1 Introduction
Siemens ' fully integrated integrated control system has great flexibility in the application of intrinsically safe explosion-proof in hazardous areas. A large number of safety explosion-proof products are available for users to design into intrinsically safe explosion-proof systems that meet different requirements, which greatly facilitates the user's choice and application. Users can involve in establishing an explosion-proof control system that best meets their own requirements according to their actual situation and financial situation. .
This article discusses and summarizes several application methods of Siemens explosion-proof system, in order to help and inspire the design and application of explosion-proof users.
2. Classification of explosive hazardous locations
The prerequisites for the safe use of electrical equipment for explosive environments in hazardous locations are reasonable selection, correct installation, and consideration of the necessary maintenance during the daily production and operation of the system. Therefore, the explosion-proof electrical equipment should be reasonably selected according to the nature of the hazardous location where it is used.
Dangerous places are places where there is a risk of fire or explosion due to the presence of flammable and explosive gases, vapors, liquids, flammable dust or flammable fibers. Typical hazardous locations, such as the environment formed during the production, processing, and storage of explosive substances in the petrochemical industry. For explosive gas environments, according to the length of time that hazardous substances exist in the place, the explosive gas environment hazardous area is divided into three zones, namely Ex.Zone0 zone, Ex.Zone1 zone and Ex.Zone2 zone.
Ex.Zone0 zone: an environment where explosive gas mixture appears continuously or for a long time.
Ex.Zone1 zone: an environment where explosive gas mixture may occur during normal operation.
Ex.Zone2 zone: an environment where explosive gas mixtures are unlikely to occur during normal operation or an environment where explosive gas mixtures exist only for a short time even if they appear.
In engineering practice, Ex.Zone0 zone generally exists only in internal gas spaces such as closed containers and storage tanks. Ex.Zone1 zone rarely exists in the actual design process, and most of them belong to Ex.Zone2 zone.
In order to achieve explosion-proof electrical equipment, a variety of explosion-proof technical methods have been adopted in the project, and the explosion-proof certification has been adopted to form explosion-proof electrical equipment to prevent the formation of explosive hazardous environments and their explosion. There are explosion-proof electrical equipment in the form of explosion-proof, intrinsic safety, increased safety, positive pressure, oil-filled, sand-filled, non-spark type. For automatic control systems, the most common are explosion-proof and intrinsically safe explosion-proof technical methods. Intrinsically safe explosion-proof technology has many advantages, such as intrinsic safety, simple structure, and live maintenance. It is the first choice in the process instrument automatic control system.
Intrinsically safe electrical equipment starts with limiting the energy in the circuit. Through reliable control circuit parameter design, the potential spark energy is reduced below the energy that can ignite the specified gas mixture. The heating temperature of the wires and components, and the surface of the housing is also Limit below the ignition temperature of the specified gas mixture. In the intrinsically safe explosion-proof type of equipment, all circuits are intrinsically safe circuits that cannot be ignited by the specified explosive gas environment under any standard prescribed conditions (including normal operation and specified fault conditions). It is divided into two grades of "ia" and "ib". "Ia" grade electrical equipment is an intrinsically safe electrical equipment that can not cause ignition under normal operation and two fault conditions under a fault and any combination; "IB" level electrical equipment is an intrinsically safe electrical equipment that cannot cause ignition under normal operation and when a fault condition is applied (see GB38364 standard). The intrinsically safe explosion-proof form has strict energy restrictions, so it can only be used in weak current equipment. Ex-ia equipment is suitable for Ex.Zone 0, 1, 2 or Ex-ib equipment is suitable for Ex.Zone 1. Zone 2. Intrinsically safe explosion-proof equipment can be repaired and calibrated under live conditions, so it is particularly suitable for process automatic control system applications.
The advantages and characteristics of intrinsically safe explosion-proof technology make it more and more widely used in the field of process automatic control. This article will focus on the application of intrinsically safe applications of automatic control systems.
3. Several application solutions of Siemens SIMATIC system in safe explosion-proof places
Due to the promotion and application of the Siemens Totally Integrated Automation (TIA) concept in the Siemens system in recent years, the Siemens SIMATIC system, especially the PCS 7 system, has added a wealth of safety explosion-proof system solutions for users to choose, greatly enhancing its safety explosion-proof Application ability in the field. Moreover, due to the popularization and application of the intrinsically safe fieldbus PROFIBUS-PA, it is becoming more mature, providing a more flexible and reliable solution for solving the traditional safety explosion-proof system design. This article mainly introduces several typical solutions to complete a safety explosion-proof system with Siemens SIMATIC system as the core framework.
(1) From point to point wiring to point to point wiring (Point to Point) solution
That is the traditional DCS / PLC + safety barrier scheme, as shown in Figure 1. This type of intrinsically safe explosion-proof interface is represented by isolated and Zener safety barriers. The application feature is that the intrinsically safe explosion-proof field instruments are connected to the safety barrier in the control cabinet of the safety zone through the cable in a point-to-point connection, and then the safety barrier is connected to the general I / O card of the control system (DCS / PLC) in the point-to-point connection. This is the traditional intrinsically safe explosion-proof interface technology.
(2) Intrinsically safe explosion-proof I / O card board solution
The intrinsically safe explosion-proof I / O card board solution is to add an intrinsically safe circuit on the basis of the DCS / PLC general-purpose I / O card board, making it an intrinsically safe explosion-proof card board, which can be directly connected to the on-site two-wire intrinsically safe instrument , Omitting the safety fence link, constitutes an intrinsically safe explosion-proof control system, as shown in Figure 2. Its essence is the same as the DCS / PLC + safety barrier scheme, but the safety barrier link is reduced and the line connection point is saved, so the system failure point can be reduced. In addition, such intrinsically safe modules, such as the intrinsically safe explosion-proof Ex I / O card boards SM322, SM321, SM331, SM332, etc. of the SIMATIC S7-300 series, have an explosion-proof grade of Ex-ibIIC and can be connected to the intrinsic zone in the Ex. An instrument. Since the intrinsically safe explosion-proof card board uses integrated safety barrier technology, the use of isolated and Zener safety barriers is reduced, so the structure is compact and space and cost are saved.
Figure 1: Intrinsically safe explosion-proof scheme for point-to-point wiring Figure 2: Intrinsically safe I / O card explosion-proof scheme
The JUK universal screw terminal block series has the typical features which are decisive for practical applications:
l The universal foot allows the terminal blocks to be easily snapped onto the NS35 or NS32 DIN Rail with G shape.
l Closed screw guide holes ensure screwdriver operation perfect.
l For terminal block with different wire cross-sectional areas, complete accessories are available, such as end plates, partition plates, etc.
l Potential distribution achieved by fixed bridges in the terminal center or insertion bridges in the clamping space.
l Same shape and pitch Grounding Terminal Blocks as the JUK universal series.
l Adopt ZB marker strip system,achieve unified identification.
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