JP2008067437A - Load current calculation method and load current calculation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate an error caused by a difference between the power factor of an outlet current and that of a power source current in calculating a load current in a distribution line. <P>SOLUTION: A load current calculation device 1 is made up of an outlet current obtaining means 2, a power source current obtaining means 3, a load current calculation means 4, and a load current output means 5. The outlet current obtaining means 2 obtains the values of currents (an active current and a reactive current) that flow in an outlet, a portion where electric power from a feeder connected to a transformer is received, in the distribution line. The power source current obtaining means 3 obtains the values of currents (an active current and a reactive current) supplied by distributed power sources (power sources such as a generator) connected to the distribution line. The load current calculation means 4 calculates a value of the load current of the distribution line by vector operation from the values of the outlet current obtained by the outlet current obtaining means 2 and those of the currents of the distributed power sources obtained by the power source current obtaining means 3. The load current output means 5 outputs the load currents of the distribution line calculated by the load current calculation means 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a load current calculation method and a load current calculation device for calculating a load current of a distribution line from a current at an outlet of the distribution line and a generated current of a power source.

Conventionally, when calculating the load current of the distribution line (hereinafter referred to as distribution line load current), the current at the outlet of the distribution line (hereinafter referred to as drawer current) and the generated current of the distributed power source (hereinafter referred to as distributed power source) The current value) and the total value was apportioned to each section. Patent Document 1 discloses a section load calculation device for a distribution line that performs the calculation.
JP 2003-61247 A

  However, with the recent spread of distributed power sources such as micro gas turbines, the number of distributed power sources connected to distribution lines tends to increase. And since there is a case where the power factor of the outlet current and the power factor of the distributed power source current are greatly different, there is a problem that an error occurs in the calculated distribution line load current.

  The present invention has been made in view of the above problems, and in calculating the distribution line load current, the main object is to eliminate errors due to the difference between the power factor of the outlet current and the power factor of the power source current. To do.

  In order to solve the above-mentioned problems, the present invention provides a load current calculation method for calculating a load current of a distribution line by an apparatus, wherein the apparatus acquires an effective current and a reactive current of an outlet of the distribution line. 1 step, a second step in which the device acquires effective current and reactive current of one or more power supplies connected to the distribution line, and the drawer in which the device has acquired in the first step. A third step of calculating the effective current and reactive current of the load of the distribution line by vector calculation from the active current and reactive current of the power source and the active current and reactive current of the power source acquired in the second step; The apparatus includes a fourth step of outputting an effective current and a reactive current of the load of the distribution line calculated in the third step.

  According to this method, when calculating the load current of the distribution line from the current of the outlet of the distribution line and the current of the power source connected to the distribution line, vector calculation is used instead of scalar calculation. Even if the power factor of the current at the outlet differs from the power factor of the power source current, the load current of the distribution line can be obtained correctly.

  Further, the present invention is a load current calculation device, wherein the outlet current acquisition means for acquiring the effective current and reactive current of the outlet of the distribution line, the effective current of one or more power sources connected to the distribution line, and A power source current acquisition unit that acquires a reactive current, an effective current and a reactive current of the extraction port acquired by the extraction port current acquisition unit, and a power source effective current and a reactive current acquired by the power source current acquisition unit, and a vector Load current calculation means for calculating the effective current and reactive current of the load of the distribution line by calculation, and load current output means for outputting the effective current and reactive current of the load of the distribution line calculated by the load current calculation means It is characterized by comprising.

  According to this configuration, when calculating the load current of the distribution line from the current of the outlet of the distribution line and the current of the power source connected to the distribution line, vector calculation is used instead of scalar calculation. Even if the power factor of the current at the outlet differs from the power factor of the power source current, the load current of the distribution line can be obtained correctly.

  In addition, the problems disclosed in the present application and the solutions thereof will be clarified by the description of the best mode for carrying out the invention and the drawings.

  According to the present invention, in calculating the distribution line load current, it is possible to eliminate an error due to the difference between the power factor of the outlet current and the power factor of the distributed power source current.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. The load current calculation device according to the embodiment of the present invention assumes that there is no phase shift of the voltage in each section of the distribution line, and from the current at the outlet of the distribution line and the generated current of the distributed power source, It is a device that calculates and outputs the load current of the distribution line by vector calculation.

≪Device configuration and operation≫
FIG. 1 is a diagram illustrating a configuration example of a load current calculation apparatus. The load current calculation device 1 includes an outlet current acquisition unit 2, a power supply current acquisition unit 3, a load current calculation unit 4, and a load current output unit 5.

