Network quality

Clean electrical networks ensure operational safety

Modern manufacturing processes based on power electronic drives and controls. Thus, considerably higher energy savings, better process optimization and an increase in production can be achieved. However, the requirements placed on clean energy are increasing and quality is more and more influenced by the power electronics used.   In advance, precise planning is required as well as qualified error detection and troubleshooting in case of problems.
 

Electricity as a resource

The importance of electricity as a resource is often underestimated. However, this factor is essential to operate machines successfully and without any errors. In general, the primary effect of electricity cannot be seen. And even if it is, this is not desired. This is also the opinion of experienced electricians: "If you can see, hear and/or smell electricity, there might be problems that are likely to be expensive."

Apart from their energy consumption, most companies pay little attention to the quality of their electricity supply as long as these effects do not occur.  In retrospect, however, this often turns out to be a mistake with far-reaching consequences.

Due to the quality of the power grid in northern Europe, especially in Germany, and a sufficient base load of ohmic or inductive consumers, there have seldom been unexpected or initially unexplainable problems or errors. These consumers produce an almost sinusoidal current flow, which is more or less phase-shifted to the voltage curve.  This phase shift could be solved by using conventional compensation technology and the desired reduction in electricity consumption could be achieved.

Due to the increasing use of power electronic control systems, this situation has been changing for some time. The percentage of purely ohmic / inductive consumers is shrinking. In industry, they are replaced by complex electronic systems, often in connection with complicated control technology. Furthermore, the situation for private consumers has also been considerably changing in previous years.  There are hardly any products not requiring an electronic power supply unit. Nowadays, this technology is used in all kinds of devices like computers, TV sets, energy-saving light bulbs and even electric toothbrushes. However, these technologies are special: They require non-sinusoidal current.
 

Background information

To classify deviations from the original sinusoidal shape, a mathematical operation is used: the so called Fourier transform, named after Jean Baptiste Joseph Fourier (1768 - 1830). As a result, this leads to the so called harmonic. The use of this complicated calculation is finding out how combinations of different equipment with differently distorted currents react. Partly, individual effects cancel each other out when different equipment is combined, partly they add-up. Additionally, an effect of the distorted current on the voltage can be noted.  This is where things get interesting. This interference has an effect on all equipment in the network, disturbances in connection with the current, however, only affect the concerning device itself and transmission media like cables, transformers and protective devices. Voltage disturbances not only have an effect on the layer where they are created, but also on layers above and below. For this reason, different limits and compatibility levels have been defined for the standardization of different networks. The German standard DIN EN 50160 "Voltage characteristics of electricity supplied by public distribution networks" only defines limits for voltage disturbances in low and medium voltage systems.
 

Application

If the limits are exceeded at a certain point in the network, the cause needs to be found. If there are several subscribers at the connection point, every single one of them needs to be checked in accordance with the "D-A-CH-CZ technical rules for the assessment of network disturbances". The level of the permissible disturbance in current consumption depends on the ratio of connected load to short circuit power at the feeding point. Ideally, an evaluation and dimensioning of possibly required compensation measures should be carried out and taken into account during planning of the facility. This is both needed to ensure the operational safety of the own facility and for the safety of other network operators.
 

Training

To avoid delays and additional costs that may arise later, experts with the appropriate technical knowledge are required for planning new facilities or expansions. Unfortunately, knowledge about this very complex problem is not yet taught at universities in Germany. For this reason, real experts in this field are rare there. Thus, different training courses of varying complexity are offered. The German association of insurers VdS for example offers a course for further training with certification as 'EMC expert VdS' and continuous further training. To obtain this qualification, a certain number of training courses has to be taken each year.

The 'Power Quality Expert (VDE)' course is a very profound certification course based on current standards and with final testing by the VDE. This test ensures that the participant is able to practically apply the calculation bases learned. Manufacturers of measuring devices or compensation units like KBR offer training courses as well.

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Summary

In any case, an evaluation and recording of the electrical network quality pays off in terms of operational safety. Even if the energy supplier does not threaten with disconnection, initially unexplainable disturbances or even damage to equipment can be explained and set in connection with certain network parameters. As soon as the cause has been detected, a solution for the problem can be found as well. Even if this solution seems to be very expensive in the first place, production failure and restricted supply capability is often much more expensive. Not to mention the damaged reputation due to deadlines not met.

If the result is a clean network, the often used statement by machine manufacturers: "There are harmonics in your network, the error has nothing to do with our machine", can easily be nullified.