EP3171382A1

EP3171382A1 - A gas insulated electric apparatus and a method for producing a gas insulated electric apparatus

Info

Publication number: EP3171382A1
Application number: EP15195013.6A
Authority: EP
Inventors: Ulf ÅKESSON
Original assignee: ABB Schweiz AG
Current assignee: ABB Schweiz AG
Priority date: 2015-11-17
Filing date: 2015-11-17
Publication date: 2017-05-24
Also published as: WO2017084994A1

Abstract

A gas insulated electric apparatus (1) comprising an enclosure (7) and an electric high voltage appliance (9) located inside the enclosure. The enclosure (7) contains an insulation gas (8) comprising at least 80 % by volume of CO₂, and the insulation gas inside the enclosure is filled to a pressure that exceeds a blocking gas pressure level of the electric apparatus by at least 20 %, at 20°C. A corresponding method for producing a corresponding gas insulated electric apparatus is also described.

Description

Technical field of the invention

The invention relates to a gas insulated electric apparatus and a method for producing a gas insulated electric apparatus.

Background

In gas insulated electric apparatuses such as, for example, medium and high voltage metal-encapsulated switchgear or control gear, the electrical active part is arranged in a gas-tight enclosure or housing, which defines an insulating space that contains an insulating gas, usually with several bar pressure, and which space separates the enclosure from the electrical active part without letting electrical current pass through. The insulation gas serves as an electric insulation medium for preventing electric discharge between the enclosure and the electrical components inside the enclosure and as a cooling medium for suppressing temperature rise due to electric current. In a switchgear, which typically comprises a circuit breaker, and/or a disconnector, the insulation gas also serves as an arc-extinguishing medium for extinguishing arcs that may occur at the switching operation. Conventionally, sulphur hexafluoride gas (SF6 gas) has been widely used as insulation gas. However, in view of the known environmental drawbacks of SF6, the use of other insulation gases has been proposed, such as carbon dioxide gas, CO₂ gas.
Generally, for gas insulated electrical apparatuses, the enclosure is filled with an insulation gas up to a predetermined operative rated gas pressure level, before it is taken into operation. The pressure level inside the gas insulated electric apparatus is measured during operation and if the gas pressure level is reduced down to a pre-set alarm level, an alarm will go off, as an indication that the enclosure should be replenished with insulation gas. If the enclosure is not topped up with insulation gas and the amount of insulation gas continues to be reduced and thus also the gas pressure continues to be reduced, it may reach a pre-set blocking pressure level (also named lock-out gas pressure level). When the blocking pressure level is reached, the function of the gas insulated electric apparatus will be blocked and cease. When the gas insulated electrical apparatuses is a switchgear, it is usually configured to react in one of two ways: either the function of the gas insulated electric apparatus will be blocked such that it will not be possible to open or close the electric contact of the switchgear, or the electric contact will be forced open and stay open.
For a gas insulated electric apparatus having SF6 as an insulation gas, the filling pressure will be up to 0.9-1.0 MPa (absolute pressure). For a gas insulated electric apparatus having CO₂ as insulation gas and NBR rubber (nitrile butadiene rubber) sealings, the enclosure is filled with gas up to 1.1 MPa in order to fulfil the circuit breaking function. As an example, the alarm pressure can then be set to a value of 1.01 MPa, and the blocking pressure can be set to a value of 1.0 MPa. Usually, the enclosure is filled with insulation gas to a rated gas pressure level at the production plant and tested. The rated gas pressure level is the working gas pressure at which the apparatus is intended to work. The gas pressure is then lowered again for storage and transport. At the installation site, the enclosure is again filled up with gas to the rated gas pressure level, before it is taken into operation.

