JP2000074981A - Method for measuring residual electric charge in diagnosing insulation of power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the charging facility scale reducible, make apparatuses of the facility simplifiable and particularly enhance the effectiveness as an insulation diagnosis method on a spot by impressing a damped oscillation voltage after impressing a d.c. or an impulse and measuring a residual electric charge. SOLUTION: In measuring a residual electric charge when diagnosing water tree deterioration of a CV power cable or the like, for example, a test cable 1 is grounded after a d.c. is impressed thereto, and then a damped oscillation wave voltage is impressed from a damped oscillation wave voltage-generating apparatus 3 in a state with a residual electric charge-measuring apparatus 7 connected to the cable. Since the residual electric charge is not detected even when measured by impressing a predetermined a.c. after the damped oscillation wave voltage is impressed, it is confirmed that the residual electric charge is emitted by the damped oscillation wave voltage. The damped oscillation wave voltage can be generated, e.g. by charging a capacitor 4 and discharging via an inductance 5. An apparatus for generating the damped oscillation wave voltage can be small in facility scale and can be carried on a small truck or the like and therefore, the apparatus is appropriate for use on a spot.

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 residual electric charge which is most suitable for insulation diagnosis of power cables, particularly for on-site insulation diagnosis.

[0002]

2. Description of the Related Art When a CV cable is used under wet conditions, water trees may be generated in an insulator.
Since water tree generation causes a decrease in insulation performance,
Many methods have been proposed for diagnosing this water tree deterioration.

For a CV cable of 22 kV class or more, there is a residual charge method as a water tree deterioration diagnosis method. In general, in the residual charge method, a DC voltage is applied as a pre-charge, then the DC current component is detected under AC voltage application, and a current signal obtained by the detection is integrated to integrate the residual electric charge. Is calculated. This method has a good correlation with the degree of water tree deterioration and breakdown voltage, and is attracting attention as an insulation diagnostic method.

[0004] The mechanism of generation of residual charges in the water-tree degraded insulator is explained as follows.

If water trees are present in the insulator, space charge is accumulated at the interface between the water tree portion and the sound insulator due to DC voltage application. If the DC applied voltage is removed by grounding after DC application, space charge remains inside the insulator,
This starts to move by the electric field (space charge electric field) formed by itself, and finally disappears.

[0006] When the ground charge (short circuit) is maintained, a direct current (reverse absorption current) that decays exponentially with time flows through the ground circuit when the space charge is moved and attenuated.
When the ground is opened, the DC voltage (residual voltage) recovers between the opened electrodes so that the DC voltage (residual voltage) saturates to a certain value with time. The generation of the reverse absorption current and the residual voltage is caused by a response delay of space charge inside the insulator with respect to a sudden change of an externally applied voltage such as grounding after DC application.

[0007] The residual charge recovered after the grounding of the DC application can also be used for the determination amount of the water tree deterioration signal. However, the time required to move and extinguish the space charge in the water tree deteriorated part is extremely long, so the time required for the residual charge observed in the measurement circuit to recover is significantly slowed. I can't.

However, when an AC voltage is applied during the measurement of the residual charge, the moving speed of the space charge existing in the water tree deterioration part is increased, and the residual charge caused by the deterioration can be realized in a short time. This is the residual charge measurement using AC charging.

[0009]

The above-mentioned residual charge method has a good correlation with the degree of water tree deterioration and breakdown voltage, and is attracting attention as an insulation diagnosis method. There are problems that the equipment becomes large because the equipment is required, that the measurement is complicated, and that the measurement cost increases.

