Contactless Torque Monitoring

Especially the torsional oscillations of a turbo generator set caused by grid malfunctions, grid interactions or operatation errors lead to fatigue of shaft components and can even cause severe mechanical damage. In some cases, the latter induce additional permanent torsional vibrations in the rotational frequency and its harmonics. It is therefore necessary to ensure continuous monitoring of a rotating drive train for torsional vibrations.

Continuous monitoring for torsional vibrations

In recent years, we have developed the software tools TorGrid, TorFat and TorAn, which, together with the non-contact torque sensor we distribute exclusively, each form a torsion detection and analysis system of varying complexity.  

Depending on the application, we use the respective system to detect and store relevant power and torsional vibrations for interaction analysis between mechanical and electrical variables (TorGrid). With a digital twin, we predict and evaluate torsional vibrations even for inaccessible components (TorAn). Stored torsional events are visualised in the time and frequency domain with the integrated tool TorVis. In addition to long-term monitoring, our torque monitoring systsms are also successfully used to determine torsional natural frequencies and mechanical damping values of the drive trains.

Our systems are installed in power plants worldwide on behalf of power plants operators. Beyond the power plant sector, our systems are suitable - in principle - for torque measurement and analysis on any rotationg drive trains with ferromagnetic shaft surfaces. In particular, our systems are an ideal extension of condition monitoring systems for many applications. We would also be happy to integrate them to monitor your shaft line.

Condition Monitoring Systems at Fraunhofer ITWM

The tasks involved in the torsion monitoring of drive trains are manifold. In the following, we present the developed methods and software tools for the different problems. Our systems are supplied with an inductive sensor for contactless torque measurement. Here we present our developed methods and software tools:

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TORGRID

TorGrid - Monitoring of grid feedback effects on conventional energy generators

Due to the significant increase in the feed-in of renewable energies and the coupling of high-voltage direct current transmission via inverters, new types of dynamic effects occur in the electrical grid. In particular, the treatment of previously unknown grid feedback effects on conventional power generation units plays a importang role.

We have developed the online monitoring system TorGrid to monitor the grid feedback effects on power plant turbines. This measuring system is available in different expansion stages

TorGrid - Basis synchronously records the torsional vibrations of the shaft train
TorGrid - Generator monitors the torsional vibrations and the respective three-phase currents and voltages at the generator
TorGrid - Generator-Grid records not only the torsional vibrations and electrical generator variables, but also the three-phase currents and voltages at the transformer on the grid side.

Based on intelligent trigger criteria, all TorGrid versions monitor the measurement signals of the torsion sensors and thus detect events that the user assesses as critical. Depending on the version, TorGrid stores not only the measured values from up to three non-contact torque sensors and the directly measured electrical variables in the event of an event, but also the electrical power determined from these measured values.

With TorGrid, our customers in the conventional power plant sector can plan their inspection and service activities even better. The long-term goal is to use the signals recorded with TorGrid to compensate for grid feedback.

TorGrid can also be used for monitoring drive trains with electric motors and thus for a variety of industrial applications.

TorFat

TorFat – Measurement Data Based Detection and Evaluation of Critical Torsional Oscillations

TorFat is a tool for online monitoring of torsional vibrations and fatigue analysis of rotating machines at the measuring trace. For this purpose, TorFat requires information about the geometry and material data at the measuring trace.

TorFat analyzes the measured torsional oscillations and checks if a relevant failure is present. If this is the case, a fatigue analysis is performed for the monitored component and added to the damage already calculated.

The main results of the damage analysis are provided in tabular form. The failure can be displayed in the time and frequency domain with the integrated visualization tool.

TorAn

TorAn – Online-Monitoring of Endangered Areas of a Drive Train

TorAn is a tool for online monitoring of torsional vibrations and for fatigue analysis of rotating machines. Based on a robust observer, TorAn estimates online the torsional oscillations at the user desired points at the shaft line based on the excitation torque as well as a torsion measurement of the contactless sensor. Thereby the number of required sensors is reduced to a minimum.

TorAn detects relevant torsional events and calculates the fatigue of the desired system components after each such an event. The fatigue, the maximum torque moments and stresses that occurred and the ratio between maximum and permitted torque moments are provided in tabular form after their calculation. The visualization of the stored events time series is also possible with TorAn.

TorVis

TorVis - Analysis of the Interaction Between Grid and Turboset

The integrated TorVis visualization software for TorGrid allows subsequent analysis of the stored torque, power, current and voltage curves in the time and frequency domain. The software thus offers the user the possibility of analyzing the cause of the torsional load on the shaft train at the time of the detected event: external feedback from the electrical grid, oscillations triggered by internal mechanisms at the generator itself or interactions between the turbine set and the electrical grid - these include, for example, subsynchronous resonances.

Torque Sensor

Contectless Torque Acquisition — © Fraunhofer ITWM
Our systems are supplied with an inductive sensor for contactless torque measurement.

Contactless Torque Monitoring

We supply our systems with an inductive sensor for contactless torque measurement. The measuring principle of the sensor is based on the Villary effect in ferromagnetic materials. Here we take advantage of the fact that the permeability in tensile and compressive direction is different in these materials, e.g. in case of torsional stress. Without torques, the permeability of the shaft is theoretically identical in both tension and compression directions. Therefore, the magnetic field in these directions is also the same. If torques are present, the permeability of the shaft material is different in the tension and compression directions. The sensor measures this difference inductively, which is proportional to the surface stresses or torque over a wide measuring range.

Technical and Geometrical Data

Parameter	Value	Error
Input voltage DC	12 V	5 Percent
Power consumption	40 mA	5 Percent
Output signal	0-4V or 4-12mA with converter box (see below)
Resolution output signal	12 bit

Temperature range	10°-70°C
Temperature compensation	Yes
Zero point adjustment	Yes, with included Software

Housing material	Aluminium
Cover material (Connector side)	Aluminium
Material coil side	PA12

Length/Width	36,9mm	1 Percent
Height without plug	18,8mm	2 Percent
Height with plug	31,7mm	2 Percent
Measuring head diameter	36,9mm	1 Percent

Converter Box
Hardware revision	2
Housing material	ABS plasitc
Input voltage	5-36V
Power consumption	10mA
Output	4-20 mA differential with ground wire