CN105703371A - Economic operation control method for distribution transformer - Google Patents

Abstract

The invention discloses an economic operation control method for a distribution transformer. The method comprises the following steps: predicted load data in each time period within a switching cycle in a certain area are acquired; fitting is carried out on the predicted load data, and a fitting cosine function curve is acquired; comprehensive power loss in the case of independent operation and combined operation by multiple distribution transformers participating in switching in the certain area is acquired; according to the relationship between the comprehensive power loss and the load, a critical load point is acquired; according to the critical load point and the fitting cosine function curve, all switching points are acquired; the switching cost and the electric price of all switching points are calculated; according to the switching cost and the electric price, a probability histogram is used for acquiring electricity saving benefits of all switching points; and according to the electricity saving benefits of all switching points and the switching times of the multiple distribution transformers participating in switching, the best switching strategy is acquired. The economic operation control method for the distribution transformer has the advantages that the electric energy loss can be reduced, the working service life of the transformer can be added, and the energy can be saved.

Description

A kind of economical operation control method of distribution transformer

Technical field

The present invention relates to transformator switching technical field, more particularly relate to the economical operation control method of a kind of distribution transformer。

Background technology

Industrial and agricultural production development, living standards of the people improve constantly in recent years, and the demand of electric energy is also increased sharply by society。Although power industry develops quickly, still can not meet the needs of the daily production of people and life, still suffer from the situation of Severe Power Shortage in some areas of China。Electric energy profound influence the development of national economy simultaneously。While greatly developing economy, it would be desirable to reduce electric energy loss by fair means or foul, improve the utilization rate of electric energy。Distribution system transformator is the very important electrical device in power system, and major function is conversion and distribution electric energy。Its total quantity and total installed capacity are all very big, and from power plant offer electric energy Transmission Lines electric energy to the process of customer consumption electricity, the loss that transformator produces probably accounts for 30 the percent of whole grid loss, constitutes about the 10 of gross generation。Simultaneously because transformator is when conversion voltage and electric energy transmit, meritorious, reactive power loss can be caused, so transformator is also the electrical equipment that power attenuation is relatively larger。For the whole nation, the electric energy loss that transformator causes for a year is sizable。

The economical operation of transformator is exactly excavate the electric energy potentiality that in transformator electric energy loss, part is wasted, and is the important aspect of the economical operation reducing power system line loss, implementation power system。

First the economical operation of transformator is the needs meeting people's electricity consumption, and simultaneously power system also is able on the basis run safely and reliably, selects the working method that transformer loss is minimum。By the load of Reasonable adjustment transformator, transformer station is carried out the modes such as transformation, as much as possible reduce transformator electricity and damage。And wherein selecting the minimum working condition of transformator electric energy loss is main contents therein。The a set of best switching scheme of preferably calculating according to transformator working method is great for electrical network energy-saving significance。

What transformer economic operation was interval obtains a kind of method that comparison is classical, and this method is exactly breakthrough technique, determines the economical operation of transformator typically by this way。The way that this method divides optimized operation zone is infallible, but load curve is not dealt with by this way, say, that the switch behave number of times of transformer station can be a lot, and in real work, the switching frequency of transformator is also limited。In practical operation, it is also contemplated that because changing the switching cost that transformer operation manners causes。Thus, the transformer group of transformer station enters optimized operation zone work can not ensure it is save electric energy, and this even can cause reverse effect because of high cost, causes final loss。

Summary of the invention

The embodiment of the present invention provides the economical operation control method of a kind of distribution transformer, reduces electric energy loss, increases the working life of transformator, saves cost。

The embodiment of the present invention provides the economical operation control method of a kind of distribution transformer, comprises the following steps:

(1) the prediction load data of each time period that obtains certain region within the switching cycle；

(2) use nonlinear least square method that described prediction load data is fitted, it is thus achieved that matching cosine function curve；

(3) power loss during multiple distribution transformer independent operatings and the combined running of certain region participation switching is obtained；

(4) relation of power loss time according to multiple distribution transformer independent operatings and combined running and load, it is thus achieved that critical load point；

