(1) Class I substations: These include AC UHV substations; substations serving power evacuation from nuclear power plants or large-scale energy bases (3,000 MW and above); and 750/500/330 kV substations serving inter-regional interconnections (between North, Central, East, Northeast, and Northwest China).
(2) Class II substations: These include 750/500/330 kV substations not classified as Class I; substations serving power evacuation from power plants (1,000 MW and above but less than 3,000 MW); 220 kV substations serving inter-provincial interconnections; and substations where the outage of a main transformer or busbar, or the failure of a circuit breaker to operate, results in a Level 4 or higher power grid incident.
(3) Class III substations: These include 220 kV substations not classified as Class II; substations serving power evacuation from power plants (300 MW and above but less than 1,000 MW); substations where the outage of a main transformer or busbar, or the failure of a circuit breaker to operate, results in a Level 5 power grid incident; and substations directly supplying power to "Level 1" or higher priority consumers.
(4) Class IV substations: These include substations rated at 35 kV and above that do not fall into Class I, II, or III.
Note: All 220 kV substations within the operational district are classified as Class III, and all substations rated at 110 kV and below are classified as Class IV.
