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According to the basic document on explosion protection in force in the European Union, which is the ATEX directive (both 114 and 153), devices designed to work in the so-called hazardous areas must meet certain requirements. The risk is associated with the presence of an explosive atmosphere, i.e. a mixture with air - in atmospheric conditions - flammable substances in the form of gas, vapor, mist or dust, in which, after ignition, combustion spreads to the entire unburned mixture. Additionally, in the section "Prevention of explosions and explosion protection" at the beginning of Art. 3 of the ATEX User Directive, the employer is required to take technical and / or organizational measures corresponding to the nature of the specific hazard, which is reflected in the concept of Integrated Safety, which is briefly presented in the diagram below.
The protection of electrical devices is included in the second layer. At the same time, there is no single, best method of minimizing - or at best: eliminating - the risk of an effective ignition source. In general, equipment intended for use in potentially explosive atmospheres is designed, manufactured, tested and marked in accordance with the requirements of:
This article focuses on one selected protection method, namely a variant of ventilated protection which is EX s pressure protection, which technology is currently offered by DACPOL. According to PN-EN 60079-2: 2015-02 - Explosive Atmospheres - Part 2: Protection of devices with overpressure "p" gas shields - consists in placing parts that may spark or heat during operation in a closed housing filled with air or other inert (non-flammable) gas under constant pressure.
The difference between the EX p and EX s systems is primarily the need for ventilation, which while in the former is a necessity, in the latter it is optionally activated after the analysis of the presence of flammable gas inside the housing. In both cases, it is necessary to have a gas sensor adapted to the currently present flammable / explosive substance in the installation and its calibration once a year. Among other technical solutions, the EX s system has a set of valves, used by a permanently connected compressor, and - when the power consumption exceeds 5A - a special contactor. The very principle of operation is based on the phenomenon of overpressure, i.e. the use of the effect of the pressure difference between the outside of the housing (where there is an explosive atmosphere) and the inside (safe zone). The inability to penetrate the aforementioned atmosphere makes the devices and components closed inside safe, which allows to place there those that do not have the ATEX certificate. It is a very convenient feature of this protection method, which makes EX s a universal solution with many applications. Gas shields with overpressure are most often used to protect high-power electric motors, especially high-voltage ones, as well as switchgear and control cabinets.
What distinguishes the pressure systems supplied by DACPOL in relation to other available on the market is the possibility of transferring a large part of the assembly to the customer. In the past, with older solutions, the procedure was such that after the BOM (list of built-in components) was established, the whole thing was assembled and delivered by the manufacturer. Currently, thanks to a special certification (just EX s), it is possible to purchase the control part itself, and the housing and assembly are the responsibility of the user. Of course, together with the Quinguard module responsible for controlling the system, a manual is provided regarding the requirements for the housing and other elements as well as the method of testing the tightness, which is absolutely required if the whole is to work in an explosive zone.
From the point of view of process safety, the EX s system is part of the so-called Of Integrated Safety, which states that the entire problem of counteracting the risk of explosion can be broken down into three layers:
The methods of protection of electrical devices that can generate the proverbial spark during their normal operation (i.e. at rated voltage and current) qualify for preventing the appearance of an ignition source. In the case of EX s protection, the situation is not so obvious that while the ignition source itself may appear, due to the overpressure, the explosion will not ignite or propagate to the vicinity of the housing. From the point of view of security layers, it is a method based on explosion isolation. Inert gas, which is forced into the inside of the sealed housing, also acts as a medium cooling the interior, which additionally reduces the risk of excessive heating of the components inside. Safety is ensured by a differential pressure monitoring system that makes up for the shortage of inert gas (or blocks the flow), and disconnects power to the circuit in the event of leakage.
The greatest advantage of the EX s pressure system is its modularity and versatility. The former manifests itself in the possibility of delivering it in various ways. For the client, these are, for example:
In the case of a detector, there is freedom here: it can be provided by the customer or the manufacturer.
Versatility, in turn, means wide possibilities of use in various conditions. The EX s system can work in gas zones 1 and 2 and dust zones 21 and 22, and also gives the possibility of securing devices or a set of components with atypical geometry. The specificity of protection means that thanks to EX s, you can adapt almost any device to work in conditions of an explosive atmosphere, because it does not have to have an ATEX certificate, and still work in the EX zone. In the case of large installations such as electrical switchgears, it is a great convenience that does not require the equipment to be moved outside the hazardous area or the use of large - and therefore costly - flameproof covers.
A solution of this type is simple and convenient to use, but at the same time requires close cooperation on the supplier-customer line from the very design stage, so contact is recommended at an early stage of implementation.
15/04/2024
22/02/2024
22/02/2024
