Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
1999-12-09
2001-03-20
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S057000
Reexamination Certificate
active
06205039
ABSTRACT:
FIELD OF THE INVENTION AND PRIOR ART
The present invention relates to a device in a line commutated valve of a high voltage converter station located at a high voltage potential level and having a plurality of valve units each having at least one semiconductor component of turn-on-type in the form of a thyristor and for each thyristor first control unit located on high voltage potential level and controlling the thyristor, said first control units being connected to a valve control unit located at a low potential level for communication between the valve control unit and the first control units, and said device being designed to supervise a voltage divider circuit connected across each thyristor and consisting of resistances and capacitors connected in series.
Such high voltage converter stations may for example be stations in plants for transmitting electric power through High Voltage Direct Current (HVDC) for converting direct voltage into alternating voltage and conversely, but the invention is not restricted thereto, but is directed to supervising of all types of high voltage converter stations, in which high voltage here typically may be voltages within the range 10-500 kV. Each valve unit has usually a plurality of semiconductor components in the form of thyristors connected in series, which are controlled simultaneously, so that they act as one single switch, and among which the voltage to be held by the valve unit in a turned-off state of said semiconductor components is distributed, since they normally only can hold 1-10 kV each.
Since high powers are handled by such a high voltage converter station and by that a drop out of parts thereof or the entire station during a certain period of time generates high costs, it is an important desire to be able to supervise different positions of said valve so as to be able to take necessary measures upon deviations from the normal state thereof for avoiding operation interruptions not planned as far as possible and minimise the closing times for maintenance by receiving information about exactly which components have a defect. Information about components starting to get deviating properties without being defect for that sake is also of interest, since correcting measures may be planned timely.
However, the different said positions are located at a high voltage potential level, which makes the supervision thereof difficult, so that the way of proceeding has until now with respect to most of the positions been restricted to carrying out a measurement of a parameter associated with the position in question at a ground potential level so as to then calculate a probable value of the parameter on high voltage potential level. It was therefore until now not possible to supervise a voltage divider circuit mentioned in the introduction, which could have led to unplanned operation interruptions.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a device of the type defined in the introduction, which improves the possibilities to check the state of said voltage divider circuit and by that of such a valve considerably and by that avoid unnecessary breakdowns of components and unplanned operation interruptions.
This object is according to the invention obtained by providing a device of the type defined in the introduction, in which the capacitors of the voltage divider circuit are of a so called self-healing type, in which the capacitance decreases gradually as of the point of time for occurring of a possible defect thereof, that the first control unit associated with the respective thyristor is arranged to register the voltage across the thyristor through said member through a first resistance of the voltage divider at an instant immediately before the turning-on of the thyristor and by that short-circuiting of the capacitor of the voltage divider and through said member register the voltage across a second resistance in the voltage divider circuit at given point of time after said instant, that said means is arranged to calculate a value of the capacitance of the capacitor of the voltage divider on the basis of said values of these two voltages and send information depending thereupon to an arrangement for supervising the valve arranged at a low potential level, and that members are adapted to compare said capacitance value with a rated value of said capacitance and the supervising arrangement is arranged to determine whether a fault has occurred in the voltage divider on the basis of this comparison. By utilising said information about the voltage across said resistances available on high voltage potential level in this way a possible fault of the voltage divider circuit in question may be reliably detected in the supervising arrangement at a “ground level”. Thus, this may take place by combining said voltage measurement with the use of so called self-healing capacitors having defined properties.
According to a preferred embodiment of the invention the supervising arrangement is adapted to determine that a capacitor fault has occurred when a capacitance value calculated falls below said rated value by a given proportion. Thus, a capacitor fault of the voltage divider circuit may in this way be detected through this comparison.
According to another preferred embodiment of the invention a supervising arrangement is adapted to determine that a resistance fault has occurred when a capacitance value calculated exceeds said rated value by a given proportion. Thus, should the capacitance value calculated suddenly exceed said rated value by a given proportion it may not be a question of any capacitor fault any longer, but the resistance has instead become to high. The probability of an occurrence of a resistance fault at the same time as a capacitor fault and that these two faults would balance each other is very low.
According to another preferred embodiment of the invention, which is directed to a device in which the first control units are connected to a valve control unit arranged on low potential level through light conductors for communication between the valve control units and the first control units while separating them galvanically, the first control units have means for treating said values detected and the first control units are adapted to utilise light conductors led back therefrom to the valve control unit to send information resulting from said treatment to the supervising arrangement.
By arranging an increased intelligence on high voltage potential level in this way, i.e. in said first control units for controlling the semiconductor components, and utilising the light conductors already there for sending information resulting from said treatment by said means to the supervising arrangement located on low potential level, it is possible to ensure a reliable supervising of the different positions of such a valve and by that receive a good picture of the state of the valve by simple means and by that at a low cost. By carrying out said measurements on high voltage potential level the parameters in question are measured exactly where the value thereof is of interest, wherethrough sources of fault are reduced to a minimum. Furthermore, no additional arrangements for bringing the values in question to the “ground” is required, since the light conductors already there are used for this purpose while obtaining the galvanic separation required between the high voltage potential level and the low potential level. The only thing required is that said first control units are supplemented by said means and the different measuring members are applied on suitable places and connected to the first control unit, which may take place through conductors of electricity.
Further advantages as well as advantageous features of the invention appear from the following description and the other dependent claims.
REFERENCES:
patent: 4651251 (1987-03-01), Thiele
patent: 5155673 (1992-10-01), Takahashi et al.
patent: 5367197 (1994-11-01), Klerfors
patent: 5452196 (1995-09-01), Itoh
patent: 5521526 (1996-05-01), Nyberg et al.
pat
Åström Urban
Asplund Gunnar
Bjorklund Hans
Nyberg Krister
Siljestrom Roland
ABB AB
Berhane Adolf Deneke
Dykema Gossett PLLC
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