An important indicator of the ongoing decentralization in mechanical and plant engineering is the almost universal use of fieldbus systems such as AS-Interface, CANopen or Profibus-DP as well as Industrial Ethernet connections via Profinet, Ethercat, Modbus TCP or Ethernet/IP. This applies to all production areas of mechanical and plant engineering as well as the entire process industry. The use of countless decentralized peripheral modules such as 'ET200SP' or field devices with protection ratings from IP54 to IP67 in the areas of drive technology, sensors and actuators for production systems in the automotive industry impressively demonstrate the continuous implementation of these trends. A large proportion of safety technology is now also gradually moving from the control cabinet directly into the field devices - safe valve terminals, for example, are already standard in production. The consequence is obvious: in some cases, the large, central supply cabinets are already 'yawningly empty'; they now only contain the main switch, various Neozed fuses and load-break switches for protecting the 400 V (AC) power supply and the switched-mode power supply units for generating the 24 V (DC) control voltage, including the fuse protection and potential distribution for the 24 V circuits.

Falling total costs

A thermal simulation ensures that the components used are optimally positioned.

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This is where the opportunities for cost savings begin: decentralization creates space in the control cabinet and opens up potential savings through smaller cabinets. And apart from the fact that small feed-in cabinets cost less money - modularization, standardization, simplified installation and optimized use of materials reduce the overall installation costs. Plus: simply bolting a small control cabinet to the next pillar without extensive planning means maximum flexibility. A secondary cost reduction results from the additional floor space available for the actual production area due to the relatively high price per square meter for the production area.

Decentralized power distribution is particularly advantageous in modular plant construction, with elongated machine configurations and in all conveyor technology - especially with regard to the cable lengths and cross-sections laid and the installation costs. Decentralized and modular concepts for automation significantly help to reduce costs in the planning, installation, operation and expansion of systems and production cells.

Lean Planning

Modern production planning pays particular attention to maximizing the flexibility of facilities and processes. The aim is to be able to react quickly to changes in markets, products and production technology. Innovative decentralized design concepts ensure a high degree of spatial flexibility for operating resources, logistics systems and supply and disposal facilities.

Additional, decentralized peripheral modules such as ET200S or other electrical and electronic equipment as well as switching and protection devices can be integrated into the multifunctional switch box for energy distribution and control technology.

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Flexible production requires modular machines that can be tailored to existing production processes and offer scope for future conversions and expansions. This is why there is still a trend towards splitting machines into their sub-processes. Automation hardware is responding to this demand with options for distributed intelligence, fast communication and decentralized power distribution in order to exploit the advantages of modular design. This enables planners to reuse sub-processes once they have been developed as often as possible.

New structures make it necessary to move away from the central control cabinet with its typical star-shaped cabling routes. The trend is clearly moving towards decentralized cabling structures. Large control cabinets often interfere with a regular structure in the production plant. Separate planning and 3D simulation are therefore always required with regard to the necessary space requirements. In the actual planning for the individual areas of the plant, the focus is on a high proportion of space for the actual production.

Copper as a cost driver

The line losses in the AC range are limited due to the higher voltage. In the 24 V (DC) control voltage range, however, 'Ohm's law' comes into play: long supply lines from the central supply cabinet to the field devices always mean laying larger cable cross-sections. At the same time, it must be ensured that the last consumers in the supply line also receive the minimum permissible voltage throughout. According to DIN EN 61131-2 (Programmable logic controllers - Part 2: Equipment requirements and tests), this voltage must be above 19.2 V (this corresponds to 24 V minus 20 %). The standard specifies the requirements for programmable logic controllers and associated peripheral devices and contains all the requirements for controlling and monitoring machines and industrial processes. The reduction of the cable cross-section from 4 mm² to 2.5 mm² and the simultaneous reduction of the cable length of a sheathed cable from an average of 100 m to 50 m mean a cost saving for electrical copper by a factor of more than 3. At a price of around 4500 euros per tonne, this is a noticeable reduction.

Automotive production as a pioneer

In the production facilities of the automotive industry, the trend is moving away from central 24 V (DC) supplies in large control cabinets towards small decentralized units directly on site. The solution developed by
E-T-A solution developed for this purpose enables thinner cables for 230 or 400 V(AC). It brings the 24 V(DC)/40 A power supply unit close to consumers such as fieldbus modules or switches. This configuration also enables short distances for the distribution of the 24 V(DC) control voltage in the field. It also ensures a significant reduction in cable length and, in some cases, cable cross-sections.

The decentralized power distributor type 'Power-D-Box V0097' includes a new power distribution concept for the 24 V (DC) control voltage in the field. It is optimized for smaller production units within long production lines, for example in the automotive industry - such as robot islands, welding units, assembly stations or subsystems in conveyor technology. Designed with IP65 protection, it can withstand ambient temperatures of up to +45 °C.

A thermal simulation during the development phase ensures that all components used - switched-mode power supply, buffer module and circuit breaker - are in the optimum position. Additional measurements with thermocouples and infrared temperature measuring devices ensure that the built-in devices are still within their specified operating range at a maximum ambient temperature of +45 °C. Thanks to an optimized arrangement of the integrated power sections and the use of low-loss components, the power distributor can be used without active cooling.

The 'Modul 18plus' modular power distributor is integrated with feed currents of up to 80 A via 16 mm² terminals for +24 V, 0 V and functional earth (FE). The flexibly expandable system offers integrated terminal blocks with screwless push-in technology for connecting two circuits per circuit breaker. This minimizes the need for additional potential distribution terminals. With a maximum of 20 slots, this results in potential distribution with integrated overcurrent protection. In this respect, plug-in devices of type 'ESS30-S' are used, which have galvanic isolation and act selectively due to their special characteristic curve. In practice, this means that the circuit breaker switches off a faulty circuit due to the built-in current limitation and the precise switch-off point without affecting the other loads or the supply unit. Designed as a "low energy breaker" for decentralized applications, the electronic circuit breakers not only offer galvanic isolation in the event of a fault, but also 40% lower power consumption than the previous standard 'ESS20' types.

Author:
Erich Fischer is Head of the Industry, Energy and Equipment division at E-T-A in Altdorf.