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(11) | EP 2 128 882 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | High voltage circuit breaker |
| (57) A high voltage live tank circuit breaker comprising a support insulator (20); at
least one horizontally arranged elongated current interrupter (10) provided on the
support insulator (20); terminals (30) connected to the ends of the current interrupter;
optionally a horizontally arranged elongated capacitor (50) and/or resistor (60) connected
between the terminals in parallel with the current interrupter (10); and at least
one corona ring (40) arranged to at least partly surround one of the terminals. The
corona ring (40) is arranged such that the vertical distance (d1) between the inner
surface of the lower end of the corona ring and a center axis (10a, 50a, 60a) of the
current interrupter (10), the optional capacitor (50), or the optional resistor (60),
whichever being located lowest, is between about 1.5 and about 4 times shorter than
the distance (d2) between the inner surface of the upper end of the corona ring and
the center axis.
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FIELD OF INVENTION
BACKGROUND OF THE INVENTION
[0002] Electrical power transmission networks are protected and controlled by high voltage circuit breakers. Such circuit breakers are divided in two classes: live tank circuit breakers (LTB) where the enclosure that contains the breaking mechanism is at line potential and the metal enclosed circuit breakers (MEB) where the enclosures are at earth potential.
[0003] The live tank circuit breakers at high voltage levels have to handle the high potential at the terminal electrodes where the tubes or cables are connected to pass the current through the circuit breaker. The high potential creates high electrical field stress at the terminal electrodes. Commonly the terminal electrodes are shielded with corona rings, which purpose is to reduce the local electrical field stress by their smooth shape and relatively large area compared to the terminals.
[0004] Two different corona ring designs are common. Either the corona rings are placed as close to the terminal electrode as possible. If capacitors or pre-insertion resistors are used the same philosophy is used. Alternatively, a circular corona ring is placed symmetrically around the circuit breaker center axis.
[0005] The live tank circuit breaker external isolation media is air. The external insulation is verified with dielectric tests following the requirements in applicable standards. These verifying tests for high voltage circuit breakers include both dry and wet tests since the high voltage circuit breaker is an out door equipment.
SUMMARY OF THE INVENTION
[0006] During such wet tests where the rain is collected all over the surface of the circuit breaker and the corona rings. The water is pouring downwards on the surface and collected at the lowest position on each individual part of the circuit breaker and finally it is falling of the surface towards ground.
[0007] The water drops will be affected by the high voltage and change shape; they will be sharper then normal and increase the local electrical field stress.
[0008] The invention is based on the realization that during switching over voltages during wet conditions the local electrical field at the corona rings lower part will increase in comparison to dry conditions.
[0009] An object of the present invention is therefore to provide a high voltage live tank circuit breaker with an improved dielectric withstand capability, in particular during wet conditions.
[0010] A further object of the invention is to provide such a high voltage circuit breaker, which is robust, accurate, uncomplicated, space-saving, and inexpensive, and which has an optimum performance and which fulfills existing safety requirements.
[0011] The above objects are attained by high voltage circuit breakers as claimed in the appended patent claims.
[0012] According to a first aspect of the invention there is provided a high voltage live tank circuit breaker comprising a support insulator, a horizontally arranged elongated current interrupter provided on the support insulator, terminals connected to the ends of the current interrupter, and at least one corona ring arranged to at least partly surround at least one of the terminals.
[0013] The corona ring is arranged such that the vertical distance between the inner surface of the lower end of the corona ring and a center axis of the horizontally arranged elongated current interrupter is between about 1.5 and about 4 times shorter than the distance between the inner surface of the upper end of the corona ring and the center axis.
[0014] If the high voltage live tank circuit breaker comprises-a horizontally arranged elongated capacitor and/or resistor connected between the terminals in parallel with the current interrupter, the above distances are measured with respect to the center axis of the current interrupter, the capacitor, if present, or the resistor, if present, whichever being located lowest.
[0015] By the high voltage circuit breaker according to the invention, a more evenly distributed electrical field around the corona ring is obtained in presence of water. As a result the high voltage circuit breaker gets improved dielectric withstand capability in wet conditions.
[0016] The wet conditions are the most severe and at the same time the hardest to theoretically calculate and dimension for each circuit breaker design. Different designs have therefore been experimentally tested in a high voltage laboratory and it has been found that the critical factor is the vertical position of the corona rings. A considerable improvement could be found within the ranges given above.
[0017] In most situations it seems like an optimum is achieved when the distance between the inner surface of the lower end of the corona ring and the center axis of the current interrupter, the capacitor, if present, or the resistor, if present, whichever being located lowest, is about 30 % of the total inner height of the corona ring.
