EP3926654B1

EP3926654B1 - Circuit breaker with field deflection element

Info

Publication number: EP3926654B1
Application number: EP20180415.0A
Authority: EP
Inventors: Andreas Blaszczyk; Bernardo Galletti; Martin Kriegel; Martin Seeger
Original assignee: Hitachi Energy Ltd
Current assignee: Hitachi Energy Ltd
Priority date: 2020-06-17
Filing date: 2020-06-17
Publication date: 2023-12-06
Anticipated expiration: 2040-06-17
Also published as: EP3926654A1

Description

FIELD OF THE INVENTION

The present disclosure relates generally to a gas-insulated high or medium voltage circuit breaker including a first arcing contact and a second arcing contact, wherein at least one of the two arcing contact is axially movable along a switching axis, wherein during a breaking operation, an electrical discharge between the first arcing contact and the second arcing contact is formed in a arcing region.

BACKGROUND OF THE INVENTION

Circuit breakers are well known in the field of medium and high voltage breaking applications. They are capable of being used for interrupting a current, when an electrical fault occurs. As an example, circuit breakers have the task of opening contacts and keeping them apart from one another in order to avoid a current flow even in case of high fault current and/or electrical potential originating from the electrical fault itself.
When interrupting the current flowing in the electrical circuit, an arc is generally generated. This arc is extinguished by the quenching gas from within the nozzle, such that the gap between the contacts repeatedly can withstand the voltage.
It is important for the reliability and durability of the circuit breaker to prevent (reduce) the risk of alternative paths of the discharge, specifically to prevent the arc from entering towards upstream volumes within the nozzle (e.g., from entering a heating channel of the nozzle towards a heating volume in which high pressure gas may be stored). For example, for arcing times shorter than minimum arcing times, a reignition occurs and the interruption takes place in the next zero crossing of the fault current. In this case, it is desired that the electric discharge originating from the reignition takes place between the arcing contacts, and that no side branching towards the upstream volumes occurs.
The utility model DE 20 2017 103 766 U1 proposes a design of the nozzle system with a main nozzle and an auxiliary nozzle, designed to avoid an alternative path of the discharge. To this purpose, the nozzle has a first channel zone opening into the breaker's arcing zone; and the main or auxiliary nozzle has an extension section in a direction parallel to the central axis bridging the first channel zone. The extension section is designed in such a way that the inner jacket of the auxiliary nozzle and the inner jacket of the main nozzle are connected to each other in a direction parallel to the central axis without interruption or substantially without interruption. In the extension section, openings connecting the arcing zone with the channel are provided.
EP 2362407 A1 describes a nozzle for a medium and/or high voltage breaker, whereby the breaker comprises at least two arcing contact members movable in relation to one another to at least one closed position where the arcing contact members are electrically connected to one another, and to at least one open position where the arcing contact members are disconnected and form an electrically insulating gap between them.
US 4420662 A describes compressed-gas circuit breaker which possesses two contact members, which move relative to one another, and a nozzle, which is made of dielectric material and is attached to a first member of the two contact members.

