Recognize and remedy poor network quality
Germany is at the top in terms of security of supply of electrical energy. However, this does not apply to high voltage and grid quality. The increasing use of non-linear consumers and power electronics as well as the increased use of HVDC lines (high-voltage direct current transmission) on land and in offshore wind farms are putting more and more pressure on grid quality. This causes problems for other systems, installations and machines; IT and telecommunications systems are particularly susceptible. In order to be able to prevent problems in good time, it is important to get to the bottom of the cause.
IT crashes, malfunctions in machine control systems, unexpected tripping of fuses and circuit breakers, damage to power capacitors or compensation systems - all of these can indicate poor power quality. It is mainly caused by the increased use of non-linear loads and power electronics. These are devices or components in which the current drawn does not have the same waveform as the voltage, e.g. rectifiers, speed control systems for motors, uninterruptible power supplies (UPS), welding equipment, induction and arc furnaces, but also lighting (LEDs) and an increasing number of single-phase devices and their power supply units. Their non-linear current consumption greatly increases the harmonic components in the power grid, i.e. the non-sinusoidal components that are superimposed on the fundamental voltage and current oscillation. This in turn influences the sinusoidal voltage, which leads to the problems mentioned above. The voltage quality is essentially influenced by the following factors:
- Harmonics of current and voltage
- Voltages and currents of more than 2 kHz
- Rapid voltage changes (flicker) and slow voltage changes
- Short-term or commutation dips
- Asymmetry of current and voltage or on individual phases
- Audio frequency ripple control signals
Measurements clearly show causes
Although the fault patterns described indicate poor power quality, they can also have other causes. Preventive measurements are therefore necessary to determine the quality of the voltage and to be able to take suitable countermeasures in good time before a failure or fault occurs. They should generally be carried out after the transformer feeds on the low-voltage side and for large consumers such as converters or rectifiers. As faults often occur unpredictably and sporadically, it is advisable to measure the power quality continuously.
An energy and power measuring device such as the econ sens3 from econ solutions is suitable for this purpose. Not only does it record all the important characteristics of electrical power, energy, currents and voltages, it also supports power quality analysis in accordance with EN 50160. The limit values from the standard are already stored in the sens3, but they can also be set individually. Depending on the grid impedance, even minor deviations can have negative consequences. If one or more limit values are exceeded, the sens3 triggers an alarm; either via a potential-free contact or via an e-mail with the type of fault in plain text and a graph of the current and voltage curve triggered at the time of the fault. It also saves the waveform of the current and voltage in the internal memory so that it can be visualized again afterwards.
Limit violations and grid events such as harmonics, voltage fluctuations, flicker, etc. are clearly displayed in an EN 50160 report. The report is available in txt format and as a JSON export. This means that the event can also be traced and documented retrospectively. For companies that also use the econ3 energy management software, the measurement data from the sens3 is automatically transferred via the network (TCP/IP) and seamlessly integrated into the software. This allows even simpler and automated evaluation.
Measures against poor power quality
The main cause of poor power quality is excessive harmonics. Reducing the harmonic content to improve the power quality is quite complex and expensive. Active or passive filters are usually used for this purpose.
Passive filters consist of a tuned absorption circuit for each harmonic consisting of inductances and capacitances. This is usually difficult to implement in practice. Another disadvantage of this solution is that it only ever improves the grid feedback behavior for the respective installation. This means that each extension may require a new investment.
Active harmonic filters offer a more convenient and better solution. Here, the compensation of grid perturbations remains effective even with installation extensions. An active harmonic filter is connected in parallel to the harmonic generators. By analysing the harmonic current generated by the non-linear loads and supplying the counter-phase compensation current, it completely neutralizes the corresponding harmonic currents at the connection point as part of the design. This means that the combination of harmonic filter and load in the grid acts like a linear load that consumes a sinusoidal current.
However, an impeccable and clearly laid out electrical installation is just as important for ensuring adequate grid quality. By measuring the differential voltage between the neutral conductor and PE in volts rms, impermissible currents can be detected immediately. The sens3 energy and power measuring device is also ideal for this, as it also enables limit value monitoring for these measurements. This ensures that the voltage in the company network is always of the required quality.