Many equipment and appliance manufacturers use California Instruments precision power sources to test products that use electric motors. These appliances and systems may include either AC or DC motors, sometimes combined with electronic controls. These motors power appliances such as vacuum cleaners and refrigerators, and commercial equipment, such as conveyors, elevators, and other industrial equipment. California Instruments power sources, such as the single phase output 3001iX Series, 5001iX Series, and 15001iX Series and the three-phase 15003iX Series are perfect for testing these products.
Electric Motor Types and Applications
Electric motors can be categorized by type, application, or even by horsepower. DC motors are often used in applications where speed control is required, or where only battery power is available. High-power DC motors are used in many public transportation systems such as subways. Brushless DC motors, either permanent magnet or Switched Reluctance (SR) types are found in appliances, such as vacuum cleaners.
AC motors can also be large or small. Many home appliances are driven by single-phase AC motors, while high power, three-phase induction motors, including wound-rotor and squirrel cage motors, are the “workhorses” of industry.
When speed control is required, solid-state, variable-frequency AC drives (VFD) are a popular choice. Because motors that use modern pulse-width modulated (PWM) variable speed drives are more energy efficient than standard induction motors, they are finding their way into many drive systems, even those that require constant speed and variable torque.
Electric Motor Test Requirements
A test plan for a motor-driven appliance or system must, first and foremost, ensure that the motor reliably converts electrical into mechanical energy efficiently. Secondarily, but nearly as important, it must do so without affecting other (electrical) equipment. This means that while efficiency and operating reliability tests are the most important tests that manufacturers run, regulatory requirements play a critical role as well. It is unacceptable for a motor or its electronic drive to cause problems for other equipment which may be connected to the same line voltage.
In many cases, choosing the right power source can make running these tests easier. For example, when running overall efficiency and efficiency vs. load tests, using a power source that can take the place of the drive allows you to assess the effect of different fundamental frequency and V/Hz settings on motor performance. In addition, choosing a power source with measurement capabilities allows you to quickly determine input power under various test conditions.
When evaluating overall efficiency, it is necessary to establish where losses come from. This may include motor-related losses such as stator I2R losses, core loss, friction loss, and stray losses. You can perform the tests described in IEEE-STD-112, IEEE Standard Test Procedure for Polyphase Induction Motors and Generators. Test Method C—Duplicate Machines can be implemented using California Instruments power sources and two identical motors.
In addition to power consumption and efficiency, it is also important to measure and line distortion caused by the motor or the controller. Current harmonics, power factor, and the influence of line voltage variations may need to be determined.
Inrush and operating current levels may also be important, and you may have to measure these parameters under various load and line voltage conditions. It may be necessary to establish current/torque at full load, locked-rotor current, and the current at breakdown torque. For AC drives, it may be necessary to evaluate the start-up behavior with different current limit settings.
For some tests, you can use California Instruments power sources to emulate variable speed drives. You can easily vary the frequency and voltage, and even sweep these values, as shown in the figure above. Using the power source allows you to easily measure motor operating temperatures for low speeds, check required skip ranges, determine the required peak current levels, and even test braking and reversed rotation capabilities.
For more information, download Application Note #114, Testing Electric Motor Driven Equipment.