Summary of the invention

It has now been found that the reduction of the amount of CO₂ insulation gas inside the enclosure down to a blocking pressure level is much quicker than for a circuit breaker with SF6 as insulation gas. It has been found that this is due to several circumstances. One such circumstance is that the rubber sealings, usually of NBR rubber (nitrile butadiene rubber) or EPDM rubber (ethylene propylene diene monomer rubber), must adapt to the metal surfaces against which they rest. During this initial adaptation process there will occur some leakage that will result in the amount of CO₂ being reduced. Further, another circumstance is that the rubber in the sealings will absorb CO₂ molecules until it is saturated. CO₂ will also diffuse through the rubber sealings. The diffusion rate will decrease with time as the sealings will be increasingly clogged. There may also be other components in the enclosure which are made of polymer materials that will absorb CO₂ to some extent. All of the mentioned occurrences will result in a reduction of the amount of insulation gas in the enclosure and consequently a reduced gas pressure level inside the enclosure. The insulation performance and the arc-extinguishing capability are thus reduced.
As a consequence, maintenance of the apparatus is required and replenishment of insulation gas must be made at fairly frequent intervals, in order not to risk that the amount of insulation gas containing CO₂ is reduced down to alarm level or even blocking level, at which the function of the apparatus will be blocked and cease.
In view of the above, there exists a need for an improved gas insulated electric apparatus, such as a high voltage circuit breaker, using an insulation gas containing CO₂, which can operate for a long time without requiring any refilling of insulation gas.
An object of the present invention is to obtain an improved gas insulated electric apparatus that deals with the problems described above.
According to the present invention is defined a gas insulated electric apparatus comprising an enclosure and an electric high voltage appliance located inside the enclosure, wherein the enclosure contains an insulation gas comprising at least 80 % by volume of CO₂, and wherein the insulation gas inside the enclosure is filled to a gas pressure that exceeds a blocking gas pressure level of the electric apparatus by at least 20 %, at 20°C. By blocking gas pressure level is meant a predetermined gas pressure level at which the function of the gas insulated electric apparatus is blocked. If, for example, the blocking gas pressure is set to 1.0 MPa, the insulation gas containing CO₂ should be filled to a pressure of at least 1.2 MPa in the enclosure. The advantage of this higher gas pressure is that there will be enough gas in the enclosure to allow for the gas consuming effects discussed above, e.g. adaptation of rubber sealings to metal surfaces, absorption of CO₂ of rubber sealings or other components in the enclosure and diffusion through rubber sealings, which typically occur during the initial service time of the apparatus, and still having a remaining gas pressure level that can secure the quenching function of the insulation gas. The insulation gas pressure level inside the enclosure will stabilize at a pressure level that will safeguard the function of the apparatus for a long period of time. Thus, the insulation gas inside the enclosure will not need any refilling for many years, even tens of years.
Preferably, the insulation gas inside the enclosure is filled to a pressure that exceeds a blocking gas pressure level by 20-40 %, at 20°C, or even a pressure that exceeds a blocking gas pressure level by 30-40 %, at 20°C. The insulation gas may also comprise O₂ that will contribute to reducing the consumption of CO₂ when an arc is quenched. The quantity of O₂ is consequently less than 20 % by volume. This 20 % remaining gas extent may also comprise a mixture of other gases than CO₂, including O₂. It may also be possible not to include any O₂ at all.
According to one additional feature, the gas insulated electric apparatus may comprise sealings made of a material comprising isobutylene isoprene rubber. It has been found in tests that this type of rubber will have a lower gas leakage rate of CO₂ than e.g. NBR or EPDM rubber. It will thus be advantageous to use IIR rubber in order to prolong the time between refillings, and perhaps avoid refillings all together.
According to one embodiment, the electric high voltage appliance may be a high voltage interrupter.
According to the invention, the gas insulated electric apparatus may be a gas insulated live tank circuit breaker, or a gas insulated dead tank circuit breaker, or a gas insulated switchgear. It may alternatively be a control gear such as a gas insulated instrument transformer. In either one of these apparatuses it will be of great value to have an apparatus that will have a reliable functionality for many years without requiring refilling of insulation gas.
The gas insulated electric apparatus may be an outdoor gas insulated electric apparatus. It is an advantage that the apparatus according to the invention is suitable for outdoor use.
According to another aspect of the present invention is defined a method for producing a gas insulated electric apparatus comprising

assembling a gas insulated electric apparatus comprising an enclosure and an electric high voltage appliance located inside the enclosure,
transporting the gas insulated electric apparatus to an installation site,
filling the enclosure, at the installation site, with an insulation gas comprising at least 80 % by volume of CO₂, to a working gas pressure level, which working gas pressure level corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by at least 20 % measured at a temperature of 20°C. This method provides advantages corresponding to the advantages already described above in relation to the apparatus.

Preferably the method may comprise filling the insulation gas inside the enclosure to a working gas pressure level that corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by 20-40 %measured at a temperature of 20°C. Or alternatively, filling insulation gas to a working gas pressure level that corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by 30-40 % measured at a temperature of 20°C.
By working gas pressure level is meant the gas pressure at which the apparatus is intended to work at the final installation site, when taken into operation.
The method may also comprise filling the enclosure, at the installation site, with an insulation gas comprising at least 80 % by volume of CO₂ and also comprising O₂.
Further, the method may comprise providing the gas insulated electric apparatus with sealings made of a material comprising isobutylene isoprene rubber.
The above features related to the method have advantages that correspond to the already described advantages related to the apparatus.
For a gas insulated electric apparatus as defined above and in particular combining the features of having sealings made of a rubber comprising IIR and having an insulation gas comprising at least 80 % by volume of CO₂, and wherein the insulation gas inside the enclosure is filled to a pressure that exceeds a blocking gas pressure level of the electric apparatus by at least 20 %, at 20°C, a refilling requirement has been determined as every 30 years, which means a leak rate per year of 0.4 to 1 %. Further, calculations have shown that such a gas insulated electric apparatus will keep its functions also at very low temperatures, even as low as down to - 50°C.
By high voltage (HV) is in the present context meant voltages above 1 000 V, in accordance with IEC 62271-1, and IEC 62271-100.
All pressure values and levels indicated in the present description refer to absolute pressure.
By sealing is meant any type of suitable element have a sealing function, such as O-rings, X-rings, gaskets, washers etc. The sealings can e.g. be of the type that is placed in a groove or on a flat surface.
Further features and advantages of the invention will also become apparent from the following detailed description of embodiments.

