Industry News Display
2017-01-13 Plant Engineering
Motor current analysis provides information on existing issues such as loose connections, burned windings, and grounded windings.
By: David Manney, L&S Electric
Several factors contribute to faults in electric motors. These include poor connections, winding contamination and shorted turns with windings. Such faults start small and insignificant, but worsen over time when unaddressed. In these cases a motor failure may occur, which impacts business productivity and profits.
With this in mind, it is important to perform certain techniques that help prevent electric motor faults and failures. One of these techniques is motor current analysis. This monitors the health and performance of your electric motor.
Motor current analysis facts
One process of evaluating the condition of an electrical motor is motor current analysis. An analyst performs this type of testing to ensure a motor's health.
It is also worth noting that motor current analysis checks for certain failure modes. These modes include:
- Loose motor foundation
- Belt defects
- Degradation or breakdown of the circuitry
- Current imbalance and loading problems
- Rotor eccentricity
- Rotor damages
- Power quality disturbances, such as power factor anomalies, voltage imbalance, and harmonics concerns.
There are three winding phases performed in a motor current analysis. The analyzer measures the impedance, inductance and winding resistance. Moreover, other areas are measured, such as the insulation resistance to ground and the phase angle. In a typical healthy motor these areas must remain in perfect balance, otherwise it is possible for a fault or failure to occur.
Online and offline motor current analysis testing
Motor current analysis testing may either be done online or offline. With online testing, the analyst conducts the tests while the motor is in use under normal conditions. Current analysis and voltage analysis are two categories of online testing.
These involve checking for:
- Broken or loose rotor bars
- Rotor eccentricity
- Coupling or misalignment belt problems
- Cracked end rings.
Voltage analysis includes the determination of power quality issues such as voltage imbalances and harmful harmonics, to name a few.
The offline testing mode requires de-energizing the motor before performing the test, which is usually preferred for the resistance to ground measurement. The measurement of the capacitance, impedance and inductance provide information on the windings' condition. For instance, the inductance helps show turn-to-turn shorts, while the capacitance to ground determines winding contamination levels. When there are changes in the capacitance and inductance, this can impact the impedance of the AC circuit's total resistance.
Motor current analysis aims to prevent motor faults and failures. The entire process takes only about 15 minutes to provide information on existing issues, such as loose connections, burned windings and grounded windings. If none of these problems are present, there is no need to worry because the motor is in excellent condition.