Building on our last newsletter, we would like to take a closer look at the topic of “Measuring and evaluating power quality”. Where, how and with which measuring device must measurements be taken in order to obtain a standard-compliant and, above all, meaningful assessment of my power quality?
High voltage quality ensures operational reliability. This is because modern production processes in particular, with their power electronic drives and control systems, are dependent on a high quality power supply. These systems enable considerable energy savings, optimize processes and increase productivity. However, it is precisely these energy consumers that degrade the voltage quality due to their load characteristics.
Standardized energy
Before we tackle the topic of “measuring power quality” in practice, let’s first look at the basics and consider the standardization of power quality.
In Germany, a standard accompanies us every day – without us even realizing it – the DIN standard. This makes it easier for us to evaluate and compare products and is valid in Germany. An example: If you buy A4 paper, you don’t need to measure the dimensions – these are specified in the standard. This standard also makes our lives easier in many other areas.
Purchasing electrical energy is no different. The only difference is that the grid quality for our energy has been standardized throughout Europe for years. There is EN 50160 – a European standard that is also valid in Germany. This standard specifies the quality of the voltage that must be made available to us at the connection point to the public electricity grid. This standard is used to assess the supply quality of the grid operator.
Another important European standard is EN 61000-2-2, which is also to be applied at the grid connection point and has been adopted by the VDE in its regulations as “0839 Part 2-2”. This is more precise for assessing the power quality due to its extended scope of measurement. EN 61000-2-4 is used for measurements and assessments in your own power grid.
Incidentally, what applies to power quality on the one hand is also relevant for systems and machines with CE marking on the other: these must function without faults if the mains voltage complies with the EN 50160 standard. If faults occur, a power quality measurement can be used to find out whether the cause lies with the power grid or the consumer.
Measuring the power quality
There are two questions that need to be answered before measuring the grid quality:
- At which point in my electricity grid should measurements be taken?
- Which measuring device should be used for the measurement?
The answer to the question of where to install the measurement depends on the task at hand. If the power quality of the grid operator is to be assessed, the measuring device must be installed at the transfer point, i.e. the energy supplier’s meter (measuring point 1). For a general power quality measurement, we recommend selecting the LVHV at the main switch as the measuring point (measuring point 2). In the event of faults in systems, the measurement should be carried out as close as possible to the faulty area (measuring point 3).
The question of the measuring device is relatively easy to answer:
In order to obtain a standard assessment of the power quality, measurements must be taken with a measuring device that is certified to “Class A”. Class A measuring devices must deliver the same results at the same measuring point for the same measurement duration, regardless of the manufacturer. KBR has certified Class A measuring devices both in both mobile and fixed installation versions.
In order to obtain a general assessment of the power quality, it is not necessarily necessary to use the high-quality and therefore expensive class A measuring devices. Particularly in the case of fixed installation measuring devices, the power quality can also be assessed well with cheaper but high-quality “standard measuring devices”. The multimess-F96 measuring device series from KBR, which has been enhanced with PQ functions such as bar graph, pointer diagram and oscilloscope, is ideal for this purpose.
Are all Class A meters equally good?
In the previous section, we reported that Class A measuring devices from different manufacturers must provide the same measured values. However, this only applies to measured values that are used for the standard.
There is a significant and non-negligible difference in the frequency range that is measured. As a rule, these measuring devices measure up to the 50th (2.5 kHz), sometimes even up to the 63rd (3.15 kHz) harmonic.
If a measuring device has not recorded any levels relevant to the power quality in its frequency measuring range during a measurement, this could lead to a false conclusion: “There is no interference potential in the power grid”. However, the clock frequencies of e.g. inverters or frequency converters are in a higher frequency range that is not usually measured by class A measuring devices. As a result, any feedback into the voltage, which means reduced operational safety, is not detected by these measuring devices.
This is where the multimess D9-PQ and multimess F144-PQ fixed installation measuring devices from KBR have a clear advantage: they can measure frequencies up to 9 kHz. This means that any potential interference in the higher frequency range can also be detected before interference occurs in systems. A major advantage of fixed installation measuring devices is that they measure and document continuously. This means that even temporary faults in the voltage can be reliably detected and evaluated.
Evaluating and interpreting the measurement data
A class A measuring device provides a large number of measured values for assessing the power quality. It is now necessary to be able to evaluate these.
For the initial standard assessment of the power quality, the software supplied free of charge with KBR PQ measuring devices provides ready-made reports in accordance with the EN 50160 standard. If the measuring devices are also integrated into KBR’s visual energy energy data management system, standard reports are automatically generated and saved on a weekly basis. These can also be sent automatically by e-mail. These reports can be used to assess at a glance whether all values relevant to the standard are below the limit values.
However, if individual limit values have been exceeded, in-depth knowledge in the area of power quality is indispensable. KBR has a department with VDE power quality experts who can carry out a competent assessment of the measurement data and prepare professional technical reports and solutions.
Conclusion
Nowadays, measuring network quality is a standard measurement – whether stationary or mobile. It is advisable to use measuring devices that can measure a wider frequency band. This ensures that interference levels from frequency converters, inverters and electronic power supply units are also recorded.
Automatically and regularly generated reports facilitate an initial assessment in accordance with the standard. However, if faults occur in the power grid, a power quality expert must be consulted. These experts have the training and experience to determine which measures can eliminate the cause of the grid problems. We will be happy to advise you on all aspects of your power quality. KBR, your partner for power quality.
