JP6869389B1 - Transmission line current calculation system and current calculation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current calculation system and a current calculation method capable of calculating a current of an arbitrary portion of a multi-terminal transmission line without synchronizing the time. An overload detection system 1 is provided by two or more terminals 21 and 22 of a multi-terminal transmission line, and is measured by measuring units 11a and 11b and measuring units 11a and 11b for measuring at least the current value of the terminals. It is provided with a calculation unit 13 that performs a calculation using the current value and calculates the current vector I of the current calculation target section of the multi-terminal transmission line. The current value is a current effective value or an amplitude value | In | and a current phase θn with reference to the self-end voltage. The calculation unit 13 converts at least the current effective value or amplitude value | In | of the terminals measured by the measurement units 11a and 11b and the current phase θn into the current vector In of each terminal, and obtains the current vector In of two or more terminals. It is configured to calculate the current vector I of the current calculation target section by the combined calculation of each current vector In. [Selection diagram] Fig. 2

Description

The present invention relates to a multi-terminal transmission line current calculation system and a current calculation method for calculating a current in an arbitrary section of a transmission line having a plurality of terminals.

Conventionally, various methods for calculating the current of a multi-terminal transmission line have been proposed, for example, in order to detect an overload of a transmission line. In order to detect the overload of the transmission line, for example, the current in the section where the overload is to be detected can be calculated, and the calculated current can be used to detect the overload by an overcurrent method or the like.

Regarding the calculation of the current in a section of the transmission line, for example, Japanese Patent Application Laid-Open No. 10-257665 (Patent Document 1) describes a transmission line composed of n terminals (n ≧ 4) connected via an intermediate branch point. A multi-terminal transmission line overload detection relay device that performs overload detection using the current information of each terminal collected from the terminal device provided at each terminal of the above is described. In this multi-terminal transmission line overload detection relay device, in order to enable overload detection in any section of the transmission line, each terminal device takes in current information flowing to each terminal, and each terminal device passes through a transmission line. Based on each current information taken in, the current flowing in the overload detection target section is calculated. As a result, an overload between arbitrary intermediate branch points, which could not be realized by a conventional relay, can be detected.

Moreover, in recent years, there has been an increasing demand for interconnection to the transmission system of general power generation companies that are not electric power companies. In October 2018, the OCCTO announced "About the concept of prior application of the N-1 electrical system in the formulation of distribution equipment maintenance plans (Article 55 of the business guidelines for power transmission and distribution, etc.)", and grid access. When conducting studies, etc., it was decided to expand the operating capacity of the local system by applying the N-1 electronic control in principle. Regarding N-1 electric control, a failure of a single electric power facility (transmission line, transformer, circuit breaker, etc.) is called an N-1 accident. The transmission line usually has a two-line configuration, and the capacity of the transmission line does not exceed 50%, so even if one transmission line is disconnected from the grid due to an N-1 accident, it will not cause any problems. It is designed to be operational. However, in recent years, there has been an increase in demand for grid connection of general power generation companies. In order to deal with this, the N-1 electronic control is a limiting method in which power generation equipment is connected in excess of capacity and the power source is limited in the event of an N-1 accident. As described above, there is an increasing demand for high-precision and inexpensive overload protection systems for transmission lines.

Japanese Unexamined Patent Publication No. 10-257665

However, in the multi-terminal transmission line overload detection relay device described in Patent Document 1, it is necessary to match the phase of the current in order to calculate the current vector by taking in only the current information without taking in the voltage information. is there. In order to match the phase of the current, it is necessary to synchronize the time. In order to accurately synchronize the time in the multi-terminal transmission line overload detection relay device described in Patent Document 1, it is necessary to synchronize the time, for example, as in the transmission line current differential relay. In the multi-terminal transmission line overload detection relay device described in Patent Document 1, for example, the method disclosed in Japanese Patent Application Laid-Open No. 62-262615 can be used as a means for time synchronization. In this method, the time from the transmission of information to the other end to the reception of the information of the other end is measured, and sampling synchronization is performed based on this time. In this method, for example, by using an optical dedicated line, it is necessary to use a communication means in which the transmission time does not change, but if an optical dedicated line is prepared for each system, the cost increases. However, as described above, there is an increasing demand for high accuracy and low cost in the overload protection system of the transmission line.

