JPH04215077A - Partial discharge measuring method - Google Patents

Abstract

PURPOSE:To measure a partial discharge without exercising any influence on a power system in a live line state by determining the phase of an applied voltage through detection of the waveform of a current flowing through a sheath to an earthing line and comparing the phase with the phase of a measuring high frequency pulse. CONSTITUTION:The sheath of a single core power cable 11 is connected at a point 11a to an earth line 23, and a high frequency core 24 and a partial discharge measuring device 17 are connected to the earth line 23. A high frequency pulse detected by a measuring device 17 is fed to a CRT 15. Meanwhile, the charge current of the earth line 23 is detected by a current transformer 28, and after the charge current is converted into a waveform signal by means of a waveform converter 30, the waveform signal is fed to the CRT 15 and monitored simultaneously with monitoring of a high frequency pulse. The phase of a charge current responding to an applied voltage and a high frequency pulse are simultaneously monitored by means of the CRT 15. Since the frequency of the generation of a partial discharge pulse at a time when an applied voltage is in a specified phase is high, a pulse generated in the specified phase can be decided as a partial discharge pulse to measure a partial discharge.

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 defects in an insulator constituting a power cable or the like.

0002

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

FIG. 3 is a block diagram showing an example of a method for measuring partial discharge using such a test transformer. When performing partial discharge measurement, the live operation of the power cable 11 is stopped, and one terminal end 12 of the power cable 11 is
Test transformer 1 is connected to cable conductor 13 pulled out from a.
4 is connected to apply a test voltage, the applied voltage waveform is taken out from the secondary winding 14a of the test transformer 14, and the waveform generator 14
A waveform signal is sent from b to the CRT 15. On the other hand, a partial discharge measuring device 17 is connected to the cable conductor 13 drawn out from the other terminal end 12b of the power cable 11 via a coupling capacitor 16, and a high frequency pulse is detected here and the CRT1
Send to 5. In the CRT 15, the applied voltage waveform and the phase of the high frequency pulse are compared. Here, when the applied voltage phase is in a phase where the probability of partial discharge occurrence is high, for example, when the phase is near the maximum value or slightly ahead of that, the high frequency pulse detected is used as the partial discharge signal of the insulator of the power cable. Determine as.

FIG. 4 is a block diagram showing another example of a partial discharge measuring method. The secondary winding of the potential transformer 18 connected to the cable conductor 13 is connected to the E/O (electrical/optical) converter 1
9, where the output voltage signal of the secondary winding is connected to E/O
converted. This signal is transmitted to the O/E via optical fiber 20.
The signal is sent to the (optical/electrical) converter 21, where it is O/E converted. The regenerated output voltage signal is converted into an AM modulator 22.
One point 11a of the sheath modulated and grounded by the ground wire 23
is injected into the power cable 11 from A high frequency iron core 24 is connected to the grounding wire 23 to increase impedance to the ground. On the other hand, a pair of metal foil electrodes 26 are provided at the insulated connection portion 25.
, 26 are attached, and the AM modulated signal wave transmitted via the power cable 11 is extracted by the metal foil electrodes 26, 26, demodulated by the AM demodulator 30, and then output to the CRT 15. Further, the high frequency pulse is applied to the metal foil electrodes 26, 2
6 is detected by the partial discharge measuring device 17 via the detection impedance 27, and monitored by the CRT 15. and,
Similar to the method shown in FIG. 3, the partial discharge signal is determined by observing the applied voltage phase and 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 live operation of the power cable had to be stopped, the power service had to be temporarily interrupted. In addition, since power is applied from the test transformer during partial discharge measurement, special equipment is required, and there are inconveniences such as the hassle of connecting these equipment.

On the other hand, in the method shown in FIG. 4, the phase of the live line voltage is detected using an instrument transformer, which plays an important role in the operation and maintenance of substations. If an accident such as a short circuit or grounding occurs in the output of the voltage transformer, the above-mentioned operation and maintenance management will be affected. In addition, in this method, the applied voltage phase is taken in through a complicated path, so there is a risk that the polarity of the terminal is reversed, and there are many factors that impede accurate measurement.

