JPH0422225B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the insulation of a high-voltage power cable under a live line, which makes it possible to measure the degree of deterioration of a high-voltage power cable under a live line economically and over a wide area.

Conventional methods for measuring the insulation under live wires of high-voltage power cables have been applied mainly to high-voltage distribution cables within the premises of large customers that receive power at extra high voltages.
Therefore, since there was only one distribution substation and the distribution cables were limited to those drawn out from there, it was sufficient to install a complete set of insulation resistance measuring equipment as fixed equipment at the distribution substation. Ta. However, in ultra-large power consumers such as steel mills, there are multiple power receiving locations, as well as substations and electrical rooms for children and grandchildren, making the power distribution cable system extremely complex. It was recognized that if the problem was solved by using multiple devices, the quantity would increase unnecessarily and the cost would increase, and even then, some cables would not be able to be measured. Furthermore, when it comes to high-voltage power cables for piping under the jurisdiction of electric power companies, not only are there an extremely large number of distribution substations, but they are also often installed after passing through overhead distribution lines. Insulation resistance measuring devices are limited in the range of cables that can be measured, and it is noticeable that the number of cables that cannot be measured increases. Therefore, there have been proposals in the past to carry portable measuring devices around to measure cables distributed in various locations.

FIG. 1 is a diagram illustrating a conventional method of measuring the insulation resistance of a high-voltage power cable under a live line using a portable rotation measuring device. 1 is an ungrounded high-voltage bus, 2 is a small-capacity grounding transformer, 3 is the high-voltage power cable selected as the measurement target, and 4 is a normally closed bus inserted between the neutral point of the grounding transformer and the earth. An electromagnetic contactor having contacts, 5 is an arrester, 6 is a vibration suppression resistor, 7 and 9 are capacitances, 8 is a chiyoke coil, 10 is an output ammeter, 11 is a stabilized DC power supply and is activated by the AC input shown in 12 do. 13 is a control power source for opening and closing the electromagnetic contactor 4; The above is installed in advance as fixed equipment at each distribution substation. Reference numeral 14 denotes a junction box that is pre-installed in the middle of the grounding wire at one end of the high-voltage power cable.
It consists of a capacitor 15, an arrester 16, and a plug seat 17. The terminal of the plug seat 17 has a function of mechanically shorting itself unless the plug 18 is inserted. Reference numeral 19 denotes a portable insulation resistance measuring device which includes an ammeter for measuring insulation resistance and other components, and the terminal of the ammeter is led to the connector 18.

We are now about to start measuring the insulation resistance under live wires of high-voltage power cables that are installed in various locations. First, power is sent from the control power supply 13 to the distribution substation at the source of the target high-voltage bus 1, and the contact of the electromagnetic contactor 4 is opened.Then, the neutral point of the grounding transformer 2 is isolated from the earth in a direct current manner. However, a safety grounding circuit comprising an arrester 5, a vibration suppressing resistor 6, and a capacitance 7 safely maintains a low-impedance AC ground. Here, when the stabilized DC power supply 11 is energized by the AC input 12 and operated, the DC voltage for measurement passes through the ammeter 10 and the choke coil 8, then the grounding transformer 2, and becomes an AC voltage to the high voltage bus 1. It is sent out in a superimposed manner. The measurement DC voltage is controlled by a timer and is automatically repeatedly applied and stopped. Next, the measurer brings the portable insulation resistance measuring device 19 and measures the target high-voltage power cable 3.
and insert the connector 18 into the connector seat 17. Then, the grounding of the high-voltage power cable 3, which was hitherto dropped to the ground by the short-circuited plug seat 17, is now grounded through the ammeter in the insulation resistance measuring device 19. At this time, the AC contact value of the shield is guaranteed by the capacitance 15 and arrester 16 built into the plug box 14. If there is an insulation resistance defect in the high voltage power cable 3, the value can be known from the ammeter built in the portable insulation resistance measuring device 19.

When the measurement is completed, the person measuring
7, and repeat the measurement by carrying the portable insulation resistance measuring device 19 around other power cables. In order to measure the power cable connected to another high voltage bus 1, the power cable must be connected to the distribution substation of the parent of that high voltage bus 1, and the grounding transformer 2 installed there.
First, open the neutral point grounding and start operation of the power supply device. Although the above-mentioned improvements have solved the problem of electric cables falling out of the measurement range, they still have the following drawbacks.

(1) If the number of distribution substations and high-voltage power cables for distribution is extremely large, such as for electric power companies and large-scale customers, it will become too expensive and impractical. In other words, a fixed DC power supply device 11 and a neutral point opening facility for the grounding transformer 2 are installed in advance for each distribution substation, and a fixed connection box 14 is installed in advance for each cable 3 to be measured. It requires that. Since the individual unit costs are high, a huge amount of capital is required to achieve wide-scale application to a large number of power cables under a large number of distribution substations.