SUMMARY OF THE INVENTION

An object of the disclosure can be considered to provide an improved gas-insulated high or medium voltage circuit breaker which reduces the abovementioned problems occurring during current interruption, and in particular which further reduces the risk of the discharge traveling towards an upstream direction of the nozzle (e.g., into the heating channel).
The invention is defined by the features of the independent claims.
In a first aspect, a gas-insulated high or medium voltage circuit breaker is provided. It comprises a pin contact and a second contact being configured to be moveable with respect to each other along a longitudinal axis of the circuit breaker between an open and a closed configuration of the circuit breaker, the pin contact and the second contact defining an arcing region in which an electrical discharge is formed during a current breaking operation; and an auxiliary nozzle comprising an electrically insulating material, that at least partially surrounds the second contact, a main nozzle comprising an electrically insulating material, that encloses the auxiliary nozzle at least partially, and a heating channel provided between the auxiliary nozzle and the main nozzle, wherein the heating channel separates the auxiliary nozzle from the main nozzle axially and radially and enables a fluid communication between the arcing zone and an upstream pressure volume, wherein at least one conductive element is embedded within the insulating material of the main nozzle and is electrically floating, wherein the at least one conductive element is arranged around the arcing region and is configured to generate an electrical field due to the presence of an electrical discharge in the arcing region, the electrical field being configured for deflecting the electrical discharge which propagates from the pin contact along an inner surface of the main nozzle towards the second contact.
In a second aspect, a method for operating a gas-insulated high or medium voltage circuit breaker is provided. The method comprises deflecting an electrical discharge which propagates from a pin contact along an inner surface of a main nozzle towards a second contact of the circuit breaker in an arcing region, wherein at least one conductive element is embedded as a floating electrode in the insulating material of the main nozzle around the arcing region and is configured to generate an electrical field due to the presence of the electrical discharge in the arcing region, and wherein the electrical field is configured for deflecting the electrical discharge (e.g., towards the second contact and/or towards a center axis of the breaker).
Thus, acording to an aspect of the invention, a floating electrode is provided for deflecting the discharge away from the upstream pressure volume, e.g., away from a channel (e.g., heating channel) leading to the upstream pressure volume.
Aspects, embodiments, and features of the present disclosure are apparent from the claims, the description, and the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following:

