CN105117560A - Method for calculating theoretic line losses of medium-voltage distribution line - Google Patents

Abstract

The invention provides a method for calculating theoretic line losses of a medium-voltage distribution line. The method includes the following steps: calculating the losses of a trunk line; calculating the losses of branch lines; calculating the copper losses of distribution transformers in the line; calculating the iron losses of the distribution transformers in the line, wherein the sum of the calculation results of the steps is the theoretic line losses. By means of the method, the calculation work of the basic theoretic line losses can be well done, the range of unclear losses in practical losses and loss reducing space can be defined, corresponding loss reducing measures can be taken accordingly, and reliable bases can be provided for power grid planning, power grid transformation, power grid capacitance reactive compensation and power grid economical operation.

Description

A kind of medium-voltage distribution circuit theoretical line loss caluclation method

Technical field

The invention belongs to medium-voltage distribution field, particularly relate to a kind of computing method of medium-voltage distribution circuit theory wire loss.

Background technology

Distribution system refers to be directly that a part of electric system that user serves, and medium voltage distribution network generally refers to from the 10kV line outlet of 110kV/10kV or 35kV/10kV step-down substation to user side.Power distribution network is as the end of power network, and its electric pressure is low, be directly connected with user, circuit distribution is wide, on-line apparatus is many, and therefore system also exists impedance, causes electric energy in conversion, conveying, assigning process inevitably along with a large amount of line loss.

Based on current basic data management present situation, all need a large amount of manpower and materials of cost to carry out line loss statistical work every year, obtain line loss whether reasonably normative reference.On the one hand, workload is complicated, has increased the weight of the work load of electric power personnel; On the other hand, the mode of data acquisition manual entry, easily causes error and inefficiency.Therefore, in the urgent need to for 10kV via net loss theory calculate and the deep research of Optimal flattening.

Summary of the invention

In view of this, the present invention proposes a kind of medium-voltage distribution circuit theoretical line loss caluclation method, for judging whether dissimilar line loss rationally provides reference frame, for the correction of the distribution line management line loss exceeding line loss scope provides data supporting.

For achieving the above object, the technical scheme of the invention is achieved in that

A kind of medium-voltage distribution circuit theoretical line loss caluclation method, comprises the steps:

(1) basic routing line loss is calculated;

(2) Branch Computed line loss;

(3) distribution transforming copper loss contained by computational scheme;

(4) distribution transforming iron loss contained by computational scheme;

(5) the result of calculation sum of step (1) to (4), is theory wire loss.

Preferably, the computing method of described basic routing line loss are:

P _main=α I ²rl

Wherein, α is trunk power load distributing coefficient, and I is trunk outlet electric current, and r is trunk resistance per unit length, and l is beam length.

Further, the defining method of trunk power load distributing factor alpha is:

A, load are uniformly distributed along the line, and trunk power load distributing factor alpha value is 1;

B, load are evenly distributed minimizing along the line, and trunk power load distributing factor alpha value is 3/5;

C, load are evenly distributed increase along the line, and trunk power load distributing factor alpha value is 8/5;

D, the load first half section that distributes along the line evenly increases, and the second half section evenly reduces, and trunk power load distributing factor alpha value is 23/20;

The first half section that E, load distributes along the line evenly reduces, and the second half section evenly increases, and trunk power load distributing factor alpha value is 9/10;

F, load distribute along the line first evenly to be increased, rear even minimizing, and trunk power load distributing factor alpha value is:

$\frac{3+6\mathrm{\η}-{\mathrm{\η}}^2}{5}$

Wherein, η is that load increases the separation reduced with load;

G, load distribute along the line and first evenly reduce, rear even increase, and trunk power load distributing factor alpha value is:

$\frac{4{\mathrm{\η}}^2-9\mathrm{\η}+8}{5}$

Wherein, η is that load reduces the separation increased with load;

Preferably, the computing method of described branched line loss are:

P _point=I _b ²r _bl _b

Wherein, I _bfor branched line average current, r _bfor branching unit length resistance, l _bfor branch length.

