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Electronic breakers can switch eight loads individually

20 February, 2014

The German transformer and power supply specialist Block has developed a pair of electronically operated circuit-breakers for 24V DC circuits which can switch individual circuits selectively via only two lines, and perform diagnostics. It says that the Power Mini and Power Compact breakers can be integrated into control and monitoring processes at low cost to improve the switching of high-capacity loads and to open up new protection possibilities.

The company claims that, for the first time, the new breakers can be used with a PLC to switch any output channel on or off, to reset tripped circuits, and to call up the status of each output using only two digital I/O. Protected circuits up to 10A can be switched individually.

By switching off loads that are not needed, the breakers can also help to cut energy consumption at a relatively low cost, avoiding the need for power relays and their controls. This will save space, simplify controls, and reduce wiring and other costs, Block suggests.

The digital switching takes place via only one wire between the PLC and the circuit-breaker. The PLC generates a pulse sequence of 17 data bits, and can control its transmission speed. The breaker synchronises automatically to the cycle. A second line provides the operating and error conditions for each output channel synchronised to the cycle.

The PLC can analyse these conditions and recognises the status of all protected circuits. For each output, it can transmit the latest operating conditions (on/off) and error conditions (tripped/overcurrent).

To simplify the programming needed to integrate the new devices with a PLC, Block is offering free functional modules for Siemens Step 7 and CoDeSys systems.

A challenge for electronic circuit-breakers is to differentiate between short circuits and high start-up or inrush currents. To the breaker, a high start-up current – often caused by capacitors – is almost identical to a short-circuit. Some electronic breakers perform badly compared to conventional breakers with thermal and magnetic tripping curves.

Block's electronic circuit-breakers communicate with a PLC via a pair of connections, allowing individual loads to be switched on or off

Block claims that, thanks to a patented switching technology and smart software algorithms, its breakers do not suffer from this problem and can differentiate precisely between long-lasting short-circuit currents and switch-on current peaks. Depending on the line impedance, a capacity of up to 500,000µF (in addition to the basic load) can be switched per output, independently of the rated current. Even under difficult switch-on conditions (short lines with large cross-sections), more than 50,000µF can be switched reliably per output. Block says this is up to five times more than rival devices.

Up to eight output channels can be switched on, not only at different times, but also depending on the load. When the current of an output channel drops, the next one is switched on with optimal timing. The inrush current for the complete application is equalised and the power supply does not need to be over-sized.

The output channels can also be switched manually, simplifying start-ups or error-tracking when servicing. The rated current for each channel can be set in 2A steps up to 10A via a front-panel switch. This allows one device to cover many different applications.

Each output on an eight-channel module occupies a width of just 5.25mm, saving rail space or allowing the use of smaller control cabinets. The breakers use push-in-connections for fast and easy installation.

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