EP1630475A1

EP1630475A1 - A construction of an illuminator

Info

Publication number: EP1630475A1
Application number: EP04396055A
Authority: EP
Inventors: Vesa Mäkelä; Mika Sumuvuori; Tarmo Rintala
Original assignee: Centaurea Oy
Current assignee: Centaurea Oy
Priority date: 2004-08-27
Filing date: 2004-08-27
Publication date: 2006-03-01
Also published as: WO2006021620A1; BRPI0514657A; NO20070601L

Abstract

The invention relates to a luminaire for zone 0 hazardous areas. The luminaire (1) comprises an illuminator (4.1), and a cable (3) for supplying electric power to illuminate the illuminator (4.1). The luminaire (1) further comprises an illumination unit (4) comprising a body (4.2) in connection with which the illuminator (4.1) is attached, and a protective cover (4.3) placed above the illuminator (4.1) for protecting the illuminator (4.1). The free space of the body (4.2) is filled with a filler to make the illumination unit (4) substantially gas tight.

Description

Field of the Invention

The present invention relates to a luminaire for zone 0 hazardous areas, the luminaire comprising an illumination source, and a cable for providing electric power to illuminate the illumination source.

Background of the Invention

Hazardous locations mean such areas in which a risk of explosions exist. The risk of explosions may be due to existence of explosive materials in such areas. These hazardous locations are, for example, petrochemical plants, etc. In addition to that, such hazardous locations may exist in normally safe areas. For example, fuel containers may be stored in service buildings. It is extremely important to eliminate any risks of sparking in such areas. The sparking must not be induced for electrostatics, inductivity, electric devices (e.g. luminaires), breakage of an electric device or any other reason. For the reasons mentioned above many requirements are set for electric devices which may be used in hazardous locations. These kind of devices must be protected against sparking, the electric power supplied to the devices must be limited, warming-up of surfaces of the devices must not exceed certain limits, etc.
The determination that areas can be classified as hazardous locations is based on the following:

the possible presence of an explosive atmosphere such as flammable gases, vapors, or liquids, combustible dusts or ignitable fibres and flyings;
the likelihood that the explosive atmosphere is present when equipment is operating; and
the ignition-related properties of the explosive atmosphere that is present.

Many Classifications of Hazardous Degrees exist around the world. For example, an Ex Classification is used in Europe.
In Europe three Zones are defined where explosive mixtures of gas or powder and air can exist. The most dangerous zone is Zone 0 in which the mixture is continuously or almost continuously present. Zone 1 is defined as a location where the mixture is likely to occur in normal operations. In Zone 2 locations the mixture is unlikely or will only exist for a short time.
The devices which are intended to be used in hazardous locations must be accepted by a Notified Body before the devices are allowed to be used in such locations.
There are some IEC standards which relate to the requirements for the devices for hazardous areas and also to the testing of such devices. For example, IEC 60079-26, section 4.2.1a discloses requirements for the devices for zone 0 hazardous areas against two faults occurring independently of each other. IEC 60079-26, section 4.2.3 describes general information of requirements for encapsulation as a sole means of protection. IEC 60079-18 section 7.3 describes maximum limits of free space in the encapsulation for two levels of protection: 100 cm³ for "mb" and 10 cm³ for "ma". IEC 60079-0 section 26.8 describes requirements for resistance to impact and section 26.8 describes requirements for thermal endurance to heat.
Electric devices to be used in locations of Zone 0 and/or Zone 1 are very demanding and many points of view have to be taken into account when designing such devices. The manufacturing of prior art Explosion-protected luminaires has been very difficult and expensive since e.g. the electric power to be supplied to the luminaire has to be limited and since the temperature loss of the luminaire has to be kept within certain limits. These limitations cause difficulties to design a luminaire which can produce enough illumination.
One other aspect when designing explosion-protected luminaires for maintenance and service work is the size and weight of the luminaire.
The luminaire should be as small and light as possible. Fluorescent lamps are not very small wherein it is not easy to reduce the size of the luminaire.

