CN1029033C - Method and device for detecting insulation state - Google Patents

Abstract

A method and device for determining whether the current flowing through the measured object is superimposed with an insulation degradation signal. One method is to determine the transmission line with insulation degradation by detecting the traveling wave caused by corona discharge or partial discharge due to insulation degradation at the location, and the other is to determine the location where the traveling wave occurs by comparing the traveling wave phase at the reference point on the bus with the traveling wave phases on multiple transmission lines branched from the bus. The device includes a first coil composed of primary and secondary coils with the same number of turns and winding direction wound on an iron core with a roughly proportional magnetic flux potential and magnetic flux density, a second coil composed of primary and secondary coils wound on a homogeneous iron core, and an impedance circuit.

Description

The invention relates to a method and device for detecting insulation state, which checks the deterioration of the insulation performance of electrical equipment and cables by detecting corona discharge and partial discharge generated when the insulation performance of electrical equipment and cables deteriorates.

Usually, the buried power cables or the power equipment connected to them often have local poor insulation due to various reasons.

The reasons for this poor insulation are: mechanical external force, chemical changes of insulating materials, and deterioration of so-called water branches. Eighty percent of major accidents are caused by this insulation deterioration, so several methods for checking insulation have been proposed in the past.

One of the methods is to check the power transmission system regularly in a power outage state. For example, firstly, check the DC voltage applied to the circuit. One is to measure partial discharge, and the other is to detect residual voltage, discharge current and residual charge. The phenomenon of dielectric relaxation, the third is to measure the insulation performance through potential decay and leakage current, and so on.

On the other hand, using the method of checking the AC voltage applied to the circuit, one is to measure the partial discharge, and the other is to measure the dielectric relaxation phenomenon related to the dielectric loss tangent, and so on.

In addition, there is a measurement method different from the above, which is a method of using a portable measuring instrument to check when the transmission line is charged.

However, the problem with the above-mentioned original detection method is that when the power transmission system is regularly cut off for inspection, it is time-consuming because each line must be measured in sequence. In addition, the places that can be measured once a power cut is also limited, Even if the insulation state is already gradually deteriorating, the tendency of this deterioration cannot be known and therefore preventive measures cannot be taken.

On the other hand, when using a portable measuring instrument to conduct inspections while the transmission line is live, of course preparations are required, and measurement personnel are required, and it is especially difficult to ensure safety, so skilled skills are required for measurement.

In view of the above-mentioned circumstances, the object of the present invention is to provide a detection method and device capable of constantly monitoring the insulation state of electric equipment or power cables when the line is charged. This method or device can determine the current flowing in the measurement object. Whether there is a degradation signal due to insulation degradation superimposed in it. The device provided by the present invention contains fundamental waves and higher harmonics of the charging current and leakage current of the insulator in the current obtained from the measurement object, indicating that the insulator is degraded. In the case of high-frequency corona discharge current, partial discharge current, and sudden pulse current, etc., whether the insulation is degraded can be detected by distinguishing the signal current indicating deterioration.

The device includes: two primary coils (11), (12) and secondary coils (13) wound on an iron core whose magnetomotive force is proportional to the magnetic flux density, with the same number of turns and the same winding direction The first coil (1), and the second coil (2) composed of the primary coil (21) and the secondary coil (22) wound on the core whose magnetomotive force is proportional to the magnetic flux density, and the impedance circuit(3);

The end point (11-b) of the primary coil (11) in the first coil (1) and the end point (12-b) of the primary coil (12) are respectively the same as the primary coil (21) of the second coil (2). The terminals (21-a), (21-b) are connected, the end terminal (11-b) of the primary coil (11) in the first coil (1) and the initial terminal (12-a) of the primary coil (12) ) is also connected to the impedance circuit (3), when the initial terminal (11-a) of the primary coil (11) of the first coil (1) and the initial terminal (12-a) of the primary coil (12) are the same as the electrical After the shell of the equipment or the shielding of the power cable is grounded, it can be connected from the two terminals (13-a), (13-b) of the secondary coil (13) of the first coil (1) or from the second coil ( 2) The two terminals (22-a) and (22-b) of the secondary coil (22) obtain signals indicating insulation degradation of the above-mentioned electrical equipment or power cables, thereby detecting the state of insulation.

Furthermore, the method provided by the present invention is that in a power transmission system with more than one system of power transmission lines, when the insulation performance of the power transmission line decreases, by detecting the traveling wave caused by the corona discharge or partial discharge generated at this part, To determine the condition of the transmission line with reduced insulation performance.

