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Hey, Motor, how you doing?

Hey, Motor, how you doing?

AC drives can be more than just speed controllers. As intelligent sensors, they can monitor important parameters and thus contribute to condition-based monitoring. Helpful here are the monitoring of mechanical vibrations, possible faults in the motor stator winding and the development of the load envelope curve.

Variable speed drives have been used for over half a century. With Industry 4.0, the role of the AC drive is shifting further in the drive system: from the once pure speed controller more and more to an intelligent component of the automation system. AC drives from Danfoss, which are equipped with three additional functions, work as intelligent sensors and enable the operator to monitor the condition of the drive system. The three functions are condition monitoring of mechanical vibrations, the motor stator winding and the load envelope. Just as a printer, for example, keeps up to date on the toner level, AC drives can also provide early warnings before the motor and drive system come to a standstill. The concept behind this is called condition-based maintenance.

The VLT AutomationDrive frequency inverter product group

The drive as an intelligent sensor

Intelligent AC drives from Danfoss collect data from various sources. They combine signals from internal and external sensors such as vibration and pressure sensors. With Edge Intelligence, the valuable information is evaluated locally in the device. Optionally, it can be sent to the cloud or to the company’s PLC system if necessary. The data is thus available wherever it is needed, enabling predictive, condition-based maintenance that increases the performance, efficiency and uptime of systems, extends the life of system components and reduces complexity.

  • The monitoring of mechanical vibrations

Many mechanical faults such as bearing wear, shaft misalignment and imbalances generate vibrations. Danfoss AC drives can monitor these vibrations together with a sensor – an external vibration transmitter. By combining the transmitter signal with internal drive signals, such as speed, the drive can detect faults at an early stage. It provides information about the status of the system. Maintenance can thus be prepared and planned in advance. The system continues to operate until the next possible maintenance pause and does not have any unexpected operating failures.

Vibration monitoring is carried out using standardized methods and threshold values provided for in standards such as ISO 13373 for condition-based monitoring and diagnostics of machines or ISO 10816/20816 for measuring and classifying mechanical vibrations. Monitoring via AC drives makes it possible to compare data with the actual operating conditions at continuous operation/ramps, load conditions or speed.

  • View of the stator winding

Errors in motor windings do not occur suddenly; they develop over time. It all starts with a small short circuit on a winding, which leads to additional heating. Now the damage continues undetected until the overcurrent protection is activated, and operation is stopped. This leads to unwanted downtime. This can be remedied by continuous condition-based monitoring of the motor by analyzing the electrical signatures.

Status information can be extracted from the motor currents and voltage signals and associated with motor or application faults, such as shaft misalignment or faults in the stator winding. The current and voltage sensors that provide this information are in any case essential components of AC drives.

Early detection of silting and Co. with the load envelope curve

A pump seems to work normally, but the intelligent drive detects a higher load than usual. This gives the decisive hint: The pump has silted up. Before major problems occur, it can be cleaned prematurely, and the system can continue to run normally. In addition, condition-based monitoring helps to save energy, as the pump can always be operated under optimal conditions.

In order to detect this fault, the drive again uses the values from the current and voltage measurement to control the motor. If the drive detects overload or underload conditions that occur in pump applications due to clogging, silting, corrosion or other causes, it will trigger a maintenance alarm.

An intelligent frequency converter monitors the condition of a pump: Commissioning takes place via software

Condition-based monitoring as a basis for predictive maintenance

Condition-based monitoring with intelligent drives allows for predictive maintenance of plants. This offers numerous advantages over corrective and preventive maintenance concepts. But condition-based monitoring is dependent on sensor data and the installation of additional sensors in plants can be expensive. However, when Danfoss drives are used in the application, they are a valuable source of data that can be used for condition monitoring. This creates added value through knowledge advantage and saves unnecessary costs due to plant downtime or increased wear.

Software easy to master

Of course, an AC drive with such capabilities needs powerful software. Danfoss offers a number of tools that simplify the configuration and documentation of drives. All tools, apps and online resources are available in the Danfoss MyDrive Suite.

Source: Danfoss A/S

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