(2) Connection box 14 installed for each cable 3 to be measured
It takes a lot of effort to maintain and manage the equipment. In other words, most of the connection boxes 14 will be installed at the bottom of utility poles on public roads, so a sturdy outdoor case and locking equipment are required. Capacitance 15, arrester 1
6. It is necessary to check whether there is any deterioration or not.

An object of the present invention is to measure the insulation resistance of high-voltage power cables distributed over a wide area under live lines without stopping power transmission, and to economically measure the degree of deterioration of the high-voltage power cables. An object of the present invention is to provide a method for measuring lower insulation.

The present invention will be described in detail below with reference to the drawings.

FIGS. 2 and 3 are diagrams illustrating a method for measuring insulation resistance under live wires of a high-voltage power cable according to the present invention.
Reference numeral 20 denotes a junction box provided in advance between the neutral point of the grounding transformer and the earth, and its contents are a junction seat shown in 21. This is because the terminals are normally mechanically short-circuited, so the neutral point of the grounding transformer 2 is equivalent to falling directly to the earth. 23 is a portable power supply device, the output of which is led to the plug 22.
This power supply device 23 consists of a resistor 24 connected in parallel to the output, a DC power supply 25, and a timer-controlled switch 26 connected in series thereto. On the other hand, the ground wire at one end of the high-voltage power cable 3 selected as the measurement target falls directly to the ground, and although there is no pre-installed connection box or the like, the measurer can use the portable insulation resistance measuring device 2 When the cable is brought to the source, a temporary interrupt connection 34 is made. The portable insulation resistance measuring device 27 is constructed by connecting a switch 28, an arrester 29, a capacitance 30, and an ammeter 31 for measuring insulation resistance in parallel.

Next, details and specific procedures of the measuring method according to the present invention will be explained. First, the portable power supply device 23 is brought to the distribution substation of the target high-voltage bus 1, and the plug 22 is inserted into the plug seat 21. Now, the neutral point of the grounding transformer 2 is grounded to the earth using a resistor 2.
Changes to grounding through 4. The resistance value of the resistor 24 is 3KV, 6KV so that it does not adversely affect the ground fault detection function of the grounding transformer 2 while it is inserted.
100 to 200Ω for application to ungrounded high voltage busbars
is the value of In other words, the capacity of the grounding transformer 2 is 3×
The current limiting resistor connected to the open end of the tertiary open triangular connection must be a few percent or less of the value converted to the primary zero-phase circuit, as it has a relatively small capacity of about 200 VA. However, if the resistance value is selected too low, the current capacity of the DC power supply 25 and the switch 26 must be increased, which is disadvantageous, so the resistance value as described above is selected as the optimum value. When the plug 22 is inserted, the timer-controlled switch 26 starts operating and automatically repeats opening and closing, and the DC power supply 25
The DC voltage for measurement is superimposed on the AC voltage and is intermittently sent out to the high voltage bus 1 via the grounding transformer 2. At this time, the resistor 24 becomes the main output load of the DC power supply 25, and the voltage drop that occurs across it becomes the DC voltage value for measurement, assuming that the required value is 50V.
It only consumes 0.5A~0.25A. Therefore, when using a storage battery as the DC power source 25, the required capacity does not need to be very large; for example, about 6AH is sufficient. The power source for driving the timer control switch 26 may be taken from the DC power source 25, or a small-capacity battery power source may be built in for exclusive use. Although the description uses a storage battery as the DC power source 25, it is of course possible to use a dry battery or one converted from an external AC power source. Further, a capacitor can be provided inside the connector box 20 in parallel with the terminal of the connector seat 21, but this is not essential. In this case, since the low resistance 24 is connected in parallel to the capacitance, there is no risk of vibration occurring, and there is no need to insert a resistor in series with the capacitance. Next, even if we consider the case where a high voltage system ground fault occurs while the plug 22 is being inserted, the abnormal voltage generated across the resistor 24 will be at most
Since the voltage is about 100V, an arrester is not necessary.
If a ground fault occurs at the same time as the DC power supply 25 is being turned on, the internal resistance of the DC power supply 25 with a much lower resistance value will be inserted in parallel with the resistor 24, causing an abnormal voltage to occur across the resistor 24. decreases further.

