Application of Monitoring Technology in a Coal-Fired Power Plant

Equipped with latest technology for power generation, the coal-fired power plant Schwarze Pumpe (‘Black Pump’) has been able to advance to the top. For the first time, a twin-unit coal facility achieved a power output of 800 megawatt per unit and an efficiency of 41%.

The use of state-of-the-art power plant technology will help to considerably reduce the facility’s impact on the environment. Dust particles and sulfur content are almost entirely removed from the exhaust gas and the formation of nitrogen oxides can largely be avoided.

That sophisticated technology helped to set new standards even when compared to other countries. Improved efficiency and increased power output however had not been the only requirements during design and development of the new power plant. In order to make sure that the facility can operate without interruption and economically feasible, a high level of reliability and dynamic availability had also been of great importance.

One of the essential factors to evaluate the economic viability of the power generation process has always been the running smoothness of the generator shaft. Any possible disturbances may result in a deviation of the shaft from its ideal position, and this in turn may cause additional dynamic stress that can lead to increased vibration and damage to the machine.

Measuring Task

Tests and observations had been done over a certain period of time in one of the 800 megawatt units in order to gather information on any possible disturbance factors on the running smoothness of the generator shaft. For that purpose it was necessary to measure the changes in height of at least three supporting bearings of the turbo generator while at the same time the machine was operated at different speeds and load changes took place. For instance, measurements were taken during power reduction to partial load and power increase to full load, as well as during temperature increase in the machine housing, heat extraction and during changes of vacuum in the capacitors. The measuring precision for this task was required to be at least ± 0.05 mm or better, so that technical conclusions could be drawn and their influence on the running smoothness.

The findings derived from the analysis of the test results were used to optimize the way in which the turbine shaft should be operated and represent significant knowledge for future shaft design.

Measuring Arrangement

The real challenge during the measurement period were the external conditions at the measuring location. The axle bearings could reach temperatures of up to 86° Celsius. Considerable levels of vibration were detected at the turbine and in its immediate vicinity. Furthermore, very strong electromagnetic fields were causing problems.

The following measuring devices for automatic monitoring of vertical displacements and real-time evaluation were taken into consideration:

  • automatic digital theodolites and total stations that have a standard deviation between 0.5 and 1 mm
  • motorized digital levels that have a standard deviation between 0.2 and 0.4 mm
  • hydrostatic leveling systems that have a standard deviation between 0.02 and 0.05 mm

However, the external conditions present at the measuring location would have caused a considerable influence on the results when using so-called open measuring systems such as theodolites and digital levels. Refractions, air turbulence and temperature changes can cause displacements of light beams. Those errors could not have been corrected within the admissible range of accuracy, so that the measurement uncertainty would have been influenced considerably.

The use of inclination sensors or electric settlement sensors would only have allowed for locally limited detection of displacements. It would not have been possible to measure differences in height directly. And it would have been impossible to establish any sort of connection to other measurement points. Only an automatic hydrostatic leveling system with a resolution of 0.005 mm per measurement was able to achieve the required level of accuracy and allow for continuous data recording.

It was determined during preparation of the project that the model ASW 2000, which was available at FPM Holding GmbH at that time, could not be used in its existing form under those circumstances. Considerable changes in design had to be made in order to measure in an environment exposed to high temperature und vibration. This led to the development of a new automatic hydrostatic leveling system, the ASW 101 N, which was able to provide precise and reliable measurement data even under the external conditions described. The device achieved a measuring precision of up to ± 0.01 mm in an environment that was exposed to extreme temperatures and vibration. Another problem was connected to the fluid that was used for the measurements. Even de-ionized water which was used as measuring fluid had a tendency to evaporate. The occurrence of bubbles in this magnitude would have resulted in unusable measuring data. This problem could be solved by using a double layer water hose and an air flushing mechanism to cool down the measuring fluid. Thanks to this cooling method the system could be operated without interruption during the entire measuring period. The turbine had already been equipped with measurement points, but those did not allow for horizontal installation of the water hoses. However, this way of installing the water hoses is essential in order to minimize any influence on the system’s accuracy. The measuring devices had to be positioned 300 mm higher to allow for horizontal installation of the water hoses. An additional support plate was required to raise the instruments, and furthermore the thermal expansion coefficient had to be adapted to the new conditions. In order to obtain accurate measuring values it is very important to correct the data of all measurement sensors to the same level of density and temperature. The value for this reference temperature is included in the software. The temperatures of the support plate and the hydrostatic leveling device were also determined each time the system ran a complete measuring cycle so that correction of the thermal expansion could be realized. Level differences of the measuring fluid caused by variations in atmospheric pressure could be eliminated by connecting all measuring units with an air hose. This allowed for pressure compensation between the individual units.

