WO2017036796A1

WO2017036796A1 - Improved interrupter

Info

Publication number: WO2017036796A1
Application number: PCT/EP2016/069500
Authority: WO
Inventors: Martin Eiselt; Lokesh Kumar; Feng Miao; Sujata PARANJAPE; Dirk Pohle; Saurabh Shrivastava; Erik D Taylor; Ke Song XIE; Cheng Xu
Original assignee: Siemens Aktiengesellschaft
Priority date: 2015-08-31
Filing date: 2016-08-17
Publication date: 2017-03-09
Also published as: CN205335165U

Abstract

An improved interrupter is disclosed in the present invention. The improved interrupter comprises an improved housing and one or more improved ribs. The one or more improved ribs are connected at one or more corners of the at least one housing.

Description

Improved interrupter The present invention relates to an improved housing for interrupters and more particularly, to an improved housing structure for vacuum interrupters to enhance external

breakdown strength of the vacuum interrupters. From last few decades there is a continuously increasing demand of electrical systems for various residential and industrial applications. Hence the electrical systems are becoming increasingly complex, heavy and powerful. An

essential requirement of a high voltage electrical system is high voltage switching equipment. High voltage switching equipment is used to control, protect and isolate electrical modules within the high voltage electrical system. The high voltage switching equipment has the property to act under special conditions. For example, high voltage switching equipment disconnects a section of the electrical system when flow of current goes beyond prescribed limits, which in turns protect the electrical system against damage.

Voltage switching elements used in the electrical systems may be disconnectors, interrupters or a combination of both. The most commonly used switching element is an interrupter.

Interrupters are used as circuit breakers in electrical systems to protect electrical systems from damage caused by overload or short circuit. Basic function of interrupters is to detect fault conditions and interrupt the flow of current. Insulating materials are used in interrupters for providing sufficient insulation between contacts when circuit breaker opens and also extinguishing electrical arc occurring between the contacts while opening the circuit breaker, especially in case of medium and high voltage applications. Most commonly used insulating materials, specifically for extinguishing electrical arc during contact opening procedure, in interrupters are oil, air, sulphur hexafluoride (SF6) gas and vacuum .

Vacuum interrupters are circuit breakers in which electrical arc quenching takes place in vacuum. Vacuum interrupters are well suited for medium voltage applications however can also be used in low or high voltage applications. A vacuum

interrupter primarily consists of a metal arc chamber placed in the centre of a symmetrically arranged ceramic insulator, known as a ceramic housing. Vacuum interrupters are

considered advantageous in comparison with other types of circuit breakers primarily because of their long service life and easy replacement procedure. Also in case of vacuum interrupters, there is no chance of fire hazard, unlike oil circuit breakers, and the vacuum interrupters are

environmental friendly in comparison of SF6 interrupters.

However maintaining high external breakdown voltage is a significant challenge for vacuum interrupters. In the case of vacuum interrupters, an external breakdown occurs when a high voltage is applied at one end of a vacuum interrupter when interrupter contacts are open, i.e. no current flow allowed through the interrupter, and dielectric strength of the material at an external part of the ceramic housing of the vacuum interrupter is not enough to hold off the high

voltage. This can result in the formation of an arc between metal parts at the two ends of the vacuum interrupter. In addition, external insulating housings are sometimes placed around the vacuum interrupters, in order to protect them from exposure to the weather in outdoor applications. Porcelain housings are often used. Breakdowns can also occur in this housing, over the outside portion of the vacuum interrupter. External breakdown voltage of a vacuum interrupter, in accordance with the state of the art, is explained hereafter.

FIG 1 illustrates a vacuum interrupter 100 in accordance with the state of the art. The vacuum interrupter 100 includes a stationary contact assembly 102, a mobile contact assembly 104 and a ceramic housing 108 as shown in FIG 1. The

stationary contact assembly 102 is an arrangement for holding a stationary contact, not shown in figures, of the vacuum interrupter 100. Similarly, the mobile contact assembly 104 provides arrangements for holding and movement of a mobile contact 106, as illustrated in FIG 1. The ceramic housing 108 of the vacuum interrupter 100 is a ceramic insulator that should be capable to avoid an external voltage breakdown, especially, when the stationary contact, not shown in

figures, and the mobile contact 106 are not connected i.e. when the vacuum interrupter 100 interrupts the flow of current i.e. open state of the vacuum interrupter 100. In addition to it, the ceramic housing 108 of the vacuum

