JPH04301774A - Measuring method of ac resistance in conductor - Google Patents

Abstract

PURPOSE:To measure the AC resistance of a conductor easily and accurately by amplifying the potential difference between two points of the conductor, detecting the phase difference before and after the amplification, measuring the electric power value by giving the flow current and the potential difference, and applying the phase difference and the correcting of amplifying degree depending on the power value, the potential difference, and the flow current. CONSTITUTION:When an AC current for deciding is induced to a closed circuit which consists of a conductor 2 and a passage 6 for a closed circuit, the current value I is given to a measuring meter group 13 by a converter 8 for current measuring. On the other hand, the potential difference V between the terminals 5A and 5B for potential difference detecting of the conductor 2 is given to an amplifier Amp, and after amplified at an amplifying level alpha, making the value as Vp=alphaV, the value is given to the meter group 13, and the phase difference phi generated between the input and the output terminals is detected by a phase indicator 12. In the meter group 13, the electric power W is measured by a wattmeter 14, the current value I is measured by an amperemeter 16, and the potential difference Vp after the amplification is measured by a voltmeter 16. And depending on these measuring values, the AC resistance can be found accurately by the detected phase difference phi and the amplifying degree alpha.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring alternating current resistance of conductors such as electric wires and cables.

0002

[Background Art] Generally, in order to measure the AC resistance of a conductor such as an electric wire or cable, an AC current is passed through the conductor, and the current I, the potential difference V between two points on the conductor, and the current and potential difference are measured. It is necessary to know the phase difference θ between However, since it is difficult to directly measure the phase difference θ, the wattmeter method has conventionally been used as one method for measuring the AC resistance of a conductor.

In this wattmeter method, since the power W when an alternating current is passed through a conductor is expressed as W=VI cosθ, cosθ can be calculated by measuring the power with a wattmeter and also measuring the current I and the potential difference V. Therefore, based on the value of cos θ found from the measured value of the current, the current I and the potential difference V, the AC resistance Rac can be found as follows: Rac = (V/I) cos θ .

0004

[Problems to be Solved by the Invention] The above-mentioned method of measuring AC resistance of a conductor using the wattmeter method has the following problems. In other words, when the potential difference is small, the measurement error of a wattmeter becomes extremely large and it becomes difficult to measure the power. In order to provide a large potential difference to the wattmeter, it was necessary to increase the length of the conductor sample (the distance between the two gauge points for measuring the potential difference) or to increase the current applied. However, if the length of the conductive sample is increased in order to give a large potential difference, the measurement equipment configuration will become larger, causing space problems, and if the current is increased, the induction of the current into the measuring device will be large. At the same time, the conductor temperature increases during measurement, which increases measurement errors, and as a result, there is a possibility that accurate measurement becomes difficult.

The present invention was made against the background of the above circumstances, and it is possible to easily and easily measure the AC resistance of a conductor without making the length of the sample extremely long or increasing the current flowing through it. The purpose of this invention is to provide a method that allows accurate measurement.

[0006]

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the conductor AC resistance measurement method of the present invention, the potential difference between two points of a conductor through which an AC current for measurement is passed is once amplified by an amplifier. We decided to determine the AC resistance of the conductor by setting the potential difference in a range that allows accurate measurement of the power value with a wattmeter, and by making corrections for the phase shift between input and output and the degree of amplification during amplification by an amplifier.

Specifically, the method for measuring AC resistance of a conductor of the present invention involves passing an AC current through the conductor to be measured, amplifying the potential difference between two points on the conductor by a predetermined amplification degree α, and The phase difference φ before and after the amplification is detected, and the energizing current and the amplified potential difference are given to a wattmeter to measure the power value W, and the amplified potential difference Vp and the energizing current I are measured. , based on the measured power value W, the potential difference Vp, and the conducting current I, the alternating current resistance of the conductor is determined by correcting the phase difference φ and the amplification degree α.

[0008]

[Operation] In the conductor AC resistance measuring method of the present invention, the potential difference V between two gauge points of a conductor through which an AC current is passed for measurement is amplified by a predetermined amplification degree α by an amplifier, and can be measured with a wattmeter. Let the potential difference Vp (=αV) be within the range. At this time, since a phase shift occurs between the input and output of the amplifier, the phase difference φ is detected for correction to be described later. It goes without saying that there is an inherent phase difference θ between the energizing current I and the potential difference V between the two gauge points of the conductor.

The power meter measures the power value W by applying the current I and the amplified potential difference Vp. The power value W at this time is the energizing current value I, the potential difference after amplification Vp (=αV
), and the original phase difference θ and the phase difference φ between the input and output of the amplifier, the following equation (1) W = Vp Icos (θ + φ) ... (1
) is given by

[0010] Therefore, cos(θ+φ) is the following (2)
Formula cos(θ+φ)=W/Vp I... (2)
is given by

Here, since W, Vp, and I are detected as measured values, cos(θ+φ
) is found. Therefore, the value of (θ+φ) is also known, but the value of φ is detected separately and is known, so the value of θ is eventually determined.

By the way, the AC resistance Rac of the conductor is as follows (3
) Formula Rac=(V/I)cosθ...(
3), but as mentioned above, Vp = αV for the amplification degree α, so V = Vp /α
... (4), and in the end, θ obtained by removing the phase difference φ in the amplifier from equation (2) and the measured potential difference V
p, the measured current value I, and the known amplification degree α, Rac=(Vp/αI)cosθ... (5
), the AC resistance Rac can be found.

