Motor testing assesses the integrity of a motor through the use of computer-supported equipment or tools that monitor trends within the motor.

Motor testing assesses the integrity of a motor through the use of computer-supported equipment or tools that monitor trends within the motor. The main objective of motor testing is to reveal hidden problems and prevent unnecessary failure. Specific to electric motors, motor testing evaluates static parameters like insulation, wire damage and electrical current leakage, as well as more dynamic parameters such as distortion, temperature fluctuations and balance.

Mechanical motor testing includes things like looking into the cracks of a motor's rotor and lamination sheet makeup. While each motor test applies to most alternating current (AC) or direct current (DC) motors, each testing method depends on the construction and application of the motor in question.

Motor testing is regulated by the Institute of Electrical and Electronics Engineers (IEEE) through standards such as IEEE 43 – Insulation Resistance and Polarization Index, IEEE 56 – Maintenance AC Hipot Test, IEEE 95 – DC Hipot Test, and IEEE 400-2001 – The Guide for Field Testing and Evaluation of the Insulation of Shielded Power Cable Systems. These standards are constantly reviewed and improved when deemed necessary by the board.

Motor testing is often used in a preventive maintenance or reliability-centered maintenance program. Motor testing with a preventive maintenance program can test motors while they're operating in their normal environment under normal loads to confirm they're running at acceptable or optimum limits. Motor testing often alludes to issues before visual inspection makes them apparent.

Making motor testing a part of a maintenance program is important because once a motor endures damage, it is often irreversible (referred to as core damage); this leads to the motor not running with the same efficiency as it once did, if at all. Motor testing lends itself to multiple benefits, including:

While the ins and outs of motor testing can be intimidating and a bit complex, knowing the basics along with using modern motor testing tools and equipment can greatly simplify the task of testing motors.

Modern motor testing tools make taking readings and analyzing a motor's current condition fairly simple once you understand how each tool works. Many testing tools are equipped with multifunction capabilities, incorporating more than one device into each tool. Having a basic toolkit with the following tools is a good place to start.

DMMs are considered a multifunction tool because they combine multiple single-function tools such as a voltmeter, ammeter and ohmmeter. This tool includes a display where measurements can be read in real time, buttons for selecting a variety of functions (depending on the model), a dial for choosing primary measurement values (amps, ohms or volts), and input jacks where test leads are inserted.

The jaws are made of ferrite iron (usually encased in plastic) and designed to detect, concentrate and measure a magnetic field that is generated by current as it flows through a conductor. Clamp-on ammeters have become multifunction testers, with some models having capabilities similar to a DMM. They are popular because they're safe and convenient, allowing technicians to forgo cutting wires to insert a meter's leads, since the clamp-on ammeter's jaws don't need to touch a conductor to take a measurement.

The amount of current depends on the applied voltage, the system's capacity, the total resistance and the temperature of the material. Generally, the higher the current, the lower the resistance. The insulation resistance value displayed on the screen is a function of three independent subcurrents: conductive leakage current, capacitive charge leakage current and polarization absorption leakage current. Routinely using a megger in your maintenance program is a good way to guarantee your circuits are safe.

Spot thermometers work by using field of view (FOV) and distance-to-spot ratio (D:S). The D:S is the ratio of the distance to the object you're measuring and the diameter of the temperature measurement area. The larger the ratio number, the better the instrument's resolution and the smaller the area that can be measured.

There are numerous motor testing techniques, especially when it comes to electrical motor testing. Most of these fall under one of two categories: online or offline testing, or static or dynamic testing. A good predictive maintenance program typically uses both.

Online dynamic testing is done while the motor is running. It gives technicians data on the power quality and operating condition of the motor. Dynamic testing equipment should be able to collect and trend all data essential to electric motors. This includes power condition, voltage level, voltage imbalance and harmonic distortions, current levels and imbalances, load levels, torque and rotor bar signatures, etc. Analyzing the collected data from online testing can reveal problems through indicators such as power condition, motor condition and performance, load assessment, and operating efficiency.

Offline static testing should be used on a regular basis to determine how the components within a motor (windings, rotor bar, etc.) are functioning as well as to perform a current and voltage analysis. Static testing often finds problems like broken or loose rotor bars, issues with end rings, an unequal air gap between the rotor and stator (eccentricity), and misalignment. As the name suggests, this type of motor testing is done when the machine is stopped. Static testing assesses things like resistance/insulation resistance, high-potential (HiPot) tests, polarization, surge tests and more.

Nearly half (48 percent) of all motor failures are due to electrical issues, according to a survey by the Electric Power Research Institute (EPRI). Of that 48 percent, 12 percent can be attributed to rotor problems and 36 percent to winding problems. To help mitigate these failures, a variety of motor tests can be performed on electric motors. Some of the most common include:

Proper rotational testing is done with a phase rotation meter. For instance, if you're installing a three-phase motor, the meter will have six leads on it — three on the motor side (lead side) and three on the line side (supply side).

This test is typically done using a digital multimeter. By touching the red (positive) lead of the multimeter to the positive end of the windings and the black (negative) lead of the multimeter to the negative end of the windings, a reading will appear on the screen in ohms. This is the resistance.

In addition to these electric motor-specific tests, other common motor testing methods can be used such as vibration analysis (especially for bearings), thermography and shaft alignment testing.

Three-phase motors (induction motors) are designed to run on the three-phase alternating current (AC) power used in most industrial applications. AC electricity switches direction (from negative to positive) and back numerous times a second. For example, the electricity in your home alternates back and forth from negative to positive, 60 times per second. These changes in power occur via a smooth continuous wave called a sine wave. Three-phase AC has three sources of AC power which are all out of phase with each other, meaning no two AC waves are ever at the same point at one time.

Three-phase motors are commonly used in commercial and industrial settings because of their ease of operation, low cost, low maintenance, speed variation, durability and high starting torque. Ensuring the health of a three-phase motor puts into practice many of the testing methods mentioned above.