Perfect drive train alignment and the “wind harvest” can start

Fig. 1: Drive train
Fig. 1: Drive train

Deutsche Windtechnik offers complete service packages for technical maintenance of onshore and increasingly also offshore wind turbines. The company focuses on the maintenance and optimization of rotor and tower, control, safety, consulting, transformer stations and repowering. The company supports more than 2,000 turbines within the framework of permanent maintenance agreements (focus on Vestas, NEG-Micon, SIEMENS, and AN Bonus). With more than 100 measurement systems of the OPTALIGN smart family made by PRUFTECHNIK, the service teams of Deutsche Windtechnik are well equipped for completing all alignment tasks on drive trains in the wind turbine nacelles.

 

Drive train alignment impacts energy output

A core issue in practical daily wind turbine maintenance is ensuring the ideal force transmission through drives coupled by shafts. Regular verification of the drive shaft alignment is highly important in wind turbines especially on the back of wear and changes caused by strong environmental influences or by the natural aging of the equipment.
Good drive train alignment is of decisive importance for wind turbines and significantly increases their energy efficiency. The impacts on service life and MTBF (Mean Time Between Failure) of the turbine parts must not be forgotten or underestimated either. The advantages are especially important in the wind energy industry due to the remoteness of wind turbines. Efforts to reach the turbine, transport parts into the nacelle, and to replace them on site involve significant logistical and time expenditures. High costs can occur. Furthermore, it must be ensured that the wind turbine can convert rotational energy into electrical energy optimally even under extreme conditions with different forces impacting the drive train, i.e. wind directions and wind speeds, and that the energy is not lost due to friction losses along the drive train.

Fig. 2: Displacements in the XY illustration under different wind conditions. A) No/little wind (right side) – B) Medium wind speed (center) – C) Strong wind (left side).
Fig. 2: Displacements in the XY illustration under different wind conditions. A) No/little wind (right side) – B) Medium wind speed (center) – C) Strong wind (left side).
Fig. 3: Schematic illustration of gap and offset
Fig. 3: Schematic illustration of gap and offset

Drive shaft alignment decisive for wind turbines

Hardly any other system as the wind turbine is subject to such severe changes during operation. A reason for the operating load is natural: Wind can abruptly change its direction and speed. This fact translates into high requirements on the material (Figure 2).
For this purpose, optimum drive train alignment is important so that the turbine components feature the smallest possible offsets and gaps in vertical and horizontal direction during operation. Thus, the system can compensate as large as possible displacements induced during operation.

 

Fig. 4: Use of straightedge (left side) and feeler gage (right side)
Fig. 4: Use of straightedge (left side) and feeler gage (right side)

Traditional shaft alignment methods

Different drive shaft alignment methods exist. A method still used is the shaft alignment using a straightedge or a feeler gage (Figure 4). The unbeatable advantages of these methods are – on the one hand – the relatively low procurement costs, and – on the other hand – the measuring instrument availability. Almost every mechanical workshop own a straightedge or a feeler gage. The greatest disadvantage of this method is the strong influence of the human factor. As the alignment condition is basically determined and evaluated with the eye, the results strongly depend on the person using the straightedge and feeler gage. Furthermore, a lot of experience is required for achieving a good alignment with this method, which can only be acquired by years of applying this method.


One of the most frequently used alignment methods is the dial gage (Figure 5). Here, different procedures are used that are difficult to compare. The radial-axial procedure and the double-axial procedure are some of the most frequent methods. The evaluation in the respective measuring procedure can either be based on calculations or a graphical illustration (mostly manually drawn line diagrams).


An advantage of using dial gages – similar to using a straightedge or feeler gage – is the low measuring instrument cost. It is further possible to align shafts with flexible coupling elements using dial gages. However, in procedures with dial gages too is the human factor of central importance. On the one hand, the user must be well trained and have be very experienced to perform precise and reliable alignments. On the other hand, achieving a good alignment result usually is time consuming.

Fig. 5
Fig. 5: A laser unit with a single laser beam hits the sensor on the opposite side
Fig. 6: Measuring principle of laser-optical measuring devices (here OPTALIGN smart RS5)
Fig. 6: Measuring principle of laser-optical measuring devices (here OPTALIGN smart RS5)

Laser-based shaft alignment – well prepared for Industry 4.0

 

In the mid-eighties, PRUFTECHNIK introduced laser-based shaft alignment into the market. OPTALIGN was a computer-aided laser-optical measuring system with a precision and repeatability unmatched by conventional methods. In the meantime, the laser-optical methods has established itself worldwide and across many industries as standard procedure for shaft alignment. Latest developments even enable the integration into Industry 4.0 technologies. Mobile terminals such as tablet PCs or smartphones can communicate with laser-optical sensor systems. This way, measuring reports can be directly sent via e-mail or uploaded into cloud-based systems.

