JP3124359B2 - Method and apparatus for measuring partial discharge of power cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring partial discharge for evaluating the insulation performance and deterioration state of a high-voltage power cable, and more particularly, to an on-site completion test by applying an AC voltage after laying the cable. The present invention relates to a partial discharge measurement method and apparatus suitable for use as a part of a system for monitoring insulation deterioration in a live state.

[0002]

2. Description of the Related Art In measuring partial discharge of a power cable or the like, identification of noise is an important factor. In the partial discharge measurement, various methods for removing the influence of noise have been conventionally studied. As a method of measuring the partial discharge that removes the influence of noise, generally, the occurrence of noise is detected by some means, and when noise enters,
A method is used in which a gate is closed for a certain period of time by a delay circuit or the like to prevent noise from entering.

For example, an antenna circuit for detecting noise is provided separately from the partial discharge measurement circuit, and when airborne noise enters the antenna, the signal measured at the same time is judged to be noise, and Close the time gate,
A method in which the detected signal is not transmitted to the measurement system, or a method in which the first impedance element is connected to the terminal of the power cable via a coupling capacitor, and the second impedance element is connected to the shield layer of the power cable to be measured. When an impedance element is connected and a signal of the same polarity is input to both the first and second impedance elements, a method of removing the noise by closing the gate or the like is considered as noise. ing.

[0004]

However, the above-mentioned conventional method has a problem that a partial discharge is observed from an oscilloscope and a human must make a final decision. In the case of measuring and judging a large number of locations, the work is difficult and requires skill.

[0005] Furthermore, in order to create a system for constantly monitoring the power cable, the measuring device and the system become considerably large. The present invention has been made in order to improve the above-described disadvantages of the related art, and it is possible to accurately and automatically monitor partial discharge of a power cable without being affected by noise or the like, It is an object of the present invention to provide a method and an apparatus for measuring a partial discharge, which can determine a location where a partial discharge occurs.

[0006]

In order to solve the above-mentioned problems, a first aspect of the present invention is to detect a partial discharge pulse generated by the occurrence of a partial discharge and generate a partial discharge based on the detected partial discharge pulse. In the partial discharge measurement method of the power cable, the AC voltage applied to the power cable is detected, and the zero cross point of the detected AC voltage is detected .
サ イ ク ル cycle from the first positive peak to positive peak, and
From the zero-cross point to the first negative peak
When a pulse signal is detected in both 1/4 cycles
Further, the occurrence of a partial discharge is determined by identifying the pulse as a partial discharge pulse .

According to a second aspect of the present invention, in the first aspect, a quarter cycle from the positive peak point of the detected AC voltage to the first zero crossing point or the negative peak point is obtained. The occurrence of partial discharge is determined by identifying a pulse signal detected within at least one of the quarter cycles up to the first zero crossing point as not a partial discharge pulse.

According to a third aspect of the present invention, in the first or second aspect, the AC voltage applied to the power cable is provided.
The partial discharge pulse identified for each cycle of
Compared with the set value, the value is larger than the predetermined set value.
Continuous pulses in each cycle of the AC voltage
If a certain number of occurrences occur, it is determined that partial discharge has occurred
It is something to do.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the number of pulses larger than a predetermined set value is set.
Detects that the pulse magnitude gradually increases with time.
In this case, the occurrence of partial discharge is determined .

[0010] The invention of claim 5 is based on claims 1, 2, 3 and
Is the detected partial discharge pulse in the invention of claim 4.
Extract two or more different frequency components from
By comparing partial discharge pulses of different frequency components,
That is, the location where the partial discharge occurs is located.

According to a sixth aspect of the present invention, the power cable is attached to a power cable.
And the power cable
Voltage detecting means for detecting an applied AC voltage, and partial discharge
The pulse signal output by the detecting means and the voltage signal output by the voltage detecting means
Partial discharge to the power cable based on the alternating voltage signal
Determination means for determining that the
The zero-cross point of the AC voltage detected by the
サ イ ク ル cycle from the first positive peak to positive peak, and
From the zero-cross point to the first negative peak
When a pulse signal is detected in both 1/4 cycles
In addition, it is configured to determine that the pulse is a partial discharge pulse .

