JP2960782B2 - Partial discharge measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge measuring method, and more particularly to a partial discharge measuring method for diagnosing insulation failure of an insulator constituting a power cable or the like.

[0002]

2. Description of the Related Art As a method of measuring partial discharge, for example, there is a method of performing measurement using a test transformer.

FIG. 3 is a block diagram showing an example of a method for performing partial discharge measurement using such a test transformer. To perform the partial discharge measurement, the live-line operation of the power cable 11 is stopped, and one end 1 of the power cable 11 is stopped.
A test transformer 14 is connected to the cable conductor 13 drawn out of the test transformer 2a to apply a test voltage, and a voltage impressed waveform is extracted from the secondary winding 14a of the test transformer 14 to obtain a waveform generator 1.
From 4b, a waveform signal is sent to the CRT 15. On the other hand, a partial discharge measuring device 17 is connected to a cable conductor 13 drawn out from the other end portion 12b of the power cable 11 via a coupling capacitor 16, where a high-frequency pulse is detected and a CRT is detected.
Send to 15. The CRT 15 compares the applied voltage waveform with the phase of the high-frequency pulse. Here, when the applied voltage phase is in a phase where the probability of occurrence of partial discharge is high, for example, a high-frequency pulse detected when it is in the vicinity of the maximum value or in a phase slightly advanced therefrom, the partial discharge signal of the insulator of the power cable is used. Is determined.

FIG. 4 is a block diagram showing another example of the partial discharge measuring method. The secondary winding of the instrument transformer 18 connected to the cable conductor 13 is an E / O (electric / optical) converter 1.
9 where the output voltage signal of the secondary winding is E / O
Is converted. This signal is transmitted through the optical fiber 20 to the O / E
It is sent to an (optical / electrical) converter 21 where it is O / E converted. The reproduced output voltage signal is output to the AM
One point 11a of the modulated and grounded ground wire 23
From the power cable 11. A high-frequency iron core 24 is connected to the ground line 23 to increase the impedance to ground. On the other hand, a pair of metal foil electrodes 2
The AM modulation signal waves transmitted through the power cable 11 are attached to the metal foil electrodes 26, 26, demodulated by the AM demodulator 30, and output to the CRT 15. The high frequency pulse is applied to the metal foil electrode 26,
26 is detected by the partial discharge measuring device 17 via the detection impedance 27 and monitored by the CRT 15. Then, similarly to the method shown in FIG. 3, the partial discharge signal is determined by observing the applied voltage phase and the high-frequency pulse.

[0004]

However, the conventional partial discharge measuring method as described above has the following problems.

[0005] In the method shown in FIG. 3, since the hot-line operation of the power cable has to be stopped, the power service has to be temporarily interrupted. In addition, since power is applied from the test transformer at the time of partial discharge measurement, a dedicated device is required, and there are inconveniences such as troublesome connection of these devices.

On the other hand, in the method shown in FIG. 4, since the phase of the hot-line voltage is detected by using an instrument transformer having an important role in the operation and maintenance of the substation, the partial discharge measurement is performed. If an accident such as a short circuit or grounding occurs in the output of the instrument transformer, the above-mentioned operation and maintenance management will be affected. Further, in this method, since the applied voltage phase is taken in through a complicated path, there is a risk that the polarity of the terminal may be taken in, and there are many factors that hinder accurate measurement.

Accordingly, an object of the present invention is to enable partial discharge measurement to be performed while the power cable is in a live state, and to perform the measurement without affecting the power system in a live state. To provide a method for measuring partial discharge.

[0008]

SUMMARY OF THE INVENTION The present invention is directed to the above-mentioned object.
To achieve a partial discharge based on the detected impedance connected to the ground wire of the sheath of the live power cable
Signal, and ground from the sheath via the ground wire.
The charging current flowing through the detection from the ground line, obtains a phase of the division voltage of the power cable from the waveform of the charging current,
Generation timing of the partial discharge signal and phase of the applied voltage
And measuring the partial discharge by comparing the partial discharges.

[0008]

In a three-phase power transmission system in which three single-phase power cables are laid, if a part or the entire sheath side of each power cable line is grounded at a single point, no sheath circuit current flows. Or can be ignored. At this time, the current flowing through the ground wire is dominated by the charging current due to the capacitance of the insulator of the power cable. In this case, the phase difference between the phase of the applied voltage and the phase of the charging current flowing through the ground line is π / 2.

Therefore, if the charging current flowing through the ground line is detected, the applied voltage phase can be obtained. In the present invention, the charging current flowing through the ground line is detected, and the charging voltage phase is obtained from the phase difference between the charging current and the charging voltage known in advance, and the indirectly detected charging voltage phase and the detected high-frequency pulse are calculated. By comparison, a high-frequency pulse detected in a specific applied voltage phase is determined as a partial discharge signal.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The partial discharge measuring method of the present invention will be described below in detail.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. In this example, for example, partial discharge measurement of each power cable in a three-phase power transmission system including three single-core power cables of U, V, and W is performed. The measurement is performed in exactly the same way when measuring the power cables of each of the U, V, and W phases. Therefore, the case of measuring the U-phase power cables will be described here as an example.

