JPH07167910A - Cable partial discharge measuring method using tuning type partial discharge measuring apparatus - Google Patents

Abstract

PURPOSE:To measure the partial discharge of a cable at a low cost by taking impedance matching by resistance. CONSTITUTION:In a cable partial discharge measuring method using a tuning type partial discharge measuring apparatus of a method in which a test voltage is applied from the start end B of a cable 1 and a partial discharge generated in the cable 1 is measured by using a tuning type partial discharge measuring apparatus 2, an LC series resonance circuit 4 with the tuning frequency of the tuning type partial discharge measuring apparatus 2 as a resonance frequency is provided at the termination A of the cable 1, and a resistance R equivalent to the characteristic impedance of the cable 1 is connected in series to the LC series resonance circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of measuring a partial discharge of a cable using a tunable partial discharge measuring instrument, and more particularly to a resistance R equivalent to the characteristic impedance of the cable which is a distributed constant circuit for impedance matching. Partial discharge measurement of a cable using a tunable partial discharge measuring instrument that is installed at one end (end) to absorb the reflected wave of partial discharge generated in the cable and make the detection sensitivity of the tunable partial discharge measuring instrument constant It is about the method.

[0002]

2. Description of the Related Art A tunable partial discharge measuring method is known as one of the methods for detecting a partial discharge generated in a cable.

FIG. 2 shows an explanatory view of a method for measuring a partial discharge of a cable using a conventional tunable partial discharge measuring instrument. In the figure, a high voltage of commercial frequency is applied to the terminal B. At that time, when the discharge is generated in the cable 1, the partial discharge pulse generated at the position Lx from the A end (termination) of the cable 1 which is the distributed constant circuit is half that Q /
2 travels toward the end A, the traveling wave is reflected and reaches the start B. And the other half Q / 2 directly reaches the B end of the starting end.

Therefore, the direct wave and the reflected wave are superposed at the B end, and the partial discharge pulse is tuned at the B end side.
The measurement sensitivity varies depending on the position Lx where the partial discharge occurs, as shown in FIG. In particular, in the tunable partial discharge measuring instrument 2 having a center frequency of 400 KHz, the partial discharge pulse at the detector has a damped oscillation waveform oscillating on both positive and negative sides as shown in FIG. There was a unique problem that the detection sensitivity was remarkably lowered due to the cancellation at the phase difference of π and an odd multiple thereof (at the positions of 125 m, 375 m and 625 m in FIG. 3).

Reference numeral 3 is a test power source, Z is a blocking impedance, and Ck is a coupling capacitor. In order to prevent the detection sensitivity from decreasing due to the superposition of the direct wave and the reflected wave, as shown in FIG. 5, an impedance matching resistor R (equal to the characteristic impedance of the cable 1 at the A end of the cable 1 is provided. Connecting the characteristic impedance of the cable) is considered. As a result, half of the partial discharge pulse Q / 2 is absorbed by the resistor R without being reflected at the end A end, and only the direct wave reaches the end B, and the partial discharge pulse generation position Lx and the cable are reached. Regardless of the length of 1, the detection sensitivity of the tunable partial discharge measuring instrument 2 can be made substantially constant.

[0006]

However, in the power cable, since a high-voltage commercial frequency is applied to the core wire of the cable 1, a high voltage is applied to the resistor R and the resistor R is also applied.
Since the value of is generally as low as 30Ω or less, the resistance R is high withstand voltage,
A high withstand voltage is required, the cost is high, and the power consumed by the resistor R is large.
Also requires a large capacity, which is a costly measurement method and has not been put to practical use.

The present invention has been made in order to solve the above-mentioned various problems of the related art. The resistance R has a low withstand voltage and a low power resistance while performing impedance matching by the resistance R, and a test is performed. It is an object of the present invention to provide a method for measuring a partial discharge of a cable using a tunable partial discharge measuring instrument capable of increasing the power supply with a small capacity.

[0008]

In order to solve the above-mentioned problems, a method of measuring a partial discharge of a cable using a tunable partial discharge measuring instrument of the present invention applies a test voltage from the beginning of the cable, In the method of measuring the partial discharge of a cable using a tunable partial discharge measuring instrument that measures the partial discharge that occurs in a cable using a tunable partial discharge measuring instrument, the tuning of the tunable partial discharge measuring instrument is performed at the end of the cable An LC series resonance circuit having a frequency as a resonance frequency is provided, and a resistor R equivalent to the characteristic impedance of the cable is connected in series with the LC series resonance circuit to measure the amount of partial discharge generated in the cable. It is characterized by having done.