[0012]

When a partial discharge occurs in the power cable, the partial discharge pulse is, as shown in FIG. 5, a 1/0 from the zero crossing point of the AC voltage applied to the power cable to the first positive polarity peak point. Occurs within 4 cycles or within 1/4 cycle from the zero crossing point to the first negative polarity peak point, and conversely, from the positive polarity peak point of the AC voltage to the first zero crossing point. Past investigations have shown that the probability of occurrence within 1/4 cycle or within 1/4 cycle from the peak point of negative polarity to the first zero crossing point is extremely small.

On the other hand, noise entering from the outside is relatively random, and the remarkable tendency as described above is not seen. When a partial discharge occurs, the peak value of the partial discharge pulse signal in each cycle is compared. As shown in FIG. 6, the value is not always constant, but slightly fluctuates. Show. Immediately before the destruction, the size rapidly increases, leading to destruction.

The present invention focuses on the characteristics of the partial discharge pulse described above, discriminates between the noise and the partial discharge pulse, and determines the occurrence of the partial discharge of the power cable, and is applied to the power cable. An AC voltage is detected, and a quarter cycle from the zero cross point to the first positive peak point of the detected AC voltage and a quarter from the zero cross point to the first negative peak point are detected. Cycle range
The pulse signal detected in the box is identified as a partial discharge pulse, and the accumulated value of the detected partial discharge pulse or FIG.
By judging the occurrence of the partial discharge by using the partial discharge characteristics shown in (1), the partial discharge of the power cable can be monitored automatically and accurately without being affected by noise or the like.

[0015] Furthermore, the partial discharge pulse generated by the partial discharge can be used to specify the location where the partial discharge occurs by utilizing the characteristic that the high frequency component is attenuated while propagating on the power cable.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a configuration of a determinator according to one embodiment of the present invention. In the figure, P is an input terminal of a partial discharge detection pulse, Q is a signal output terminal for waveform check, 11 is an amplifier, 12 is a first filter, 13 is a second filter,
14-1 is a first comparison / counting unit, 14a is a first high-speed comparator, 14b is a second high-speed comparator, 14c
Is a third high-speed comparator, 14d is a first counter,
14e is the second counter, 14f is the third counter, 1
4g is a general purpose interface (hereinafter, referred to as an interface), 14-2 is a second comparing / counting unit, 15 is a processor, 16 is a voltage detector, 17 is a phase adjuster, 18 is zero cross / positive / negative detection. Vessel, 19 is a display,
Reference numeral 20 denotes a recorder, 21 denotes an alarm, 22 denotes a local station, and 23 denotes a master station. The amplifier 11, the first and second filters 12, 13, the first and second comparison / counting units 14-1. , 14-2, processor 15, phase adjuster 17, zero cross / positive / negative detector 18,
The judgment device 2 is constituted by the display device 19, the recorder 20, and the alarm device 21.
4 is constituted.

A partial discharge detection pulse detected by a foil electrode provided at a cable connection portion is input to a partial discharge detection pulse input terminal P in FIG. A measuring instrument or the like is connected to the signal output terminal Q for waveform check at the time of waveform check. The partial discharge detection pulse input terminal P is connected to the amplifier 1
1, the amplifier 11 amplifies the signal given from the partial discharge detection pulse input terminal P. A first filter 12 and a second filter 13 are provided on the output side of the amplifier 11.

The first filter 12 and the second filter 13 are band-pass filters that pass a partial discharge detection pulse in a predetermined frequency band. In the present embodiment, they are 1 MHz to 10 MHz and 10 MHz, respectively.
It has been selected from z to 30 MHz. The pass frequency band of the band-pass filter can be narrower than the above value, but the lower limit is desirably 1 MHz or more.

The first to third high-speed comparators 14a, 14b, 1 provided in the first comparing / counting section 14-1
4c compares the output signal of the filter 12 with a predetermined set value, and outputs an output when the output signal of the filter 12 exceeds the set value set in each of the first to third high-speed comparators 14a, 14b, 14c. A first to third high-speed comparators 14a, 14b, 14
c outputs a first to third counter 1
4d, 14e, and 14f count every quarter cycle.

The interface 14g is a means for providing an interface between the first to third counters 14d, 14e, 14f and the processor 15, and the outputs of the first to third counters 14d, 14e, 14f are transmitted through the interface 14g. The processor 15 analyzes the input signal to determine the occurrence of the partial discharge and the location of the occurrence.

