JP2008191113A - Partial discharge detector for cable end - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a partial discharge detector for a cable end terminal part, capable of detecting easily and highly sensitively a partial discharge current, without enlarging the size of a closed loop. <P>SOLUTION: A partial discharge detecting CT 41 is attached to an arrester bar 7A provided in the cable end terminal part 3 in an end terminal part of an electric power cable line, and the partial discharge current flowing through an arrester 6 is detected by the partial discharge detecting CT 41. A pulse current (partial discharge current) detected by the partial discharge detecting CT 41 is amplified by a tuned amplifier 43 having a predetermined frequency range, after converted into a voltage by a current/voltage converter 42, and an amplified output is monitored by an oscilloscope 44. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a partial discharge detection device for a cable end portion that detects a partial discharge (PD) from the end portion of a power cable line.

  As a method for confirming the soundness of a cable line such as a power cable and its connection part, there is a method of applying a predetermined voltage to the line and electrically measuring and detecting a partial discharge generated at this time. This confirmation method detects a partial discharge, which is a precursor phenomenon of the dielectric breakdown of the cable line, and therefore has an advantage that the presence or absence of the defect can be detected without destroying the cable line.

  As a partial discharge detection method, a partial discharge measurement device is known in which a pair of metal foil electrodes are attached to the surface of a corrosion-resistant vinyl sheath of an insulating connection portion, and a partial discharge measuring device is connected to these metal foil electrodes via a detection impedance. (For example, Non-Patent Document 1).

  In addition, as a partial discharge detection device that does not use a metal foil electrode, a CT (current transformer) is inserted into the ground wire of a three-phase AC cable, and the frequency component of the partial discharge current is extracted from the current signal detected by CT. There is a partial discharge detection device that determines partial discharge by doing this (for example, see Patent Document 1).

Furthermore, there is also known a live activated partial discharge detection device that inserts CT into a cable shield line, detects and amplifies a partial discharge current, and observes the output signal (for example, see Non-Patent Document 2).
“Hitachi Cable” No. 16 (1997-1) 42p JP 2004-347424 A "Fujikura Technical Review" No.106, April 2004, 39-42p

  However, according to the conventional partial discharge detection device described in Non-Patent Document 1, since it is necessary to attach a metal foil electrode having a complicated configuration to the insulating connection portion, it requires a lot of labor and time, and the measurement cost is high. There is an inconvenience that it becomes high.

  Further, according to the conventional partial discharge detection device described in Patent Document 1 and Non-Patent Document 2, when a pulse current accompanying partial discharge is detected via CT provided on a ground line or a cable shielding line, gas insulation The closed loop of the path | route which flows into the electrostatic capacitance by the main insulation of a cable connection apparatus is formed through the metal stand of cable connection apparatuses, such as a switchgear (GIS). Since this closed loop is orders of magnitude larger than the foil electrode method disclosed in Non-Patent Document 1, the attenuation of the signal is larger than that of the foil electrode method, and the external noise also increases, so that high sensitivity detection is expected. Can not.

  Usually, the cable termination is in a substation, but when the substation is outdoors, air corona from the air termination often occurs. For this reason, when the closed loop becomes large, it becomes easy to detect the pulsed electromagnetic waves accompanying the corona in the air, and much effort is required for the countermeasure. Furthermore, in the detection of partial discharge, it is necessary to lower the detection frequency in order to reduce signal attenuation. However, if the closed loop is large, the noise level becomes high and sufficient detection sensitivity cannot be obtained.

  Accordingly, it is an object of the present invention to provide a partial discharge detection device for a cable terminal that can detect a partial discharge current easily and with high sensitivity without increasing the closed loop.

  In order to achieve the above object, the present invention provides a current detection unit that detects a partial discharge current flowing in an abnormal voltage protection unit provided at a cable terminal portion of a power cable line, and the partial discharge current output from the current detection unit. A partial discharge detection device having a partial discharge detection unit for detecting partial discharge based on the above.

  According to the present invention, partial discharge at the cable end can be detected easily and with high sensitivity without increasing the closed loop.

[Embodiment]
(Configuration of partial discharge detection system)
FIG. 1 is a connection diagram showing a partial discharge detection system according to an embodiment of the present invention.

