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

Abstract

The invention discloses a method for controlling the economical operation of a distribution transformer, comprising the following steps: obtaining forecasted load data in each time period of a switching cycle in a certain area; fitting the forecasted load data to obtain a fitted cosine function curve ; Obtain the comprehensive power loss of multiple distribution transformers participating in switching in a certain area during independent operation and combined operation; according to the relationship between the comprehensive power loss and the load, obtain the critical load point; according to the critical load point and the fitting cosine function curve , to obtain all switching points; calculate the switching cost and electricity price of all switching points; according to the switching cost and electricity price, use the probability histogram to obtain the power saving profit of all switching points; according to the power saving of all switching points Profit, as well as the switching times of multiple distribution transformers involved in switching, obtain the best switching strategy. This economical operation control method of distribution transformers can reduce power loss; it can increase the working life of transformers and save energy. .

Description

A control method for economical operation of distribution transformers

technical field

The invention relates to the technical field of transformer switching, in particular to a control method for economical operation of distribution transformers.

Background technique

In recent years, with the continuous development of industrial and agricultural production and the continuous improvement of people's living standards, the society's demand for electric energy has also increased rapidly. Despite the rapid development of the power industry, it still cannot meet the needs of people's daily production and life, and there are still severe power shortages in some areas of our country. At the same time, electric energy has a profound impact on the development of the national economy. While vigorously developing the economy, we need to do everything possible to reduce power consumption and improve the utilization rate of power. Distribution system transformer is a very important power device in the power system, and its main function is to convert and distribute electric energy. Its total quantity and total installed capacity are very large. During the process from the power plant providing power transmission line to the user's consumption of power, the loss generated by the transformer accounts for about 30% of the entire power grid loss, accounting for about 30% of the total power grid loss. ten percent of the electricity produced. At the same time, since the transformer will cause active and reactive power loss when converting voltage and electric energy transmission, the transformer is also an electrical device with relatively large power loss. For the whole country, the annual power loss caused by the transformer is quite large.

The economical operation of the transformer is to tap the wasted power potential in the power loss of the transformer. It is an important plan to reduce the line loss of the power system and implement the economical operation of the power system.

The economical operation of the transformer is firstly to meet people's needs for electricity consumption, and at the same time, on the basis of the safe and reliable operation of the power system, select the working mode with the least loss of the transformer. By rationally adjusting the load of the transformer and transforming the substation, etc., the power loss of the transformer can be reduced as much as possible. Among them, selecting the working condition with the smallest power loss of the transformer is the main content. Calculating a set of optimal switching schemes based on the optimal working mode of transformers is of great significance for power grid energy saving.

There is a more classic method to obtain the economical operation range of transformers. This method is the critical point method, which is usually used to determine the economical operation of transformers. This method of dividing the economic operation interval is indeed reliable, but this method does not deal with the load curve, that is to say, the switching times of the substation will be many, and in actual work, the switching times of the transformer are also limited. In actual operation, the switching cost caused by changing the operation mode of the transformer should also be considered. Therefore, the operation of the transformer group in the substation in the economical operating range cannot guarantee the saving of electric energy, which may even lead to the opposite effect due to the high cost, resulting in a final loss.

Contents of the invention

The embodiment of the present invention provides an economical operation control method of a power distribution transformer, which reduces power loss, increases the working life of the transformer, and saves costs.

An embodiment of the present invention provides a method for controlling economical operation of a distribution transformer, including the following steps:

(1) Obtain the forecasted load data of a certain area in each time period in the switching cycle;

(2) Fitting the predicted load data using the nonlinear least squares method to obtain a fitted cosine function curve;

(3) Obtain the comprehensive power loss of multiple distribution transformers participating in switching in a certain area during independent operation and combined operation;

(4) Obtain the critical load point according to the relationship between the comprehensive power loss and the load when multiple distribution transformers operate independently and in combination;

(5) According to the critical load point and the fitted cosine function curve, all switching points are obtained;

(6) Obtain the switching cost and electricity price of all switching points;

(7) According to the switching cost and electricity price of all switching points, use the probability histogram to obtain the electricity saving profit of all switching points;

(8) According to the power-saving profits of all switching points and the switching times of multiple distribution transformers involved in switching, the optimal switching strategy is obtained.

Further, the plurality of distribution transformers participating in switching in the above step (3) are two double-winding distribution transformers, which are respectively the first distribution transformer and the second distribution transformer, and participating in the switching in the step (3) The comprehensive power loss of multiple transformers cut independently and in combination is: the comprehensive power loss of the first distribution transformer when it operates independently, the comprehensive power loss of the second distribution transformer when it operates independently, and the first distribution transformer and the second distribution transformer. The comprehensive power loss when the two distribution transformers operate in parallel.

