500 kV substations undertake important tasks of electric supply and long-time stoppage of their busbar differen-tial protections are generally unacceptable.Taking the 500 kV busbar protection of an actual 500 kV substation of Chongqing Power Grid as an exemplary case,this paper elaborates two different technological upgrade schemes of the dif-ferential protection.One is the upgrade with electric supply interruption,in which circuit breakers on all sides of bus I or II are switched off simultaneously,resulting in stoppage from operation of both two protection device sets to undergo up-grade process.The other is the upgrade without supply interruption implemented by changing grid operation mode and power flow distribution,and by alternately switching off different side circuit breakers,so as to enable one-by-one stop-page and upgrade between the two protection device sets.The paper also compares advantages and disadvantages as well as applicability of each technological upgrade scheme.
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