The present invention has been made in order to solve such a problem, and a method for solving the above problem by measuring the residual charge by selecting a type of an imposed voltage with a small equipment scale. It is intended to provide.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention applies a DC voltage or an impulse voltage to a power cable, grounds the power cable, and then applies an AC voltage to measure a residual charge. In the method for diagnosing insulation of a power cable, residual voltage is measured by applying a damped oscillatory wave voltage as the AC voltage application.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an apparatus for measuring residual charges using a damped oscillatory wave according to the present invention. In FIG. 1, first, the changeover switch 6 is connected to the contact 6a side, and a DC voltage from the DC power supply device 2 is applied to the test cable 1 for a predetermined time. Thereafter, the changeover switch 6 is switched to the contact 6c, and the test cable 1 is grounded. Next, the changeover switch 6 is switched to the contact 6 b and connected to the damped oscillatory wave voltage generator 3. The damped oscillatory wave voltage is basically generated by charging the capacitor 4 and discharging it via the inductance 5. The residual charge measuring device 7 is connected between the ground terminal of the damped oscillatory wave voltage generator 3 and the shielding layer of the test cable 1 via ground.

Under the above-described residual charge measurement state, the residual charge is measured by applying the damped oscillatory wave voltage shown in FIG. 2 to the test cable 1.

Normally, a sample in which the residual charge signal shown in FIG. 3 is obtained by AC power application is applied with the damped oscillatory wave voltage shown in FIG. 2 after DC application, and then the residual charge is applied by AC application. In the case of the measurement, as shown in FIG. 4, no signal corresponding to the residual charge is detected, and it can be seen that the residual charge is released by the damped oscillatory wave voltage.

FIG. 5 shows the result of measurement of the residual charge when the damping oscillatory wave voltage shown in FIG. 2 was applied. From FIG. 5, it is confirmed that the residual charge signal is also measured by applying the damped oscillatory wave voltage, and that the damped oscillatory wave is effective as a waveform of the applied voltage after DC application at the time of the residual charge measurement. I understand.

[0016] The damped oscillatory wave voltage generator is small in terms of equipment scale, and already exists as equipment enough to be mounted on a small truck, so that it is most suitable for on-site measurement.

The degree of insulation deterioration due to the water tree is determined by applying the damped oscillatory wave voltage to the test cable and measuring the DC component of the charging current.

[0018]

As described above, in the residual charge measurement by the application of the damped oscillatory wave voltage according to the present invention, the equipment scale of the damped oscillatory wave voltage generator is small and the apparatus is simple. This eliminates the need for a large-scale AC power supply facility, and eliminates the complexity of residual charge measurement, which is effective as a power cable insulation diagnosis method on site.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram of a residual charge measurement using a damped oscillatory wave voltage according to the present invention.

FIG. 2 is an explanatory diagram of an applied damped oscillatory wave voltage according to the present invention.

FIG. 3 is an explanatory diagram showing a residual charge signal measured by conventional AC charging.

FIG. 4 is an explanatory diagram showing a residual charge signal measured by applying an AC voltage after applying a damped oscillatory wave voltage.

FIG. 5 is an explanatory view showing a residual charge signal measured by applying a damped oscillatory wave voltage according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Test cable 2 DC generator 3 Damped oscillatory wave generator 4 Capacitor 5 Inductance 6 Changeover switch 7 Residual charge measuring device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Manabu Yoshida 42-1 Shintomi, Futtsu-shi, Chiba Inside Fujikura Futtsu Plant (72) Inventor Kazuo Watanabe 42-1 Shintomi, Futtsu-shi, Chiba Fujikura Futtsu Plant (72) Inventor Tsuneo Toda 1 Higashi-Shinmachi, Higashi-ku, Nagoya City, Aichi Prefecture Inside Chubu Electric Power Co., Inc. (72) Inventor Mitsuru Naruse 1, Higashi-Shinmachi, Higashi-ku, Nagoya City, Aichi Prefecture Chubu Electric Power Co., Inc. 2G015 AA27 CA05 CA06 CA08

Claims (1)

[Claims] 1. A method for performing insulation diagnosis of a power cable by applying a DC voltage or an impulse voltage to a power cable, grounding the applied power cable, and thereafter applying an AC voltage to measure a residual charge. A method for measuring residual charges in power cable insulation diagnosis, comprising applying a damped oscillating wave voltage as electricity and measuring residual charges.