(5) according to critical load point and matching cosine function curve, it is thus achieved that all switching points；

(6) switching cost and the electricity price of all switchings point are obtained；

(7) according to the switching cost of all switching points and electricity price, probability histogram is utilized to obtain the economize on electricity profit of all switching points；

(8) the economize on electricity profit according to all switching points, and participate in the switching frequency of multiple distribution transformers of switching, it is thus achieved that best Switching Strategy。

Further, the multiple distribution transformers participating in switching in above-mentioned steps (3) are two double winding distribution transformers, respectively the first distribution transformer and the second distribution transformer, power loss when participating in multiple transformator independent operatings and the combined running of switching in described step (3) is: power loss when power loss when power loss during the first distribution transformer independent operating, the second distribution transformer independent operating and the first distribution transformer and the second distribution transformer paired running。

Further, in above-mentioned steps (4), it is thus achieved that critical load point comprises the following steps:

A, acquisition participate in the first distribution transformer of switching and the rated capacity S of the second distribution transformer_N, no-load current I₀, open circuit loss P₀, short-circuit voltage U_kWith short circuit loss P_k；

Described rated capacity S_NComputing formula beWherein U_NFor rated voltage；I_NFor rated current；

Described no-load current I₀Computing formula beWherein I₀% is the percentage ratio shared by no-load current, I_1NIt is the first distribution transformer or load current value that the second distribution transformer is once surveyed；

Described open circuit loss P₀Being under rated voltage, electric current time in distribution transformer iron core without any load makes produced loss when sexually revising of magnetic flux generating period, and computing formula is P₀=P_h+P_b+P_s, wherein P_hFor magnetic hystersis loss, P_bFor eddy-current loss, P_hAnd P_bBoth are calculated by no load test sum, also referred to as basic iron loss；Ps is added losses, takes the 17% of basic iron loss；

Described short-circuit voltage U_kComputing formula beWherein, U_1NIt is the first distribution transformer or load voltage value that the second distribution transformer is once surveyed；

Described short circuit loss P_kComputing formula be P_k=P_r+P_s=I_1N ²r₁+I_2N ²r₂+P_s, wherein Pr is basic short circuit loss, and Ps is added losses, I_1NIt is the first distribution transformer or load current value that the second distribution transformer is once surveyed, r₁It is the first distribution transformer or rated value of resistance that the second distribution transformer is once surveyed, I_2NIt is the first distribution transformer or the load current value of the second distribution transformer secondary survey, r₂It is the first distribution transformer or the rated value of resistance of the second distribution transformer secondary survey；

B, calculate the leakage field reactive power Q of the first distribution transformer and the second distribution transformer participating in switching according to formula (1)～formula (2)₀；Leakage field reactive power Q₀Computing formula be:

$Q_0=\sqrt{{S_0}^2-{P_0}^2}---\left(1\right);$

Wherein S₀Computing formula be

The excitation reactive power power Q of the first distribution transformer and the second distribution transformer participating in switching is calculated according to formula (3)～formula (4)_k；Excitation reactive power power Q_kComputing formula be

$Q_k=\sqrt{{S_k}^2-{P_k}^2}---\left(3\right);$

Wherein S_kComputing formula be

C, according to formula (5) calculate participate in switching the first distribution transformer independent operating time power attenuation Δ P_Z1, power attenuation Δ P during the second distribution transformer independent operating_Z2；

${\mathrm{\ΔP}}_Z=P_{0Z}+{\left(\frac{S}{S_N}\right)}^2{P}_{KZ}---\left(5\right)$

In formula (5), S is actual loading when actual loading during the first distribution transformer independent operating or the second distribution transformer independent operating；S_NIt it is the rated capacity of the first distribution transformer rated capacity or the second distribution transformer；

In formula (5), P_ozUnloaded power loss when unloaded power loss when being the first distribution transformer independent operating or the second distribution transformer independent operating；It is calculated according to formula (6),

P_0Z=p₀+K_QQ₀+K_PP₀(6)

