Motor circuit analysis (also known by its acronym MCA) is a very effective method for assessing the condition of a motor. This analysis can detect voltage imbalances and/or insulation degradation before they show obvious signs of failure, which makes MCA a valuable predictive maintenance and condition-based maintenance tool.

 

First, a clarification: Motor Circuit Analysis vs. Current Analysis

Motor circuit analysis should not be confused with motor current analysis, which is also known by the acronym MCA. To avoid misunderstanding, we will refer to current analysis as MCSA, for “motor current signature analysis”. While MCSA is also an important test for assessing motor condition, it is part of a larger group of tests that are included in MCA.

 

How does motor circuit analysis work?

The basic motor circuit is divided into 3 RLC circuits (circuits with a resistance, an inductor, and a capacitor, connected in series or parallel), which are responsible for its resistance, inductance, and electrical capacitance.

 

Motor circuit analysis measures these electrical characteristics of the motor, phase-phase, and phase-phase-ground. Each of the phases must have the same characteristics, as they are manufactured identically. In addition, it includes the measurements of electrical impedance, phase angle, the current/frequency ratio, the dissipation factor, the static test value, and the dynamic signature of stator and rotor.

 

The set of these tests makes it possible to identify defects, anomalies, and imbalances in the motor circuit. In particular, phase-phase tests detect problems that go unnoticed in the megohmmeter or multimeter. In fact, it is estimated that multimeters only identify around 10% of faults.

 

Voltage imbalances create leakage currents. In turn, these currents lead to overheating. Motor overheating accelerates the degradation of motor parts and insulation, which shortens the life of the equipment and deteriorates safety conditions. The variations and amplitude of the waves are a good indicator of the origin of the problem or degraded zone.

 

In addition, it is important to note that MCA is divided into two types. One is an analysis of the engine “offline”, while it is switched off. The other is an “online” analysis, while it is running, which breaks down between current analysis and voltage analysis.

 

  • Current analysis: focuses on the rotating components of the motor, which can be misaligned, loosened, or broken, rotor eccentricity, among others. 

 

  • Voltage analysis: which assesses resonance frequencies, voltage, and voltage imbalances, such as voltage being too high or too low. 

 

With this in mind, we can use motor circuit analysis in different contexts:

 

  • MCA when starting the equipment: if we look at the bathtub curve, we know that it is not strange for equipment to fail even when they are new, due to manufacturing, installation, or assembly errors. MCA can be used à priori to understand if a new piece of equipment, or one that has been recently repaired, is in good condition.

 

  • During the equipment’s lifetime: during the equipment’s lifetime, MCA serves two functions. If used regularly, trends and patterns allow the detection of wear and tear, overheating, or excessive vibration before failure or downtime (predictive maintenance). For example, a variation of more than 3% in the static test value indicates deterioration.

 

Circuit analysis can also be performed occasionally if a problem is suspected. Here are some examples of situations that justify an MCA:

  • you do not know the electrical condition of the motor of a particular piece of equipment or of an old motor;
  • you want to test a motor that was repaired recently and has not recovered its usual performance;
  • you want to understand whether you need to repair the whole motor or just some components.

 

What are the benefits of motor circuit analysis?

Now that we have a better understanding of how motor circuit analysis works, we can highlight the main advantages of MCA:

  • Improve equipment reliability;
  • Increase the useful life of the equipment;
  • Decrease safety risks in installations;
  • Assessing the state of the equipment even while it is switched on, in a non-invasive way.

 

Applications of motor circuit analysis

Most equipment has some form of electric motor. MCA can be applied to:

  • AC and DC motors;
  • traction motors;
  • generators; 
  • servomotors. 

 

This means it has applications in virtually any industry, including petrochemical, automotive, pharmaceutical, aerospace, wood processing, bottling machines, food processing, cement production, oil extraction, mining, and many others. 

 

What is the return on investment of motor circuit analysis?

There are still many questions about the return of predictive maintenance. We have already addressed the ROI of predictive maintenance in another article, where we concluded that it is possible to reduce costs, decrease planned downtime, and avoid safety risks with predictive maintenance.

 

Regarding motor circuit analysis, a 2003 publication suggested that it could result in savings of 10-15%. Given that MCA technology is far more accessible now – almost 20 years later – we would venture to say that the ROI will be higher. 
 
But to know if it’s really worth it for you, you need to analyse the type of breakdowns in your facility, their origin, and the damage they cause. (That’s the advantage of having all the data organised in your software!) Then compare that figure with the investment in MCA and the likelihood of detecting those faults. How much would you save per year?

 

Infraspeak is an intelligent maintenance management platform where you can centralise all the information you need. If you want to know more about how it works, book a demo with one of our experts.