JPH0575980B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Application The present invention relates to a method for locating faulty points of cable insulation under live wires for locating faulty points of high-voltage power cables during power transmission.

(b) Background technology and its problems In recent years, cable insulation monitoring equipment under live wires has been put into practical use, and it is possible to monitor the faulty resistance of main body insulation, the faulty resistance of corrosion protection layer insulation, and whether the cable is connected during transmission of high-voltage power cables. It is now possible to know the insulation resistance value of the entire high voltage system. However, although it is possible to know the fact that an insulation defect has occurred in a cable and the extent of the defect during power transmission, it is difficult to know where the defective point is located in the entire length of the cable. Inconveniently, information crucial to determining handling procedures must be obtained by disconnecting the cable, removing its terminal from the busbar, and then measuring it using the bridge method or other conventional methods. Therefore, the present applicant has previously proposed a method for locating the location of a defective point without power outage as a method for detecting a defective point in cable insulation under a live wire. This method will be explained below with reference to FIGS. 1 and 2.

In FIG. 1, 1 is a conductor of a cable with poor insulation, and has a main body insulation defect point at a position x ₁ away from measurement terminal A, and a corrosion protection layer insulation defect point at a position further x ₂ away from x ₁ . x ₃ are anti-corrosion layer insulation defective points and other terminals
At the distance from A′, x ₁ +x ₂ +x ₃ =l is the total length of the poorly insulated cable. Reference numeral 2 denotes a shield for the poorly insulated cable, and between this shield 2 and the poorly insulated cable conductor 1 there is a main body insulation resistor 3 having a value of R ₁ . Between the insulation layer 2 and the ground, there is a corrosion protection layer insulation failure resistor 4 having a resistance value R ₃ .
At the other terminal A' of the poorly insulated cable, the end of shield 2 is connected to each end of shield 5 and 6 of the sound return cable to form a loop, and
is for measuring current supply, and Shiyahei 6 is for other terminals.
It is used to guide the low potential of A' to measurement terminal A. An AC grounding capacitor 7 is connected between each shield 2, 5, 6 and the ground. moreover,
A measurement power source 8 and a switch 9 are connected in series to the open end on the measurement side of the loop formed by the insulation failure cable shield 2 and the sound return cable shield 5. The three terminals A are connected to a live high voltage bus 10, a grounding transformer 11 is connected to this high voltage bus, and a grounding transformer 11 is connected to the high voltage bus.
An AC grounding capacitor 12 is connected between the primary side neutral point N and the earth. Note that the resistor 13 connected between the neutral point N and the ground represents the insulation resistance to the ground of the entire high voltage bus 10, and its value is
It is R _B. Problem with the poor insulation cable 2
Select the measurement end side potential L ₀ or the other terminal side potential L ₁₀₀ derived from the healthy cable shield 6 (or the measurement end side potential L ₂₀₀ of the sound cable shield 5, but not shown). A changeover switch 14 is provided for this purpose, and the terminal potential on the selected side is forcibly dropped to ground. A microcurrent detection means 15 such as a microcurrent or microvoltmeter is connected between the primary side neutral point N of the grounding transformer 11 and the earth.

FIG. 2 shows the equivalent circuit of FIG. 1 described above, and in FIG. 2, R ₁ , R ₂ , and R ₃ are the distances x ₁ , x ₂ , and x _{3 ,} respectively.
It shows the resistance value of the cable with poor insulation corresponding to the resistance value. The reason why the resistances of the shields 5 and 6 of the healthy return cable are not shown in the equivalent circuit of Fig. 2 is that these resistance values are based on the value of the measured current flowing from the measuring power supply 8 to the loop circuit and the effective utilization. This is because although it affects the voltage value, it is not directly related to the operating principle of the circuit. Therefore, the resistance values of the shields 5 and 6 do not need to be the same as that of the shield 2, and any suitable return cable may be used.