Preferably, the computing method of described distribution transforming copper loss are:

$P_{Cu}=\underset{i=1}{\overset{m_r}{\mathrm{\Σ}}}{\mathrm{\ΔP}}_{ki}\×{\left(\frac{I_{pi}}{I_{ei}}\right)}^2$

Wherein, m _tit is the total number of units of circuit substation transformer; Δ P _kiit is the i-th station power distribution transformer short-circuit loss power; I _piit is the electric current flowing through the i-th station power distribution transformer; I _giit is the i-th station power distribution transformer rated current.

Preferably, the computing method of described distribution transforming iron loss are:

$P_{Fe}=\underset{i=1}{\overset{m_r}{\mathrm{\Σ}}}{\mathrm{\ΔP}}_{0i}\×{\left(\frac{U_{avi}}{U_{fi}}\right)}^2$

Wherein, m _tit is the total number of units of circuit substation transformer; Δ P _oithe i-th station power distribution transformer noload losses power; U _fithe i-th station power distribution load tap changer voltage (kV); U _avithe i-th station power distribution transformer access point voltage.

Relative to prior art, a kind of medium-voltage distribution circuit theoretical line loss caluclation method of the present invention has following advantage:

Pass through the present invention, the work of basic theory line loss calculation can be carried out, to define in practical line loss the scope of not clear loss and fall the space of damage, thus formulating corresponding reducing loss measure, for Electric Power Network Planning, transformation and capacitance reactive compensation, economical operation provide reliable foundation.

On the one hand, for judging whether dissimilar line loss rationally provides reference frame, thus alleviating the MV distribution systems loss statistical work amount of grass-roots unit, avoiding the input of a large amount of manpower and materials, reduce human cost and improve work efficiency; On the other hand, be convenient to accurately grasp the MV distribution systems exhaustion range eliminated beyond operational management factor, for the correction of the distribution line management line loss exceeding line loss scope provides data supporting, to enhancing electrical network anti-accident ability, improve Regulation maintenance levels and there is important more practical value and realistic meaning.

Accompanying drawing explanation

The accompanying drawing forming a part of the present invention is used to provide a further understanding of the present invention, and schematic description and description of the present invention, for explaining the present invention, does not form inappropriate limitation of the present invention.In the accompanying drawings:

Fig. 1 is calculation process schematic diagram of the present invention.

Fig. 2 is the first load distribution schematic diagram along the line.

Fig. 3 is the second load distribution schematic diagram along the line.

Fig. 4 is the third load distribution schematic diagram along the line.

Fig. 5 is the 4th kind of load distribution schematic diagram along the line.

Fig. 6 is the 5th kind of load distribution schematic diagram along the line.

Fig. 7 is the 6th kind of load distribution schematic diagram along the line.

Fig. 8 is the 7th kind of load distribution schematic diagram along the line.

Embodiment

It should be noted that, when not conflicting, the feature in embodiments of the invention and embodiment can combine mutually.

Below with reference to the accompanying drawings and describe the present invention in detail in conjunction with the embodiments.

Loss analysis for 10KV MV distribution systems:

10kV via net loss affects by many factors, can be divided into three major types according to each factor character, is grid equipment factor, electric power network technique factor, power load distributing respectively.

Grid equipment factor mainly comprises the factors such as transformer, circuit, reactive-load compensation equipment.

Electric power network technique factor mainly refers to, to the influential different equipment technology of line loss tool, mainly comprise: voltage-regulating technique and reactive power compensation technology etc.

Power load distributing refers to the type that load distributes along circuit.

One: grid equipment factor

1. transformer affects 10kV via net loss

Transformer is selected to be mainly manifested in transformer capacity, number transformer and transformer model (S7 is serial, S9 is serial, S11 is serial) line loss impact.

To identical load, there is the transformer capacity making transformer loss minimum, when departing from this capacity, transformer loss will increase.To same time 10kV circuit, number transformer affects loss.

