JPH0572256A - Measurement method of optical discharge for cable - Google Patents

Abstract

PURPOSE:To prevent any possible breakdown fault which may occur under a hot-wire state of a power cable by performing a positional assessment of partial discharge accurately using a discharge detector with a simple construction eliminating the need for improving the insulation, airtight structure or the like of the cable. CONSTITUTION:In this measurement method of partial discharge for a cable, a final end connection part of a power cable 10 is arranged and a sheath insulating parts 12 and 13 for insulating a sheath 11 electrically at an intermediate part thereof to measure a partial discharge from the power cable 10 under a hot-wire state and a testing state. A detector 14 comprising a balan is provided outside the power cable 10 to detect a partial discharge pulse which is branched off from the plurality of sheath insulating parts 12 and 13 to propagate. Thus. the position at which the partial discharge pulse is generated is calculated and assessed from an arrival time difference of the partial discharge pulses which are propagated from the sheath insulating parts 12 and 13 and detected with the detector 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable partial discharge measuring method for evaluating the degree of insulation deterioration of a power cable in a live state or a test state.

[0002]

2. Description of the Related Art The main causes of dielectric breakdown of power cables such as CV cables are external damage, defective construction, and defects (such as water trees) in the live power cables.
Due to external damage or poor construction, a certain amount of partial discharge will occur,
Eventually, this partial insulation breakdown part (called an electrical tree) develops, and the entire path of the cable is destroyed. Similarly, damage from minute defects in the water tree and inside the cable will also cause partial dielectric breakdown, and eventually lead to all-way damage.
A partial discharge current always flows before the cable is broken.

In addition, OF cables and duct air (GIL)
Also in the cable, not only the main insulating portion such as oil and SF6 but also the composite insulating portion such as the connecting portion and the insulating support may be defective, or the metal piece or the like may cause partial discharge. Therefore, partial discharge measurement is very important as a method for evaluating insulation of power cables. There have been various methods for evaluating the generation position of such an internal partial discharge, and the typical method is to measure the reflection or propagation velocity of the partial discharge pulse and calculate the generation position from these. there were. This is a method of measuring the partial discharge pulse propagating inside the cable and evaluating the position.

[0004]

However, in the above-described partial discharge measuring method, since the position evaluation is performed only from the partial discharge pulse propagating inside the cable, the termination connection in which the conductor portion is exposed is performed. Part, or inside the cable or in the intermediate connection, it is necessary to install a special partial discharge detector. For this purpose, it is necessary to improve the insulation of the cable, the airtight structure, and the like, which causes a problem that the structure of the cable and the connecting portion becomes complicated and the manufacturing cost becomes high.

The present invention has been made in view of the above problems, and it is not necessary to improve the insulation and airtight structure of a cable, and the position of a partial discharge can be accurately evaluated by using a partial discharge detector having a simple structure. It is an object of the present invention to provide a method for measuring a partial discharge of a cable that can perform

[0006]

In order to achieve the above object, the present invention is provided with a terminal connecting portion of a power cable and a sheath insulating portion for electrically insulating a sheath in an intermediate portion thereof, so And a method for measuring a partial discharge of a cable for measuring a partial discharge from the power cable under a test condition, detecting a partial discharge pulse that is branched from the plurality of sheath insulation parts to a sheath and propagates to the outside of the power cable. There is provided a method for measuring partial discharge of a cable, wherein the detecting means is provided, and the generation position of the partial discharge pulse is evaluated according to the arrival time difference of the propagating partial discharge pulses.

[0007]

The detecting means is provided outside the power cable to detect the partial discharge pulse split into the sheath, and the partial discharge occurrence position is calculated from the arrival time difference. Therefore, it becomes easy to detect the partial discharge pulse, and it becomes possible to measure the partial discharge occurrence position of the power cable with high accuracy.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings of FIGS. FIG. 1 is a principle diagram for explaining the principle of the partial discharge measuring method according to the present invention. In the figure, the power cable 10 includes a terminal connecting portion and a sheath insulating portion in which a sheath 11 is electrically insulated in an intermediate portion (an insulating connecting portion in a CV cable, an insulating flange portion of a spacer in a GIL cable corresponds to this). 12 and 13, and are installed at intervals of a length L from the sheath insulating portions 12 and 13. Further, in the power cable 10, it is assumed that a partial discharge has occurred at point A in the figure. The partial discharge pulse propagates right and left inside the cable 10 respectively, and when reaching the sheath insulating portions 12 and 13, a part of the pulse signal is demultiplexed and the sheath 11 side (usually between the sheath and the ground) is respectively separated. Propagate left and right.

