JP3355857B2 - Voltage reactive power control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for calculating an optimum voltage reactive power allocation for a power flow state at an arbitrary time section.

[0002]

[Prior art]

(1) The Institute of Electrical Engineers of Japan, Measures to Maintain Voltage Stability in Power Systems, Technical Report of the Institute of Electrical Engineers of Japan No. II-73, 43-45 (1979) The above-mentioned documents are known examples of voltage reactive power control methods. Among them, there are (a) a method using a judgment function, (b) a method of allocating at an equal margin, and (c) a method of allocating with a minimum transmission loss. The method of allocating using the judgment function of (a) is to calculate the amount of change in the judgment function for all the adjustment devices in the target system, select the adjustment device that gives the largest decrease in the judgment function, and adjust the adjustment device within the upper and lower limits of the adjustment. Perform the operation. This process is repeated until the monitoring point constraint is satisfied. Further, in the method (b), a group of generators for adjusting the deviation of the reference voltage of the voltage monitoring device in the power system is previously associated with a system characteristic constant, and each unit in the group is included in the group. Is determined so that the same margin ratio is obtained within the defined reactive power adjustment range. In the method (c) of distributing with the minimum transmission loss, the average value of the deviation from the reference value of the voltage at various points in the system is reduced, and the thermal power of the interconnecting point approaches the reference value. Controls the total value of reactive power.

(2) Japanese Patent Application Laid-Open No. 5-108177 A feature of the method of the known example (2) is that each voltage reactive power control device has a restriction on the number of operations, and a control object having a restriction on the number of operations. By configuring the device to perform control in consideration of the constraint value, an average frequency of use of each control device can be secured, and at the time of a sudden change in demand, the control followability is secured.

[0004]

SUMMARY OF THE INVENTION In the above prior art,
(1) The method (a) has a drawback that the number of repetitions of calculation for adjusting the voltage and the reactive power increases when the voltage and the reactive power amount change significantly. Further, in the method of (1) and (b) of distributing at equal margin rates, the reference voltage needs to be changed when the system configuration of the target power system is significantly changed, and this operation greatly increases the work. In addition, in the method of (1) and (c), in which distribution is performed with the minimum transmission loss, only the adjustment of the reactive power output of the generator is a control variable. The adjustment of the transformer taps needs to be included in the control variables.

Further, the known example (2) is an improvement over the above-mentioned known example in that the restriction on the number of operations of the phase adjustment equipment is taken into account and the number of operations for the same phase adjustment equipment is not concentrated. Since the improvement measure in this known example changes the weight coefficient of the evaluation function of the phase adjustment device, it is necessary to change the weight coefficient for the evaluation function every time the system state changes or the control target device changes. is there. For this reason, the calculation efficiency does not increase, and there is a problem in using it as online control.

[0006] The voltage reactive power control device in the prior art is based on the concept that voltage reactive power control devices in all the target power systems are considered to be controlled, that is, the concept of performing so-called collective control of the entire system. Reactive power control is being performed. In this method of collective operation of the entire system, the solution obtained by the calculation may not meet the guidelines for the actual operation of the power system. For example, it is a case where the operation of the generator reactive power output farther from the voltage control bus having a higher operation sensitivity to the voltage than that of the phase adjusting device around the voltage control bus having the lower operation sensitivity to the voltage is selected as optimal. Similarly, in the known example (1), since the voltage sensitivity coefficients of the individual voltage reactive power control devices are obtained collectively for the entire system, the phenomenon of device selection as described above occurs. for that reason,
Without consistent voltage control, control results often differ from realistic operations.

According to the present invention, the target system is dynamically divided into sub-systems, and the reactive power is distributed in consideration of the reactive power balance for each sub-system to prevent the reverse control phenomenon in the entire system. The present invention performs only the simple addition, subtraction, multiplication, and division calculations other than the power flow calculation, performs the entire calculation at high speed, realizes online voltage reactive power control, and furthermore, the process of selecting the reactive power control device is performed by a power system operator. It is another object of the present invention to provide a voltage reactive power control device which is easy to understand.

[0008]

According to the present invention, this power system is divided into a target power system, and a matching state between a reactive power generation source and a reactive power consumption source is determined in the divided power system. The calculation controls the reactive power generation device of the power system.

