CN104217120A - Method for evaluating reliability of digital transformer substation relay protection system - Google Patents

Abstract

The invention provides a method for evaluating the reliability of a digital transformer substation relay protection system. According to the method, a model for analyzing the reliability of the digital transformer substation relay protection system is built by using information stream of a protection function as a study object and using the pattern modeling and reliability diagram analysis principle as the basis according to the composition and the characteristics of digital relay protection, and in addition, the example calculation is used as a concrete implementation mode. According to the reliability analysis method provided by the invention, the analysis and the calculation are carried out by using the known element reliability of elements for forming the relay protection system as the basis, the result can be used for evaluating the reliability of systems adopting different structures, so a more proper system composition mode is selected out, and the method can be used for early-stage planning of a digital transformer substation. A reliability modeling and calculation method provided by the method disclosed by the invention is more visual, the thinking is clear, and a reliability calculation model can be directly abstracted out directly through topological graphs of the digital transformer substation.

Description

A kind of method assessing digital substation relay protection system reliability

Technical field

The present invention relates to the appraisal procedure of digital substation relay protection system reliability, belong to substation relay protection systems technology field.

Background technology

In the eighties in 20th century, fail-safe analysis starts to be applied among electric system, is expanded to the various aspects of electric system by initial planning fail-safe analysis gradually.In relay protection system; the indexs such as initial conventional performance factor, mean time between failures (MTBF), mean lifetime (MTTF) are used as the evaluation index of reliability; but these indexs can only carry out an evaluation roughly by data in the past to system reliability; and the unpredictable reliability that may have with an estimation system, instructing the application in relay protection system construction, there is certain limitation.

At present in protection reliability assessment modeling and index solve, be mainly divided into analytical method and simulation two kinds.Analytical method mainly utilizes the logical relation between the structure of system self and each element of internal system, set up the computation model of reliability, the processes such as interative computation are carried out again by substituting into numerical value, finally calculate the reliability index of system, the mainly Markov model method, Fault Tree etc. that extensively adopt in reliability assessment, also have more novel successful flow method (Goal Oriented, GO) in addition, all belong to the category of Analytic Method reliability.And to simulate rule be utilize statistical method, by selecting and estimated state, comprising Monte Carlo simulation approach and non-exponential distribution etc. probability distribution sampling.Analytical method and simulation have respective relative merits respectively, the physical concept of analytical method is comparatively speaking more clear, the precision of model is higher, but calculated amount is bigger than normal, especially for the system of complexity, it calculates duration and exponentially can rise along with the complexity of system, the method of calculation with imitation method reliability is comparatively directly perceived, but because it is relevant to statistical property, result of calculation accuracy is poor, and computing time and precision are closely related.

Digital transformer substation, by being incorporated in the automation control system of transformer station by emerge sciences such as the network communications technology, microelectric technique, photoelectric technologies, makes the information transmission in transformer station more trend towards digitizing and networking.Along with the development of the new technology such as unconventional mutual inductor and intelligent breaker and the proposition of IEC61850 standard, digital transformer substation forms primary equipment intellectuality gradually, the structure system of secondary device networking, in electric substation automation system, information was difficult to share in the past, do not possess interoperability between equipment, the weak points such as system ductile difference will be overcome.

As the first line of defence ensureing electric power netting safe running; relay protection system is that electric system normally runs indispensable ingredient; whether its correct operation will produce directly impact to power equipment safety and power supply reliability; just because of the special status residing for it; relay protection system is generally required to have the very high degree of reliability, being reliably failure to actuate when action message when comprising fault and non-faulting.Reliability assessment is accurately carried out to relay protection system, can find that weak link wherein is also overcome and corrects, significant to the improvement of relay protection system.