In addition, another device for detecting the state of insulation is provided, which includes: in a power transmission system with more than one power transmission line, it can detect corona discharge or partial discharge generated by the part when the insulation performance of the power transmission line is reduced A sensor S of the induced traveling wave, and a measuring section 53 for measuring its length with a signal from the sensor S as an input. The above-mentioned sensor S is a detection device for the insulation state. It has a linear BH characteristic in which the magnetomotive force and the magnetic flux density are approximately proportional, and the magnetic permeability is approximately constant from the low frequency region to the high frequency region. The first coil M1 and the second coil M2 whose ends are short-circuited.

The present invention is illustrated below in conjunction with accompanying drawing.

Fig. 1 shows the schematic structural diagram of the first device of the present invention;

Figure 2 shows an embodiment of the device of the present invention;

Figure 3 shows the relationship curves of main circuit current i ₁ , detection signal voltage eE caused by low frequency current iE, and detection signal voltage eP caused by high frequency current iP with time;

Shown in Fig. 4 is an application example of the present invention, and it adopts the device shown in Fig. 2, constitutes the regular monitoring device of the insulation degradation situation of detecting high voltage cable;

Figure 5-1 shows the application of DC high voltage test or AC withstand voltage test;

Figure 5-2 shows the same situation applied to Figure 5-1, but with the device implemented according to the invention placed on the high pressure side.

6 to 14 are embodiments of the second device of the present invention. Figure 6 is the overall block diagram, Figure 7 is the circuit diagram of the sensor part, Figure 8 (A), (B) is the front view of the sensor, Figure 9 is the BH characteristic curve of the core for the sensor, Figure 10 is the frequency characteristic curve, Figure 11 is a graph showing detection results of traveling waves, FIG. 12 is a block diagram of a signal processing circuit, and FIGS. 13 and 14 are graphs showing measurement results.

First, the insulation degradation detection device for electrical equipment and cables implemented in accordance with the present invention will be described with reference to FIGS. 1 to 5-2. It has a schematic structure as shown in Figure 1.

1 and 2 are coils respectively, and contain iron cores 1A and 2A. These iron cores have high magnetic permeability, and the magnetic permeability is almost constant from the low frequency region to the high frequency region. The remanence and coercive force are very small, and they have a Linear B-H magnetic characteristic curve.

3 is an impedance circuit composed of capacitors, resistors, reactance coils, semiconductor components, etc. alone or in combination.

4 is a main circuit through which a current to be detected including an insulation degradation signal flows.

11 and 12 are the primary coils of the coil 1, which are wound on the iron core 1A, and the number of coils and the winding direction are the same.

13 is the secondary coil of coil 1.

21 is the primary coil of the coil 2 .

22 is the secondary coil of the coil 2 .

11-a is an initial terminal of the primary coil 11 of the coil 1, and 11-b is an end terminal of the coil.

12-a is the initial terminal of the primary coil 12 of the coil 1, and 12-b is the terminal terminal of this coil.

21 - a , 21 - b are the end points of the primary coil 21 of the coil 2 .

22 - a, 22 - b are the end points of the secondary coil 22 of the coil 2 .

Terminals 11-b and 21-a, 12-b and 21-b are connected through external The lines are connected, and in addition, the impedance circuit 3 is connected between the terminals 11-b and 12-a.

The terminals 11 - a and 12 - a are connected to the main circuit 4 , and the detected current including the insulation degradation signal flows through the main circuit 4 .

The insulation degradation signal output is obtained from the two end points 13-a, 13-b of the secondary coil 13 of the coil 1 or from the two end points 22-a, 22-b of the secondary coil 22 of the coil 2, depending on the You can use any one of the above two signal outputs, or use both of them at the same time.

When the fundamental wave and its higher harmonics of the charging current and leakage current of the insulating material, the high-frequency corona discharge current indicating the deterioration of the insulating material, the partial discharge current, and the current of the sudden pulse current overlapping with each other flow through the main circuit 4 , then in the primary coil 11 of the coil 1, all the current of the main circuit flows, and in the primary coil 12 of the coil 1, the total current of the main circuit is deducted from the total current of the main circuit according to the vector calculation method and flows through the impedance 3. current after current. This current flows through the primary coil 21 of the coil 2 in series.