In formula (6), P₀With Q₀The respectively open circuit loss of distribution transformer itself and leakage field reactive power；K_QFor reactive distribution, computing formula isΔP_QThe value added of active power loss in caused power network is increased for reactive loss in distribution transformer；Δ Δ Q is the increasing value of Reactive Power in Distributing Transformer loss；K_pFor active power Economic Equivalent, computing formula isΔP_PIncrease amount for the power network active loss that the increase of active loss among transformator causes；Δ Δ P is the increasing value of the active power loss of transformator；

In formula (5), P_kzIt it is load power loss when load power loss during the first distribution transformer independent operating or the second distribution transformer independent operating；It is calculated according to formula (7)；

P_kZ=P_k+K_QQ_k+K_PP_k(7)

P in formula (7)_kFor participating in the short circuit loss of the distribution transformer of switching, Q_kReactive power loss during for distribution transformer short circuit and excitation loss, computing formula isWherein S_kComputing formula be

Power loss Δ P when the first distribution transformer and the second distribution transformer paired running is calculated according to formula (8)_Z12；

ΔP_Z12=Δ P_Z1+ΔP_Z2(8)；

Power loss curve when power loss curve when D, power loss curve when drawing the first distribution transformer independent operating participating in switching in the coordinate system of same load and loss, the second distribution transformer independent operating and the first distribution transformer and the second distribution transformer paired running；

E calculates critical load point；

Power attenuation Δ P when the first distribution transformer independent operating_Z1Power attenuation Δ during with the second distribution transformer independent operating_PZ2Time equal, try to achieve the first critical load point S^1～2；

Power attenuation Δ P when the first distribution transformer independent operating_Z1Power loss Δ P during with the first distribution transformer and the second distribution transformer paired running_Z12Time equal, try to achieve the second critical load point S^1～12；

Power attenuation Δ P when the second distribution transformer independent operating_Z2Power loss Δ P during with the first distribution transformer and the second distribution transformer paired running_Z12Time equal, try to achieve the 3rd critical load point S^2～12。

Further, the switching cost of all switching points described in step (6), utilize triangle probability distribution to ask for, described electricity price also utilizes triangle probability distribution to ask for。

The present invention having the beneficial effects that compared with prior art:

Transformator is according to the switching frequency switching point switching in bigger economize on electricity profit, it is possible to reduce electric energy loss；Increasing the working life of transformator, save the energy, when energy scarcity now, the energy-conservation sustainable development to realizing national economy has very important significance。

Accompanying drawing explanation

In order to be illustrated more clearly that the embodiment of the present invention or technical scheme of the prior art, the accompanying drawing used required in embodiment or description of the prior art will be briefly described below, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the premise not paying creative work, it is also possible to obtain other accompanying drawing according to these accompanying drawings。

Fig. 1 is the FB(flow block) of the present invention。

Fig. 2 is embodiment of the present invention transformer station original loads 60 day data and matching cosine function curve。

Fig. 3 is three kinds of situation loss figure of two distribution transformers of the embodiment of the present invention。

Fig. 4 is embodiment of the present invention matching cosine function curve and critical point straight line intersection figure。

Fig. 5 (a) is the economize on electricity profit probability histogram of the in the embodiment of the present invention the 11st day switching。

Fig. 5 (b) is the economize on electricity profit probability histogram of the in the embodiment of the present invention the 28th day switching。

Fig. 5 (c) is the economize on electricity profit probability histogram of the in the embodiment of the present invention the 45th day switching。

Detailed description of the invention

Below in conjunction with the accompanying drawing in Fig. 1 and the embodiment of the present invention; technical scheme in the embodiment of the present invention is clearly and completely described; obviously; described embodiment is only a part of embodiment of the present invention; rather than whole embodiments; based on the embodiment in the present invention, the every other embodiment that those of ordinary skill in the art obtain under not making creative work premise, broadly fall into the scope of protection of the invention。

As it is shown in figure 1, S1: the prediction load data of each time period that obtains certain region within the switching cycle。

Certain region is that any one at least needs the region that two distribution transformers control, it is possible to be a certain community or a certain transformer station。

The switching cycle is following a period of time, it is possible to be 30 days, 60 days or 1 year。Each time period is at set intervals, and a period of time can be every day, every 12 hours or every 6 hours etc.。

