CN105337275A - Medium-voltage power distribution network power supply capacity evaluation method based on reliability of power distribution system - Google Patents

Abstract

The invention discloses a medium-voltage power distribution network power supply capacity evaluation method based on reliability of a power distribution system. The medium-voltage power distribution network power supply capacity evaluation method comprises the steps of: establishing a medium-voltage power distribution network power supply capacity evaluation model based on reliability of the power distribution system; providing a solution method for the medium-voltage power distribution network power supply capacity evaluation model based on reliability of the power distribution system, wherein the solution method includes the two aspects of performing solution calculation of reliability of the power distribution system and verifying whether the reliability meets a reliability constraint, and calculating power supply capacity of the power distribution system; and providing a medium-voltage power distribution network power supply capacity evaluation process based on reliability of the power distribution system. The medium-voltage power distribution network power supply capacity evaluation method can analyze the reliability of the existing power distribution system grid structure from the perspective of the power distribution system grid structure, regards a reliability index in the power distribution system as a constraint condition, further releases the power supply capacity margin of the power distribution system on the premise of satisfying the reliability constraint of the power distribution system in a targeted manner, and excavates the power supply potential. The medium-voltage power distribution network power supply capacity evaluation method can provide support for improving power supply capacity of the existing power distribution network structure, and promotes reasonable development of construction structure and planning technology of the urban power grid.

Description

A kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability

Technical field

The present invention relates to a kind of medium voltage distribution network evaluation of power supply capability method.Particularly relate to a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability for urban distribution network planning.

Background technology

Distribution system as the important step of electrical energy production, transmission and use, be contact user with send out, the tie of transmission system, science, the power supply capacity reasonably calculating distribution system are the key components of current city electrical network assessment development.Consider in urban area, be difficult to the underpass obtaining newly-built substation location again from the planning and transformation of distribution system and newly establish feeder line.Therefore, the power supply capacity of the existing distribution system of reasonable assessment and excavate its optimize after power supply potential receive increasing concern, power supply capacity also becomes gradually evaluates a leading indicator of power distribution network, has important directive significance to the planning of power distribution network and operation.

The current major embodiment of computational methods about distribution system power supply capacity is two classes, namely based on the method for distribution power system load flow calculation and the method based on power distribution network safety criterion.Based in the method for distribution power system load flow calculation, main it is considered that trial-and-error method, namely obtain by constantly changing system loading and carrying out Load flow calculation the peak load value that system can bear; And other power supply capacity computational methods proposed based on various tide model, these class methods can try to achieve the peak load that distribution system can bear under the system constraints such as node voltage, power loop, and in this, as the foundation of evaluating system power supply capacity.In the method based on power distribution network safety criterion, most typical is the power distribution network evaluation of power supply capability method taking into account N-1 safety criterion, from the angle of power supply continuity, and considers main transformer interconnecting relation, the factors such as the load transfer plan between transformer station, verify its power supply capacity under N-1 criterion.

But for the conventional distribution system power supply capacity computational methods taking into account N-1 safety criterion, what adopt is a kind of rigid constraint, there is certain problem in the planning of reality.The first, in view of the complex relationship between apparatus of load rate and system reliability, N-1 criterion more trends towards a necessity criterion, and therefore separately consideration has been not enough to guarantee system and can has good power supply quality; Second, because the duration of distribution network load peak value is very short, the several times of peakload normally equal duty value, and also there is certain difference for the demand of power supply reliability in dissimilar load, therefore, the system power supply ability of trying to achieve according to N-1 criterion has certain nargin.Consider the importance of power system reliability in distribution system planning, power distribution network evaluation of power supply capability method based on this flexible index of system reliability is proposed, more can adapt to the feature of distribution network construction and operation, and then excavate power distribution network power supply potential, play the utilization of resources usefulness of power distribution network larger, promote the economy of power grid construction and operation.

Summary of the invention

Technical problem to be solved by this invention is, provides a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability that can provide support for the raising of existing distribution net work structure power supply capacity.