interrupter 100 also provides the electrical insulation during voltage stress, particularly during special conditions for example, but not limited to, lightning impulse withstand voltage testing and power frequency withstand voltage

testing . Sometimes the ceramic insulator of the ceramic housing 108 is too short to avoid external voltage breakdown of the vacuum interrupter 100 when high voltage is applied either at the stationary contact assembly 102 or at the mobile contact assembly 104 of the vacuum interrupter 100. Hence to

externally enhance the insulating property of the ceramic insulator, so that it can withstand a high external voltage, is a well known challenge for system designers and engineers. However some techniques for enhancing the insulating property of an external part of the ceramic housing 108 are suggested in the state of the art. One of the most common techniques is to increase the length of external insulating surface of the ceramic housing 108 but the ceramic housing 100 with

increased length makes the vacuum interrupter 100 difficult to handle, expensive and also increases resistance of the vacuum interrupter 100.

Another technique for increase the external breakdown

strength of the vacuum interrupter 100 is to externally coat „

the ceramic housing 108 with a material having high

dielectric breakdown strength and a high electrical

permittivity. The materials that can be used for externally coating the ceramic housing 108 may include, but not limited to, silicone, polyurethane and rubber. The external coating of the insulating material can follow the contour of the vacuum interrupter 100. It may also include large number of small waves, known as ribs 110A, HOB, HOC, HOD, over the surface of the ceramic housing 108, as illustrated in FIG 1. The ribs 110A, HOB, HOC, HOD increase outer diameter of external insulation allowing a shorter vacuum interrupter to meet external creepage requirements for polluted

environments. However, these small ribs have little or no effect on the breakdown strength, as compared to a flat surface. The insulating material coating serves two primary purposes i.e. it increases the voltage breakdown strength of the vacuum interrupters 100, specifically at triple points, and it also increase an effective distance between the exposed metal parts i.e. the stationary contact assembly 102 and the mobile contact assembly 104 of the vacuum interrupter 100. Triple points in the vacuum interrupter 100 are points where the ceramic i.e. insulating material, metal, and air come together and are well known in the state of the art. It is also known to a person ordinarily skilled in the art that in any electrical system, triple points are most common source of electrical breakdowns.

According to the state of the art, the ribs HOA, HOB, HOC, HOD are small in size and the size of the ribs HOA, HOB, HOC, HOD cannot be extended over a limit due to structural limitations associated with the vacuum interrupter 100. Hence the ribs HOA, HOB, HOC, HOD only increases outer diameter of the ceramic housing 108 or the external coating by 5-10%. Due to small size and limited effect of the ribs HOA, HOB, HOC, HOD on the outer diameter of the ceramic housing 108 or the external coating, an overall effect of the ribs HOA, HOB, HOC, HOD has very less effect of external breakdown strength of the vacuum interrupter 100. In other words, the ribs 110A, HOB, HOC, HOD are only useful for increasing the creepage distance between the stationary contact assembly 102 and the mobile contact assembly 104 of the vacuum

interrupter 100. Another disadvantage associated with the small ribs 110A, HOB, HOC, HOD is, in case of high

external voltage, an external flashover can travel over the tip of the ribs HOA, HOB, HOC, HOD and can cause the external breakdown. From the above mentioned problem associated with the small ribs of a vacuum interrupter, it is clearly evident that there is a strong need of an improved vacuum interrupter having higher external breakdown voltage without much

effecting the size and weight of the vacuum interrupter known in the state of the art.

It is therefore an object of the present invention to provide an improved vacuum interrupter having high external breakdown voltage .

The object is achieved by providing an improved interrupter according to claim 1. Further embodiments of the present invention are addressed in the dependent claims. In the present invention, an improved interrupter is

disclosed. The improved interrupter comprises an improved housing and one or more improved ribs. The one or more improved ribs are connected at one or more corners of the at least one housing.

In accordance with the present invention, the improved interrupter also comprises at least one stationary contact assembly and at least one mobile contact assembly. Accordingly, the present invention provides an improved interrupter having high voltage breakdown strength. The present invention is further described hereinafter with reference to illustrated embodiments shown in the

accompanying drawings, in which:

FIG 1 illustrates vacuum interrupter in accordance

with the state of the art, and

FIG 2 illustrates improved vacuum interrupter in

accordance with an embodiment of the present invention .