Therefore, an object of the present invention is to provide a current calculation system and a current calculation method capable of calculating the current of an arbitrary portion of a multi-terminal transmission line without synchronizing the times.

The present inventors have diligently studied a current calculation system and a current calculation method that enable the calculation of the current of an arbitrary part of a multi-terminal transmission line without synchronizing the time. As a result, the current calculation system and the current calculation method of the present invention are configured as follows.

The current calculation system according to the present invention is provided at two or more terminals of a multi-terminal transmission line and performs calculations using a measuring unit that measures at least the current value of the terminals and a current value measured by the measuring unit. It is provided with a calculation unit for calculating the current vector I of the current calculation target section of the terminal transmission line. The current value is a current effective value or an amplitude value | In | and a current phase θn with reference to the self-end voltage. The arithmetic unit converts at least the current effective value or amplitude value | In | of the terminals measured by each measuring unit and the current phase θn into the current vector In of each terminal, and each current obtained for two or more terminals. It is configured to calculate the current vector I of the current calculation target section by the combined calculation of the vector In.

In the current calculation method according to the present invention, the calculation unit performs a calculation using at least the current values of two or more terminals of the multi-terminal transmission line, and calculates the current vector I of the current calculation target section of the multi-terminal transmission line. In the method, the current value is the current effective value or the amplitude value | In | and the current phase θn based on the own end voltage, and the calculation unit has at least the current effective value or the amplitude value | In | of the terminal. The current phase θn is converted into the current vector In of each terminal, and the current vector I of the current calculation target section is calculated by the combined calculation of the respective current vectors In obtained for the two or more terminals.

As described above, according to the present invention, it is possible to provide an overload detection system and an overload detection method capable of detecting an overload of an arbitrary portion of a multi-terminal transmission line at low cost.

It is a figure which shows typically each section of the transmission line in which the overload detection system of this invention is installed. It is a block diagram which shows 1st Embodiment of the overload detection system of this invention. It is a flowchart which shows the control process of the arithmetic part of the overload detection system of 1st Embodiment of this invention. It is a block diagram which shows the 2nd Embodiment of the overload detection system of this invention. It is a flowchart which shows the control process of the arithmetic part of the overload detection system of the 2nd Embodiment of this invention. It is a schematic diagram of the configuration including the terminal of the overload detection system and the overload detection target section when correcting the charging current in the overload detection system of the second embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiments shown below, and various modifications can be made without departing from the technical idea of the present invention.

<First Embodiment>
The current calculation system of the present invention can be used, for example, as an overload detection system. FIG. 1 is a diagram schematically showing each section of a transmission line in which an overload detection system is installed as one form of the current calculation system of the present invention. As shown in FIG. 1, the transmission line has a plurality of terminals and branch points. For example, a calculation unit is installed at the power supply end (terminal 21) as a parent device of the overload detection system, and a child device including a measurement unit is installed up to the branch before the overload detection target section for detecting the overload. The overload detection target section is an example of the current calculation target section of the multi-terminal transmission line. The current value and voltage value measured by the measuring unit of the child device of each terminal are collected in the parent device.

FIG. 2 is a configuration diagram showing a first embodiment of the overload detection system of the present invention. As shown in FIG. 2, the overload detection system 1 includes measuring units 11a and 11b provided at each terminal 21 and 22 of the multi-terminal transmission line 2 and measuring the current value and voltage value of the terminals 21 and 22 and a measuring unit. It is provided with a calculation unit 13 that performs a calculation using the current value and the voltage value measured by 11a and 11b and calculates the current vector of the overload detection target section 2a. The calculation unit 13 may be provided in any of the measurement units 11a and 11b, or may be provided separately from the measurement units 11a and 11b.