The second comparing / counting section 14-2 has the same configuration as the first comparing / counting section 14-1. The second comparing / counting section 14-2 operates on the output of the second filter 13 as described above.
The same process as -1 is performed. The voltage detector 16 is a means for detecting the voltage of the power cable. The output of the voltage detector 16 is adjusted by a phase adjuster 17 for a phase delay caused by a transmission delay or the like. Positive / negative is detected and supplied to the processor 15 as an interrupt signal.

The display 19 has red, yellow and blue lamps 19a.
To 19f are provided, and the lamps 19a to 19f are provided.
Reference numeral 9c denotes a lamp which turns on or blinks when the partial discharge is determined based on the output of the filter 12, and lamps 19d to 19f turn on or flashes when the partial discharge is determined based on the output of the filter 13. Then, as described later, the lamps 19a through 19
c and the lighting state of the lamps 19d to 19f make it possible to determine the location of the occurrence of the partial discharge.

The output of the display 19 is provided by the recorder 2
0, the alarm 21 is connected, the recorder 20 records the state of the occurrence of the partial discharge analyzed by the processor, and the alarm 21 is used when the partial discharge occurs which leads to the breakage of the power cable. Raise an alarm. local·
The station 22 is provided for each monitoring point on the power cable, receives output signals of a plurality of determiners provided at each monitoring point, and comprehensively detects a partial discharge detected at the local station installation point. In addition to the judgment, the judgment result is transmitted to the master station 23 provided at the center.

FIG. 2 is a diagram showing the overall configuration of the monitoring system according to the present embodiment. The same components as those shown in FIG. 1 are denoted by the same reference numerals. In the figure, 16 is a voltage detector, 22 is a local station, 23 is a master station, 24 is a judgment unit shown in FIG.
1 is a power cable, 32 is an intermediate connection part (NJ part), 33
Is an insulating intermediate connection portion (IJ portion), 34 is a foil electrode for detecting partial discharge, 35 is a detection impedance, 36 is an optical fiber cable, 37 is an alarm, and 38 is a display device.

In the figure, the voltage detector 16 is connected to the end of the power cable 31 and
Is detected and transmitted to each determiner 24.
The foil electrode 34 is provided on the power cable 31 in the vicinity of the insulating intermediate connection part (IJ part) 33, and the foil electrode 34 is connected to the detection impedance 35. When a partial discharge occurs in the power cable 31, a partial discharge pulse is generated at both ends of the detection impedance 35, and the detection pulse is given to each of the determiners 24.

Judgment unit 24, local station 22
The master station 23 and the master station 23 are the same as those shown in FIG.
The output of the local station 22 is sent to the master station 23 via the optical fiber cable 36.

Next, the monitoring operation of the partial discharge in this embodiment will be described with reference to FIGS. 2, when a partial discharge occurs in the power cable 31, a partial discharge pulse is detected by the foil electrode 34 and the detection impedance 35 provided on the power cable 31, and sent to the determiner 24 shown in FIG.

The partial discharge pulse including the noise signal detected by the foil electrode 34 and the detection impedance 35 is shown in FIG.
Is applied to the input terminal P of the partial discharge detection pulse of the determiner 24 shown in FIG.
The signal is input to the second filter 13. First filter 12
Is the detected pulse signal from 1 MHz to 10 MHz.
, And the second filter 13 passes a signal having a frequency component of 10 MHz to 30 MHz.

The pulse signal that has passed through the first filter 12 is supplied to a first comparing / counting unit 14-1 and set in the first to third high-speed comparators 14a, 14b, 14c to set values q ₁ , q ₂ , q ₃ (q ₁ <q ₂ <q ₃ ), and when a pulse signal exceeding the set value q ₁ , q ₂ , q ₃ is detected, it is output to the counters 14 d, 14 e, 14 f.

When pulse signals are input from the first to third high-speed comparators 14a, 14b, and 14c, the counters 14d, 14e, and 14f count the number of pulses for each quarter cycle of the voltage applied to the power cable. And sends the count value to the processor 15 via the interface 14g. Further, the second comparison / counting unit 14-
2 also has the same configuration as the first comparing / counting unit 14-1.
The second comparing / counting unit 14-2 performs the same process on the output of the second filter 13, and outputs a count value to the processor 15.

