Are electrical motor faults and failures a prominent cause of downtime in your facility? Then you should be engaging in methods to increase the lifespan of your equipment.
In our latest series on Condition Monitoring, we’re unpacking the various means of predictive maintenance and equipment preservation.
In Part 1, we start by reviewing the various benefits of a condition monitoring system, the commonly used techniques and the different types of condition monitoring systems that are implemented.
In Part 2 and Part 3, we unpack vibration monitoring. We progress in the series with Part 4 – an over view of motor circuit analysis. We end the series with Part 5 - residual current monitoring.
Motor Circuit Analysis (MCA), as one of the techniques implemented in condition monitoring, assists in preventing downtime by improving the lifespan of electrical motors.
In this article, we give an overview of motor circuit analysis – the types of testing it involves, as well as the potential faults that it can help to detect.
What is Motor Circuit Analysis?
Motor Circuit Analysis (MCA) is a diagnostic technique used in predictive maintenance. It is a de-energized low voltage test method that assesses the health of the motor and the associated cabling. It allows maintenance personnel to pinpoint the exact defects inside the electrical components of motors. A predictive maintenance expert will use vibration analysis or infrared imaging to detect faults, but these techniques alone may not determine the exact cause.
Can MCA be used on all types of motors?
MCA can be used on both AC and DC electrical motors. MCA can be initiated from the motor control centre (MCC) or directly at the motor. The advantage of testing at the MCC is that it allows for the entire electrical portion of the motor system to be evaluated. This includes the connections and the cables between the test point and the motor.
What faults can MCA detect in a motor?
As mentioned previously, MCA is implemented to assess the health of a motor. It assists in identifying the following faults:
- Resistance anomalies
- Winding contamination
- Winding shorts
- Insulation to ground
- Imbalances
- Rotor and back iron anomalies
These faults are found through the detection of electrical imbalances in the motor and the detection of insulation degradation. Imbalances that exist in the motor will create stray, circulating currents through the motor. These circulating currents create excessive heat in the motor, which accelerates the degradation of insulation. Ultimately, this could lead to inefficient operation as well as ineffective control techniques in certain motors. When a motor experiences insulation degradation, the result is reduced motor life and unsafe operating conditions.
What are the different types of MCA testing?
Motor circuit analysis consists of online and offline testing. Online testing, as the name suggests, is performed when the motor is operating in normal conditions whilst offline testing is done when the motor is de-energized.
MCA online testing is subdivided into current analysis and voltage analysis. Current analysis focuses on the rotating components such as loose or broken rotor bars, cracked end rings, rotor eccentricity, misalignment, and coupling/belt problems. Voltage analysis is performed to identify power quality issues such as harmful harmonics, voltage imbalances and under/over voltages.
MCA offline testing is commonly used for the measuring of resistance-to-ground. Measuring electrical characteristics such as impedance, inductance and capacitance will indicate the condition of the windings. The measurement of the inductance is a great indication of turn-to-turn shorts.
The measurement of capacitance to ground determines the amount of winding contamination (water, dirt, dust, etc.). A change in these parameters affects the impedance (total resistance of an AC circuit). These characteristics are measured phase-to-phase, as well as phase-to-ground, and then compared to each other. The percentage change obtained is then compared to the baseline to identify motor circuit defects.
Why should regular testing be scheduled?
Certain tests can be performed once-off, whilst others are required to be done on a regular basis to determine the trend and understand the defect progression. It is thus best to test these motors on a set schedule. It will enable you to properly trend these characteristics and gives the reliability program the best chance to identify motor circuit defects.
Does your facility experience downtime more regularly than you would like?
A comprehensive, failure modes-driven maintenance strategy for electric motors will help to reduce costly stoppages.
CHAT to us to find out more!