Summary of the Invention

It is an aim of the present invention to provide an improvement to the prior art luminaires for zone 0 hazardous areas. The present invention is based on the idea that the illumination source is positioned inside a casing and the free space between the outer surface of the illumination source and the inner surface of the casing is filled with a filler material. The thickness of the casing is designed so that the distance from the outer surface of the casing to the electrically active part of the illumination source is greater or equal than a predetermined minimum. This kind of structure is called as strengthened casting and some limit values are defined in IEC standards. In an advantageous embodiment the casing is shaped so that at least the form of the inner surface of the casing follows the shape of the outer surface of the illumination source. The aim of this arrangement is to make the gap between the illumination source and the casing as small as possible. To put it more precisely, the luminaire according to the present invention is primarily characterised in that the luminaire further comprises an illumination unit comprising a body in connection with which the illuminator is attached, and a protective cover placed above the illuminator for protecting the illuminator, and that the free space of the body is filled with a filler to make the illumination unit substantially gas tight.
Considerable advantages are achieved by the present invention when compared with prior art explosion-protected luminaires. The illumination source of the explosion-protected luminaire of the present invention comprises light emitting diodes (LED) which are not very sensible to impacts and they don't induce electric spikes (voltage and/or current) if they are broken. The LEDs also have the advantage that they don't generate too much heat so there is no need to arrange any cooling apparatus inside the casing where the LEDs are situated. The use of LEDs also makes it possible to design smaller luminaires than if normal illumination sources, e.g. fluorescent lamps were used.
The illuminator according to the present invention is rather easy to manufacture. The illuminator is gas tight so that no sparks which may occur inside the casing can not easily affect an explosion of gas.

Description of the Drawings

In the following the invention will be described in more detail with reference to the attached drawings, in which

Fig. 1: shows an explosion-protected luminaire according to an advantageous embodiment of the present invention,
Fig. 2: shows the parts of the luminaire of Fig. 1,
Fig. 3a―3c: show some details of the luminaire of Fig. 1, and
Fig. 4: shows the cross-section of the luminaire at point A―A.

Detailed Description of the Invention

In the following the luminaire 1 according to the present invention will be described in more detail with reference to Fig. 1. The luminaire 1 comprises the casing 2. In this example embodiment the casing 2 has a central section 2.1 and a first 2.2 and a second end section 2.3. The second end section is constructed from two parts 2.3a, 2.3b. The power cable 3 is connected inside the casing 2 of the luminaire 1 through the second end section 2.2. The central section 2.1 of the casing is at least partly transparent to enable the illumination generated by the illumination unit 4 to radiate from the luminaire 1. The electric power is supplied to the luminaire 1 by a supply unit 5 which generates a proper voltage for the luminaire. The supply unit 5 also limits the electric power so that it does not exceed a certain safety limit. The supply unit 5 for zone 0 hazardous area devices has to tolerate a combination of any of two independent different faults. It should be mentioned here that the supply unit 5 need not be located into the zone 0 area but into zone 1 or zone 2 areas. The operation of the supply unit 5 is known as such so it is not necessary to describe it in more detail in this application.
The central section 2.1 of the casing 2 is preferably made of a polycarbonate tube 2.1 a which is treated to be antistatic when necessary. The first 2.2 and the second end section 2.3 are also made of antistatic material or they are treated to be antistatic.
The power cable 3 is connected through the second end section 2.3 of the casing 2 and secured with an attachment unit 6 (Fig. 2) to the second end section 2.3. The attachment unit 6 has a sealing plate 6.1 for sealing the cable via of the second end section 2.3. The power cable 3 is ended at a circuit board 4.4 to which the illumination unit 4 is also connected. At the first end section 2.1 there is also a hook 8.
Next, the structure of the illumination unit 4 of an example embodiment will be described in more detail with reference to Figs. 3a―3c. The illumination unit 4 is formed of a body 4.2, illuminators 4.1 attached on the circuit board 4.4 and a protective cover 4.3 for the illuminators 4.1. The illuminators 4.1 are for example soldered to the circuit board 4.4. In this embodiment there are three illuminators 4.1 in the illumination unit 4 but it is obvious that the number of illuminators 4.1 may be different in different embodiments. The circuit board 4.4 contains wirings (not shown) to conduct electric power from the power cable 3 to the illuminators 4.1. The illuminators 4.1 are protected by attaching a protective cover 4.3 on the illuminators 4.1. The protective cover 4.3 is shaped so that the surface 4.3a of the protective cover 4.3 follows the shape of the illuminators 4.1 in order to minimise the free space between the surface of the illuminators 4.1 and the protective cover 4.3. There are also sealing rings 4.5 between the protective cover 4.3 and the illuminators 4.1 which add the tightness of the structure of the illumination unit 4. The illumination unit 4 is attached to the body 4.2 of the central section 2.1 of the luminaire 1. The body 4.2 has a flat section onto which the circuit board 4.4 can be slided, for example. The flat section 4.2a forms a kind of a groove in the body 4.2 for the illumination unit 4. The groove is so dimensioned that the illumination unit 4 fits very tightly into the groove. This makes the seams between the body 4.2 and the circuit board 4.4 and the protective cover 4.3 of the illumination unit 4 very narrow. After the illumination unit 4 is attached to the body 4.2, the protective cover 4.3 and the circuit board 4.4 and/or the flat section 4.2a of the body delimit some kind of a cavity in which there is some free space. The free space of the groove can be filled with filler such as silicon or other viscose material. The filler makes the seams substantially gas tight to prevent gas flowing into the groove. Fig. 3a illustrates the different parts of the illumination unit 4 and the assembling steps of them. Fig. 3b illustrates the structure of the illumination unit 4 as a top view and as cross sections from different locations of the illumination unit 4. Fig. 3c shows a more detailed view of the structure of the illumination unit 4 at the location of the illuminator 4.1.
The body 4.2 of the central section can be made of e.g. aluminium because it conducts heat quite well. The heat conduction can further be increased by the flat section of the body because the circuit board 4.4 is laying on the flat section. The good heat conduction induces the temperature of the illuminators 4.1 to stay at a lower level which increases the life time of the illuminators 4.1.
When the body 4.2 of the illumination unit 4 is filled with the filler 9, the filler 9 surrounds the illuminators 4.1, the circuit board 4.4, the power cable 3 and the protective cover 4.3 thus making the body 4.2 gas tight. The body 4.2 can then be placed inside the tube 2.1 a of the central body 2.1. After that the first 2.2 and the second end sections 2.3 are attached with the central section 2.1 wherein the luminaire 1 according to the present invention is ready for use.
The filler 9 also makes the attachment of the power cable 3 to the luminaire 1 more secure and thus improves the reliability of the luminaire 1 against mechanical forces.
The critical dimensions of the luminaire 1 can be analysed with the help of Fig. 3c. The electrically active parts of the luminaire 1 are inside the illuminators 4.1. If the illuminators 4.1 are LEDs, there is a chip (a radiating element) 4.1 a inside the casing 4.1 b of the illuminators 4.1 which emits radiation (light). The casing of the illuminators 4.1 is filled with a filler which is not necessarily the same filler than the filler of the body 4.2. Usually the distance from the chip to the outer surface of the LED is about 1.5 mm ( 0.5 mm filler and 1 mm cover). The thickness of the protective cover 4.3 has to be at least 1.5 mm so that the distance from the chip to the outer surface of the body 4.2 is at least 3 mm which is defined as a minimum limit for mastructures according to the standard IEC 60079-18 section 7.3. Therefore, the present invention provides a structure which fulfils inter alia the requirements of IEC 60079-18 section 7.3.
It is also possible to use other illuminators than LEDs in the luminaire according to the present invention. The thickness of the protective cover 4.3 can be varied in different embodiments so that the above mentioned condition is fulfilled.
The cross section of the body 4.2 and of the other parts of the luminaire 1 can also differ from the cross sections of the above described embodiment.