FIG. 1 shows a circuit breaker according to an embodiment of the disclosure;
FIG. 2A shows an exemplary illustration of a conductive element as of embodiments of the disclosure during a breaking operation;
FIG. 2B shows the conductive element of Fig. 2A at a later point in time during the breaking operation;
FIG. 3 shows a circuit breaker according to an embodiment of the disclosure, with a detailed view on a field deflection element;
FIG. 4 shows a circuit breaker according to an embodiment of the disclosure, with a detailed view on a field deflection element;
FIG. 5A shows a partial illustration of a conductive element as of embodiments of the disclosure;
FIG. 5B shows a further partial illustration of a part of a conductive element as of embodiments of the disclosure.
FIG. 6 shows a cross-sectional view of a conductive element according to embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference will now be made in detail to the various embodiments of the disclosure, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the disclosure and is not meant as a limitation of the disclosure. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.
No special definition of a term or phrase, i.e. a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e. a meaning other than that understood by skilled artisans, such a special definition will be expressly set forth in the specification in a definitional manner that directly and unequivocally provides the special definition for the term or phrase.
The term circuit breaker generally refers to a gas-insulated high or medium voltage circuit breaker. The circuit breaker may be a puffer type circuit breaker or a self-blast circuit breaker or a combination thereof. Generally, the terms "deflection" and "push-out effect", as well as "deflect" and "push" are used interchangeably herein.
With exemplary reference to Figs. 1 to 5B, embodiments of a gas-insulated high or medium voltage circuit breaker 100 according to the present disclosure are described.
Fig. 1 shows a schematic sectional view of an embodiment of a circuit breaker 100, which can be combined with other embodiments described herein. The gas-insulated high or medium voltage circuit breaker 100 includes a pin contact 120 and a second contact 130 being configured to be moveable with respect to each other along a longitudinal axis 190 of the circuit breaker 100 between an open and a closed configuration of the circuit breaker. The pin contact 120 and the second contact 130 define an arcing region 180 in which an electrical discharge 160 is formed during a current breaking operation.
An auxiliary nozzle 150 comprises an electrically insulating material that at least partially surrounds the second contact 130. A main nozzle 110 comprises an electrically insulating material that encloses the auxiliary nozzle 150 at least partially. The insulating material is typically PTFE, but may be any other suitable material. A heating channel 140 is provided between the auxiliary nozzle and the main nozzle, wherein the heating channel 140 separates the auxiliary nozzle from the main nozzle axially and radially. It enables a fluid communication between the arcing zone 180 and an upstream pressure volume 155. The heating channel 140 enters the arcing volume 180 via a heating channel entrance 145.
The circuit breaker 100 is shown in the course of a breaking operation, when an electrical discharge 160 occurs in the arcing region 180. The electrical discharge 160 propagates from the pin contact 120 along an inner surface 175 of the main nozzle 110 towards the second contact 130 in a direction along the longitudinal axis 190 of the circuit breaker 100.
According to embodiments, the at least one conductive element 360 is provided in the main nozzle 110. The at least one conductive element 360 is embedded within the insulating material of the main nozzle 110. The conductive element is electrically floating, that is, it is entirely embedded in the insulating material of the main nozzle 110.
In embodiments, the at least one conductive element 360 is typically annularly shaped, in particular rotational symmetric, and is arranged substantially concentric with the arcing region 180, hence it has the longitudinal axis 190 as a middle axis or axis of rotational symmetry. As is described further below, in embodiments, the conductive element 360 may be a continuous ring, or may be segmented ring or ring structure with segments located along a circumferential path.
The conductive element 360 is electrically isolated from and has no connection to any metallic or conductive parts of the circuit breaker 100. The at least one conductive element 360 is configured to generate an electrical field when an electrical discharge 160 occurs in the arcing region 180. The electrical field is configured - which is described below - for deflecting the electrical discharge 160, which propagates from the pin contact 120 along an inner surface 175 of the main nozzle 110 towards the second contact 130. Further, the electrical field is configured so that the electrical discharge is deflected away from the inner wall 175 of the main nozzle 110. Consequently, it is also deflected away from the heating channel entrance 145 which opens in the inner wall 175.
Hence, according to embodiments, the electrical discharge 160, or a fraction of it, is prevented from entering the heating channel 140 via the heating channel entrance 145. The electrical field of the conductive element 360 is generated by the influence of the charge of the electrical discharge 160, having an electrical field which is present in the insulating material of the main nozzle 110 and thus also in the conductive element 360. A charge separation or charge displacement is caused by the electrical field inside the at least one conductive element 360.
