Research On Unlocking The Electromagnetic Loop Network Between Provinces In Northeast Grid

Lines with different voltage circled by transformer is called electromagnetic loop network. It has to take this type to get power economically and satisfy the customer's largest request before the higher voltage networks strong enough.The main hidden danger of the electromagnetic loop network mode is that a large amount of power flow pour into the lower voltage grid when the higher voltage grid is cut off,it can easily cause overload, protection misoperation and even destroy the system stability.This mode also leads to the difficulty to control power flow,large short circuit current,complexity of protection setting,etc. It has been accepted that we should unlock the electromagnetic loop network especially to the connect lines between provinces.With the increase of power flow from north to south in Northeast grid, the transfer capability of 500kV grid has been limited because of the overload of 220kV grid. With the strengthening of 500kV channels,the 220kV connect lines become less important,the time of unlocking the electromagnetic loop network has come.According to the current situation in Northeast grid,it made 4 plans.It calculated the largest operation mode of Northeast grid in 2009 with PSASP,analyzed the results between two operation modes and decided whether it should be unlocked,cosidering the power flow,N-1, short circuit current level, net loss, supply reliability and system stability.The result proved that the electromagnetic loop network between provinces can be unlocked. It also evaluated whether it should be unlocked by AHP and fuzzy evaluation, chose the best scheme in math,the result proved the same as the PSASP.At last,it drew a conclution that the electromagnetic loop network of 500/220kV between provinces in Northeast grid can be unlocked.