[0018] Efforts have also been made to reproduce the result by means of 3D electrical field calculations. The limitations in modeling of water drops, however, make the results of the calculations uncertain.
[0019] Further characteristics of the invention and advantages thereof, will be evident from the following detailed description of preferred embodiments of the present invention given hereinafter and the accompanying Figs. 1-4, which are given by way of illustration only and are thus not limitative of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
Fig. 1 illustrates schematically in a side elevation view a high voltage circuit breaker according to an embodiment of the invention.
Fig. 2 illustrates schematically in an end view a current interrupter and a corona ring as being comprised in the high voltage circuit breaker of Fig. 1.
Fig. 3 illustrates schematically in an end view a current interrupter, a capacitor and a corona ring as being comprised in a high voltage circuit breaker according to a further embodiment of the invention.
Fig. 4 illustrates schematically in an end view a current interrupter, a capacitor, a resistor, and a corona ring as being comprised in a high voltage circuit breaker according to a yet further embodiment of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0021] In the following a detailed description of preferred embodiments of the present invention will be given. In this description, the term high voltage will be used for voltages of 1 kV and higher. It shall, however, be noted that the present invention is primarily intended for high voltage circuit breakers with much higher voltage ratings, such as 245 kV and above.
[0022] Fig. 1 illustrates schematically in a side elevation view a one-phase high voltage live tank circuit breaker, which comprises two horizontally arranged and serially connected elongated current interrupters 10 arranged on a support insulator 20. The current interrupters 10 may be referred to as breaker or extinguishing chambers and the assembly of two current interrupters 10 may be referred to as a breaking unit. Each of the current interrupters 10 is connected to a terminal 30 at its far end and to a connection flange 32 at its inner end.
[0023] Further, the circuit breaker comprises a respective corona ring 40 arranged to at least partly surround the terminal 30 connected to the far ends of the serially interconnected current interrupters 10, that is, typically no corona rings are arranged around the connection flanges 32, which interconnects the current interrupters 10.
[0024] Fig. 2 illustrates schematically in an end view one of the current interrupters 10 and one of the corona rings 40 of the high voltage circuit breaker of Fig. 1. The supports 41 holding the corona ring 40 are illustrated.
[0025] According to the invention each of the corona rings 40 is located such that the vertical distance d1 between the inner surface of the lower end of the corona ring 40 and a center axis 10a of the current interrupter 10 is between about 1.5 and about 4 times shorter than the distance d2 between the inner surface of the upper end of the corona ring 40 and the center axis 10a.
[0026] Preferably, the vertical distance d1 between the inner surface of the lower end of the corona ring 40 and the center axis 10a is between about 2 and about 3 times, and preferably about 7/3, shorter than the distance d2 between the inner surface of the upper end of the corona ring and the center axis.
[0027] In other words, the distance d1 is between 20 and 40 %, preferably between 25 and 33 %, and most preferably about 30 %, of the sum of the distances d1 and d2.
[0028] It shall be appreciated that the corona rings 40 may be closed or open-ended and they can have different shapes, though the corona rings 40 in Figs. 1-2 are torus shaped.
[0029] Provided that the corona rings are arranged symmetrically around the current interrupters 10 in the lateral plane the sum of the distances d1 and d2 corresponds to the inner diameter of the corona rings 40.
[0030] It shall further be appreciated that there can be arranged more corona rings around each terminal. Commonly, the corona rings are provided in pairs with a short fixed distance in between.
[0031] It shall further be appreciated that circuit breaker may, for each current interrupter, comprise a horizontally arranged elongated capacitor and/or resistor connected between the terminals in parallel with the current interrupter. In such instance, each corona ring is arranged such that the vertical distance between the inner surface of the lower end of the corona ring 40 and a center axis of the current interrupter (10), of the elongated capacitor, or of the resistor, whichever being located lowest, is between about 1.5 and about 4 times shorter than the distance between the inner surface of the upper end of the corona ring and that center axis.
[0032] Figs. 3 and 4 illustrate circuit breakers with the above mentioned capacitor and/or resistor.
[0033] Fig. 3 illustrates schematically in an end view a current interrupter 10, a capacitor 50 and a corona ring 40 as being comprised in a high voltage circuit breaker according to an embodiment of the invention. Here, the corona ring 40 has an upper essentially horizontal bar 40a and a lower essentially horizontal bar 40b and the vertical distance d1+d2 between the inner surface of the lower end of the corona ring and the inner surface of the upper end of the corona ring is the distance between the bars 40a-b.
