Modeling of residual-current device for direct current circuits

The authors have reviewed the model of residual-current device for direct current circuits with high precision Hall-effect based residual current sensor which also provides galvanic isolation of logic from power circuits. The scheme based on microcontroller with built-in analog-to-digital converter and analog peripherals part with comparators, which provides different ways of signal processing is reviewed. The authors have offered the schemes with analog and digital signal processing of leakage current and load current sensors signals. The modeling is done with Simulink software, using transfer functions of current sensors and main scheme elements. Measurement of reviewed signal processing schemes performance is done by applying linear signal to system input, simulating load or leakage current rise over preset limit. Output signal of the system is the signal to break circuit, connected to the breaking relay. Performance of the scheme can be determined by measuring the delay from current limit crossing point to presence of breaking output signal. Looking at the every element delay it is possible to estimate its contribution to overall performance. The authors have analyzed and compared the performance of each signal processing scheme and contribution of elements to overall performance. The authors have compared signal processing capabilities of each scheme such as noise filtering and current sensor nonlinearity correction. The authors have analyzed the pros and cons of reviewed schemes, their ability to protect man and machinery from leakage current damage in home or industrial use, with respect to protection requirements based on government standards for high and low load current residual-current devices. Considered device can be used in direct current power circuits of a spacecraft to prevent accident situations. The authors give recommendations for future scheme improvements, aiming on performance improvement, which will provide universal use scenario of reviewed device. The performance requirements for breaking device and given recommendations for its implementation are determined.