The FG-ASW101N measuring devices were positioned on both sides of three shaft bearings of the turbine, so that changes in height could be determined and to allow for evaluation of the running smoothness:

  • to the right and to the left of front bearing 1 of the high-compression compartment (HDT)
  • to the right and to the left of bearing 2 between the high-compression compartment and medium-compression compartment (MDT)
  • to the right and to the left of bearing 3 between the medium-compression compartment and first low-compression compartment (NDT)

beformationsmessungapp braunkohle kw 01

The water hoses between the six measuring devices were positioned approximately 1.5 meters above the turbine deck with a maximum height difference of ± 1 cm.

After an initial assessment of the measured data it seemed to make sense to install temperature sensors at the pillars and the machine housing so that the measurement results could be interpreted. The measuring unit placed at bearing 1 to the left was chosen as point of reference. All measurement cycles were displayed relative to the position of that unit at bearing 1 to the left. The changes in height over time were depicted graphically relative to a reference cycle. That cycle was determined immediately after installation of the measuring system had been completed. The six devices provided measurement values with a resolution of 0.005 mm. The temperature sensors used for density correction operated with an accuracy of 0.1° Celsius. The main impact on accuracy was caused by extreme vibrations in the vicinity of the measuring positions. The values that were obtained thus had an accuracy of ± 0.025 mm. All measuring units were set to run a measurement cycle simultaneously every five minutes. Each day the system ran 288 measurement cycles (1,728 individual measurements per day), that way allowing for continuous monitoring of the turbine bearing shafts during the entire measurement period.

Measurement Results

The time span between each measurement cycle was set to 5 minutes and was never changed. Using the recorded data it was possible to reconstruct movement patterns that only could have been obtained with a system that takes measurements simultaneously at all measuring positions. It could be demonstrated that the movements depended strongly on exterior temperatures and the stuffing box’ mode of operation. Some of the ASW 101 N units had to deal with forces that could not have been predicted in their magnitude, and some of those forces exceeded the admissible limits of operation.

The changes in height detected by the hydrostatic leveling system ASW 101 N were continuously compared to the current level of running smoothness, especially that of high-pressure and medium-pressure compartment. Moreover, operation modes that resulted in a change of vibration amplitude could be evaluated with regard to their influence on changes in height. Information on changes in height and their influence on running smoothness and vertical displacements caused by different operation modes of the turbine, such as load reduction, technologically required reduction, deterioration of the vacuum, changes in heating power and controlled shutdown of the turbine house ventilation, could also be obtained. More importantly, it could be demonstrated that it was possible to reproduce the curve progression in each case.

The hydrostatic leveling system ASW 101 N has proven its worth in the course of a difficult measuring project which was carried out to determine and evaluate changes in height at the bearings and base plate of an 800 megawatt turbine. Given the fact that this system allows for taking continuous and simultaneous measurements at multiple measurement points, it is in fact the best equipment for conduction this type of research.


Hochmuth, R.-U.: Messbericht - Automatische kontinuierliche Deformationsmessung: 800 MW - Turbosatz im Bereich Lager 1 bis 3, Dresden 2000 (Hochmuth, R.-U.: Measurement Report – Continuous Automatic Monitoring of Deformation Processes: 800 MW turbine bearings 1 to 3, Dresden 2000)

Saretz, M.: Bewertung des Laufverhaltens des Turbosatzes A, KSP während der Höhenverlagerungsmessungen an den Traglagern 1 - 3, Jänschwalde 2000 (Saretz, M.: Evaluation of the Running Smoothness of Turbine A, KSP in the course of measurements of changes in height at shaft bearings 1 – 3, Jänschwalde 2000)