Further, in the above-mentioned step (4), obtaining the critical load point includes the following steps:

A. Obtain the rated capacity S _N , no-load current I ₀ , no-load loss P ₀ , short-circuit voltage U _k and short-circuit loss P _k of the first distribution transformer and the second distribution transformer involved in switching;

The formula for calculating the rated capacity _SN is Among them, U _N is the rated voltage; I _N is the rated current;

The calculation formula of the no-load current I ₀ is Among them, I ₀ % is the percentage of no-load current, and I _1N is the rated current value of the first distribution transformer or the second distribution transformer;

The no-load loss P ₀ is the loss generated when the magnetic flux changes periodically due to the current when there is no load in the iron core of the distribution transformer at the rated voltage, and the calculation formula is P ₀ =P _h +P _b + P _s , where _{Ph is the hysteresis loss, P b is the eddy current loss, the sum of Ph and P b is calculated by} the no-load experiment, and is also called the basic iron loss; Ps is the additional loss, which is taken as the basic iron loss 17% is enough;

The calculation formula of the short-circuit voltage _Uk is Among them, U _1N is the rated voltage value of the first distribution transformer or the second distribution transformer;

The calculation formula of the short-circuit loss P _k is P _k =P _r +P _s =I _1N ² r ₁ +I _2N ² r ₂ +P _s , where Pr is the basic short-circuit loss, Ps is the additional loss, and I _1N is the second The rated current value of the first distribution transformer or the second distribution transformer, r ₁ is the rated resistance value of the first distribution transformer or the second distribution transformer, I _2N is the first distribution transformer or the second distribution transformer The rated current value of the secondary measurement of the electric transformer, _r2 is the rated resistance value of the secondary measurement of the first distribution transformer or the second distribution transformer;

B. Calculate the magnetic flux leakage reactive power Q ₀ of the first distribution transformer and the second distribution transformer participating in switching according to formula (1) ~ formula (2); the calculation formula of magnetic flux leakage reactive power Q ₀ is:

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\sqrt{{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

The calculation formula of S ₀ is

Calculate the excitation reactive power Q _{k of the first distribution transformer and the second distribution transformer involved in switching according to formula (3) ~ formula (4); the calculation formula of excitation reactive power Q k is}

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\sqrt{{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

The calculation formula of S _k is

C. According to formula (5), calculate the power loss ΔP _Z1 of the first distribution transformer participating in switching when it operates independently, and the power loss ΔP _Z2 of the second distribution transformer when it operates independently;

${\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; Z</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; S</span>}}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

In formula (5), S is the actual load when the first distribution transformer operates independently or the actual load when the second distribution transformer operates independently; S _N is the rated capacity of the first distribution transformer or the rated capacity of the second distribution transformer capacity;

In formula (5), P _oz is the no-load comprehensive power loss when the first distribution transformer operates independently or the no-load comprehensive power loss when the second distribution transformer operates independently; according to formula (6), it is calculated,

P _0Z ＝p ₀ +K _Q Q ₀ +K _P P ₀ (6)

In formula (6), P ₀ and Q ₀ are the no-load loss and flux leakage reactive power of the distribution transformer, respectively; K _Q is the economic equivalent of reactive power, and the calculation formula is ΔP _Q is the increased value of active power loss in the power grid caused by the increase of reactive power loss in distribution transformers; ΔΔQ is the increased value of reactive power loss in distribution transformers; K _p is the economic equivalent of active power, and the calculation formula is ΔP _P is the increase in the active power loss of the power grid caused by the increase in the active power loss in the transformer; ΔΔP is the increase in the active power loss of the transformer;

In formula (5), P _kz is the load integrated power loss when the first distribution transformer operates independently or the load integrated power loss when the second distribution transformer operates independently; it is calculated according to formula (7);

P _kZ ＝P _k +K _Q Q _k +K _P P _k (7)

In formula (7), P _k is the short-circuit loss of the distribution transformer involved in switching, and Q _k is the reactive power loss when the distribution transformer is short-circuited, that is, the excitation loss. The calculation formula is The calculation formula of S _k is

Calculate the comprehensive power loss ΔP _Z12 when the first distribution transformer and the second distribution transformer operate in parallel according to formula (8);

ΔP _Z12 = ΔP _Z1 + ΔP _Z2 (8);

D. In the same load and loss coordinate system, draw the comprehensive power loss curve of the first distribution transformer participating in switching when it operates independently, the comprehensive power loss curve of the second distribution transformer when it operates independently, and the first distribution transformer and The comprehensive power loss curve when the second distribution transformer operates in parallel;

E calculates the critical load point;

When the power loss ΔP _Z1 of the first distribution transformer in independent operation and the power loss Δ _PZ2 of the second distribution transformer in independent operation are equal, the first critical load point S ^1-2 is obtained;

When the power loss ΔP _Z1 of the first distribution transformer operating independently and the comprehensive power loss ΔP _Z12 of the parallel operation of the first distribution transformer and the second distribution transformer are equal, the second critical load point S ^1-12 is obtained;

When the power loss ΔP _Z2 of the second distribution transformer operating independently is equal to the comprehensive power loss ΔP _Z12 of the first distribution transformer and the second distribution transformer operating in parallel, the third critical load point S ^{2 ~ 12} is obtained.