The measuring units 11a and 11b include a current input unit 111, a voltage input unit 112, an effective value phase calculation unit 113, and an information transmission unit 114.

The current input unit 111 measures the current of each of the terminals 21 and 22. The voltage input unit 112 measures the voltage of each of the terminals 21 and 22.

Rms phase calculation unit 113, based on the voltage measured by the current and voltage input unit 112 measured by the current input section 111, in general, effective current value | I n _| and the local end voltage The reference current phase θ _n is calculated. That is, the effective value phase calculation unit 113 of the terminal 21 calculates the current effective value | I _{21 | and the current phase θ 21 based} on the own end voltage, and the effective value phase calculation unit 113 of the terminal 22 calculates the current effective value. | I ₂₂ | and the current phase θ _{22 based} on the self-end voltage are calculated. The current amplitude value may be calculated instead of the current effective value.

Information transmitting unit 114, the current effective value computed by the effective value phase calculation unit _{113 | I n | (| I} 21 |, | I 22 |) between the current phase _{θ n (θ 21, θ 22} ) an arithmetic unit 13 Send to.

The calculation unit 13 includes an information receiving unit 131, a current synthesis calculation unit 132, and an overload determination unit 135.

FIG. 3 is a flowchart showing a control process of a calculation unit of the overload detection system according to the first embodiment of the present invention. As shown in FIG. 3, the calculation unit 13 performs the following processing.

In step S11, the calculation unit 13 converts the current effective value | I ₂₁ | and the current phase θ _{21 transmitted from the information transmission unit 114 of the terminal 21} into the current vector I 21 and from the information transmission unit 114 of the terminal 22. transmitted current effective value _| converts between the current phase theta ₂₂ to the current vector _{I 22} | _{I 22.}

In step S12, the calculation unit 13 determines the next section ( _{current vectors I 21} and I ₂₂ when the two sections are sections 221 and 222) in each of the two sections connected to the same branch. When the two sections are sections 221 and 222, the current vector I of the section 2a) is calculated in the next section.

Considering that the voltage change due to the transmission line accident is removed in a short time by protection, the voltage phase difference between the measurement time points can be regarded as only due to the voltage drop due to the line. When it is considered that the voltage drop due to the line is smaller than the original voltage and there is no voltage phase difference for each measurement point due to the voltage drop, the following using _{the current vectors I 21} and I _{22 of the two sections 221,222} The current vector I in the next section 2a is calculated by the addition calculation.
I = I _21- I ₂₂

In step S13, the calculation unit 13 determines whether or not the next section (section 2a) is the last section to be calculated. If it is the last section, the process proceeds to step S14. If it is not the last section, the section is advanced by one in step S15, and the process returns to step S12.

In step S14, the calculation unit 13 detects the overload of the overload detection target section from the magnitude of the current vector I, for example, by the overcurrent method.

Step S12 repeats the calculation of the current vector of the new overload detection target section with another adjacent section as a new overload target section, and repeats until the current vector is calculated for all the sections of the system. You may.

As described above, the overload of the section 2a shown in FIG. 1 is obtained from the current vectors of the section 221 and the section 222, and the overload of the next section 2b is the current vector of the section 2a (that is, the current vector of the section 221 and the section 222). ) And the current vector of the section 223, and the overload of the next section 2c is obtained from the current vector of the section 2b (that is, the section 221 and the section 222 and the section 223) and the current vector of the section 224. In this way, if necessary, the current vector can be obtained for all sections of the system. When the current calculation system is used as the overload detection system as in this embodiment, the overload of each section may be obtained based on the obtained current vector of each section, and the overload may be obtained for all the sections of the system. A load may be required.