S2: use nonlinear least square method that described prediction load data is fitted, it is thus achieved that matching cosine function curve。

S3: obtain power loss during multiple distribution transformer independent operatings and the combined running of certain region participation switching。

Distribution transformer can be that two or three are even more。

S4: the relation of power loss during according to multiple distribution transformer independent operatings and combined running and load, it is thus achieved that critical load point。

Mathematical formulae relation according to the intersection point of the curve of power loss and load in multiple situation or power loss and load, it is thus achieved that critical load point。

S5: according to critical load point and matching cosine function curve, it is thus achieved that all switching points。

The intersection point of critical load point straight line and matching cosine function curve is all of switching point。

S6: calculate switching cost and the electricity price of all switchings point。

Switching cost and the electricity price of all switching points can be calculated according to triangle probability distribution。

S7: according to described switching cost and electricity price, utilizes probability histogram to obtain the economize on electricity profit of all switching points。

S8: the economize on electricity profit according to all switching points, and participate in the switching frequency of multiple distribution transformers of switching, it is thus achieved that best Switching Strategy。

Setting certain region in the following examples as certain transformer station, the switching cycle is 60 days, and each time period is every day。

(1) related technical data of two double winding distribution transformers of transformer station is as shown in table 1。

Table 1 double winding distribution transformer nominal parameter

(2) the known transformer station load data by load prediction gained in 60 days is as shown in table 2。

Table 2 transformer station prediction load data

Wherein the load data of every day is the meansigma methods of 24 hours integral point load values。

Here set and in 60 days, allow switching frequency as 1 time, it is desirable to calculate the optimum Switching Strategy in 60 days。

(3) matching load data

Use nonlinear least square method by prediction load data fit to time t (my god) cosine function, the transformer station's load prediction data in table 2 is fitted, shown in fitting result such as formula (9)。

G (t)=4553.2cos (2 × π × 1.7696 × t/60-6.8146)+11209 (9)

(4) original predictive load data curve is drawn with matching cosine function curve as shown in Figure 2 with Matlab。

(5) critical load point is obtained

1. according to I₀% and U_k% calculates the leakage field reactive power Q of the first distribution transformer and the second distribution transformer respectively according to formula (10)～(17)₀With excitation reactive power power Q_k。

$S_{01}=\sqrt{3}{I}_{01}{U}_{1N}=I_{10}{\mathrm{\%S}}_{N1}\×{10}^{-2}---\left(10\right)$

$Q_{01}=\sqrt{{S_{01}}^2-{P_{01}}^2}---\left(11\right)$

$S_{k1}=\sqrt{3}{I}_{1N}{U}_{k1}=U_{k1}{\mathrm{\%S}}_{N2}\×{10}^{-2}---\left(12\right)$

$Q_{k1}=\sqrt{{S_{k1}}^2-{P_{k1}}^2}---\left(13\right)$

$S_{02}=\sqrt{3}{I}_{02}{U}_{2N}=I_{02}{\mathrm{\%S}}_{N2}\×{10}^{-2}---\left(14\right)$

$Q_{02}=\sqrt{{S_{02}}^2-{P_{02}}^2}---\left(15\right)$

$S_{k2}=\sqrt{3}{I}_{2N}{U}_k=U_{k2}{\mathrm{\%S}}_{N2}\×{10}^{-2}---\left(16\right)$

$Q_{k2}=\sqrt{{S_{k1}}^2-{P_{k1}}^2}---\left(17\right)$

2. power loss Δ P during the first distribution transformer independent operating is calculated_Z1, power loss Δ P during the second distribution transformer independent operating_Z2, and power loss Δ P when the first distribution transformer and the second distribution transformer paired running_Z12, as formula (18)～(20) calculate。

${\mathrm{\ΔP}}_{ZI}=P_{0Z1}+{\left(\frac{S}{S_{N1}}\right)}^2{P}_{KZ1}---\left(18\right)$

${\mathrm{\ΔP}}_{Z2}=P_{0Z2}+{\left(\frac{S}{S_{N2}}\right)}^2{P}_{KZ2}---\left(19\right)$

