What are the three lines of defense for compliance management of State Grid?

The three lines of defense for compliance management of State Grid are relay protection, load shedding stability control device for overload cutting machine, and low-frequency and low-voltage out-of-step disconnection device. When a high probability common single fault occurs in the power grid, the power system should maintain stable operation and normal power supply to users, which refers to the requirement of ensuring stable and reliable power supply to the power grid when the power system is disturbed by various kinds.

The importance of managing three lines of defense

Fast and reliable relay protection, effective preventive and control measures to ensure the stable operation of the power grid and normal power supply when a common single fault occurs, and emergency control measures such as stability control device, machine cut-off and load cut-off are adopted to ensure the continuous stable operation of the power grid when a serious fault occurs with low probability.

Set out-of-step and out-of-sequence, frequency and voltage emergency control devices. When the power grid is stably destroyed by several serious accidents with low probability, these devices are relied on to prevent accidents from expanding and large-scale power outages. When there are rare multiple faults in the power grid, the power system may be unstable, but predetermined measures should be taken to minimize the impact range and shorten the impact time.

When a high probability common single fault occurs in the power grid, the power system should maintain stable operation and normal power supply to users. When a single fault with serious nature but low probability occurs in the power grid, the power system should maintain stable operation, but some loads are allowed to be lost.