  The partial discharge detection system 100 includes a device 1 connected to a cable, a power cable 2 such as a bus, a cable terminal 3 connecting the device 1 and the power cable 2 connected to the cable, and a cable terminal 3. A partial discharge detection unit 4 connected thereto is provided.

  In the present embodiment, the device 1 connected to the cable is a GIS and is installed on a metal mount 5 and includes a bushing 11, a corona shield ring 12, a high-voltage conductor 13, and the like.

  The power cable 2 is, for example, a CV cable (cross-linked polyethylene insulation / polyvinyl chloride sheath cable).

  The cable end portion 3 includes a protective copper tube 31A, 31B and a sheath insulating tube 32 disposed so as to partition the protective copper tube 31A, 31B. A ground wire 33 is connected between the protective copper tube 31B and the ground.

  Between the protective copper tube 31A and the protective copper tube 31B, an arrester 6 as an abnormal voltage protection unit is connected via arrester bars 7A and 7B. The arrester bars 7A and 7B can be replaced with lead wires. Further, depending on the power cable line, both ends of the sheath insulating cylinder 32 may be connected by a short-circuit bar without using the arrester 6.

  The arrester 6 is an abnormal voltage protection unit that becomes an insulator when a voltage in an allowable range is applied and becomes a conductor when a voltage exceeding the allowable range is applied. For example, a zinc oxide element is used. be able to.

(Configuration of partial discharge detector)
The partial discharge detection unit 4 is provided as a current detection unit and includes a current / voltage converter 42 that converts current detected by the arrester bar 7A or the partial discharge detection CT 41 inserted in the short-circuit bar into a voltage, and a current / voltage A tuning amplifier 43 that amplifies the signal output from the converter 42, an oscilloscope 44 that is connected to the tuning amplifier 43 and that observes the waveform, and a calibration pulse oscillator 45 that oscillates a calibration pulse to be injected into the cable termination unit 3 are provided. Configured.

  The tuning amplifier 43 has the same frequency band as the resonance frequency determined by the elements including the capacitance of the arrester 6, the capacitance of the device 1 and the power cable 2 connected to the cable, and the inductance of the arrester bars 7A and 7B. It has a circuit configuration.

  When the tuning amplifier 43 has a configuration in which the tuning frequency can be varied, a spectrum (S) when the calibration pulse is injected from the calibration pulse oscillator 45 to both ends of the sheath insulating cylinder 32 and a noise spectrum when the calibration pulse is not injected. The tuning frequency is set so that the ratio S / N of (N) is maximized.

(Operation of partial discharge detection system)
Next, the operation of the partial discharge detection system will be described with reference to FIG. When a partial discharge is generated in the system in which the cable terminal 3 is interposed, a pulse voltage accompanying the partial discharge is generated at both ends of the sheath insulation cylinder 32, and a pulse current is applied to the arrester 6 via the arrester bars 7A and 7B. Flowing. This pulse current is detected by the partial discharge detection CT41.

  The pulse current detected by the partial discharge detection CT 41 is converted to a voltage by the current / voltage converter 42 and then applied to the tuning amplifier 43. The tuning amplifier 43 amplifies a signal in a preset frequency band with respect to the signal output from the current / voltage converter 42.

  When the discharge charge amount is calibrated, calibration pulse oscillators 45 are connected to both ends of the sheath insulation cylinder 32. At this time, a pulse current corresponding to the calibration pulse charge amount flows to the arrester 6 via the arrester bars 7A and 7B and is detected by the partial discharge detection CT41. In this way, by determining the relationship between the discharge charge amount and the detection pulse current value in advance, the charge amount of partial discharge generated when a voltage is applied to the sample can be determined.

  The signal amplified by the tuning amplifier 43 is monitored by the operator with the oscilloscope 44, and it is determined whether or not it is a partial discharge from the observed waveform. Further, the partial discharge detection result is recorded by a data recorder (not shown) or the like as necessary.

(Equivalent circuit of partial discharge detection system)
FIG. 2 is an equivalent circuit of the partial discharge detection system 100 of FIG.
As shown in FIG. 2, the equivalent circuit, the capacitance Cc and the arrester bar 7A arrester 6 between the protective copper tube 31A and the protective copper tube 31B, 7B of the inductance L ₀ is connected in series, the power cable 2 conductors (Not shown), an electrostatic capacitance Ck of equipment main insulation is connected between the conductor 8 that collectively refers to the high-voltage conductor 13 and the conductor (not shown) in the cable terminal portion 3 and the protective copper tube 31A. The capacitance Ca of the insulating part of the power cable 2 is connected between the protective copper tube 31B.