Next, the procedure for locating the accident point using the measurement circuit described above will be explained. The primary side neutral point N of the grounding transformer 11, which is normally linearly grounded, is brought into an AC grounded state through the capacitor 12 as described above, and is brought into an open state in terms of DC. From this state, press the selector switch 14.
Set it to the L ₀ side, close the switch 9, and turn off the measurement power source 8.
A measurement current is passed through the loop circuit consisting of the mustard wires 2 and 5, and the deflection d ₀ of the minute current detection means 15 is obtained. This d ₀ is proportional to the voltage drop caused by the measurement current across R ₁ , ie, x ₁ . At this time, the main body insulation failure resistance value R _I acts as a multiplier resistance for the minute current detection means 15, and if the value is large, it acts in a direction to reduce the deflection of the minute current detection means 15. Furthermore, in this case, since the high voltage system overall insulation resistance value R _B is connected in parallel to the minute current detection means 15, if it is small, it works in the direction of reducing the swing of the minute current detection means 15. Furthermore, the anti-corrosion layer insulation failure resistance value R _S is connected in parallel to R ₁ + R ₂ , so if it is small, it will work in the direction of making R ₁ smaller, resulting in a measurement error, but normally It is assumed that the corrosion protection layer insulation failure resistance value R _S is much higher than the resistance value of the insulation layer, and the error is ignored.

After obtaining the deflection d ₀ , the selector switch 14 is switched to the L ₁₀₀ side while the measurement current is flowing through the loop circuit, and the deflection d ₁₀₀ of the minute current detection means is obtained. this
d ₁₀₀ is the voltage drop caused by the measured current across R ₂ + R ₃ ,
That is, it is proportional to x ₂ + x ₃ . In this case as well, the main body insulation resistance value R _I acts as a multiplier resistance for the minute current detection means 15, and the high voltage system overall insulation resistance value R _B
are connected in parallel to the minute current detection means 15. In addition, the anti-corrosion layer insulation failure resistance R _S is connected in parallel with R ₃ , so if it is small, R ₂ + R ₃
Although this case also causes the problem of measurement error because it works in the direction of reducing , the error is ignored as in the above case.

At this point, the measurement is completed, and the distance ratio X ₁ =x ₁ /l from the measurement end to the insulation failure point of the main body is determined as follows.

X ₁ = d ₀ /d ₀ −d ₁₀₀ or ignoring polarity, X ₁ = |d ₀ |/|d ₀ |+|d ₁₀₀ |.

The above-mentioned method for detecting insulation defects in cables under live wires avoids being influenced by the corrosion protection layer insulation defect resistance R _S , which is often much lower than the main insulation defect resistance R _I. This is a practical invention that provides a method for easily locating defective points in the main body insulation using a displacement method. however,
Problems (i), (ii), and (iii) exist as shown below.

(i) The minute current detection means 15 is directly connected between the primary side neutral point N of the grounding transformer 11 and the earth. However, experience has shown that the effects of poor insulation in the entire high-voltage system and local batteries often appear concentrated in this area, resulting in a DC potential that exhibits temporal instability. Therefore, if the vibration of the minute current detection means 15 does not come to a stable standstill, it becomes impossible to carry out the orientation work.

(ii) Although orientation is carried out on the premise that the corrosion protection layer insulation failure resistance value R _S is much higher than the corrosion resistance value, in some cases this condition may not be maintained. This results in large orientation errors.

(iii) To locate the corrosion protection layer insulation failure point, connect the minute current detection means 15 between the changeover switch 14 and the ground, and perform measurement using the deflection method again in the same manner as described above (at this time, the grounding Either the primary neutral point N of the transformer 11 can be grounded directly to the earth, or it can remain grounded through the capacitor 12), the deflection is proportional to R ₁ + R ₂ d′ ₀ is proportional to R ₃ Obtaining the deflection d′ ₁₀₀ , the _{distance ratio from the} measuring _end to the defective point _of the anticorrosion layer insulation _is : We can obtain d′ ₀ |+|d′ ₁₀₀ |. However, in this orientation, the main body insulation failure resistance value R _I is the corrosion protection layer insulation failure resistance value.
The assumption is that it is much higher than R _S ,
If this condition cannot be maintained, large orientation errors will occur.

(C) Purpose This invention has been made based on the above circumstances, and its purpose is to locate the positions of main body insulation defects and corrosion protection layer insulation defects of a high-voltage power cable during power transmission by using a deviation method. It is an object of the present invention to provide a method for locating a cable insulation defect point under a live wire, which can be easily and stably measured with few errors.