Further, the switching costs of all switching points mentioned in step (6) are obtained by using a triangular probability distribution, and the electricity price is also obtained by using a triangular probability distribution.

The beneficial effect of the present invention compared with prior art is:

The transformer is switched at the switching point with a large power-saving profit according to the number of switching times, which can reduce power loss; increase the working life of the transformer and save energy. In today's energy shortage situation, energy saving is very important for the sustainable development of the national economy. Significance.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is a flowchart of the present invention.

Fig. 2 is the 60-day data of the original load of the substation and the fitting cosine function curve according to the embodiment of the present invention.

Fig. 3 is a loss diagram of two distribution transformers under three conditions according to the embodiment of the present invention.

Fig. 4 is an intersection diagram of a fitted cosine function curve and a critical point straight line according to an embodiment of the present invention.

Fig. 5(a) is a histogram of electricity-saving profit probability for switching on the 11th day in the embodiment of the present invention.

Fig. 5(b) is a histogram of electricity-saving profit probability for switching on the 28th day in the embodiment of the present invention.

Fig. 5(c) is a histogram of electricity-saving profit probability for switching on the 45th day in the embodiment of the present invention.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with FIG. 1 and the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. For example, based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

As shown in Figure 1, S1: Obtain the forecasted load data of a certain area in each time period of the switching cycle.

A certain area is any area that requires at least two distribution transformers to control, and it can be a certain community or a certain substation.

The switching period is a period of time in the future, which can be 30 days, 60 days or one year. Each period of time is every other period of time, and the period of time may be every day, every 12 hours, or every 6 hours.

S2: Fitting the predicted load data using a nonlinear least square method to obtain a fitted cosine function curve.

S3: Obtain the comprehensive power loss of multiple distribution transformers participating in switching in a certain area when they are operating independently or in combination.

Distribution transformers can be two or three or even more.

S4: Obtain the critical load point according to the relationship between the comprehensive power loss and the load when multiple distribution transformers operate independently or in combination.

The critical load point is obtained according to the intersection of the curves of integrated power loss and load or the mathematical formula relationship between integrated power loss and load in various situations.

S5: According to the critical load point and the fitted cosine function curve, all switching points are obtained.

The intersection points of the critical load point straight line and the fitted cosine function curve are all switching points.

S6: Calculate the switching cost and electricity price of all switching points.

The switching cost and electricity price of all switching points can be calculated according to the triangular probability distribution.

S7: According to the switching cost and electricity price, use the probability histogram to obtain the electricity saving profits of all switching points.

S8: According to the power-saving profits of all switching points and the switching times of multiple distribution transformers involved in switching, the optimal switching strategy is obtained.

In the following embodiment, a certain area is set as a certain substation, the switching cycle is 60 days, and each time period is every day.

(1) The relevant technical data of the two double-winding distribution transformers in the substation are shown in Table 1.

Table 1 Rated parameters of double winding distribution transformer

(2) The load data of known substations within 60 days through load forecasting are shown in Table 2.

Table 2 Substation forecast load data

The daily load data is the average value of the 24-hour hourly load value.

Here, it is set that the number of switching allowed within 60 days is 1, and it is required to calculate the optimal switching strategy within 60 days.

(3) Fitting load data

The predicted load data is fitted to the cosine function of time t (day) using the nonlinear least squares method, and the substation load forecast data in Table 2 are fitted. The fitting results are shown in formula (9).

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

(4) Use Matlab to draw the original predicted load data curve and the fitted cosine function curve as shown in Figure 2.

(5) Obtain the critical load point

① Calculate the magnetic leakage reactive power Q ₀ and excitation reactive power Q _k of the first distribution transformer and the second distribution transformer respectively according to I ₀ % and U _k % according to formulas (10) to (17).

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 10</span>}}{\mathrm{<span\; class="notranslate">\; \%S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 10</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}<span\; class="notranslate">\; =</span>\sqrt{{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 01</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 11</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \%S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\sqrt{{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}{\mathrm{<span\; class="notranslate">\; \%S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}<span\; class="notranslate">\; =</span>\sqrt{{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 02</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\sqrt{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \%S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; 10</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 16</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\sqrt{{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 17</span>}<span\; class="notranslate">\; )</span>$

② Calculate the comprehensive power loss ΔP _Z1 when the first distribution transformer operates independently, the comprehensive power loss ΔP _Z2 when the second distribution transformer operates independently, and the comprehensive power when the first distribution transformer and the second distribution transformer operate in parallel Loss ΔP _Z12 , as calculated by formulas (18) to (20).