Claims

A luminaire for zone 0 hazardous areas, the luminaire comprising an illuminator (4.1), and a cable (3) for supplying electric power to illuminate the illuminator (4.1), characterised in that the luminaire (1) further comprises an illumination unit (4) comprising a body (4.2) in connection with which the illuminator (4.1) is attached, and a protective cover (4.3) placed above the illuminator (4.1) for protecting the illuminator (4.1), and that the free space of the body (4.2) is filled with a filler to make the illumination unit (4) substantially gas tight.
A luminaire according to claim 1, characterised in that the luminaire (1) further comprises, a casing (2), and that said illumination unit (4) is placed inside the casing (2).
A luminaire according to claim 1 or 2, characterised in that said illumination unit (4) comprises a circuit board (4.4), and that the illuminator (4.1) and the power cable (3) are attached to the circuit board (4.4).
A luminaire according to claim 3, characterised in that said protective cover (4.3) and said circuit board (4.4) delimit a cavity, and the free space of the cavity is filled with said filler, wherein the filler secures the attachment of the power cable (3) to the circuit board (4.4).
A luminaire according to claims 2, 3 or 4, characterised in that said casing (2) comprises a central section (2.1) and a first (2.2) and a second end section (2.3).
A luminaire according to claim 5, characterised in that said central section (2.1), said first end section (2.2) and said second end section (2.3) are antistatic.
A luminaire according to claim 5 or 6, characterised in that said power cable (3) is connected through the second end section (2.3) of the casing 2 and secured with an attachment unit (6) to the second end section (2.3).
A luminaire according to any of the claims 1 to 7, characterised in that said protective cover (4.3) is shaped so that the surface (4.3a) of the protective cover (4.3) follows the shape of the illuminators (4.1) in order to minimise the free space between the surface of the illuminators (4.1) and the protective cover (4.3).
A luminaire according to any of the claims 1 to 8, characterised in that the illuminator (4.1) comprises a casing (4.1b), and a radiating element (4.1 a) inside the casing (4.1b).
A luminaire according to claim 9, characterised in that the distance from the inner surface of the casing (4.1b) of the illuminator (4.1) to the outer surface of the protective cover (4.3) is greater or equal than 3 mm.
A luminaire according to any of the claims 1 to 10, characterised in that it comprises two or more illuminators (4.1).
A luminaire according to any of the claims 1 to 11, characterised in that the illuminator (4.1) is a power LED.