(d) Embodiments Examples of the present invention will be described below with reference to FIGS. 3 to 8. There are three variations of this invention, of which the first method will be explained with reference to FIGS. 3 and 4, and the second method will be explained with reference to FIGS. 5 and 6.

Furthermore, as a prerequisite for the orientation of the present invention, it is essential to know three values using a known method. In other words, the main body insulation failure resistance value R _I of the insulation failure cable measured under live wires, and the insulation failure resistance value of the anticorrosive layer.
This is the insulation resistance value R _B of the entire high voltage system to which R _S and the poorly insulated cable are connected. Of these, the high-voltage system overall insulation resistance value R _B is precisely the result of calculating the parallel effect exerted on R _B by the main body insulation resistance value R _I of the poorly insulated cable itself.

First, a first embodiment (first orientation method) will be described based on FIGS. 3 and 4. Note that the same reference numerals are given to the same parts as in the case of FIG. 1, and the explanation thereof will be omitted. The difference from the case in FIG. 1 is that one end of the minute current detection means 15 connected to the changeover switch 14 is not grounded, and the minute current detection means
The other end of 5 is connected to a changeover switch 16.
The changeover switch 16 selectively connects either the primary side neutral point N of the grounding transformer 11 or the earth E by switching.

When performing orientation work, the primary side neutral point N of the grounding transformer 11, which is normally directly grounded, is grounded through the capacitor 12. In this state, the selector switch 16 is switched to the primary side neutral point N side, and the selector switch 14 is switched to the _L0 side. Next, the switch 9 is closed and a measurement current is caused to flow from the measurement power supply 8 to the loop circuit consisting of the shield 2 of the poorly insulated cable and the shield 5 of the sound return cable, and the deflection of the minute current detection means 15 is caused. , we get g ₀ . The equivalent circuit at this time is shown in FIG. Here, g ₀ is the resistance of insulation 2 from the measuring end to the location where the apparent insulation failure resistance value R' _I exists, R ₁ + R _2a , as shown in Figure 4.
It is proportional to the voltage drop caused by the measurement current generated above, or in other words, it is proportional to the distance x _a of the shield 2 from the measurement end to the position of _R'I . This means that
This shows that the resistance value R ₂ existing in the interval x ₂ between the main body insulation failure point and the corrosion protection layer insulation failure point is divided into R _2a and R _2b . Here, the resistance R _2a and the resistance
The size of R _2b can be obtained by converting a triangular circuit whose sides are R ₂ , R ₁ and R _B -R _S into a star circuit using the Δ-Y electric circuit conversion theorem. That is, the original triangular circuit shown in FIG. 9 has been converted into the star-shaped circuit shown in FIG. a in Figure 9,
The inside of the three points b and c is electrically equivalent to (in the case of Fig. 4, Fig. 10,
). Each constant of the star-shaped circuit is obtained as follows using each constant of the triangular circuit.

R _2a = R ₂ R ₁ / R ₁ + R _B + R _S + R ₂ , R _2b = R ₂ (R _B + R _S ) / R ₁ + R _B + R _S + R ₂ , R′ ₁ = R ₁ (R _B + R _S ) /R ₁ +R _B +R _S +R ₂ , where we focus on the denominator (R ₁ +R _B +R _S +R ₂ ), we find that the real values of R ₁ , R _B , and R _S range from megohms to kiloohms. On the other hand, R ₂ is several ohms or less. Therefore, since the denominators of each constant can be set as ≈R ₁ , R _B , and R _S , each constant can be approximately expressed as follows.

That is, R _2a ≒R ₂ R ₁ /R ₁ +R _B +R _S (1) R _2b ≒R ₂ (R _B +R _S ) /R ₁ +R _B +R _S (2) R′ ₁ ≒R ₁ (R _B +R _S )/R ₁ +R _B +R _S (3) Next, while the loop circuit is still energized, switch 14 is switched to L ₁₀₀ side, and minute current detection means 1
Get the swing g ₁₀₀ of 5. This g ₁₀₀ is proportional to the voltage drop due to the measurement current generated on the resistor R _2b +R ₃ of the shield 2, and is proportional to the distance x _b of the shield 2. And the magnitude of R _2b is as shown in equation (2). In both cases of runout g ₀ and g ₁₀₀ , the apparent insulation failure resistance value R' ₁ located at the contact point between R _2a and R _2b acts as a multiplier resistance for the minute current detection means 15. And the magnitude of R′ ₁ is as shown in equation (3).

