CN111062557A - A method for evaluating the total frequency of power failures at load points - Google Patents

Abstract

The invention discloses a total frequency evaluation method for power failure faults of a load point. The result obtained by calculation is high in accuracy.

Description

A method for evaluating the total frequency of power failures at load points

technical field

The invention relates to the technical field of power grids, in particular to a method for evaluating the total frequency of power failure at a load point.

Background technique

With the development of society, power users pay more attention to the reliability of power supply of the power system. Relevant statistics show that about 80%-95% of the unavailability of power supply at the load point is caused by the failure of the power distribution system. Therefore, the assessment of the total frequency of outage faults at the load point of the distribution system is an important task for the planning and operation of the power sector.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies of the prior art, and to provide a method for evaluating the total frequency of power failure at a load point with high accuracy.

For achieving the above object, the technical scheme provided by the present invention is:

A method for evaluating the total frequency of power outage faults at a load point, comprising the following steps:

S1. Obtain the fault data caused by the three-section and three-connection urban distribution network power supply system, distribution lines, load busbar grounding, short circuit, and lightning strike factors when both the working system and the backup system power supply are connected by double busbars from the relevant database in the assessed area;

S2. Calculate the failure rates λ _SAm1a , λ _SAm1b , λ _SCm1a , λ SCm1b of the power systems Am1a, Am1b, Cm1a, _Cm1b ; the first working system and the second working system distribution line failure rate λ _SALi , i=1,2, 3, NA is the number of distribution lines in the working system _A , NA ₌ 3; the distribution line failure rate λ _SCLi of the first backup system and the second backup system, i=1, 2, 3, NC is the power supply of the system _C Number of distribution lines from system Cm1 to tie switch 2 N _C =2; tie power line failure rate λ _SL2 ; working system A load bus failure rate λ _SAi , i=1, 2, 3, the first standby system and the second standby system System load bus failure rate λ _SCi , i=1,2,3;

S3. Obtain the maintenance data caused by grounding, short-circuit, and lightning strike factors such as the power supply system, distribution line, load bus, etc. of the three-section and three-contact urban power distribution network when the power supply of the working system and the contact system adopts double-bus connection from the relevant database;

S4. Calculate the maintenance rates μ _SAm1a , μ _SAm1b , μ _SCm1a , μ _{SCm1b of the power systems Am1a, Am1b, Cm1a, Cm1b} ; the distribution line maintenance rates μ _SALi of the first working system and the second working system, i=1, 2,3; distribution line maintenance rate μ _SCLi of the first standby system and the second standby system, i=1,2,3; tie line maintenance rate μ _SL1 ; load bus maintenance rate of the first working system and the second working system μ _SAi , i=1,2,3; load bus maintenance rate μ _SCi of the first backup system and the second backup system, i=1,2,3;

内只发生单一或m元件重复故障的概率；S5. According to the connection relationship between the first working system and the power supply of the large system, as well as the fault rate and maintenance rate characteristics of the distribution line and the load bus, for the relative relationship between the second load bus of different negative system A and the power bus Am1a, consider Seven components of large system power supply Am1a, Am1b, load side power supply busbar Am1, distribution lines AL1, AL2 and load busbars A1 and A2 on system A, as well as large system power supply Cm1a, Cm1b, load side power supply busbar Cm1, distribution line on system C Eight elements of electrical lines CL1, CL2, load bus bars C1, C2 and tie line L2, calculation time

The probability that only a single or m element repeats failure occurs within;

S6. Construct the five-state space for the reliability assessment of the power supply of the second load bus LA2 of the urban distribution network system A with three sections and three connections when the power supplies are connected by double bus bars;

S7. Calculate the unavailability rate U of power failure of the first load bus of the three-section three-connection urban distribution network system A when the system power supply adopts double-bus connection, that is, P _C5 ;

S8. Calculate the total maintenance rate of the second load bus A2 of the working system A and the total frequency of power failures.

