JPH03246473A - Partial discharge measuring method - Google Patents

Abstract

PURPOSE:To measure partial discharging without interrupting power service by detecting the phase of the hot-line voltage of a power and deciding detected high frequency wave pulses as a partial discharging signal when the detected phase is a specific phase. CONSTITUTION:When a high voltage is applied from the high voltage charging conductor 3 of a substation S, partial discharge is caused if the insulator of the cable 1 deteriorates to induce the high frequency pulses between a cable conductor and a metallic sheath 4; if there is an external noise, the high fre quency pulses are induced in e metallic sheath 4. Those high frequency pulses are detected by metallic foil electrodes 5 and 5 which are set opposite the metallic sheath 4 across a vinyl sheath 4a, measured as a signal of the potential difference between both ends of detection impedance 6, and displayed on a CRT 8. Then the phase of the hot-line voltage is detected from the secondary winding of a transformer 10 for an instrument to decide the high frequency pulses as the partial discharging signal when the detected phase slightly leads a peak value or as external noises in other cases.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a partial discharge measuring method, and particularly to a partial discharge measuring method that can be used for diagnosing deterioration of insulators such as power cables.

[Background technology]

As a partial discharge measurement method, for example, a test voltage is applied from a test transformer to the cable conductor of a power cable line whose live line operation has been stopped, a high-frequency pulse is detected from the power cable in the energized state, and the phase of the test voltage is determined. Attempts have been made to determine a high-frequency pulse detected when the phase is slightly advanced, including the maximum value and its vicinity, as a partial discharge signal of the insulator of the power unit.

According to this partial discharge measurement method, when the test voltage is not in the above-mentioned phase, for example, a high frequency pulse detected at a phase near the zero cross point is caused by external noise on the power cable 41!
The deterioration of the insulator is diagnosed by determining that it is superimposed on the signal and excluding it from the signal to be measured.

In addition, high-frequency pulses caused by external noise occur even if the application of the test voltage is stopped, whereas high-frequency pulses caused by partial discharges do not occur when the application of the test voltage is stopped. It is also possible to distinguish between external noise and partial discharge signals by comparing the high frequency pulses generated based on the presence or absence of .

[Problem to be solved by the invention]

However, according to the partial discharge measurement method using the test transformer described above, since the live line operation must be stopped, the power service must be interrupted from time to time, and the Since electricity is charged, there is the inconvenience of requiring a dedicated device and the hassle of connecting it.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a partial discharge measuring method that can be carried out without interrupting power service.

Another object of the present invention is to provide a partial discharge measuring method that does not require dedicated equipment.

[Means to solve the problem]

The present invention detects the phase of the live voltage from the existing equipment of the power cable and adjusts the phase to a predetermined phase in order to continue the power service and measure partial discharge in the insulator without using specialized equipment. A partial discharge measuring method is provided for determining that a high frequency pulse detected from a power cable at a certain time is a partial discharge signal.

The above-mentioned predetermined phase is the phase at which the live line voltage reaches its maximum absolute value and a phase that is slightly ahead of the phase that includes this, and the phase of the live line voltage is the phase at which the live line voltage reaches its maximum absolute value. Instrument transformers, voltage detection terminals, etc. permanently installed in
It can be detected using the ground capacitance of overhead lines, distribution transformers, etc.

When the movement detection section is far away from the partial discharge measurement position, the phase signal may be transmitted to the measurement position using a transmission medium, for example, an electrical cable line to be measured.