Brief description of the drawings

The invention will now be described in more detail, with reference being made to the enclosed schematic drawings illustrating different aspects and embodiments of the invention, given as examples only, and in which:

Fig. 1 shows a schematic perspective view of an embodiment of a gas insulated electric apparatus according to the invention, with a partial detail enlargement,
Fig. 2 shows a partial cross section view of an embodiment of a gas insulated electric apparatus according to the invention, and
Fig. 3 is a schematic diagram showing the main steps of a method according to the invention.

Elements that are the same or represent corresponding or equivalent elements have been given the same reference numbers in the different figures.

Detailed description

In fig. 1 is schematically illustrated a gas insulated electric apparatus 1 according to the invention. The electric apparatus in the example is a circuit breaker, e.g. a circuit breaker for one pole in a three pole circuit breaker assembly. The circuit breaker 1 comprises a hollow upper high voltage (HV) unit insulator 3 and a hollow lower support insulator 5. The upper insulator and the lower insulator are connected to each other by means of a lower end of the upper insulator being connected to an upper end of the lower insulator. Together, the hollow upper insulator 3 and the hollow lower insulator 5 form an enclosure 7 that delimits an insulation space 10. The enclosure 7 is filled with an insulation gas 8.
The gas insulated electric apparatus of the example further includes an electric high voltage appliance 9 located inside the enclosure 7, in the insulation space 10. In the illustrated example showing a circuit breaker, the high voltage appliance is a high voltage interrupter that is located inside the upper insulator 3, see also Fig. 2. The interrupter may e.g. be a puffer type interrupter, as shown in Fig. 2. The upper end of the upper insulator 3 is closed off by a top cover 11.
At the lower end of the lower insulator 5 is arranged a mechanism housing 13. Inside the mechanism housing 13 is located a link mechanism 15 that connects a lower end of a support insulator pull rod 17 to an operating shaft 19, as is shown in the enlarged detail view of Fig. 1. The pull rod extends all the way up through the lower insulator and into the upper insulator where it is connected to the interrupter 9. Thus the interrupter 9 of the circuit breaker can be operated by means of the operating shaft 19. In a three pole circuit breaker assembly, the operating shaft 19 will be connected to the circuit breakers of all three poles and they can consequently be operated simultaneously. The mechanism housing 13 also includes connections (not shown) to a gas pipe (not shown) for filling the enclosure with gas and e.g. a connection (not shown) to a gas density monitor device (not shown).
The enclosure 7 is sealed off with sealings 21 at all connection areas and the gas pipe connection comprises a non-return valve.
According to the invention, the insulation gas 8 comprises at least 80 % by volume of CO₂, and the enclosure 7 is filled with insulation gas to a gas pressure that exceeds a blocking gas pressure level of the electric apparatus, i.e. the circuit breaker in the example, by at least 20 %, at approximately 20°C.
Preferably, the insulation gas inside the enclosure is filled to a gas pressure that exceeds a blocking gas pressure level by 20-40 %, at 20°C, or alternatively to a gas pressure that exceeds a blocking gas pressure level by 30-40 %, at 20°C.
The insulation gas also comprises O₂, or another gas to an extent of less than 20 % by volume. This 20 % remaining gas extent may also comprise a mixture of other gases than CO₂, including O₂.
A mentioned, the electric apparatus also comprises sealings 21, and at least some of these sealings are made of a material comprising isobutylene isoprene rubber (IIR) as the main component. The sealings may be sealings located in contact areas between metal parts, between metal and polymer or rubber materials, or between parts made of rubber or polymer materials. The sealings are located in different contact areas of the parts of the apparatus, both for sealing of the enclosure towards the exterior as well as sealings applied to parts and components inside the enclosure. Examples of sealing areas where sealings are used are the contact area between the upper insulator 3 and the lower insulator 5, the contact area between the upper insulator 3 and the top cover 11, sealings between the lower insulator 5 and the mechanism housing 13 and parts of the mechanism housing, sealings associated with the HV interrupter or other HV electric appliance of the electric apparatus.
In the given example, the gas insulated electric apparatus has been illustrated as a gas insulated circuit breaker. It can then find its application as a gas insulated live tank circuit breaker or a gas insulated dead tank circuit breaker. Alternatively, the gas insulated electric apparatus may e.g. be a gas insulated switchgear, or a control gear such as a gas insulated instrument transformer. The gas insulated apparatus in the example is suitable for use outdoors.
In Fig. 3 is illustrated the main steps of an embodiment of a method, according to the invention, for producing a gas insulated electric apparatus 1 comprising the steps of