The measuring principle of the OPTALIGN smart family used at Deutsche Windtechnik is as follows: The measuring sensor system is positioned on a drive coupling. The measuring sensor system consists of two components. A laser unit with a single laser beam hits the sensor on the opposite side (Figure 5). The sensor contains two position-sensitive
detectors and an inclinometer that record the exact position of the laser beam during shaft rotation. This measuring procedure is worldwide the only procedure supporting the “Live Move” function for concurrent monitoring of vertical and horizontal machine corrections with the sensor at any angle position.

Laser-optical shaft alignment offers outstanding advantages, among others:

 

  • Precise alignment without measured value entry, graphical or numerical
    calculations.
  • Graphical display of the alignment results at the force transmission level
    of the coupling, and shim and offset corrections at the machine feet.
  • No coupling disassembly required during measurement value acquisition.
  • No fixed measuring locations required for measurement value acquisition.
  • Precise and repeatable results with excellent operator friendliness.
  • Results can be electronically stored and printed.
  • Measuring system calibration according to ISO 9001 including certificate.
  • Universal bracket for almost all alignment applications.
  • Display of vertical and horizontal corrections in real time during machine movement.
  • Integrated tolerance tables clearly showing whether the alignment
    condition is poor, acceptable, or excellent.
  • Powerful PC software for measurement archiving, documentation, and
    analysis

 

With the use of a computer-aided laser-optical shaft alignment system, the possible error causes of conventional measuring methods are automatically eliminated.

Fig. 6: The OPTALIGN smart RS laser alignment system
Fig. 7: The OPTALIGN smart RS laser alignment system
Fig. 7: OPTALIGN smart RS5 in action
Fig. 8: OPTALIGN smart RS5 in action

Deutsche Windtechnik employs state-of-the art technology for alignment


The service teams of Deutsche Windtechnik use more than 100 laser-optical measuring systems on a daily basis. The service provider relies on the OPTALIGN smart made by PRUFTECHNIK, which are ideally suitable for the wind industry (Figure 7).
“We are very satisfied with the measuring systems made by PRUFTECHNIK. Not only the technical side suits our needs perfectly, but also the personal collaboration is highly professional. We receive regular training sessions. Three PRUFTECHNIK employees are always available to support our service team. This all-around package ensures the successful deployment of the laser measuring technology”, reports Gerrit Gehrk of Deutsche WINDTECHNIK.

PRUFTECHNIK is a pioneer in the area of laser-optical shaft alignment. Since the introduction of the technology in the eighties, precision and user comfort of shaft alignment using laser technology have improved rapidly.

 

Alignment can be completed in three quick and easy steps

Fig. 8: Measurement sequence of shaft misalignment using a modern laser-based shaft alignment system
Fig. 9: Measurement sequence of shaft misalignment using a modern laser-based shaft alignment system

Ease of use and handling

 

Handling and working with the OPTALIGN are very easy. Alignment can be performed by anybody after a short briefing and training session. Workflow sequences guide the user from the first measurement to the aligned aggregate. Next, the data is available in electronic form and can be reproduced at any time. Different solutions exist for mounting the measuring components. Using a chain bracketing system provides the easiest solution.


Alignment can be completed in three quick and easy steps:

  • Enter dimensions
  • Perform measurement
  • Display results


After activating and starting up the hand-held computer, the dimensions of the machine to be measured are entered first. This file is stored in the alignment systems and used as template for further aggregates, which significantly simplifies the work of the service teams at Deutsche Windtechnik. Next, the measurement is performed. A suitable measuring mode can be selected for different coupling types and rotating conditions. This will ensure a safe measurement with high repeatability. After measurement completion, the results are clearly presented together with the alignment condition (see Figure 9).

After the machine is repositioned, a final measurement should verify and ensure that it is properly aligned. Creating an informative and clear measurement report is one of the standard features of a modern alignment device. This function ensures compliance with the requirements of Quality Assurance and Management. The service provider can hand the respective report over to the client immediately after work completion. Additional PC software supports data archiving and analysis as well as the preparation of measuring tasks.

 

Good alignment pays off

Rotating machines, such as the drive shafts of wind turbines, are susceptible to misalignments. If a new machine is correctly aligned at start-up and regularly checked later on, operating and maintenance costs can be reduced by a significant amount. Alignment using state-of-the art laser technology increases the machine usability, as its failure rate lowers. Furthermore, the machine is protected and product quality increased, as vibrations are reduced. In the case of a misalignment, the load on the coupling increases as reset forces are generated at the coupling. The following list shows an overview of the advantages of good alignment in wind technology:

  • Low wear on bearings, seals, shafts, and couplings
  • No high temperatures at bearings and couplings
  • No excess vibrations
  • No shaft damage
  • No loosening of generator base screws.


In summary, costs can be saved in many ways. Side effects of good alignment is the contribution to environmental protection.

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