JP2628738B2 - Power cable test equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a test apparatus used for measuring withstand voltage characteristics, partial discharge characteristics, tan δ, and the like required for power cable performance evaluation.

(Prior art)

2. Description of the Related Art Hitherto, a withstand voltage test, an internal partial discharge test, and a tan δ measurement have been performed in a development test or a shipping test of a power cable. In particular, for solid insulated cables such as cross-linked polyethylene insulated cables, internal partial discharge tests for inspecting for defects (voids, foreign substances, etc.) inside the insulator and defects (projections, peeling, etc.) at the interface between the insulator and the semiconductive layer. The tan δ measurement, which mainly reflects the properties of the materials used for the insulator and the semiconductive layer, is an important test item. Of course, even for oil immersion insulated (OF) cables and conduit air cables, it is necessary to inspect not only the main insulating parts such as oil and SF ₆ gas, but also the joints, insulating supports and other composite insulating parts for defects. But these tests are important.

Conventionally, as one method of conducting an internal partial discharge test, an inductance called a blocking coil is inserted between the voltage application terminal of the cable and the test transformer, and the signal from the standard capacitor and the pulse from the cable under test are inserted. There is a method of comparing with a sex signal. In this case, the blocking coil is provided to suppress discharge noise generated on the air side of the external connection portion, the test transformer, or the like.
In addition, a discharge (corona) from the air becomes an external noise at the time of tan δ measurement and causes a measurement error. Therefore, a countermeasure using a blocking coil is also effective in this case. On the other hand, the standard capacitor is installed to confirm that no internal partial discharge has occurred in the system before testing the cable.Comparing the signal from the standard capacitor with the signal from the test cable, noise and partial The discharge signal can be identified, and the partial discharge signal from the test cable can be clearly grasped.

The blocking coil and the standard capacitor can be installed as a part of a gas insulation test terminal installed between the voltage application end of the cable and the test transformer.
An example is shown in FIG. The high voltage generated by the power supply voltage regulator 11, the test voltmeter 12, the conductor 13, the air terminal connection 15, the gas terminal connection 16, the blocking coil 18,
The voltage is applied to the test power cable 26 via the high-voltage conductor 20 and the terminal connection part 22 in gas. A cylindrical electrode 30 is coaxially mounted on the outer periphery of the high-voltage conductor 20, and both of them constitute a standard capacitor. The shields 14, 17, 19, 21, and 29 are for reducing local electric field concentration so as not to cause partial discharge at each location. 23 and 25 are protective metals, 24 is an insulating tube, 27 is a gas insulation test container on the voltage application end side, and 28 is a gas insulation test container on the non-voltage application end side. SF ₆ gas in the test container 27, nitrogen gas, the insulating gas such as mixed gas is sealed.

The cylindrical electrode 30 of the standard capacitor is connected to the detection impedance 32 outside the test container 27 through the insulating bush 31. The sheath of the test cable 26 is insulated from the gas insulation test container 27 by the insulating tube 24, and the detection impedance 33
It is connected to the.

In such a configuration, the 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 by an oscilloscope or the like. By the way, standard capacitors are used to compare whether a pulse generated from a cable is a noise or a signal (partial discharge pulse) or to extract a signal to the outside, as described above. It is also possible to use it as a voltage detector using electric capacity. This can be achieved by using a capacitor having a large capacitance as the detection impedance 23 and measuring the voltage generated at both ends of the capacitor. That is, the high voltage is divided by the standard capacitor including the high-voltage conductor 20 and the cylindrical electrode 30 and the capacitor constituting the detection impedance 23, and the voltage is measured.

The standard capacitor has no dielectric loss, so tanδ
It can be used as a standard capacitor for measurement.
In this case, by measuring the phase difference between the currents flowing through the detection impedances 32 and 33, the tan δ of the cable under test is measured.

〔Task〕

When performing an internal partial discharge test or tan δ measurement, the method using a blocking coil or a standard capacitor is certainly effective, as described above. However, nothing happens if the standard capacitor itself is discharging. Because the standard capacitor is directly connected to the test cable, noise due to discharge in the standard capacitor cannot be blocked by the blocking coil and all enters the measurement system. In particular, when the above-described cylindrical electrode is used, it is important that the shape of both ends is formed so as not to cause discharge. For that purpose, both ends need to have a large curvature, and the degree of surface finish needs to be considerably smooth. Therefore, cylindrical electrodes are quite costly.

Even if the shape of both ends of the cylindrical electrode is as described above, an error is likely to occur in the measured value due to the influence of the capacitance at both ends. This is because the capacitance is determined by the positional relationship and shape between the electrode ends and the test container,
It is extremely difficult to finish as designed for capacitance. This effect is particularly large during voltage measurement.

There is a similar problem when measuring tan δ. In other words, when a voltage is applied, a minute current due to the stray capacitance of that part flows in from both ends of the cylindrical electrode, or a minute current due to the potential difference between the electrode and the ground flows in. The error tends to increase due to measurement. Particularly, in the case of a crosslinked polyethylene insulated cable, since the value of tan δ is small, the above error is often not negligible.