In the actual calculation, the original AC resistance Ra
Before calculating c, that is, before adding correction for the phase difference φ caused by the amplifier, cos(
Using the value of θ+φ) as is, the apparent AC resistance value R
acp, Racp = (V/I) cos (θ+φ) = (Vp /
αI) cos(θ+φ) ... (6) is calculated, and then correction is made by the phase difference φ of the amplifier, and (
Of course, the original AC resistance Rac defined by equation 5) may also be found.

In any case, based on the measured power value W, the measured potential difference Vp, and the measured current value I, the AC resistance Rac can be determined by correcting the phase difference φ and the amplification degree α in the amplifier. .

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the overall configuration of an apparatus for carrying out the method of the present invention.

The cable 1 to be measured is, for example, a conductor 2.
An insulating coating and a shielding layer 3 are formed on the outer surface. The conductor 2 is exposed near both ends of the cable 1, and potential difference detection terminals 5A and 5B are attached to the exposed conductor portions.

Further, a closed circuit forming current conducting path 6 is connected to both ends of the conductor 2 so as to constitute a closed circuit as a whole. A current-carrying coil 7 is attached to one end of the closed-circuit forming current-carrying path 6 for supplying an alternating current for measurement to the closed circuit formed by the current-carrying path 6 and the conductor 2. Further, a current measuring current transformer 8 is attached to the other end side of the closed circuit forming energizing path 6.

Each of the potential difference detection terminals 5A, 5B includes:
Two potential difference detection lead wires 91A and 92A, respectively;
91B and 92B are connected. Two of these potential difference detection lead wires are wound around the cable 1 in opposite directions at the same pitch, and are connected to the potential difference detection terminal 5A.
, 5B at the center position between the lead wires 91A, 92A.
are short-circuited to each other, and the lead wires 91B and 92B are short-circuited to each other, and the lead wires 93 and 94 are twisted and drawn out toward the measuring device main body 10 from the short-circuit point. Here, as mentioned above, the two potential difference detection lead wires 91A, 92A; 91B, 92B are wound around the cable 1 at the same pitch in opposite directions, so that they are not affected by the induction caused by the current. In other words, the induced current is canceled out and detected in a non-induced state.

[0019] Inside the measuring device main body 10, an amplifier 11 is provided.
, a phase meter 12, and a measuring instrument group 13 are provided, and the measuring instrument group 13 is composed of a wattmeter 14, an ammeter 15, and a voltmeter 16. The lead wires 93 and 94 are connected to the input terminals of an amplifier 11, and the output terminal of the amplifier 11 is electrically led to the measurement instrument group 13. Further, the phase meter 12 is connected between the input terminal and the output terminal of the amplifier 11. On the other hand, the output of the aforementioned current measuring current transformer 8 is also electrically led to the measuring instrument group 13.

In the above embodiment, when an alternating current is passed through the current-carrying coil 7 by an alternating current power supply, an alternating current for measurement is induced in the closed circuit consisting of the conductor 2 and the closed circuit forming passage 6. The current value I of this alternating current for measurement is picked up by the current measuring current transformer 8 and is given to the measuring instrument group 13. On the other hand, the potential difference V between the potential difference detection terminals 5A and 5B in the conductor 2 of the cable 1 is determined by the lead wires 91A and 9
2A; 91B and 92B to the amplifier 11, where it is amplified by the amplification degree α, and then applied to the measurement instrument group 13 as a value of Vp = αV. Input terminal of amplifier 11 -
A phase shift occurs between the output terminals, and the phase difference φ is detected by the phase meter 12. In the measurement instrument group 13, the power meter 14 measures the power value W, that is, the above (1).
The value given by the formula is measured, and an ammeter 15,
The voltmeter 16 measures the current value I and the amplified potential difference Vp. Then, from these measured values, the phase difference φ detected by the phase meter 12, and the amplification degree α, the AC resistance Rac is determined as already described.

[0021] The specific means for this final calculation is arbitrary, and it may be calculated by a computer or the like based on the values read from each meter, or the measured value signal may be output from the meter as a digital signal. In such a case, the signal may be directly input to a computer or the like for arithmetic processing. Furthermore, although it is common to use a DC amplifier as the amplifier 11, an AC amplifier may also be used.

[0022]

[Effects of the Invention] As is clear from the above explanation, although a wattmeter is used in the conductor AC resistance measurement method of the present invention, the potential difference signal input to the wattmeter is amplified in advance. Therefore, even if the potential difference between the measurement points between the conductors is extremely small, the power value can be detected accurately and the AC resistance of the conductor can be accurately determined. Since the potential difference between the measurement points between the conductors does not need to be small in this way, the length of the measurement conductor sample can be shortened, so the overall configuration of the measurement device can be made smaller, which is advantageous in terms of space. In addition, since there is no need to increase the current flowing, it is possible to prevent the effects of induction on the measuring instrument due to excessive current flowing, and the temperature rise of the conductor during measurement is also reduced.As a result, measurement errors can be sufficiently reduced. can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the conductor AC resistance measuring method of the present invention.

[Explanation of symbols]

2 Conductor 11 Amplifier 12 Phase meter 14 Power meter 15 Ammeter 16 Voltmeter

Claims (1)

[Claims] [Claim 1] Applying an alternating current to the conductor to be measured, amplifying the potential difference between two points of the conductor with a predetermined amplification degree α using an amplifier, and detecting the phase difference φ before and after the amplification. The current and the amplified potential difference are applied to a wattmeter, and the wattmeter measures the power value W, and also measures the amplified potential difference Vp and the energizing current I, and calculates the measured power value W, the potential difference Vp, and the energizing current I. Based on the phase difference φ
A method for measuring AC resistance of a conductor, characterized in that the AC resistance of the conductor is determined by adding correction for the amplification factor α.