Courtesy of PdMA, here are four tips regarding electric motor testing:
Click the tip title to expand.
[toggle state=”closed” title=”High Inductance on a DC Armature? “] During testing if DC armature inductance values are higher than expected, when compared to previous tests or like motors, stop what you are doing and re-evaluate the circuit under test for energized equipment. Occasionally we get reports of the DC field being left energized. An energized DC field will have a dramatic influence on the DC armature readings. [/toggle]
[toggle state=”closed” title=”Failure Criteria“] When developing a testing program, it is imperative to define “failure” criteria for each component to be tested. For example, a “Voltage Failure” can be defined as a system voltage that exceeds upper or lower boundaries. A 480 Volt system may have failure points of +/- 5% (504V/456V respectively), which, if exceeded, constitutes a “Voltage Failure”. Although typical components such as voltage, current, % imbalance, etc. are considered, any system parameter being measured that is determined to be value added should have “failure criteria” defined. For online analysis, some of these may be Total Harmonic Distortion (THD), Harmonic Voltage Factor, Power Factor, etc. For offline analysis, some parameters that may be considered for failure criteria are: Capacitance-to-ground (CTG), Resistance-to-ground (RTG), winding or system resistance, etc. The PdMA MCEGold software establishes default alarm set-points for the failure criteria of each measured value. Remember though, MCEGold allows you to adjust these values as necessary to better fit your applications and failure criteria. [/toggle]
[toggle state=”closed” title=”Tools vs. Solutions “] Sometimes predictive maintenance technologies are used as tools, not always solutions. By definition a Tool is a device that aids in accomplishing a task, whereas a Solution is an action or process in solving a problem. Problems will arise, and the earlier the problematic condition is identified the less expensive it is to correct. The question then is whether or not the tool identifies the problem. Tools can perform tasks but if the person using the tool is not solution oriented then the data derived from the tool will not be utilized properly to prevent a future catastrophic failure within the plant. Establishing an education plan and building a data analysis and communication process around a predictive tool can turn the tool into a solution. Applying this strategy creates a proactive culture within the plant and combined with operational, design, procurement, installation, and storage practices ensures the success of the plant. [/toggle]
[toggle state=”closed” title=”Check Your Current Probes Before Testing! “] When performing Motor Current Signature Analysis you must verify that you are using the correct probes for the application, verify the software being used has the proper probe settings, and verify the probes are in the proper setting and direction. One component of test data to look at when analyzing current signature is current imbalance. Depending on the trend characteristics and load level, an increasing current imbalance on any of the phases may indicate early stages of stator problems such as: Improper Stator Winding, Shorted Stator Turns, Shorted Stator Laminations, or High Resistance winding connections. When this occurs, a closer inspection of the motor history may be necessary along with additional off-line test data to determine the severity. [/toggle]
You are invited to submit an Electrical Motor Testing Tip of your own and receive a free PdMA mug or hat if we publish it. Contact Lou .