That is, in the present invention, the voltage / reactive power adjusting device, which has been obtained as a whole for the target power system, is divided into several sub-systems. In the known examples so far, there is a known example in which a specific kind of electric reactive power adjusting device having high voltage sensitivity is divided into partial systems only (known examples (1) and (b)). The system is divided into substations of the main system and its subordinate systems, or a system with the same power supply as one unit. In this division method, when the demand and the supply of the reactive power cannot be balanced, the optimal sub-system division is performed by repeating fusion and division with the adjacent sub-system. The reactive power balance is obtained for each of the divided sub-systems, and an optimum voltage reactive power adjusting device is obtained for each of the sub-systems.

In order to calculate the optimum voltage / reactive power adjusting device to be controlled for each sub-system, in addition to the conventionally used algorithm, a case of similar system status is searched from past history data, and the past A method of selecting an optimal voltage reactive power control device based on the result is used. Also, by combining this idea with the tidal current state prediction support system several hours ahead in the future, it is possible to deal with the ever-changing system state. In addition, the result of the reactive power operation device and the power flow state at each time point are learned, and used for calculation of the optimum reactive power control device at the next time point.

[0011]

After predicting the power flow state at a future time point, the entire target system is divided into a plurality of sub-systems in a form suitable for each power flow state. By integrating and dividing the target system into optimal sub-systems by repeating fusion and division while taking into account the amount of generation and consumption of reactive power, and performing reactive power distribution calculation, consistent control without reverse control phenomena in the entire system can be achieved. It becomes possible. Further, the power flow state at the time of execution of the calculation is compared with a similar power flow state in the past history data, and the amount of difference in the time section is reflected in the control state on the similar day to perform the reactive power distribution. Here, the optimum distribution of the reactive power is determined in consideration of the margin of the voltage reactive power adjusting device. With this method, only simple calculations are required except for executing the tidal flow calculation, so that high-speed processing can be performed.

[0012]

Next, an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows a power system voltage reactive power control device 1 according to the present invention.
It is a block diagram. The present invention relates to a target power system 101, a data reading device 102 for reading necessary data from the power system 101, a state estimating device 103 for estimating a likely system state at the time from the read data, and implementation of voltage reactive power control. System power flow state prediction device 1 for predicting the power system several hours ahead from the power system partial system division calculation device 104 as the pre-process for performing
05, a reactive power optimum distribution calculation device 106, device 1 for selecting a voltage reactive power control device to be operated for optimal reactive power distribution from the predicted power flow state obtained from the device.
06, a reactive power distribution command device 107 that issues a command to the operating device based on the result of 06, and an output device 108 that outputs the operation result
Consists of

The details of each of the following devices will be described. The data reading device 102 obtains information from each facility through the communication line 251 and further reduces the target system.
A process for storing the system information in the format as described above is performed. The processing result of the device 102 is sent to the state estimating device 103 via the communication line 252. The state estimating device 103 is means for estimating a likely state in the power system at that time using a method represented by the following known example.

Lars Holten, Anders Gjelsvik, Sverre A
dam, FF Wu and Wen-Hsiung E. Liu, Comparison of
Diffeent Methods for State Estimation. IEEE Trans.
Power Syst., 3 (1988), 1798-1806. The estimation result in the device 103 is sent to the future system power flow state prediction device through the communication line 253. Here, the function is to predict the power flow state of the power system at a future time based on the past total power demand, data on the generator, load data of each substation, and the result of the device 103. The details are described in detail in the following known examples.

A few hours ahead tidal current state prediction system (DP) for Nakajima, Okubo, Matsumoto, Ishida, Tamura, next Central Power Distribution Center
F) System development, 1995 IEEJ National Convention, 13
96 (1995).

The power system sub-system division calculation device 104 is a characteristic device of the present invention. The device 104 obtains power system data from the data reading device 102 through the communication line 258, and further obtains a state estimation result obtained by the device 103 or a power flow state prediction result obtained by the device 105. Based on the above data, the present device divides the power system for performing the voltage reactive power control into optimal sub-systems. The details of the system division method performed by this apparatus will be described with reference to FIG. First, the target system is divided by the means 301 into a system having a main system substation and its lower system as a unit. An actual example of this division will be described with reference to FIG. In the example system shown in FIG. 4, the main substation is A
s / s to Cs / s. The other substations are lower system substations. The target power system of FIG. 4 is divided into 401, 402, and 403 sub-systems by means 301.