Next, when the selector switch 14 is switched to the L ₀ side with the selector switch 16 switched to the earth E side, the deflection g' ₀ of the minute current detection means 15 (Shiyahei 2
(proportional to the distance x′ _a ) is obtained. Next, the deflection g' ₁₀₀ (proportional to the distance x' _b of the shield 2) of the minute current detection means 15 when the changeover switch 14 is switched to the L ₁₀₀ side is obtained. The equivalent circuit in this state is the fourth
Illustrated by the figure. At this time, the apparent insulation failure resistance value R _'s , which acts as a multiplier resistance for the minute current detection means 15, is located at the dividing point where _R2 is divided into _R'2a and _R'2b . here,
The magnitudes of R′ _2a , R′ _2b , and R′ _s are each expressed as follows.

R′ _2a ≒R ₂ (R _I +R _B ) / R _I +R _B +R _S (4) R′ _2b ≒R ₂ R _S /R _I +R _B +R _S (5) R′ _s ≒R _S (R _I +R _B ) / R _I + R _B + R _S (6) The orientation work is now completed, and the distance ratio from the measuring end to the main body insulation failure point is calculated by performing the calculation process as shown below.
Find the distance ratio between X ₁ and the corrosion protection layer insulation defect point X ₂ . First, check the apparent insulation failure resistance from the measurement end.
Find the distance ratio X _a to the point of existence of R′ _I.

X _a = x ₁ + x _2a l = |g ₀ | / | g ₀ | + | g ₁₀₀ | (7) Next, the distance ratio X′ _a from the measurement end to the point where the apparent insulation failure resistance R′ _s exists seek.

X′ _a =x ₁ +x′ _2a /l=｜g′ ₀ |/｜g′ ₀ |+｜g′ _{10
0 ｜ ( 8} ) Subtract _{equation (} 7 ₎ from equation ( ₈ ) _{and get}
=R ₂ (R _B +R _I )−R ₂ R ₁ /R _I +R _B +R _S /R ₁ +R ₂ +R ₃ =R ₂ R _B
/R _I +R _B +R _S /R ₁ +R ₂ +R ₃ =R _B /R _I +R _B +R _S ×R ₂ /R ₁ +R ₂ +R ₃ ∴R ₂ /R ₁ +R ₂ +R ₃ =x ₂ /l= X′ _a −X _a /R _B /R _I +R _B +
R _S = R _I + R _B + R _S /R _B (X′ _a −X _a ) (9) In this way, the distance ratio x ₂ /l, which indicates the distance between the main body insulation defect point and the corrosion protection layer insulation defect point, is determined. It will be done.
_The required distance ratios X ₁ and _{X 2} are _: X _{1 = x 1} /l = _{X a -}
−R ₂ R ₁ /R _I +R _B +R _S /R ₁ +R ₂ +R ₃ =X _a −R _I /R _I +R _B +R _S ×R ₂ /R ₁ +R ₂ +R ₃ =X _a −R _I /
R _B (X′ _a −X _a )(10) X ₂ =X ₁ +x ₂ /l=X _a −R _I /R _B (X′ _a −X _a )+R _I +R _B +R _S
/R _B (X′ _a −X _a )=X _a +R _B +R _S /R _B (X′ _a −X _a ) (11) As mentioned above, the three known R _I , R _S , and R _B The positions of the main body insulation failure point and the anticorrosive layer insulation failure point can be separated and accurately determined from the resistance value and the two distance ratios of X _a and X _′ a obtained through the location work.

In the first location method described above, the other end of the minute current detection means 15, that is, the changeover switch 16, is connected to the contact point between the insulation resistance value R _I of the main body and the insulation resistance value R _B of the entire high voltage system, and between this R _B and the corrosion protection It can be seen that the difference in X _a and X' _a is caused by switching to the contact point with the layer insulation defect resistance value R _S and measuring it. in this way,
If we search for other _orientation methods that _{produce the} difference between _{X a and} by. In the first orientation method, R _B is always inserted between R _I and R _S , and there are two cases: when R _B is assigned to the edge on the R _S side, and when it is assigned to the edge on the R _I side. The difference caused the difference in X _a and X′ _a .

