What do motors and drives have to do with wireless? Wireless sensors are diagnostics tools to support condition monitoring of motors and drives. Before you can install your first wireless sensor you need to create the infrastructure of gateways, backhaul network, and data gathering software in the parts of your facility where you plan to install the sensors.
The key parameters for motors and drives that are monitored to provide the condition monitoring inputs include vibration, temperature, motor current and electrical “signatures.”
Vibration
Vibration is one of the most effective methods for detecting mechanical faults, which is why hard-wired, dedicated vibration monitoring systems have been installed on large and critical motors and drives for decades.
Wireless sensors, usually accelerometers, make it possible to add vibration analysis to any machine on a permanent or short-term basis—when an operator finds a machine is consistently misbehaving, and manual surveys do not tell the story, for example. Continuous measurement means it will be there whenever the anomaly occurs and correlate it to what is happening in the process—certain part of the operating curve, ramp up, ramp down—at that time.
Temperature
Wireless temperature sensors can be mounted on the motor case or bearings to monitor excessive heat. Overheating, as indicated by abnormally elevated temperatures, is a major indicator of impending motor failure. Causes of the high temperatures include:
- Motor or drive is overloaded and operating beyond its design capacity;
- Bearing wear or lack of lubrication resulting in high friction;
- Blocked vents or a malfunctioning fan preventing sufficient air flow to effectively cool the motor or drive; and
- Winding damage or insulation degradation, causing short circuits between winding turns, reducing the motor’s total winding resistance and increasing generated heat.
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Motor current
Motor current signature analysis (MCSA) uses wireless current sensors to analyze the electrical current drawn by the motor. Changes in current frequency can reveal mechanical and electrical faults in the motor and driven equipment, making MCSA effective for detecting:
- Rotor bar failures affecting current draw and longer ramp up times with a corresponding decrease in motor efficiency;
- Stator winding faults, reducing motor torque and in severe cases insufficient starting torque; and
- Eccentricity and air gap issues, leading to winding damage and, if bad enough, rotor-stator damage.
MCSA also predicts cavitation in pumps or turbulence in fans driven by the motor.
Electrical signatures
Drives have unique electrical signatures that are indicative of potential problems. Current signatures in which changes such as sidebands, harmonics, or noise floor, and voltage signatures to monitor for harmonic distortion, phase imbalance, and voltage peaks can be analyzed to detect faults in the drive's rectifier or inverter circuits. They can also monitor power quality for harmonic distortion, voltage sags/swells, or other power quality issues that affect the drive's performance and lifespan with similar impacts as described for vibration and temperature.
Without analysis, data is a net loss to the organization. It must be turned into actionable activities to improve overall plant performance. Turning the diagnostic data into action can be done by the local engineering and maintenance teams for their analysis. However, it is also sent to the manufacturer’s cloud where it can be anonymized and added to a data repository for further analysis.
Patterns can be found, based on equipment information combined with that of thousands of machines in similar applications to enable earlier warnings so repair/replacement of a motor or drive can happen when it is convenient. More data equals better models leading to better results and wireless is the enabler to economically collect that data full time or as required so that your plant runs better.