Next, a reactive power balance is obtained by means 302 based on the reactive power consumption and the reactive power generation amount or the reactive power generation possible amount for each of the divided subsystems. After the reactive power balance is obtained by the means 302, the means 303 determines whether or not the reactive power balance is appropriate. The means 303 determines whether the reactive power balance is appropriate based on the following equation.

[0018]

(Reactive power consumption amount) ≦ (reactive power generation amount or possible generation amount) (Equation 1) When Expression 1 is satisfied, the processing of the power system partial system division calculation device ends. Otherwise, a sub-system that does not satisfy Equation 1 is selected, one of the adjacent sub-systems is merged by means 304, and a reactive power balance for the merged sub-system is calculated by means 305. For example, taking the power system of FIG. 4 as an example, if the reactive power balance of the partial system 402 is not appropriate, the partial system 401 and the partial system 402 are merged, and the reactive power balance of both the partial systems is calculated. Next, the means 306 checks the reactive power balance after the fusion. Here, when Equation 1 is satisfied, the sub-system division calculation processing ends. If Expression 1 is not satisfied, the unit 307 sets a flag for which the integration has been considered for the sub-system merged by the unit 304, and the unit 308 divides the sub-system merged by the unit 304. Next, means 30
At 9, it is confirmed whether or not the flag for which the fusion has been considered is set in all the adjacent sub-systems. If the flag is set for all adjacent sub-systems, the means 310 indicates that the system configuration needs to be changed, and the system division processing ends. If the flag has not been set yet, the process returns to the means 304 to continue the processing.

The results of the system status prediction device 105 and the power system partial system division calculation means 104 are sent to the reactive power optimum allocation calculation device via communication lines 254 and 255, respectively. Details of the reactive power optimum distribution calculation device will be described with reference to FIG.

First, the result obtained by the future system state prediction device 105 of FIG. Next, means 502
Sets an objective function for performing optimal voltage reactive power distribution. In this embodiment, as an example of the objective function, any one of the active power loss and the reactive power loss of the transmission line shown in Expressions 2 and 3 is used.

[0021]

(Equation 2)

[0022]

(Equation 3)

Next, means 503 sets restrictions on the reactive power balance for each sub-system divided by the device 104 in FIG. The restrictions here are as follows:
The upper and lower limits of the generated and consumed reactive power, the output power upper and lower limit constraint curves for the generator, and the transformer tap set the upper and lower limits of operation. Using the set value here, the distribution of the reactive power for each sub-system in the means 504 is calculated.

As an embodiment of the reactive power distribution calculation, an optimal reactive power distribution method using a case-based method, which is one of the features of the present invention, will be described with reference to FIGS. FIG. 6 is a flowchart showing an optimum reactive power distribution method using the case-based method. First, an initial setting for executing the calculation by the means 601 is performed. The processing here is the initial setting of an evaluation function value for each voltage reactive power adjusting device described later and a threshold value for determining whether to actually control the operating device,
Further, the transmission loss amount to be calculated later is initialized. After the end of this process, the means 602 calculates the transmission loss coefficient of each reactive power control facility. This coefficient means the amount by which the power transmission loss decreases or increases when the phase adjustment equipment operating as a discrete variable, the reactive power output of the generator, and the transformer tap change by one unit. Examples of the transmission loss coefficient are detailed in the following documents.

The Institute of Electrical Engineers of Japan, Measures for maintaining stable voltage of power system,
IEEJ Technical Report II-73, 43-45 (197
9).

Next, means 603 executes an optimum distribution calculation of reactive power. This will be described in detail with reference to FIG. In the reactive power optimal distribution calculation according to the present invention, data that is most similar to the power flow state of the time section is searched from past history data using a certain similarity evaluation function, and the search result and the time section are searched. The target reactive power control device is set using the state quantity of the control variable of the voltage reactive power control device. This will be described in detail with reference to FIG. A graph 701 in FIG. 7 is an example of a physical quantity representing a power flow state at an arbitrary time section. In each of the graphs, the vertical axis represents the predicted change with time of each physical quantity, and the horizontal axis represents the time elapsed. Graphs 721 to 724 show changes in physical quantities in the past several hours up to the system calculation corresponding time section, graph 7
11 to 714 are examples of the case where the similarity is the most similar in the past history data in which the similarity search index is the minimum.

