JP2000292464A - Correction method of induced error in current measurement - Google Patents

Abstract

(57) [Problem] To correct a measurement error in a transmission and distribution line of a current detection sensor using an optical magnetic field sensor so that correct current measurement can be performed. SOLUTION: A sensor 1 is provided by a current flowing through each phase A, B, C of a transmission / distribution line 4 arranged in one horizontal line or one vertical line.
The vector of the apparent measurement signal for each phase A, B, and C of the transmission and distribution line 4 induced by a to 1c is easily corrected by using the easily obtained three vector sum i _ERR. So that correct current measurement can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting an induced error in current measurement using an optical magnetic field sensor.

[0002]

2. Description of the Related Art It is known that an optical crystal such as BSO, BGO or ZnSe has a Faraday effect in which a polarization plane rotates when a magnetic field is applied. In the optical magnetic field sensor using this Faraday element, since the sensor section and the signal converter are connected by a highly insulating optical fiber, there is no fear of insulation breakdown or short circuit. It is used to measure the current inside and around the electrical equipment inside.

That is, as shown in FIG. 8A, an optical magnetic field sensor 1 composed of a Faraday element has optical fibers 3 and 3 'attached to both sides thereof. It is sandwiched between the provided gap portions and fitted into the transmission line 4. Then, the light emitted from the light emitting portion of the signal converter 5 installed at a position distant from the transmission line 4 is
The light returns to the light receiving section of the signal converter 5 via the optical sensor 1 and the optical fiber 3 '. At this time, the light incident on the optical magnetic field sensor 1 is subjected to intensity modulation by the Faraday element unit by a magnetic field generated in proportion to the current flowing through the transmission line 4, and then reaches the light receiving unit of the signal converter 5, and the actual current A signal I ′ corresponding to I is detected (see FIG. 3B).

Conventionally, such an optical magnetic field sensor 1 has been attached to, for example, each of the three phases of a transmission or distribution line arranged horizontally or vertically.

[0005]

However, in the above-described measuring method, there is a problem that the optical magnetic field sensors attached to each of the three phases generate errors due to electromagnetic induction from other phases.

That is, the above-mentioned structure requires a gap of about 20 to 30 mm because of the structure in which the optical magnetic field sensor is sandwiched by the gap of the iron core. When the gap is wide as described above, the number of lines of magnetic force from other phases passing through the gap increases, and the magnetic field changes by being combined with the magnetic field of the original phase. As a result, an error occurs in the current value detected by the optical magnetic field sensor.

An object of the present invention is to correct a current value error detected by an optical magnetic field sensor so that correct measurement can be performed.

[0008]

According to the present invention, an optical magnetic field sensor is provided for each of three phases of a horizontal or vertical transmission and distribution line, and an apparent measurement signal of each phase is detected. And the combined vector of the three signals is corrected based on the following equation to obtain a value closer to the true value of the current of each line.

[0009]

(Equation 2)

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, as shown in FIG.
The present invention is applied to a current measuring system of a horizontal or vertical transmission and distribution system, and includes three-phase transmission lines A, B. Each of the current sensors 1a, 1b, 1c attached to C is connected to the signal converter 5.

Each of the current sensors 1a, 1b, and 1c is provided with the optical magnetic field sensor 1 on the iron core 2 shown in FIG. 8, and as described above, the optical magnetic field sensor 1 is provided on the gap provided on the iron core 2. And outputs an optical output that has been subjected to intensity modulation in accordance with the strength of the magnetic field generated in the lines A, B, and C inserted through the iron core 2.

The signal converter 5 has a calculating means and calculates a more accurate current value of each of the lines A, B and C based on the correction method of the present invention. Therefore, the principle will be described in detail below.

For example, as shown in FIG. 2A, the transmission and distribution line B whose arrangement is located at the center is referred to as a B phase here. Of the transmission and distribution lines on both sides of the phase B, the phase of either line is advanced by approximately 120 ° from the phase B, and
A phase delayed by about 120 ° from the B phase is referred to as a C phase.

In FIG. 2A, the order is A, B, and C from the left. However, the following description is the same when the order is A, B, and C from the right. Will be described.

The distance between the lines A, B, and C is A to B
The interval is between B and C.

Then, the vectors of the apparent measurement signals detected by the sensors 1a, 1b, and 1c in accordance with the phase currents of the phases A, B, and C are respectively represented by:

[0018]

(Equation 3)

And the vector of the true signal corresponding to the actual current at that time is

[0020]

(Equation 4)

It is assumed that

After defining as described above,
The current of each of the phase, the B phase, and the C phase will be examined.

First, the phase A will be examined. That is,
Induction from phase B to phase A

[0024]

(Equation 5)

And the component derived from phase C is

[0026]

(Equation 6)

As follows:

[0028]

(Equation 7)

And

[0030]

(Equation 8)

The composite vector of

[0032]

(Equation 9)

It is assumed that

By the way, the current

[0035]

(Equation 10)

The strength of the magnetic field at a point at a distance r from the flowing conductor

[0037]

[Equation 11]

Is

[0039]

(Equation 12)

Which is inversely proportional to the distance r.

Therefore, the magnetic field from phase B to phase A

[0042]

(Equation 13)

The vector of the signal corresponding to

[0044]

[Equation 14]

Is

[0046]

(Equation 15)

And the magnetic field from phase C to phase A

[0048]

(Equation 16)

The signal vector corresponding to

[0050]

[Equation 17]

Is

[0052]

(Equation 18)

Is as follows.

