WO1992015993A1

WO1992015993A1 - A method for treatment of air in a closed air transport system comprising at least one series of switchgear cubicles

Info

Publication number: WO1992015993A1
Application number: PCT/SE1992/000108
Authority: WO
Inventors: Rolf Edlund
Original assignee: Asea Brown Boveri Ab
Priority date: 1991-03-01
Filing date: 1992-02-25
Publication date: 1992-09-17
Also published as: NO933089D0; SE9100599D0; FI111122B; SE9100599L; FI933801A7; FI933801A0; NO933089L; NO307851B1; SE467945B

Abstract

The invention comprises a method for treating air in a closed air transport system in a series of electric switchgear cubicles (1a-1d), placed side-by-side and closed to the ambient air, by means of at least one air treatment unit (2) common to the cubicles. The method for air treatment comprises passing cleaned, pressurized, possibly also cooled and/or dried air, from an air treatment unit (2) via a common channel (3) and further via parallel branch pipes (4a-4d) with pressure regulating devices (5a-5d) for regulating the air flow, directly to each individual switchgear cubicle, these switchgear cubicles being adapted to receive the treated air, distribute the air for cooling purposes over electric equipment present in the cubicles, the distributed air being adapted to be collected and returned, via connections (6a-6d) arranged between the cubicles, to the air treatment unit (2) where an extra intake (8) for ambient air is adapted to supply extra air to the air transport system in order to create an overpressure in the system while at the same time replacing an air loss caused by a leakage flow of air out of the cubicle series. The direction of the air flow through the system may be reversed.

Description

A method for trea men o a r n a c ose a r ranspor system comprising at least one series of switchgear cubicles TECHNICAL FIELD

The present invention relates to a method of treating air in electric switchgear cubicles, such as, for example, in switchgear and similar plants . The air treatment means an adaptation to the requirements for temperature and quality of the air of the equipment located in the cubicles .

BACKGROUND ART

Electric or electronic equipment utilized in industrial processes, switchgear and similar use is generally enclosed in a casing of metal, usually some form of apparatus cub¬ icle. The casing or the cubicle is utilized, inter alia, as frame for internal installation of electric components but also as protective casing for the electric equipment with respect to the effect of dust, moisture, aggressive agents etc., as well as semiprotection for reasons of personal safety. In connection with this enclosure, the problem arises concerning the removal of heat given off by the com¬ ponents present in the cubicles by the power developed in these components.

Thermal dissipation may be arranged in many different ways, for example through radiation from the walls of the cubicles themselves, aeration of the cubicles through self-convection with the aid of ventilating openings, aeration with the aid of fans and filters, forced aeration by means of heat exchangers and conditioning by means of refrigerating machines.

If cooling is performed with ambient air, treatment of the air in the form of, for example, cleaning or drying may become necessary in those cases where the cubicles are positioned in a fouled or moist environment. Such cleaning may comprise filtering of the air or removal of corrosive gases from the ambient air before this air is supplied, cleaned, to the interior of the cubicles for cooling of the components located therei .

Known are a number different part solutions for cleaning or treating air in the above-mentioned manner in individual apparatus cubicles for the purpose of removing excess heat from the cubicles. Such single-cubicle solutions are described, inter alia, in the patent specifications EP, 3,57411, FR,A1,2 568 712 and -JP 58-241 936.

In switchgear or in other types of industrial plants where the electric equipment is extensive, it may be required that a number of cubicles extended into a series of cubicles be arranged. A cubicle series of this kind is generally designed as a series of cubicles arranged in one or more rows with the individual cubicles placed side-by-side close to each other. For removal of heat from electric equipment in a cubicle series of the mentioned kind, the single- cubicle solutions according to the above are not applicable. Providing each individual cubicle with its own air-treatment unit cannot be justified from an economical point of view. Instead, it is common to use an air-treatment, or as it is also called, air-conditioning plant to cool, moisten, dry or clean the air in the entire room where the cubicles in a series of cubicles are stored. With this method, it is possible to achieve the desirable cooling and/or cleaning of air to the electric equipment in the cubicles. The method can also be supplemented by fans in the individual cubicles to prevent the formation of stationary hot air zones inside the cubicles.

