TEST & MEASUREMENT FEATURE
Testing motors under live operating conditions
Electric motors can account for up to 70 per cent of the total energy consumed in an industrial plant. Given their critical nature for industrial processes, the cost of downtime associated with failed motors can be very significant. Ensuring that motors are efficient and operate reliably, is one of the most important tasks that engineers face on a daily basis
the users are typically specialist organisations. In traditional motor testing methods ‘real world’ operating conditions are not taken into account.
ELECTRIC MOTOR PARAMETERS I
n many circumstances, energy
efficiency can mean the difference between profitability and financial losses. Since motors consume such a significant portion of energy in industry, they have become a prime target for generating savings and maintaining profitability. Additionally, the desire to identify savings through efficiency improvements, and reduce dependency on natural resources, is driving many companies to adopt industry standards such as ISO 50001. The ISO 50001 standard provides a framework and requirements for establishing, implementing and maintaining an energy management system, for the purpose of delivering sustainable savings.
TRADITIONAL MOTOR TESTING The traditional method for measuring electric motor performance and efficiency is well defined, but the process can be costly to set up and difficult to apply in working processes. In many cases, motor performance checks require a complete system shutdown, which can result in costly downtime. The traditional method of measuring motor performance first requires technicians to install the motor into a motor test bed. However, a motor test bed that is able to cover a wide range of motors is expensive and
Electric motors are designed for specific kinds of applications depending on the load, and as such, each motor has different characteristics. These characteristics are classified according to IEC standards and have a direct effect on the operation and efficiency of the motor. Each motor has a nameplate that details key motor operating parameters and efficiency information, in accordance with IEC recommendations. The data on the name plate can be used to compare the requirements of the motor against the true operating use mode. When comparing these values you may
learn that a motor is exceeding its expected speed or torque specification, in which case the motor’s life may be shortened, or premature failure may occur. Other effects, such as voltage or current unbalance and harmonics associated with poor power quality, may also decrease motor performance. If any of these conditions exist the motor must be ‘derated’, which could result in a disruption to the process if not enough power is produced.
REAL WORLD OPERATING CONDITIONS Testing electric motors on a motor test bed usually means the motor is being tested under the best possible conditions. Conversely, when the motor is used in service, the best operating conditions do not typically exist. These variances in operating conditions all contribute to the degradation of the motor’s performance. For example, inside an industrial facility there may be loads installed that have a direct effect on the power quality, causing unbalance in the system, or causing harmonics. Each of these conditions can severely affect motor
A NEW APPROACH The Fluke 438-II Power Quality and Motor Analyser provides a streamlined and cost effective method for testing motor efficiency, while eliminating the need for external mechanical sensors and costly downtime. The Fluke 438-II has the full capability to measure power quality, while also measuring mechanical parameters for direct-on-line electric motors. Using data from the motor name plate, coupled with three-phase power measurements, the 438-II calculates the real time motor performance data including speed, torque, mechanical power and efficiency, without the need for additional torque and speed sensors. The 438-II also directly calculates the motor derating factor in operating mode. While the traditional methods for
measuring electric motor performance and efficiency are well defined, they are not necessarily widely implemented. This is in large part due to the cost of downtime associated with taking motors, and sometimes entire systems, offline for testing purposes. The Fluke 438-II provides extremely useful information that until now has been extremely difficult and expensive to acquire. Additionally, the Fluke 438-II uses its advanced power quality analysis capabilities to measure the state of power quality health, while the system is in real operating mode. This gives technicians the ability to decrease downtime, and an opportunity to trend motor performance over time, giving them a better picture of overall system health and making it possible to see changes that may indicate motor failure.
Fluke
www.fluke.co.uk
ELECTRICAL ENGINEERING | DECEMBER/JANUARY 2017 21
performance. In addition, the load being driven by the motor may not be optimal or consistent with the motor’s original design. Capturing these anomalies can be difficult and time-consuming, making effective troubleshooting problematic.
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