Construction criteria, structure, element characteristic and communication mode that digital transformer substation is exclusive, make its relay protection system be faced with diverse present situation, mainly contain: (1) element is numerous.The element do not had in traditional transformer stations such as such as merge cells, intelligent terminal and switch has appeared in digitized relay protection system, brings easily simultaneously, also create certain impact to its unfailing performance to defencive function.(2) complex structure.In the past point-to-point transmission mode replace by Ethernet; the network be made up of switch changes in the past single topological structure; make it to become more complicated, thus the mode of connection of switch determines the reliability of whole relay protection system truck to a great extent.(3) Network Transmitting of information.Digital transformer substation, with the network communication mode communication of message formula, always can have insecure factor, likely the phenomenon such as packet loss or network storm can occur, and this is do not allow to occur in relay protection system.Therefore such as VLAN subregion isolation technology, priority query's technology, RSTP, IGMPSnooping multicast filtering technology etc. will be applied among digital transformer substation, to guarantee the reliability of Internet Transmission.

Information when having synchronous pair in digital substation relay protection system, with the sample information of SV message form transmission, with the breaker control of GOOSE message form transmission and status information three kinds of information flows; the connectivity pair of three kinds of information flows is most important in the reliability of relay protection system; in addition; some defencive functions can need to coordinate with other protected locations, so sometimes also can there is the exchange of GOOSE message between protected location.

The present invention utilizes the analysis principle of reliability block diagram, and in conjunction with the feature of digital substation relay protection system information flows, type is touched in the analysis setting up reliability, proposes a kind of reliability estimation method for digital substation relay protection system.The analytical approach of reliability block diagram utilizes the logical relation between internal system element, shows with the form of node and line, and final block diagram carries out mathematical analysis thus draws the method for system reliability.This analytical approach is structurally very clear, clearly can know the relation between system and its internal constitutional elements, clear logic, and computation process is simple, and computing velocity is fast.In reliability block diagram, have node and line two kinds of structures, it is all abstract from the physical arrangement of reality, represents wherein each element.Each element has self reliability values, is called element fiduciary level, sometimes in order to convenience of calculation, can not considers the reliability values of line.Each reliability block diagram represents the realization of one or more functions, its possibility that can be successfully completed, namely the reliability of this function is both relevant with element fiduciary level, also relevant with the structural relation between element, the analytical approach of reliability block diagram considers this 2 point exactly, utilize the computing method of mathematics, obtain final result.

For the system that is made up of some elements, if arbitrary element fault or lost efficacy will cause the system failure, the structure of this system is just called as cascaded structure, and the relation in this system between element is exactly series relationship, as shown in Figure 1.

For the system that is composed in series by m element, its reliability expression is:

$R_{\mathrm{sys}}=\underset{i=1}{\overset{m}{\mathrm{\Π}}}{R}_i---\left(1\right)$

R in formula _sysfor the reliability value of whole cascade system, m is the total number of cascade system element, R _i(i=1,2 ..., m) be the reliability value of i-th element.

For the system that is made up of some elements, if arbitrary element normally works can ensure that system is in normal operating conditions, the structure of this system is just called as parallel-connection structure, and the relation in this system between element is exactly parallel relationship, as shown in Figure 2.

For the system that is made up of m element in parallel, its reliability expression is:

$R_{\mathrm{sys}}=1-\underset{i=1}{\overset{m}{\mathrm{\Π}}}(1-R_i)---\left(2\right)$

It is pointed out that if there is same element A in two paths, so when these two path reliability are multiplied, component reliability RA must merge into one, i.e. R _ar _a=R _a.

Summary of the invention

The object of the invention is; a kind of appraisal procedure to digital substation relay protection system reliability is provided; the convenient and swift model setting up the relay protection system of digital transformer substation of technician can be helped; calculate the reliability of whole system, as evaluation system the need of the basis improved further.

For reaching this object, the present invention by the following technical solutions.

A kind of appraisal procedure to digital substation relay protection system reliability of the present invention, described method is equivalent to the structure of a singly-terminal pair formula the information flow system of whole intelligent substation, system will complete its function, the necessary loop that its element connects into must be communicated with, and now the probability of circuit communication just can as the reliability values of this system; Described method utilizes Mini-routing to solve singly-terminal pair reliability;

The Diagram Model in system chart model, SV message information loop, isolating switch loop GOOSE message information circuits Diagram Model and auxiliary protection element loop GOOSE message information circuits Diagram Model when described method utilizes Diagram Model to set up synchronous pair of digital transformer substation, thus obtain corresponding information circuits;

Described method, on the basis of described information circuits and element, solves the global reliability of digital substation relay protection system.

