The protection system of substation includes line

bus and transformer protection businesses and so on. Most of the existing evaluation methods carries on a certain single business and adopt multidimensional evaluation to characterize the reliability of the system

thus they could not consider the device crossing different businesses and lacks integrity. In recognizing the above problem

this paper proposes the overall reliability evaluation method for substation protection system based on the defined business basis that can cover different business. The details are as follows: first

the idea of the business basis is introduced

and 7 typical business bases of protection system are defined; Secondly

the relation between the business basis and the actual protection business is presented; Thirdly

the calculation method of the availability of business basis and the method of determining the weight of business basis combined with subjective and objective weighting is given; Then

based on the idea of system reliability expressed with defined business basis

the reliability of the overall protection system can be obtained by comprehensive weighting of the availability of business basis; Finally

the 110kV substation and 220kV substation with structure mode

are taken as examples to evaluate the reliability of their protection system.