by Frank Healy, Fluke Power Quality Products
Electric motors transfer electrical power to mechanical rotational forces that are the muscle of the industrial world. Measuring and analyzing those forces—
mechanical power, torque. and speed—as well as power quality
characteristics—are important to assessing performance of
These measurements can not only help predict failure
and thus help avert downtime, they can also help quickly
determine whether additional inspections—such as vibration
testing, shaft alignment analysis, or insulation testing—are
needed to corroborate the findings.
Traditionally, obtaining accurate motor analysis data required costly equipment shutdowns to allow for the installation of mechanical sensors. Not only can it be extremely
difficult (and sometimes impossible) to properly install mechanical sensors, the sensors themselves are often cost
prohibitive and introduce variables that decrease overall
Modern motor analysis tools make it easier than ever to
troubleshoot direct on-line electric motors by significantly simplifying the process and reducing the number of components
and tools necessary to make critical maintenance decisions.
For instance, the new Fluke 438-II Power Quality and Motor Analyzer enables technicians to discover electrical and
mechanical performance of electric motors, and evaluate
power quality by measuring the three-phase input to the
motor, without mechanical sensors.
Here are FOUR KEYS to understanding overall motor efficiency and system performance.
1. Poor power quality has a direct
correlation with motor performance
Power anomalies such as transients, harmonics, and
unbalance can cause critical damage to electrical motors.
Transients can cause serious damage to motor insulation
and can also trip overvoltage circuits, causing monetary
losses. Harmonics, which create distortion of both voltage
and current, have a similar negative impact and can cause
motors and transformers to run hot, potentially leading to
overheating, or even failure.
In addition to harmonics, unbalance can occur in both
voltage and current, and is often the root cause of elevated
motor temperature and long term wear including burnt windings. Using three-phase measurements on the motors input,
technicians capture the broad range of data that can help
indicate the overall state of power quality health helping them
better troubleshoot the root causes of motor inefficiency.
2. The impact of torque on overall
performance and efficiency
Torque is the amount of rotational force developed by a
motor and transmitted to a driven mechanical load, while
speed is defined as the rate at which a motor shaft is rotating.
A motors torque is the single most critical variable that
characterizes instantaneous mechanical performance. While
traditionally mechanical torque has been measured with
mechanical sensors, the Fluke 438-II calculates torque using
electrical parameters (instantaneous voltage and current) in
combination with motor rating plate data. Measuring torque
can give a direct insight into the state of health of the motor,
the load and even the process itself. By ensuring the motor
is running at the torque level within the stated specification
ensures reliable operation over time and minimizes maintenance costs.
3. Motor rating data and expected performance
Motors are classified by NEMA (National Electrical Manufacturers Association) and IEC (International Electrical
Commission) rating data. These ratings include key electrical
and mechanical parameters such as rated motor power, full
load current, motor speed, and nominal full load efficiency
and provide a description of the overall expected motor
performance under normal conditions.
Using sophisticated algorithms, modern motor analysis
tools are able to compare three-phase electrical measurements with the rated values to provide insight into the motors
performance under real load conditions. The difference
between running a motor within the manufacturer’s specification or outside those parameters is significant.
Running motors in mechanical overload conditions causes
stress to motor components including bearings, insulation
and couplings decreasing efficiency and leading to premature failure.
4. Motor efficiency has a direct impact
on the bottom line
More than ever, industry is striving to reduce energy consumption and increase motor efficiency through “green”
initiatives. In some countries these green initiatives are
One recent study said motors consume 69% of all industrial electricity and 46% of all global electricity consumption.
By identifying poorly performing or faulty motors and either
repairing or replacing them, you keep energy consumption
and efficiency in check.
Power quality and motor analysis provides data to identify
and confirm excess energy consumption and inefficiencies.
Plus, the same analytics can verify the improvements upon
repair or replacement. In addition, knowing the condition of
motors and being able to intervene before failure also reduces
exposure to potential safety and environmental incidents.
Power quality and motor data are not static. As conditions
change, so do measurements. Motor failures were recently
identified by 75% of respondents to an industry survey as
causing 1 to 5 days of plant downtime a year, and 90% of
respondents reported failures of larger 50 hp motors with
less than a month warning (36% said they had less than
a day warning).
Collecting baseline data is a first step to a predictive or preventive maintenance program. Begin with accurate baseline
readings of motors and then take subsequent measurements
and track trends.
For the best results, the measurements are made under
consistent, repeatable operating conditions, ideally at the
same time of day, in order to create like-kind comparisons.
Such methodology can be adopted with power quality data
(harmonics, unbalance, voltage, etc.) as well as motor analytics (torque, speed, mechanical power, efficiency).
By adding electrical and mechanical analysis of electric
motors to your tool belt you can ensure that you have the
data you need to help keep your plant up and running.
Modern motor analysis tools make it easier than ever to troubleshoot direct on-line electric motors by signifcantly simplifying
the process and reducing the number of components and tools necessary to make critical maintenance decisions.
of all industrial
46% of all
faulty motors and
either repairing or
you keep energy
effciency in check.
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