The technical solution adopted in the present invention is: a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability, comprises the steps:

1) the medium voltage distribution network evaluation of power supply capability model based on distribution Power System Reliability is set up

Distribution system power supply capacity model is built using reliability as flexible constraint condition, target function be meet system reliability require under power distribution network peak load deliverability, for the power distribution network containing multiple mutual contact transformer station, power supply capacity computing formula is as follows:

$\max psc=\underset{i}{\Σ}\left(R_i{T}_i\right)---\left(1\right)$

In formula, psc by the power supply capacity of calculating distribution system; R _iit is the rated capacity of i-th main transformer; T _iit is the load factor of i-th main transformer;

2) based on the method for solving of the medium voltage distribution network evaluation of power supply capability model of distribution Power System Reliability

Whole computational process comprises two aspects, one be distribution Power System Reliability solve calculating, and inspection whether meet reliability constraint; Two is that distribution system power supply capacity calculates;

3) the medium voltage distribution network evaluation of power supply capability flow process based on distribution Power System Reliability is proposed.

Step 1) described in using reliability as flexible constraint condition, be in conjunction with distribution system self-operating feature, have following constraints:

(1) reliability equality constraint, (2) reliability inequality constraints condition, (3) load constraints and (4) load factor constraints.

Described reliability equality constraint, it is the corresponding reliability index obtained according to distribution system structure, average power supply availability ASAI in reliability index is chosen as equality constraint when the power supply capacity of evaluating system, the implication of average power supply availability refers to the ratio of total power supply hourage that the hourage that do not have a power failure that user stands in official hour requires with user, and concrete computational methods are:

In formula, T is need electricity hourage at the appointed time; U _jfor the idle time in year of load bus j; T _jfor the number of users of load bus j; N _jfor the number of users of load bus j.

Described reliability inequality constraints condition, be according to different distribution system structure for reliability requirement set by different reliability objectives, concrete manifestation form is:

ASAI≥E(3)

In formula, E is for running the reliability objectives set by basis in conjunction with distribution system.

Described load constraints, be the capacity relationship in distribution system between each main transformer be connected feeder line, concrete manifestation form is:

$R_i{T}_i=\underset{q}{\Σ}{R}_{iq}{T}_{iq}---\left(4\right)$

In formula, R _iqrepresent the rated capacity of the q article of feeder line be connected with i-th main transformer; T _iqrepresent the load factor of the q article of feeder line be connected with i-th main transformer.

That described load factor constraints represents is described each main transformer load factor T _iwith each feeder line load factor T _iqspan, concrete manifestation form is:

0≤T _i≤1(5)

0≤T _iq≤1(6)。

Step 2) described in distribution Power System Reliability calculate, it is the method adopting Feeder partitioning, and the average power supply availability ASAI of the dependability parameter computing system of each element in coupling system, step 1) (1) in give the computational methods of average power supply availability, the number of users N of load bus j in the concrete process calculated _jfollowing formula is adopted to calculate:

N _j＝n _jT _j(7)

In formula, n _jwhen load capacity for load bus j place feeder line reaches 100%, the number of users of load bus j; T _jfor the load factor of load bus j place feeder line;

Therefore average power supply availability is expressed as again:

$ASAI=1-\frac{{\mathrm{\ΣU}}_j{n}_j{T}_j}{{\mathrm{T\Σn}}_j{T}_j}---\left(8\right)$

In formula, idle time in the year U of load point j _jlosing the account form in the reliability assessment under the connective time be completely:

$U_j=\underset{r\∈I_P\left(j\right)}{\Σ}{p}_r{\mathrm{\λ}}_r{t}_{rj}---\left(9\right)$

In formula, I _{p (j)}element r in set will cause the lasting power failure of load point j when there is destructive malfunction; p _rfor the action message rate of the recloser of respective action during element r generation destructive malfunction; λ _rfor the average year destructive malfunction rate of element r; t _rjfor causing the interruption duration of load point node j when destructive malfunction occurs element r, t _rjit may be fault correction time or fail-over time.

Step 2) described in distribution system power supply capacity calculate, under the prerequisite meeting reliability constraint, be optimized the load factor of feeder line, the target function of optimization is that the power supply capacity of system is maximum, and the distribution system power supply capacity computation model based on reliability is specific as follows:

$\max psc=\underset{i}{\Σ}\left(R_i{T}_i\right)$

s.t.

$\left\{\begin{array}{c}ASAI=1-\frac{{\mathrm{\ΣU}}_j{n}_j{T}_j}{{\mathrm{T\Σn}}_j{T}_j}\\ U_j=\underset{r\∈I_P\left(j\right)}{\Σ}{p}_r{\mathrm{\λ}}_r{t}_{rj}\\ ASAI\≥E\\ R_i{T}_i=\underset{q}{\Σ}{R}_{iq}{T}_{iq}\\ 0\≤T_i\≤1\\ 0\≤T_j\≤1\end{array}\right..$

Step 3) described in the medium voltage distribution network evaluation of power supply capability flow process based on distribution Power System Reliability, comprising:

(1) systems reliability analysis: according to the failure rate of element, analysis list one element fault cause the interruption duration of load point, and the Failure Mode Effective Analysis table FMEA setting up system according to this shows;

(2) the solving of reliability index: the initial load rate of feeder line in initialization system, and the Failure Mode Effective Analysis table FMEA of coupling system shows the idle time in year of each load point in computing system, thus the average power supply availability of solving system;

(3) constraints verification: comparison step 2) in the magnitude relationship of reliability objectives E of the average power supply availability ASAI index that calculates and Operation system setting, if meet ASAI >=E relation, then calculate initial power supply capacity in the case; Otherwise, in optimization system feeder line load factor after recalculate the average power supply availability ASAI index of system.

(4) feeder line load factor is optimized: the load factor utilizing feeder line in genetic algorithm optimization system, and the computational process repeated in step (3), all need after often carrying out a suboptimization to verify the reliability objectives E whether meeting system, if can meet, carry out the calculating of power supply capacity, otherwise eliminate current feeder line load factor, proceed to optimize, until result of calculation tends towards stability or calculates reach corresponding iterations.

(5) system power supply capability analysis: by the distribution system power supply capacity computation model based on reliability, utilize the net capability of Matlab solving system.

A kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability of the present invention, can from the angle of distribution system grid structure, existing distribution network structure reliability of structure is analyzed, and using the reliability index in distribution system as constraints, and then under the prerequisite meeting distribution Power System Reliability constraint, discharge the nargin of distribution system power supply capacity targetedly, excavate power supply potential.The present invention can provide support for the raising of existing distribution net work structure power supply capacity, is conducive to the managerial skills promoting urban distribution network planning, promotes the Rational Development of Construction of Intercity Network structure and planning technology.

Accompanying drawing explanation

Fig. 1 is the flow chart of the medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability;

Fig. 2 is system main transformer communication relationship schematic diagram;

Fig. 3 is relation between reliability objectives and system power supply ability.

Embodiment

Below in conjunction with embodiment and accompanying drawing, a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability of the present invention is described in detail.

As shown in Figure 1, a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability of the present invention, comprises the steps:

1) the medium voltage distribution network evaluation of power supply capability model based on distribution Power System Reliability is set up

Distribution Power System Reliability refers to that electric power system provides measuring of the ability of electric power and electricity to power consumer incessantly by the quality standard that can accept and requirement, mainly to provide the ability of continual qualified electric energy to power consumer in order to tolerance and assessment electric power system.

Power supply capacity refers under the condition meeting certain safety criterion, the maximum ability supplying user power utilization of power distribution network in certain area, namely power distribution network meet certain safety criterion by maximum amount of power.

Proposed by the invention is at the net capability meeting intermediate distribution system under reliability constraint, and be namely source with high voltage substation, middle pressure feeder line is net, and considers that the contact of main transformer between station turns the net capability for relation computing system.