Treating all the air in a room to attain the desired effect with respect to, for example, the cooling requirement or cleaning requirement is no good solution. The air volume that has to be treated is large, which means that the air treatment plant must be dimensioned for an air volume which is many times larger than the air volume which really passes through the apparatus cubicles for the purposes of cooling. This renders the air treatment plant more expensive than necessary. .Another difficulty is that the room climate must satisfy the requirements for human comfort, since personnel may be present in the rooms mentioned. In this way it is not possible to optimize, for example, air temperature or air composition according to the primary requirements of the electric equipment. The temperature of treated air supplied to the room where the apparatus cubicles are erected is nor- mally varied within an interval of a couple of degrees above or below room temperature.

It is known that as large a percentage as 60-70% of normal operating environments for electric and electronic equipment in certain industries as, for example, paper and pulp indus¬ tries, are so corrosive that they have a marked influence on the reliability of service and the service life of the equipment. Currently, therefore, this problem is often solved by air treatment comprising chemical filtering of the air in the whole of the room where the electric equipment in question is located, which entails treatment of a dispropor¬ tionately large air volume. A solution to the problem of preventing attacks from corrosive or degrading components in air which is used for removal of heat from electric com- ponents in apparatus cubicles, possibly performed by cooled air but while simultaneously minimizing the air flow and the efforts for cleaning, filtering and dehumidification is desirable.

It is also known that the service life of certain components of semiconductor type is greatly temperature-dependent. For these components, as low a temperature as possible in the immediate surroundings of the component is therefore aimed at. For electric equipment such as apparatus and electric busbars, the allowed working temperature is normally maxi¬ mized in dependence on the temperature durability of the conductors and/or the insulating materials. The working temperature is dependent on both the immediate ambient tern- perature and the self-heating of the apparatus during normal loading. A increase of the temperature also provides an increase of the resistance of electric conductors in the equipment, which results in increased power output and a f rther increase of the temperature.

For the purpose of cooling electric components in apparatus cubicles without having to treat the air in the whole of the room where the cubicle are located, it is known from German Patent DE 2 537 295 to distribute cooled air in a closed air transport system comprising a series of apparatus cubicles. However, this specification does not show any solution to the problem of treatment of the air in the system in the case of corrosive and aggressive environments.

SUMMARY OF THE INVENTION

The invention comprises a method for treatment of the air in a closed air transport system in a series of electric switchgear cubicles, which are placed side-by-side and closed to the surrounding air, by means of at least one air- treatment unit common to the cubicles in order to reduce the treated air quantity. The method for air treatment compri¬ ses passing cleaned, pressurized, possibly also cooled and/or dried air, from an air treatment unit via a common channel and further via parallel branch pipes with pressure regulating devices for regulating the air flow, directly to each individual switchgear cubicle, these switchgear cubic¬ les being adapted to receive the treated air, distribute the air for cooling purposes over electric equipment present in the cubicles, the distributed air being adapted to be col¬ lected and returned, via connections arranged between the cubicles, to the air treatment unit where an extra intake for ambient air is adapted to supply extra air to the air transport system in order to create an overpressure in the system while at the same time replacing an air loss caused by a leakage flow of air out of the cubicle series. The direction of the air current through the system may be reversed.

To avoid corrosive attacks from the air circulating inside the switchgear cubicles, a combination of particle cleaning, gas cleaning, dehumidification, cooling and pressurization is carried out in the air transport through the switchgear cubicles. Each sub-treatment is important for the protec¬ tion of components and conduits in the cubicles, but in special cases the cooling may be omitted, depending on the surrounding temperature and the electric load in the cubicle.

The air transport system is intended to constitute protection against corrosion on electronics and conductor material in the switchgear cubicles and to increase the highest permissible output on electric components mounted in the cubicles with a minimum of air flow, necessary cooling effect and consumption of media in connection with the air treatment mentioned, which according to the known technique requires the contribution of several air treatment units for treatment of the air to the individual cubicles according to the treatment methods mentioned.

Parallel air flows with cleaned air traverse each individual cubicle.

