduced to 3-5% per year. If motors are not managed, failure rates can run as high as 15% per year or greater. The more motor failures that are experienced per year, the greater will be the downtime and maintenance costs associated with these failures.

Background

Davidson Water, Inc., is one of the largest rural water systems in the United States. It serves portions of four North Carolina counties with 43,000 connections and 18 pumping stations, with 64 motors between 5 and 200 horsepower, 26 water tanks and 1500 miles of water lines. Davidson Water's 12 million gallon a day surface water plant is currently being expanded to 20 million gallons a day.

Problem

Davidson Water wanted to review its motors to decrease costs and improve reliability as part of its expansion. After surveying the pumps motors, Advanced Energy's motor team made a variety of motor replacement recommendations based on the various motor applications.

Advanced Energy Assistance

At Davidson Water, Inc., twenty-four motors were surveyed using Advanced Energy's portable InSitu device. InSitu testing revealed overloading problems with several motors and identified good candidates for replacement based on efficiency improvements.

Three 40 hp Davidson Water motors (two existing, one new energy efficient replacement) were taken to Advanced Energy for full dynamometer tests. These laboratory tests revealed that the two existing motors ran 12.5°C and 17.7°C hotter respectively than the replacement. Testing at Advanced Energy has shown that new energy efficient motors on average run about 15°C cooler than their older standard efficiency counterparts. This directly relates to the life expectancy of a motor.

Solution

Advanced Energy recommended using existing new energy efficient motors to replace existing motors found to be overloaded, purchasing correctly sized motors for application in the expansion project, and setting a schedule for replacing specific motors at failure. The expected benefits of Advanced Energy's recommendations include a $32,000 annual savings, three year payback on a $100,000 marginal investment, and improved reliability based on proper motor sizing.

At the same time these calculations do not include any consideration of other economic or intangible benefits (e.g., improved reliability or reduced overtime labor for motor changeouts at night and on weekends) that will result from replacement of the older, hotter running and/or overloaded motors. Other intangible benefits will include fewer interruptions in water service.

Specific recommendations for motor management in water systems:

Pay attention to your motors. Since electric motor driven pumps comprise the largest electrical costs in water systems, it is important for water system operators to be knowledgeable about pumps and motors and monitor and evaluate the specific pumps and motors in their systems.
Be aware that motors supplied as part of a pump package are sometimes selected by the pump supplier with more consideration to low first cost (which he has to pay) than to low life-cycle cost (which you have to pay). This can result in a purchase of motors that cost more to operate (lower efficiency) and may not last as they could due to higher operating temperature and/or overloaded operating conditions (smaller is cheaper).
Modern energy efficient motors are available today that outperform the best motors that were available even 10 or 15 years ago. A logically planned and executed motor evaluation and replacement program can provide benefits to you and your water customers that will extend into the next two decades.

For More Information

Contact Advanced Energy at (919) 857-9000 or moreinfo@advancedenergy.org.