As described above, in the overload detection system 1 of the present invention, the current in the overload detection target section is calculated by combining the current vector calculated based on the current effective value or amplitude value measured by the measuring unit and the current phase. Since the size is calculated, there is no need to synchronize the time. In addition, the section and direction of the overload are specified, and the power source that causes the overload is accurately identified.

When an overload is detected, the calculation unit 13 can, for example, transmit a control command according to the section and the current direction, and perform power supply limitation, load limitation, system change, and the like to eliminate the overload. When an overload is detected by the overload detection system or the overload detection method of the present invention, appropriate measures may be taken as necessary. The overload detection system and overload detection method of the present invention can be applied not only to N-1 accidents and N-1 electronic control, but also to overloads in general.

When communicating from the information transmission unit 114 to the calculation unit 13 through the transmission line, the communication interval may be a time sufficiently smaller than the overload detection time of several tens of seconds to several tens of minutes. In addition, accurate time synchronization is not required, and similarly, timing deviations of several tens of seconds to a sufficiently small time compared to several tens of seconds are allowed.

The transmission line of the present invention may be connected to an existing TCP / IP network or the like for communication on the order of 0.1 seconds, and time synchronization is not required, so that the equipment is very inexpensive.

As described above, the overload detection system 1 of the first embodiment of the present invention includes measuring units 11a and 11b provided at two or more terminals 21 and 22 of the multi-terminal transmission line and measuring at least the current value of the terminals. It is provided with a calculation unit 13 that performs a calculation using the current values measured by the measurement units 11a and 11b and calculates the current vector I of the current calculation target section of the multi-terminal transmission line. The current value is a current effective value or an amplitude value | In | and a current phase θn with reference to the self-end voltage. The calculation unit 13 converts at least the current effective value or amplitude value | In | of the terminals measured by the measurement units 11a and 11b and the current phase θn into the current vector In of each terminal, and obtains the current vector In of two or more terminals. It is configured to calculate the current vector I of the current calculation target section by the combined calculation of each current vector In.

Further, in the overload detection system 1 of the first embodiment, the calculation unit 13 is configured to detect the overload of the current calculation target section from the magnitude of the current vector I of the current calculation target section.

Further, in the method of calculating the current vector performed in the overload detection system 1 of the first embodiment of the present invention, the calculation unit 13 calculates using at least the current values of two or more terminals 21 and 22 of the multi-terminal transmission line. This is a method of calculating the current vector I of the current calculation target section of the multi-terminal transmission line, in which the current value is the current effective value or the amplitude value | In | and the current phase θn based on the own end voltage. , The calculation unit 13 converts at least the current effective value or amplitude value | In | of the terminals and the current phase θn into the current vector In of each terminal, and calculates the combined calculation of the respective current vectors In obtained for the two or more terminals. The current vector I of the current calculation target section is calculated.

Further, in the current vector calculation method performed in the overload detection system 1 of the first embodiment, the calculation unit 13 detects the overload of the current calculation target section from the magnitude of the current vector I of the current calculation target section. ..

As described above, according to the present invention, it is possible to provide a current calculation system and a current calculation method capable of calculating the current of an arbitrary portion of a multi-terminal transmission line without synchronizing the times. ..

In this embodiment, the overload detection system has been described as an example of the current calculation system, but the current calculation system of the present invention calculates the current vector for various purposes such as control, protection, and measurement. Can be applied to various systems in which is required.

Further, each of the measuring units 11a and 11b detects the overload of its own section based on the current information measured internally, independently of the current synthesis calculation in the current calculation system and the current calculation method according to the present invention. -It may be configured to be controllable.

