ABSTRACT
Figure 1 shows the schematic of residual current devices. It is a three-phase, four-wire, and lowvoltage distribution network; according to circuit theory, when the system is operating normally, the three-phase circuit is symmetrical. In this case, the output of the zero sequence current transformer TA is zero, that is,
I I I Ia b c o+ = 0 (1)
1 INTRODUCTION
In low-voltage distribution networks, especially in the rural low voltage power grids, due to improper use of electrical appliances, electrical accidents, such as electric shock or short circuit, occur frequently. In order to protect people’s lives and to ensure safety in low-voltage power supply networks, the installations of residual current devices are performed in the distribution network. But there are still some problems in traditional residual current devices which are installed in the system, such as the circuit breaks frequently, because of which the application of residual current devices in the distribution network is limited (Deng Xiaolin (2007), Gu Huimin (2006)). In order to solve the residual current problem in the low-voltage distribution network, it is important to develop an intelligent residual current device which can adapt to changes in low-voltage distribution networks.
