JPH02203285A - Testing device for power cable - Google Patents

Abstract

PURPOSE:To efficiently reduce a noise generating at the inside of a device by providing a cylindrical electrode of electrostatic capacitance type in a coaxial state with a high voltage conductor and electrically dividing the electrode into three parts in the axial direction through insulation slits arranged near the both ends. CONSTITUTION:The cylindrical electrode 30 of electrostatic capacitance type is provided in a coaxial state on the periphery of the high voltage conductor 20 and the electrode 30 is divided into three parts through the insulation slits 41 arranged near the both ends. The slits 41 are formed so that each pole part 30b, 30c are connected by bolts to the center electrode part 30a leaving spaces. The electrode 30a is supported to a gas insulation test container 27 by an insulated support 43. The electrodes 30a-30c are arranged so that they can be connected to a detection impedance 32, lead to the ground or short-circuited mutually, in a housing 45 through each lead wire 44a-44c. An optical sensor is used for the impedance 23 and the detected signal is transmitted to an O/E converter 47 through an optical fiber 46. The test can be easily performed by only replacing the impedance 32 in accordance with the measuring items.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a test device used to measure withstand voltage characteristics, partial discharge characteristics, jan δ, etc., which are important for performance evaluation of power cables. Prior Art] Conventionally, a withstand voltage test, an internal partial discharge test, and a tan δ determination have been carried out in the development test or shipping test of power cables. In particular, for solid insulated cables such as cross-linked polyethylene insulated cables, internal partial discharge tests are conducted to check for defects inside the insulator (voids, foreign objects, etc.) and defects at the insulator-semiconductor layer interface (protrusions, peeling, etc.). The tan 6 measurement, which mainly reflects the properties of the materials used for insulators and semiconducting layers, is an important test item. Of course, for oil immersion (○F) cables and pipeline aerial cables, we inspect not only the main insulating parts such as oil, SF & gas, but also the composite insulating parts such as connections and insulating supports for defects. But these tests are important.

Traditionally, one of the methods for conducting internal partial discharge tests is
One method involves inserting an inductance called a blocking coil between the voltage application end of the cable and the test transformer, and comparing the signal from the standard capacitor with the pulsed signal from the test cable. In this case, the advancing coil is installed in order to suppress discharge noise generated on the air side of the external wiring section, the test transformer, and the like. Furthermore, since discharge (corona) from the air becomes external noise and causes measurement errors when measuring tan δ, the countermeasure using a pronging coil is also effective in this case. On the other hand, standard capacitors are installed to ensure that no internal partial discharge occurs in the system before testing the cable.
By comparing the signal from the standard capacitor and the signal from the cable under test, it is possible to distinguish between noise and the partial discharge signal, and it becomes possible to clearly understand the partial discharge signal from the cable under test.

This blocking coil and standard capacitor can be installed as part of a gas-insulated test terminal installed between the voltage application end of the cable and the test transformer. An example is shown in Figure 2. The high voltage generated by the power supply voltage regulator 11 and the test transformer B12 is applied to the conductor 13, the air termination connection 15, the gas termination connection 16, the blocking coil 18, the high voltage conductor 20, the gas termination connection 22, etc. The power under test is applied to the cable 26 via the power cable 26 . High voltage conductor 2
A cylindrical electrode 30 is coaxially installed on the outer periphery of 0, and both constitute a standard capacitor. shield 14,
F. 19.21.29 is for relaxing local electric field concentration to prevent partial discharge from occurring at each location. A4. ft No. 23.251. [Safeguard, 24hav!
A-rim cylindrical tube, 27 is a gas insulation test container on the voltage application end side, 2
Day is the gas insulated test container on the non-voltage application end side. The test containers 27 and 28 are filled with insulating gas such as SF&gas, nitrogen gas, and mixed gas.

The cylindrical electrode 30 of the standard capacitor is connected through an insulating bushing 31 to a detection impedance 32 outside the test container 27 . In addition, the sheath of the test cable 26 is the insulated tube 2
4 and is insulated from the gas insulation test container 27 and connected to the detection impedance 33.

In such a configuration, partial discharge signals emitted from the test cable 26 and the standard capacitor are detected by the detection impedances 32 and 33, respectively, amplified and waveform processed by the partial discharge measuring device 34, and observed with an oscilloscope, etc. be done.