内只发生单一或m元件重复故障的概率的具体过程如下：Further, the calculation time in the step S5

The specific process of the probability of repeated failure of only a single or m element occurs as follows:

S5.1. The power bus Am1a of the large system fails, and at the same time, the corresponding standby circuit breaker is closed to transfer the load to the power system bus Am1b, and the first working system is transferred to the second working system, that is, the system is transferred from state 1 to state 2; its The transition probability is:

p ₁₂ =λ _SAm1a ;

内由故障状态维修到正常工作状态，同时由相应备用断路器闭合将负荷恢复由电源系统母线Am1a供电，第二工作系统转移到第一工作系统，即系统由状态2转移到状态1；其转移概率为：For repairable large system power bus Am1a, at research time

It is repaired from the fault state to the normal working state, and the corresponding standby circuit breaker is closed to restore the load to the power supply system bus Am1a, and the second working system is transferred to the first working system, that is, the system is transferred from state 2 to state 1; its transfer The probability is:

p ₂₁ = μ _SAm1a ;

S5.2. If the power bus Am1b of the large system fails, the first working system still works normally, that is, whether the power bus Am1b of the large system fails does not affect the reliability of the first working system;

S5.3. If any one of the load side power bus Am1, distribution lines AL1, AL2, and load bus A1 fails, both the first working system and the second working system fail; at the same time, the corresponding standby tie breaker is closed to transfer the load to the power system The bus Cm1a supplies power, and the first working system is directly transferred to the first standby system, that is, the system transfers from state 1 to state 3; the transition probability is:

其中，N_A＝2；

Wherein, N _A =2;

内对应元件由故障状态维修到正常工作状态，同时由相应断路器操作闭合将负荷恢复由电源系统母线Am1a供电，第一备用系统转移到第一工作系统，即系统由状态3转移到状态1；其转移概率为：For the repairable load-side power bus Am1, distribution lines AL1, AL2, and load bus A1, the time

The internal corresponding components are repaired from the fault state to the normal working state, and at the same time, the corresponding circuit breaker is operated and closed to restore the load to the power supply system bus Am1a, and the first standby system is transferred to the first working system, that is, the system is transferred from state 3 to state 1; Its transition probability is:

in,

S5.4. The load bus A2 fails, and the load on it is powered off; that is, the system transfers from state 1 to state 5; its transition probability is:

p ₁₅ =λ _SA2 ;

For the repairable load bus A2, it is repaired from the fault state to the normal working state, and at the same time, the corresponding circuit breaker is operated to restore the load to the power supply system bus Am1a, that is, the system transfers from state 5 to state 1; the transition probability is:

内它可以返回状态1，也可以过渡到状态3，即大系统电源母线Am1b、负荷侧电源母线Am1、配电线路AL1再发生任一故障，同时由相应备用联络断路器闭合将负荷转由电源系统母线Cm1a供电，第二工作系统转移到第一备用系统，即系统由状态2转移到状态3；其转移概率为：S5.5. The system is in state 2, at study time

It can return to state 1 or transition to state 3, that is, if any fault occurs on the large system power bus Am1b, the load side power bus Am1, and the distribution line AL1, the corresponding standby tie breaker is closed to transfer the load to the power source. The system bus Cm1a supplies power, and the second working system transfers to the first standby system, that is, the system transfers from state 2 to state 3; the transition probability is:

p ₂₃ =λ _SAm1b ;

For the repairable large system power bus Am1b, it is repaired from the fault state to the normal working state. At the same time, the corresponding circuit breaker operates to transfer the load from the power system bus Cm1a to the power system bus Am1b for power supply, and the first standby system is transferred to the second working system. That is, the system transitions from state 3 to state 2; its transition probability is:

内对应元件的故障修复它可以返回状态1和状态2，也可以过渡到状态4和状态5；S5.6. The system is in state 3, at study time

It can return to state 1 and state 2, and can also transition to state 4 and state 5;

When Cm1a fails, the first backup system fails, and the corresponding circuit breaker operates to transfer the load to the power system;

The system bus Cm1b supplies power, that is, the system transitions from state 3 to state 4; the transition probability is:

p ₃₄ =λ _SCm1a ;

内由故障状态维修到正常工作状态，同时由相应断路器操作将负荷由电源系统母线Cm1b转移到电源系统母线Am1a供电，第一备用系统1转移到第二工作系统，即系统由状态4转移到状态3；For the repairable large system power bus Cm1a, at the research time

It is repaired from the fault state to the normal working state, and at the same time, the corresponding circuit breaker operates to transfer the load from the power system bus Cm1b to the power system bus Am1a for power supply, and the first standby system 1 is transferred to the second working system, that is, the system is transferred from state 4 to state 3;

