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Table 1 Security standards of supply for urban China (common load groups in distribution networks)

From: A diagnostic method for distribution networks based on power supply safety standards

Supply level Scope of load groups (MW) N-1” outage N-1-1” outage comment
A ≤2 After maintenance: restore load groups No requirement  
B 2 ~ 12 (1) In 3 h: load restored = load groups-2 MW
(2)After maintenance: restore load groups
No requirement  
C 12 ~ 180 (1) In 15 min: load restored ≥ min (load groups-12 MW, 2/3 load groups).
(2) In 3 h: restore load groups
No requirement *[a]
  1. *[a]: User group is generally supplied by two (or more than two) normally-closed circuits or one circuit but can be switch to other circuits by artificial or automatic switch. The load group is the maximum load of the use group
  2. The table above shows that the “N-1” outage is the main point to be considered in distribution networks