<Second Embodiment>
FIG. 4 is a configuration diagram showing a second embodiment of the overload detection system as another embodiment of the current calculation system of the present invention. As shown in FIG. 4, the overload detection system 1b includes measuring units 11a and 11b provided at each terminal 21 and 22 of the multi-terminal transmission line 2 and measuring the current value and voltage value of the terminals 21 and 22 and the measuring unit. It is provided with a calculation unit 13 that performs a calculation using the current value and the voltage value measured by 11a and 11b and calculates the current in the overload detection target section 2a. The calculation unit 13 may be provided in any of the measurement units 11a and 11b, or may be provided separately from the measurement units 11a and 11b.

The measuring units 11a and 11b include a current input unit 111, a voltage input unit 112, an effective value phase calculation unit 113, and an information transmission unit 114.

The current input unit 111 measures the current of each of the terminals 21 and 22. The voltage input unit 112 measures the voltage of each terminal 21 and 22.

Rms phase calculation unit 113, based on the voltage measured by the current and voltage input unit 112 measured by the current input section 111, in general, effective current value | I n _| a, voltage effective value V _{n and the current phase θ n} with reference to the self-end voltage are calculated. That is, the effective value phase calculation unit 113 of the terminal 21 calculates the current effective value | I ₂₁ |, the voltage effective value | V _{21 |, and the current phase θ 21 based} on the own end voltage, and the effective value of the terminal 22 is calculated. The value phase calculation unit 113 calculates the current effective value | I ₂₂ |, the voltage effective value | V ₂₂ |, and the current phase θ _{22 based} on the own end voltage. The current amplitude value may be calculated instead of the current effective value, or the voltage amplitude value may be calculated instead of the voltage effective value.

Information transmitting unit 114, the calculated current effective value by an effective value phase calculation unit _{113 | I n | (| I} 21 |, | I 22 |) and the voltage effective value _{| V n | (| V 21} |, | V ₂₂ |) and the current phase θ _n (θ ₂₁ , θ ₂₂ ) are transmitted to the calculation unit 13.

The calculation unit 13 includes an information receiving unit 131, a current synthesis calculation unit 132, an internal memory 133, a phase correction calculation unit 134, and an overload determination unit 135.

FIG. 5 is a flowchart showing a control process of the calculation unit of the overload detection system of the present invention. As shown in FIG. 5, the calculation unit 13 performs the following processing.

In step S21, the calculation unit 13 converts the current effective value | I ₂₁ | and the current phase θ ₂₁ transmitted from the information transmission unit 114 of the terminal 21 into the current vector I _21, and from the information transmission unit 114 of the terminal 22. transmitted current effective value _| converts between the current phase theta ₂₂ to the current vector _{I 22} | _{I 22.}

In step S22, the calculation unit 13 sets the current vectors I ₂₁ and I ₂₂ , the effective voltage values | V ₂₁ |, | V ₂₂ |, and the preset line impedance Z in each of the two sections connected to the same branch. The voltage phase difference θ between the reference voltage and the self-end voltage is calculated based on _n (Z ₂₁ , Z _22).

In step S23, the arithmetic unit 13 the phase of the current vector _{I n (I 21, I 22} ), corrected by the voltage phase difference of the calculated reference voltage and Zidane voltage θ in step S22, the phase reference in common. At each terminal, the phase of the voltage changes by the amount of the voltage drop on the line. Therefore, the voltage and current values obtained for each terminal, inputs the preset line impedance Z _n, to correct the phase difference between the voltage by the following calculation.

