Maintenance, testing and repair of­ electrical machines

Furthermore, a study has shown that if alignment is improved even by only a few 1/100 mm, which is very easily achieved with a laser alignment system, there will be an energy saving of at least .5 per cent.

Fast, precise machine alignment with a laser has replaced the traditional, established method with a straightedge and dial gauge. The laser not only determines the setting of the machine and coupling geometry but also measures the rotational axes.

How does laser optical measurement work?
Laser optical measuring instruments determine the extent of the offset by measuring the displacement of the shafts. The laser/detector unit (sensor) and the reflector are attached to either side of the coupling using infinitely adjustable clamping devices. The laser beam from the transmitter passes through the coupling and enters a glass prism in the reflector, from where it is reflected back and strikes a position detector in the sensor.

Rotating the shafts by 60°, once clockwise and once anti-clockwise, is generally sufficient to determine the alignment status of the coupling very precisely. The rotational axes are in alignment if, when the shafts are rotated, the point of impact of the laser beam remains radially constant on the surface of the detector. Deviations in the points of impact are recorded as parallel and angular offsets. The computer calculates the coupling values (parallel offset and gap) and correction values from the changes in the points of impact. The same principle is also used to observe the machine movements ‘online’ while the alignment is being corrected, via the display on the measuring instrument.

This measuring principle and the way it is carried out offer users many practical advantages. The variety of different measurement techniques make it possible to take almost every conceivable situation into account when aligning a machine. For example, it is not difficult to align non-coupled shafts precisely with the appropriate measurement function. Laser optical alignment is generally faster and costs less than traditional methods and produces more accurate results.


Poor alignment = high energy consumption!
The link between the alignment within a machine and its energy consumption was investigated in a study by ICI Chemicals in northern England, which made it possible to state the amount of energy that can be saved by proper machine alignment.

The unit at ICI on which the study was carried out consumes approximately 80 MW, 50 MW of which can be directly influenced by shaft alignment. It was discovered that an average shaft offset of 35/100mm can be assumed. The energy consumption in this alignment scenario increases by .8 per cent for jaw couplings and .5 per cent for boom couplings.

This shows that if alignment is improved even by only a few 1/100 mm, which is very easily achieved with a laser alignment system, there will be an energy saving of at least .5 per cent.

Our services in detail:

• Determination of the condition the machinery is in
• Measurement of coupling offset, coupling gap and machine tilt
• Screen-guided correction of each anti-vibration mounting
• Evaluate the recorded data
• Advise the customer and decide together what measures to take
• Implement measures, taking customer’s deadlines into account

1. Safety: An extremely reliable rapid-response safety system (emergency shut-off) can be created based on sensor data analysed in real time. Most of the current systems, including vibration sensors, are much less precise and do not contribute to explaining why and how damage occurs. Online condition monitoring makes it possible to shut off the machine based on the data that has been recorded, therefore also making it possible to analyse the factor that caused the disturbance.
2. Machine efficiency: Monitoring the machine’s condition is the essential prerequisite for "condition-oriented maintenance", a new strategy that replaces the previously widely used “preventive” maintenance. Preventive maintenance involved shutting down a machine at regular intervals to check components and replace them if necessary and often resulted in intact components being exchanged, wasting their remaining useful life.

Condition monitoring places extreme demands on the sensors and measurement processing and requires in-depth knowledge of the equipment being monitored. However, it also offers the greatest potential cost savings, because critical machine elements are used virtually until the end of their service life and any maintenance can be scheduled to fit in with the production plan.

Condition-oriented monitoring is an interdisciplinary field drawing from mechanics, acoustics, system theory, electronics and informatics and has not yet been fully researched, though it is developing very rapidly. While it has already proved to be unerringly accurate in the monitoring of individual components, condition-oriented monitoring of complex machinery grows less precise as the number of signals originating from different places within a system rises. There has also been a lack of suitable sensors capable of picking up signals directly in the zones where the wear and tear and damage occur. Microsystems technology may provide the answer here in the future, for example by applying sensors in thin-film technology that can be applied directly to the structure to be monitored.

The challenges:

• Finding suitable measuring points and sensors
• Identifying parameters that provide more information (condition parameters) about damage to the relevant components
• The targeted application of signal analysis and pattern recognition
• Dealing with the enormous amount of data.

Putting it simply: what needs to be monitored, when, how and what with?
What condition monitoring can not do is to recognise and prevent spontaneous failures such as fatigue fractures in shafts. 

This is where indirect damage detection using regular measurement of the machine vibrations, followed by computer-supported evaluation, comes in. Measuring-systems of this type comprise fixed measuring points, a portable measurement sensor and a PC with special software.

Vibration analysis detects machine imbalance, machine offsets and bearing damage before damage occurs. Trend monitoring uses the shock pulse method to analyse high-frequency bearing vibrations. The results indicate the development of the characteristic condition parameters of the machine bearings.

Regular recording of these parameters makes it possible to detect bearing damage in the early stages and accurately assess the condition of the bearings. For example, it is possible to find out whether a bearing is adequately lubricated or is running dry. These advantages, together with its ease of use, have made the shock pulse method very popular in the maintenance world. Selected preventive measures, including alignment, balancing and changing the bearings make unexpected, uneconomic "first aid" measures a thing of the past.