And the system transitions from state 4 to state 3, and its transition probability is:

p ₄₃ = μ _SCm1a ;

When any of the load-side power busbar Cm1, distribution lines CL1, CL2, load busbars C1, C2 and tie line L2 on the backup system fails, both the first backup system and the second backup system fail, and the load bus A2 is powered off; that is, the system From state 3 to state 5, the transition probability is:

其中，N_C＝2；

Wherein, N _C =2;

For the repairable load-side power bus Cm1, distribution lines CL1, CL2, load bus C1, C2 and tie line L2, the fault repair system of the corresponding component can return from state 5 to state 3; the transition probability is:

其中，N_C＝2，

where N _C =2,

N _C = 2, it is the system C distribution line from the tie breaker or tie switch to the load power busbar Cm1, and it is also the system C load bus from the tie breaker or tie switch to the load side power busbar Cm1 total;

S5.7. The system is in state 4, the fault repair system of the corresponding component Cm1a can return to state 3, or it can transition to state 5; that is, when the large system power bus Cm1b, the second backup system fails, and the load bus A1 is powered off, its transition probability for:

p ₄₅ =λ _SCm1b ;

For the corresponding repairable large system power busbar Cm1b, load side power busbar Cm1, distribution lines CL1, CL2, load busbars C1, C2 and tie line L2 fault repair, the system can return from state 5 to state 4, and its transition probability is:

S5.8. The system is in state 5, the fault repair system of the corresponding component can return to state 4, can return to state 3, and can return to state 1.

Further, the specific process of the step S6 is as follows:

The five-state space for the reliability assessment of the power supply of the second load bus LA2 of the three-segment and three-connection urban distribution network system A when the power sources are all connected by double busbars:

In the formula, p ₂₁ =μ _SAm1a , p ₁₂ =λ _SAm1a ,

p₁₅＝λ_SA2，p ₂₃ =λ _SAm1b ,

p ₁₅ =λ _SA2 ,

p ₄₃ =μ _SCm1a , p ₃₄ =λ _SCm1a ,

p ₄₅ =λ _SCm1b ,

Wherein, N _C =2, N _A =2, and the sum of the elements of each row of the matrix Pc is 1.

Further, the specific process of the step S7 is as follows:

Using [P _C1 P _C2 P _C3 P _C4 P _C5 ]·Pc=[P _C1 P _C2 P _C3 P _C4 P _C5 ] and P _C1 +P _C2 +P _C3 +P _C4 +P _C5 =1, the above equations are combined Form the new equivalent matrix form:

The steady-state probability of the system staying in the corresponding state can be obtained by solving the equation set, and the unavailability rate U of the first load bus of the three-section and three-connection urban distribution network system A when the power supply of the system is all connected by double busbars is calculated by MATLAB programming, Namely _PC5 .

Further, the details of the step S8 are:

The total maintenance rate of the second load bus A2 of system A:

μ ₂ =p ₅₁ +p ₅₃ +p ₅₄

The total frequency of power failure of the second load bus A2 of system A:

f ₂ =P _C5 ×(p ₅₁ +p ₅₃ +p ₅₄ ).

Compared with the prior art, the principle and advantages of this scheme are as follows:

This scheme first calculates the failure rate and maintenance rate of the power system and each line, and then calculates the probability of repeated failure of the components, then constructs the state space, calculates the unavailability rate of power failure of the load bus, and finally calculates the total frequency of power failures. The results calculated by this scheme have high accuracy.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the services required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only For some embodiments of the present invention, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

Figure 1 is a diagram of the expansion of the second load bus of the three-section three-connection urban distribution network system A to the connection system;

FIG. 2 is a principle flow chart of a method for evaluating the total frequency of power failure at a load point according to the present invention.