The similarity search index is calculated using the following equation.

[0028]

(Equation 4)

Where t: number of time sections to be processed n: physical quantity (eg, transmission line active power flow, reactive power flow, substation load, etc.) used as a measure of voltage reactive power control for each sub-system The following describes how to select a reactive power adjusting device and how to determine the amount of operation when the result of the graph 702 is searched for the voltage reactive power control amount as a result of searching the history data based on the index. Here, the power transmission loss coefficient obtained for each of the above-mentioned voltage reactive power adjusting devices, the actual data at that time, and the difference amount of the data of the search result are used. Here, the difference amount is a difference between a search result at the time of execution of the calculation and a result value obtained for each facility. In the example of the graph 702 of FIG.
Shows the actual values, and the dotted lines in the graphs 741 to 744 show the search results. In this case, in the upper graph, the difference amount between the graph 731 and the graph 741 is meant.
Based on this amount, an evaluation function for each voltage reactive power control equipment is obtained by means 604 according to the following equation.

[0030]

(Evaluation function of equipment i) = (transmission loss coefficient) i × (difference between history data and actual data) i × (equipment margin) (Equation 5) When performing voltage reactive power control It is desirable to select a device having the greatest control effect as a device to be controlled. Therefore, in the present invention, the voltage reactive power adjusting equipment having the largest evaluation function among the evaluation functions of the voltage reactive power control equipment obtained by the equation 5 is selected as the control target device (means 605).

Depending on the target power system, operating the voltage reactive power control device may not have an effect on the reduction of the target function. In order to omit the processing in that case, it is necessary not to issue an operation command when the evaluation function value is less than a certain value. This processing is performed by means 606.
If the determination condition in the means 606 is satisfied, the power flow is calculated in the means 607, the amount of power transmission loss is obtained in the means 608, and the power flow state after the operation is determined. This processing is executed as long as there is a facility to be adjusted that satisfies this condition through the means 609 and 610 and the power transmission loss is reduced.

When the calculation of the reactive power distribution is completed for each sub-system, the presence or absence of a power flow constraint violation is confirmed by means 505 in FIG. If the means 505 determines that there is a constraint violation, the means 507 and 508 use (Equation 2) and (Equation 3) to find the transmission line with the largest transmission loss. When the transmission loss is large, the voltage at both ends of the transmission line often deviates from the reference value. For this purpose, the voltage at both ends of the transmission line is checked. If the node voltage exceeds the reference value, the means 513 sets the node voltage to the reference value and executes the reactive power distribution calculation of the means 504. This process is continued through means 510 and 511 until there is no more transmission line to be considered. If there is a violation of the equipment constraint related to the voltage reactive power and there is no abnormality in the voltage value of the node in the sub-system, an alarm is presented to the driver and a warning is issued to investigate the trouble occurring in the power system. I do.

As described above, the reactive power optimum distribution calculating device 10
The description of 7 ends. The result is sent to the actual device by the device 107 through the communication line 256 in FIG. 1 and the result is output to the output device through the communication line 257.

As described above, the present method dynamically divides the target system into sub-systems and distributes the reactive power while considering the reactive power balance for each sub-system. Can be prevented. Also, the present invention consists of simple addition / subtraction multiplication / division calculations other than power flow calculations,
Since the whole calculation can be executed at high speed, online voltage reactive power control can be realized. Further, there is an advantage that the process of selecting the reactive power control device can be easily understood by the operator of the power system.

Further, in the above-described embodiment of the present invention, the method of voltage reactive power control in the offline mode has been described.
The present invention is not limited to this, and can be used in an offline state. For example, the data of the power system input by the data reading device shown in FIG. 2 is not stored in real time but is stored in a storage device in the control system in advance, so that it can be used as a simulator of the reactive power of the entire power system. That is clear.

[0036]

As described above, the present invention has the following effects.