Fig. 2A shows a detailed view on the conductive element 360 of Fig. 1 shown during a breaking operation of circuit breaker 100. The electrical discharge 160 comes from the pin contact 120 and propagates along the inner wall 175 of the main nozzle 110 (direction of propagation indicated by arrow). The discharge, which for the sake of illustration is supposed to have positive polarity, has a discharge head 165. The discharge head 165 is thus the first part of the electrical discharge coming into the vicinity of the conductive element 360. This moment is shown in Fig. 2A. More precisely, as is illustrated, the first part of the conductive element 360 which is affected by the discharge head 165 is the first portion 300. As the electrical discharge 160, as well as the discharge head 165 being part of it, comprises ionized, positively charged molecules of the quenching gas, it is positively charged. Thus, the discharge head 165 attracts with its electrical field, through the insulating material of the main nozzle 110 (not shown in Fig. 2A, refer to Fig. 1), negative charges in the at least one conductive element 360 at the first portion 300. Simultaneously and consequently, charges with the same positive polarity as the discharge 160 are pushed towards the second portion 310 of the conductive element 360. This happens in a very short time, so that the charge separation in the conductive element 360 may be regarded to be present as soon as the discharge head 165 has reached the vicinity of the first portion 300 of the conductive element 360, hence the situation as shown in Fig. 2A. While the abovementioned discharge has been described as a positive discharge for the sake of illustration, the discharge and charge separation scenarios are valid, in an analogous manner, for a negative discharge as well; in this case the polarities shown in Fig. 2A are reverse.
Due to the high speed of charge separation - which was examined by the inventors experimentally to be at least one order of magnitude faster than the speed of the propagating discharge head 165 of discharge 160 - the positive charge induced in the second portion 310 of conductive element 360 will push away the discharge head 165 from the surface 175 of the nozzle body 110. This is happening in a very short period of time after the situation depicted in Fig. 2A, namely when the discharge head 165 has further propagated in the direction (arrow) towards the second portion 310 of the conducting element 360, which is depicted in Fig. 2B.
Fig. 2B shows a situation when the discharge head 165 has already moved along second portion 310 of conductive element 320. Due to the discharge head 165 being a part of the electrical discharge 160 and thus having positive polarity, the discharge head is pushed away from the second portion 310 due to the positive charge of the second portion 310. Consequently, as the electrical discharge 160 moves constantly towards the second contact 130 of the circuit breaker 100 (as shown in Fig. 1), every part of the electrical discharge - differently expressed, every ion comprised therein - is pushed away by the positive charge accumulated in second portion 310 of the conductive element, resulting in the situation as depicted in Fig. 2B and in Fig. 1.
Since the second portion 310 of the conductive element 360 is typically located in the vicinity of the entrance 145 of the heating channel 140, this "push-out" effect avoids a heating-channel discharge or flash-over, which is generally highly undesirable and which may leave traces in the heating channel.
The charge displacement of the charge carriers within the conductive element 360, which is induced by the electrical field of the discharge head 165, takes place in a time period which is much shorter, as was described at least one order of magnitude, than that which the discharge head 165 requires to move along the distance from the first portion 300 of the conductive element to the second portion 310. In other words, the desired charge separation/displacement within the conductive element 360 is finished long before the discharge head 165 and hence the discharge 160 reaches the entrance of the heating channel 145, which is typically located close to, or directly besides, the conductive element 360, refer to Fig. 1.
The time needed for the charge separation in the conductive element 360, and thus the situation shown on Fig. 2A, may in embodiments be approximately 0.25 ns. This is significantly less than the time to breakdown, which is the complete development of an electrical discharge 160 between pin contacts 120 and second contact 130, which is typically in a range between 200 ns and 2 ms according to experimental results.
Furthermore, the time needed for the charge separation was experimentally shown to be at least 1-2 orders of magnitude less than the time needed by the discharge head 165 to move along the distance of the axial length of the conductive element 360. As an example, for a conductive element 360 with a height (axial length) of about 23mm, an expected travel time of the discharge head 165 may be about 20 ns.
In Fig. 3, a circuit breaker 100 according to embodiments is shown, with a detailed sectional view on the conductive element 360 and its placement within the main nozzle 110. The at least one conductive element 360 may in embodiments be placed within a certain distance from the inner surface 175 of the main nozzle 110, as is particularly visible in the enlarged section. The inner surface 175 is subject to ablation of the insulating material, typically PTFE, caused by the hot plasma of the electrical discharge 160. The distance of the conductive element 360, more precisely of its first portion 300 and its second portion 310 may thus be chosen to account for this ablation. That is, the distance may be chosen so that also after a significant amount of switching processes of the circuit breaker 100, the conductive element is still covered by a layer of insulating material. For switching operations at the start of the lifetime of the circuit breaker 100 (the situation as shown in Fig. 3), this distance may thus contribute to even moderately reduce the above-described, intended push-out effect of the electrical discharge 160 by the second portion 310 of the conductive element 360. However, this is partially compensated by the protecting effect of the sharp edge 350 of the non-ablated main nozzle 110 at the heating channel entrance 145. With a progressing ablation the distance between propagating discharge 160 and the at least one conductive element 360 will be decreased, and the push-out effect of the electrical discharge 160 by the conductive element 360 becomes stronger.
