Condition Based Monitoring
 

Optimising availability with new maintenance concepts

Digitalisation is making headway in the area of installation maintenance. Intelligent frequency converters from Danfoss are able to warn users at an early stage before motors and systems come to a standstill. The concept behind this is known as condition-based monitoring, or CBM.

Data from internal and external sensors are collected and stored before being evaluated by the frequency converter, after which the results are transferred to the cloud or to a local control system so that they are available where needed. The collected data enables predictive, condition-based maintenance, which enhances the performance, efficiency and uptime of installations, extends the lifespan of installation components and reduces complexity at the same time.

Installation is very simple: depending on the application, there are two options. In the first case, the converter will automatically learn in parallel with the operation for a given period of time, whereas in the second, the industrial user conducts an identification run, also known as a baseline run. This means that the converter will run the machine through the entire speed range and then create a model to be used for monitoring purposes.

Prevent damage caused by cavitation with CBM

Cavitation – the formation and implosion of vapour bubbles in liquid – is caused by pressure changes in liquids and causes damage to pumps. Danfoss frequency converters with condition-based monitoring (CBM) detect cavitation at an early stage via current signature analysis. This makes it possible to take quick action and prevent damage.

By avoiding cavitation with CBM, you extend the service life of your pumps and optimise energy efficiency. In addition, it leads to lower maintenance costs thanks to predictive maintenance and more reliable operation of your systems.

Early wear and tear detection: monitoring mechanical vibrations

Many mechanical faults, such as the wear and tear of bearings, shaft misalignment and imbalance, cause vibrations. With an intelligent Danfoss frequency converter in combination with an external vibration sensor, the accelerated wear and tear of the mechanical components of a Power Drive System can be prevented. By comparing the sensor signal with internal signals, such as the speed range or other signals relevant to the application, the drive can quickly detect errors. Information on the state of the system is provided in order to prevent breakdowns, and maintenance can be prepared and scheduled in advance while the installation remains in operation until the next planned maintenance break.

Monitoring vibration in frequency converters is carried out using standardised methods and thresholds laid down in standards such as ISO 13373 for monitoring the condition and diagnosis of machines, or ISO 10816/20816 for measuring and classifying mechanical vibrations. The advantage of such monitoring in the converter is that it can compare the data with the actual operating conditions during continuous operation/start-up, load conditions or speed ranges.
 

Detection of motor winding errors before motor failure

Errors in motor windings do not occur suddenly, but develop over time. A seemingly minor short circuit in a winding will lead to additional heating, and the damage this will result in will remain unnoticed until eventually the overcurrent protection is activated and the installation is shut down. 

This will lead to unwanted downtime. Fortunately, this problem can be remedied by continuously monitoring the motor's condition through analysing its electrical signature.

Status information can be generated from the motor currents and voltage signals which can be linked to motor or application errors, such as shaft misalignment or stator winding errors. The current and voltage sensors that provide this information are in any case essential components of variable frequency converters, and so there are no additional costs for the use of external sensors.
 

Monitoring the casing curve: early detection of issues such as pump contamination

The pump appears to be operating normally, but the intelligent Danfoss frequency converter has activated a maintenance alarm. It has detected a heavier load, and so it is sending a clear signal to warn you that the pump is dirty. Fortunately, it is now possible to clean it more quickly than in the past before more serious problems occur, which ensures that the installation can continue to operate normally.

In order to recognise this error, the frequency converter uses the data from the current and voltage measurements to control the motor. The parameters calculated on this basis, such as motor power, energy, current motor speed or torque, can also be used to monitor the motor load for under or overload.

For more information, please contact your itsme branch.

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