[0007] Therefore, an object of the present invention is to make it possible to perform partial discharge measurements while the power cable is in a live state, and to be able to reliably perform measurements without affecting the live power system. An object of the present invention is to provide a method for measuring partial discharge.

[0008]

[Means for Solving the Problems] In order to enable measurement to be performed while the power cable is in a live state, and to be able to reliably perform partial discharge measurement without affecting the power system in the live state, the present invention includes the following steps: Detect the charging current flowing through the ground wire of the sheath of the live power cable, determine the phase of the applied voltage from the waveform of this charging current, and calculate the phase of the applied voltage and the high-frequency pulse measured by the partial discharge meter. A partial discharge measuring method is provided in which partial discharge is determined from comparison.

[0008]

[Operation] In a three-phase power transmission system consisting of three single-phase power cables, if a portion or the entire sheath side of each power cable line is grounded at one point, no sheath circuit current will flow. 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 wire is π/2.

Therefore, by detecting the charging current flowing through the ground wire, the phase of the applied voltage can be determined. In the present invention, the charging current flowing through the grounding wire is detected, the applied voltage phase is determined from the phase difference between the charging current and the applied voltage, which is known in advance, and this indirectly detected applied voltage phase and the detected high-frequency pulse are calculated. A high-frequency pulse detected at a specific applied voltage phase is determined to be a partial discharge signal.

0010

EXAMPLES The partial discharge measuring method of the present invention will be explained in detail below.

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

A cable conductor 13 is drawn out from the terminal end 12 of the single-core power cable 11 . The sheath of this single-core cable system is grounded by a grounding wire 23 only at one point 11a. A high frequency iron core 24 is connected to this grounding wire 23 in order to increase high frequency impedance. This ground line 23 is connected to a 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 the charging current is installed on this grounding wire 23, and this current transformer 28 is connected to a waveform converter 30 via a resistor 29 connected in parallel.
The current signal is integrated here. 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 in place of the resistor 29, and the voltage waveform may be obtained directly from both ends of the capacitor.

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 a specific phase of the applied voltage. Since partial discharge pulses appear more frequently when the applied voltage is in a particular phase, a pulse that appears in that phase can be determined as a partial discharge pulse. Therefore, it is possible to perform partial discharge measurement while clearly distinguishing it from external noise.

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

[0017] Also, a signal corresponding to the phase of the applied voltage obtained from the charging current is input together with the high-frequency pulse signal to the gate circuit, and the high-frequency pulse signal is output and evaluated only when the applied voltage has a predetermined phase. By doing so, determination of the partial discharge signal becomes more reliable and easier.

FIG. 2 shows an example of partial discharge measurement on a line in which the sheath circuits are separated by insulated connections and the sheaths in each section are individually grounded.

In this case, a plurality of insulating connection parts 25a and 2
The sheaths in each section separated by 5b are individually grounded by grounding wires 23a, 23b, and 23c. By attaching the same measurement system as shown in Fig. 1 to any grounding wire of the line and detecting the charging current and high-frequency pulse signals from this system, it is possible to perform the same measurement system as in the embodiment shown in Fig. 1. partial discharge measurements can be performed.

[0020]

[Effects of the Invention] As explained above, according to the partial discharge measuring method of the present invention, the applied voltage phase is determined by detecting the charging current flowing through the grounding wire, so that the live operation of the power cable can be stopped. This eliminates the need for insulation diagnosis and allows insulation diagnosis to be performed without interrupting the power supply service. Furthermore, since the output of the instrument transformer or the like is not used for measurement, there is no fear that the operation of these substations will be affected. Furthermore, since the applied voltage signal is extracted through a relatively simple path, there are fewer factors that may cause erroneous connections, and highly accurate measurements can be performed.

[Brief explanation of the drawing]

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

[Explanation of symbols]

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

Claims (1)

[Claims] [Claim 1] The charging current flowing through the ground wire of the sheath of a live power cable is detected, the phase of the applied voltage is determined from the waveform of this charging current, and the phase of the applied voltage and the partial discharge measuring device are measured. A partial discharge measuring method characterized by determining partial discharge from phase comparison with a high-frequency pulse.