A cable conductor 13 is drawn out from a terminal portion 12 of the single-core power cable 11. The sheath of the single-core cable system is grounded by the ground wire 23 only at one point 11a. A high-frequency iron core 24 is connected to the ground wire 23 to increase the high-frequency impedance.
This ground line 23 is connected to the partial discharge measuring device 17, and the high-frequency pulse signal detected here is sent to the CRT 15.

On the other hand, a current transformer 28 for detecting a charging current is provided on the ground line 23. The current transformer 28 is connected to a waveform converter 30 via a resistor 29 connected in parallel.
, Where the integration processing of the current signal is performed. The obtained charging current waveform signal is sent to the CRT 15, where it is monitored simultaneously with the high frequency pulse. Note that a capacitor may be connected instead of the resistor 29, and a voltage waveform may be obtained directly from both ends.

In the above configuration, when the phase of the charging current corresponding to the applied voltage and the high-frequency pulse are simultaneously observed on the CRT 15, the high-frequency pulse is detected at the specific phase of the applied voltage. Since the partial discharge pulse frequently appears when the applied voltage has a specific phase, the pulse appearing at that phase can be determined as a partial discharge pulse. Therefore, it is possible to perform partial discharge measurement while clearly distinguishing external noise.

From the relationship between the applied voltage phase and the polarity of the partial discharge pulse, whether the obtained partial discharge signal is from the power cable 11 of the sample system where the partial discharge measurement is performed,
Alternatively, it is also possible to determine whether the cable is from a source other than the power cable 11 of the sample system.

In addition, a signal corresponding to the phase of the applied voltage obtained from the charging current is input to the gate circuit together with the high-frequency pulse signal, and the high-frequency pulse signal is output only when the applied voltage has a predetermined phase and evaluated. By doing so, the determination of the partial discharge signal becomes more reliable and easier.

FIG. 2 shows an example in which a partial discharge measurement is performed on a line in which a sheath circuit is independent by an insulated connecting portion and a sheath in each section is independently grounded.

In this case, the plurality of insulated connecting portions 25a and 25a
The sheath of each section sectioned by 5b is independently grounded by grounding wires 23a, 23b and 23c. The same measurement system as that shown in FIG. 1 is attached to an arbitrary ground line of the line, and the charging current and the high-frequency pulse signals are detected from this system, so that it is completely the same as the embodiment shown in FIG. The partial discharge measurement can be performed.

[0020]

As described above, according to the partial discharge measuring method of the present invention, the voltage application phase is obtained by detecting the charging current flowing through the ground line, so that the live operation of the power cable is stopped. This eliminates the need and allows the insulation diagnosis to be performed without interrupting the power supply service. In addition, since the output of the instrument transformer or the like is not used for measurement, there is no possibility that the operation of these substations will be affected. Further, since the imposed voltage signal is extracted through a relatively simple path, factors that cause erroneous connection and the like are reduced, and highly accurate measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a partial discharge measuring method according to the present invention.

FIG. 2 is a block diagram showing another embodiment of the partial discharge measuring method of the present invention.

FIG. 3 is a block diagram showing a conventional partial discharge measuring method.

FIG. 4 is a block diagram showing another example of a conventional partial discharge measurement method.

[Explanation of symbols]

11 Power cable 11a
Grounding sheath 12 Cable termination 13
Cable conductor 15 CRT 17
High frequency measuring device 23, 23a, 23b Ground wire 24
High frequency iron core 25, 25a, 25b Insulated connection 28
Current transformer 29 Resistance 30
Waveform converter

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Kan Endo 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture Inside the Electric Wire Research Laboratory, Hitachi Cable Co., Ltd. 1-1 1-1 Nippon Electric Cable Co., Ltd. (72) Inventor Tomoaki Imai 5-1-1 Hidakacho, Hitachi City, Ibaraki Pref. Nippon Electric Cable Co., Ltd. (56) References JP 52-137384 (JP, A) JP-A-61-230065 (JP, A) JP-A-2-122284 (JP, A) JP-A-2-154170 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01R 31/12

Claims (1)

(57) [Claims] 1. A partial discharge based on a detected impedance connected to a ground wire of a sheath of a power cable in a live state.
Signal, and ground from the sheath via the ground wire.
The charging current flowing through the detection from the ground line, obtains a phase of the division voltage of the power cable from the waveform of the charging current,
Generation timing of the partial discharge signal and phase of the applied voltage
And measuring the partial discharge by comparing the partial discharges.