Distribution system power supply capacity model is built using reliability as flexible constraint condition, target function be meet system reliability require under power distribution network peak load deliverability, for the power distribution network containing multiple mutual contact transformer station, power supply capacity computing formula is as follows:

$\max psc=\underset{i}{\Σ}\left(R_i{T}_i\right)---\left(1\right)$

In formula, psc by the power supply capacity of calculating distribution system; R _iit is the rated capacity of i-th main transformer; T _iit is the load factor of i-th main transformer;

Using reliability as constraints, in conjunction with distribution system self-operating feature, constraints has following:

(1) reliability equality constraint

What described reliability equality constraint represented is the corresponding reliability index obtained according to distribution system structure, average power supply availability ASAI in reliability index is chosen as equality constraint when the power supply capacity of evaluating system, the implication of average power supply availability refers to the ratio of total power supply hourage that the hourage that do not have a power failure that user stands in official hour requires with user, and concrete computational methods are:

In formula, T is need electricity hourage at the appointed time; U _jfor the idle time in year of load bus j; T _jfor the number of users of load bus j; N _jfor the number of users of load bus j.

(2) reliability inequality constraints

What described reliability inequality constraints condition represented is according to different distribution system structure for reliability requirement set by different reliability objectives, concrete manifestation form is:

ASAI≥E(3)

In formula, E is for running the reliability objectives set by basis in conjunction with distribution system.

(3) load constraint

The capacity relationship that what described load constraints represented is in distribution system between each main transformer be connected feeder line, concrete manifestation form is:

$R_i{T}_i=\underset{q}{\Σ}{R}_{iq}{T}_{iq}---\left(4\right)$

In formula, R _iqrepresent the rated capacity of the q article of feeder line be connected with i-th main transformer; T _iqrepresent the load factor of the q article of feeder line be connected with i-th main transformer.

(4) load factor constraint

That described load factor constraints represents is described each main transformer load factor T _iwith each feeder line load factor T _iqspan, concrete manifestation form is:

0≤T _i≤1(5)

0≤T _iq≤1(6)

2) based on the method for solving of the medium voltage distribution network evaluation of power supply capability model of distribution Power System Reliability

From last point of analysis for distribution system power supply capacity model, the evaluation of power supply capability problem based on reliability is a non-linear optimum programming problem comprising multiple variable, multiple constraint.Whole computational process comprises two aspects, i.e. the solving of system reliability, and whether inspection meets reliability constraint; And the solving of system power supply ability.To be specifically described these two parts below.

(1) distribution Power System Reliability calculates

Adopt the method for Feeder partitioning, and the average power supply availability ASAI of the dependability parameter computing system of each element in coupling system, step 1) (1) in give the computational methods of average power supply availability, the number of users N of load bus j in the concrete process calculated _jfollowing formula is adopted to calculate:

N _j＝n _jT _j(7)

In formula, n _jwhen load capacity for load bus j place feeder line reaches 100%, the number of users of load bus j; T _jfor the load factor of load bus j place feeder line.

Therefore average power supply availability can be expressed as again:

$ASAI=1-\frac{{\mathrm{\ΣU}}_j{n}_j{T}_j}{{\mathrm{T\Σn}}_j{T}_j}---\left(8\right)$

In formula, idle time in the year U of load point j _jlosing the account form in the reliability assessment under connectedness (TLOC) event be completely:

$U_j=\underset{r\∈I_P\left(j\right)}{\Σ}{p}_r{\mathrm{\λ}}_r{t}_{rj}---\left(9\right)$

In formula, I _{p (j)}element r in set will cause the lasting power failure of load point j when there is destructive malfunction; p _rfor the action message rate of the recloser of respective action during element r generation destructive malfunction; λ _rfor the average year destructive malfunction rate of element r; t _rjfor causing the interruption duration of load point node j when destructive malfunction occurs element r, t _rjit may be fault correction time or fail-over time.

Based on said process, in method mentioned by the present invention the key step of Calculation of Reliability be according to the dependability parameter of element calculate all kinds of single element fault cause the interruption duration of load point and set up the Failure Mode Effective Analysis table (FMEA table) of system, and then calculate the year interruption duration of each load point, finally calculate the reliability index of system, availability of namely on average powering.

(2) distribution system power supply capacity calculates

Under the prerequisite meeting reliability constraint, be optimized the load factor of feeder line, the target function of optimization is that the power supply capacity of system is maximum, and the distribution system power supply capacity computation model based on reliability is specific as follows:

$\max psc=\underset{i}{\Σ}\left(R_i{T}_i\right)$

s.t.

$\left\{\begin{array}{c}ASAI=1-\frac{{\mathrm{\ΣU}}_j{n}_j{T}_j}{{\mathrm{T\Σn}}_j{T}_j}\\ U_j=\underset{r\∈I_P\left(j\right)}{\Σ}{p}_r{\mathrm{\λ}}_r{t}_{rj}\\ ASAI\≥E\\ R_i{T}_i=\underset{q}{\Σ}{R}_{iq}{T}_{iq}\\ 0\≤T_i\≤1\\ 0\≤T_j\≤1\end{array}\right..$

3) the medium voltage distribution network evaluation of power supply capability flow process based on distribution Power System Reliability is proposed

(1) systems reliability analysis: according to the failure rate of element, analysis list one element fault cause the interruption duration of load point, and the Failure Mode Effective Analysis table FMEA setting up system according to this shows;

(2) the solving of reliability index: the initial load rate of feeder line in initialization system, and the Failure Mode Effective Analysis table FMEA of coupling system shows the idle time in year of each load point in computing system, thus the average power supply availability of solving system;

(3) constraints verification: comparison step 2) in the magnitude relationship of reliability objectives E of the average power supply availability ASAI index that calculates and Operation system setting, if meet ASAI >=E relation, then calculate initial power supply capacity in the case; Otherwise, in optimization system feeder line load factor after recalculate the average power supply availability ASAI index of system.

(4) feeder line load factor is optimized: the load factor utilizing feeder line in genetic algorithm optimization system, and the computational process repeated in step (3), all need after often carrying out a suboptimization to verify the reliability objectives E whether meeting system, if can meet, carry out the calculating of power supply capacity, otherwise eliminate current feeder line load factor, proceed to optimize, until result of calculation tends towards stability or calculates reach corresponding iterations.

(5) system power supply capability analysis: by the distribution system power supply capacity computation model based on reliability, utilize the net capability of Matlab solving system.

Provide preferred example below

With the actual distribution net work structure in somewhere for example, set up the contact model based on main transformer interconnecting relation, and expanded to feeder line aspect according to N-1 criterion and load constraint, the reliability of its grid structure is analyzed, and under the constraints of reliability index, calculates the net capability under this grid structure.

(1) determination of grid structure reliability

The contact structure of the change interconnecting relation of this area as shown in Figure 2, each transformer station relevant information is as shown in table 1, in the process of carrying out Calculation of Reliability, emphasis considers the impact of fault for load point of single element in grid structure, specifically comprise: main transformer fault, busbar fault, distribution transformer fault, circuit breaker failure, line fault and switch fault etc., the dependability parameter of each class component is as shown in table 2.

Transformer station's configuring condition table in table 1 example

Main element dependability parameter in table 2 system

Element	λ	r	r p
				Bus	0.001	5	－
Feeder line	0.065	5	－
				Distribution transformer	0.013	－	5
Block switch	0.006	5	－
				Main transformer	0.01	200	－
Primary cut-out	0.002	50	－
				Low-voltage circuit breaker	0.005	20	－

In table 2, λ is the failure rate of each element, and unit is times/year, is Ci/˙ km for feeder line, is time/Tai ˙ for main transformer; R is mean time to repair, r _pfor mean time between replacement, unit is hour.

Based on above-mentioned explanation, the overall condition of example comprises the distribution transformer of three transformer stations, six main transformers, 28 feeder lines, 352 load buses (11 industrial load nodes, 62 Commercial Load nodes, 279 resident load nodes), 436 315kV.