${\mathrm{\ΔP}}_{Z12}={\mathrm{\ΔP}}_{Z1}+{\mathrm{\ΔP}}_{Z2}+{\left(\frac{S}{S_{N1}+S_{N2}}\right)}^2(P_{KZ1}+P_{KZ2})---\left(20\right)$

Wherein, S (kVA) is current actual load, P_0zAnd P_kzAs formula (21), (22) calculate。

P_0Z=P₀+K_QQ₀(21)

P_KZ=P_K+K_QQ_K(22)

3., in the same coordinate system, the load damage curve of three kinds of different ruuning situations of distribution transformer is drawn, as shown in Figure 3。

4. critical load point is calculated。

Make formula (18), (19) equal, obtain shown in critical load point such as formula (23)。

$S^{1~2}=S_{N1}{S}_{N2}\sqrt{\frac{P_{0Z2}-P_{0Z1}}{{S_{N2}}^2{P}_{KZ1}-{S_{N1}}^2{P}_{KZ2}}}---\left(23\right)$

Make formula (18) equal with (20), obtain shown in critical load point such as formula (24)。

$S^{1~12}=S_{N1}(S_{N1}+S_{N2})\sqrt{\frac{P_{0Z2}}{(2S_{N1}{S}_{N2}+{S_{N2}}^2)P_{KZ1}-{S_{N1}}^2{P}_{KZ2}}}---\left(24\right)$

Make formula (19) equal with (20), obtain shown in critical load point such as formula (25)。

$S^{2~12}=S_{N2}(S_{N1}+S_{N2})\sqrt{\frac{P_{0Z1}}{(2S_{N1}{S}_{N2}+{S_{N1}}^2)P_{KZ2}-{S_{N2}}^2{P}_{KZ1}}}---\left(25\right)$

As it is shown on figure 3, with Matlab program critical load point is S^1～2=3820.1；S^1～12=11377；S^2～12=6123.8；

Minimum critical load point is S^1～2=3820.1, maximum critical load point is S^1～12=11377, economic work interval division is as follows:

Economic work interval 1: during load S < 3820.1, the second distribution transformer works alone and relatively economizes on electricity；

Economic work interval 2: during load 3820.1 < S < 11377, the first distribution transformer works alone and relatively economizes on electricity；

Economic work interval 3: during load 11377 < S, the first distribution transformer and the second distribution transformer work side by side and relatively economize on electricity。

(6) all switchings point is obtained

With critical load point straight line S^1～2=3820.1；S^2～12=6123.8 and S^1～12=11377 intersect with load curve g (t) of matching respectively, calculate all of switching point, as shown in Figure 4。

As can be drawn from Figure 4 all switching points be t1=11, t2=28 and t3=45 (my god)

When t1=11 days, the second distribution transformer is deactivated, and changes the first distribution transformer into and works alone；

When t2=28 days, the second distribution transformer is deactivated, and changes the first distribution transformer into and the second distribution transformer works side by side；

When t3=45 days, the second distribution transformer is deactivated, and changes the first distribution transformer into and works alone。

(7) best Switching Strategy is asked for

Best Switching Strategy is relevant with the economize on electricity profit of the number of switching point, switching frequency and switching point, and switching frequency less than the number of switching point, must be chosen the big switching point of economize on electricity profit according to switching frequency and carry out the Switching Strategy that switching is the best。

Switching cost and electricity price randomization are calculated, calculate t1=11 (my god), t2=28 (my god), t3=45 (my god) switching benefit, the difference between the two is economize on electricity profit。

T1=11 (my god), t2=28 (my god), t3=45 (my god) economize on electricity profit probability histogram such as Fig. 5 (a), Fig. 5 (b) and Fig. 5 (c) shown in。

Maximum economize on electricity profit respectively G11=-1000 (unit) during maximum probability value；G28=2500 (unit)；G45=-1000 (unit)。

If only allowing 1 switching in 60 days, the then switching when obtaining maximum economize on electricity profit G28=2500 (unit), optimum Switching Strategy is (when assuming without switching, transformer station's the first distribution transformer works alone), when t2=28 days, worked by the first distribution transformer, change the first distribution transformer into and the second distribution transformer works side by side。

