JPS5866068A - Cable insulation monitoring method under live wires - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cable insulation monitoring method for measuring and monitoring the insulation resistance of a power cable under a live line.

FIG. 1 is a diagram illustrating a conventional method for measuring and monitoring cable insulation resistance under live wire conditions. BACKGROUND ART A method and apparatus are already known that are installed in a power receiving substation, switch power cables from which electricity is distributed to various directions one by one, and measure the insulation resistance of each individual cable under live wires.

However, the cables to be measured are not all cables that are grouped together in a place that is easy to measure, and even if they are connected to the same bus, they must be connected to the power substation or power station via cables or overhead lines. There are cables that are installed after the cable is installed, that is, cables that connect to the tail of the cable, cables that connect to the tail of the overhead line, and cables that are branched at various points along the way of the overhead line. Conventionally, the method shown in FIG. 1 has been used to measure and monitor the insulation resistance of such cables under live wire conditions. In Figure 1, 1 is a main wire installed at the receiving substation, 2 is one of the power cables connected to the main wire 1 and sent out, followed by child and grandchild cables to be measured. Therefore, it is called a family cable. 3 is a cable insulation measuring device installed at the receiving substation, and its contents include the function of sending measurement voltage to the high voltage system through the grounding transformer, and the insulation of the main cable 2 and other individual cables sent out from the receiving substation. It has the function of measuring the current that returns to the measurement power source through the resistance defective part. In addition, in Fig. 1, the main cable 2 cable is shown to be directly connected to the cable insulation measuring device B, but of course there are many cables other than the main cable 2 at the power receiving substation. Needless to say, a cable switching device is required between the cable insulation measuring device 6 and the cable insulation measuring device 6. 4 is a grounding transformer connected to the main bus 1, and the neutral point of its negative side star-shaped connection is grounded through the cable insulation measuring device 3; however, when measuring cable insulation resistance, the cable insulation measuring device B Since the measurement voltage is sent between the neutral point and the earth from the measurement power supply prepared inside, it is superimposed on the AC working voltage to the entire high voltage system via the winding of the grounding transformer 4. A measurement voltage is applied.

Reference numeral 5 denotes a child busbar to which power is supplied by the parent cable 2 and installed at a location different from the power receiving substation. Usually, this will be a busbar within a child or grandchild substation. The parent bus 1!1 and the child bus 5 are not necessarily connected only by the parent cable 2, but by an overhead wire connected in series with the parent cable 2, or directly by an overhead wire without going through the parent cable 2. In some cases, the parent/child bus line 5 itself may be an overhead line.

Here, the child cables 6, 6' to be measured are connected to the single child bus 5. 7, 7'... is child cable 6
．． 6ζ.

Jack box installed in Noshiyahei grounding circuit, 8
is a portable insulation resistance measuring device, and by inserting the plug of its test cord 9 into the jack box 7.7', the insulation resistance measuring voltage is applied to the faulty insulation resistance of the cable under test, and the voltage is applied to the faulty insulation resistance of the cable under test. Since it measures the current flowing through the insulation, it directly indicates the insulation resistance value using Ohm's law. The current returns to the power source for measurement in the cable insulation measuring device installed at the receiving substation through the ground.

Now, a specific method for measuring the insulation resistance of the secondary capacitors 6, 61, etc. will be explained. Portable, remote protection 11
The measuring person brings the measuring device 8 to the terminal of the child cable B,
Insert the plug of the test cord 9 into the jack box 7. As a result, the shielding of the secondary cable, which until now has been directly grounded through short circuits and grooves in the jack box 7, will now be grounded through a high-sensitivity ammeter in the portable insulation resistance measuring device 8. Of course, as a safety device, an arrester and a capacitor held in the box 7 or the portable insulation resistance measuring device 8 are inserted in parallel with the high-sensitivity ammeter. By sending the measured voltage from the cable insulation measuring device 3 to the main bus 1 via the grounding transformer 4, the measured voltage can be sent to the personnel located next to the cable insulation measuring device B, or at a predetermined time. At this time, the cable insulation measuring device 6 measures the insulation resistance of the cable directly connected to the split busbar 1 of the parent cable 2.
However, it is not a problem (it is only necessary that the measurement voltage is applied to the entire high-voltage system. The measurement voltage sent to the main bus 1 naturally reaches the child bus 5, and the insulation resistance of the child cable 6 increases. The leakage current returns to the power source for measurement via the ground via the highly sensitive ammeter in the portable insulation resistance measuring device 8, which has been prepared.Since the highly sensitive ammeter is graduated based on the insulation resistance value, The insulation resistance value of the cable 6 can be directly read.When the measurement of the sub cable 6 is completed, the application of the measurement voltage is stopped, the plug of the test cord 9 is unplugged from the jack box 7, and then the jack of the sub cable 6' is unplugged. box 7'
The insulation resistance of the child cable 6' is measured by inserting it into the child cable 6' and applying the measurement voltage again. At this time, the portable insulation resistance measuring device 8 may not be moved, and the plug of the test cord 9 may be simply moved from the jack box 7 to the jack box 7'. Once a series of child cables have been measured at this location, the system moves to another location where another child bus or grandchild bus is present, and measures the insulation resistance of the child and grandchild cables that connect to them.

This conventional method of measuring and monitoring cable insulation resistance under live wire conditions has the following drawbacks. Since the portable insulation resistance measuring instrument 8 does not have a function to send out the insulation resistance measuring voltage, the measuring voltage cannot be applied at will by the measurer. Although the application of measurement voltage must be initiated indirectly at a remote location using some communication means, close communication means must be established between all measurement locations and the cable insulation measuring device at the receiving substation. It is almost impossible to obtain (and in some places it may become impossible to implement.If the measurement voltage is automatically turned on and off according to a set time limit, it is almost impossible to Therefore, it is impossible to expect quick measurement work.Furthermore, since the measurement voltage is not applied at hand, even if the measured value is good, it is difficult to know if it is the true value. Or is it because the measurement voltage is not being applied due to some kind of error?
If the person taking the measurement is filled with doubts, they will not have confidence in the measurement results.

An object of the present invention is to provide a cable insulation monitoring method suitable for measuring and monitoring the insulation resistance of a large number of power cables scattered in various locations and connected to the same high-voltage system under live lines. be.

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

FIG. 2 is a diagram showing an embodiment of the cable insulation monitoring method under live wires for measuring and monitoring the insulation resistance of a power cable under live wires according to the present invention. 1 is a main cable installed at the power receiving substation, 2 is one of the power cables connected to the main cable 1 and sent out, and the child and grandchild cables to be measured follow behind it, so it is called the main cable. to be called. 3 is a cable insulation measuring device installed at the power receiving substation, and its contents are as follows. The neutral point of the star-shaped wire on the primary side of the grounding transformer 4 is normally dropped directly to the ground, and when voltage for measurement is applied, it is opened.
1, and a capacitor 32 inserted between the neutral point and the ground in parallel with the switch 61 in order to continue grounding the neutral point with low impedance in terms of alternating current when the switch 31 is opened.
, the resonance suppression resistor 33 connected in series with this capacitance 32, the insulation resistance measurement power supply 35, the output switch 34 of this power supply 65, and the cable to be measured at ℃ and ground. and a high-sensitivity ammeter 36 for direct indication of cable insulation resistance inserted between the cable insulation resistance and the cable insulation resistance. In Figures 1 and 2, the main cable 2 cable is shown to be directly connected to the high-sensitivity ammeter 36, but of course there are many other cables in addition to the main cable 2 at the receiving substation. Needless to say, a cable switching device is required between them and the high-sensitivity ammeter 66. In addition to the above, there are arresters, filters, etc. for safety and f-waves in the cable insulation measuring device 3, but these are omitted in FIG. 4 is a grounding transformer connected to the main wire 1. The neutral point of the star-shaped connection on the next side is normally dropped directly to the ground by the switch 61, but when measuring the insulation resistance of the main cable 2 and other cables existing in the receiving substation, the switch 31 is It is opened and replaced with grounding by a series circuit of the capacitance 32 and the resonance suppressing resistor 5B. Then, when the switch 34 is closed and the measuring voltage is sent out from the measuring power supply 35', the measuring voltage is applied to the parent @ line 1 through the winding of the grounding transformer 40 in a manner superimposed on the AC working voltage.

At this time, for example, the high-sensitivity ammeter 36 connected to the main cable 2 indicates a current value that is inversely proportional to the insulation resistance of the main cable 2, so if you scale the high-sensitivity ammeter 36 with the insulation resistance in advance, you can insure the insulation. You can read the resistance value directly. However, in the present invention, it is not intended to measure the insulation resistance of the cable connected to the main rib i11, so for the purpose of the present invention, the cable insulation measuring device 3 is simply a neutral Direct grounding at the point (it is sufficient to prepare a low impedance grounding circuit using capacitance in place of the switching mechanism, and a voltage application mechanism for insulation resistance measurement or an insulation resistance measurement mechanism, that is, a switch in Figure 2). 64, the measurement power source 55 and the high-sensitivity ammeter 56 are not essential. 5 is a child-mother bond that is supplied with power by the parent cable 2 and installed at a location different from the power receiving substation.

Usually, this will be the busbar within a child or grandchild substation.

The main wire 1 and the child bus 5 are not necessarily connected only by the parent cable 2, but may also be connected by an overhead wire connected in series with the parent cable 2 or directly without going through the parent cable 2. In some cases, the parent/child bus line 5 itself is an overhead line.

Here, the child cables 6, 6, . . . to be measured are connected to the child bus 5. 7, 71 is child cable 6.6/
... Jack box 8 installed in the Noshiyahei grounding circuit, 8 is a portable insulation resistance measuring device, and by inserting the plug of the test cord 9 into the jack box 7.71, it interrupts the Noshiyahei grounding circuit. An insulation resistance measuring circuit is formed using the following steps. The internal function of the portable insulation resistance measuring instrument 8 is to measure the current flowing through the defective insulation resistance part of the cable under test using the measurement voltage superimposed on the bus bar, and measure the insulation resistance according to Ohm's law. The value is displayed directly. In other words, the cable insulation measuring device installed in the power receiving substation is equipped with a highly sensitive ammeter 36, and the current returns to the power source for insulation resistance measurement through the ground. This is the location and method of applying the power. Reference numeral 10 denotes a reactor having a three-phase star-shaped connection and connected to the child bus 5 in advance. If a grounding transformer is originally installed at this location, it can be used in place of the reactor of the present invention.

Its neutral point is connected to earth through the reactor ground box shown at 16. The contents of the reactor ground box 13 are not directly grounded (grounded through capacitance, and a safety device such as an arrester is installed in parallel with the capacitance). It is the impedance connected between the ground and the impedance is desirable to be high, but by using a three-phase star reactor, even if the neutral point and the ground are directly connected, the current will be the same as the current passing through each phase reactor. Since the total sum is zero, the principle of non-grounded systems (Zuzu Kotobana) will not adversely affect the operation of the grounding transformer. 11 is a portable power supply for measuring insulation resistance. Plug cord 12 into reactor ground box 13
By inserting the capacitance into the reactor 10, a circuit is constructed that applies a measurement voltage between the neutral point of the reactor 10 and the ground, that is, across both poles of the capacitance built into the reactor grounding box 13. 0
3.The voltage for measurement is actually applied to the insulation resistance measurement power supply 11.
This is due to the switch that the company has.

Now, a specific method for measuring the insulation resistance of the child cable 6.6/etc. will be explained. First, the direct grounding of the primary star-connected neutral point of the grounding transformer 40 connected to the main frame wire 1 is released. This is achieved by simply opening the switch 61. Do not close the switch 34 and apply the measuring voltage to the main wire 1 at this location. Furthermore, if there are grounding transformers installed in the same high-voltage system in addition to the equipment wires, all direct grounding of their neutral points must also be opened. The measurer brings the portable insulation resistance measuring device 8 and the portable insulation resistance measuring power supply 11 to the terminal of the secondary cable O, and connects the plug of the test cord 9 to the jack box 7 and the plug of the measurement voltage application cord 12. are respectively inserted into the reactor grounding box 16. As a result, the cable end of the secondary cable 6, which was previously directly grounded through the short circuit mechanism in the jack box 7, will now be grounded through the high-sensitivity ammeter in the portable insulation resistance measuring device 8. Of course, as a safety device, an arrester and a capacitor held in the jack box 7 or the portable insulation resistance measuring device 8 are inserted in parallel with the high-sensitivity ammeter. The measuring person operates the portable insulation resistance measurement power source 11, and the measuring voltage is sent to the child bus 5 at one end through the ground and at the other end through the neutral point and winding of the three-phase star reactor 1°. The leakage current through the insulation resistance of the cable 6 passes through the highly sensitive ammeter in the portable insulation resistance measuring device 8, which has been completely prepared, and returns to the power source for measurement via the ground. Since the high-sensitivity ammeter is graduated based on the insulation resistance value,
The insulation resistance value can be directly read.

When the measurement of the secondary cable 6 is completed, the application of the voltage for measurement is stopped, the plug of the test cord 9 is unplugged from the jack box 7 and transferred to the jack box 7', and the high-sensitivity current inside the portable insulation resistance measuring instrument 8 is measured. After waiting for the meter to be ready for measurement, the voltage for measurement is applied again to measure the insulation resistance of the sub cable 6'. At this time, the portable insulation resistance measuring device 8 may not be moved, and the plug of the measuring cord r9 may be simply moved from the jack box 7 to the jack box 7'. In the explanation so far, the portable insulation resistance measuring power source 11 and the portable insulation resistance measuring device 8 have been treated as separate units, but they may of course be integrated if the weight 11 volume allows. However, it is expected that some flexibility may be lost due to the mutual relationship between the installation position of the reactor grounding box 13 and the installation position of the sub cable jack boxes 7, 7'... It is necessary to take measures such as making the insulation resistance longer.Alternatively, if a power source is easily available at this location, a pre-fixed power source for insulation resistance measurement can be used instead of a portable type. Once the measurement of a series of child cables is completed, the system moves to a location where another child bus or grand bus is present, and a three-phase star reactor 10 and a reactor grounding box 13 are installed in advance at those locations. The insulation resistance of the nearby child and grandchild cables is measured on the spot at any time by applying the voltage for insulation resistance measurement.When all measurements are completed, the primary side neutral point of the grounding transformer 4 is The open state is directly returned to the grounded state by closing the switch 31, and the entire work is completed.

The effects of the present invention include the following. First, since the person measuring the insulation resistance can directly apply the voltage for measuring insulation resistance at any time required at the measurement location, a) there is no need for a means of communication between the measurement location and the receiving substation; A person can be stationed at the receiving substation to manually turn on and off the voltage application for measurement, or an automatic mechanism can be installed to turn on and off the application of the measurement voltage.
There is no need to turn it off (c).There is no waiting time, so you can perform measurement tasks quickly. In other words, it is easy to implement.

Next, since the measurer can confirm the application of the measurement voltage himself, even if a good insulation resistance value is obtained (the high-sensitivity ammeter does not swing at all), the measurement voltage can be applied at a remote location. The measurer can provide measurement results with confidence, since there is no chance of him becoming suspicious that the measurement voltage is not being applied, which is the case when the measurement voltage is not being applied.

The field of application of the invention is a live cable insulation monitoring device, in particular a portable live cable insulation monitoring device.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a conventional method for measuring and monitoring cable insulation resistance under live wires, and FIG. 2 is a diagram showing an embodiment of the method for monitoring cable insulation under live wires according to the present invention. 1: Main wire 2: Main cable 3: Cable insulation measuring device 4: Grounding transformer 5: Child bus bar 6
．． 6': Child cable 7.7'... Bow jack box 8: Portable insulation resistance measuring device 9: Test cord 10: Three-phase star reactor 11:
Measurement power supply 12: Measurement voltage application tool 113:
Reactor ground box 31, 34: Switch filter 2: Capacitance
36: Resonance suppression resistor 35: Measurement power supply 3
6: High-sensitivity ammeter (two other people) Pole J diagram

Claims (1)

[Claims] In the cable insulation monitoring method, the insulation resistance of a large number of power cables scattered in various places and connected to the same system is measured under live wire conditions by visiting each cable installation location. Open the direct grounding of the neutral point of the primary star-shaped connection to create a grounding circuit using capacitance, and apply the voltage for insulation resistance measurement between the bus bar and the ground through a three-phase star-shaped reactor connected in advance to the skeleton wire. Cable insulation under live wires, characterized in that a portable insulation resistance measuring device is connected between the shield and the ground of the power cable existing in the vicinity to measure the insulation resistance of each cable and monitor the insulation of the cable. Monitoring method.