Fig. 4 shows a circuit breaker 100 according to embodiments, after a significant amount of switching processes, as described above. The sharp edge shown in Fig. 3 was rounded by ablation, and the edge 400 now exhibits a rounded or smoothed area 400 instead. As was described, due to the lowered distance between the electrical discharge 160 and the second portion 310 of the conductive element 360 during a switching in comparison to the situation as shown in Fig. 3, the push-out effect, hence the deflection of the electrical discharge 160 away from the heating channel entrance 145, becomes stronger due to the ablated inner surface 175 of the main nozzle 110, which also caused the rounding of edge 400.
Differently expressed, a first portion 300 of the conductive element 360 and the second portion 310 of the conductive element are then closer to the inner surface 175 of the main nozzle 110. Thus, with the progressing ablation, the distance between the propagating electrical discharge 160 and the conductive element 360, being a floating electrode, is decreased and the conductive element 360 will gradually take over the protecting role by deflecting electrical discharge 160, when edge 400 becomes more rounded.
Typically, in embodiments, the at least one conductive element 360 has a first portion 300 (see e.g. FIG 2A) protruding towards the longitudinal axis 190. The at least one conductive element 360 also has a second portion 310 (see e.g. FIG 2A), protruding towards the longitudinal axis 190. The at least one conductive element 360 typically also has a third portion 320. The third portion 320 is typically arranged recessed with respect to the first 300 and/or second 310 portion.
In Fig. 5A, a conductive element 360 according to embodiments is shown. The conductive element 360 is typically concave (in cross-sectional view as shown in Fig. 5A), and in particular can have a C-shape with its opening directed towards the axis 190. The C-shape may be considered in a cross-sectional view as shown in the respective drawings e.g. FIG. 2A to 5B. In other words, the at least one conductive element 360 typically has a kind of cavity or recess (e.g. the third portion 320) between first portion 300 and the second portion 310. The cavity may be directed towards the inner surface 175 of the main nozzle 110 where the discharge 160 propagates as shown e.g. in Fig. 1, 2A and 2B.
An advantage of the concave C-shape is related to surface capacitances between the discharge head and the conductive element, which is responsible for the local propagation behavior of the discharge head 165. The enhanced surface capacitance in the vicinity of the first portion 300 and the reduced surface capacitance in the vicinity of the third portion 320 of the conductive element 360 promotes discharge branching in circumferential direction in addition to the axial propagation between contacts 120 and 130. Consequently, a larger amount of surface charge will be accumulated along the circumference of the inner wall 175 of the main nozzle 110 in the vicinity of the first portion 300 of the conductive element 360. This will again contribute to an increase of the charge separation and consequently enhance the "push out" effect of the second portion 310 of the conductive element 360.
The conductive element 360 of Fig. 5A therefore corresponds to a rotational body, which results from the imagination that the conductive element 360 is rotational symmetric about the longitudinal axis 190 of the circuit breaker 100. In this case, the conductive element 360 has the shape of a single piece, such as a torus.
In Fig. 5B, a conductive element according to further embodiments is depicted. Thereby, only segments of the ring-shaped structure (as shown in Fig. 5A) may be arranged as the at least one conductive element 360 in the material of the nozzle body 110. Therefore, in a further embodiment, which may be combined with one or more other embodiments, at least two conductive elements 360 may be arranged along a circular path. The conductive elements 360 may substantially be equally spaced and the circular path is substantially concentric with the arcing region 180. In other words, the one or more conductive elements 360 may be arranged similar to "orange slices" in an orange or "pie-slices". In FIG. 5B, only one of those slices of a conductive element is shown. The element shown in FIG. 5B may have an angle, with respect to a round and complete conductive element, of about 20° or larger, as an example 45°. Any other angle is possible.
A plurality of these conductive elements 360, with same or different angle with respect to each other, may be arranged such that they form a ring similar to that as shown in FIG 5A, but with the difference that this ring is an interrupted ring. In other words, the single elements may form a ring-like structure, but the single elements do not have a conductive connection among each other. This segmentation of the ring structure of the conductive element 360 prevents an interference between the charge separation in the different segments.
In embodiments, the at least one conductive element 360 may have a solid structure, thus may comprise a solid material. In embodiments, the conductive element 360 may also be implemented in the main nozzle 110 as a hollow structure with a conductive surface. This hollow space may have conductive walls, wherein the conductivity may be provided by conductive paint or other ways of surface metallization.
In embodiments, a minimum distance between a surface of the at least one conductive element 360 and an inner surface 175 of the main nozzle 110 may typically be greater than a minimum distance between the surface of the at least one conductive element 360 and the entrance 145 of the heating channel 140.
Fig. 6 shows a conductive element 360 according to embodiments. The part of the conductive element 360 which is first reached by the discharge head 165, which is first portion 300, has a larger area (in the cross-sectional view) or volume or thickness (in axial direction of the breaker) than the second portion 310. This configuration was found to have an improving effect with respect to the push-out effect on the electrical discharge 160 described above.