The line is busy that to damage proportion comparatively large in transformer loss, and answer emphasis to carry out considering total volume and the quantity of transformer, load factor 30% transformer of such as 10 SCB10-500, is calculated as follows:

When calculating minimal losses, replace with max cap. model SCB10-2500 equivalence in current SCB10 type, be equivalent to the SCB10-2500 transformer 10*500/2500=2 platform of load factor 30%.Then the SCB10-2500 transformer loss minimal losses the most of these 2 load factors 30% is calculated.

When calculating maximum loss, with in current SCB10 type minimum capacity model SCB10-250 equivalence replace: be equivalent to load factor be 30% SCB10-250 number of units be 10*500/250=20 platform, then calculate the SCB10-250 transformer loss maximum loss the most then calculating these 2 load factors 30%.

2. circuit affects 10kV via net loss

The wire type of circuit, line length, system of laying, arrangement of conductor even earthing mode etc. all have impact to loss.

When conductor cross-section increases, resistance reduces, and loss will be caused to decline; Otherwise when conductor cross-section reduces, resistance increases, and loss will be caused to rise.

When line length increases, resistance increases, and loss will be caused to rise; Otherwise when line length reduces, resistance reduces, and loss will be caused to decline.

Conductor laying mode, arrangement of conductor (horizontal, homeotropic alignment, triangle arrangement and wire spacing) have impact on line parameter circuit value (admittance, electric capacity, reactance), thus have influence on line loss.

In reality, conductor laying mode, arrangement of conductor and earthing mode are less on line loss impact, and wire type and line length are on the impact of line loss to answer emphasis to consider.

3. reactive-load compensation is on the impact of 10kV via net loss

Reactive-load compensation is mainly through compensation capacity, compensation way and compensation system distribution influence line loss.

When Reactive Power Device capacity configuration is different, power network current by different, thus affects line loss; Different compensation ways also affects line loss.Current Reactive Compensation Mode is roughly divided into fixed compensation and auto-compensation.The magnitude numerical value that fixed compensation is equivalent to change power network current is stable, and the power network current size that auto-compensation is equivalent to change different loads is different, thus affects line loss.In addition, the distribution of reactive power compensator also has impact to line loss.For low-voltage compensation, when only installing reactive power compensator in substation transformer low-pressure side, not affecting the electric current of low-voltage circuit, only the above system of substation transformer being had an impact; And when installing reactive power compensator in user side, then can reduce the electric current of low-voltage circuit, the above system of substation transformer is had an impact too, thus line loss is had an impact.

Known by above analysis, reactive-load compensation, by the idle transmission at electrical network of impact, changes power network current, and square being directly proportional of line loss and electric current, thus reactive-load compensation produces considerable influence to line loss, therefore, should consider that Reactive Power Device is on the impact of line loss from the angle of line current.

4. other equipment are on the impact of 10kV via net loss

Circuit widely used iron or aluminum metal-ware, switch, automation installation and metering outfit etc. also can have an impact to line loss due to its model difference, and such as stem-winder loss monthly can reach 1kWh, and electronic watch loss is that the half of stem-winder is even less.But the region larger for user power utilization electricity, the impact of above factor on line loss is less, can not consider.

Two: electric power network technique factor

1, voltage-regulating technique is on the impact of 10kV via net loss

Electrical network is in operation, and voltage is not stablize constant, but change along with the change of load, voltage-regulating technique can change line voltage, make the whole network voltage in allowed band in more by a small margin.The voltage-regulating technique of voltage mainly contains transformer regulating (without excitation pressure regulation, on-load voltage regulation) and reactive-load compensation.When load is constant, adopts Voltage Technique that voltage is raised, can electric current be reduced, circuit line loss is reduced, and the now fixed loss of transformer will raise; Then inverse variation is produced when voltage is reduced.

Therefore, should consider that voltage-regulating technique is on the impact of 10kV via net loss from the angle of line current.