  The outlet current acquisition means 2 acquires the value of current (effective current and reactive current) flowing through the outlet that is a part that receives power supply from a feeder connected to the transformer in the distribution line. Specifically, it may be acquired directly from an ammeter installed at or near the outlet, or data input by a person in charge of the electric power company who saw the ammeter may be acquired. The power source current acquisition unit 3 acquires values of currents (active current and reactive current) supplied by a distributed power source (power source such as a generator) connected to the distribution line. Specifically, it may be acquired directly from a distributed power source or an ammeter installed in the vicinity thereof, or data input by a person in charge of an electric power company who viewed the ammeter may be acquired. The outlet current acquisition means 2 and the power supply current acquisition means 3 are realized by an interface for acquiring a current value from an ammeter or an input device such as a keyboard or a mouse provided in the load current calculation device 1.

  The load current calculation unit 4 calculates the distribution line load current value by vector calculation from the value of the extraction port current acquired by the extraction port current acquisition unit 2 and the value of the distributed power supply current acquired by the power supply current acquisition unit 3. calculate. Each current includes an active current and a reactive current, and a vector operation can be performed by adding the currents. Details will be described later. The load current calculation means 4 is realized by execution of a program by a CPU (Central Processing Unit) or operation of an arithmetic circuit as hardware. The load current output means 5 outputs the distribution line load current calculated by the load current calculation means 4. Specifically, it may be displayed on a display provided in the load current calculation device 1 or may be output to another device via a network or other interface.

  FIG. 2 is a diagram for explaining the vector calculation performed by the load current calculation means 4. Fig.2 (a) shows the structural example of a distribution line. The distribution line L is divided into sections S1, S2, and S3 by the outlet F and the switches A1 and A2. A generator (power source) G is connected to the section S2 of the distribution line L. The current flowing through the outlet F is indicated by a vector IFCB, and the current supplied from the generator G is indicated by a vector IG. And the load current which flows through area S3 of the distribution line L is shown by vector IL. 2A shows one generator G, the present invention is not limited to this, and two or more power sources may be connected to the distribution line L.

FIG. 2B shows the calculation of the current vector. Conventionally, the magnitude of the distribution line load current IL has been calculated as in the following Expression 1.
| IL | = | IFCB | + | IG |

  Equation 1 is to obtain a scalar sum, and the power factor of the extraction port current IFCB and the power factor of the distributed power source current IG are the same, that is, the slope of the vector IFCB in FIG. When the inclination of IG is the same, it can be used without any problem. However, when the power factor of the current, that is, the gradient of the vector is different, the magnitude of the distribution line load current IL obtained by Expression 1 becomes a value including an error.

Therefore, in the embodiment of the present invention, the magnitude of the distribution line load current IL is calculated as the following Expression 2.
| IL | = | IFCB + IG |

Equation 2 calculates the magnitude after obtaining the vector sum. If the magnitude of the active current of each vector is indicated by the subscript r, the magnitude of the reactive current is indicated by the subscript i, and the imaginary unit is j, the magnitude of the distribution line load current IL is as shown in Equation 3. Desired.
IFCB = IFCBr + j · IFCBi
IG = IGr + j · IGi
| IL | = | IFCBr + IGr + j · (IFCBi + IGi) |
= √ {(IFCBr + IGr) ² + (IFCBi + IGi) ² } Equation 3

  Note that the load current output means 5 may output a vector IL (effective current and reactive current), or may output the magnitude | IL | of the vector IL. Whether the load current output means 5 outputs the vector IL or the magnitude | IL | can be appropriately changed depending on how the output data on the side receiving the output from the load current output means 5 is used.

≪Effect of calculation method≫
The load current calculation means 4 of the load current calculation device 1 performs vector calculation on the distribution line load current, which has been conventionally scalar calculation, so that the difference between the power factor of the outlet current and the power factor of the power source current can be reduced. Since it is taken into consideration, it is possible to calculate with high accuracy. According to this, in the case of load accommodation at the time of a power failure, even if it is conventionally determined that accommodation is not possible, it may be determined that accommodation is possible. And voltage calculation can be performed accurately by calculating the load of a distribution line accurately. Hereinafter, such an effect will be described using a specific example.

<Examples of load accommodation during power outages>
FIG. 3 is a diagram illustrating an example of load accommodation during a power failure. The distribution line L1 is divided into sections S1, S2, and S3 by the outlet F1 and the switches A1 and A2. A generator (power source) G1 is connected to the section S3 of the distribution line L1. On the other hand, the distribution line L2 is divided into sections S4, S5, and S6 by the outlet F2 and the switches A3 and A4. A generator (power source) G2 is connected to the section S6 of the distribution line L2. The section S3 of the distribution line L1 and the section S6 of the distribution line L2 are connected by a switch A5.