With voltage _{V 22a} and the current _{I 22a} of terminal 22 relative to the voltage _{V 21} of the terminal 21, the voltage _{V 20} at the branch 20 is expressed as follows.
V ₂₀ = V _21- Z ₂₁ · I ₂₁ = V _22a + Z ₂₂ · I _22a ... (1)
_{The voltage V 22} and the current I ₂₂ actually measured by the measuring units 11a and 11b of the terminal 22 are out of phase by V _{22 based} on the V _21. Since the current is measured with the same voltage reference, the phase shifts by the same amount. Assuming that the phase of V ₂₂ with respect to V ₂₁ is θ, the actually measured voltage V ₂₂ and current I ₂₂ are expressed as follows.
V ₂₂ = V _22a · e ^jθ
I ₂₂ = I _22a · e ^jθ
_{The voltage V 22a} and the current I _22a of the terminal 22 with reference to the voltage V ₂₁ are expressed as follows.
V _22a = V ₂₂ / e ^jθ ... (2a)
I _22a = I ₂₂ / e ^jθ ... (2b)
Substitute equations 2a and 2b into equation 1.
V ₂₀ = V ₂₁ −Z ₂₁ · I ₂₁ = V ₂₂ / e ^jθ + Z ₂₂ · I ₂₂ / e ^jθ
e ^jθ = (V ₂₂ + Z ₂₂ · I ₂₂ ) / (V ₂₁ −Z ₂₁ · I ₂₁ )

In step S24, the calculation unit 13 performs the following addition calculation using the current vectors of the two sections (current vectors I ₂₁ and I ₂₂ when the two sections are sections 221 and 222) to perform the next section (two sections). When is a section 221,222, the next section calculates the current vector I of the section 2a).
I = I _21- I _22a = I _21- I ₂₂ / e ^jθ

The charging current is corrected as follows. FIG. 6 is a schematic diagram of a configuration including terminals 21 and 22 of the overload detection system and an overload detection target section when the charging current is corrected.

In FIG. 6, I _21b and I _22b are currents obtained from the measurement points, and I _22b is the current after phase correction. C ₂₁ and C ₂₂ are positive phase capacitances. _IC21 and _IC22 are charging currents.

The basic composition formula is as follows.
I = I _21a- I _22a ... (3)
The current obtained at the measurement point from FIG. 6 is expressed as follows.
I _21b = I _21a + _IC21
I _22b = I _{22a- IC22}
I _21a = I _{21b- IC21} ... (4a)
I _22a = I _22b + _IC22 ... (4b)
From Equations 3, 4a and 4b
I = I _21b- I _22b- I _C21- I _C22
When you place the _{I C = I C21 + I C22} ,
I ₌ I _{21b -I} 22b _{-I C}
When combined with the calculation in step S3,
^{_{I = I 21b -I 22b / e}} jθ -I C
The calculation method of the charging current is shown below. Positive-phase capacitance C _21, C _22, given a is present distributed constant type to the line are concentrated to the V ₂₀ point for simplicity,
_{I C} = I C21 ₊ I _C22
= V ₂₀・ jωC ₂₁ + V ・ jωC ₂₂
However, V ₂₀ is the phase voltage, and from Equation 1,
V ₂₀ = V _21- Z ₂₁ · I ₂₁
Is.

Although _{it is assumed that C 21} and C ₂₂ are _{concentrated at the V 20} point, it may be considered that C ₂₁ is _{concentrated at V 21} and C ₂₂ is _{concentrated at V 22} , assuming a π-type line. It may be assumed that _{C 21} is _{concentrated in V 21} and V ₂₀ and C ₂₂ is _{concentrated in V 22} and V _{20 by 1/2.}

In step S25, the calculation unit 13 determines whether or not the next section (section 2a) is the last section to be calculated. If it is the last section, the process proceeds to step S26. If it is not the last section, the section is advanced by one in step S27, and the process returns to step S22.

In step S26, the calculation unit 13 detects the overload of the overload detection target section from the magnitude of the current vector I, for example, by the overcurrent method.

After step S25, the current vector of the new overload detection target section may be repeatedly calculated with another adjacent section as a new overload target section, and the current vector may be calculated for all the sections of the system. ..

When an overload is detected, the calculation unit 13 transmits a control command according to the section and the current direction, and performs power supply limitation, load limitation, system change, etc. to eliminate the overload.