2, reactive power compensation technology is on the impact of 10kV via net loss

Reactive-load compensation is the key factor affecting line loss, the impact of reactive power compensation technology on line loss is embodied in reactive power compensator automatization level, as fixed compensation, grouping switching robotization compensate and dynamic auto compensation technique, improve line current, line loss is impacted.Therefore, should consider that reactive power compensation technology is on the impact of 10kV via net loss from the angle of line current.

Three: power load distributing factor

Payload and power load distributing all have considerable influence to line loss: under voltage certain condition, power network line loss power and transformer variable loss power are directly proportional to load square, load is larger, and loss power is larger, has different power attenuation rates under different load level; Power load distributing is different, also has impact to line loss.When load concentrates on supply line's end, line loss is maximum, and loss minimization when concentrating on circuit head end, under other distributed condition, line loss is between both.

Therefore, should consider that payload is on the impact of line loss from the angle of line current, and consider seven kinds of power load distributing coefficients (1, load is uniformly distributed; 2, load evenly successively decreases distribution; 3, load uniform increments distribution; 4, load first half section uniform increments, second half section evenly successively decrease; 5, load first half section evenly successively decrease, second half section uniform increments; 6, load first uniform increments along the line, evenly to successively decrease afterwards; 7, load along the line first evenly to successively decrease, rear uniform increments) impact on line loss.

Four: environmental factor

The change of meteorological condition, will cause the change of electrical network parameter on the one hand, thus cause line loss to change.As temperature raises, resistance will be caused to increase; Humidity increases, and leakage reactance will be caused to diminish; Rainy weather will make soil resistivity reduce, and stake resistance is reduced.Meeting acceleration equipment is aging on the other hand, has an impact to the power supply facilities maintenances such as line corridor and health status, as aging in multicore low-voltage insulation, and Leakage Current increases, increasing device loss to a certain extent; Trees cleaning under line corridor not in time, may cause tree electric discharge, increasing device loss.But the above impact that these produce line loss is less, so substantially do not consider.

Therefore, the factor affecting 10kV via net loss mainly comprises capacity of distribution transform combination, distribution transforming on-position, the combination of trunk resistance, the combination of basic routing line length, branch resistance, branched line length, backbone current, branch current and power load distributing coefficient 9 factors.Wherein, capacity of distribution transform combination and distribution transforming on-position determine the loss of transformer; The combination of trunk resistance, the combination of basic routing line length, branch resistance, branched line length, backbone current, branch current and power load distributing coefficient determine the loss of circuit.

Therefore, with circuit and transformer two elemental network elements for the starting point, build overhead transmission line and the cable line loss model of different load distribution pattern according to the combination of trunk resistance, the combination of basic routing line length, branch resistance, branched line length, backbone current and branch current; The computation models such as transformer copper loss and iron loss are built according to capacity of distribution transform combination and distribution transforming on-position; Obtain 10kV via net loss computation model on this basis.

Derivation is below under being based upon various power load distributing situation, on the basis that identical, the along the line rated voltage of overhead transmission line outlet electric current is equal, conductor resistance rate is identical.Wherein L is overhead transmission line length (km); P is under load is uniformly distributed situation along the line, each load point three phase power (i.e. three-phase load density) (kW*km ^-1); P ' is in load non-uniform Distribution situation along the line, each load point power (i.e. load density) (kW*km ^-1); P _i(i=1,2 ..., 7) and be circuit top transmission three phases active power (kW) that 7 kinds of power load distributing are corresponding; I _i(i=1,2 ..., 7) be 7 kinds of power load distributing corresponding be along line current (A); U is rated voltage along the line (kV); cos it is power factor; P _si(i=1,2 ..., 7) and be line power loss (kW) that 7 kinds of power load distributing are corresponding; R is the resistance (Ω) of wire; R is resistance per unit length (Ω/km); K _si(i=1,2 ..., 7) and be 7 kinds of power load distributing coefficients; I is line outlet single-phase current effective value (A).

One: line loss calculates (power load distributing coefficient calculations)

(1) load is uniformly distributed along the line

As shown in Figure 2, as 0<=Lx<L, active power and the line loss expression formula of line transmission are as follows in equation:

At Lx place, the active power of line transmission is:

$P_1={\&Integral;}_{Lx}^{L}pdLx=p(L-Lx)$

Total track length active loss is:

By above analysis, under load is uniformly distributed situation along the line, the value of power load distributing coefficient gets 1.