The temperature of the cooling air may be reduced to below room temperature, which results in increased service life of electric components in the equipment and permits a more energy dense design inside each cubicle. For electric equipment it is also possible to design apparatus and elec¬ tric busbars for higher current ratings. Alternatively, energy losses in the system are reduced. All this can be achieved while at the same time considerably reducing the treated air volume, which entails reduced dimensions of the air treatment equipment and less costly such equipment. In addition, it is possible to chemically filter or otherwise chemically treat the air, which perhaps cannot be realized if personnel is to be present in the room with cubicles.

BRIEF DESCRIPTION OF THE DRAWING

The figure shows an example of an air transport system with an air-conditioning unit which treats the air in a series comprising four switchgear cubicles.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred example of how the method according to the invention is carried out will be described with reference to the accompanying figure.

A number of switchgear cubicles la - Id are erected side-by- side. These switchgear cubicles comprise electric equipment where there is a need to remove heat. This removal of heat is carried out with air as active medium, whereby the air as the active medium is treated to attain the desired quality of this as a non-corrosive medium. The treatment of the air is performed by an air-conditioning unit 2, also called air- treatment unit. The treated air is passed through a main channel 3 to the switchgear cubicles la-Id after parallel distribution of the air to the cubicles by means of branch pipes 4a-4d. The air quantity to each separate cubicle may be adjusted with the aid of regulating valves 5a-5d on each branch pipe 4a-4d.

The parallel air flows flowing through the cubicles are collected via openings 6a-6d at the bottom sides between adjoining cubicles, are collected and returned to the air treatment unit 2 via the return conduit 7.

The apparatus cubicles la-Id are adapted to closed air transport by all openable doors and bushings being sealed with rubber strips and rubber seals or similar means. In addition, the cubicles are provided at the top or on the back with openable covers for connection to the branch pipes 4a-4d. The openings 6a-6c at the bottom between the cubic¬ les are achieved by arranging, during installation of a cubicle series, normally tightly sealing doors to be opened in two adjoining cubicles placed side-by-side, so as to create a common opening 6a-6c for these adjoining cubicles. Through these openings, consumed treated air is passed through the respective cubicles to an opening 6d, arranged in the same way from the last cubicle Id of the cubicle series, in this case arranged for connection to the return conduit 7.

In the switchgear cubicles a certain overpressure prevails, since the air transport system is provided with extra intake air from the surroundings via an intake 8 with a regulating device 9. This extra intake air is intended to replace a possible leakage flow out of the cubicle series and at the same time serves as a guarantee that uncleaned or untreated ambient air does not leak into the system. With the regula- ting device 9 the quantity of ambient air into the air transport system may be regulated. The overpressure in the cubicles is regulated to suitably 15-20 Pa but may, of course, be given other magnitudes. The intention is that this overpressure should ensure that no foreign, undesirable gases or particles penetrate into the cubicles.

It is of importance that the air flow through each cubicle la-Id can be controlled and influenced to avoid that any cubicle in the series receives too small an air flow or that backward flows occur. By a well-balanced air pressure into each individual cubicle by means of the regulating valves 5a-5d, such a balancing can be achieved.

Since all air treatment takes place in the air treatment unit 2, it is possible to comprise different types of desi¬ rable treatment forms of the air, according to requirements. The present invention utilizes particle cleaning, gas clean¬ ing, dehumidification and cooling (where required) of the air which passes the air treatment unit 2 in the air trans¬ port system.

To bring about particle cleaning, air filters are placed upstream of the other cleaning devices to capture particles, preferably in the overpressure air. After the active air filter with active media for gas cleaning, an absolute fil¬ ter is mounted, which prevents particles from the active filtering media from spreading in the air transport system.

Gas cleaning is performed where gases with both a high (about 5 ppm for a short time) and a low (less than 0.3 ppm) concentration are separated in an active filter, a gas cleaning filter. The filtering degree is such that the concentration of filtered-away gases becomes as low as a few Ppb downstream of the filter. Gases to be separated are preferably H₂S, SO₂, different chloride compounds, nitrogen compounds, mercaptans and ammonia. The active medium for gas separation consists of a medium available on the market, such as active carbon and impregnated aluminium oxide.