The inventive method comprises following content:

(1) information flow system of whole intelligent substation is equivalent to the structure of a singly-terminal pair formula, system will complete its function, the necessary loop that its element connects into must be communicated with, and now the probability of circuit communication just can as the reliability values of this system.

Recycling Mini-routing solves singly-terminal pair reliability.The set of minimal path sets and all minimal paths.Path refers to a set that top node and terminal node can be made to keep line and the node be communicated with.Wherein remove any line segment or a node, the path that top is just no longer communicated with terminal is called as minimal path.

When utilizing minimal path sets algorithm to ask for the reliability of network, first to find minimal path L all between this grid first and last node _i(i=1,2,3 ..., n), wherein n is minimal path quantity.Each element of every paths is exactly cascaded structure, by formula (1) its reliability expression known such as formula (3).

$P\left(L_i\right)=\underset{j=1}{\overset{m}{\mathrm{\Π}}}{R}_j---\left(3\right)$

P (L in formula _i) be minimal path L _ithe probability be communicated with, namely path L _ireliability values, R _j(j=1,2,3 ... m) for forming minimal path L _ithe reliability of a jth element.

For system, as long as there is a minimal path conducting, system is normal work just, can think relation in parallel, then can show that the expression formula of system reliability is such as formula shown in (4) by formula (2) between therefore all minimal paths.

$R_{\mathrm{sys}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_i\right))---\left(4\right)$

(2) system chart model when setting up synchronous pair of digital transformer substation.When synchronous pair, the starting point of information circuits is synchronous clock source, and intelligent electronic device when terminal is each synchronous pair of needs, mainly comprises merge cells, protected location and intelligent terminal etc.When during existing digital transformer substation pair, mode mainly contains pulse pair, coding pair time and network pair time three kinds, wherein process layer the most frequently used be coding pair time in IRIG-B code pair time and network pair time in IEEE 1588 couples time.When pair time mode different time, its topological structure also can change to some extent.

During pulse pair and coding pair time need special setting network, be directly connected with equipment when to need pair by transmission medium by synchronous clock source, be generally hub-and-spoke configuration or classification hub-and-spoke configuration, Figure 3 shows that hub-and-spoke configuration.

During network pair need by switch during network enabled pair and consisting of Ethernet, its Topological General is tree-like path, pair time information set out by synchronous clock source and arrive equipment when to need pair through network that switch forms, redundance is higher, as shown in Figure 4.

(3) Diagram Model in digital transformer substation SV message information loop is set up.The information circuits of SV message originates in mutual inductor; after merge cells and switch network; final arrival protected location; its reliability model figure as shown in Figure 5; wherein switch network is represented by dashed line, is that some stipulations only supports point-to-point transmission because sampled value transmission can adopt different stipulations; do not need switch net, corresponding model need be set up according to actual conditions.

(4) digital transformer substation isolating switch loop GOOSE message information circuits Diagram Model is set up.In relay protection system; GOOSE message is generally as jumping the carrier closing the information such as noisy signal, position of the switch information and block signal; transmit between protected location and intelligent terminal, and finally reach the object controlling isolating switch, the information circuits of GOOSE message as shown in Figure 6.Identical with SV message, GOOSE can adopt point-to-point mode to connect, and also can adopt the mode of networking.

(5) digital transformer substation auxiliary protection element loop GOOSE message information circuits Diagram Model is set up.Some defencive function needs to protect coordinating of element with other, and accept the information such as lock-reclosing lock, start failure protection that other protection elements are sent, it is auxiliary protection unit that the present invention defines this part protected location.Between main protection unit and auxiliary protection unit, the unimpeded of truck is also absolutely necessary, and auxiliary protection element loop GOOSE message information circuits, is transmitted between main protection unit and auxiliary protection unit by switch network; Information circuits structured flowchart as shown in Figure 7.