(2) load is evenly distributed minimizing along the line

As shown in Figure 3, as 0<=Lx<L, active power and the line loss expression formula of line transmission are as follows in equation:

$P_2={\&Integral;}_{Lx}^L\frac{-p^{\&prime;}(Lx-L)}{L}dLx=\frac{p^{\&prime;}{(L-Lx)}^2}{2L}$

As Lx=0, P be had ₂=P ₁, then need: p'=2p

By above analysis, load is evenly distributed in minimizing situation along the line, and the value of power load distributing coefficient gets 3/5.

(3) load is evenly distributed increase along the line

As shown in Figure 4, as 0<=Lx<L, active power and the line loss expression formula of line transmission are as follows in equation:

$P_3={\&Integral;}_{Lx}^L\frac{p^{\&prime;}Lx}{L}dLx=\frac{p^{\&prime;}(L^2-{\mathrm{Lx}}^2)}{2L}$

As Lx=0, P be had ₃=P ₁(outlet power is identical), then need: p'=2p

By above analysis, load is evenly distributed in minimizing situation along the line, and the value of power load distributing coefficient gets 8/5.

(4) the load first half section that distributes along the line evenly increases, and the second half section evenly reduces

As shown in Figure 5, as 0<=Lx<L/2, when disregarding the active power of second half section load, at Lx place, line transmission active power is:

$P_{\left(4\right)}^{\&prime;}={\&Integral;}_{Lx}^{L/2}\frac{2p^{\&prime;}Lx}{L}dLx=\frac{p^{\&prime;}(L^2/4-{\mathrm{Lx}}^2)}{L}$

As L/2<=Lx<L, at Lx place, line transmission active power is:

$P_{\left(4\right)}^{\&prime;\&prime;}={\&Integral;}_{Lx}^L\frac{-2p^{\&prime;}(Lx-L)}{L}dLx=\frac{p^{\&prime;}{(L-Lx)}^2}{L}$

As 0<=Lx<L/2, when considering the burden with power of circuit second half section, at Lx place, line transmission active power is:

$P_4^{\&prime;}=P_{\left(4\right)}^{\&prime;}+P_{\left(4\right)}^{\&prime;\&prime;}{|}_{Lx=L/2}=\frac{p^{\&prime;}(L^2/2-{\mathrm{Lx}}^2)}{L}$

As Lx=0, P be had ₄'=P ₁, then need: p'=2p

The circuit active loss of first half section is:

As L/2<=Lx<L:

$P_4^{\&prime;\&prime;}=P_{\left(4\right)}^{\&prime;\&prime;}=\frac{p^{\&prime;}{(L-Lx)}^2}{L}=\frac{2p{(L-Lx)}^2}{L}$

By above analysis, load distributes that first half section evenly increases along the line and in second half section evenly minimizing situation, power load distributing coefficient gets 23/20.

(5) the load first half section that distributes along the line evenly reduces, and the second half section evenly increases

As shown in Figure 6, as 0<=Lx<L/2, when disregarding the active power of second half section load, at Lx place, line transmission active power is:

$P_{\left(5\right)}^{\&prime;}={\&Integral;}_{Lx}^{L/2}\frac{-2p^{\&prime;}(Lx-L/2)}{L}dLx=\frac{p^{\&prime;}{(L-2Lx)}^2}{4L}$

As L/2<=Lx<L, at Lx place, line transmission active power is:

$P_{\left(5\right)}^{\&prime;\&prime;}={\&Integral;}_{Lx}^L\frac{2p^{\&prime;}(Lx-L/2)}{L}dLx=\frac{p^{\&prime;}Lx(L-Lx)}{L}$

As 0<=Lx<L/2, when considering the burden with power of circuit second half section, at Lx place, line transmission active power is:

$P_5^{\&prime;}=P_{\left(5\right)}^{\&prime;}+P_{\left(5\right)}^{\&prime;\&prime;}{|}_{Lx=L/2}=\frac{p^{\&prime;}(L^2/2+{\mathrm{Lx}}^2-LxL)}{L}$

As Lx=0, P be had ₅'=P ₁, then need: p'=2p

The circuit active loss of first half section is:

As L/2<=Lx<L:

$P_5^{\&prime;\&prime;}=P_{\left(5\right)}^{\&prime;\&prime;}=\frac{2pLx(L-Lx)}{L}$

By above analysis, the load first half section that distributes along the line evenly reduces, and in second half section evenly increase situation, power load distributing coefficient gets 9/10.

(6) load distributes along the line first evenly increases, rear even minimizing

As shown in Figure 7, as 0<=Lx< η L, do not consider the load of η L to L this section of circuit, in the active power of Lx place line transmission be:

$P_{\left(6\right)}^{\&prime;}={\&Integral;}_{Lx}^{\mathrm{\&eta;}L}\frac{p^{\&prime;}Lx}{\mathrm{\&eta;}L}dLx=\frac{p^{\&prime;}({\mathrm{\&eta;}}^2{L}^2-{\mathrm{Lx}}^2)}{2\mathrm{\&eta;}L}$

As η L<=Lx<=L, in the active power of Lx place line transmission be:

$P_{\left(6\right)}^{\&prime;\&prime;}={\&Integral;}_{Lx}^L\frac{-p^{\&prime;}(Lx-L)}{L-\mathrm{\&eta;}L}dLx=\frac{p^{\&prime;}{(L-Lx)}^2}{2(1-\mathrm{\&eta;})L}$

As 0<=Lx< η L, consider the load of η L to L this section of circuit, in the active power of Lx place line transmission be:

$P_6^{\&prime;}=P_{\left(6\right)}^{\&prime;}+P_{\left(6\right)}^{\&prime;\&prime;}{|}_{Lx=\mathrm{\&eta;}L}=\frac{p^{\&prime;}({\mathrm{\&eta;}}^2{L}^2-{\mathrm{Lx}}^2)}{2\mathrm{\&eta;}L}+\frac{p^{\&prime;}(L-\mathrm{\&eta;}L)}{2}=\frac{p^{\&prime;}}{2}(L-\frac{{\mathrm{Lx}}^2}{\mathrm{\&eta;}L})$

As Lx=0, P be had ₆'=P ₁, then need: p'=2p

The active power that circuit leading portion (0 to η L) consumes is:

As η L<=Lx<=L,

$P_6^{\&prime;\&prime;}=P_{\left(6\right)}^{\&prime;\&prime;}=\frac{p{(L-Lx)}^2}{(1-\mathrm{\&eta;})L}$

The active power that circuit back segment (η L to L) consumes is:

The active power of total track length consumption is:

$\begin{array}{c}{P}_{s6}=P_{s6}^{\&prime;}+P_{s6}^{\&prime;\&prime;}=3(\mathrm{\&eta;}-\frac{2{\mathrm{\&eta;}}^2}{3}+\frac{{\mathrm{\&eta;}}^3}{5})I^{2}R+\frac{3{(1-\mathrm{\&eta;})}^3}{5}{I}^{2}R\\ \frac{3+6\mathrm{\&eta;}-{\mathrm{\&eta;}}^2}{5}{I}^{2}R=K_{s6}\&times;I^{2}R\end{array}$

By above analysis, load is after distributing along the line and first evenly increasing in even minimizing situation, and power load distributing coefficient is got

(7) load distributes along the line and first evenly reduces, rear even increase

As shown in Figure 8, as 0<=Lx< η L, do not consider the load of η L to L this section of circuit, in the active power of Lx place line transmission be:

$P_{\left(7\right)}^{\&prime;}={\&Integral;}_{Lx}^{\mathrm{\&eta;}L}\frac{-p^{\&prime;}(Lx-\mathrm{\&eta;}L)}{\mathrm{\&eta;}L}dLx=\frac{p^{\&prime;}{(\mathrm{\&eta;}L-Lx)}^2}{2\mathrm{\&eta;}L}$