On the other hand, the voltage detected by the voltage detector 16 provided at the end of the power cable in FIG. 2 is adjusted for the phase shift due to the transmission delay by the phase adjuster 17 shown in FIG. At 18, the zero crossing point and the sign of the voltage are detected and input to the processor 15 as an interrupt signal. Here, when a partial discharge occurs in the power cable, the generation phase of the partial discharge pulse is, as shown in FIG.
Between the cross point and the positive and negative peak values,
Conversely, the probability that a partial discharge pulse is generated from the positive and negative peak values to the zero crossing point is extremely low, and this tendency does not change for EMJ (extrusion type connection) or PJ (prefab type connection). Has been found from past surveys.

In addition, immediately before the power cable is destroyed, EMJ
(Push-out connection), the number of pulses near the peak value
Increases and the PJ (prefabricated connection) becomes zero
・ As the number of pulses increases near the cross,
Immediately before breaking the power cable, the partial discharge pulse
Increases have been found in past surveys. Figure 3
The voltage v applied to the power cable and the partial discharge pulse s
Setting value q₁, Q _Two, Q_ThreeFIG.
As shown, the partial discharge pulse s is applied to the power cable.
Voltage phase from 0 to 90 degrees and 180 to 270 degrees
Occurs during this period, and does not occur during other periods.

Based on the above-described principle, the processor 15 shown in FIG. 1 uses the count value of the partial discharge pulse read through the interface 14g and the voltage phase applied to the power cable read from the zero-cross / positive / negative detector 18. The occurrence of partial discharge in the power cable is determined as follows. The processor 15 ignores the pulse signals detected in the sections of θn ₂ and θn ₄ among the voltage phases shown in FIG.
Only the count value of the pulse signal detected in the section of ₁ and θn ₃ is used in the process of determining the occurrence of partial discharge.

In this case, as described above, immediately before the breakage of the power cable, in the EMJ (extrusion type connection), the number of partial discharge pulses increases near the peak value, and the PJ (2 prefabricated type connection) increases. )), The voltage phase sections θn ₂ and θn are taken into consideration in consideration of the fact that the number of pulses increases near the zero cross and that the voltage phase detected by the voltage detector 16 shifts due to transmission delay or the like.
₄ is approximately 10 times on either side of the peak and zero crossing points.
It is desirable to spread it one by one.

FIG. 4 is a diagram showing the principle of determining the occurrence of partial discharge in the processor 15. In FIG. 4, q ₁ , q
₂ and q ₃ are set values in the high-speed comparators 14a, 14b and 14c, and θn ₁ to θn ₄ are voltage phases of the power cable. Processor 15 as shown in FIG. 4, a high speed comparator 14a, 14b, each of the count values of each value q _1, q _2, q ₃ a pulse signal exceeds the 14c, the count value of .theta.n ₁ interval .theta.n ₁ q And the product of the count values θn ₃ q in the θn ₃ section θnq = θn ₁ q × θ
n ₃ q is obtained, and the occurrence of the partial discharge is determined based on the value.

At that time, the processor 15 outputs the output of the first comparing / counting unit 14-1 and the second comparing / counting unit 14-
The above process is performed for the output of No. 2 to determine the occurrence of partial discharge. The following method can be used as a specific method for determining the occurrence of partial discharge in the processor 15. (A) θnq ₁ the product of the count value in .theta.n ₁ section and .theta.n ₃ sections of the pulse signal exceeds a set value q _1, the count value in .theta.n ₁ section and .theta.n ₃ sections of the pulse signal exceeds a set value q ₂ Assuming that the product is θnq ₂ and the product of the count values of the pulse signal exceeding the set value q ₃ in the θn ₁ section and the θn ₃ section is θnq ₃ , the accumulated value Σθnq _{1 for} m cycles (m ≧ 1) Σθnq ₂ , Σθn
determine the q ₃ in the following manner.

[0037] _{Σθnq 1 = θ 1 q 1 +} θ 2 q 1 + ... + θmq 1 Σθnq 2 = θ 1 q 2 + θ 2 q 2 + ... + θmq 2 Σθnq 3 = θ 1 q 3 + θ 2 q 3 + ... + θmq 3 incidentally, Q1, Q2, and Q3 are calculated by the following equations, and the occurrence of partial discharge is determined based on these values.

