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The risk of cascading failure in power grid can be integrated the possibility and severity of cascading failure severity. The possibility in traditional risk assessment only considered the line failure rate, but the line overload outage is one of the important reasons lead to cascading failure too. In order to consider the complex uncertainty in actual power system, according to the line protection actions, environmental and weather factors and human errors caused by the line fault and line overload to get the line outage probability, further set up cascading failure risk assessment model of power grid considering line outage rate .The simulation of the WSCC-9 buses system proved that the proposed method is with correctness and objectivity, provided with engineering value.

A large number of distributed generators access to low-voltage distribution network, in case of failure disturbance, the system is easy to enter a low power quality instability islanding operation state. When the power capacity of the island is much smaller than the load demand(there is a high power shortage), it is the key to realize the island's automatic restoration to normal operation by improving the protection coordination scheme. The paper analyzes the shortcomings of the prior setting scheme for under-frequency load-shedding device and automatic switching device, especially when large power shortage happens in an unstable island network, and then proposed a zero increase investment method for island self-healing in smart distribution network. The proposed method aims to give priority to ensuring the safety of the unit, achieve the goal of optimal unit safety by improving the protection coordination scheme, and ensure the automatic grid-connected operation of the power supply with zero loss. By actual grid fault simulation analysis, it is proved that the proposed method improves the reliability of power supply and avoids unit into an unstable operating state. It has great engineering application value, and now has been applied in a certain city Power Grid of Jiangsu province.