Vision Power Quality / application
Vision Power Quality is an application which transforms measurement data about voltage quality into useful information. This is achieved by means of smart processing, aggregation and visualisation. The application uses classification to report the PQ levels in a uniform and comparable way.
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Main screen with overview of the different PQ aspects
Configuration settings of classification
Classification results of the PQ flicker aspect
Chart with 10-min. average Plt values over a week
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Classification
The Vision Power Quality application is based on the classification methodology introduced by Dr. J.F.G. Cobben°.
This classification technique is analogous to the one already in use to classify the energy efficiency of household appliances such as washing machines. This ABC classification uses letters combined with colours to label the various levels of quality. The same format is adapted for voltage quality, where A stands for a very good quality (green) and F stands for a very poor quality (red). The voltage quality is devided into six aspects:
- voltage variations
- voltage dips
- frequency variations
- flicker Plt
- THD
- unbalance.
The classification method for this voltage quality is based on the Standard deviation, Average Value (STAV) method.
This means that for a week of measurements the average (m) and standard deviation (σ) are calculated for every aspect. So each aspect is represented by a single point on the (m, σ) plane. Dips are handled in an alternative way. The different classes are set as lines in the (m, σ) plane which represents a fixed probability of (not) exceeding a certain m.
The limits sets by the Dutch national regulator (mainly based on the European standard EN50160) are incorporated in the classification. These limits are set as the boundary between the classes C and D.
User interface
The Vision Power Quality application presents the information in different overviews to its users. In the main screen the PQ levels of each aspect for the measurements locations are shown in separate bars. In the left part of the main screen, the names of the measurements are shown in a tree. This tree allows for grouping different voltage levels, years, weeks or locations.
For instance, MV and LV measurements. User can navigate into the tree: accordingly to the selected node the aggregation and visualisation is performed over all underlying nodes.
Example
In the top figure on the right it is seen that the quality level is mostly of class A and B, which is good, except for flicker (4th bar from the left) in a certain location and period where only class F is met.
The user can now decide to get more detail, and look only to the classification of the aspect of flicker. In the figure below, the graph of the classification results are shown for the aspect of flicker. It is shown that the PQ level of phase L3 in some locations in week 15 is located near the F class outside boundary.
If the user still wants more detail the 10-minute average measurements of the selected week for a single measurement location can be plotted into a chart (see the graph).
From this chart it is clearly seen that for the L3 phase the limit set by the Dutch national regulator of 1% Plt is exceeded for the first half of the week.
° J.F.G. Cobben, 2007,
“Power Quality, Implications at the Point of Connection”
ISBN: 978-90-386-1030-6