Detailed ways

Below in conjunction with specific embodiment, the present invention will be further described:

This embodiment is based on a three-section three-connect urban distribution network system. In the three-section and three-connect urban distribution network system, the second load bus tie line and the circuit breaker on the system A in the three-section and three-connect urban distribution network system are connected with the second line of system C. Load bus connection, for the second load bus on system A, system A is in working state, system C is in standby state, system A is called the working system, and system C is called the standby system. Considering that the power supply of system A and system C are connected by double busbars, system A is correspondingly divided into working system 1 and working system 2. Working system 1 is connected to the low-voltage power busbar Am1a of the substation through a circuit breaker, and is connected by the load-side power busbar Am1, It consists of sectional circuit breakers, three distribution lines and three load buses A1, A2 and A3. The working system 2 is connected to the low-voltage power busbar Am1b of the substation through the circuit breaker, and is composed of the power busbar Am1 on the load side, the sectional circuit breaker, three distribution lines and three load busbars A1, A2, and A3. System C is correspondingly divided into standby system 1 and standby system 2. Standby system 1 is connected to the substation low-voltage power busbar Cm1a, and consists of the load-side power busbar Cm1, sectional circuit breaker, tie breaker, tie line and two distribution lines CL1 , CL2 and 2 load busbars C1, C2; the backup system 2 is connected to the substation low-voltage power busbar Cm1b, and consists of the load side power busbar Cm1, segment circuit breaker, tie circuit breaker, tie line and 2 distribution lines CL1 , CL2 and 2 load busbars C1, C2. Specifically as shown in Figure 1.

As shown in FIG. 2 , the method for evaluating the total frequency of power failure at a load point described in this embodiment includes the following steps:

S1. Obtain the fault data caused by the three-section and three-connection urban distribution network power supply system, distribution lines, load busbar grounding, short circuit, and lightning strike factors when both the working system and the backup system power supply are connected by double busbars from the relevant database in the assessed area;

S2. Calculate the failure rates λ _SAm1a , λ _SAm1b , λ _SCm1a , λ SCm1b of the power systems Am1a, Am1b, Cm1a, _Cm1b ; the first working system and the second working system distribution line failure rate λ _SALi , i=1,2, 3, NA is the number of distribution lines in the working system _A , NA ₌ 3; the distribution line failure rate λ _SCLi of the first backup system and the second backup system, i=1, 2, 3, NC is the power supply of the system _C Number of distribution lines from system Cm1 to tie switch 2 N _C =2; tie power line failure rate λ _SL2 ; working system A load bus failure rate λ _SAi , i=1, 2, 3, the first standby system and the second standby system System load bus failure rate λ _SCi , i=1,2,3;

S3. Obtain the maintenance data caused by grounding, short-circuit, and lightning strike factors such as the power supply system, distribution line, load bus, etc. of the three-section and three-contact urban power distribution network when the power supply of the working system and the contact system adopts double-bus connection from the relevant database;

S4. Calculate the maintenance rates μ _SAm1a , μ _SAm1b , μ _SCm1a , μ _{SCm1b of the power systems Am1a, Am1b, Cm1a, Cm1b} ; the distribution line maintenance rates μ _SALi of the first working system and the second working system, i=1, 2,3; distribution line maintenance rate μ _SCLi of the first standby system and the second standby system, i=1,2,3; tie line maintenance rate μ _SL1 ; load bus maintenance rate of the first working system and the second working system μ _SAi , i=1,2,3; load bus maintenance rate μ _SCi of the first backup system and the second backup system, i=1,2,3;

内只发生单一或m元件重复故障的概率；具体过程如下：S5. According to the connection relationship between the first working system and the power supply of the large system, as well as the fault rate and maintenance rate characteristics of the distribution line and the load bus, for the relative relationship between the second load bus of different negative system A and the power bus Am1a, consider Seven components of large system power supply Am1a, Am1b, load side power supply busbar Am1, distribution lines AL1, AL2 and load busbars A1 and A2 on system A, as well as large system power supply Cm1a, Cm1b, load side power supply busbar Cm1, distribution line on system C Eight elements of electrical lines CL1, CL2, load bus bars C1, C2 and tie line L2, calculation time

The probability that only a single or m element repeats failure occurs within; the specific process is as follows:

S5.1. The power bus Am1a of the large system fails, and at the same time, the corresponding standby circuit breaker is closed to transfer the load to the power system bus Am1b, and the first working system is transferred to the second working system, that is, the system is transferred from state 1 to state 2; its The transition probability is:

p ₁₂ =λ _SAm1a ;

内由故障状态维修到正常工作状态，同时由相应备用断路器闭合将负荷恢复由电源系统母线Am1a供电，第二工作系统转移到第一工作系统，即系统由状态2转移到状态1；其转移概率为：For repairable large system power bus Am1a, at research time