  Capacitance Ca is obtained by connecting in series a capacitance Cb of a normal portion (a portion where a defect such as a water tree is not generated) in the power cable 2 and a capacitance Cg of a defective portion where a partial discharge is generated. It is the capacity | capacitance of the cable insulation part represented.

Arrester 6, the effect of the capacitor, and since arrester bars 7A, 7B is to the action of the inductance L _0, and the series resonance at a certain frequency, the impedance of the partial discharge measurement circuit is minimized, the current flowing through the arrester 6 Increases the detection sensitivity. Therefore, in the present embodiment, the current flowing through the arrester 6 is detected by the partial discharge detection CT 41.

(Effect of embodiment)
According to the present embodiment, the following effects are obtained.
(1) By detecting the partial discharge current flowing through the arrester 6 with the partial discharge detection CT 41, the closed loop through which the partial discharge signal passes is reduced, the S / N ratio is improved, and the signal level of the partial discharge signal is minimized. Can be limited.

  In order to increase the detection sensitivity of the partial discharge signal, it is necessary to increase the S / N ratio. Normally, however, the partial discharge signal (S) has a loss and a distribution when passing through the capacitance and inductance in the detection circuit. Decreases due to pressure and diversion. However, according to the present embodiment, since the metal mount 5 and the ground wire 33 are not used as the measurement path, the closed loop through which the partial discharge signal passes can be reduced, and as a result, the S / N ratio is improved.

(2) Since the metal foil electrode is not used, the mounting work for that purpose can be omitted, and the working manpower and work time can be reduced as compared with the detection method using the conventional metal foil electrode.

(3) Since the resonance phenomenon between the electrostatic capacitance in the cable terminal portion 3 and the inductance in the arrester 6 and the arrester bars 7A and 7B is utilized, the impedance due to the electrostatic capacitance and the inductance in the closed loop is canceled. It is possible to prevent the partial discharge signal from being lowered.

(4) Since the partial discharge signal detected by the partial discharge detection CT 41 is amplified by the tuning amplifier 43, the loss of the partial discharge current caused by the arrester 6 and the arrester bars 7A and 7B can be reduced.

[Comparative example]
FIG. 3 is a connection diagram illustrating a partial discharge detection system according to a comparative example. In this comparative example, the arrester 6 and the arrester bars 7A and 7B are removed from the configuration of the embodiment of the present invention shown in FIG. 1, and a partial discharge is detected on the ground line 33 connected between the protective copper tube 31B and the ground. CT41 is inserted.

  An amplifier 9 is connected to the partial discharge detection CT 41, and an oscilloscope 44 is connected to the amplifier 9.

  In the partial discharge detection system of the comparative example, when a partial discharge is generated in the system in which the cable terminal portion 3 is interposed, a pulse current accompanying the partial discharge flows through the ground line 33. This pulse current is detected by the partial discharge detection CT41.

  The pulse current detected by the partial discharge detection CT 41 is amplified by the amplifier 9 and then monitored by the oscilloscope 44, and the operator determines whether or not the partial discharge is based on the observed waveform.

(Equivalent circuit of partial discharge detection system)
FIG. 4 is an equivalent circuit of a comparative example.
As shown in FIG. 4, in the equivalent circuit, the inductance L ₁ of the metal mount 5, the CT 41 for partial discharge detection and the inductance L _{2 of the} ground wire 33 are connected in series between the protective copper tube 31 A and the protective copper tube 31 B, and the power An electrostatic capacitance Ck of equipment main insulation is connected between the conductor 8 in the cable terminal 3 connecting the conductor (not shown) of the cable 2 and the high voltage conductor 13 and the protective copper tube 31A, and the conductor 8 is protected. The capacitance Ca of the insulating part of the power cable 2 is connected between the copper tube 31B.

As is clear from the equivalent circuit of FIG. 2, the equivalent circuit of FIG. 4 includes the inductance L ₁ of the metal mount 5 and the ground wire 33 in the path from the protective copper tubes 31 A and 31 B to the partial discharge detection CT 41 side. there are inductance L _2, but the capacitance does not include.