[Means for solving the problem and its operation]

The present invention provides a power cable test apparatus provided with a blocking coil for removing electrical noise in a gas insulation test container, on the voltage application side of a test cable, in order to solve the above-described problems. A capacitance type cylindrical electrode is provided coaxially with the conductor on the side of the cable under test or the non-voltage application end of the cable under test from the blocking coil, and this cylindrical electrode is axially connected through insulating slits provided near both ends thereof. Electrically divided into three directions and connected to each electrode part with a lead wire that extends outside the gas insulation test container, so that each electrode part can be grounded and short-circuited outside the gas insulation test container. It is a feature.

In order to minimize the loss due to tan δ, it is desirable that the above-mentioned capacitance type cylindrical electrode is insulated from the internal conductor by gas. The installation position is desirably inside the gas insulation test container between the test cable and the blocking coil. However, the non-voltage application end side of the test cable (if multiple test cables are connected in series, ).

At the time of the partial discharge test, the cylindrical electrode is used as a standard capacitor (also referred to as a coupling capacitor) for comparing and distinguishing a signal from the cable under test with noise. At this time, by dropping both electrode parts to ground and connecting only the central electrode part to the measurement system, noise at both ends flows to the ground system, and only the signal of the central electrode part is measured. Will be. Therefore, it is not necessary to pay much attention to the curvature and the surface finish at both ends.

The same effect can be obtained by using the same method in voltage measurement. Since the center electrode portion is straight, the capacitance can be finished as set and accurate measurement can be performed.

Further, in the case of tan δ measurement, by connecting the electrode portions at both ends to the guard terminal of the tan δ measuring device and the central electrode portion to the measurement terminal, highly accurate measurement becomes possible. The reason for this is that the potential of the guard electrode and the potential of the electrode of the measuring section can be made the same, so that leakage current from both end electrode portions does not flow into the measuring section during measurement. In this measurement, the center electrode part is used as a lossless standard capacitor.

The above measures are quite effective. However, the accuracy of each measurement is often affected by the measurement impedance and external noise entering from the measurement leads. In order to eliminate this effect, it is preferable that each of the current and voltage is detected by an optical sensor, and the detection signal is transmitted by an optical fiber. By using such a signal detection and transmission system in combination with the above-described electrode structure, it is possible to further increase the measurement accuracy and reliability as a whole.

Tanδ can also be measured by detecting the current flowing from the cylindrical electrode to the ground and the current flowing from the test cable to the ground, respectively, and detecting the phase difference. It is good to use together the current detection by the optical transmission and the signal transmission by the optical fiber.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail by measuring FIG.

In FIG. 1, the same parts as those in FIG. 2 are denoted by the same reference numerals. FIG. 1 shows only the main parts of the test apparatus related to the present invention, but other configurations are the same as those in FIG.

In this test apparatus, an electrostatic capacitance type cylindrical electrode 30 is provided coaxially around the high voltage conductor 20 between the blocking coil and the test cable, and the cylindrical electrode 30 is provided with insulating slits provided near both ends thereof. The central electrode portion 30a and the two-end electrode portions 30b and 30c are divided into three parts via 41. Insulation slit 41
Is the electrode part 30a with a bolt 42 made of tetrafluoroethylene resin.
And 30b, and 30a and 30c are connected with a gap therebetween. The center electrode portion 30a is supported on the gas insulation test container 27 by an insulating support 43.

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 bolt 42. In such a case, both end electrode portions 30b and 30c may be supported by the gas insulation test container 27 by the insulating support.

Lead wires 44a to 44c are connected to the respective electrode portions 30a to 30c, and these lead wires 44a to 44c are connected to the housing 45 outside the gas insulation test container 27 through the hermetic insulating bush 31.
Is derived within. The ends of the lead wires 44a to 44c can be connected to the detection impedance 32, dropped to ground, or short-circuited with each other in the housing 45. The housing 45 is made of metal so as to have an electric shielding function.

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

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

〔The invention's effect〕

As described above, according to the present invention, it is possible to efficiently reduce noise generated inside the test apparatus at a relatively low cost by using a three-part cylindrical electrode, and improve measurement accuracy, A series of tests such as an internal partial discharge test, a withstand voltage test, and a tan δ measurement can be easily performed simply by changing the detection impedance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part of a power cable test apparatus according to one embodiment of the present invention, and FIG. 2 is a conceptual diagram showing the entire configuration of a conventional power cable test apparatus. 12: Test transformer, 18: Blocking coil, 20: High voltage conductor, 26: Test power cable, 27/28: Gas insulation test container,
30: capacitance type cylindrical electrode, 30a: central electrode part, 30b / 30c:
Both electrode portions, 32: detection impedance, 41: insulating slit, 44a / 44b / 44c: lead wire, 45: housing, 46: optical fiber, 47: O / E converter, 48: amplifier, 49: display device.

Claims (1)

(57) [Claims] In a power cable test apparatus provided with a blocking coil for removing electrical noise in a gas insulation test vessel on a voltage application side of a test cable, the test cable side or the test cable side of the blocking coil is provided. A capacitance type cylindrical electrode is provided coaxially with the conductor on the non-voltage application end side of the test cable, and this cylindrical electrode is electrically divided into three parts in the axial direction through insulating slits provided near both ends thereof. And a lead wire extending to the outside of the gas insulation test container is connected to each electrode portion, so that each electrode portion can be grounded and short-circuited outside the gas insulation test container. Cable test equipment.