EVERYTHING IN THE GREEN AREA – SYSTEM FAILED
… and this despite conformity of the voltage quality
Now, suppose…
The industrial park has just been completed. All plants and systems are modern and state of the art. During planning and implementation, strict attention was paid to ensuring that all equipment and machines used comply with the EMC directives regarding emission and immission.
In addition, a statistical evaluation of the electrical network parameters according to standard EN 50160 confirms that all parameters are within the green range (see graph below). A comprehensive energy monitoring system records all consumption data. The entire system works optimally, is energy efficient and breaks down twice a week.
This phenomenon is not unique. Usually the operators are faced with a mystery. Despite careful planning and compliance with all regulations, serious faults occur which cannot be identified with any of the measuring equipment used. The reason for this is the complexity of today’s plants.
In the worst case, the addition of interference levels can affect the system. Network phenomena do not affect the overall statistical evaluation if they occur individually, which in total leads to an incorrect assessment of the plant reliability.
What is conformity assessment?
These are statistical network quality evaluations in order to prove required conformity or identify possible problems on a statistical basis. However, caution is required. Such a statistically averaged evaluation does not imply that no events took place during the period under consideration.
Standards such as EN50160 (Europe), IEEE519 (US), GB/T (China), etc. can be used to prepare conformity assessments. A statistical minimum period of 7 days should not be underrun when generating the ratings. As a rule, the evaluations are then issued in a report form, whereby the format of the report is not subject to any standard.
Events are missing in the statistical evaluation
A glance at the definition of EN 50160 quickly makes it clear that even voltage dips, as shown on the left, do not appear in the statistical analysis. The reason lies in the statistical evaluation, as only 10-minute averages are considered. Therefore the events remain “invisible” in a purely statistical evaluation. As a result, machines or plants can be affected even though the statistics are set to “green”.
Excerpt from EN 50160
- at least 95 % (LV) or 99 % (MV) of all 10-minute mean values of the effective value of the supply voltage must be within the specified
Limit values - no 10-minute average value of the effective value of the supply voltage must be outside the limit of +10 % / -15 % Un (NS) or ±15 %.
Uc (MS)
Conclusion
Even if the statistical evaluation (e.g. according to EN50160, etc.) confirms conformity, machines and plants can be affected due to poor power quality.