[0034] As can be seen in Fig. 3 the central axis 50a of the capacitor 50 is located below the central axis 10a of the current interrupter 10. As a result the corona ring 40 is arranged as above with respect to the central axis 50a of the capacitor 50. The distances d1 and d2 are indicated in Fig. 3, whereas the corona ring supports have been omitted.
[0035] Fig. 4 illustrates schematically in an end view a current interrupter 10, a capacitor 50, a resistor 60 and a corona ring 40 as being comprised in a high voltage circuit breaker according to an embodiment of the invention.
[0036] As can be seen the central axis 60a of the capacitor 60 is located below the central axis 10a of the current interrupter 10 and below the central axis 50a of the capacitor. As a result the corona ring 40 is arranged as above with respect to the central axis 60a of the resistor 60. The distances d1 and d2 are indicated in Fig. 4, whereas the corona ring supports have been omitted.
1. A high voltage live tank circuit breaker comprising:
- a support insulator (20);
- at least one horizontally arranged elongated current interrupter (10) provided on said support insulator (20);
- terminals (30) connected to the ends of said current interrupter; and
- at least one corona ring (40) arranged to at least partly surround one of the terminals,
characterised in that
- said corona ring (40) is arranged such that the vertical distance (d1) between the inner surface of the lower end of said corona ring and a center axis (10a) of said horizontally arranged elongated current interrupter (10) is between about 1.5 and about 4 times shorter than the distance (d2) between the inner surface of the upper end of said corona ring and said center axis.
2. The circuit breaker of claim 1 wherein the vertical distance (d1) between the inner
surface of the lower end of said corona ring and said center axis (10a) is between
about 2 and about 3 times, and preferably about 7/3, shorter than the distance (d2)
between the inner surface of the upper end of said corona ring and said center axis.
3. A high voltage live tank circuit breaker comprising:
- a support insulator (20);
- at least one horizontally arranged elongated current interrupter (10) provided on said support insulator (20);
- terminals (30) connected to the ends of said current interrupter;
- a horizontally arranged elongated capacitor (50) and/or resistor (60) connected between the terminals in parallel with the current interrupter (10); and
- at least one corona ring (50) arranged to at least partly surround one of the terminals,
characterised in that
- said corona ring (40) is arranged such that the vertical distance (d1) between the inner surface of the lower end of said corona ring and a center axis (10a, 50a, 60a) of said horizontally arranged elongated current interrupter (10), of said horizontally arranged elongated capacitor (50), or of said horizontally arranged elongated resistor (60), whichever being located lowest, is between about 1.5 and about 4 times shorter than the distance (d2) between the inner surface of the upper end of said corona ring and said center axis.
4. The circuit breaker of claim 1 wherein the vertical distance (d1) between the inner
surface of the lower end of said corona ring and said center axis (10a) is between
about 2 and about 3 times, and preferably about 7/3, shorter than the distance (d2)
between the inner surface of the upper end of said corona ring and said center axis.
5. The circuit breaker of any of claims 1-4 wherein the corona ring has a torus shape
and the vertical distance (d1+d2) between the inner surface of the lower end of said
corona ring and the inner surface of the upper end of said corona ring is the inner
diameter of said corona ring.
6. The circuit breaker of any of claims 1-4 wherein the corona ring has an upper essentially
horizontal bar and a lower essentially horizontal bar and the vertical distance (d1+d2)
between the inner surface of the lower end of said corona ring and the inner surface
of the upper end of said corona ring is the distance between said bars.
7. The circuit breaker of any of claims 1-6 wherein the corona ring is open-ended.
8. The circuit breaker of any of claims 1-7 comprising a corona ring arranged to at least
partly surround said one of the terminals, the corona rings being arranged concentrically
with respect to one another.
9. The circuit breaker of any of claims 1-8 comprising a corona ring arranged to at least
partly surround another one of the terminals, the corona rings being arranged concentrically
with respect to one another.
10. The circuit breaker of any of claims 1-7 comprising a horizontally arranged elongated
current interrupter (10) and terminals (30) connected to the ends of the current interrupter,
the current interrupters being arranged concentrically with respect to one another
and being serially connected, wherein said one of the terminals, which is at least
partly surrounded by the corona ring (40), is an outer terminal of said serially connected
current interrupters; and further comprising a corona ring (40) arranged to at least
partly surround the other outer terminal of said serially connected current interrupters,
the corona rings being arranged concentrically with respect to one another.
11. A three-phase high voltage live tank circuit breaker comprising three of the circuit
breaker of any of claims 1-10, one for each phase.