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

Protection and Control of Modern Power Systems

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

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]

*[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
The table above shows that the “N-1” outage is the main point to be considered in distribution networks