The desire for higher availability of machines and systems has risen steadily in recent years. As a result, the 24 V (DC) supply system is now viewed in a much more differentiated way than it was a few years ago.

For systems with high availability, a distinction must first be made between supplying and protecting. When supplying, it is essential to use high-quality components to ensure smooth operation over a long period of time. This begins with the feed-in of a system and extends to the consumer.

Protecting the system is about ensuring operation and reliably protecting the various components and cables from damage or even failure. The term protection covers various faults that can occur during operation and bring the system to a standstill. These include issues such as overvoltage protection, overcurrent protection and short-circuit protection - but the start-up of loads can also prove to be disruptive, as they sometimes require more than 10 times the rated current during the start-up process. Contactors also include buffering the supply voltage to prevent a voltage dip. The time that can be bridged depends on the size of the buffer.

Protect against overvoltage

Suitable surge protection should be considered in every system. If it is designed incorrectly or not at all, it can lead to failures in the system, which often results in costly repairs. It therefore makes sense to use type 1+2 and type 3 surge protection devices to prevent expensive repairs as a result of surges.

Switch-mode power supply units have established themselves as the standard for supplying switchgear. They always supply a constant voltage with high efficiency. They also offer helpful additional functions - for example, the power boost for reliable starting of loads or to cover a sudden increase in power requirements when additional loads are switched on.

In extensive systems, a DC/DC converter can also be used - to generate other voltage levels, to refresh dropped voltage and thus stabilize it, or to decouple different parts of the system from each other. Decoupling prevents unwanted feedback caused by switching operations. Feedback into other machine parts can also be avoided in this way.

Energy buffering and redundancy

Supply and protection take place in several stages:

(1) Surge protection from type 1 to type 3

(2) Power supply with UPS for reliable supply

(3) Protection against overcurrents and short circuits

(4) Convenient distribution of potential

© Phoenix Contact

Energy buffering helps to maintain the system voltage even in critical situations. The background to this is that the supply to the entire system can no longer be guaranteed in the event of a voltage dip. The buffering counteracts the voltage dip by additionally supplying the system with the stored energy. In this way, the user can bridge a short period of time to bring the system to a safe, defined state.

System availability is also significantly increased if the supply is set up redundantly. For this purpose, two decoupled power supplies are connected in parallel. This decoupling is achieved with an active redundancy module or a diode module. In this case, one power supply can fail completely, as the system continues to be supplied via the second power supply. It is important here that each power supply is utilized at less than 50 % in order to take over in the event of a fault. Active redundancy modules have a significantly lower power loss and also offer extended diagnostic and signaling functions. This means that the entire system is supplied with energy by a power supply in good time. The defective power supply can then be replaced without interrupting operation.

Protect and distribute

Different miniature circuit-breakers - from modular single-channel devices (left) to compact multi-channel circuit-breakers (right) - increase the reliability of machines and systems.

© Phoenix Contact

For effective protection, the circuits behind a power supply should be divided and, if possible, selectively fused. This protects the individual consumer circuits - they can be switched off separately in the event of a fault. It is important to protect the supply voltage, because if a fault occurs during operation, this can collapse. The entire system operation is then at risk.

Protection is often already provided by electronic fuses. Compared to conventional circuit breakers, these require a much lower current in the event of a fault and therefore trip safely. Parallel circuits can continue to operate without impairment.

With devices in different designs, Phoenix Contact offers the right protection for every application. Flexible protection can be achieved with modular single-channel circuit breakers, for example, and the exact number of protection circuits can be set quickly and easily.

Suitable protection is also provided by compact multi-channel miniature circuit-breakers, which can be installed quickly and put into operation with virtually no wiring.