Centralized installation and decentralized installation

Without a doubt, the most popular form of installation is the centralized installation of the VSD in the control cabinet. The advantages of centralized control cabinet technology lie first and foremost in the protected installation of devices and centralized access to them for power, control, maintenance and fault analysis.

When installing in the control cabinet, the main aspect that must be considered is heat management, not only the heat management of the equipment, but also the heat management of the entire installation process. Additional cooling of the control cabinet may be required due to heat dissipation in the control cabinet.

According to the VSD manufacturer's installation regulations, a minimum distance must be maintained above and below the device and between the device and adjacent components. In order to better heat dissipation, it is recommended to install directly on the back wall of the control cabinet. Some manufacturers also specify a minimum distance between individual units. However, if possible, it is best to install units side by side in order to make efficient use of the mounting surface area.

In some cases, the disadvantage of centralized installation is that the cable length to the motor is longer. Although the use of shielded cables will undoubtedly reduce the RFI effects of motor cables, these effects have not been completely eliminated.

As an alternative to centralized installation, a decentralized layout can also be chosen to lay out facilities. The VSD is located very close to or directly on the motor here.

Thus, the length of the motor cable is reduced to a minimum. In addition, a distributed installation has advantages in fault detection because the relationship between the controller and its associated motors is easy to view. In a decentralized configuration, a fieldbus is usually used to control the drive.

When planning a distributed installation, factors such as ambient temperature, main voltage drop, and motor cable length limitation must be considered. Important factors such as these are often overlooked in the advanced design of engineering projects.

For example, not only the dispersion equipment but also the power supply cable must be suitable for the installation environment. For example, fieldbus cables must be suitable for harsher environments and sometimes for flexible types. In addition, equipment should be avoided in inaccessible locations to ensure quick maintenance.

Another major consideration is the segmentation of a decentralized network. For economic reasons, it is beneficial to combine units into groups or segments. Careful consideration must be given when determining which segments require other segments to operate and which segments can, must, may, or should continue to operate autonomously. For example, if some chemical process cannot be interrupted, the failure of a low-level segment should not be allowed to destroy an important segment.

Finally, the expertise required to install a decentralized network should not be underestimated. In addition to understanding the fieldbus system being used, the technician must also understand the structure (what happens to the entire system if a single unit fails) and the environmental conditions of the decentralized network, and must be able to estimate these effects.

Although decentralized devices are always more expensive than centralized ones, a well-conceived decentralized concept can save about 25% over centralized systems. The potential reasons for the savings in installation costs are the reduction in cable length and the reduction in nodules in the form of the use of equipment nodules, which have been manufactured and tested by the machine manufacturer or supplier.