assembling a gas insulated electric apparatus 1 comprising an enclosure 7 and an electric high voltage appliance 9 located inside the enclosure, step 100,
transporting the gas insulated electric apparatus 1 to an installation site, step 200,
filling the enclosure 7, at the installation site, with an insulation gas 8 comprising at least 80 % by volume of CO₂, to a working gas pressure level, which working gas pressure level corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by at least 20 % measured at a temperature of 20°C, step 300.

To be more precise, the method may comprise filling the insulation gas inside the enclosure to a working gas pressure level that corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by 20-40 % measured at a temperature of 20°C, or filling the insulation gas inside the enclosure to a working gas pressure level that corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by 30-40 % measured at a temperature of 20°C.
In addition, the method may comprise filling the enclosure, at the installation site, with an insulation gas comprising at least 80 % by volume of CO₂ and also comprising O₂.
The method may further comprise the step of providing the gas insulated electric apparatus 1 with sealings 21 made of a material comprising isobutylene isoprene rubber.
Also as previously mentioned, the apparatus is usually tested before transported to the installation site. The enclosure is then filled with insulation gas to the working gas pressure level (rated gas pressure level) at the production plant and tested. The gas pressure is then lowered again for storage and transport.
The invention shall not be considered limited to the illustrated embodiments, but can be modified and altered in many ways, as realised by a person skilled in the art, without departing from the scope defined in the appended claims.

Claims

A gas insulated electric apparatus (1) comprising an enclosure (7) and an electric high voltage appliance (9) located inside the enclosure, wherein the enclosure (7) contains an insulation gas (8) comprising at least 80 % by volume of CO₂, and wherein the insulation gas inside the enclosure is filled to a gas pressure that exceeds a blocking gas pressure level of the electric apparatus by at least 20 %, at 20°C.
The gas insulated electric apparatus according to claim 1, wherein the insulation gas (8) inside the enclosure (7) is filled to a pressure that exceeds a blocking gas pressure level by 20-40 %, at 20°C.
The gas insulated electric apparatus according to claim 1, wherein the insulation gas (8) inside the enclosure (7) is filled to a pressure that exceeds a blocking gas pressure level by 30-40 %, at 20°C.
The gas insulated electric apparatus according to any one of the preceding claims, wherein the insulation gas (8) also comprises O₂.
The gas insulated electric apparatus according to any one of the preceding claims, wherein it comprises sealings (21) made of a material comprising isobutylene isoprene rubber.
The gas insulated electric apparatus according to any one of the preceding claims, wherein the electric high voltage appliance (9) is a high voltage interrupter.
The gas insulated electric apparatus according to any one of the preceding claims, wherein it is a gas insulated live tank circuit breaker, or a gas insulated dead tank circuit breaker, or a gas insulated switchgear.
The gas insulated electric apparatus according to any one of the preceding claims, wherein it is an outdoor gas insulated electric apparatus.
A method for producing a gas insulated electric apparatus (1) comprising
- assembling a gas insulated electric apparatus comprising an enclosure (7) and an electric high voltage appliance (9) located inside the enclosure (7),

- transporting the gas insulated electric apparatus (1) to an installation site,

- filling the enclosure (7), at the installation site, with an insulation gas (8) comprising at least 80 % by volume of CO₂, to a working gas pressure level, which working gas pressure level corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by at least 20 % measured at a temperature of 20°C.
The method according to claim 9, comprising filling the insulation gas (8) inside the enclosure (7) to a working gas pressure level that corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by 20-40 % measured at a temperature of 20°C.
The method according to claim 9, comprising filling the insulation gas (8) inside the enclosure (7) to a working gas pressure level that corresponds to a gas pressure, measured at a temperature of 20°C, that exceeds a blocking gas pressure level of the apparatus by 30-40 % measured at a temperature of 20°C.
The method according to any one of claims 9-11, comprising filling the enclosure (7), at the installation site, with an insulation gas (8) comprising at least 80 % by volume of CO₂ and also comprising O₂.
The method according to any one of claims 9-12, comprising providing the gas insulated electric apparatus (1) with sealings (21) made of a material comprising isobutylene isoprene rubber.