Utilize Feeder partitioning method to calculate the reliability index of this power distribution system network, the average power supply availability index (ASAI) obtaining this power distribution system network is 0.9993.Consider for different areas, different power load distributing, the reliability index for distribution system has different requirements.Therefore, then choose average power supply availability index (ASAI) from 0.9900 to 0.9990 as constraints, calculate the net capability of distribution system under this constraints, result of calculation is as shown in table 3:

Relationship analysis between table 3 reliability objectives and power supply capacity

The above results is depicted as curve chart the trend of showing result to be better described, curve chart as shown in Figure 3:

Can analyze according to the above results and obtain: within the scope of certain reliability, the net capability of system remains unchanged; If improve the reliability index of system namely on average to power availability, mean that turned confession the nargin of load in system increases, and in system with load reduction, cause power supply capacity to decline.Different reliability index constraints can obtain different power supply capacity results, and therefore, the constraints based on reliability used in the present invention belongs to a kind of flexible constraint condition, can adjust different results according to different reliability requirements.In current power grid construction, grid structure is relatively shaping, therefore be difficult to from existing grid structure, make effective expansion again, therefore the present invention passes through flexible constraints on the basis of existing grid structure, the requirement in production run can either be met, can power supply potential be discharged again, more practical and there is certain directive significance in the distribution network planning of reality.

Claims (9)

1., based on a medium voltage distribution network evaluation of power supply capability method for distribution Power System Reliability, it is characterized in that, comprise the steps:

1) the medium voltage distribution network evaluation of power supply capability model based on distribution Power System Reliability is set up

Distribution system power supply capacity model is built using reliability as flexible constraint condition, target function be meet system reliability require under power distribution network peak load deliverability, for the power distribution network containing multiple mutual contact transformer station, power supply capacity computing formula is as follows:

$\max psc=\underset{i}{\Σ}\left(R_i{T}_i\right)---\left(1\right)$

In formula, psc by the power supply capacity of calculating distribution system; R _iit is the rated capacity of i-th main transformer; T _iit is the load factor of i-th main transformer;

2) based on the method for solving of the medium voltage distribution network evaluation of power supply capability model of distribution Power System Reliability

Whole computational process comprises two aspects, one be distribution Power System Reliability solve calculating, and inspection whether meet reliability constraint; Two is that distribution system power supply capacity calculates;

3) the medium voltage distribution network evaluation of power supply capability flow process based on distribution Power System Reliability is proposed.

2. a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability according to claim 1, it is characterized in that, step 1) described in using reliability as flexible constraint condition, be in conjunction with distribution system self-operating feature, have following constraints:

(1) reliability equality constraint, (2) reliability inequality constraints condition, (3) load constraints and (4) load factor constraints.

3. a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability according to claim 2, it is characterized in that, described reliability equality constraint, it is the corresponding reliability index obtained according to distribution system structure, average power supply availability ASAI in reliability index is chosen as equality constraint when the power supply capacity of evaluating system, the implication of average power supply availability refers to the ratio of total power supply hourage that the hourage that do not have a power failure that user stands in official hour requires with user, and concrete computational methods are:

In formula, T is need electricity hourage at the appointed time; U _jfor the idle time in year of load bus j; T _jfor the number of users of load bus j; N _jfor the number of users of load bus j.

4. a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability according to claim 2, it is characterized in that, described reliability inequality constraints condition, be according to different distribution system structure for reliability requirement set by different reliability objectives, concrete manifestation form is:

ASAI≥E(3)

In formula, E is for running the reliability objectives set by basis in conjunction with distribution system.

5. a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability according to claim 2, it is characterized in that, described load constraints, be the capacity relationship in distribution system between each main transformer be connected feeder line, concrete manifestation form is:

$R_i{T}_i=\underset{q}{\Σ}{R}_{iq}{T}_{iq}---\left(4\right)$

In formula, R _iqrepresent the rated capacity of the q article of feeder line be connected with i-th main transformer; T _iqrepresent the load factor of the q article of feeder line be connected with i-th main transformer.

