Protection device with directional zone selective interlock functionality

A protection device for enabling a circuit breaker in a power distribution network to implement directional zone selective interlock, the circuit breaker including an interface unit capable of sending or receiving an interlock signal, the protection device comprising:

• a first port pair, including a first input port and a first output port, each connectable to the interface unit;
• a second port and a third port, coupleable to corresponding ports of a directional zone selective interlock (DZSI) protection device of another circuit breaker in the power distribution network, to transmit the interlock signal;
• an internal input bus, configured to be connected to the first input port and the second and third ports, to transmit an interlock signal received by the protection device;
• an internal output bus, configured to be connected to the second and third ports, to transmit an interlock signal to be sent from the protection device;
• and
• a control unit, for controlling the first port pair and the second and third ports, configured to enable one of the second and third ports as a second output port and the other one of the second and third ports as a second input port, in response to a detected direction of a current currently flowing through the circuit breaker;
• and configured to at least one of forward the interlock signal on the input bus that is received from the first input port onto the internal output bus, and forward an interlock signal on the input bus that is received from the second input port to the first output port, wherein
• the first input port is connected to a first input circuit, coupled to the input bus and comprising a driving power supply, for transmitting an interlock signal on the input bus to the control unit,
• the first output port is connected to a first output circuit, coupled to the first output port, for sending from the first output port an interlock signal from the control unit by way of signal isolation, and
• the control unit is connected to a second output circuit, coupled to the output bus, for outputting an interlock signal from the control unit to the output bus by way of signal isolation.