Here, in the distribution system shown in FIG. 3, in order to perform a power failure operation in the section S2 of the distribution line L1, consider the case where the power in the section S3 is interchanged from the distribution line L2. The outlet current of the distribution lines L1 and L2 before the power failure is 100 + j20 [A], and the generated current of the generators G1 and G2 is 30-j10 [A]. In this case, the distribution line load current is 130 + j10 [A] for both the distribution lines L1 and L2. In the conventional calculation method, the outlet current is 102.0 (= √ (100 ² +20 ² )) [A], and the generator current is 31.6 (= √ (30 ² +10 ² )) [A]. The sum of the distribution line load current is 133.6 [A].

The section load ratio of the distribution lines L1 and L2 is set to section S1: section S2: section S3 = section S4: section S5: section S6 = 0: 1: 1. In this case, the current value to be accommodated from the distribution line L2 is (130 + j10) / 2 = 65 + j5 [A], and the outlet current of the distribution line L2 after accommodation is | 130 + j10 + 65 + j5 | = √ (195 ² +15 ² ) = 195.6 [A]. In the conventional calculation method, the current value to be accommodated from the distribution line L2 is 133.6 / 2 = 66.8 [A], and the outlet current of the distribution line L2 after the interchange is 133.6 + 66.8 = 200. 4 [A].

  In the case where the upper limit value of the outlet current of the distribution line L2 is 200 [A], it has been determined that 200.4> 200 in the conventional calculation method and the interchange is impossible, but in the embodiment of the present invention, Since 195.6 <200, it is determined that the system can be accommodated, and the power distribution system can be operated more efficiently. In addition, when receiving power interchange from the distribution line L2 to the section S3 of the distribution line L1, the generator G1 connected to the section S3 and the generator G2 connected to the section S6 are disconnected (stopped). The outlet current after accommodation is calculated in a state where the generator G1 and the generator G2 are disconnected.

<Example of voltage determination 1>
FIG. 4 is a diagram illustrating calculation of a voltage drop to determine whether or not the voltage can be accommodated (an example of voltage determination). The configurations of the distribution lines L1 and L2 are the same as those in FIG. However, the generators G1 and G2 are assumed to be in a disconnected state and are not illustrated. In this case, the voltage drop is expressed by the following equation 4.
ΔV≈I (R cos θ + X sin θ) × √3 Equation 4
(R: resistance component of impedance,
X: reactance component of impedance,
cos θ: load power factor)

  In this example, assuming that the impedance of each section of the distribution line is R + jX = 0.5 + j1.5 [Ω], the voltage drop at the time of interchange (generator disconnected state) is calculated. The load power factor is defined for each distribution line and is calculated as 0.99.

  The conventional calculation method is as follows. The voltage drop in the section S4 is 200.4 × (0.5 × 0.99 + 1.5 × 0.14) × √3 = 244.7 [V]. The voltage drop in the section S5 is (200.4 + 133.6) / 2 × (0.5 × 0.99 + 1.5 × 0.14) × √3 = 203.9 [V]. The voltage drop in the section S6 is (133.6 + 66.8) / 2 × (0.5 × 0.99 + 1.5 × 0.14) × √3 = 12.4 [V]. The voltage drop in the section S3 is 66.8 / 2 × (0.5 × 0.99 + 1.5 × 0.14) × √3 = 40.8 [V]. The overall voltage drop is 244.7 + 203.9 + 122.4 + 40.8 = 611.8 [V]. When the power transmission terminal voltage is 6700 [V], the terminal voltage is 6700−611.8 = 6088.2 [V].

  The calculation method according to the embodiment of the present invention is as follows. The average current of the section S4 is | 195 + j15 | = 195.6 [A], and the voltage drop is 195.6 × (0.5 × 0.99 + 1.5 × 0.14) × √3 = 23.88 [ V]. The average section current in section S5 is | (195 + j15 + 130 + j10) /2|=163.0 [A], and the voltage drop is 163.0 × (0.5 × 0.99 + 1.5 × 0.14) × √3 = It becomes 199.0 [V]. The average section current in section S6 is | (130 + j10 + 65 + j5) /2|=97.8 [A], and the voltage drop is 97.8 × (0.5 × 0.99 + 1.5 × 0.14) × √3 = 119.4 [V]. The average section current of section 3 is | (65 + j5) /2|=32.6, and the voltage drop is 32.6 × (0.5 × 0.99 + 1.5 × 0.14) × √3 = 39.8. [V]. The overall voltage drop is 238.8 + 199.0 + 119.4 + 39.8 = 597.0 [V]. When the power transmission terminal voltage is 6700 [V], the terminal voltage is 6700−597.0 = 6103.0 [V].

  According to this, since 6103.0> 6088.2, the result of the calculation method according to the embodiment of the present invention has a smaller voltage drop and a higher terminal voltage than the result of the conventional calculation method. Even if the conventional calculation method has a large voltage drop and the terminal voltage is low and cannot be accommodated, it may be determined that the calculation method according to the embodiment of the present invention is interchangeable.