It is repaired from the fault state to the normal working state, and the corresponding standby circuit breaker is closed to restore the load to the power supply system bus Am1a, and the second working system is transferred to the first working system, that is, the system is transferred from state 2 to state 1; its transfer The probability is:

p ₂₁ = μ _SAm1a ;

S5.2. If the power bus Am1b of the large system fails, the first working system still works normally, that is, whether the power bus Am1b of the large system fails does not affect the reliability of the first working system;

S5.3. If any one of the load side power bus Am1, distribution lines AL1, AL2, and load bus A1 fails, both the first working system and the second working system fail; at the same time, the corresponding standby tie breaker is closed to transfer the load to the power system The bus Cm1a supplies power, and the first working system is directly transferred to the first standby system, that is, the system transfers from state 1 to state 3; the transition probability is:

其中，N_A＝2；

Wherein, N _A =2;

内对应元件由故障状态维修到正常工作状态，同时由相应断路器操作闭合将负荷恢复由电源系统母线Am1a供电，第一备用系统转移到第一工作系统，即系统由状态3转移到状态1；其转移概率为：For the repairable load-side power bus Am1, distribution lines AL1, AL2, and load bus A1, the time

The internal corresponding components are repaired from the fault state to the normal working state, and at the same time, the corresponding circuit breaker is operated and closed to restore the load to the power supply system bus Am1a, and the first standby system is transferred to the first working system, that is, the system is transferred from state 3 to state 1; Its transition probability is:

in,

S5.4. The load bus A2 fails, and the load on it is powered off; that is, the system transfers from state 1 to state 5; its transition probability is:

p ₁₅ =λ _SA2 ;

For the repairable load bus A2, it is repaired from the fault state to the normal working state, and at the same time, the corresponding circuit breaker is operated to restore the load to the power supply system bus Am1a, that is, the system transfers from state 5 to state 1; the transition probability is:

内它可以返回状态1，也可以过渡到状态3，即大系统电源母线Am1b、负荷侧电源母线Am1、配电线路AL1再发生任一故障，同时由相应备用联络断路器闭合将负荷转由电源系统母线Cm1a供电，第二工作系统转移到第一备用系统，即系统由状态2转移到状态3；其转移概率为：S5.5. The system is in state 2, at study time

It can return to state 1 or transition to state 3, that is, if any fault occurs on the large system power bus Am1b, the load side power bus Am1, and the distribution line AL1, the corresponding standby tie breaker is closed to transfer the load to the power source. The system bus Cm1a supplies power, and the second working system transfers to the first standby system, that is, the system transfers from state 2 to state 3; the transition probability is:

p ₂₃ =λ _SAm1b ;

For the repairable large system power bus Am1b, it is repaired from the fault state to the normal working state. At the same time, the corresponding circuit breaker operates to transfer the load from the power system bus Cm1a to the power system bus Am1b for power supply, and the first standby system is transferred to the second working system. That is, the system transitions from state 3 to state 2; its transition probability is:

内对应元件的故障修复它可以返回状态1和状态2，也可以过渡到状态4和状态5；S5.6. The system is in state 3, at study time

It can return to state 1 and state 2, and can also transition to state 4 and state 5;

When Cm1a fails, the first backup system fails, and the corresponding circuit breaker operates to transfer the load to the power system;

The system bus Cm1b supplies power, that is, the system transitions from state 3 to state 4; the transition probability is:

p ₃₄ =λ _SCm1a ;

内由故障状态维修到正常工作状态，同时由相应断路器操作将负荷由电源系统母线Cm1b转移到电源系统母线Am1a供电，第一备用系统1转移到第二工作系统，即系统由状态4转移到状态3；For the repairable large system power bus Cm1a, at the research time

It is repaired from the fault state to the normal working state, and at the same time, the corresponding circuit breaker operates to transfer the load from the power system bus Cm1b to the power system bus Am1a for power supply, and the first standby system 1 is transferred to the second working system, that is, the system is transferred from state 4 to state 3;

And the system transitions from state 4 to state 3, and its transition probability is:

p ₄₃ = μ _SCm1a ;

When any of the load-side power busbar Cm1, distribution lines CL1, CL2, load busbars C1, C2 and tie line L2 on the backup system fails, both the first backup system and the second backup system fail, and the load bus A2 is powered off; that is, the system From state 3 to state 5, the transition probability is:

其中，N_C＝2；

Wherein, N _C =2;

For the repairable load-side power bus Cm1, distribution lines CL1, CL2, load bus C1, C2 and tie line L2, the fault repair system of the corresponding component can return from state 5 to state 3; the transition probability is:

其中，N_C＝2，

where N _C =2,

N _C = 2, it is the system C distribution line from the tie breaker or tie switch to the load power busbar Cm1, and it is also the system C load bus from the tie breaker or tie switch to the load side power busbar Cm1 total;

S5.7. The system is in state 4, the fault repair system of the corresponding component Cm1a can return to state 3, or it can transition to state 5; that is, when the large system power bus Cm1b, the second backup system fails, and the load bus A1 is powered off, its transition probability for:

p ₄₅ =λ _SCm1b ;

For the corresponding repairable large system power busbar Cm1b, load side power busbar Cm1, distribution lines CL1, CL2, load busbars C1, C2 and tie line L2 fault repair, the system can return from state 5 to state 4, and its transition probability is:

S5.8. The system is in state 5, the fault repair system of the corresponding component can return to state 4, can return to state 3, and can return to state 1.

S6. The five-state space for the reliability assessment of the power supply reliability of the second load bus LA2 of the three-segment and three-connected urban distribution network system A when the power sources are all connected by double busbars:

In the formula, p ₂₁ =μ _SAm1a , p ₁₂ =λ _SAm1a ,

p₁₅＝λ_SA2，p ₂₃ =λ _SAm1b ,

p ₁₅ =λ _SA2 ,

p ₄₃ =μ _SCm1a , p ₃₄ =λ _SCm1a ,

p ₄₅ =λ _SCm1b ,

Wherein, N _C =2, N _A =2, and the sum of the elements of each row of the matrix Pc is 1.

S7. Using [P _C1 P _C2 P _C3 P _C4 P _C5 ]·Pc=[P _C1 P _C2 P _C3 P _C4 P _C5 ] and P _C1 + P _C2 + P _C3 + P _C4 + P _C5 =1, the above formula Simultaneously form a new equivalent matrix form:

The steady-state probability of the system staying in the corresponding state can be obtained by solving the equation set, and the unavailability rate U of the first load bus of the three-section and three-connection urban distribution network system A when the power supply of the system is all connected by double busbars is calculated by MATLAB programming, i.e. _PC5 ;

S8. Calculate the total maintenance rate of the second load bus A2 of system A:

μ ₂ =p ₅₁ +p ₅₃ +p ₅₄ ;

Calculate the total frequency of power failure of the second load bus A2 of system A:

f ₂ =P _C5 ×(p ₅₁ +p ₅₃ +p ₅₄ ).

The above-mentioned embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of implementation of the present invention. Therefore, any changes made according to the shape and principle of the present invention should be included within the protection scope of the present invention.

Claims (5)

1. A total frequency evaluation method for power failure faults of a load point is characterized by comprising the following steps:

s1, acquiring fault data caused by factors of grounding, short circuit and lightning stroke of a three-section and three-contact urban distribution network power supply system, a distribution line, a load bus when a working system and a standby system power supply adopt double-bus wiring from a related database of an evaluated area;

s2, calculating the fault rates lambda of the power supply systems Am1a, Am1b, Cm1a and Cm1b_SAm1a、λ_SAm1b、λ_SCm1a、λ_SCm1b(ii) a First operating system and second operating system distribution line fault rate lambda_SALi，i＝1,2,3，N_ANumber N of distribution lines for working system A_A3; distribution line fault rate lambda of first standby system and second standby system_SCLi，i＝1,2,3，N_CNumber N of distribution lines from power supply system Cm1 of system C to tie switch 2_C2; fault rate lambda of interconnection line_SL2(ii) a Failure rate lambda of A load bus of working system_SAiI 1,2,3, first and second backup system load bus failure rate λ_SCi，i＝1,2,3；