${\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; I</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; S</span>}}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 18</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; S</span>}}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 19</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; S</span>}}{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 20</span>}<span\; class="notranslate">\; )</span>$

Among them, S(kVA) is the current actual load, and P _0z and P _kz are calculated according to formulas (21) and (22).

P _0Z ＝P ₀ +K _Q Q ₀ (21)

P K _Z =P _K +K _Q Q _K (22)

③ In the same coordinate system, draw the load loss curves of the distribution transformer under three different operating conditions, as shown in Figure 3.

④ Calculate the critical load point.

Making equations (18) and (19) equal, the critical load point is shown in equation (23).

${\mathrm{<span\; class="notranslate">\; S</span>}}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ~</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; three</span>}<span\; class="notranslate">\; )</span>$

Make equation (18) and (20) equal, and the critical load point is shown in equation (24).

${\mathrm{<span\; class="notranslate">\; S</span>}}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ~</span>\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; four</span>}<span\; class="notranslate">\; )</span>$

Make equation (19) and (20) equal, and the critical load point is shown in equation (25).

${\mathrm{<span\; class="notranslate">\; S</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ~</span>\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; K</span>}\mathrm{<span\; class="notranslate">\; Z</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 25</span>}<span\; class="notranslate">\; )</span>$

As shown in Figure 3, the critical load point programmed with Matlab is S ^1~2 = 3820.1; S ^1~12 = 11377; S ^2~12 = 6123.8;

The minimum critical load point is S ^1～2 = 3820.1, the maximum critical load point is S ^1～12 = 11377, and the economic working range is divided as follows:

Economic working range 1: When the load S<3820.1, the second distribution transformer works independently and relatively saves electricity;

Economic working range 2: When the load is 3820.1<S<11377, the first distribution transformer works independently and relatively saves electricity;

Economic working range 3: When the load is 11377<S, the parallel operation of the first distribution transformer and the second distribution transformer is relatively power-saving.

(6) Obtain all switching points

Use the critical load point straight line S ^1~2 =3820.1; S ^2~12 =6123.8 and S ^1~12 =11377 to intersect with the fitted load curve g(t) respectively, and calculate all switching points, as shown in Figure 4 .

From Fig. 4, it can be drawn that all switching points are t1=11, t2=28 and t3=45 (days)

When t1 = 11 days, the second distribution transformer quits work and changes to the first distribution transformer to work independently;

When t2=28 days, the second distribution transformer quits work, and the first distribution transformer and the second distribution transformer work in parallel;

When t3 = 45 days, the second distribution transformer quits work and changes to the first distribution transformer to work independently.

(7) Find the best switching strategy

The optimal switching strategy is related to the number of switching points, switching times, and the power-saving profit of switching points. Switching at the cut point is the best switching strategy.

Probabilistically calculate the switching cost and electricity price, and calculate the switching benefits of t1=11 (days), t2=28 (days), and t3=45 (days), and the difference between the two is the electricity saving profit.

The histograms of power-saving profit probability for t1=11 (day), t2=28 (day), and t3=45 (day) are shown in Figure 5(a), Figure 5(b) and Figure 5(c).

The maximum power-saving profit at the maximum probability is G11=-1000 (yuan); G28=2500 (yuan); G45=-1000 (yuan).

If only one switch is allowed within 60 days, switch when the maximum power-saving profit G28 = 2500 (yuan), the optimal switch strategy is (assuming that the first distribution transformer of the substation works independently ), and at t2=28 days, the first distribution transformer works instead of the first distribution transformer and the second distribution transformer working in parallel.

The switching cycle can be 30 days, 60 days or one year in the future. In terms of the size of the electricity saving profit, the larger the switching cycle is equivalent to providing more time for obtaining the electricity saving profit. There are two cases of the optimal switching strategy: one is that within the switching period, the limit of switching times is stipulated, and the best switching plan is obtained; the other is that within the switching period, there is no regulation on switching The number of times is limited to find the best switching plan. This "unspecified switching times" must be within the total number of possible switching points.

Switching the transformer at the best switching time can reduce power loss; the service life of the transformer working in the economical operating range can be greatly extended; energy saving, in the current energy shortage situation, energy saving is of great importance to the realization of the national economy. Sustained development is of great significance.

While preferred embodiments of the invention have been described, additional changes and modifications to these embodiments can be made by those skilled in the art once the basic inventive concept is appreciated. Therefore, it is intended that the appended claims be construed to cover the preferred embodiment as well as all changes and modifications which fall within the scope of the invention.

Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and equivalent technologies thereof, the present invention also intends to include these modifications and variations.

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。