JPH0574787B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring AC resistance of a power cable conductor, which can measure the AC resistance of a power cable conductor with high accuracy using a small-capacity power source.

[Prior art]

It is known that when an alternating current is passed through a power cable, the electrical resistance increases more than when a direct current is passed. This is due to the influence of the skin effect, and in recent years various methods have been proposed for actually measuring this AC resistance.

All of these measurements are performed using an AC bridge or an AC potentiometer.
The figure shows the configuration of a measurement circuit using an AC bridge. In this figure, the power cable conductor 1 constitutes a closed circuit C together with the return path Q, while the lead wires 3 and 4 connected to the voltage input terminal 2a of the AC bridge 2 connect the first side B1 of the bridge B constitutes the impedance of Then, an alternating current is passed from the alternating current power supply V to the closed circuit C via the transformer 5, and after this current value is converted to an appropriate value by the current transformer 6, the current input terminal 2b of the alternating current bridge 2 is supplied to the second side B2 of the bridge B.
Here, the variable impedance Z (=x+jy/w) of the fourth side B4 of the bridge B is adjusted, and the resistance R of the first side B1 (resistance of the power cable conductor 1) and the inductance L of the second side B2 are adjusted. The self-inductance M and the resistance r of the third side B3 are set in equilibrium, and the equilibrium condition of the bridge B (rR+My=0, L=
AC resistance R of the power cable conductor 1 is calculated from M(1+x/R)). In addition, in this type of measurement, since the resistance R of the power cable conductor 1 is very small, it is necessary to flow a large current of 1000 to 3000 A through the closed circuit C.

FIG. 3 is a schematic diagram showing a conventional AC resistance measurement method of a power cable conductor that embodies the above measurement circuit. In this measurement method, the sheath of the power cable 7 is used as the return path Q shown in FIG. 8 is used.

In such a measuring method, since there is almost no need to process the sample, ie, the power cable 7, work efficiency is high, but there are drawbacks as shown below.

A Disadvantages of using a sheath as a return path POF (pipe type oil filled) cables, etc.
Cables without sheaths cannot be measured.

An Al (aluminum) sheath or a lead sheath has a large resistance, and in order to flow the aforementioned large current, a transformer 5 with a large capacity output must be used. Furthermore, in this case, the sheath may generate heat and the anticorrosion layer such as vinyl may melt. Furthermore, when measuring the temperature characteristics of AC resistance, if the sheath generates heat, it is difficult to achieve a desired temperature, making it impossible to perform highly accurate measurements.

B. Error caused by external magnetic field Since a closed loop P is formed between the lead wires 3 and 4 and the power cable conductor 1, when a magnetic field acts on this from the outside, a measurement error occurs due to this influence.

Therefore, in order to compensate for the above-mentioned drawbacks, a measuring method shown in FIG. 4 was proposed. This uses a power cable conductor 9 or a copper rod instead of the sheath 8 as the return path Q, and has lead wires 3 and 4 wound around the power cable conductor 1 in the same direction at a constant pitch. With this configuration, the return path Q
Since a sheath is not used as a sheath, the above drawback A is solved. Also, regarding the effect of B above,
By winding the lead wires 3 and 4,
4 and the power cable conductor 1.
Since the area of the sensor is reduced, it is less susceptible to external magnetic noise, and its influence can be eliminated.

However, this configuration causes new drawbacks as shown below.

C Increase in the size of the closed circuit C Proximity effect due to the power cable conductor 9 (a phenomenon in which the magnetic field generated from the power cable conductor 9 acts on the power cable conductor 1, the current density in the power cable conductor 1 becomes uneven, and the resistance increases) ), the power cable conductor 1,
The distance H between 9 must be at least 3 m or more. However, this increases the space required for the experiment and also increases the self-impedance of the closed circuit C, and in order to flow the aforementioned large current, a large capacity transformer 5 is still required.

D Effect of magnetic field generated from power cable conductor 1 Since the lead wires 3 and 4 are wound in the same direction, an induced voltage is generated in the lead wires 3 and 4 due to the magnetic flux generated from the power cable conductor 1. This causes errors in the measurements.

As is clear from the above, the conventional method for measuring AC resistance of power cable conductors requires a large-capacity power source and cannot perform highly accurate measurements.

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a method for measuring AC resistance of a power cable conductor, which can measure AC resistance of a power cable conductor with high precision using a small-capacity power source.

[Structure of the invention]

In order to achieve the above object, the present invention has a power cable conductor as a first side, a secondary coil of a current transformer as a second side, a constant resistance as a third side, a variable impedance as a fourth side, and the power The cable conductor, the return path, and the primary coil of the current transformer are connected to an AC power source to form a closed circuit to constitute an AC bridge, and the power cable conductor is energized to adjust the voltage in a predetermined section of the power cable conductor. In a method for measuring the AC resistance of a power cable conductor that determines the AC resistance of the power cable conductor from the drop, a dummy rod whose AC resistance is known and the power cable conductor are connected to each other with a sufficiently thick wall and a conductive cross-sectional area that is The power cable conductor and the columnar conductor constitute a closed circuit, and are wound around the outer periphery of the columnar conductor in reverse mirror symmetry. , each end of a pair of lead wires forming an extremely small closed loop with the power cable conductor is connected to both ends of the predetermined section to detect the voltage drop and make necessary corrections. .

[Effect]

By constructing a closed circuit using columnar conductors, power loss in the closed circuit is extremely reduced. Further, by winding the pair of lead wires around the outer periphery of the columnar conductor in reverse mirror symmetry, the number of magnetic fluxes generated from the power cable conductor that interlinks with the pair of lead wires becomes zero as a whole. Therefore, the induced voltage induced in the lead wire by the magnetic flux generated from the power cable conductor becomes zero. Also,
Measurements are performed using a dummy rod with known AC resistance, and the measured values for the power cable conductor are corrected based on the measurement results.