Q1 = (Σθnq ₁ / m) × 100% Q2 = (Σθnq ₂ / m) × 100% Q3 = (Σθnq ₃ / m) × 100% Also, according to the values of Q1, Q2 and Q3, For example, Q
When the values of 1, Q2, and Q3 exceed 70% to 80%, the yellow or red lamps of the lamps 19a to 19f of the display 19 are turned on or blinked to indicate the occurrence of partial discharge, When a partial discharge has occurred, the alarm 21 can also notify.

The number m of cycles for obtaining the accumulated value can be set externally. It is also possible to set m to "1" and determine partial discharge based on a detection pulse for one cycle. It is. (B) The upper limit value Qtlmt of the total pulse count set from the outside and the above Δθnq ₁ , Δθnq ₂ , Δθnq ₃
Are compared by the following equation to determine the partial discharge. Σθnq ₁ ≦ Qtlmt …… No partial discharge detected Σθnq ₂ <Qtlmt ≦ Σθnq ₁ …… Slight partial discharge occurs Σθnq ₃ <Qtlmt ≦ Σθnq ₂ … Moderate partial discharge occurs Qtlmt ≦ Σθnq ₃ … Severe partial discharge In addition, in the above case, the blue lamp 19c of the display 19
Is lit, and in the case of, the yellow lamp 19b is lit,
In the case of (1), the red lamp 19a is turned on. In the case of (2), the red lamp 19a is turned on and off, and the alarm 21 can be used to notify the occurrence of the partial discharge that may cause the break of the power cable. (C) When the partial discharge occurs, the peak value of the partial discharge pulse signal in each cycle is compared, and the value is not always constant, but shows a gradually increasing phenomenon as a whole while slightly fluctuating. It is known that immediately before the destruction, the size rapidly increases, leading to destruction.

FIG. 6 shows an insulator having a needle inserted into the insulator.
This figure shows the partial discharge characteristics of a 5 mm 110 kV 150 mm ² CV cable. As shown in the figure, in the first short time, it becomes 10 pc (pico-coulomb, the same applies hereinafter) or more, and the state of several tens to several hundreds pc is obtained. It lasts for several minutes to several hours, and reaches several hundred pcs just before destruction. Therefore, using the partial discharge characteristics described above, the accumulated value Σ
By storing θnq ₁ , Σθnq ₂ , Σθnq _{3, and the} like, and determining the rate of change (dq / dt), it is possible to grasp the progress of partial discharge, and when the rate of change becomes large, It can be determined that the partial discharge has progressed and the power cable has reached just before breaking.

This determination can be made automatically in the processor 15, or it can be made to be recorded by the recorder 20 and made based on the recording result. Further, as described above, immediately before the breakage of the power cable, in the EMJ (extrusion connection) using polyethylene,
The number of pulses increases near the peak value, and P using epoxy
It is known that at J (prefabricated connection), the number of pulses increases near the zero cross.

Therefore, a method of observing the original waveform of the partial discharge pulse and counting the number of pulses near the peak value or the number of pulses near the zero cross to determine the progress of the partial discharge is used in combination with the above method. Accordingly, the partial discharge can be detected with higher accuracy. (D) The above Δθnq ₁ , Δθnq ₂ , Δθnq ₃ or Q1 obtained from the output of the first comparing / counting unit 14-1
Σθnq ₁ , Σθnq ₂ , Σθnq obtained from the values of Q3 to Q3 and the output of the second comparing / counting unit 14-2.
_The location of the occurrence of the partial discharge can be determined by the value of ₃ or Q1 to Q3.

That is, in general, the high frequency component of the partial discharge pulse generated by the partial discharge is attenuated while propagating on the power cable. For this reason, when partial discharge occurs at a location away from the location where the partial discharge detector is installed,
Compared to the output of the second comparing / counting section 14-2 to which the output of the filter 13 having a relatively high frequency band is provided, the first to which the output of the filter 12 having a relatively low frequency band is provided.
The output of the comparing / counting unit 14-1 has a larger pulse count value.