[Effect]

A high voltage is applied to the cable conductor of the power cable from a high voltage conductor connected to a high voltage power source. Deterioration of the power cable insulation causes partial discharges, which induce high frequency pulses between the cable conductor and the metal sheath. At the same time, external noise is induced in the metal ground as a high frequency pulse. These high-frequency pulses are detected by, for example, a foil-shaped electrode that faces a metal sheath through a vinyl sheath, and are measured by a partial discharge detection device as a potential difference signal between both ends of a detection impedance, and are displayed on a monitor such as a CRT as necessary. Is displayed. On the other hand, the phase of the live line voltage is detected from the secondary winding of the potential transformer, and the high-frequency pulse detected when this phase is at the peak value and a phase slightly ahead of that including the peak value is used as a partial discharge signal. and other high-frequency pulses are determined to be external noise. This relationship between the phase and the partial discharge signal is based on the experimental results of many researchers so far.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

[Example 1] FIG. 1 shows an example of a partial discharge measuring method according to the present invention. In FIG. 1, a power cable 1 is connected at a cable end 2 to a high-voltage carrying conductor 3, while an insulated connection 4 is provided. A pair of metal foil electrodes 5, 5 are provided on the insulated connection portion 4.
are attached to both sides of the insulating tube 4a. The metal foil electrodes 5, 5 are each connected to both ends of a detection impedance 6, and a measuring device 7 is connected to the detection impedance 6.

The output of the measuring device 7 is connected to a CRT 8.

An AM demodulator 9 is also connected to the metal foil electrode 5.5, and its demodulated output is connected to the CRT 8.

The high-voltage conductor 3 of the substation S is equipped with a potential transformer (PT).
Ten primary windings are connected to ground. The secondary winding of the instrument transformer 10 is an Elo (electrical/optical) converter 11
One E10 converter is connected to an O/E (optical/electrical) converter 12 by an optical fiber 13. O/
The output of the E-transducer I2 is connected to an AM modulator 14, whose output 8 is connected to the grounding sheath 1 of the terminal connection of the cable 1 under test.
connected to a. Ground wire 1b from ground sheath 1a
A high frequency iron core 5 is attached to. 3a shows an aerial power transmission line.

The operation of the configuration of FIG. 1 is as follows.

Partial discharge pulses are detected by a metal foil electrode 5.5 and measured via a detection impedance 6 in a measuring device 7.

The waveform of the output of the measuring device 7 is reproduced by the CRT 8. The output voltage of the secondary winding of the instrument transformer 10 is determined by the E10 converter 11.
is converted to E10, transmitted by optical fiber fly 3, and O
The /E converter 12 performs O/E conversion. The AM modulator 14 performs AM modulation on this phase information signal, and the modulated signal wave is injected into the cable under test 1 from the grounded sheath 1a of the terminal connection. The impedance of the grounding wire 1b from the grounding sheath 1a to the signal wave is determined by the attached high-frequency iron core 15.
It is enhanced by

The signal wave transmitted through the cable under test 1 is extracted by the metal foil electrode 5.5, demodulated by the AM demodulator 9, and then CR
Played on T8.

Fig. 2 shows detection pulses HP, -H reproduced by CRT8.
3 shows an example of the waveforms of P and the applied voltage phase information signal P. FIG. 2(a) shows the waveform of the phase information signal P. Figure 2 (b
) shows pulse waveforms HP, -HP4 observed through the detection impedance 6. Four pulse groups are recognized in Fig. 2(b), but when viewed from the relationship with the applied voltage phase,
Pulse group HP2. There is a strong possibility that HP is a noisy pulse. On the other hand, the pulse groups HP, , HP, are highly likely to be partial discharge pulses, considering the characteristic that partial discharge occurs near the peak value of the phase of the applied voltage or in a phase slightly ahead of the peak value.

A power step-down transformer may be used instead of the potential transformer 10. In this case, there is a slight phase error in the phase information, but since there is a range in the phase at which partial discharge occurs, this is rarely a problem.