The switching cycle can be following 30 days, 60 days or 1 year, and with regard to the size of profit of economizing on electricity, the switching cycle is equivalent to more greatly provide the more time for the acquirement of profit of economizing on electricity。Optimum Switching Strategy has two kinds of situations: a kind of situation is within the switching cycle, it is stipulated that the restriction of switching frequency, asks for best switching scheme；Another kind of situation is in the switching cycle, it does not have regulation switching frequency limit, asks for best switching scheme, and this " switching frequency being not specified by " must within possible switching point sum。

Transformator is at best switching time switching, it is possible to reduce electric energy loss；The service life of the transformator being operated in optimized operation zone can largely be extended；Saving the energy, when energy scarcity now, the energy-conservation sustainable development to realizing national economy has very important significance。

Although preferred embodiments of the present invention have been described, but those skilled in the art are once know basic creative concept, then these embodiments can be made other change and amendment。So, claims are intended to be construed to include preferred embodiment and fall into all changes and the amendment of the scope of the invention。

Obviously, the present invention can be carried out various change and modification without deviating from the spirit and scope of the present invention by those skilled in the art。So, if these amendments of the present invention and modification belong within the scope of the claims in the present invention and equivalent technologies thereof, then the present invention is also intended to comprise these change and modification。

Claims (4)

1. the economical operation control method of a distribution transformer, it is characterised in that comprise the following steps:

(1) the prediction load data of each time period that obtains certain region within the switching cycle；

(2) use nonlinear least square method that described prediction load data is fitted, it is thus achieved that matching cosine function curve；

(3) power loss during multiple distribution transformer independent operatings and the combined running of certain region participation switching is obtained；

(4) relation of power loss time according to multiple distribution transformer independent operatings and combined running and load, it is thus achieved that critical load point；

(5) according to critical load point and matching cosine function curve, it is thus achieved that all switching points；

(6) switching cost and the electricity price of all switchings point are calculated；

(7) according to described switching cost and electricity price, probability histogram is utilized to obtain the economize on electricity profit of all switching points；

(8) the economize on electricity profit according to all switching points, and participate in the switching frequency of multiple distribution transformers of switching, it is thus achieved that best Switching Strategy。

2. the economical operation control method of distribution transformer as claimed in claim 1, it is characterized in that, the multiple distribution transformers participating in switching in described step (3) are two double winding distribution transformers, respectively the first distribution transformer and the second distribution transformer, power loss when participating in multiple transformator independent operatings and the combined running of switching in described step (3) is: power loss during the first distribution transformer independent operating, power loss when power loss during the second distribution transformer independent operating and the first distribution transformer and the second distribution transformer paired running。

3. the economical operation control method of distribution transformer as claimed in claim 2, it is characterised in that in described step (4), it is thus achieved that critical load point comprises the following steps:

A, acquisition participate in the first distribution transformer of switching and the rated capacity S of the second distribution transformer_N, no-load current I₀, open circuit loss P₀, short-circuit voltage U_kWith short circuit loss P_k；

Described rated capacity S_NComputing formula beWherein U_NFor rated voltage；I_NFor rated current；

Described no-load current I₀Computing formula beWherein I₀% is the percentage ratio shared by no-load current, I_1NIt is the first distribution transformer or load current value that the second distribution transformer is once surveyed；

Described open circuit loss P₀Being under rated voltage, electric current time in distribution transformer iron core without any load makes produced loss when sexually revising of magnetic flux generating period, and computing formula is P₀=P_h+P_b+P_s, wherein P_hFor magnetic hystersis loss, P_bFor eddy-current loss, P_hAnd P_bBoth are calculated by no load test sum, also referred to as basic iron loss；Ps is added losses, takes the 17% of basic iron loss；

Described short-circuit voltage U_kComputing formula beWherein, U_1NIt is the first distribution transformer or load voltage value that the second distribution transformer is once surveyed；

