Quality of care
The following criteria are summarized under the quality of supply in electricity supply networks:
- Availability or reliability of supply;
- Voltage quality
- Grid frequency stability .
Sometimes the term service quality is also mentioned, which refers to the quality of the relationship between supplier and customer.
The term “power quality” is often used in German for the quality of supply.
criteria
reliability
The reliability of the supply is expressed in the absence of longer supply interruptions and is related to a specific connection point or a region of the supply area. The "Customer Minutes Lost" variable shows the minutes lost per year and customer; the smaller this value, the higher the availability. The power supply in Germany is very good here in an international comparison.
Voltage quality
The voltage quality is also always related to a certain connection point, such as a customer connection, and is divided into various criteria, the most important of which is the current level of the effective mains voltage in a fixed tolerance range around the nominal voltage . Furthermore, the voltage quality only includes a minimal proportion of flicker , transients and harmonics .
Grid frequency stability
In the usual supraregional supply networks for alternating current, the network frequency is a uniform quality factor in the entire network and is not related to a specific connection point.
The larger an interconnected network and the better power plants can be controlled, the more stable the network frequency can be kept within a tolerance range. The figure on the right shows the course of the grid frequency and its deviation over 48 hours for some control areas, which all fluctuate around the nominal value of 50 Hz. The smallest deviations occur in the West and Central European Network System (UCTE). However, in recent years, due to the exchange of electricity in blocks, frequency deviations have often been observed when power plants set the new output value at the change of hour and no longer continuously adjust the generator output to the control area load in load following operation . In the control area NORDEL which among other things, Sweden includes short-term load fluctuations are well-balanced, long-term variations over a few hours but are clearly visible. The island network in the United Kingdom , which includes the ENTSO-E control area Regional Group UK , shows the clearest deviations due to its size restrictions and the low reserves operated network in Singapore .
In the European network system, frequency errors are compensated for in the long term using the quaternary control so that the deviation is never more than 1000 periods.
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In extreme cases, failures or errors can lead to an underfrequency , which is often associated with load shedding and widespread power outages and thus reduces the reliability of the supply.
literature
- Adolf Schwab: electrical energy systems . Springer-Verlag, Berlin 2006, ISBN 978-3-540-29664-5 .
- Math Bollen, Irene Yu-Hua Gu: Signal Processing Of Power Quality Disturbances . Wiley-Interscience, 2006, ISBN 978-0-471-73168-9 .
Individual evidence
- ↑ Tobias Weißbach and Ernst Welfonder: High Frequency Deviations within the European Power System, Origins and Proposals for Improvement (PDF; 6.5 MB), VGB PowerTech 06/2009, pp. 26–34.