〔Example〕

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

FIG. 1 is a schematic diagram showing a method for measuring AC resistance of a power cable conductor according to an embodiment of the present invention.
The same reference numerals are given, and the explanation thereof will be omitted.

In this figure, a power cable 10 is arranged within a pipe-like conductor 11,
is used as the feedback path Q in the closed circuit C. Here, the pipe-shaped conductor 11 is a hollow cylinder made of copper, has a sufficiently thick wall, and has a conductive cross-sectional area larger than the cross-sectional area of the power cable conductor 1. In addition, near both ends of the pipe-shaped conductor 11,
Holes 11a and 11b are formed, each penetrating in the radial direction.

A pair of lead wires 12 and 13 are each spirally wound at a constant pitch around the outer periphery of the pipe-shaped conductor 11 in a mirror-symmetrical relationship. That is, the lead wire 12 is wound in Z turns, and the lead wire 13 is wound in S turns. And these lead wires 12,1
One end 12a, 13a of 3 is connected to the hole 11a, respectively.
11b and is inserted vertically into the pipe-like conductor 11 and connected to points A and B on the power cable conductor 1, which are separated by a predetermined distance l in the longitudinal direction. Further, the other ends 12b, 1 of the lead wires 12, 13
3b are twisted at the center between the holes 11a and 11b, and then connected to the voltage input end 2a of the AC bridge 2.
It is connected to the.

In such a configuration, via the transformer 5,
A large current is passed through a closed circuit C composed of a power cable conductor 1 and a pipe-shaped conductor 11. In this case, since the conductive cross-sectional area of the pipe-shaped conductor 11 is sufficiently large and is made of copper, power loss in the pipe-shaped conductor 11 in the closed circuit C is extremely small. Therefore, a desired current value can be obtained without using a large capacity transformer 5. This current is then converted to an appropriate magnitude by a current transformer 6 and supplied to the AC bridge 2. At the same time,
This AC bridge 2 is supplied with the voltage drop value between A and B of the power cable conductor 1 by means of lead wires 12, 13. In this case, this voltage drop value does not include the induced noise induced by the voltage cable conductor 1. That is, since the lead wires 12 and 13 are wound mirror-symmetrically, the number of magnetic fluxes interlinked with them is zero as a whole, and is induced in the lead wires 12 and 13 by the magnetic field generated in the power cable conductor 11. The induced voltage is zero.

Next, the variable impedance (not shown) of the AC bridge 2 is adjusted to bring the internal circuit into a balanced state.
From this result, the AC resistance of the power cable conductor 1 between A and B, that is, the length l is determined.

In this way, highly accurate measurements are possible with a small-capacity power supply.

Further, as is clear from the present embodiment, this measurement method can measure the AC resistance of all types of cables, regardless of whether or not the power cable is equipped with a sheath. Also, regarding magnetism from the outside, the lead wire 12,
13 and the power cable conductor form a closed loop P
Since the area of is extremely small, its influence is excluded from the measurement results.

Note that an eddy current is generated in the pipe-shaped conductor 11 due to the magnetic flux generated from the power cable conductor 1, and an error due to this eddy current loss is included in the measured value.
Therefore, measurements are performed in advance using a dummy rod whose alternating current resistance is known to determine the error due to the eddy current loss, and the measured values are corrected using the results.

〔Effect of the invention〕

As explained above, according to the present invention, a dummy rod with a known AC resistance and a power cable conductor are formed into a hollow columnar shape having a sufficiently thick wall and a conductive cross-sectional area greater than or equal to the cross-sectional area of the power cable conductor. A closed loop having an extremely small area with the power cable conductor, which is arranged within the conductor, forms a closed circuit with the power cable conductor and the columnar conductor, and is wound around the outer periphery of the columnar conductor in reverse mirror symmetry. Each end of a pair of lead wires forming the voltage drop is connected to both ends of the predetermined section to detect the voltage drop and make necessary corrections.
AC resistance of power cable conductors can be measured with high precision.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a method for measuring AC resistance of a power cable conductor according to an embodiment of the present invention, and FIG.
The figure is a diagram for explaining the principle of an AC resistance measuring method, and FIGS. 3 and 4 are schematic diagrams each showing a conventional AC resistance measuring method of a power cable conductor. 1... Power cable conductor (power cable conductor), 3, 4, 12, 13... Lead wire, 7, 1
0...Power cable, 11...Pipe-shaped conductor (column-shaped conductor), C...Closed circuit, R...AC resistance.

Claims (1)

[Scope of Claims] 1 The power cable conductor is the first side, the secondary coil of the current transformer is the second side, the constant resistance is the third side, the variable impedance is the fourth side, and the power cable conductor and the return path are connected to each other. and the primary coil of the current transformer are connected to an AC power source to form a closed circuit to constitute an AC bridge, and the power cable conductor is energized, and the power cable conductor is energized from the voltage drop in a predetermined section of the power cable conductor. In a method for measuring the AC resistance of a power cable conductor to determine the AC resistance of the conductor, a dummy rod with a known AC resistance and the power cable conductor are connected so that the wall thickness is sufficiently thick and the conductive cross-sectional area is equal to the cross-sectional area of the power cable conductor. The power cable conductor is disposed within the above-mentioned hollow columnar conductor, the power cable conductor and the columnar conductor constitute a closed circuit, and the power cable conductor is wound around the outer periphery of the columnar conductor in reverse mirror symmetry. An alternating current of a power cable conductor, characterized in that each end of a pair of lead wires forming a closed loop with an extremely small area is connected to both ends of the predetermined section to detect the voltage drop and make necessary corrections. How to measure resistance.