By the way, as mentioned earlier, standard capacitors are used to compare whether the pulse generated by the cable is noise or a signal (partial discharge pulse), and to extract the signal to the outside. It is also possible to use it as a voltage detector. To do this, a capacitor with a large capacitance may be used as the detection impedance 23, and the voltage generated across the capacitor may be measured. In other words, a high voltage is divided between a standard capacitor consisting of a high voltage conductor 20 and a cylindrical electrode 30, and a capacitor constituting the detection impedance 23, and the voltage is measured.

In addition, standard capacitors have no dielectric loss, so tanδ
It can also be used as a standard capacitor during measurements.

In this case, by measuring the phase difference of the current flowing through the detection impedance 32.33, the ta of the test cable can be determined.
nδ will be measured.

(Issue) When performing internal part number tests and tand measurements, the method of using bronking coils and standard capacitors as mentioned above is certainly effective.However, what happens if the standard capacitor itself causes discharge? This is because the standard capacitor is directly connected to the cable under test, so the noise caused by the discharge inside the standard capacitor cannot be blocked by the blocking coil, and all of it enters the measurement system. Particularly when using a cylindrical electrode as described above, it is important to shape both ends of the electrode in such a way that no discharge occurs.To do this, both ends must have a large curvature, and The surface finish also needs to be fairly smooth.

Therefore, cylindrical electrodes are quite expensive.

Furthermore, even if the shapes of both ends of the cylindrical electrode are made as described above, errors are likely to occur in the measured values due to the influence of the capacitance at both ends. This is because it is determined by the positional relationship and shape of the capacitance, and it is extremely difficult to finish the capacitance as designed.

This effect is particularly significant when measuring voltage.

A similar problem also occurs when measuring tan δ. In other words, when a voltage is applied, a minute current flows from both ends of the cylindrical electrode due to the stray capacitance of that part, or a minute current due to the potential difference between the electrode and the ground, but tan δ
Since this minute current is also measured during measurement, the error tends to increase. In particular, crosslinked polyethylene insulated cables have a small value of tan δ, so the above-mentioned error is often not negligible.

[Means for solving problems and their effects]

In order to solve the above-mentioned problems, the present invention provides a power cable testing device in which a blocking coil for removing electrical noise is provided on the voltage application side of the test cable in a gas-insulated test container. A capacitive cylindrical electrode is provided coaxially with the conductor on the test cable side or the non-voltage application end side of the test cable from the blocking coil, and this cylindrical electrode is connected to the axis through insulating slits provided near both ends. It is electrically divided into three parts in the direction, and each electrode part is connected to a lead wire extending outside the gas insulated test container, so that each electrode part can be grounded and shorted outside the gas insulated test container. This is a characteristic feature.

The capacitive cylindrical electrode described above is desirably insulated from the internal conductor by gas in order to minimize loss due to tan δ. The preferred installation location is inside the gas-insulated test container between the test cable and the blocking coil, but the non-voltage application end of the test cable (if multiple test cables are connected in series, the connection point should be (including).

During partial discharge tests, this cylindrical rod is used as a standard capacitor (also called a coupling capacitor) to compare and distinguish the signal from the cable under test from noise. In this case, by grounding the electrodes at both ends and connecting only the center electrode to the measurement system, the noise at both ends will flow to the ground system, and only the signal at the center electrode will be measured. It turns out. Therefore, there is no need to pay much attention to the curvature or surface finish of both ends.

Similar effects can be obtained by using the same method when measuring voltage. Since the center electrode part is straight, the capacitance can be finished as designed, allowing for highly accurate measurements.

Furthermore, when measuring tanδ, the electrodes at both ends should be
Highly accurate measurement is possible by connecting the central electrode portion to the measurement terminal and the guard terminal of the δ measuring device. The reason is that the potential of the guard electrode and the measuring part electrode are the same,
This is because leakage current from the electrode portions at both ends can be prevented from flowing into the measuring section during measurement. In this measurement, the central electrode section is used as a lossless standard capacitor.

The above measures are quite effective. However, the accuracy of each measurement is often affected by external noise that enters through the measurement impedance and measurement leads. In order to reduce this influence, it is preferable to perform each current and voltage detection using an optical sensor and transmit the detection signal using an optical fiber. By using such a signal detection and transmission method together with the electrode structure described above, total measurement accuracy and
It becomes possible to further improve credibility.