In the second orientation method explained below, there are two different ways: when R _B is assigned to the edge on the R _S side, and when it is assigned to the edge on the R _I side with R _B short-circuited (i.e., R _B = 0). This causes a difference between X _a and X′ _a . Similarly _, as _{the third} orientation method, the _difference in X _{a and} It is also possible to cause The details of this third orientation method can be inferred from the description of the first and second orientation methods, so the details will be omitted.
Regardless of the orientation method, it will affect the circuit configuration state.
This method takes advantage of the fact that the location of the apparent insulation failure point changes due to the influence of R _B.

5 and 6 show a second embodiment (second orientation method), and parts that overlap with those in FIG. 1 are denoted by the same reference numerals, and explanations thereof will be omitted. In this case, the other end of the minute current detection means 15 (not grounded) connected to the changeover switch 14 is always connected to the primary neutral point N of the grounding transformer 11 (the third orientation method Then this is always connected to the earth). A short-circuit switch 17 is connected between the primary side neutral point N and the earth, and short-circuits or opens the value R _B of the resistor 13 connected in parallel with the capacitor 12 (also in the third location method). similar).

When performing orientation work, the short circuit switch 17 is opened and the changeover switch 14 is switched to the _L0 side. Next, the switch 9 is closed, and the measurement current is passed from the measurement power supply 8 to the loop circuit consisting of the insulation failure cable shield 2 and the sound return cable shield 5.
The deflection h ₀ of the minute current detection means 15 is obtained. The equivalent circuit in this state is shown in FIG. 6, which is equivalent to the equivalent circuit in FIG. Next, while the loop circuit is energized, the selector switch 14 is switched to the _L100 side to obtain the deflection _h100 of the minute current detection means 15. Here, x _c , x _2c , x _d , x _2d , R _2c , and R _2d in Fig. 6 correspond to x _a , x _2a , x _b , x _2b , R _2a , and R _2b in Fig. 4, respectively. ing. Similarly to equations (1), (2), and (3) above, R _2c ≒R ₂ R _I /R _I +R _B +R _S (12) R _2d ≒R ₂ (R _B +R _S )/R _I +R _B +R _S (13) We obtain R′ _I ≒R _I (R _B +R _S )/R _I +R _B +R _S (14).

Next, the short circuit switch 17 is closed and the selector switch 14 is switched to the L ₀ side to obtain the swing h' ₀ (proportional to x' _c ) of the minute current detection means 15. Next, switch 1
Micro current detection means 1 when switching 4 to L ₁₀₀ side
5's deflection h' ₁₀₀ (proportional to x' _d ) is obtained. An equivalent circuit in this state is shown in FIG. The apparent insulation failure resistance value R' _S that acts as a multiplier resistance for the minute current detection means 15 is located at the dividing point where R ₂ is divided into R' _2c and R' _2d , and R' _2c , R' _2d , R _′s
The magnitude of is the same as when R _B =0 in equations (4), (5), and (6), and is expressed as follows.

R′ _2c ≒R ₂ R _I ／R _I ＋R _S (15) R′ _2d ≒R ₂ R _S ／R _I ＋R _S (16) R′ _s ≒R _I R _S ／R _I ＋R _S (17) After the orientation work is completed, the following calculation process is performed to determine the distance ratio X ₁ from the measurement end to the main body insulation failure point and the distance ratio X ₂ from the corrosion protection layer insulation failure point.
When calculated in the same manner as equations (7), (8), (9), (10), and (11) above, the following results are obtained.