(6) global reliability of digital substation relay protection system is solved.Regard transmission medium as internodal line; and node regarded as by other elements; so digital relay protection system just can be regarded as a network system be communicated with, and the reliability in the various information loop described in (2) ~ (5) just can use Mini-routing to calculate singly-terminal pair connected ratio.

Pair time loop component reliability comparatively special; primary position calculation should be placed on; because elements such as merge cells, protected location and intelligent terminals when to need pair; when to only have pair, loop keeps being communicated with; just likely correctly work; so pair time loop reliability should add the reliability of equipment itself, form revised component reliability expression formula, as follows.

$\left.\begin{array}{c}{R^{\′}}_{\mathrm{MU}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_{\mathrm{TS}-\mathrm{MU}.i}\right))\\ {R^{\′}}_{\mathrm{PR}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_{\mathrm{TS}-\mathrm{PR},i}\right))\\ {R^{\′}}_{\mathrm{IT}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_{\mathrm{IT}-\mathrm{MU},i}\right))\end{array}\right\}---\left(5\right)$

In formula: R' _mU, R' _pRand R' _iTrepresent the reliability of revised merge cells, protected location and intelligent terminal respectively; L _{tS-MU, i}, L _{tS-PR, i}and L _{tS-IT, i}represent that synchronous clock source divides i-th minimal path being clipped to merge cells, protected location and intelligent terminal respectively, n represents the quantity of minimal path.

A SV information circuits is there is between each mutual inductor to main protection unit; a GOOSE information circuits is there is between each isolating switch to main protection unit; use Mini-routing, the reliability of SV information circuits, GOOSE information circuits can solve by formula (6).

$\left.\begin{array}{c}{R}_{\mathrm{SV},j}=1-\underset{i=1}{\overset{n}{\mathrm{\Σ}}}(1-P\left(L_{\mathrm{MI}-\mathrm{PR},i}\right))\\ R_{\mathrm{GOOSE},j}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_{\mathrm{PR}-\mathrm{BR},i}\right))\end{array}\right\}---\left(6\right)$

Wherein, R _{sV, j}represent the reliability of the SV information circuits corresponding to a jth mutual inductor, R _{gOOSE, j}represent the reliability of the GOOSE information circuits corresponding to a jth isolating switch, L _{mI-PR, i}and L _{pR-BR, i}represent the i-th paths of jth bar SV information circuits and jth bar GOOSE information circuits respectively.

SV information reliability and GOOSE information reliability are then that series relationship or parallel relationship calculate according to each paths; if a protected location need gather multiple mutual inductor information; or control multiple stage isolating switch; then the reliability of every bar information is series relationship, and SV information reliability and GOOSE information reliability solve by formula (7).

$\left.\begin{array}{c}{R}_{\mathrm{SV}}=\underset{j=1}{\overset{n}{\mathrm{\Σ}}}{R}_{\mathrm{SV},j}\\ R_{\mathrm{GOOSE}}=\underset{j=1}{\overset{n}{\mathrm{\Π}}}{R}_{\mathrm{GOOSE},j}\end{array}\right\}---\left(7\right)$

For a set of protection, it needs the normal work simultaneously of SV information and GOOSE information, and be therefore series relationship between the two, its Calculation of Reliability expression formula is such as formula shown in (8).

R _SYS,i＝R _SV·R _GOOSE (8)

In formula, R _{sYS, i}represent the reliability of the list cover relay protection that i-th protected location is corresponding.

Finally calculate the global reliability expression formula of system according to single cover reliability of relay protection expression formula, shown in (9).

$R_{\mathrm{SYS}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-R_{\mathrm{SYS},i})---\left(9\right)$

The invention has the beneficial effects as follows, modeling and the comparison for calculation methods of this reliability are directly perceived, clear thinking, the computation model of reliability directly directly can be taken out by the topological diagram of digital transformer substation, and Unified Model is higher, similar Fault Tree is there will not be to cause the difference on model because different people's ideas is different.