[Example 2] FIG. 3 shows another configuration for performing partial discharge measurement using the method of the present invention. In FIG. 3, the power cable 1, the cable termination 2, the high-voltage conductor 3, the insulated connection 4, and the pair of metal foil electrodes 5, 5 are the same as in FIG. Metal foil electrode 5
, 5 are connected to both ends of the detection impedance 6, and are also connected to the AM demodulator 9. The detection impedance 6 is connected to an amplifier 31 , the output of the amplifier 31 is connected to a multi-gate circuit 32 , and the output of the multi-gate circuit 32 is connected to the input of a trigger circuit 33 . The output signal of the trigger circuit 33 is sent to the pulse counting device E.
34. The multi-gate circuit 32 is composed of five unit gates (not shown), and a time and a corresponding potential range are set for each unit gate. The gate is set so that the gate opens near the peak value of the phase of the applied voltage at which partial discharge selectively occurs or at a phase slightly ahead of the peak value. The multi-gate circuit 32 includes
AM as a gate signal for time setting of unit gate.
The demodulated output from the demodulator 9 is input. Instrument transformer 1
0, E10 converter 11.0/E converter 12, optical fiber 13, AM modulator 14, ground sheath 1a, ground wire 1b,
The high frequency core 15 is the same as that shown in FIG.

The operation of the configuration of FIG. 3 is as follows.

When a partial discharge occurs near the insulated connection portion 4, the partial discharge pulse generates a potential difference between both ends of the detection impedance 6. This potential difference is amplified to an appropriate magnitude by an amplifier 31 and then input to a multi-gate circuit 32. When the input pulse satisfies all the setting conditions of each unit gate of the multi-gate circuit 32, an output signal is given to the trigger circuit 33, and the output of the trigger circuit 33 is input to the pulse counting device 34.

The pulse counting device 34 generates a trigger output only in response to an output signal that satisfies all the setting conditions of each unit gate of the multi-gate circuit 32, which is set using the phase information signal input as a gate signal as a time reference. is counted.

Even if a potential difference occurs due to a noisy pulse across the detection impedance 6, it does not satisfy the setting conditions of the multi-gate circuit 32, so it is not counted by the pulse counting device 34, and only partial discharge pulses are counted by the pulse counting device 34. .

〔Effect of the invention〕

According to the invention, partial discharge measurements can be performed without interrupting power service. Furthermore, no special equipment is required to apply electricity to the power cable when measuring partial discharge.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration used in an embodiment of the partial discharge measurement method according to the present invention, FIG. The figure is a block diagram showing a configuration used in another embodiment of the partial discharge measuring method according to the present invention. Explanation of symbols ■-・・・・・Power cable 1 a −−−−−− Grounding sheath 1 b of the terminal connection part −
・・Grounding wire 2・−・−−−−−−Cable end portion 3−・・−−−−−−−・High voltage charging conductor 4・−・−−・
...--Insulated connection part 4a--Insulating tube 5--Metal foil electrode 6---1--Detection impedance 7--1--
------ Measuring device 8 ------- CRT 9 ---- AM demodulator 10 --- Instrument transformer 11 = --- E10 conversion equipment 12...---0/E converter 13-----optical fiber 14----A M modulator 15~--high frequency core 31-----Amplifier 32.・---Multi-gate circuit 33～・～・Trigger circuit 34・・・Pulse counting device

Claims (3)

[Claims] (1) Detecting a high frequency pulse from a power cable line under a live line, detecting the phase of the voltage applied to the power cable line, and detecting the high frequency pulse when the phase is at a predetermined phase. A partial discharge measuring method, characterized in that: is determined as a partial discharge signal of the power cable line. (2) The phase of the voltage is determined through one means selected from the voltage transformer connected to the power cable line, the voltage detection terminal, the ground capacitance of the aerial power transmission line, and the distribution transformer. 2. The partial discharge measuring method according to claim 1, wherein the predetermined phase is detected, and the predetermined phase is a phase at which the phase of the voltage reaches a maximum absolute value and a phase slightly advanced from the phase including the vicinity of the phase. . (3) The partial discharge measuring method according to claim 2, wherein the phase of the voltage is transmitted to a partial discharge measuring point via the power cable line.