JPS5952788B2 - Method for measuring the skin effect coefficient of power cables - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for measuring the skin effect coefficient of power cables.

In general, the AC resistance of a power cable conductor is greater than the DC resistance due to skin effect and proximity effect.

The rate of increase in AC resistance due to the skin effect is called the skin effect coefficient (hereinafter referred to as Fs). When measuring this Fs value, the following method has conventionally been used. That is, as shown in FIG. 1, two power cables 1,
2 are laid in parallel, and both ends of the conductors 3 of cables 1 and 2 are short-circuited to form a closed circuit as shown in the figure.A current I is passed through this using a ring transformer 4, and the current value changes. Measurement is performed using a current meter 5 and a current measuring device 6.

On the other hand, the voltage drop V in the section l between the appropriate points A and B of the conductor 3 of the cable 1 at that time is determined by connecting both ends to the points A and B of the conductor 3, respectively, and parallel to the length direction of the conductor 3. A voltage lead wire 7 is provided, cut in the middle, and measured using this lead wire 7 and an AC potentiometer 8. The skin effect coefficient Fs is determined from the current I and the voltage drop V using the following formula. Ta. I
V)・c0sf Fs=,・・・・・・・・・・・・・・・・・・・・・
・・・・・・(1) 111-RDc・φ: Phase difference between V and I.

RDC: Direct current resistance of conductor 3 between A and B.

By the way, when using this measurement method, cable 1
The measured value of the voltage drop V varies depending on the attachment angle θ of the voltage lead wire 7 (see FIG. 2), and the value of Fs also varies.

Then, if we increase the distance d between conductors 3 of cables 1 and 2,
When the amount of change in the value of Fs due to the mounting angle θ is reduced and d is expanded to a certain value, the value of Fs converges to approximately the theoretical value. Therefore, conventionally, the value of Fs was converged by changing the conductor interval d, and the value of Fs at that time was determined.

Therefore, it has been extremely difficult to measure Fs in cases where the conductor spacing d cannot be changed as in existing lines. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for measuring the skin effect coefficient of a power cable, which eliminates the drawbacks of the above-mentioned prior art and can easily and accurately measure the skin effect coefficient.

A feature of the present invention is that when measuring the voltage drop between the conductor of a power cable and a given section, both ends are connected to points separated by a given distance on the conductor of the power cable, and extend in the length direction of the power cable. Install four or more voltage lead wires arranged at equal intervals on the outer circle of the cable, cut them in the middle, measure the voltage drop at each part, and calculate the skin effect of the power cable from the average value. This is the point at which the coefficients are calculated.

The present invention will be described in detail below with reference to the embodiment shown in FIG. 2 and FIGS. 3 and 4.

The procedure for measuring the skin effect coefficient of the present invention is the same as that described using FIG. 1, but in the present invention, the arrangement of the voltage lead wires is different.

FIG. 2 is a sectional view showing an example of the arrangement of voltage lead wires in the case of the present invention. In FIG. 2, 1 and 2 are conductors of power cables 1 and 2, and 9a to 91 are voltage lead wires, A total of 12 of these are arranged on the outer periphery of the power cable 1 at equal intervals, that is, with an attachment angle θ of every 30 degrees. Both ends of these voltage lead wires 9a to 91 are respectively connected to points A and B of the conductor 3 of the power cable 1, as shown in FIG. 1, and extend in the length direction of the conductor 3. Each of the voltage lead wires 9a to 9 is cut in the middle, and an AC potentiometer 8 is connected thereto.
When measuring the skin effect coefficient Fs of the power cable 1, a current 1 is passed through the conductor 3, and the voltage drop V between points A and B on the conductor 3 at that time is calculated by connecting the voltage leads 9a to 91 and the AC potentiometer 7. As in the case of Fig.
), the apparent skin effect coefficient F″S is obtained, and the average value of each F″S is set as Fs. Now, in the case of a power cable whose conductor is a copper rod with a length of 5.5 m and a diameter of 32 mm, if the distance 1 between A and B is 4] T) m, and the distance d between the conductors is 10 mm, then each voltage lead line 9
The apparent skin effect coefficient F″S obtained from the voltage drop V between A and B measured in steps a to 91 is as shown in FIG.

In Fig. 3, the horizontal axis is the installation angle θ of the voltage lead wire, and the vertical axis is the apparent skin effect coefficient F″S.In this way, the theoretical value a is shown as a straight line, and the measured value is shown as the curve b. Although it varies sinusoidally depending on the mounting angle θ, if the average value of each measured value is taken, the average value almost matches the theoretical value.

Therefore, in the present invention, each voltage lead wire 9a
The apparent skin effect coefficient F''S was calculated from equation (1) using the voltage drop V measured in 91 to 91, and the average value thereof was taken as the skin effect coefficient Fs. Figure 4 shows the measurement results of the present invention. This is a diagram showing the relationship between the conductor spacing d and the measured value of the skin effect coefficient Fs when using the method. In the range, the mark ○ is the measured value of the skin effect coefficient Fs that is averaged according to the present invention.From this, the smaller the value of d, the larger the apparent variation in the skin effect coefficient. As shown, it is constant regardless of d, and almost coincides with the theoretical value shown by the dotted line,
It can be seen that accurate measurements can be made.

According to the embodiment of the present invention, there is no need to change the conductor spacing d as in the conventional case, so measurement is easy, and even if there are other power supply circuits or steel materials near the measurement circuit, the degree of influence caused by them can be reduced. are canceled by averaging, so accurate measurements can be made.

Furthermore, even if the conductor spacing d cannot be changed, it is possible to measure only the skin effect coefficient independently.

In the embodiment shown in FIG. 2, there are 12 sets of voltage lead wires, but four or more sets are sufficient as long as they are equally spaced, and almost the same effect can be obtained.

As explained above, according to the present invention, there is a remarkable effect that the skin effect coefficient can be easily and accurately measured.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional skin effect coefficient measurement method, FIG. 2 is a sectional view showing an example of the arrangement of voltage lead wires in the skin effect coefficient measurement method of the present invention, and FIG. Lead wire attachment angle θ and apparent skin effect coefficient F
Figure 4 is a diagram showing the relationship between the conductor spacing d and the skin effect coefficient Fs according to the present invention. 1, 2: power cable, 3: conductor, 4: link transformer, 5 : Current transformer, 6: Current measuring device, 8: AC potentiometer, 9
a-91: Voltage lead wire.

Claims (1)

[Claims] 1. Lay multiple power cables to be measured in parallel, and configure a closed circuit by short-circuiting both ends of the conductors of two of the cables, and the current flowing through the closed circuit and the cable In a skin effect coefficient measurement method for determining a skin effect coefficient from a voltage drop in a predetermined section of a conductor of one of the cables, the voltage drop is measured at both ends of the cable conductor at points separated by a predetermined distance from each other along the length of the cable. The skin effect coefficient of the power cable conductor is determined from the average of the measured values by measuring four or more voltage lead wires arranged at equal intervals around the outer circumference of the cable that extends in the horizontal direction at each section cut in the middle. A method for measuring a skin effect coefficient, characterized in that: