JPS6011176A - Insulation measuring method in hot-line state of high- voltage power cable - Google Patents

Abstract

PURPOSE:To measure economically a degree of degradation in the hot-line state by providing a receptacle between the neutral point of an earthing transformer and the ground and applying a DC voltage from a portable power supply device and connecting an insulation resistance measurer to the halfway position of a shielding earth line of a high-voltage power cable by bridge cut off at each time of measurement. CONSTITUTION:A portable power supply device 23 is carried to a distributing substation of the source of a high-voltage bus 1, and its plug 22 is inserted to a receptacle 21. Earthing of the neutral point of an earthing trasformer to the ground is switched to earthing thereof through a resistance 24. The operation of a timer control switch 26 is started to repeat automatically its switching, and a measuring DC voltage is interruptedly superposed onto the AC voltage on the high-voltage bus from a DC power source 25 through the earthing transformer 2. A portable insulation resistance measurer 27 is connected to a halfway position 34 of the shielding earth line of a high-voltage power cable 3 selected as a target by bridge cut off. If an insulation resistance defect exists in the high-voltage power cable 3, an insulation resistance value is detected by deflection of an insulation resistance measuring ammeter 31.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for measuring the insulation of high-voltage electrical cables under live lines, which makes it possible to measure the degree of deterioration of high-voltage electrical cables economically and over a wide area. Regarding.

The conventional method for measuring the insulation under live wires of high-voltage cables has been mainly applied to high-voltage distribution cables within the premises of large customers that receive power at extra high voltages. -Therefore, there is only one distribution substation, and the distribution cables are limited to those drawn out from there, so if a complete set of insulation resistance measuring equipment is installed as fixed equipment at the distribution substation, that is all there is to it. I've had enough. However, in the case of very large power consumers such as steel plants, there are multiple power receiving fields B1, and there are substations, electrical rooms, etc. of children and grandchildren, and the distribution cable system has become extremely complex. It was found that if the resistance measurement device was used in multiple ways, the quantity would increase unnecessarily and the cost would increase, and even then, some couples would not be measured. Furthermore, when it comes to high-voltage electrical cables for piping under the jurisdiction of electric power companies, not only are there an extremely large number of distribution substations, but they are often installed after passing through overhead distribution lines, so installations are only available at distribution substations. With the fixed insulation resistance measuring device, the range of cables that can be measured is limited, 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 source under a live line using a portable rotation measuring device. 1 is an ungrounded high-voltage bus, 2 is a small-capacity grounding transformer, 6 is the high-voltage electrical cable selected as the measurement target, and 4 is a constant-time power supply inserted between the neutral point of the grounding transformer and the earth. 5 is an arrester, 6 is a vibration suppression resistor, 7 and 9 are capacitances, 8 is a choke coil, 10 is an output ammeter, 11 is a stabilized DC power supply, and 12 is an AC Activated by input. 16 is a control power source for opening and closing the electromagnetic contact 4. The above is installed in advance as fixed equipment at each distribution substation. Reference numeral 14 denotes a plug box which is pre-installed in the middle of the ground wire at one end of the shield for the high-voltage electric sol, and is composed 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 plug 18.

We are now about to start measuring the insulation resistance under live wires of high-voltage electrical cables that are installed in various locations. First, power is sent from the control power supply 16 to the distribution substation that is the source of the target high-voltage bus 1, and the contact of the electromagnetic contactor 4 is connected to the contact point υ1]<, then the neutral point of the grounding transformer 2 is connected to the earth in a direct current manner. Although insulated, a safety grounding circuit consisting of 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 human power 12 and operated, the DC voltage for measurement passes through the ammeter 10 and the choke coil 8 to the grounding transformer 2.
The voltage is superimposed on the AC voltage and sent out to the high voltage electricity 111!1 via. 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 to the target high-voltage electrical cable 6 and inserts the plug 18 into the plug seat 17.

Then, the grounding of the high-voltage electric 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 alternating current grounding of the doorway is ensured by the capacitance 15 and arrester 16 built into the connection box 14. If there is a defective insulation resistance in the high-voltage electrical cable B, the value can be determined by the ammeter built into the portable insulation resistance measuring device 19.

When the measurement is completed, the measurer removes the plug 18 from the plug seat 17, carries the portable insulation resistance measuring device 19 around under other power cables, and repeats the measurement.

To measure the power cable connected to another high voltage bus 1,
The system reaches the distribution substation at the source of the high-voltage bus 1, and first opens the neutral point of the grounding transformer 2 installed there and starts operating the power supply device. Due to the improvements mentioned above, it is outside the measurement range.

Although the problems with electric cables have been solved, they still have the following drawbacks:

(1) If the number of power distribution substations or high-voltage cables for power distribution is extremely large, such as in the case of a power company or a super customer, the cost will be too high and the feasibility will be lost. In other words, each distribution substation has a fixed DC electrolyte device 11 and a grounding transformer 2σ.
) It is necessary to install neutral point opening equipment in advance and to install a fixed connection box 14 in advance for each cable 6 to be measured. While the individual unit cost is low, achieving widespread application to a large number of power cables under a large number of distribution substations requires a large amount of capital.

(2) It takes time to maintain and manage the connection box 14 installed for each cable 3 to be measured. 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, and it is necessary to check whether rain or dew has entered the plug seat 17 and whether the built-in capacitance 15 and arrester 16 have deteriorated.

The object of the present invention is to provide a high-voltage electric cable that enables economical measurement of the degree of deterioration by measuring the insulation resistance of high-voltage electric cables distributed over a wide range of tL14 under live lines without stopping power transmission. An object of the present invention is to provide a method for measuring insulation under a cable live wire.

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

FIGS. 2 and 6 are diagrams for explaining the method of measuring insulation resistance under live wires of a high-voltage electric cable according to the present invention.

Reference numeral 20 designates a connection box that is provided in advance between the neutral point of the grounding transformer and the ground, and its contents are a connection 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. 26 is a portable power supply device, the output of which is led to the plug 22.

This power supply device 26 includes 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 high-voltage electrical box selected for measurement
The ground wire at one end of the pull 6 cable falls directly to the ground, and there is no pre-installed connection box, etc., but the measurer brought a portable insulation resistance measuring device 27 and tested the source of the cable. When this happens, a temporary interrupt connection 64 is made. The portable insulation resistance measuring device 27 includes a switch 28, an arrester 29, and a capacitance 30. It is constructed by connecting all the ammeters 61 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 26 is brought to the distribution substation of the target high-voltage m-line 1, and the plug 22 is inserted into the plug seat 211C. This changes the grounding of the neutral point of the grounding transformer 2 to the earth through the resistor 24. The resistance value of the resistor 24 is 3KV, since it does not adversely affect the ground fault detection function of the grounding transformer 2 while it is inserted.
100~2 to apply to 6KV ungrounded high voltage bus
The value is 00Ω. In other words, the capacity of the grounding transformer 2 is 6×2
The current limiting resistor connected to the open end of the tertiary-side 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 0.00 VA. However, if you choose too low, the DC power supply 25 and switch 2
The resistance value as described above is selected as the optimum value since it is disadvantageous that the current capacity of 6 must be increased. When the plug 22 is inserted, the timer-controlled switch 26 starts operating and automatically repeats opening and closing, and the DC voltage for measurement is transferred from the DC power supply 25 to the high voltage U line 1 via the grounding transformer 2.
It is superimposed on AC voltage and sent out intermittently.

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, or 0.5A to 0.25A assuming that the required value is 50V.
There is no doubt that it will be consumed. 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, it may be provided inside the capacitive junction box 20 in parallel with the terminal of the junction 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 is at most about 1 oov, so an arrester is not necessary.

If the ground fault coincides with the time when 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, so the abnormal voltage generated across the resistor 240 will be even higher. descend.

Next, referring to FIG. 6, the measurer brings the portable insulation resistance measuring device 27 to the high-voltage electrical cable 3 selected as the target, and immediately ground the electrical cable 3. The provision of the interrupt connection 64 in the middle of the line will be explained.

Figure 6 (1) shows a state 32 in which the ends of the two input lead wires to the portable insulation resistance measuring device 27 are connected to points α and 6 selected at appropriate intervals in the middle of the ground wire. shows.