As η L<=Lx<=L, in the active power of Lx place line transmission be:

$P_{\left(7\right)}^{\&prime;\&prime;}={\&Integral;}_{Lx}^L\frac{p^{\&prime;}(Lx-\mathrm{\&eta;}L)}{(1-\mathrm{\&eta;})L}dLx=\frac{p^{\&prime;}\&lsqb;(1-2\mathrm{\&eta;})L^2-{\mathrm{Lx}}^2+2\mathrm{\&eta;}LLx\&rsqb;}{2(1-\mathrm{\&eta;})L}$

As 0<=Lx< η L, consider the load of η L to L this section of circuit, in the active power of Lx place line transmission be:

$P_7^{\&prime;}=P_{\left(7\right)}^{\&prime;}+P_{\left(7\right)}^{\&prime;\&prime;}{|}_{Lx=\mathrm{\&eta;}L}=\frac{p^{\&prime;}{(\mathrm{\&eta;}L-Lx)}^2}{2\mathrm{\&eta;}L}+\frac{p^{\&prime;}(1-\mathrm{\&eta;})L}{2}=\frac{p^{\&prime;}({\mathrm{Lx}}^2-2\mathrm{\&eta;}LLx+{\mathrm{\&eta;L}}^2)}{2\mathrm{\&eta;}L}$

As Lx=0, P be had ₇'=P ₁, then need: p'=2p

The active power that circuit leading portion (0 to η L) consumes is:

As η L<=Lx<=L,

$P_7^{\&prime;\&prime;}=P_{\left(7\right)}^{\&prime;\&prime;}=\frac{p^{\&prime;}\&lsqb;(1-2\mathrm{\&eta;})L^2-{\mathrm{Lx}}^2+2\mathrm{\&eta;}LLx\&rsqb;}{2(1-\mathrm{\&eta;})L}=\frac{p\&lsqb;(1-2\mathrm{\&eta;})L^2-{\mathrm{Lx}}^2+2\mathrm{\&eta;}LLx\&rsqb;}{(1-\mathrm{\&eta;})L}$

The active power that circuit back segment (η L to L) consumes is:

The active power of total track length consumption is:

$\begin{array}{c}{P}_{s7}=P_{s7}^{\&prime;}+P_{s7}^{\&prime;\&prime;}=3(\mathrm{\&eta;}-\frac{4{\mathrm{\&eta;}}^2}{3}+\frac{8{\mathrm{\&eta;}}^3}{15})I^{2}R+\frac{8}{5}{(1-\mathrm{\&eta;})}^3{I}^{2}R\\ =\frac{4{\mathrm{\&eta;}}^2-9\mathrm{\&eta;}+8}{5}{I}^{2}R=K_{s7}\&times;I^{2}R\end{array}$

By above analysis, load is after distributing along the line and first evenly reducing in even increase situation, and power load distributing coefficient is got

Two: substation transformer winding loss calculates (transformer copper loss)

Transformer copper loss is divided into basic copper loss and additional copper loss two parts, the former refers to the ohmic loss that a winding and Secondary Winding electric current cause in the windings, the latter is a part of copper loss additionally increased due to kelvin effect and proximity effect, and numerical value is less, negligible.The loss value sum that the resistance that copper loss can be expressed as former secondary coil causes.Then copper loss P _cuexpression formula is as follows:

$P_{Cu}=\underset{i=1}{\overset{m_r}{\mathrm{\&Sigma;}}}{\mathrm{\&Delta;P}}_{ki}\&times;{\left(\frac{I_{pi}}{I_{ei}}\right)}^2$

Wherein, m _tit is the total number of units of circuit substation transformer; Δ P _kiit is the i-th station power distribution transformer short-circuit loss power; I _piit is the electric current flowing through the i-th station power distribution transformer; I _giit is the i-th station power distribution transformer rated current.