Next, referring to FIG. 3, the measurer brings the portable insulation resistance measuring device 27 to the high-voltage power cable 3 selected as the target, and connects it to the middle of the weak grounding wire of the power cable 3. The provision of the interrupt connection 34 will be explained below. Figure 3 shows how to connect the ends of the two input lead wires to the portable insulation resistance measuring device 27 with an appropriate distance between them and the ground wire.
A state 32 is shown in which points 1 and 2 are selected and connected to them. At this time, the switch 28 is closed. The ground wire was not cut. Figure 3 shows a state 33 in which the ground wire is cut between points a and b. At this time, the switch 28 is also closed. Interrupt connection 34 in Figure 2
This is a state in which the switch 28 is opened after state 33 in FIG. 3 and insulation resistance is being measured. FIG. 3 shows a state 35 in which the switch 28 is closed after the measurement is completed, and a sleeve is inserted into the cut portion of the flexible ground wire between points a and b to make a connection. Figure 3 shows that after this, the lead wires to the insulation resistance measuring device 27 are removed at points a and b, and insulating tape is wrapped to cover all of point a, the connection sleeve, and point b, and then grounded. A state 36 is shown in which the line has been repaired. In this way, the portable insulation resistance measuring device 27 can be connected, removed, and repaired in the middle of the loose grounding wire of the high-voltage power cable 3 during live operation, even if it is not possible even momentarily. This can be done in such a way that the ground does not float in the air. In the interrupt connection 34 to the ground wire shown in FIG. 2, if the high-voltage power cable 3 has poor insulation resistance, the current flowing through it when the DC voltage for measurement is applied via the high-voltage bus 1 will be insulated from the It exits to the ground through the resistance measuring ammeter 31 and returns to the DC power supply 25. Therefore, the ammeter 3 for measuring insulation resistance
The insulation resistance value can be determined by the deviation of 1.
Once the ground wire has been repaired, repeat the measurements using the previous procedure on the other cable.
In order to measure the power cable connected to another high voltage bus 1, the operation of the portable power supply device 23 must be stopped and the connection plug 2
2 from the connector seat 21, bring the portable power supply device 23 to the distribution substation that is the source of another high-voltage bus 1, and start its operation.

The method for measuring insulation under a live wire of the present invention has the following effects.

(1) For electric power companies and very large power consumers, an economical method can be obtained that enables measurement of insulation resistance under live wires for preventive maintenance of a large number of cables with a small investment. In other words, only the simple connection box 20 is required as fixed equipment for each distribution substation, and no fixed equipment is required for each cable 3 to be measured. In addition, if you have one simple portable power supply device 23 and one portable insulation resistance measuring device 27, you can handle any number of distribution substations and any number of cables, so the investment capital is minimal. Yes, the feasibility is very high.

(2) The same performance as conventional methods can be obtained. The basic principle of the measurement circuit is that the current that appears due to the superimposition of the DC measurement voltage on the AC voltage or poor cable insulation is read with an ammeter inserted in the middle of the grounding wire, which is different from the conventional method. Since it does not change at all, the obtained insulation resistance value will not change or the numerical value will be different.

(3) There is no need for maintenance and management of the connection box 20. The plug box 20 is only installed at the distribution substation, and since this is an indoor facility and is accessible only to a limited number of people, there is no need to worry about tampering or intrusion of rain or dew.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a conventional method for measuring the insulation resistance of a high-voltage power cable under a live line, and FIGS. 2 and 3 are diagrams explaining a method of measuring the insulation resistance of a high-voltage power cable under a live line according to the present invention. It is. 1: High voltage busbar, 2: Grounding transformer, 3: Target high voltage power cable, 4: Magnetic contact, 5, 16, 2
9: Arrester, 6: Vibration suppression resistor, 7,9,1
5, 30: Capacitance, 8: Chi York coil, 1
0: Output ammeter, 11: Stabilized DC power supply, 12:
AC input, 13: Control power supply, 14, 20: Junction box, 17, 21: Junction seat, 18, 22: Junction, 1
9: Portable insulation resistance measuring device, 23: Portable power supply device, 25: DC power supply, 27: Portable insulation resistance measuring device, 31: Ammeter for measuring insulation resistance, 34: Interrupt connection.

Claims (1)

[Claims] 1. A grounding system whose terminals are normally self-shorted between the neutral point of a grounding transformer of an ungrounded high-voltage bus to be measured and the ground, with the neutral point dropping directly to the ground. A plug seat is provided, and a plug suitable for the plug seat is inserted into the plug seat from the DC power source in the portable power supply device, and a DC voltage is applied superimposed on the AC voltage to the target high voltage bus, and the target voltage is applied. Connect the two input leads of the portable insulation resistance measuring device at an appropriate interval between the flexible grounding wires of the high-voltage power cable, and connect the flexible grounding wires between the connections. The insulation resistance is measured by cutting, and after the measurement is completed, the input lead wire is removed after connecting the cut point, and a switch is not installed between the input lead wires inside the portable insulation resistance measuring device except during the measurement. This method measures the insulation resistance value of the target power cable using a method that maintains a short circuit by making an interrupt connection each time a measurement is made and using an insulation resistance measuring ammeter in a portable insulation resistance measuring device that is inserted. A method for measuring insulation under live wires of high-voltage power cables. 2. Insertion of a low resistance between the neutral point and the earth with a value that does not affect the earth fault detection function of the earthing transformer when applying DC voltage by the portable power supply device, and both ends of the resistance. 2. A method for measuring insulation under a live line of a high-voltage power cable according to claim 1, which utilizes a voltage drop caused by energization from a DC power source.