JPH0636018B2 - Leakage current measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a leakage current measuring device for monitoring the condition of insulation deterioration of a three-phase power cable.

[Prior Art] Generally, in a power cable, when a large number of water voids are formed in an insulating layer due to water supply or the like, insulation deterioration called so-called water tree deterioration occurs and a leakage current is generated.
In particular, a sudden increase in leakage current is observed when a penetrating water tree occurs. In addition, even when a chemical tree is generated due to the deterioration of the insulating layer due to chemical factors such as oil and chemicals, the leakage current is detected and can be used as an index indicating the degree of insulation deterioration. Therefore, in order to evaluate the condition of insulation deterioration of power test pieces,
The presence or absence of leakage current and its magnitude are measured.

The conventional leakage current measurement is usually performed by disconnecting the power cable from the power supply and newly connecting the test power supply and the leakage current measuring device in the state of the power failure. A DC power supply is used as the test power supply, and a leakage current characteristic is obtained by applying a DC voltage to the DUT. Therefore, it is necessary to stop the power transmission to the object to be measured and disconnect the object to be measured from the power source each time the leakage current is measured, which requires not only a long time and a large number of personnel for the measurement work but also the measurement. Since the power transmission to the device under test is stopped, the device under test cannot be used or operated. For example, a power cable also has a secondary drawback that power transmission to the destination is stopped. Further, since the power cable normally operates with an AC voltage, it is necessary to accurately grasp the correlation between the leakage current characteristic when a DC voltage is applied and the characteristic with an AC voltage.

[Object of the Invention] It is an object of the present invention to provide a leakage current measuring device capable of constantly monitoring the leakage current state of a three-phase power cable in a short time in a small number of people under a live line condition.

[Summary of the Invention] The gist of the present invention for achieving the above object is to detect a leakage current from an insulating layer of a plurality of sets of three-phase power cables from a three-phase power supply source through a transformer. Power is supplied to the phase power cable, the neutral point of the secondary coil of the transformer is grounded, the shield layer of each three-phase power cable is grounded by a ground wire, and the set and ground wire of each three-phase power cable are detected. It is characterized in that the coil is wound, the dielectric voltage by these detection coils is selectively received by the measurement unit to measure the leakage current, and the control analysis unit controls the operation of the measurement unit and analyzes the measurement data. This is a leakage current measuring device.

Embodiments of the Invention The present invention will be described in detail based on the illustrated embodiments.

FIG. 1 shows an overall configuration diagram of a leakage current measuring device according to the present invention. For example, in a power plant or a large factory, a large number of power cables are laid for power supply, but in the drawing, the main three main cables are provided. Three-phase three-phase power cables Ca, Cb, Cc are branched from the phase power cable S. This device is, for example, to measure the leakage current at a plurality of locations of the power cable attached in this way, each power cable Ca, Cb,
At the branch from the main power cable S of Cc, ZCT
The detectors 1a, 1b, and 1c, each of which includes a detection coil and the like, are attached. Detectors 1a, 1b, 1c
Each output of is connected to the measuring unit 3 via the changeover switch 2. The output of the measurement unit 3 is connected to a control analysis unit 4 such as a microcomputer, and the output of the control analysis unit 4 is connected to a printer 5 and a display 6 which are terminals.
The switching of the changeover switch 2 and the operation of the measuring unit 3 are performed by a command from the control analyzing unit 4.

FIG. 2 is a circuit configuration diagram showing the configurations of the detection unit 1 and the measurement unit 3, and the conductors of the three-phase power cables Wa, Wb, and Wc are respectively connected through the secondary coils of the pole transformers Ta, Tb, and Tc to the middle. Sex point N
One end of each of the primary coils of the pole transformers Ta and Tb18Tc is grounded and the other end is connected to the three-phase power supply source 10 of 50 Hz or 60 Hz. In addition, the shield layers of the three power cables Wa, Wb, Wc are grounded via the ground line G, respectively, and the power cables Wa, Wb, Wc are used as the detection unit 1.
And a detection coil 11 around which the ground wire G is wound. Although the output of the detection coil 11 is directly connected to the measurement unit 3, as shown in FIG.
Since 1 is installed in each of the detection units 1a, 1b, and 1c, it is selectively connected via the changeover switch 2. The measuring unit 3 includes a filter 31 for removing noise,
A leakage current meter 32 and an A / D converter 33 are connected in sequence, the output of the detection coil 11 is connected to the filter 31, and the output of the A / D converter 33 is the control analysis unit 4 shown in FIG. It is connected to the.

