Is Sub Transmission part of the main transmission grid?

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Subtransmission sits as an intermediate layer between the high-voltage transmission network and the local distribution system. The main transmission grid is the long-distance, high-voltage backbone that moves large amounts of power across regions. Subtransmission carries bulk power from transmission substations to distribution substations at intermediate voltages, acting as a separate tier rather than the primary backbone. Because of its role as the bridge to distribution, it’s not considered part of the main transmission grid. It delivers power regionally and feeds into distribution, not the long-haul transport that defines the main grid. So the correct view is that subtransmission is a different layer, not part of the main transmission grid.