Accompanying drawing explanation

Fig. 1 is cascaded structure block diagram; Fig. 2 is parallel-connection structure block diagram;

When Fig. 3 is pulse pair and coding pair time pair time loop structure figure;

When Fig. 4 is network pair pair time loop structure figure;

Fig. 5 is SV message information loop structure figure;

Fig. 6 is isolating switch loop GOOSE message information circuits structural drawing;

Fig. 7 is auxiliary protection unit GOOSE message information circuits block diagram;

Fig. 8 is embodiment digital substation relay protection system chart.

Embodiment

Technical scheme of the present invention is further illustrated below in conjunction with accompanying drawing and by the embodiment of example.

Certain 220kV digital substation relay protection system architecture diagram as shown in Figure 8.Form during this system employing IRIG-B code pair, setting network is hub-and-spoke configuration, and MI1 is current transformer, and MI2 is voltage transformer (VT); TS is synchronous clock source, and MU1, MU2 are merge cells, and SW1-4 is switch; PR1, PR2 are protected location, and IT1, IT2 are intelligent terminal, and BR is isolating switch.The equal duplicate system retrofit of merge cells, protected location and intelligent terminal, SV sampled value transmission protocol is IEC61850-9-2, and switch network adopts the form of independent two net, and GOOSE loop adopts direct-connected form.The numbering of what the digital 1-24 in Fig. 8 represented the is various communication lines of signal transmission.

First, the correction of the reliability in loop when to carry out pair element, as shown in table 1, wherein TM is transmission medium.

Need compensating element	Pair time loop path	Pair time loop reliability expression	Element expression formula after revising
				MU1	TS-TM3-MU1	R TSR TM3R MU1	MU1’
PR1	TS-TM2-PR1	R TSR TM2R PR1	PR1’
				IT1	TS-TM1-IT1	R TSR TM1R IT1	IT1’
MU2	TS-TM4-MU2	R TSR TM4R MU2	MU2’
				PR2	TS-TM5-PR2	R TSR TM5R PR2	PR2’
IT2	TS-TM6-IT2	R TSR TM6R IT2	IT2’

Owing to there is the protected location of two redundant configuration, so first calculate the list cover reliability of relay protection expression formula of protection one.For protection one, it has two SV information circuits, and there are two minimal paths in every bar loop, is respectively:

SV1：L1：MI1-TM7-MU1'-TM11-SW1-TM15-PR1'

L2：MI1-TM7-MU1'-TM12-SW2-TM16-PR1'

SV1：L1：MI2-TM9-MU1'-TM11-SW1-TM15-PR1'

L2：MI2-TM9-MU1'-TM12-SW2-TM16-PR1'

Owing to being series relationship between SV1 and SV2, can obtain according to formula (7):

R _SV＝R _SV1·R _SV2

Also have a GOOSE loop in addition, comprise two minimal paths as follows.

GOOSE：L1：PR1'-TM19-IT1'-TM23-BR

L2：PR1'-TM20-IT2'-TM24-BR

The list of one can be protected to overlap reliability of relay protection expression formula according to formula (8) to be:

R _SYS,1＝R _SV·R _GOOSE

For protection two, similar with above-mentioned protection one reliability calculation method, the reliability of two finally can be protected to be R _{sYS, 2}, the reliability obtaining whole protection system according to formula (9) is:

R _SYS＝1-(1-R _SYS,1)·(1-R _SYS,2)

Suppose that same type element is reliably identical, and respectively as value below, R _tS=0.9990, R _sW=0.9700, R _mI=0.9999, R _pR=0.9990, R _mu=0.9960, R _it=0.9990, R _tM=0.9999, R _bR=0.9900, above formula expands into:

$\begin{array}{c}{R}_{\mathrm{SYS}}=R_{\mathrm{TS}}{R}_{\mathrm{MI}}^2{R}_{\mathrm{TM}}^3{R}_{\mathrm{MU}}\·(1-{(1-R_{\mathrm{SW}}{R}_{\mathrm{TM}}^2)}^2)\·R_{\mathrm{TM}}{R}_{\mathrm{PR}}\·(1-{(1-R_{\mathrm{IT}}{R}_{\mathrm{TM}}^3)}^2)\·R_{\mathrm{BR}}\\ +R_{\mathrm{TS}}{R}_{\mathrm{MI}}^2{R}_{\mathrm{TM}}^3{R}_{\mathrm{MU}}\·(1-{(1-R_{\mathrm{SW}}{R}_{\mathrm{TM}}^2)}^2)\·R_{\mathrm{TM}}{R}_{\mathrm{PR}}\·(1-{(1-R_{\mathrm{TI}}{R}_{\mathrm{TM}}^3)}^2)\·R_{\mathrm{BR}}\end{array}$

$\begin{array}{c}-R_{\mathrm{TS}}{R}_{\mathrm{MI}}^2{R}_{\mathrm{TM}}^6{R}_{\mathrm{MU}}^2\·\left({1-(1-R_{\mathrm{SW}}{R}_{\mathrm{TM}}^2)}^2\right)\·R_{\mathrm{TM}}^2{R}_{\mathrm{TM}}^2{R}_{\mathrm{BR}}\·(R_{\mathrm{TM}}^4{R}_{\mathrm{IT}}+R_{\mathrm{TM}}^6{R}_{\mathrm{IT}}^2\\ -R_{\mathrm{TM}}^7{R}_{\mathrm{ITI}}^2+R_{\mathrm{TM}}^6{R}_{\mathrm{IT}}^2+R_{\mathrm{TM}}^4{R}_{\mathrm{IT}}-R_{\mathrm{TM}}^7{R}_{\mathrm{IT}}^2-R_{\mathrm{TM}}^7{R}_{\mathrm{IT}}^2-R_{\mathrm{TM}}^7{R}_{\mathrm{IT}}^2{R}_{\mathrm{IT}}^2+R_{\mathrm{TM}}^8{R}_{\mathrm{IT}}^2)\end{array}$

Each component reliability value is substituted into above formula, and the reliability that just can calculate this relay protection system is 0.9888.

Claims (4)

1. assess a method for digital substation relay protection system reliability, it is characterized in that, comprise,

Described method is equivalent to the structure of a singly-terminal pair formula the information flow system of whole intelligent substation, system will complete its function, the necessary loop that its element connects into must be communicated with, and now the probability of circuit communication just can as the reliability values of this system; Described method utilizes Mini-routing to solve singly-terminal pair reliability;

The Diagram Model in system chart model, SV message information loop, isolating switch loop GOOSE message information circuits Diagram Model and auxiliary protection element loop GOOSE message information circuits Diagram Model when described method utilizes Diagram Model to set up synchronous pair of digital transformer substation, thus obtain corresponding information circuits;

Described method, on the basis of described information circuits and element, solves the global reliability of digital substation relay protection system.

2. the method for assessment digital substation relay protection system reliability according to claim 1, it is characterized in that, when described method solves the global reliability of digital substation relay protection system, regard transmission medium as internodal line, and node regarded as by other elements, digital relay protection system just can be regarded as a network system be communicated with, system chart model when described synchronous pair, SV message information loop, the reliability in the various information loop of isolating switch loop GOOSE message information circuits and auxiliary protection element loop GOOSE message information circuits uses Mini-routing to calculate singly-terminal pair connected ratio.

