Electric motors: 5 cases of condition analysis

April 26, 2024

Faults in electric motors can result in very high costs for companies. That’s why it’s important to implement monitoring systems that can properly supervise them and thus predict or anticipate possible future problems.

In the case of electric motors, one way is automated monitoring of pumping systems. This is based on the measurement of voltages and currents, which makes it possible to assess efficiency in real time, also to detect faults accurately.

With a view to offering ways of monitoring the health and performance of electrical assets, Dynamox offers a current and voltage monitoring solution through Enging.

Enging: the solution for monitoring electric motors 

Founded in 2011, Enging is a Portuguese company specializing in industrial solutions for Predictive Maintenance and Fault Detection for Transformers, Rotating Machines and Power Electronics.

As part of its integration into the Dynamox group, Enging allows electrical analysis to be added to vibration and temperature analysis. In this way, using exclusively electrical variables, the company develops non-invasive, real-time monitoring solutions that enable early and accurate fault detection through the web platform.

Split-core current transformers are used to measure current signals, and voltage signals are collected using galvanic isolation transducers. This data is made available on the platform and spectral analysis is carried out on it. The increase in amplitude indicates a worsening of the operating condition, making it possible to identify faults such as:

  • Problems related to motor supply voltages (such as unbalance or frequency inverter problems)
  • Stator circuit (insulation or connection problems) 
  • Rotor condition (broken bars, slip rings, brush problems)
  • Eccentricity/mechanical unbalance (coupling, misalignment, bent/deformed parts, bearing looseness)
  • Load variation (pulley/belt problems, gearbox problems).

What’s more, by monitoring the data over time, it’s possible to track down incipient problems in specific parts of the electric motor drive and get a clear indication of how quickly anomalies are evolving over time.

Here are some fault analyses detected with the monitoring system:

Deformation of the slip ring in a wound rotor motor

Over the course of a few months, both the rotor failure indicator and the mechanical failure indicator steadily increased and exceeded the recommended limits. As a result, some stops were made for offline testing, but the results were inconclusive and the engine continued to run with increasing rotor failure indicators until a catastrophic failure occurred.

During the repair process, it was discovered that the slip rings were deformed, causing intensive wear and overheating at the slip ring/brush interface, resulting in the failure. Thus, after the repair process was completed, all the fault indicators returned to normal values. In this particular case, an alert for problems on the rotor side was triggered more than two months before the failure occurred, as can be seen in the graph in Figure 1.

rotor failure in the slip rings
1 – Component replacement
2 – Mechanical deformation of the slip rings caused by wear and intensive heating until failure
3 – Rapid evolution of the rotor failure indicator
4- Simultaneous evolution of the mechanical failure indicator

Figure 1: Data and photos of a rotor failure in the slip rings of a wound rotor motor at a cement company.

Insulation problems in the stator circuit

The data from this water pumping station indicated that the fault was related to problems in the stator circuit, which was at a warning level (Figure 6).

Visible corrosion and high humidity levels inside the junction box
1 – Visible corrosion and high humidity levels inside the junction box
2 – Visible damage and cuts to cable insulation
3 – Stator fault indicator
4 – Warning level
5 – Terminal maintenance performed

Figure 2: Data and photos of stator insulation problems in a pumping drive at a clean water station.

Although the motor was relatively new and apparently showing no signs of degradation, opening the junction box revealed high levels of corrosion and damage to the cable insulation. After the repairs, the stator fault indicator decreased to normal values, thus avoiding a possible catastrophic failure. 

Rotor cage problems in a medium voltage motor

The monitoring system installed on a medium-voltage motor at a refinery indicated problems with the rotor. Within a few days, the situation worsened and the indicator rose above the critical limit. In addition, visual inspection showed problems with the connection of several bars to the short-circuit rings.

squirrel cage medium voltage rotor
1 – Rotor fault indicator raised above critical limit
2 – Visible cracks in bar connections with short-circuit rings

Figure 3: Data and photos of a medium-voltage squirrel-cage motor with rotor bar problems.

Mechanical deformation/excentricity

In the case of a steel company’s pump, the first samples indicated mechanical problems. A few days later, the indicator in question increased further and began to reach critical values (Figure 8). With the motor stopped, severe damage was detected on the inner periphery of the motor’s stator caused by rotor deformation.

engine with a severe mechanical problem
1 – Mechanical failure indicator above critical limit
2 – Internal defects in the stator due to rotor deformation/excentricity

Figure 4: Data and photos of an engine with a severe mechanical problem.

Load variation due to belt vibration

The application of the monitoring system to a fan (with pulley/belt coupling) showed high values with an increasing trend for load variation. After a planned maintenance stop, belt degradation/problems were confirmed. After replacement and mechanical adjustments, the values returned to normal (see Figure 9).

fan with belt problems
1 – Indicator of load variation above critical limit

Figure 5: Data and photos of a fan in a steel company with belt problems.

Early detection of these problems helped prevent catastrophic failures and unplanned downtime. In addition, the diagnostics allowed for greater precision in corrective actions, reducing maintenance costs and increasing operational efficiency.

By providing a complete analysis of engine performance and power system health, the proposed monitoring empowers industrial operators to make informed decisions about the maintenance and optimization of their equipment. This contributes not only to improving the reliability and productivity of industrial systems, but also to reducing operating costs and increasing competitiveness in the market.

Looking to increase the reliability of your assets? Discover the Dynamox Solution!

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