Overcurrent protection

The primary function of electronic circuit breakers is to monitor 24V circuits for overcurrent and short circuits to protect connected loads and their feed wire lines. With Power Mini and Power Compact BLOCK has developed two new electronically operated circuit breakers, with capabilities that go beyond just selectively switching off the faulty circuit. Diagnosis capability, as well as the specific switching of individual circuits via only two wire lines, creates new possibilities.

In almost every control cabinet there is a 24V power supply, which is protected against total failure caused by failure of single electrical loads or their feed wire lines by being divided into a number of circuits, each of which is secured separately. This is increasingly being achieved using electronic circuit breakers.

In developing the Power Mini and Power Compact, Block has addressed the question of how the performance of the complete system can be improved.

In combination with a PLC, the new electronic circuit breakers offer the possibility to actively switch any output channel on or off, reset tripped circuits and at the same call up the actual status of each output via only two digital I/Os. During running operation, circuits protected up to 10 amps can be switched specifically.

Single circuits without additional components can be switched off, enabling energy efficient applications at a reasonable price. This saves space, simplifies the control and reduces the wiring when compared to previous methods requiring power relays and associated controls.

The digital switching takes place via only one wire line between the PLC and the circuit breaker. The PLC generates a pulse sequence consisting of 17 data bits; the transmission speed can be selected variably according to the performance of the PLC. Due to the fact that this pulse sequence is sent Manchester coded, the circuit breaker synchronises automatically to the used cycle. Via a second line it 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 the latest operation conditions (on/off) as well as the error conditions (tripped/overcurrent) are transmitted.

To minimise the programming effort for the integration of new devices in a PLC, BLOCK provides a functional module for Siemens Step 7 as well as for the CoDeSys-systems free of charge.  

The signal contact usually applied in electronic circuit breakers is also integrated in new devices. Through this, tripped circuits can be signaled as sum messages.

In normal use, the challenge for electronic circuit breakers is to quickly separate the faulty line in case of a short circuit as well as to switch-on consumers with high start-up or inrush currents reliably. For the electronics in a circuit breaker, a high start-up current during the first milliseconds – caused by capacitors in many loads – is almost identical to a short circuit current. Due to the fact that the electronics in a circuit breaker also have to be protected against overload, often the switch-on capability for capacity loads suffers. Addressing this issue, the new BLOCK-modules offer a much improved performance.

Thanks to a patented switch technology and smart software algorithms, it is possible to differentiate precisely between long lasting short circuit currents and the tolerable switch-on current peaks. Per output, depending on the line impedance, a capacity of up to 500.000µF additionally to the basic load can be switched independent from the set rated current. Even under difficult switch-on conditions (short lines at maximum line cross section) more than 50.000µF capacity can be reliably switched per output. This is up to five times more than some alternative devices.

Switching of the up to eight integrated output channels is timed and also load dependent. As soon as the set rated current of an output channel is lower, the next one is switched on with optimal timing. The inrush current for the complete application is levelled; the power supply unit does not have to be over dimensional.