Claims

A gas-insulated high or medium voltage circuit breaker (100) comprising:
a pin contact (120) and a second contact (130) being configured to be moveable with respect to each other along a longitudinal axis (190) of the circuit breaker (100) between an open and a closed configuration of the circuit breaker (100), the pin contact (120) and the second contact (130) defining an arcing region (180) in which an electrical discharge (160) is formed during a current breaking operation; and

an auxiliary nozzle (150) comprising an electrically insulating material, that at least partially surrounds the second contact (130), a main nozzle (110) comprising an electrically insulating material, that encloses the auxiliary nozzle (150) at least partially, and a heating channel (140) provided between the auxiliary nozzle (150) and the main nozzle (110), wherein the heating channel (140) separates the auxiliary nozzle (150) from the main nozzle (100) axially and radially and enables a fluid communication between the arcing zone (180) and an upstream pressure volume (155), wherein

at least one conductive element (360) is embedded within the insulating material of the main nozzle (110) and is electrically floating,

the at least one conductive element (360) is arranged around the arcing region (180) and is configured to generate an electrical field due to the presence of an electrical discharge (160) in the arcing region (180), the electrical field being configured for deflecting the electrical discharge (160) which propagates from the pin contact (120) along an inner surface (175) of the main nozzle (110) towards the second contact (130), and

the conductive element (360) is located adjacent to the heating channel entrance (145) on a side of the heating channel entrance (145) towards the pin contact (120),

characterized in that the conductive element (360) is substantially annularly shaped, in particular may be a continuous ring, or may be segmented ring or ring structure with segments located along a circumferential path and is having a recess directed to the inner surface (175) of the main nozzle (110).
The circuit breaker (100) according to the preceding claim, wherein at least two conductive elements (360) are arranged along a circular path, wherein the conductive elements (360) are substantially equally spaced and the circular path is substantially concentric around the arcing region (180).
The circuit breaker (100) according to any preceding claim, wherein the at least one conductive element (360) has a solid structure or a hollow structure with a conductive surface.
The circuit breaker (100) according to any preceding claim, wherein a minimum distance between the surface of the at least one conductive element (360) and an inner wall of the main nozzle (110) is greater than a minimum distance between the surface of the at least one conductive element (360) and the entrance (145) of the heating channel (140).
The circuit breaker (100) according to any preceding claim, wherein the at least one conductive element has a first portion (300), protruding towards the longitudinal axis (190).
The circuit breaker (100) according to any preceding claim, wherein the at least one conductive element (360) has a second portion (310), protruding towards the longitudinal axis (190).
The circuit breaker (100) according to any preceding claim, wherein the at least one conductive element (360) has a third portion (320), recessed with respect to the first (300) portion and/or second (310) portion.
The circuit breaker (100) according to any preceding claim, wherein a cross-section of the at least one conductive element (360) is concave towards the longitudinal axis (190).
The circuit breaker (100) according to any of the preceding claims, wherein a cross-section of the at least one conductive element (360) is substantially "C"-shaped with its concave opening directed towards the longitudinal axis (190).
The circuit breaker (100) according to any of the preceding claims, wherein an axial length of the at least one conductive element (360) is greater than 15 mm.
A method for operating a gas-insulated high or medium voltage circuit breaker (100), the method comprising:
deflecting an electrical discharge (160) which propagates from a pin contact (120) along an inner surface (175) of a main nozzle (110) towards a second contact (130) of the circuit breaker (100) in an arcing region (180), wherein

at least one conductive element (360) is embedded as a floating electrode in the insulating material of the main nozzle (110) around the arcing region (180) and is configured to generate an electrical field due to the presence of the electrical discharge (160) in the arcing region (180), and wherein the electrical field is configured for deflecting the electrical discharge (160), and

the at least one conductive element (360) is located adjacent to the heating channel entrance (145) on a side of the heating channel entrance (145) towards the pin contact (120),

characterized in that the conductive element (360) is substantially annularly shaped, in particular may be a continuous ring, or may be segmented ring or ring structure with segments located along a circumferential path and is having a recess directed to the inner surface (175) of the main nozzle (110).