As described above, in the overload detection system 1b of the second embodiment, the measurement units 11a and 11b are the measurement units 11a and 11b that further measure the voltage values of the terminals 21 and 22, and the voltage values are voltage effective. It is a value or an amplitude value, and the calculation unit 13 calculates the voltage phase difference θ between the reference voltage and the self-end voltage based on the current vector In, the voltage effective value or the amplitude value | Vn |, and the preset line impedance Zn. , The current phase θn is corrected by the voltage phase difference θ so that the phase reference is common.

Further, in the method of calculating the current vector performed in the overload detection system 1b of the second embodiment, the calculation unit 13 further performs a calculation using the voltage values of the terminals 21 and 22, and the voltage value is the voltage effective value. Alternatively, the calculation unit 13 calculates the voltage phase difference θ between the reference voltage and the self-end voltage based on the current vector In and the voltage effective value or the amplitude value | Vn | and the preset line impedance Zn. The current phase θn is corrected by the voltage phase difference θ to make the phase reference common.

Other configurations of the overload detection system 1b and the overload detection method of the second embodiment are the same as those of the first embodiment.

In this embodiment, the overload detection system has been described as an example of the current calculation system, but the current calculation system of the present invention calculates the current vector for various purposes such as control, protection, and measurement. Can be applied to various systems in which is required.

It should be considered that the embodiments and examples disclosed above are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims, not the above embodiments and examples, and includes all modifications and modifications within the meaning and scope equivalent to the scope of claims.

1,1b: Overload detection system, 11a, 11b: Measurement unit, 13: Calculation unit,
2: Multi-terminal transmission line, 21, 22: Terminal.

Claims (6)

A measuring unit provided at two or more terminals of a multi-terminal transmission line and measuring at least the current value of the terminal,
It is provided with a calculation unit that performs a calculation using the current value measured by the measurement unit and calculates the current vector I of the current calculation target section of the multi-terminal transmission line.
The current value is a current effective value or an amplitude value | In | and a current phase θn with reference to the self-end voltage.
The calculation unit is at least
The current effective value or amplitude value | In | of the terminal measured by each measuring unit and the current phase θn are converted into the current vector In of each terminal.
It is configured to calculate the current vector I of the current calculation target section by the combined calculation of the current vector In obtained for each of the two or more terminals.
Current calculation system. The measuring unit is a measuring unit that further measures the voltage value of the terminal.
The voltage value is a voltage effective value or an amplitude value, and is
The calculation unit calculates the voltage phase difference θ between the reference voltage and its own end voltage based on the current vector In, the voltage effective value or the amplitude value | Vn |, and the preset line impedance Zn, and the current phase θn. The current calculation system according to claim 1, wherein the voltage phase difference θ is corrected by the voltage phase difference θ to make the phase reference common. The current calculation system according to claim 1 or 2, wherein the calculation unit is configured to detect an overload in the current calculation target section from the magnitude of the current vector I in the current calculation target section. .. A method in which the calculation unit performs a calculation using at least the current values of two or more terminals of the multi-terminal transmission line, and calculates the current vector I of the current calculation target section of the multi-terminal transmission line.
The current value is a current effective value or an amplitude value | In | and a current phase θn with reference to the self-end voltage.
The calculation unit converts at least the current effective value or amplitude value | In | of the terminal and the current phase θn into the current vector In of each terminal.
A current calculation method for calculating the current vector I of the current calculation target section by a combined calculation of the current vector In obtained for each of the two or more terminals. The calculation unit further performs a calculation using the voltage value of the terminal, and then performs a calculation.
The voltage value is a voltage effective value or an amplitude value, and is
The calculation unit calculates the voltage phase difference θ between the reference voltage and its own end voltage based on the current vector In, the voltage effective value or the amplitude value | Vn |, and the preset line impedance Zn, and the current phase θn. The method according to claim 4, wherein is corrected by the voltage phase difference θ to make the phase reference common. The current calculation method according to claim 4 or 5, wherein the calculation unit detects an overload in the current calculation target section from the magnitude of the current vector I in the current calculation target section.

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