Three: substation transformer core loss calculates (transformer iron loss)

Transformer iron loss can be divided into basic iron loss and additional iron losses, and the former refers to that the magnetic hysteresis that main flux causes in the core which under normal circumstances flows loss with misfortune; The latter comprises because silicon steel sheet insulating damages the local eddy currents loss caused in the core which and the eddy current loss etc. caused in structure member, negligible.Then, iron loss P _feexpression formula is as follows:

$P_{Fe}=\underset{i=1}{\overset{m_r}{\mathrm{\&Sigma;}}}{\mathrm{\&Delta;P}}_{0i}\&times;{\left(\frac{U_{avi}}{U_{fi}}\right)}^2$

Wherein, m _tit is the total number of units of circuit substation transformer; Δ P _oithe i-th station power distribution transformer noload losses power; U _fithe i-th station power distribution load tap changer voltage (kV); U _avithe i-th station power distribution transformer access point voltage.

In sum, theoretical line loss caluclation flow process as shown in Figure 1, calculates basic routing line loss; Branch Computed line loss; Distribution transforming copper loss contained by computational scheme; Distribution transforming iron loss contained by computational scheme; The result of calculation sum of above-mentioned steps, is theory wire loss.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (6)

1. a medium-voltage distribution circuit theoretical line loss caluclation method, is characterized in that, comprise the steps:

(1) basic routing line loss is calculated;

(2) Branch Computed line loss;

(3) distribution transforming copper loss contained by computational scheme;

(4) distribution transforming iron loss contained by computational scheme;

(5) the result of calculation sum of step (1) to (4), is theory wire loss.

2. a kind of medium-voltage distribution circuit theoretical line loss caluclation method according to claim 1, it is characterized in that, the computing method of described basic routing line loss are:

P _main=α I ²rl

Wherein, α is trunk power load distributing coefficient, and I is trunk outlet electric current, and r is trunk resistance per unit length, and l is beam length.

3. a kind of medium-voltage distribution circuit theoretical line loss caluclation method according to claim 2, it is characterized in that, the defining method of trunk power load distributing factor alpha is:

A, load are uniformly distributed along the line, and trunk power load distributing factor alpha value is 1;

B, load are evenly distributed minimizing along the line, and trunk power load distributing factor alpha value is 3/5;

C, load are evenly distributed increase along the line, and trunk power load distributing factor alpha value is 8/5;

D, the load first half section that distributes along the line evenly increases, and the second half section evenly reduces, and trunk power load distributing factor alpha value is 23/20;

The first half section that E, load distributes along the line evenly reduces, and the second half section evenly increases, and trunk power load distributing factor alpha value is 9/10;

F, load distribute along the line first evenly to be increased, rear even minimizing, and trunk power load distributing factor alpha value is:

Wherein, η is that load increases the separation reduced with load;

G, load distribute along the line and first evenly reduce, rear even increase, and trunk power load distributing factor alpha value is:

Wherein, η is that load reduces the separation increased with load.

4. a kind of medium-voltage distribution circuit theoretical line loss caluclation method according to claim 1, it is characterized in that, the computing method of described branched line loss are:

P _point=I _b ²r _bl _b

Wherein, I _bfor branched line average current, r _bfor branching unit length resistance, l _bfor branch length.

5. a kind of medium-voltage distribution circuit theoretical line loss caluclation method according to claim 1, it is characterized in that, the computing method of described distribution transforming copper loss are:

Wherein, m _tit is the total number of units of circuit substation transformer; Δ P _kiit is the i-th station power distribution transformer short-circuit loss power; I _piit is the electric current flowing through the i-th station power distribution transformer; I _giit is the i-th station power distribution transformer rated current.

6. a kind of medium-voltage distribution circuit theoretical line loss caluclation method according to claim 1, it is characterized in that, the computing method of described distribution transforming iron loss are:

Wherein, m _tit is the total number of units of circuit substation transformer; Δ P _oithe i-th station power distribution transformer noload losses power; U _fithe i-th station power distribution load tap changer voltage (kV); U _avithe i-th station power distribution transformer access point voltage.