In addition, tan δ is the it flow flowing from the cylindrical electrode to the ground,
Detect the current flowing from the test cable to the ground,
It can also be measured by detecting the phase difference, but in this case as well, it is preferable to use the electrode structure described above, current detection using an optical sensor, and signal transmission using an optical fiber.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG.

In FIG. 1, the same parts as in FIG. 2 are given the same reference numerals. In FIG. 1, only the main parts of the test apparatus related to the present invention are shown, but the other configuration is the same as that in FIG. 2.

In this test device, a capacitive cylindrical electrode 30 is coaxially provided on the outer periphery of a high voltage conductor 20 between the blocking coil and the test cable, and this cylindrical electrode 30 has insulating slits provided near both ends thereof. Central electrode portion 30 via 41
It is divided into three parts: a and electrode parts 30b and 30c at both ends.

The insulating slit 41 is formed by connecting the electrode portions 30a and 30b130a and 30c with a gap between them using a bolt 42 made of tetrafluoroethylene resin. The central electrode portion 30a is supported in the gas insulated test vessel 27 by V@edge supports 43.

Note that from the viewpoint of surge resistance, it is preferable to use a structure in which each electrode portion is insulated with gas without using the port 42. In that case, the electrode portions 30b and 30c at both ends may also be supported by the gas insulation test container 27 using insulating supports.

Each electrode portion 30a to 30c has a lead wire 44a.
~44c are connected, and these leads 44a~44C
is led out of the gas-insulated test container 27 into the housing 45 through an airtight insulating bushing 31.

The ends of the lead wires 44a to 44c are connected to the housing 45.
Inside, they can be connected to the detection impedance 32, grounded, or shorted together.

The housing 45 is made of metal to provide an electrical shielding function.

In this embodiment, an optical sensor is used as the detection impedance 32, and its detection signal is transmitted through an optical fiber 46.
It is now transmitted by The detection signal transmitted through the optical fiber 46 is converted into an electrical signal by an O/E converter 47, amplified by an amplifier 48, and displayed on a display device 49. If the optical sensor is not used, an electric wire is used instead of the optical fiber 46, and the O/E converter 47 is omitted.

In the case of zero partial discharge measurement, where the detection impedance 32 is replaced by the measurement item, a parallel circuit of a resistor and a capacitor can be used. In the case of electric field measurement,
Capacitors for voltage division and crystal-based optical electric field sensors can be used. In addition, in the case of tan δ measurement, there is a method of simply connecting the central lead wire 44a to a bridge-type measuring device, but in actual measurement, a photocurrent sensor that detects the magnetic field generated by the current using the Faraday effect is used. Good results were obtained. In this case, the lead wires 40b and 4 at both ends
0c is either grounded or connected to the guard terminal of the measuring instrument.

〔Effect of the invention〕

As explained above, according to the present invention, by using a cylindrical electrode divided into three parts, the noise generated inside the test device can be efficiently reduced at a relatively low cost, and measurement accuracy is improved. Internal partial discharge test, withstand voltage test,
A series of tests such as tan δ measurement can be easily performed by simply changing the detection impedance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts of a power cable testing device according to an embodiment of the present invention, and FIG. 2 is a conceptual diagram showing the overall configuration of a conventional power cable testing device. 12: Test transformer, 18 Niblocking coil, 20
: High voltage conductor, 26: Test type capeple, 27/28: Gas insulation test container, 30: Capacitance type cylindrical electrode, 30a:
Center electrode part, 30b/30c: Both side electrode part, 32:
@ Output impedance, 41 = insulation slit, 44a −
44b -+t4c: Lead wire, 45: Housing,
46: Optical fiber, 47: O/E converter, 48: Amplifier, 49: Display device. Procedure Neho Seisho (self-motivated) March 7, 1989

Claims (1)

[Claims] 1. In a power cable testing device in which a blocking coil for removing electrical noise is installed on the voltage application side of the test cable in a gas-insulated test container, A capacitive cylindrical electrode is provided coaxially with the conductor at the non-voltage application end, and this cylindrical electrode is electrically divided into three parts in the axial direction via insulating slits provided near both ends. , and each electrode portion is connected to a lead wire extending outside the gas insulation test container, so that each electrode portion can be grounded and short-circuited outside the gas insulation test container. .