Since the target power system is dynamically divided into sub-systems and the reactive power is distributed in consideration of the reactive power balance for each sub-system, the reverse control phenomenon in the entire system is prevented. Becomes possible. Further, the present invention can be realized only by simple addition, subtraction, multiplication, and division calculations except for the power flow calculation, and the entire calculation can be executed at a high speed. Therefore, online voltage reactive power control can be realized. Further, there is an advantage that the process of selecting the reactive power control device can be easily understood by the operator of the power system.

[Brief description of the drawings]

FIG. 1 is a diagram showing features of the present invention.

FIG. 2 shows an example of data types read by a data reading device.

FIG. 3 is a flowchart illustrating a process of dividing an entire target system into sub-systems.

FIG. 4 is a diagram illustrating an example of a process of dividing an entire target system into partial systems.

FIG. 5 is a flowchart showing the flow of processing of the entire voltage reactive power optimal distribution method.

FIG. 6 is a flowchart illustrating a detailed process of a voltage reactive power optimal distribution method.

FIG. 7 is a diagram illustrating an example of a voltage reactive power optimal distribution method based on similar case selection.

[Explanation of symbols]

101: target power system, 102: data reading device, 103: state estimation device, 104: power system partial system division calculation device, 105: future system power flow state prediction device,
106: reactive power optimal distribution calculation device, 107: reactive power distribution command device, 108: output device, 201: example of system constant production, 202: generator output, bus load database reading example, 251: from power system A communication line for supplying the state quantity in the system to the data reading device; 252 a communication line connecting the data reading device and the state estimating device;
253: Communication line connecting the state estimation device and the future system power flow state prediction device, 254 ... Communication line connecting the power system sub-system division device and the reactive power optimum allocation calculation device, 255 ...
The future system power flow state prediction device is a communication line connecting the reactive power distribution calculation device, 256 ... a communication line connecting the reactive power optimal distribution device and the reactive power distribution command device, and 257 ... A communication line connecting the reactive power distribution command device and the output device. Communication line 258: Communication line connecting the data reading device and the power system partial system division calculation device; 301: Initial state of system division, 302, 3
05: reactive power balance calculating device, 303, 306: reactive power balance determining device, 304: partial system fusion means,
307, 309: considered sub-system determination processing, 308: sub-system division means, 310: message output device, 401,
402, 403: an example of a partial system, 501: a data acquisition device, 502: a target function setting means, 503: a reactive power balance setting device, 504: a reactive power distribution calculating device,
505: Constraint violation detecting device, 506: Calculation continuation determining device, 507: Transmission loss calculating device, 508: Maximum loss generating transmission line detecting device, 509: Transmission line end node constraint violation detecting device, 510, 511: Calculation continuation determining device , 512 ...
Alarm output device, 513: Reference voltage setting device, 601
... Initial setting device, 602 ... Transmission loss coefficient calculation device, 60
3 ... Reactive power optimal distribution calculation device, 604 ... Evaluation function calculation device, 605 ... Reactive power operation device setting device, 606 ... Calculation continuation judgment device, 607, 611 ... Power flow calculation device, 60
8: Transmission loss calculation device, 609, 610: Calculation continuation determination device, 612: Transmission loss calculation device, 701: Graph showing time transition of reactive power distribution calculation input variable, 702: Time transition of reactive power distribution calculation control variable Graph showing 7
11: a graph showing the time transition of the substation active power load in the past history data, 712: a graph showing the time transition of the substation reactive power load in the past history data, 713 ...
A graph showing a time transition of the interconnection line effective power flow in the past history data; 714 a graph showing a time transition of the interconnection line invalid power flow in the past history data; 721 a substation active power load in the actual data; Graph 722 showing time transition
... Graph showing the time transition of the substation reactive power load in the actual data, 723... Graph showing the time transition of the interconnected line active power flow in the actual data, 724… Time of the interconnected line reactive power flow in the actual data Graph showing transition, 731 ...
A graph representing a time transition of the phase adjustment equipment usage amount in the actual data, 732 a graph representing a temporal transition of the tap ratio in the actual data, 733 a graph representing a temporal transition of the generator reactive power output in the actual data, 734 … A graph showing the time transition of the bus voltage in the actual data, 741… a graph showing the time transition of the phase adjustment equipment usage in the past history data,
742: a graph showing the time change of the tap ratio in the past history data, 743 ... a graph showing the time change of the generator reactive power output in the past history data, 744 ... the time change of the bus voltage in the past history data A graph representing.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J 3/00-5/00 G05F 1/70