Here, in a normal power transmission and distribution system, since the three-phase currents are almost equal in magnitude, approximately

[0055]

[Equation 19]

Can be obtained. That is,

[0057]

(Equation 20)

Is as follows.

Therefore, when a vector diagram of each signal is made based on this, the result is as shown in FIG.

[0060]

(Equation 21)

Is obtained.

At this time,

[0063]

(Equation 22)

Is

[0065]

(Equation 23)

Since it is sufficiently large compared to

[0067]

(Equation 24)

Can be obtained.

Similarly, in the case of phase B, the derivation from phase A with respect to phase B is

[0070]

(Equation 25)

And the amount derived from phase C is

[0072]

(Equation 26)

As

[0074]

[Equation 27]

The composite vector of

[0076]

[Equation 28]

It is assumed that

At this time, since the B phase is at the center position, the magnetic field from the A phase to the B phase

[0079]

(Equation 29)

Magnetic field from phase C to phase B

[0081]

[Equation 30]

The signal vector corresponding to

[0083]

(Equation 31)

Is

[0085]

(Equation 32)

[0086]

From these results, a vector diagram of each signal is made as shown in FIG.

[0088]

[Equation 33]

[0089]

(Equation 34)

## EQU10 ##

On the other hand, in the case of phase C, the amount derived from phase A

[0092]

(Equation 35)

And the amount derived from phase B is

[0094]

[Equation 36]

[0095]

[0096]

(37)

And

[0098]

(38)

The composite vector of

[0100]

[Equation 39]

It is assumed that

At this time, since the distance between the phases A to C is 2l and the distance between the phases B to C is 1 from FIG. 2A, as described for the phase A,

[0103]

(Equation 40)

[0104] Therefore, when the vector diagram of the signal is drawn in the same manner as in the case of the A phase and the B phase, the result is as shown in FIG.

[0105]

[Equation 41]

Can be obtained.

Now, the vector of the apparent measurement signal including the components derived from the A, B, and C phases.

[0108]

(Equation 42)

Vector composite value

[0110]

[Equation 43]

Is

[0112]

[Equation 44]

And each measurement signal is

[0114]

[Equation 45]

Therefore, when this is substituted into the above equation,

[0116]

[Equation 46]

Is obtained.

At this time, since the sum of the three phase currents becomes 0 in the preceding term on the right side,

[0119]

[Equation 47]

Is obtained.

Here, from FIG. 3 and FIG. 4, the magnitude and phase of the error signal are:

[0122]

[Equation 48]

The signal vector is as shown in FIG.

From this figure

[0125]

[Equation 49]

Becomes

[0127]

[Equation 50]

Is as follows.

This equation (4) is converted into equations (1), (2) and (3)
Substituting into

[0130]

(Equation 51)

Is obtained.

That is, the current detection sensors 1a, 1
b, 1c synthesize the vector of the apparent measurement signal detected and its absolute value

[0133]

(Equation 52)

By calculating the current value, a current value closer to the true value can be calculated very easily.

As described above, since it is possible to correct the induced component which has not been considered in the related art, it is possible to reduce the measurement error to one tenth or less as compared with the conventional measured value without correction.

Further, as a second embodiment, FIG. 7 is a block diagram schematically showing the synthesizing circuit 20.

That is, as shown in FIG.
0 can be constituted by an analog circuit using a simple adder of one operational amplifier.

On the other hand, in the second embodiment, the synthesizing circuit is shown in analog form, but it can be easily realized by a digital method as described below, and will be described below as a third embodiment.

[0139] That is, even in the case of digital processing using the A / D converter, for example, when i chronological sample data group of _a signal _{i a1, i a2 ··· i an} ··· i b signal sequence sample data group i _b1, i _b2 ··· i when _bn · · · i chronological sample data group i _c1 of _C signal, i _c2 and _{··· i cn ···, (i a} + i b + i c _{) = (i a1 + i b1} + i c1), may be the calculation of the data group _{(i a2 + i b2 + i} c2) ··· ·········· (i an + i bn + i cn).

As described above, since the present invention can be applied with a simple circuit or operation, the conventional measurement accuracy can be easily improved.

Although FIG. 2 shows the horizontal arrangement, it is apparent that the arrangement may be vertical.

[0142]

According to the present invention, as described above, the current measurement error can be greatly reduced by using the conventional sensor output without adding any special device.

[Brief description of the drawings]

FIG. 1 is a block diagram of a first embodiment.

FIG. 2A is an explanatory diagram of an operation of the first embodiment. FIG. 2B is an explanatory diagram of an operation of the first embodiment.

FIG. 3 is a vector diagram of an A-phase signal according to the first embodiment;

FIG. 4 is a vector diagram of a B-phase signal according to the first embodiment;

FIG. 5 is a vector diagram of a C-phase signal according to the first embodiment.

FIG. 6 is a vector diagram of a signal of an error signal according to the first embodiment.

FIG. 7 is a block circuit diagram according to a second embodiment;

8A is a block diagram of an optical magnetic field sensor. FIG. 8B is an output waveform diagram of an optical magnetic field sensor.

[Explanation of symbols]

 1a to 1c Optical magnetic field sensor 4 Transmission and distribution line

(Equation 53)

Claims (1)

[Claims] 1. A horizontal or vertical arrangement of transmission and distribution lines 3
An optical magnetic field sensor is provided for each phase, and a more accurate current value of each line is obtained based on the following equation from the apparent measurement signal vector of each phase detected and the composite vector of the three signals. A method for correcting an induced error in current measurement. (Equation 1)