At this time, the magnetomotive force of the core 1A is synthesized by the magnetomotive force generated by the current in the primary coil 11 and the magnetomotive force generated by the current in the primary coil 12. However, since the winding directions of the coils 11 and 12 are the same, the flow The direction of the current passing through the coil 11 and the direction of the current flowing through the coil 12 are opposite to each other for the beginning and end of the coil, so the magnetomotive force of the core 1A is the magnetomotive force generated by the current of the primary coil 11 and The vector difference of the magnetomotive force generated by the current of the primary coil 12 constitutes. Due to the change in the magnetomotive force of the core 1A, a voltage is generated across the secondary coil 13 of the coil 1 .

In addition, the magnetomotive force of the core 2A is generated by the current after subtracting the current flowing through the impedance circuit 3 from the total current of the main circuit in a vector manner. generate voltage.

Therefore, by properly selecting the size and shape of the core 1A and the core 2A, and the number of turns of each coil and other magnetic circuits, and properly selecting the impedance type and characteristic constants in the impedance circuit 3, the secondary coil of the coil 1 can be 12 or the secondary coil 22 of the coil 2, the degradation signal component of the insulation made of high-frequency signal or pulse signal superimposed on the main circuit current is obtained in the form of a distinguishable voltage signal.

A specific embodiment of the first device is described below.

Fig. 2 shows the structure of an embodiment of the insulation deterioration detection device of electric equipment and cable of the present invention, is suitable for use under the working state of high-voltage power cable, and 100 and 200 are the iron cores that are made of cobalt series amorphous alloy, It has high magnetic permeability, and its magnetic permeability is almost constant from low frequency to high frequency range, and has gentle hysteresis characteristics, such as VATROVAC manufactured by Baku Muxie Solutsェ-6025F etc. The coils 101 and 102 pass through the core 100 once in the same direction, and the secondary coil 103 for detecting signals is wound on the core, thus forming the coil 104, and the primary coil 201 and the secondary coil 202 are wound on the core 200 , constituting the coil 203, and C is a capacitor element constituting an impedance circuit. 300 is a magnetically shielded case for preventing the intrusion of noise signals from the outside. 400 is the object to be tested-power cable, its structure is to wrap conductor 401 with insulator 402, shielding layer 403 is housed above it, and insulating sheath 404 is housed above it again. In this case, the main circuit current i required for the measurement is taken out from the insulating case 404 . During the test, the test was performed while measuring the ground voltage from the cable joint 405 .

At this time, if the main circuit current i1 is the low-frequency current iE composed of the charging current of the insulator, the fundamental wave of the leakage current and its high-order harmonics, and the corona discharge current, partial discharge current and sudden pulse that constitute the insulator degradation signal When the high-frequency current iP of the current is superimposed, the main circuit current i1 flows through the primary coil 101 of the coil 104 . The primary coil 201 of the coil 203 has a large inductive reactance to the high-frequency current and a small inductive reactance to the low-frequency current, while the capacitor C has a small capacitive reactance to the high-frequency current and a large capacitive reactance to the low-frequency current, so the high The high-frequency current iP flows through the capacitor C, the low-frequency current iE passes through the primary coil 201 of the coil 203 , and then flows through the primary coil 102 of the coil 104 .

Therefore, the magnetomotive force of the core 100 is only composed of the part of the magnetomotive force generated by the high-frequency current iP, without the component generated by the low-frequency current. The signal voltage eP.

Likewise, from the secondary coil 202 of the coil 203, a signal voltage eE generated by the low-frequency current iE can be obtained.

FIG. 3 shows the relationship curves of the circuit current i1, the detection signal voltage eE generated by the low frequency current iE, and the detection signal voltage eP generated by the high frequency current iP as a function of time.

Fig. 4 shows an application example of the present invention, that is, the device shown in Fig. 2 is used to constitute a regular monitoring device for detecting insulation degradation of high-voltage cables. In this figure, 500 is the insulation degradation detection part 501, 502 which is constituted by the present invention is the terminal point for obtaining the signal voltage eP generated by the high-frequency current iP in the embodiment shown in Fig. The endpoint of the signal voltage eE generated by the current iE. In FIG. 4 , the primary coils 101 , 102 in FIG. 2 are replaced by coaxial cables 505 . Z is the impedance. When the low-frequency current such as the charging current is large, in order to prevent the iron core from reaching magnetic saturation, a secondary coil 204 is wound on the iron core 200. 600 is a signal receiving device, which is composed of a pulse wave input circuit 601, a fundamental wave Input circuit 602, amplifiers 603, 604, phase comparator 605, pulse counter 606, clock pulse circuit 607, time setting circuit 608 and output circuit 609 constitute.