X _c = x ₁ + x _2c / l = | h ₀ | / | h ₀ | + | h ₁₀₀ | (18) The distance ratio X′ _c from the measurement end to the point where the apparent insulation defect resistance value R′ _s exists is , X′ _c =x ₁ +x′ _2c /l=｜h′ ₀ |/｜h′ ₀ |+｜h′ _{100
｜ ( 19 ) _ _ _ _ _}
R ₂ R ₁ /R _I +R _S −R ₂ R ₁ /R _I +R _B +R _S /R ₁ +R ₂ +R ₃ =R ₂ R ₁ (
R _I + R _B + R _S − R _I − R _S ) / ( R _I + R _S ) ( R _I + R _B + R _S ) / R ₁
+R ₂ +R ₃ = R _I R _B / (R _I + R _S ) (R _I + R _B + R _S ) × R ₂ / R ₁ + R ₂ + R ₃
(20) ∴R ₂ /R ₁ +R ₂ +R ₃ =x ₂ /l=X′ _c −X _c /R _B R _I /(R _I +R _S
)(R _I +R _B +R _S )=R _I +R _B +R _S /R _B (X′ _c −X _c )×R _I +
_{R S / R I ( 21 ) _ _ _ _
1} +R ₂ +R ₃ =X _c −R _I +R _S /R _B (X′ _c −X _c )(22) X ₂ =X ₁ +x ₂ /l=X _c −R _I +R _S /R _B (X′ _c −X _c ) +(R _I +R _S )(R _I +R _B +R _S )/R _B R _I (X′ _c −X _c ) =X _c +(R _B +R _S )(R _I +R _S )/ R _B R _I (X′ _c −X _c )(2
3) As mentioned above, the second orientation method also uses the known
Based on the three resistance values R _I , R _S , and R _B and _{the two distance ratios X c and} You can find it accurately.

Although omitted in the above-mentioned orientation method for the sake of simplification, in reality, the influence of local batteries present in various parts of the circuit is large. Therefore, these influences must be eliminated during actual orientation work.
Figure 7 shows the local batteries that exist in each of R _B , R _I , and R _S
This shows that E _B , E _I , and E _S are equivalently represented by one local battery E' _I in series with the apparent poor insulation resistance, and FIGS. 7 and 7 are equivalent.
_Rv in FIG. 7 indicates the internal resistance of the minute current detection means 15.

In order to find out the approximate number of the equivalent local battery E′ _I , calculations will be made based on the following assumptions. That is, R _I =100M
Ω, R _B = 10MΩ, R _S = 1MΩ, E _I = 9V, E _B = 1V,
Assume E _S =0.2V. From equation (14), R' _I = 100 (10 + 1) / 100 + 10 + 1 = 9.910 (MΩ) Also, E' _I = [9/100 + 1 + 0.2/10 + 1] / [1/100 + 1
/10+1] = 1.9730 (V).

The value of this equivalent local battery _E'I is a value that cannot be ignored compared to the voltage drop across the shield that occurs when the measurement current is passed through the loop circuit.

In order to eliminate the influence of the local battery, the current based on the local battery flowing through the minute current detection means 15 is reversed from a ground current canceling device inserted in series or parallel to the minute current detection means 15 before the measurement current is applied. There is a known method for making the current zero by flowing phase currents, but here we will explain another method. Taking the circuits of FIGS. 3 and 4 as examples, under each circuit condition, before applying the measurement current from the measurement power source 8, the fluctuation that appears in the minute current detection means 15 due to the influence of the local battery is first determined. Let g _c be.
At this time, the switching position of the changeover switch 14 may be either the L ₀ side or the L ₁₀₀ side, and the same value can be obtained on either side. After this, if g ₀ and g ₁₀₀ are obtained according to the first orientation method described above, the distance ratio
is determined by the following equation.

X=g ₀ −g _c /g ₀ −g ₁₀₀ =R ₁ +R _2a /R ₁ +R _2a +R _2b +R ₃ (
24) (Proof) If α is the sensitivity constant of the minute current detection means 15, the deflection before the measurement current is applied is g _c = αE′ _I R _v /R′ _I +R _v , and the deviation on the L ₀ side after the measurement current I is applied. is g ₀ = α [E′ _I −I (R _I + R _2a )] R _v /R′ _I + R _vThe deflection on the L ₁₀₀ side after applying the measurement current I is g ₁₀₀ = α [E′ _I + I (R _2b + R ₃ )] R _v /R′ _I + R _v .

∴g ₀ −g _c /g ₀ −g ₁₀₀ =R ₁ +R _2a /R ₁ +R _2a +R _2b +R ₃ (End of proof) As mentioned above, the measurement of the deflection g _c before applying the measurement current is carried out by the minute current detection means 15 This must be done every time the connection changes (excluding switching between L ₀ and L ₁₀₀ ), but this eliminates the influence of local batteries, regardless of their size, and enables accurate positioning.

(E) Orientation Simulation Example of Embodiment In order to demonstrate that the above-described orientation method is effective, orientation simulation will be performed using the measurement circuit shown in FIG. In the case of FIG. 8, unlike the above explanation, the positional relationship of R _I and R _S from the measurement end is reversed.