Claims (9)

(57) [Claims] 1. A power system data capturing means for capturing a system state of a power system to be controlled, a power system power flow state determining means for determining a power system flow state using the power system data, and a power system to be controlled. And a power system sub-system division calculating means for calculating a matching state between the reactive power generation source and the reactive power consumption source in the divided power system, and an output from the power system sub-system division calculating means. make use of,
And a reactive power distribution command output means for sending a control signal to disable the power generating device of the electric power system, the power system portion grid dividing calculating means, free of the partial systems
Split and merge sub-systems using active power demand and supply
A voltage reactive power control device characterized in that a target power system is divided into a plurality of sub-systems while performing the power control. 2. A system state of a power system to be controlled is taken in.
Power system data capturing means, and determining a power flow state of the power system using the power system data;
Power system power flow state determination means, and a target power system.
Within the device to measure the match between the reactive power source and the reactive power source.
Using the power system partial system division calculation means to calculate, and the output from the power system partial system division calculation means,
Invalidating a control signal to the reactive power generator of the power system
Power distribution command output means, and the power system partial system division calculating means comprises a power system
System substation as a unit, and the reactive power demand
Do not divide or merge sub-systems using the required and supplied quantities.
A voltage reactive power control device, wherein the target power system is divided into a plurality of partial systems . 3. A system state of a power system to be controlled is taken in.
Power system data capturing means, and determining a power flow state of the power system using the power system data;
Power system power flow state determination means, and a target power system.
Within the device to measure the match between the reactive power source and the reactive power source.
Using the power system partial system division calculation means to calculate, and the output from the power system partial system division calculation means,
Invalidating a control signal to the reactive power generator of the power system
Power distribution command output means, and the power system partial system division calculating means includes
Using historical power demand and supply,
Search for similar system status and allocate from similar system status
Calculate the state, split and merge the sub-systems
A voltage reactive power control device, wherein a power system is divided into a plurality of partial systems . 4. An active power and a reactive power with respect to a load amount and a power generation amount of an electric power system at an arbitrary time section, a system constant at the time section, a use amount of a phase adjustment facility at the time section, an operation curve thereof, and a time. The magnitude of the bus voltage at the substation in the cross section, the tap value of the transformer, a data reading device for reading the required data, a state estimating device for estimating the internal state of the power system, and the current power flow state obtained from the state estimating device A future system state prediction device for estimating a power flow state at a future time, a power system partial system division calculation device for dividing a target power system so that a reactive power generation source and a reactive power consumption source are balanced, A reactive power optimum allocation calculating device that optimally allocates the amount of reactive power generated to a power system from a future system power flow state predicting device, and the reactive power optimum allocation calculating device Results based on having a reactive power distribution command device for sending a control signal to disable the power generator, the power system
The sub-system division calculator calculates the reactive power demand of each sub-system.
Do not split or merge the sub-systems based on the
In particular, it is important to divide the entire target system into multiple sub-systems.
Voltage reactive power control device according to symptoms. 5. The voltage reactive power control device according to claim 4 , wherein said power sub-system division calculation device divides a target system. 6. A voltage reactive power controller according to claim 4, wherein the power system the subsystem division computing device, the voltage reactive power control apparatus characterized by dividing the division of power system mission-critical substation units . 7. The voltage reactive power control device according to claim 1, 2 or 3 , wherein the reactive power control amount independently divided for each power system sub-system divided by the power system sub-system division calculation device. And a voltage reactive power control device . 8. The voltage reactive power control device according to claim 4 , wherein said reactive power optimum allocation calculating device searches for a similar system status from past history data and calculates a reactive power optimum allocation calculation. A voltage reactive power control device, wherein an optimum distribution result is calculated by using the following. 9. The voltage reactive power control device according to claim 4 , wherein the reactive power optimum distribution calculating device determines the optimum reactive power distribution by using the device as a criterion for selecting a voltage reactive power control device to be adjusted. Voltage reactive power control, characterized in that the reactive power control amount is calculated by using each of the equipment margin, transmission line loss coefficient, actual value at the time of execution of the calculation, and the difference amount of the similar date search result at the corresponding time Equipment .