Why are there harmonic frequencies on the electricity grid? Understanding of the frequency content of signals makes us identify the individual harmonic frequencies and what they can be attributed to in the electrical installation. Harmonics is the most difficult to understand in power quality and this course is a good start for a beginner. It briefly describes what generates the harmonious voltages and some of the challenges there are present on the electricity grid. After having completed the course, it can be accessed for review of individual parts.
Training opportunities
Learn troubleshooting here and now with E-learning
Power quality is a big and important topic for preventing problems. The theoretically most difficult part is understanding signals, harmonic voltages and currents. This e-learning course provides a basic understanding without having to understand the Fourier transform. For troubleshooting industrial plants, for example, a power quality logger is a powerful tool. However, it's important to understand both the measuring instrument and the structure of the components that load the grid. Frequency converters present many challenges and it is recommended to complete both the harmonic currents and Motor Drives course.
Deeper understanding of power quality
Rohde Consulting offers a 3-day course on power quality with practical exercises. Through this, you can gain a deeper insight into power quality and share experiences. We also look at grid connection requirements, in particular, many errors are made when connecting consumer products over 50 kW.
Center of knowledge
Rohde Consulting has extensive experience with power quality challenges and has created a small knowledge center here. Here are some examples of challenges we have faced during our consulting engineering services.
10 kV grid contaminated by factory
In both Denmark and the Faroe Islands, we have seen several examples of large installations with 6-pulse frequency converters in weak grids that have caused problems in an entire city. Experience shows that especially 15th to 35th harmonic currents connect to the 10 kV grid and are distributed to private consumers. Many consumers are not bothered by the harmonic interference, but some have sensitive equipment that is challenged by the interference and complain to the grid operator.
Complaints from many consumers
Dimmer flashes
Dimmer turns up and down
Control and communication failures in industrial plants
Frequency converter failures can lead to a lot of disturbance. An error we have experienced on both smaller plants where a machine failed and on frequency driven cooling plants where the entire power grid up to 10 kV was affected: If the grid impedance is too high, the frequency converter cannot maintain its correct current draw and will produce both DC and a lot of noise in a large frequency spectra (large harmonic current). When operating a generator, special attention must be paid to grid conditions. Often 6-8 times the generator's nominal output is required.
Communication errors suddenly occur
Controls goes down
Transformers overheat
Power imbalance
Frequency converter faults are a big topic and a faulty frequency converter can continue to work without an error message. If a part of the input stage is defective, there is a skewed current flow between the phases, resulting in imbalance and harmonic noise, current. Start by examining the current draw of the frequency converter, see more in the Motor Drives course or the physical power quality course
Power imbalance
Equal harmonics on the grid
Wind turbine noise filter
Many power generators have a filter that removes harmonic noise generated by, for example, a wind turbine. These harmonic current filters have a lifetime and if not serviced they will fail and cause problems.
Complaints from larger service area
Dimmer flashes
Generator cannot couple in
Offshore installations
Generator disconnects
The generator on, for example, an offshore installation with many frequency converters has difficulty coupling due to harmonic currents. A standard 6 pulse frequency converter generates a lot of 5th harmonic currents and these are against the direction of the generator and will disrupt the control of the generator. One solution could be to install an active harmonic filter.
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