By utilizing this principle, the count value in the first comparing / counting section 14-1 and the second comparing / counting section 14-1
It is possible to determine the location of the occurrence of the partial discharge based on the count value in -2 (in this regard,
See Japanese Patent Application No. 3-129632). Further, according to the location of the occurrence of the partial discharge, the lighting state of the lamps 19a to 19c of the display 19 which is turned on by the output of the first comparing / counting section 14-1, and the lighting state of the second comparing / counting section 14-2. Since the lighting state of the lamps 19d to 19f that are lit by the output changes (when partial discharge occurs nearby, the lamps 19d to 19f are turned on).
a to 19c and the lamps 19d to 19f are turned on, and if a partial discharge occurs at a distance, the lamp 1
Only the lamps 9a to 19c are turned on), and it is also possible to determine whether the partial discharge has occurred near or far from the lighting state of the lamps 19a to 19f.

The above-described partial discharge determination methods (A), (B), and (C) can be used alone or in combination of several methods. Also,
In the above-described determination method, the function allocation among the determiner 24, the local station 22, and the master station 23 can be appropriately determined according to the situation. For example, the determination unit 24 makes a preliminary determination of the partial discharge by the determination method (A) or (B), and the display 19 roughly displays the location where the partial discharge has occurred. The final determination is performed by the determination method (D), and the determination method (D)
Thus, the location of the occurrence of the partial discharge can be determined and the location can be displayed.

Further, in the above determination method, θn ₁
The product of the count values of the section and the section θn ₃ θnq = θn ₁ q
By obtaining the × .theta.n ₃ q, an example has been described for determining partial discharge, mosquito .theta.n ₁ interval and .theta.n ₃ sections
Or determines the occurrence of partial discharge by count value, it obtains the respective accumulated values of several cycles of the count value of the accumulated value and .theta.n ₃ sections of several cycles of the count value of .theta.n ₁ interval, obtains the product Thus, the determination of the partial discharge can be performed.

Further, the accumulated value is obtained as described above.
Instead, the count value θnq₁, Θnq_Two, Θnq_ThreeEtc.
When a certain number of non-zero cycles occur consecutively
In addition, it can be determined that partial discharge has occurred.
θn₁Section count value, θn _ThreeUse the count value of the section
Then, the determination of the partial discharge may be performed. As above
Therefore, the processor 15 determines the occurrence of the partial discharge, and
The result is sent to the local station 22.

The local station 22 determines the occurrence of partial discharge by summarizing a plurality of determination results (for example, nine locations in the case of three lines and three phases) at the same detection location, When a discharge occurs, the determination result is transmitted to the master station 2 via the optical fiber 36.
Transmit to 3. At this time, if an abnormal portion is determined, the original waveform of the partial discharge pulse is detected and transmitted to the master station 23 via the optical fiber 36.

The master station 23 is a local
The temporal change of the partial discharge charge amount or the phase characteristic change of the partial discharge pulse maximum value is obtained from the partial discharge pulse original waveform transmitted by the station 22, and the results 38a and 38b are displayed on the display device 38 and the like. Or a final determination of partial discharge is made, and a final alarm is notified by the alarm device 37.

In the above embodiment, the master
Although the original partial discharge pulse waveform is configured to be transmitted to the station 23, if the local station 22 can monitor the eventual occurrence of the partial discharge, the master station 23 determines whether the partial station has generated the partial discharge pulse. It can also be configured to transmit only the result.

The master station 23
In the case of transmitting only the judgment result at the station, a piezoelectric element is attached to the optical fiber 36 for each local station 22, and mechanical vibration is applied to the optical fiber at a different frequency for each local station 22. , The polarization plane fluctuation is generated in the optical fiber 36, and the occurrence of the partial discharge and the location of the occurrence can be transmitted to the master station 23.

With this configuration, each local station 22 can be connected to the master station 23 without cutting the optical fiber 36, and the occurrence of partial discharge can be transmitted to the master station 23. If the number of detected partial discharge locations is small, an optical signal is transmitted to each measurement location via an E / O converter (electrical-optical converter) and an optical fiber, and O / E conversion (optical (Electrical conversion), the determination unit, the local station, and the master station can be gathered in one place.

Further, in the above embodiment, a voltage detector is provided at the end of the cable to detect the voltage applied to the power cable. For example, a magnetic field sensor or the like is provided at each partial discharge detection point. , The current flowing in the power cable is detected, and the detected current phase is adjusted by the phase adjuster, thereby detecting a zero point of the voltage applied to the power cable.

