Electric filter equipment
AssigneeASEA Aktiebolag
InventorBernt Bergdahl
Life of this patent
Estimating the term…
Abstract
An electric filter, for example an harmonic filter in an HVDC convertor, has, in addition to the main filter, a low power model filter having the same frequency characteristic as the main filter. The model filter is supplied with a voltage which is a scaled-down version of the voltage appearing across the main filter. The currents in the main and model filters are sensed at corresponding places in the filters and compared. If a deviation occurs between the sensed currents in the main and model filters, an indicating signal is generated which indicates a deterioration in the performance of the main filter.
Claims6
In an HVDC converter plant having a pair of DC voltage output lines, a harmonic filter comprising:
- a main electrical harmonic filter connected between said output lines for suppressing harmonic signals;
- a model filter having a filter structure and frequency response substantially the same as said main electrical harmonic filter, and a power handling ability substantially less than said main electrical harmonic filter, said model filter connected to receive a fractional representative portion of the voltage on said output lines;
- means connected to structurally corresponding portions of said filters for providing first and second currents representing currents flowing through each of said filters;
- and
- means for sensing a difference between said first and second currents, said means generating an indicating signal when said difference changes whereby an unacceptable change in said main electrical filter is detected.
Dependencies are inferred from the claim text.