6. a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability according to claim 2, is characterized in that, that described load factor constraints represents is described each main transformer load factor T _iwith each feeder line load factor T _iqspan, concrete manifestation form is:

0≤T _i≤1(5)

0≤T _iq≤1(6)。

7. a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability according to claim 1, it is characterized in that, step 2) described in distribution Power System Reliability calculate, it is the method adopting Feeder partitioning, and the average power supply availability ASAI of the dependability parameter computing system of each element in coupling system, step 1) (1) in give the computational methods of average power supply availability, the number of users N of load bus j in the concrete process calculated _jfollowing formula is adopted to calculate:

N _j＝n _jT _j(7)

In formula, n _jwhen load capacity for load bus j place feeder line reaches 100%, the number of users of load bus j; T _jfor the load factor of load bus j place feeder line;

Therefore average power supply availability is expressed as again:

$ASAI=1-\frac{{\mathrm{\ΣU}}_j{n}_j{T}_j}{{\mathrm{T\Σn}}_j{T}_j}---\left(8\right)$

In formula, idle time in the year U of load point j _jlosing the account form in the reliability assessment under the connective time be completely:

$U_j=\underset{r\∈I_P\left(j\right)}{\Σ}{p}_r{\mathrm{\λ}}_r{t}_{rj}---\left(9\right)$

In formula, I _{p (j)}element r in set will cause the lasting power failure of load point j when there is destructive malfunction; p _rfor the action message rate of the recloser of respective action during element r generation destructive malfunction; λ _rfor the average year destructive malfunction rate of element r; t _rjfor causing the interruption duration of load point node j when destructive malfunction occurs element r, t _rjit may be fault correction time or fail-over time.

8. a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability according to claim 1, it is characterized in that, step 2) described in distribution system power supply capacity calculate, under the prerequisite meeting reliability constraint, the load factor of feeder line is optimized, the target function optimized is that the power supply capacity of system is maximum, and the distribution system power supply capacity computation model based on reliability is specific as follows:

$\max psc=\underset{i}{\Σ}\left(R_i{T}_i\right)$

s.t.

$\left\{\begin{array}{c}ASAI=1-\frac{{\mathrm{\ΣU}}_j{n}_j{T}_j}{{\mathrm{T\Σn}}_j{T}_j}\\ U_j=\underset{r\∈I_P\left(j\right)}{\Σ}{p}_r{\mathrm{\λ}}_r{t}_{rj}\\ ASAI\≥E\\ R_i{T}_i=\underset{q}{\Σ}{R}_{iq}{T}_{iq}\\ 0\≤T_i\≤1\\ 0\≤T_j\≤1\end{array}\right..$

9. a kind of medium voltage distribution network evaluation of power supply capability method based on distribution Power System Reliability according to claim 1, is characterized in that, step 3) described in the medium voltage distribution network evaluation of power supply capability flow process based on distribution Power System Reliability, comprising:

(1) systems reliability analysis: according to the failure rate of element, analysis list one element fault cause the interruption duration of load point, and the Failure Mode Effective Analysis table FMEA setting up system according to this shows;

(2) the solving of reliability index: the initial load rate of feeder line in initialization system, and the Failure Mode Effective Analysis table FMEA of coupling system shows the idle time in year of each load point in computing system, thus the average power supply availability of solving system;

(3) constraints verification: comparison step 2) in the magnitude relationship of reliability objectives E of the average power supply availability ASAI index that calculates and Operation system setting, if meet ASAI >=E relation, then calculate initial power supply capacity in the case; Otherwise, in optimization system feeder line load factor after recalculate the average power supply availability ASAI index of system.

(4) feeder line load factor is optimized: the load factor utilizing feeder line in genetic algorithm optimization system, and the computational process repeated in step (3), all need after often carrying out a suboptimization to verify the reliability objectives E whether meeting system, if can meet, carry out the calculating of power supply capacity, otherwise eliminate current feeder line load factor, proceed to optimize, until result of calculation tends towards stability or calculates reach corresponding iterations.

(5) system power supply capability analysis: by the distribution system power supply capacity computation model based on reliability, utilize the net capability of Matlab solving system.