At this time, the switch 28 is closed. The ground wire was not cut. FIG. 6 (11) shows a state 63 in which the interference ground wire is cut between point 0 and point b. At this time, switch 28
is closed. The interrupt connection 64 in FIG.
) After state 33, the switch 28 is opened and insulation resistance is being measured. FIG. 3 GID shows a state 65 in which the switch 28 is closed after the measurement is completed, and a sleeve is inserted into the cut portion of the shielding ground wire between the α point and the b point to make the connection. Figure 6 (1v) shows that after removing the wires to the insulation resistance measuring device 27 at points 0 and 6, insulating tape was wrapped to cover the α point, the connection sleeve, and all 6 points. A state 66 is shown in which the ground wire has been repaired. In this way, the portable insulation resistance measuring device 27 can be connected to the middle of the ground wire of the high-voltage power cable 6 during live operation, removed, or repaired even if the high-voltage power cable 6 is in operation. Jiyahei's grounding can be done without floating in the air. In the interrupt connection 64 to the ground wire shown in FIG. 2, if there is poor insulation resistance in the high-voltage electrical cable B, the current flowing through it will be interrupted when the DC voltage for measurement is applied via the high-voltage bus 1. The current is connected to the ground through the insulation resistance measuring ammeter 31 and returns to the DC power supply 25. Therefore, the insulation resistance value can be determined by the fluctuation of the current flow 31 for measuring insulation resistance. Once the ground wire has been repaired, repeat the measurement using the same procedure as described above on the other cable. To measure the power cable connected to another high-voltage bus 1, stop the operation of the portable power supply device 26, remove the connector 22 from the connector seat 21, and connect the power cable to another high-voltage bus 1.
The process starts by bringing the portable power supply device 26 to the distribution substation of the parent's home and starting its operation.

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

(1) In the case of electric power companies and very large electric 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,
All that is required as fixed equipment for each power distribution substation is a simple plug box 20, and no fixed equipment is required for each Kusol 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 easily handle a large number of distribution substations even if there are many cables, so the investment capital is small. , and the feasibility is a dog.

(2) Performance that does not change compared to conventional methods can be obtained. The basic principle of the measurement circuit is completely different from the conventional method, such as superimposing the DC measurement voltage on the AC voltage and reading the current that appears slowly due to poor cable insulation with an ammeter inserted in the middle of the grounding wire. There is no possibility that the obtained insulation resistance value will change or the value will be different.

(3) There is no need for maintenance and management of the connection box 20.

The connection box 20 is only installed at a distribution substation, and this is an indoor facility.1. Since the area is accessible only by authorized personnel, there is no need to worry about mischief or rain or dew intrusion.

[Brief explanation of drawings]

Figure 1 is a diagram illustrating a conventional method for measuring the insulation resistance of a high-voltage cable under a live line, and Figures 2 and 3 are diagrams showing the method of measuring the insulation resistance of a high-voltage cable under a live line according to the present invention. FIG. 1: High voltage busbar 2: Grounding transformer 3: Target high voltage electrical cable 4: Magnetic contact 5.16.
29: Arrester 6: Vibration suppression resistor 7.9, 15.3
0: Capacitance 8: Choke coil 10: Output ammeter 1
1 = Stabilized DC power supply 12: AC input 16: Control power supply 14.20: Junction box 17, 21: Junction seat 18.22:
Junction 19: Portable insulation resistance measuring device 23: Portable power supply device 25: DC power source 27: Portable insulation resistance measuring device 61: Insulation resistance measurement, flow meter 64: Interrupt connection patent applicant Sumitomo Electric Industries, Ltd. (4 people outside)

Claims (1)

[Claims] (1) A junction seat is usually installed between the neutral point of the grounding transformer of the ungrounded high voltage bus of the measurement target and the earth, whose terminals are self-shorted and the neutral point drops directly to the earth. , a direct current voltage superimposed on an alternating current voltage is applied to a target high voltage bus bar from a DC power source in a portable power supply device through a plug that fits the connector base, and a DC voltage is applied superimposed on an AC voltage to the target high voltage bus. Insulation resistance measurement in a portable insulation resistance measuring device that is inserted in the middle of the cable shielding ground wire by making an interrupt connection each time the cable is measured in a way that does not allow the cable shielding ground to become suspended in the air even for a moment. 1. A method for measuring insulation under a live wire of a high-voltage electric cable, the method comprising measuring the insulation resistance value of a target electric power cable using a commercial ammeter. (2. In claim 1, the application of DC voltage by the portable power supply device is performed at a neutral point with a low resistance that does not affect the ground fault detection function of the grounding transformer. 1. A method for measuring the insulation under a live wire of a high-voltage electrical cable, which is characterized by inserting the resistor between the top and the bottom and utilizing a voltage drop caused by energization from a DC power source that occurs across the resistor.