Because the main part of the air flow circulates in a limi¬ ted space, a high separation in combination with a low ser¬ vice life and a small amount of active medium is achieved. The contact time for the gas mixing with/in the active medium is to exceed 1 second.

Harmful, corrosion-promoting water/moisture in the air is removed to make it possible to maintain a relatively low temperature in the cubicles and hence make possible an increased power output as well as increased service life of the electric components in the cubicles.

The air is cooled in the applications where this is necessary. This is done by installing a refrigerating machine in the air treatment unit 2 or by an external refrigerating medium. Tests carried out with an air transport plant according to the invention have shown surprisingly good results with regard to, for example, preventing corrosive attacks on, for example, conduction material, as copper, also in the severest environments.

If desired, there is nothing preventing conducting the air in the system in a direction which is opposite to the one assumed above.

In the embodiment described, air has been assumed to be the coolant throughout. This is, of course, not necessary. If another gas or gas mixture is desirable as coolant, there is nothing preventing this . Also the intake 9 may be supplied with other gas than ambient air.

Further, an embodiment with a series of cubicles comprising four switchgear cubicles has been described. Also in this case, there is nothing preventing applying the invention to any cubicle series comprising at least two switchgear cubicles la-Id. If considered desirable, more than one air treatment unit 2 may be arranged in the system.

Claims

1. A method for treatment of air in a closed air transport system comprising at least one series of switchgear cubicles (la-Id), positioned side-by-side and isolated against the surroundings, by means of at least one air treatment unit (2) common to the cubicles (la-Id) , from where treated air is distributed to the cubicles (la-Id) through a common channel (7) and to which return air is brought back for renewed treatment through a common channel (3) , characterized in that the air in the system is pressu¬ rized, mechanically cleaned, freed from contents of corro¬ sive gases and, where necessary, cooled in the air treatment unit (2) .

2. A method for treatment of air according to claim 1, characterized in that the air in the system is dehumidi¬ fied in the air treatment unit (2) .

3. A method for treatment of air according to claim 1 or 2, characterized in that the air is filtered in the air treatment unit (2) in a gas separation filter over active media, such as active carbon or impregnated aluminium oxide, for separation of preferably the gases H2S, SO2, different chloride compounds, nitrogen compounds, mercaptans and ammonia.

4. A method for treatment of air according to claim 3, characterized in that the air is freed from particles in the air treatment unit (2) by means of mechanical filters, positioned both upstream of and downstream of the gas separation filter.

5. A method for treating air according to claim 4, characterized in that the treated air is distributed through a common main channel (3) and further through branch pipes (4a-4d) provided with regulating valves (5a-5d) to the respective switchgear cubicles (la-Id) and past electric equipment through each individual cubicle.

6. A method for treating air according to claim 4, characterized in that the treated air is distributed serially, through a common channel (7), to the cubicles (la- Id) in the cubicle series and is collected through parallel branch pipes (4a-4d) , equipped with regulating valves (5a- 5d) , to a common air return channel (3), each of the respec- tive branch pipes being connected to one of the switchgear cubicles.

7. A method for treating air according to any of the preceding claims, characterized in that

- the intake air to the switchgear cubicles (la-Id) in the series is received and distributed and that consumed air is delivered via openings (6a-6d) to adjoining cubicles or to the return conduit (7) ,

- the switchgear cubicles in the series are connected to the branch pipes (4a-4d) by means of connections which are normally provided with lids,

- the switchgear cubicles in the series are isolated against the surrounding atmosphere by means of seals at any gaps in the cubicle casings which are facing the surroundings.

8. A method for treating air according to claim 1 or 2, characterized in that the air in the system exhibits a higher pressure, suitably within the interval 15-20 Pa, than the air surrounding the cubicles because the air transport system is supplied with extra ambient air or some other gas through an adjustable intake (8) at the air treatment unit to replace a leakage air flow out of the cubicle series and to prevent ambient air from penetrating into the air transport system.

9. A method for treating air according to any of claims 1- 8, characterized in that the air in the air transport system is replaced by some other gas or gas mixture.