<Example 2 of voltage determination>
In the first voltage determination example, the voltage drop is scalar-calculated, but the accuracy can be further improved by performing a vector operation on the voltage drop. In this case, the voltage drop is expressed by the following Equation 5.

  The calculation method according to the embodiment of the present invention is as follows. The voltage drop in the section S4 is 195.6 × {(0.5 × 0.99 + 1.5 × 0.14) + j (1.5 × 0.99−0.5 × 0.14)} × √3 = 238.8 + j479.4 [V]. The voltage drop in section 5 is 163.0 × {(0.5 × 0.99 + 1.5 × 0.14) + j (1.5 × 0.99−0.5 × 0.14)} × √3 = It becomes 199.0 + j399.5 [V]. The voltage drop of the section 6 is 97.8 × {(0.5 × 0.99 + 1.5 × 0.14) + j (1.5 × 0.99−0.5 × 0.14)} × √3 = 119.4 + j239.7 [V]. The voltage drop in section 3 is 32.6 × {(0.5 × 0.99 + 1.5 × 0.14) + j (1.5 × 0.99−0.5 × 0.14)} × √3 = 39.8 + j79.9 [V].

  The overall voltage drop is the above vector sum, which is 597.0 + j118.5. When the power transmission end voltage is 6700 [V], the terminal voltage is | 6700-597.0-j118.5 | = 6219.6 [V].

  According to the effect of the calculation method described above, the power outage can be reduced in the short term, and the countermeasure cost for the power outage can be suppressed in the long term.

  According to the embodiment of the present invention described above, when the load current calculation unit 4 of the load current calculation device 1 calculates the distribution line load current from the extraction port current and the distributed power source current, Considering the power factor and the power factor of the power source current, by calculating the total value of the current by vector calculation, even if the power factor of the outlet current and the power factor of the distributed power source current are significantly different, Distribution line load current can be obtained correctly. If the distribution line load current is correctly known, the voltage drop can be correctly understood. Therefore, the vector calculation can be effectively applied even when determining whether or not power supply is possible based on the value of the voltage drop. In other words, when the distribution line load current is obtained by scalar calculation in the past, it has been determined that the necessary power supply cannot be performed as a result of overestimation of the distribution line load current. Thus, it is possible to determine that power can be supplied by accurately evaluating the distribution line load current.

  In addition, when the embodiment of the present invention is compared with a strict calculation method (AC method power flow calculation or the like) considering the voltage phase shift, it is assumed that there is no voltage phase shift in each section of the distribution line. Since the distribution line load current is obtained by simple calculation, programming and arithmetic circuit design can be easily performed, and resources such as memory can be reduced. Therefore, the apparatus (load current calculation apparatus 1) for realizing this can be configured simply and the calculation process can be performed at high speed. According to this, when power is interchanged for power outage work, etc., it can respond quickly.

  Although the best mode for carrying out the present invention has been described above, the above embodiment is intended to facilitate understanding of the present invention and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and equivalents thereof are also included in the present invention.

It is a figure which shows the structural example of the load current calculation apparatus which concerns on embodiment of this invention. It is a figure explaining the vector calculation which the load current calculation means of a load current calculation apparatus performs, (a) shows the example of a structure of a distribution line, (b) shows the calculation of a current vector. It is a figure which shows the example of the load accommodation at the time of a power failure. It is a figure which shows the example of voltage determination.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Load current calculation apparatus 2 Drawer outlet current acquisition means 3 Power supply current acquisition means 4 Load current calculation means 5 Load current output means L, L1, L2 Distribution line G, G1, G2 Generator (power supply)

Claims (2)

A load current calculation method for calculating a load current of a distribution line by a device,
A first step in which the apparatus obtains an effective current and a reactive current of the outlet of the distribution line;
A second step in which the apparatus obtains active and reactive currents of one or more power supplies connected to the distribution line;
From the effective current and reactive current of the outlet acquired in the first step and the effective current and reactive current of the power source acquired in the second step, the device calculates the load of the distribution line by vector calculation. A third step of calculating active and reactive currents;
A fourth step in which the device outputs an effective current and a reactive current of the load of the distribution line calculated in the third step;
The load current calculation method characterized by including. An outlet current acquisition means for acquiring an effective current and a reactive current of the outlet of the distribution line;
Power supply current acquisition means for acquiring effective current and reactive current of one or more power supplies connected to the distribution line;
From the effective current and reactive current of the outlet acquired by the outlet current acquisition means and the effective current and reactive current of the power source acquired by the power supply current acquisition means, the effective current of the load of the distribution line and Load current calculation means for calculating reactive current;
Load current output means for outputting effective current and reactive current of the load of the distribution line calculated by the load current calculating means;
A load current calculation device comprising:

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