3. power distribution station according to claim 1 low voltage method of discrimination, is characterized in that, described in solve whole relay protection system reliability and undertaken by step below:

Pair (1) time, the component reliability in loop is comparatively special, should be placed on primary position calculation, pair time loop reliability should add the reliability of equipment itself, form revised component reliability expression formula, as follows:

$\left.\begin{array}{c}{R^{\′}}_{\mathrm{MU}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_{\mathrm{TS}-\mathrm{MU}.i}\right))\\ {R^{\′}}_{\mathrm{PR}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_{\mathrm{TS}-\mathrm{PR},i}\right))\\ {R^{\′}}_{\mathrm{IT}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_{\mathrm{IT}-\mathrm{MU},i}\right))\end{array}\right\}$

In formula: R' _mU, R' _pRand R' _iTrepresent the reliability of revised merge cells, protected location and intelligent terminal respectively; L _{tS-MU, i}, L _{tS-PR, i}and L _{tS-IT, i}represent that synchronous clock source divides i-th minimal path being clipped to merge cells, protected location and intelligent terminal respectively, n represents the quantity of minimal path; P (L _{tS-PR, i}), P (L _{tS-PR, i}) and P (L _{tS-IT, i}) represent L respectively _{tS-MU, i}, L _{tS-PR, i}and L _{tS-IT, i}reliability;

There is a SV information circuits between each mutual inductor to main protection unit, there is a GOOSE information circuits between each isolating switch to main protection unit, use Mini-routing, the reliability of SV information circuits, GOOSE information circuits can solve by following formula;

$\left.\begin{array}{c}{R}_{\mathrm{SV},j}=1-\underset{i=1}{\overset{n}{\mathrm{\Σ}}}(1-P\left(L_{\mathrm{MI}-\mathrm{PR},i}\right))\\ R_{\mathrm{GOOSE},j}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-P\left(L_{\mathrm{PR}-\mathrm{BR},i}\right))\end{array}\right\}$

Wherein, R _{sV, j}represent the reliability of the SV information circuits corresponding to a jth mutual inductor, R _{gOOSE, j}represent the reliability of the GOOSE information circuits corresponding to a jth isolating switch, L _{mI-PR, i}and L _{pR-BR, i}represent the i-th paths of jth bar SV information circuits and jth bar GOOSE information circuits respectively;

(2) SV information reliability and GOOSE information reliability are then that series relationship or parallel relationship calculate according to each paths; if a protected location need gather multiple mutual inductor information; or control multiple stage isolating switch; then the reliability of every bar information is series relationship, and SV information reliability and GOOSE information reliability solve by following formula:

$\left.\begin{array}{c}{R}_{\mathrm{SV}}=\underset{j=1}{\overset{n}{\mathrm{\Σ}}}{R}_{\mathrm{SV},j}\\ R_{\mathrm{GOOSE}}=\underset{j=1}{\overset{n}{\mathrm{\Π}}}{R}_{\mathrm{GOOSE},j}\end{array}\right\}$

For a set of protection, it needs the normal work simultaneously of SV information and GOOSE information, and be therefore series relationship between the two, its Calculation of Reliability expression formula is shown below:

R _SYS,i＝R _SV·R _GOOSE

In formula, R _{sYS, i}represent the reliability of the list cover relay protection that i-th protected location is corresponding;

(3) calculate the global reliability expression formula of system according to single cover reliability of relay protection expression formula, be shown below:

$R_{\mathrm{SYS}}=1-\underset{i=1}{\overset{n}{\mathrm{\Π}}}(1-R_{\mathrm{SYS},i}).$

4. a kind of method assessing digital substation relay protection system reliability according to claim 1, it is characterized in that, when described synchronous pair in system chart model, when synchronous pair, the starting point of information circuits is synchronous clock source, intelligent electronic device when terminal is each synchronous pair of needs, comprises merge cells, protected location and intelligent terminal; In the Diagram Model in described SV message information loop, the information circuits of SV message originates in mutual inductor, after merge cells and switch network, finally arrives protected location; In the GOOSE message information circuits Diagram Model of described isolating switch loop, GOOSE message information circuits, GOOSE message closes the carrier of noisy signal, position of the switch information and block signal information as jumping, transmitted between protected location and intelligent terminal by switch network, and finally reach control isolating switch; GOOSE message information circuits Diagram Model, auxiliary protection element loop GOOSE message information circuits, is transmitted between main protection unit and auxiliary protection unit by switch network.