Various embodiments are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purpose of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident that such embodiments may be practiced without these specific details. FIG 2 illustrates an improved vacuum interrupter 200 in accordance with an embodiment of the present invention. The improved vacuum interrupter 200 includes the stationary contact assembly 102, the mobile contact assembly 104 and the mobile contact 106 similar to the vacuum interrupter 100, shown in FIG 1. The improved vacuum interrupter 200 also includes an improved housing 202, as illustrated in FIG 2. The material of the improved housing 202 may be similar, but not limited to, to the material used for the ceramic housing 108 of the vacuum interrupter 100 of FIG 1. However the shape of the improved housing 202, shown in FIG 2, is significantly different from the shape of the ceramic housing 108 of FIG 1. The improved housing 202 of the improved vacuum interrupter 200 has four improved ribs 204A, 204B, 204C, 204D as shown in FIG 2. The improved ribs 204A, 204B, 204C, 204D are placed at each corner of the improved housing 202 of the improved vacuum interrupter 200. The improved ribs 204A, 204B, 204C, 204D substantially increase electrical breakdown path between the stationary contact assembly 102 and the mobile contact assembly 104 of the improved vacuum interrupter 200 which leads to higher external breakdown voltage for the improved vacuum interrupter 200. The improved ribs 204A, 204B, 204C, 204D, shown in FIG 2, have an outer diameter at least, but not limited to, 15-20% larger than the ribs 110A, HOB, HOC, HOD of FIG 1. Also, the improved ribs 204A, 204B, 204C, 204D, shown in FIG 2, are at least, but not limited to, 25- 35% larger than the ribs 110A, HOB, HOC, HOD of FIG 1. The improved ribs 204A, 204B, 204C, 204D of the improved vacuum interrupter 200 are facing upwards, as illustrated in FIG 2. The upwards facing of the improved ribs 204A, 204B, 204C, 204D prevents a free flow of ionized air towards the improved vacuum interrupter 200 during an external voltage breakdown. However in other embodiments of the present invention all the improved ribs 204A, 204B, 204C, 204D may face in one or different directions depending upon application. Also in various embodiment of the present invention, the improved vacuum interrupter 200 may has one, two, or three improved ribs 204A, 204B, 204C, 204D.

It is clearly evident from the structure of the improved vacuum interrupter 200, illustrated in FIG 2 that an external breakdown path must go completely around at least two of the improved ribs 204A, 204B, 204C, 204D thereby external

breakdown strength of the improved vacuum interrupter 200 is increased without increasing the length of the vacuum

interrupter 200. The improved vacuum interrupter 200 can be used, but not limited to, in air and also in one or more external insulating housings, with air or another gases between the improved vacuum interrupter 200 and the one or more external housings.

The ribs HOA, HOB, HOC, HOD, used for the vacuum

interrupter 100, shown in FIG 1, serve only to meet creepage length requirements but do not improve the electrical

breakdown strength because the ribs HOA, HOB, HOC, HOD are too small, and breakdown voltage can jump over the small ribs HOA, HOB, HOC, HOD. On the other hand, the large diameter and much smaller number of the improved ribs 204A, 204B, 204C, 204D of the improved vacuum interrupter 200, disclosed in the present invention, force voltage breakdown path to go around the one or more improved ribs 204A, 204B, 204C, 204D, and thereby increase the voltage breakdown strength of the improved vacuum interrupter 200. An added advantage of the invention disclosed here is, due to small number of large diameter improved ribs 204A, 204B, 204C, 204D are used to increase the voltage breakdown strength without increasing the length of the improved vacuum interrupter 200. Furthermore a sufficient creepage length can also be

established due to the improved ribs.

While the present invention has been described in detail with reference to certain embodiments, it should be appreciated that the present invention is not limited to those

embodiments. In view of the present disclosure, many

modifications and variations would present themselves, to those of skill in the art without departing from the scope of various embodiments of the present invention, as described herein. The scope of the present invention is, therefore, indicated by the following claims rather than by the

foregoing description. All changes, modifications, and variations coming within the meaning and range of equivalency of the claims are to be considered within their scope.

Claims

Claims :

1. An improved interrupter (200) comprises:

-at least one improved housing (202); and

-one or more improved ribs (204A, 204B, 204C, 204D)

wherein the one or more improved ribs (204A, 204B, 204C, 204D) are connected at one or more corners of the at least one improved housing (202) .

2. The improved interrupter (200) according to claim 1

further comprises at least one stationary contact assembly (102) .

3. The improved interrupter (200) according to claim 1

further comprises at least one mobile contact assembly (104) .

4. The improved interrupter (200) according to claim 1

wherein the one or more improved ribs (204A, 204B, 204C, 204D) are in upwards direction to prevent free flow of ionized air over the improved interrupter (200) .