In FIG. 2, the neutral point N of the power cables Wa, Wb, Wc is grounded under a live line condition in which power is being supplied from the three-phase power supply source 10 to the three power cables Wa, Wb, Wc. Therefore, the total change in magnetic flux on the detection coil 11 is always zero. For this reason, no induction voltage is generated in the detection coil 11 due to electromagnetic induction, but one of the three power cables Wa, Wb, and Wc, for example, the insulation deterioration as shown by the resistance Rf in the power cable Wa. When the leakage current If occurs, the leakage current If from the pole transformer Ta side, the conductor, the resistance Rf,
It flows through the shield layer of the power cable Wa and the ground wire G in order. At this time, since the leakage current If passes through the detection coil 11 twice from the pole transformer Ta side and once from the opposite direction, an induction voltage due to electromagnetic induction is generated in the detection coil 11.

With respect to the induced voltage generated by the above-described principle, noise is removed by the filter 31 of the measurement unit 3, the resistance value Rf caused by insulation deterioration is measured by the leakage ammeter 32, and A / D
It is converted into a digital signal by the converter 33.

For example, the control analysis unit 4 is programmed to perform automatic measurement only during a specific hour, for example, of one day, and during that hour, the changeover switch 2 is automatically and sequentially switched to operate and the power cable Ca , Cb, Cc, ... Continue to measure the leakage current. The digital output of the measurement value output from the measurement unit 3 is sequentially captured by the control analysis unit 4, and after the measurement is finished, the average value of the data obtained for each power cable Ca, Cb, Cc, ... It is calculated.

FIG. 3 shows the measurement data output by the control analysis unit 4 on the screen of the display 6, and the power cables Ca, Cb, Cc, ...
Each day, the average value of one day is graphed and displayed from January to October. Normally, in a power plant or the like, the detection unit 1 has 20
.About.30 points are required, and these data are displayed by switching the screen of the display 6 and printed out from the printer 5.

In this way, if the detection unit 1 is permanently installed in advance for each of the power cables Ca, Cb, Cc, ... And the measurement is performed by automatically changing the changeover switch 2 by the control analysis unit 4 under a live line condition, it is efficient. It is possible to save labor. Also, each changeover switch 2
If a plurality of detecting portions 1 are installed in each of the above, the magnitude of the leakage current between the detecting portions 1 can be known by the differential output, and it is possible to identify the portion where the insulation deterioration is severe.

[Effects of the Invention] As described above, the leakage current measuring device according to the present invention is
The detection coil is installed in each of the multiple sets of three-phase power cables, and the control analysis unit controls the operation of the measurement unit so that the output is selectively received and the measurement unit performs the measurement. It is possible to perform measurements automatically during normal operation or use. Therefore, not only the labor saving of human power at the time of measurement can be realized, but also it is not necessary to stop the operation, which is extremely efficient.

[Brief description of drawings]

The drawings show one embodiment of the leakage current measuring device according to the present invention. FIG. 1 is an overall configuration diagram, FIG. 2 is a circuit configuration diagram, and FIG. 3 is a display diagram of a display screen. Reference numeral 1 is a detection unit, 11 is a detection coil, 2 is a changeover switch, 3 is a measurement unit, 31 is a filter, 32 is a leakage ammeter,
Reference numeral 33 is an A / D converter, and 4 is a control analysis unit.

Front page continuation (72) Inventor Tomoji Minoh 1008 Shinbori, Kumagaya, Saitama Mitsubishi Cable Industries, Ltd. Kumagaya Manufacturing Co., Ltd. (56) Reference JP-A 1-234012 (JP, A) (JP, U) Actually opened 63-2170 (JP, U) Actually opened 55-9437 (JP, U)

Claims (1)

[Claims] 1. When detecting a leakage current from an insulating layer of a plurality of sets of three-phase power cables, power is supplied from a three-phase power supply source to the three-phase power cables through a transformer, and the secondary of the transformer. The neutral point of the coil is grounded, the shield layer of each three-phase power cable is grounded by the ground wire, the detection coil is wound around each three-phase power cable group and ground wire, and the induced voltage by these detection coils is measured. A leak current measuring device, wherein the unit selectively receives and measures the leak current, and the control analysis unit controls the operation of the measurement unit and analyzes the measurement data.