Probability Of Relay Protection Failure And Its Impact On Operational Reliability Of Power Transmission System

Failure probability model of relay protection is an important aspect of the reliability evaluation for power transmission system operation, so correlative basic theories and application technologies are leading topics which is worthy of being deeply studied.Firstly, the framework and principle of software and hardware in microprocessor relay protection system are analyzed, and two types of failure mechanism are expatiated. Considering the close relationship between relay protection principles, real-time condition of power grids and second-type failure conditional probability, the algorithm is systematical researched. Secondly, in view of the impact of relay protection, the algorithm of real-time outage probability of primary components is put forward. Then the effect of outages is estimated based on electric connectivity analysis and optimal load curtailment, after that cascading failure possibility through calculating trip probability of backup protection is evaluated. Finally, a set of operational reliability indices of relay protection are proposed. At the same time, a framework of online reliability supervision and evaluation system of power transmission system is designed.The main contents in detail are included in the following:(1)The so-called first-type failure results from hardware of relay protection system, and that relay protection scheme is not compatible with real-time condition of power grids results in the so-called second-type failure. Based on these definitions, an equivalent reliability model of multiple relay protection system is proposed in view of two different failure mechanisms. The probabilities of first-type failure operation and false operation are gotten through a statistic method. At the same time, the second-type ones is worked out according to relay protection scheme and condition of power grids while the percentage of various short-circuit faults is considered. The characteristic of hidden relay protection failures is definitely showed through these conditional probabilities. So the problem is resolved that in the past relational research relay protection is considered as equivalent component of power system, and its failure probability has to be guesstimated according to the statistic, and power transmission system operational reliability evaluation has got the support of theory and algorithm.(2)Differential protection, direction protection, distance protection, zero-sequence current protection and phase current protection are usually used in power transmission system. Based on the principle and scheme of various relay protection, the probabilities of first-type failure operation and false operation during real-time short circuit in power grids are work out: 1. The formulae of inaction probability distribution are deduced based on the circle performance characters of various impedance relays. 2. According to the real-time sensitivity and coverage of zero-sequence current protection or phase current protection, the models of second-type failure probability distribution are set up. 3. Based on the tripping curve and required minimal sensitivity of transformer differential protection, the formulae of the inaction probability distribution are deduced, the algorithm of the second-type failure probability according to the real-time span of differentia quantity and restraint quantity is expatiated. 4. Both of the block signal startup-mode and coverage of direction protection affect the second-type failure probability.(3)The operational reliability models of transmission line and transformer are put forward considering the impact of weather, power flow and relay protection,and the real-time probability of the single and correlated outage occurrences can be worked out. Thereafter, considering substation structure in power grids model, an efficient method of founding predictive contingency set is studied through combining device state analysis and power transmission system topology. Electrical connectivity analysis and optimal load curtailment algorithm are used to reveal how the occurrences in the set affect power system, and forecast the possibility of cascading failure. In addition a new set of reliability indices are proposed to describe the scale of cascading failure.(4) The main framework of online reliability supervision and evaluation system of power transmission system is designed, which includes protection device message management server and work station in dispatching center, primary system message management server, operational reliability analysis sub-system, visual message displaying sub-system. The functions of these parts and methods of getting messages from integrated autoimmunization system of substation and SCADA systems are discussed. Lastly an application is clarified using IEEE RBTS of six nodes to show the approach of calculating the probability of relay protection failure, primary component outage and cascading failure. As a result, partial data of operational reliability indices considering the effect of relay protection are shown.