For this reason, the pulse current (partial discharge current) accompanying the partial discharge flows from the ground line 33 to the electrostatic capacitance Ck by the main insulation of the cable connection device via the metal mount 5, and the embodiment of the present invention and the foil electrode method As compared with the above, the signal attenuation caused by the inductances L ₁ and L ₂ is increased, and the external noise is increased due to the loop passing through the metal mount 5 and the ground wire 33.

Next, examples will be described.
FIG. 5 is a characteristic diagram showing a measurement result of partial discharge from a prefabricated cable end portion with simulated defects in which the equivalent circuit of FIG. 2 is established. The vertical axis of the graph indicates the value obtained by converting the detected pulse current value into the discharge charge amount based on the “discharge charge amount calibration curve”.

  The horizontal axis of the graph is the time axis. Here, since it is displayed in synchronization with the applied voltage phase, the horizontal axis can be read as applied voltage phase information as it is.

  The plot on the graph shows the peak value of the pulse waveform with partial discharge. For this reason, the number of pulses generated during the recording period of this graph is the same as the number of plots.

Here, the tuning amplifier 43 has a tuning frequency of 30 MHz at which the S / N ratio is highest. Moreover, it implemented on condition of the following.
Measurement time: 1 minute Measurement frequency: 30.0 MHz

  As a result, the number of pulses is 396 (issue), the occurrence frequency is 6.61 (issue / second), the maximum value is 27.0 (pC), the average value is 4.6 (pC), and the maximum average value is 9.3 (pC). It was confirmed that partial discharge occurred from the simulated defect.

[Other embodiments]
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. For example, the combination of the component between each embodiment can be performed arbitrarily.

  For example, at the time of partial discharge detection, the tuning frequency of the tuning amplifier 43 can be set to a parallel resonance frequency determined by the capacitance of the sheath insulation cylinder 32 and the inductance of a short-circuit bar that short-circuits both ends thereof. With this configuration, the partial discharge detection sensitivity can be increased.

  In the above embodiment, the tuning frequency of the tuning amplifier 43 is adjusted to the resonance frequency due to the capacitance of the sheath insulation cylinder 32 (or arrester 6) and the inductance of the shorting bar (or arrester bars 7A and 7B). Since the signal level of the resonance frequency can be reduced, the tuning amplifier 43 in the subsequent stage can be omitted, and the measurement system can be made inexpensive. Alternatively, an inexpensive measurement system can be provided by changing the tuning amplifier 43 to an RF (high frequency) amplifier.

It is a connection diagram showing a partial discharge detection system according to an embodiment of the present invention. It is an equivalent circuit of the partial discharge detection system of FIG. It is a connection diagram which shows the partial discharge detection system by a comparative example. It is an equivalent circuit of a comparative example. It is a characteristic view which shows the measurement result of the partial discharge from the prefabricated type | mold cable terminal part with a simulated defect which was made to materialize the equivalent circuit of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Apparatus 2 Power cable 3 Cable termination part 4 Partial discharge detection part 5 Metal mount 6 Arrester 7A, 7B Arrester bar 8 Conductor 9 Amplifier 11 Bushing 12 Corona shield ring 13 High voltage conductor 31A, 31B Protective copper tube 32 Sheath insulation cylinder 33 Grounding wire 41 CT for partial discharge detection
42 Current / Voltage Converter 43 Tuning Amplifier 44 Oscilloscope 45 Calibration Pulse Oscillator 100 Partial Discharge Detection System Ca, Cc, Ck, Cg Capacitance L ₀ , L ₁ , L ₂ Inductance

Claims (3)

A current detection unit for detecting a partial discharge current flowing in the abnormal voltage protection unit provided at the cable terminal portion of the power cable line; and
A partial discharge detection device for a cable termination unit, comprising: a partial discharge detection unit that detects partial discharge based on the partial discharge current output from the current detection unit.   2. The partial discharge detection device for a cable termination according to claim 1, wherein the current detection unit is an arrester bar, a short-circuit bar, or a current transformer attached to a lead wire connecting the arrester.   The partial discharge detector is detected by the current detector through an amplifier having the same frequency band as a resonance frequency determined by an element including the capacitance of the arrester as the abnormal voltage protection unit and the inductance of the connection member of the arrester. The partial discharge detection device for a cable terminal according to claim 1, wherein the partial discharge current is amplified.

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