Further, in the above-described embodiment, an example is shown in which the partial discharge detector is provided at the insulated intermediate connection portion (IJ portion) of the power cable, but a PJ (prefabricated connection portion) or the like is used as the connection portion. Accordingly, when the detection sensitivity of the partial discharge at the connection portion can be increased, a partial discharge detector can be provided at the intermediate connection portion (NJ portion).

[0055]

As is apparent from the above description,
In the present invention, an AC voltage applied to a power cable is detected, and a quarter cycle from a zero crossing point of the detected AC voltage to a first positive peak point, and
1 / from the zero crossing point to the first negative polarity peak point
The pulse signal detected within the range of 4 cycles is identified as a partial discharge pulse, and the occurrence of the partial discharge is determined, so that the measurement of the partial discharge in the power cable can be performed accurately and automatically. .

Since the measurement of the partial discharge can be performed automatically without human intervention, it is possible to construct a system for constantly monitoring the power cable.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a determination unit according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an overall configuration of a system according to an embodiment of the present invention.

FIG. 3 is a diagram showing partial discharge pulses in each quarter cycle of an AC voltage.

FIG. 4 is a diagram illustrating a determination process in a processor.

FIG. 5 is a diagram showing a relationship between a voltage phase and a partial discharge pulse.

FIG. 6 is a diagram showing a change in a partial discharge charge amount.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Amplifier 12, 13 Filter 14-1, 14-2 Comparison / Counting part 14a, 14b, 14c High-speed comparator 14d, 14e, 14f Counter 14g General purpose interface 15 Processor 16 Voltage detector 17 Phase adjuster 18 Zero cross / Positive / negative detector 19 Indicator 20 Recorder 21 Alarm 22 Local station 23 Master station 31 Power cable 32 Intermediate connection (NJ) 33 Insulation intermediate connection (IJ) 34 Foil electrode for partial discharge detection 35 Detection impedance 36 Optical fiber cable 37 Alarm 38 Display

Continuation of the front page (56) References JP-A-56-160665 (JP, A) JP-A-3-175374 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 31 / 12

Claims (6)

(57) [Claims] 1. A method for measuring a partial discharge of a power cable, comprising detecting a partial discharge pulse generated by the occurrence of the partial discharge, and determining the occurrence of the partial discharge based on the detected partial discharge pulse. And the first positive polarity from the zero cross point of the detected AC voltage
1/4 cycle to the peak point of
1/4 cycle from the ground point to the first negative peak
When a pulse signal is detected in both
And measuring the partial discharge of the power cable. 2. A quarter cycle from the peak point of the positive polarity of the detected AC voltage to the first zero-cross point, or a quarter cycle from the peak point of the negative polarity to the first zero-cross point. 2. The method according to claim 1, wherein a pulse signal detected within at least one of the ranges is identified as not a partial discharge pulse. 3. An AC voltage applied to a power cable.
Predetermined partial discharge pulse identified for each cycle
Compared with the set value, a pulse larger than the predetermined set value
Occurs more than a certain number of times continuously in each cycle of
3. The method according to claim 1, wherein it is determined that a partial discharge has occurred . 4. A pulse larger than a predetermined set value.
Number or pulse size gradually increases with time
The occurrence of partial discharge by detecting
Partial discharge measurement method of the power cable of claim 1, characterized in that that. 5. The method according to claim 1, wherein two or more pulses are detected from the detected partial discharge pulse.
Extracting different frequency components, two or more different frequency components
By comparing the partial discharge pulses for
The location of occurrence is located.
A method for measuring partial discharge of a power cable according to claim 4. 6. A partial discharge attached to a power cable.
Pulse detection means and AC voltage applied to the power cable
Voltage detection means for detecting the voltage , a pulse signal output from the partial discharge detection means , and a voltage detection means.
Based on the AC voltage signal output by the stage,
Determining means for determining that a partial discharge has occurred, wherein the determining means includes a zero cross point of the detected AC voltage.
1/4 cycle from the first positive peak point to
And from the zero cross point to the first negative peak
When a pulse signal is detected in both 1/4 cycles of
A partial discharge measuring device for a power cable, which determines that the pulse is a partial discharge pulse .