S3, acquiring maintenance data caused by grounding, short circuit and lightning stroke factors of a power supply system, a distribution line, a load bus and the like of the three-section three-contact urban distribution network when the power supply of the working system and the contact system adopts double-bus wiring from the related database;

s4, calculating the maintenance rate mu of the power supply systems Am1a, Am1b, Cm1a and Cm1b_SAm1a、μ_SAm1b、μ_SCm1a、μ_SCm1b(ii) a Maintenance rate mu of distribution lines of first working system and second working system_SALiI is 1,2, 3; first standby system and second standby system distribution line maintenance rate mu_SCLiI is 1,2, 3; maintenance rate mu of interconnection line_SL1(ii) a Maintenance rate mu of load bus of first working system and second working system_SAiI is 1,2, 3; first and second backup system load bus maintenance rate mu_SCi，i＝1,2,3；

S5, according to the connection relation between the first working system and the large system power supply and the fault rate and maintenance rate characteristics of the distribution lines and the load buses, regarding the relative relation between the 2 nd load buses of different negative systems A and the power buses Am1a, seven elements of the large system power supplies Am1a, Am1b, the load side power bus Am1, the distribution lines AL1 and AL2 and the load buses A1 and A2 on the system A and eight elements of the large system power supplies Cm1a, Cm1b, the load side power supply Cm bus 1, the distribution lines CL1 and CL2, the load buses C1 and C2 and the connecting line L2 on the system C are considered, and time is calculated

Probability of occurrence of only single or m-element repeat failures within;

s6, constructing a five-state space for evaluating the power supply reliability of the 2 nd load bus LA2 of the three-section three-contact urban power distribution network system A when the power supply adopts double-bus connection;

s7, calculating the power failure unavailability rate U, namely P, of the 1 st load bus of the three-section three-contact urban power distribution network system A when the system power supply adopts double-bus wiring_C5；

And S8, calculating the total maintenance rate of the No. 2 load bus A2 of the working system A and the total frequency of power failure faults of the working system A.

2. The method as claimed in claim 1, wherein the time calculated in step S5 is the time calculated in the step S5

The specific process of probability of occurrence of only a single or m-element repeated failure is as follows:

s5.1, a power bus Am1a of the large system fails, a corresponding standby circuit breaker is closed to supply power to a load by a power bus Am1b, the first working system is transferred to the second working system, and the system is transferred from a state 1 to a state 2; the transition probability is:

p₁₂＝λ_SAm1a；

for the repairable large system power bus Am1a, the research time is

The system is maintained from a fault state to a normal working state, meanwhile, a corresponding standby circuit breaker is closed to recover the load and supply power by a power system bus Am1a, and the second working system is transferred to the first working system, namely the system is transferred from a state 2 to a state 1; the transition probability is:

p₂₁＝μ_SAm1a；

s5.2, if the large system power bus Am1b fails, the first working system still works normally, namely, whether the large system power bus Am1b fails or not does not influence the reliability of the first working system;

s5.3, when any fault occurs in the load side power bus Am1, the distribution lines AL1, AL2 and the load bus A1, both the first working system and the second working system fail; simultaneously, the corresponding standby interconnection breaker is closed to transfer the load from the power system bus Cm1a to supply power, and the first working system is directly transferred to the first standby system, namely the system is transferred from the state 1 to the state 3; the transition probability is:

wherein N is_A＝2；

Time for repairable load side power bus Am1, distribution lines AL1, AL2, and load bus A1

The internal corresponding element is maintained to be in a normal working state from a fault state, meanwhile, the corresponding circuit breaker is operated to be closed to recover the load to be supplied with power by a power system bus Am1a, and the first standby system is transferred to the first working system, namely the system is transferred to the state 1 from the state 3; the transition probability is:

wherein,

s5.4, when the load bus A2 has a fault, the load on the load bus A is powered off; namely, the system is transferred from the state 1 to the state 5; the transition probability is:

p₁₅＝λ_SA2；

for the repairable load bus A2, the normal working state is maintained from the fault state, and simultaneously the load is restored to be supplied with power by the power system bus Am1a by the corresponding breaker operation, namely the system is transferred from the state 5 to the state 1; the transition probability is:

s5.5. System in State 2, at study time

The system can return to the state 1 and also can transit to the state 3, namely, any fault occurs again on the power bus Am1b of the large system, the power bus Am1 of the load side and the distribution line AL1, meanwhile, the corresponding standby interconnection breaker is closed to transfer the load from the power bus Cm1a for power supply, and the second working system is transferred to the first standby system, namely, the system is transferred from the state 2 to the state 3; the transition probability is:

p₂₃＝λ_SAm1b；

for the repairable large system power bus Am1b, the large system power bus Am1b is repaired from the fault state to the normal working state, and simultaneously the load is transferred to the power system bus Am1b for power supply from the power system bus Cm1a by the operation of the corresponding circuit breaker, the first standby system is transferred to the second working system, namely the system is transferred from the state 3 to the state 2; the transition probability is:

s5.6. System in State 3, at study time

The failure repair of the internal corresponding element can return to the state 1 and the state 2, and can also transit to the state 4 and the state 5;

when Cm1a fails, the first backup system fails, transferring load from the power train by operation of the respective circuit breaker;

the system bus Cm1b is powered, namely the system is transferred from the state 3 to the state 4; the transition probability is:

p₃₄＝λ_SCm1a；

for the repairable large system power bus Cm1a, at study time

The system is maintained from a fault state to a normal working state, meanwhile, the corresponding circuit breaker operates to transfer the load from the power system bus Cm1b to the power system bus Am1a for supplying power, and the first standby system 1 is transferred to the second working system, namely, the system is transferred from the state 4 to the state 3;

and the system is transferred from the state 4 to the state 3, and the transfer probability is as follows:

p₄₃＝μ_SCm1a；

when any one of the load side power bus Cm1, the distribution lines CL1, CL2, the load buses C1, C2 and the connecting line L2 on the standby system fails, the first standby system and the second standby system both fail, and the load bus A2 fails; namely, the system is transferred from the state 3 to the state 5, and the transfer probability is as follows:

wherein N is_C＝2；

For the repairable load side power bus Cm1, the distribution lines CL1, CL2, the load buses C1, C2, and the tie line L2, the fault repair system corresponding to the corresponding element can return from state 5 to state 3; the transition probability is:

wherein N is_C＝2，

N_C2, the total number of system C distribution lines from the tie breaker or the tie switch to the load power bus Cm1 and the total number of system C load buses from the tie breaker or the tie switch to the load power bus Cm 1;

s5.7, the system is in a state 4, the fault repairing system corresponding to the element Cm1a can return to a state 3, and can also transit to a state 5; namely, when the power bus Cm1b of the large system and the second standby system have faults, the load bus A1 has power failure, and the transition probability is as follows:

p₄₅＝λ_SCm1b；

for the fault repair of the correspondingly repairable large system power bus Cm1b, the load side power bus Cm1, the distribution lines CL1, CL2, the load buses C1, C2 and the tie line L2, the system can return from state 5 to state 4, and the transition probability is as follows:

and S5.8, the system is in a state 5, and the fault repairing system of the corresponding element can return to a state 4, can return to a state 3 and can return to a state 1.

3. The method for evaluating the total frequency of the power failure fault of the load point as claimed in claim 1, wherein the specific process of the step S6 is as follows:

constructing five state spaces for evaluating the power supply reliability of the 2 nd load bus LA2 of the three-section three-contact urban distribution network system A when the power supply adopts double-bus connection:

in the formula, p₂₁＝μ_SAm1a，p₁₂＝λ_SAm1a，

p₂₃＝λ_SAm1b，

p₁₅＝λ_SA2，

p₄₃＝μ_SCm1a，p₃₄＝λ_SCm1a，

p₄₅＝λ_SCm1b，

Wherein N is_C＝2，N_A2 and the sum of the elements of each row of the matrix Pc is 1.

4. The method for evaluating the total frequency of the power failure fault of the load point as claimed in claim 1, wherein the specific process of the step S7 is as follows:

by using [ P ]_C1P_C2P_C3P_C4P_C5]·Pc＝[P_C1P_C2P_C3P_C4P_C5]And P_C1+P_C2+P_C3+P_C4+P_C51, the above formula forms a new equivalent matrix form simultaneously:

solving the equation set can obtain the steady-state probability that the system stays in the corresponding state, and calculating the power failure unavailability U (P) of the 1 st load bus of the three-section three-contact urban power distribution network system A when the system power supply adopts double-bus wiring by utilizing MATLAB programming_C5。

5. The method as claimed in claim 4, wherein the step S8 specifically comprises:

system a2 nd load busbar a2 total maintenance rate:

μ₂＝p₅₁+p₅₃+p₅₄

total frequency of power failure fault of system a No. 2 load bus a 2:

f₂＝P_C5×(p₅₁+p₅₃+p₅₄)。

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