(Example 1): R _I = 100MΩ, R _B = 1MΩ, R _S = 0.01M
Ω, E _I = 9V, E _B = 1V, E _S = 0.2V, R _v = 0.1M
Ω, I=1A, Method: First method, selector switch 16 is in N position, shorting switch 17 is open, R _2a = 5 x 1.01/100 + 1 + 0.01 = 0.050 (Ω) R _2b = 5 x 100/100 + 1 + 0 .01=4.950(Ω) R′ _I =100(1+0.01)/100+1+0.01=0.9999(M
Ω) E′ _I = [9/100+1+0.2/1+0.01]/[1/100+
1/1 + 0.01] = 1.278 (V) Assuming that the deviation of the minute current detection means is read under the performance of 4 effective digits and 0.1 mV resolution, it will be as follows.

g _c = 1.278 × 0.1 / 0.9999 + 0.1 = 0.1162 (V) g ₀ = [1.278 - 1 × (2 + 0.050)] × 0.1 / 0.9999 + 0.1 = -0.0702 (V) g ₁₀₀ = [1.278 + 1 × (4.950+3)〕×0.1/0.9999+0
_.1 = 0.8390 (V) _Apparent insulation failure point
7 is in the open state, R' _2a = 5 × 0.01/100 + 1 + 0.01 = 0.0005 (Ω) R' _2b = 5 × 100 + 1/100 + 1 + 0.01 = 4.9995 (Ω) R' _s = 0.01 (100 + 1) / 100 + 1 + 0.01 =0.009999(M
Ω) E′ _s = [9-1/100+1+0.2/0.01]/[
1/100+1+1/0.01〕=0.2008(V) g′ _c =0.2008×0.1/0.009999+0.1=0.1825
(V) g′ ₀ = [0.2008−1×(2+0.0005]×0.1
/0.009999+0.1=-1.636(V) g′ ₁₀₀ = [0.2008+1×(4.9995+3)]×
0.1/0.009999 _{+ 0.1} =7.455 ₍ V) 0.2050) = 0.705 (true value 0.700) The _distance ratio X ₂ to the corrosion protection layer insulation failure point is
) = 0.200 (true value 0.200) (Example 2): R _I = 50MΩ, R _B = 10MΩ, R _S = 1MΩ,
E _I =0V, E _B =0.5V, E _S =0.1V, R _V =0.1MΩ,
I=1A and use the first orientation method. Calculating in the same way as above, X ₁ = 0.698 (true value
0.700) and X ₂ =0.200 (true value 0.200).

(Example 3): R _I = 50MΩ, R _B = 10MΩ, R _S = 1MΩ,
E _I =0V, E _B =0.5V, E _S =0.1V, R _V =0.1MΩ,
Let I=1A and use the second orientation method. Omitting intermediate calculations, X ₁ = 0.698 (true value
0.700), X ₂ = 0.200 (true value 0.200).

(c) Effects As explained above, according to the present invention, there is a small amount of electricity between the neutral point on the primary side of the DC-open grounding transformer and the earth, which exhibits the most unstable local battery behavior in high-voltage live-line systems. Since direct insertion of the current detection means is avoided, the fluctuation will not become unstable and measurement will not be possible. In addition, in the conventional method, the circuit conditions that increase the orientation error, i.e., when the corrosion protection layer insulation failure resistance value is as low as the resistance value, or the main body insulation failure resistance value is equivalent to the corrosion protection layer insulation failure resistance value. Even in such cases, it is possible to separate the main body insulation defective point and the anticorrosion layer insulation defective point and accurately locate them under the live wire.
Therefore, the reliability of cable maintenance work under live lines can be significantly improved.