[0009]

Since the resonance frequency of the LC series resonance circuit is made to match the tuning frequency of the tunable partial discharge measuring instrument, the cable is impedance-matched by the resistor R at the tuning frequency, and the cable termination is performed. Does not generate reflected waves. Therefore, the direct wave and the reflected wave do not cancel each other at the beginning of the cable, and the detection sensitivity of the tunable partial discharge measuring instrument becomes almost constant.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of an embodiment of a cable partial discharge measuring method using a tunable partial discharge measuring instrument according to the present invention.

In FIG. 1, the end A of the cable 1 is
An LC series resonance circuit 4 including an inductance L and a capacitor C is connected to the end core wire, and a resistor R having a value equal to the characteristic impedance of the cable 1 is connected between the LC series resonance circuit 4 and the ground. .

The tuning type partial discharge measuring instrument 2 is, for example, in principle disclosed in Japanese Patent Publication No. 42-23236 and Japanese Patent Publication 60.
The one equivalent to that disclosed in Japanese Patent Publication No. 029075 is used, and the tuning frequency of the tuning frequency amplifier has a center frequency of 400 KHz so as not to be disturbed by broadcast waves.

Therefore, if the inductance L and the capacitor C are selected so that the resonance frequency of the LC series resonance circuit 4 matches the tuning frequency 400 KHz of the tunable partial discharge measuring instrument 2, a frequency of 0 to 5 MHz or more is usually set. Among the frequency components of the partial discharge pulse having a component, the tuning frequency of 400 KHz of the tuning partial discharge measuring instrument 2 is in the form of impedance matching with the resistor R at the end A of the cable 1.

Therefore, since the reflected wave of the tuning frequency of 400 KHz does not return to the B end which is the starting end of the cable 1, the tuning frequency of 400 KHz does not cancel each other with the direct wave and the partial discharge pulse is not generated. Only 400 KHz components of the frequency component of the direct wave are input to the tunable partial discharge measuring instrument 2, and the detection sensitivity of the tunable partial discharge measuring instrument 2 is irrespective of the generation position Lx of the partial discharge pulse and the length of the cable 1. Is almost constant.

Since the LC series resonance circuit 4 has a high impedance with respect to the commercial frequency test voltage of the test power supply 3, the voltage applied to the resistor R is low and its power consumption is also low.

Therefore, the withstand voltage and withstand power of the resistor R can be small, and the capacity of the test power supply 3 can be small.

[0017]

As described above, according to the present invention, the LC series resonance circuit having the resonance frequency matching the tuning frequency of the tuning type partial discharge measuring instrument is connected in series to the resistance R having the same value as the characteristic impedance of the cable. Since this is connected to the end of the cable for impedance matching, the impedance matching resistor can have low withstand voltage and low power consumption, and can measure the partial discharge of the cable at low cost.

Further, the capacitor C used in the LC series resonance circuit can have a withstand voltage of the same level as that of the commonly used coupling capacitor Ck, and can be inexpensive. The same applies to the inductor chair L.

The capacity of the test power supply can be small.

[0020]

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of a method for measuring a partial discharge of a cable using a tunable partial discharge measuring instrument according to the present invention.

[0021]

FIG. 2 is an explanatory view of a method for measuring a partial discharge of a cable using a conventional tunable partial discharge measuring instrument.

[0022]

FIG. 3 is a characteristic explanatory diagram of a conventional partial discharge position and detection sensitivity.

[0023]

FIG. 4 is an explanatory diagram of a detection waveform of a tunable partial discharge measuring instrument.

[0024]

5 is an explanatory view of the improved partial discharge measurement method of FIG.

[0025]

[Explanation of symbols]

 1 Cable 2 Tuning Partial Discharge Measuring Instrument 3 Test Power Source 4 LC Series Resonant Circuit Ck Coupling Capacitor C Capacitor L Inductance R Characteristic Impedance of Cable

Claims (1)

[Claims] 1. A test voltage is applied from the beginning of the cable,
In the method of measuring the partial discharge of a cable using a tunable partial discharge measuring instrument that measures the partial discharge generated in the cable with a tunable partial discharge measuring instrument, a tunable partial discharge measurement is made at the end of the cable. An LC series resonance circuit whose resonance frequency is the tuning frequency of the device is installed, and a resistor R equivalent to the characteristic impedance of the cable is connected in series with the LC series resonance circuit to measure the amount of partial discharge generated in the cable. A method for measuring the partial discharge of a cable using a tunable partial discharge measuring instrument characterized in that