A detector 14 is provided near the outside of the power cable 10, and a part of the sheath demultiplexed signals demultiplexed by the sheath insulating portions 12 and 13 propagates to the sheath 11 side and is detected respectively. It reaches the container 14 and is detected there.
The detector 14 has a positive polarity when a negative signal is input from the right side and a negative polarity when a negative signal is input from the left side.

Here, when the partial discharge pulse signal is a positive pulse, the signal branched by the sheath insulating portion 12 generally has a negative reflected wave and a passing wave, It has a positive polarity. Further, the time taken for the sheath demultiplexed signal to reach the detector 14 is t1, t2, the distance between the sheath insulating portion 13 and the point A is x, and the sheath insulating portion 13 and the detector 14 are
Let y be the distance of
Arrival time t1 of the sheath demultiplexing signals returning side is, t1 = (L-x) / v c + (L-y) / v s ... (1) propagates to the right, returning the sheath 11 side arrival time t2 of the sheath component wave _{signal, t2 = x / v c +} y / v s ... (2) where, v _c is the conductor side - propagation velocity v _s of the (conductor between the sheath) sheath side (sheath - between earth ) Is the propagation velocity.

Here, the arrival time Δt is Δt = t1−t
2 So, Equation (1) - (2), is expressed by Δt = (L-2x) / v c + (L-2y) / v s ... (3). Ie, x is, x = 1/2 {L -v c Δt + (L-2y) v c / v s} ... (4) Equation (4) from v _c, v _s is that you pre-measured Since L and y can be actually measured, if Δt can be measured, the generation position x can be calculated.

When y is "0" or "L", it means that the detector is attached to the sheath insulating portion, and y is "L / L".
In the case of "2", it means that the detector is attached to the central part.
When y is “L / 2”, x has the formula x = ½ (L−v _c Δt) (5), which has the effect of simplifying the calculation.
This is because the propagation times of the waves propagating on the sheath side are equal on the left and right.

Next, an embodiment for verifying the system for measuring partial discharge according to the present invention is shown in FIG. In the figure,
In this embodiment, the length is 200 [m] and the outer diameter is 5.8 [mm].
3C-2V coaxial cable 20 is used as a simulated cable, and the insulation connection portions 22 are provided at both ends of the coaxial cable 20.
23 is provided, and the insulated connection portions 22 and 23 are connectors with the sheath 21 cut off. Further, after connecting cables 30 and 40 of 10 [m], both ends of the cables 30 and 40 are matched with 75 [Ω]. Matched with resistance R. Further, a ground wire (copper plate) is provided along the cable, and the signal propagation speed v _c on the conductor side is 200 [m / μse.
c], the propagation velocity v _s of the signal on the sheath side is 215 [m /
μsec].

The detector 24 is installed in the central portion of the cable 20 (at a position 100 [m] from the insulating connection portion 22). A pulse generator (simulated partial discharge pulse generator) 25 is connected as a partial discharge simulation at a position 90 [m] from one end (insulated connection portion 23) of the cable 20 to simulate the positive polarity of the cable 20. A discharge pulse (rising 4 to 30 [ns]) is input, and when the positive polarity simulated discharge pulse reaches the insulating connection portions 22 and 23,
A part of the signal is demultiplexed and propagates in the sheath 21.

The measuring apparatus used in the partial discharge measuring method according to the present invention comprises a detector 24, an amplifier 26, a bandpass filter circuit 27, an oscilloscope 28, and an arithmetic circuit (CPU) 29. The detection unit 24 is
Two metal foils are wound around the sheath 21 at intervals of 1 [m], and the signals branched by the balun are differentially detected as electric signals. That is, the detection unit 24 detects the sheath reflected wave reflected by the insulating connection units 22 and 23.

The electric signals detected by the detectors 23 and 24 are amplified by the amplifier 26, pass through the bandpass filter circuit 27, and are passed through the oscilloscope 28 and the CPU 29.
To enter. The amplifier 26 is a 22 [dB] amplifier,
The detected electric signal is amplified and output to the bandpass filter circuit 27.