[Brief explanation of drawings]

Figure 1 is a conventional location circuit configuration diagram, and Figure 2 is a diagram of the 1st location circuit.
3 is a configuration diagram of a location circuit showing the first embodiment of the present invention, FIG. 4 is an equivalent circuit diagram when locating in the location circuit of FIG. 3, and FIG. 5 is an equivalent circuit diagram of the location circuit shown in FIG. A locating circuit configuration diagram showing a second embodiment of the present invention, FIG. 6, is an equivalent circuit diagram when locating in the locating circuit of FIG. 5, FIG.
is an equivalent circuit diagram when considering the influence of local batteries when locating, FIG. 8 is a circuit diagram used to show a numerical example using the locating method of this invention, and FIG. 9 is shown in FIG. 4. An explanatory diagram showing a triangular circuit and a star circuit equivalent to the circuit, Figure 10, is the fourth
FIG. 2 is an explanatory diagram showing a triangular circuit and a star-shaped circuit equivalent to the circuit shown in the figure. 1... Cable conductor with poor insulation, 2, 5, 6... Resistance with poor insulation, 3... Resistance with poor insulation on the main body, 4... Resistance with poor insulation in the anti-corrosion layer, 7, 12... Capacitor for AC grounding, 8... Power supply for measurement, 9... Switching/closing 10... High voltage bus bar, 11... Grounding transformer, 13... Resistor, 14... Selector switch,
15...Minute current detection means, 16...Switching switch,
17...Short switch.

Claims (1)

[Claims] 1. Separately measured main body insulation failure resistance value of the high voltage power cable under live wires, corrosion protection layer insulation failure resistance value, and this high voltage power cable of the entire high voltage system to which the high voltage power cable is connected. Knowing the three resistance values of the removed insulation resistance values, the main body insulation failure point and the anticorrosion layer insulation failure point of the high voltage power cable are biased by energizing a loop circuit consisting of the cable sheath and the sound return wire. This is a method of locating from the terminal using the position method, in which one end of the minute current detection means is connected to the primary neutral point of a high-voltage grounding transformer (A.1) or to the earth (A. The first set of 2) and the primary side neutral point itself are open from the ground in a direct current manner (B.1) or are connected to the ground (B.2).
Considering the second set of (A.1) and (B.1)
and (A.1) and (B.2), or one of the above combinations of (A.2) and (B.1) and (A.2) and (B.2). The other end of the minute current detection means is connected to the weak end of the poorly insulated cable at the open end of the loop circuit and the sound return end of the above (A.1), (A.2), ( B.1), (B.2)
The two positions of apparent insulation failure points are determined by the deflection of the minute current detection means by switching each time of each measurement, and the body insulation failure is determined by calculation from the two apparent insulation failure point positions and the three known resistance values. A method for locating defective cable insulation points under live wires, characterized by determining points and corrosion protection layer insulation defective points. 2 Separately measured main body insulation resistance value of the high-voltage power cable under live wires, anti-corrosion layer insulation failure resistance value, and insulation resistance value of the entire high-voltage system to which the high-voltage power cable is connected excluding this high-voltage power cable. 3
Knowing the two resistance values, locate the defective point in the main body insulation of the high-voltage power cable and the defective point in the insulation of the anti-corrosion layer from the terminal using the deflection method by energizing a loop circuit consisting of the power cable's sheath and sound return wire. A first method in which one end of the minute current detection means is connected to the primary side neutral point of a high-voltage grounding transformer (A.1) or to the earth (A.2). and a second set when the primary side neutral point itself is DC-free from the ground (B.1) or connected to the ground (B.2), and this first set and the second set are considered. Second
A combination of the above (A.1) and (B.1) and (A.2) and (B.1) from among the sets, or the above (A.1)
and (B.1) and (A.1) and (B.2), or the combinations of (A.2) and (B.1) and (A.2) and (B.2) above. The other end of the minute current detection means is connected to the weak end of the poorly insulated cable at the open end of the loop circuit and the sound return end of the above (A.1), ( A.2), (B.1), (B.2)
After each measurement, the two apparent insulation failure points are determined by the deflection of the minute current detection means, and the main body is calculated from the two apparent insulation failure points and the three known resistance values. This method performs a measurement method to determine insulation failure points and corrosion protection layer insulation failure points, and furthermore, before energizing the loop circuit, the vibration caused in the minute current detection means by the local battery of the loop circuit is detected in the minute current detection means. In the case where the current is made zero by flowing a current of the opposite phase from an earth current canceling device inserted in series or parallel, or after the deflection value is measured, the measurement is performed using the above-mentioned measurement method, and the deflection value is measured. 2. A method for locating a cable insulation defect point under a live wire, comprising the step of performing a correction calculation to eliminate the influence of the deflection.