Described short circuit loss P_kComputing formula be P_k=P_r+P_s=I_1N ²r₁+I_2N ²r₂+P_s, wherein Pr is basic short circuit loss, and Ps is added losses, I_1NIt is the first distribution transformer or load current value that the second distribution transformer is once surveyed, r₁It is the first distribution transformer or rated value of resistance that the second distribution transformer is once surveyed, I_2NIt is the first distribution transformer or the load current value of the second distribution transformer secondary survey, r₂It is the first distribution transformer or the rated value of resistance of the second distribution transformer secondary survey；

B, calculate the leakage field reactive power Q of the first distribution transformer and the second distribution transformer participating in switching according to formula (1)～formula (2)₀；Leakage field reactive power Q₀Computing formula be:

$Q_0=\sqrt{{S_0}^2-{P_0}^2}---\left(1\right);$

Wherein S₀Computing formula be

The excitation reactive power power Q of the first distribution transformer and the second distribution transformer participating in switching is calculated according to formula (3)～formula (4)_k；Excitation reactive power power Q_kComputing formula be

$Q_k=\sqrt{{S_k}^2-{P_k}^2}---\left(3\right);$

Wherein S_kComputing formula be

C, according to formula (5) calculate participate in switching the first distribution transformer independent operating time power attenuation Δ P_Z1, power attenuation Δ P during the second distribution transformer independent operating_Z2；

${\mathrm{\&Delta;P}}_Z=P_{0Z}+{\left(\frac{S}{S_N}\right)}^2{P}_{KZ}---\left(5\right)$

In formula (5), S is actual loading when actual loading during the first distribution transformer independent operating or the second distribution transformer independent operating；S_NIt it is the rated capacity of the first distribution transformer rated capacity or the second distribution transformer；

In formula (5), P_ozUnloaded power loss when unloaded power loss when being the first distribution transformer independent operating or the second distribution transformer independent operating；It is calculated according to formula (6),

P_0Z=P₀+K_QQ₀+K_PP₀(6)

In formula (6), P₀With Q₀The respectively open circuit loss of distribution transformer itself and leakage field reactive power；K_QFor reactive distribution, computing formula isΔP_QThe value added of active power loss in caused power network is increased for reactive loss in distribution transformer；Δ Δ Q is the increasing value of Reactive Power in Distributing Transformer loss；K_pFor active power Economic Equivalent, computing formula isΔP_PIncrease amount for the power network active loss that the increase of active loss among transformator causes；Δ Δ P is the increasing value of the active power loss of transformator；

In formula (5), P_kzIt it is load power loss when load power loss during the first distribution transformer independent operating or the second distribution transformer independent operating；It is calculated according to formula (7)；

P_kZ=P_k+K_QQ_k+K_PP_k(7)

P in formula (7)_kFor participating in the short circuit loss of the distribution transformer of switching, Q_kReactive power loss during for distribution transformer short circuit and excitation loss, computing formula isWherein S_kComputing formula be

Power loss Δ P when the first distribution transformer and the second distribution transformer paired running is calculated according to formula (8)_Z12；

ΔP_Z12=Δ P_Z1+ΔP_Z2(8)；

Power loss curve when power loss curve when D, power loss curve when drawing the first distribution transformer independent operating participating in switching in the coordinate system of same load and loss, the second distribution transformer independent operating and the first distribution transformer and the second distribution transformer paired running；

E calculates critical load point；

Power attenuation Δ P when the first distribution transformer independent operating_Z1Power attenuation Δ P during with the second distribution transformer independent operating_Z2Time equal, try to achieve the first critical load point S^1～2；

Power attenuation Δ P when the first distribution transformer independent operating_Z1Power loss Δ P during with the first distribution transformer and the second distribution transformer paired running_Z12Time equal, try to achieve the second critical load point S^1～12；

Power attenuation Δ P when the second distribution transformer independent operating_Z2Power loss Δ P during with the first distribution transformer and the second distribution transformer paired running_Z12Time equal, try to achieve the 3rd critical load point S^2～12。

4. the economical operation control method of distribution transformer as claimed in claim 1, it is characterized in that, the switching cost of all switching points described in step (6), utilizes triangle probability distribution to ask for, and described electricity price also utilizes triangle probability distribution to ask for。