The bandpass filter circuit 27 is 1 [MH
A filter circuit having a wide band of z] to 100 [MHz] allows a high frequency component of the detected electric signal to pass. The oscilloscope 28 observes the input electric signal as a waveform of a signal component having a voltage characteristic as shown in FIG. The arrival time difference Δt of the sheath demultiplexed signal (sheath reflected wave) shown in FIG. 1 is about 100 [nsec] (= 0.1 [μsec]) in the example of the observed waveform of FIG.

The CPU 29 is a circuit for realizing the calculation of the above-mentioned formulas (1) to (5), and executes the calculation on the input high-frequency component signal to evaluate the generation position of the partial discharge pulse. .. That is, in the present embodiment, the arrival time difference Δt of the sheath reflected waves is about 100 [nsec], and therefore the equation (5)
The generation position of the simulated discharge pulse is calculated as x = 1/2 (200 [m] -200 [m / μsec] × 0.1 [μsec]) = 90 [m].

As a result, the generation position measured and calculated by the CPU 29 coincided with the generation position of the simulated partial discharge pulse. Therefore, in this embodiment, since the partial discharge pulse split into the sheath is detected and the partial discharge generation position is calculated from the arrival time difference, the partial discharge pulse can be detected with high accuracy, and the present invention is verified by this verification. The effectiveness of the method for measuring the partial discharge of cables related to the above was confirmed. Further, the detector has a simple structure and can be easily attached to and detached from the cable.

In this embodiment, the trigger is applied by the input pulse of the simulated partial discharge pulse generator. However, when the partial discharge measuring method according to the present invention is actually used, a digital oscilloscope or a continuous It is a method to monitor the data and reprocess only the data at the time of pulse generation. Further, in the present embodiment, the partial discharge pulse is detected by one set of detectors provided between the sheath insulating portions, but the present invention is not limited to this, and a plurality of sets of detectors may be provided to detect the partial discharge pulse. For example, it is possible to perform a more sensitive partial discharge measurement. Further, in order to perform the measurement with higher sensitivity and accuracy, it is possible to use an optical fiber for the transmission section of the partial discharge pulse signal and a CPU or the like for the measurement section.

[0021]

As described above, according to the present invention, the terminal connecting portion of the power cable and the sheath insulating portion that electrically insulates the sheath are provided in the intermediate portion, so that the sheath is electrically activated under the live condition and the test condition. In the cable partial discharge measuring method for measuring partial discharge from the power cable, a detecting means is provided outside the power cable to detect a partial discharge pulse that is demultiplexed from the plurality of sheath insulating portions into a sheath and propagates. , Since the position of occurrence of the partial discharge pulse is evaluated according to the arrival time difference of the propagating partial discharge pulse, it is not necessary to improve the insulation or airtight structure of the cable, and the partial discharge detector having a simple structure is used. It is possible to accurately evaluate the position of the partial discharge, and thereby prevent a dielectric breakdown accident that occurs under a live state of the power cable.

[Brief description of drawings]

FIG. 1 is a principle diagram for explaining the principle of a partial discharge measuring method according to the present invention.

FIG. 2 is a block diagram showing an embodiment of a partial discharge measuring apparatus for verifying the partial discharge measuring system according to the present invention.

FIG. 3 is a diagram showing an example of measurement of voltage characteristics of a signal detected in FIG.

[Explanation of symbols]

10, 20, 30, 40 Power cable 11, 21 Sheath 12, 13, 22, 23 Sheath insulation part (insulation connection part) 14, 24 Detector 25 Pulse generator (simulated partial discharge pulse generator) 26 Amplifier 27 Band pass filter Circuit 28 Oscilloscope 29 Arithmetic circuit (CPU)

Claims (1)

[Claims] 1. A terminating connection portion of a power cable and a sheath insulating portion for electrically insulating a sheath are provided in an intermediate portion,
In a partial discharge measuring method of a cable for measuring a partial discharge from the power cable under a live line condition and a test condition, a portion that is demultiplexed into a sheath from a plurality of the sheath insulating parts and propagates to the outside of the power cable. A method for measuring a partial discharge of a cable, characterized in that detection means for detecting a discharge pulse is provided, and the position of occurrence of the partial discharge pulse is evaluated according to the arrival time difference of the propagating partial discharge pulses.