When the insulation performance of the insulator 402 of the power cable 400 deteriorates due to water tree branch deterioration, electric tree branch deterioration, or trauma, the corona discharge current, partial discharge current , or a sudden discharge current, that is, the insulation degradation signal current is superimposed on the charging current of the insulator 402 and flows into the ground through the shielding layer 403 . The insulation degradation detection section 500 uses the pulse wave input circuit 601 and the fundamental wave input circuit 602 to discriminate the signal component formed by the insulation degradation signal current and the signal component formed by the charging current, and inputs it to the signal receiving device 600 .

In the signal receiving device 600, the output of the pulse wave input circuit 601 and the output of the fundamental wave input circuit 602 are respectively amplified by the amplifiers 603 and 604, and then added to the phase comparator 605 to detect whether there is a charging current corresponding to the fundamental wave. The pulse wave of the insulation degradation signal current of each phase of the signal is counted in the pulse counting circuit 606, and the pulse counting circuit 606 uses the time setting circuit 608 to count the clock pulse circuit 607, and the standard clock pulse generated is counted out in the pulse counting circuit 606. The insulation degradation signal pulse within the specified time is set, and when the count value exceeds the specified value, an output signal is sent to the output circuit 609 .

In this way, in the output circuit 609, an alarm indicating that the insulation deterioration signal is detected is issued, and at the same time, a disconnection signal is sent to a circuit breaker not shown in the figure, so that the power cable 400 is disconnected from the power supply. In this way, the data processing device analyzes and processes data such as the frequency of occurrence of insulation degradation pulses corresponding to each phase of the charging current that constitutes the fundamental wave, and judges the degree of degradation and analyzes the cause of degradation.

Furthermore, in FIG. 4, the zero-phase voltage of an instrument grounding transformer not shown in the figure is added to the input of the fundamental wave input circuit 602, and weak grounding can be detected by this change.

In this way, using the device shown in FIG. 4, the insulation degradation of the high-voltage cable can always be monitored with a high degree of reliability with a simple structure, and accidents can be prevented in advance according to the degradation of the high-voltage cable.

As shown in Figure 5-1, the device shown in Figure 4 is applied to a DC high voltage test or an AC withstand voltage test. The purpose of Figure 5-2 is the same as that of Figure 5-1, except that the device implemented according to the present invention is placed on the high-voltage side, which can eliminate the influence of the test device when there is system leakage. In Figure 5-1 and 5-2 In both figures, 500 is the insulation deterioration detection part shown in FIG. 4 , 600 is the signal receiving device, 700 is the pressurizing device for withstand voltage test, and 800 is the object under test. Combined with the pressurizing device in this way, using the device of the present invention, the deterioration state of the insulator can be known, and when the external high voltage is dangerous, the test can be stopped by operation, and the insulation damage of the tested object can be prevented before it happens.

In the structure shown in Fig. 2, when the cores 100 and 200 use the above-mentioned cobalt-based amorphous core VATROVAC-6025F manufactured by Bakumu Schumercai Co., Ltd., assume that the insulation degradation signal level is S, the charging current and leakage of the insulator The signal level of the sum of the currents is N, and the ratio S/N can easily reach 120 decibels.

In this way, the insulation degradation detection device for electrical equipment and cables can achieve the goals of simple structure, large S/N ratio, low price, small size and light weight.

The above-mentioned cobalt-based amorphous alloy is composed of cobalt (Co), iron (Fe), silicon (Si), boron (B), molybdenum (Mo) and nickel (Ni), with the following formula

(Co)a(Fe)b(Si)c(B)d(Mo)e(Ni)f said,

In the formula, a to f represent the atomic percentage of each element composition.

a=50～90, b=1～10, c=5～20,

d=0～20, e=0～20, f=1～5,

And the sum of a~f is 100.

The cores 100 and 200 are annular cores formed by winding a ribbon made of the cobalt-based amorphous alloy many times. The cobalt-based amorphous alloy annular core is heat-treated at a temperature of 150-450° C. for 5-180 minutes to obtain the required magnetic permeability during annular forming. Furthermore, it is best to conduct heat treatment in a DC magnetic field or an AC magnetic field to make the properties uniform. In addition, to perform the heat treatment in a nitrogen environment can make the properties more stable.

As mentioned above, if the first device of the present invention is used, the degree of deterioration of its insulator can be detected with high sensitivity when the electrical equipment and cables are in working condition. If the device is applied to a regular monitoring device, the Accidents can be prevented before they happen, and an inexpensive, compact, and lightweight insulation deterioration detection device for electrical equipment and cables can be obtained.

Next, it is explained that in a system with more than one output line In a power transmission system, when the insulation performance of a transmission line is degraded, the method and device for determining the transmission line with degraded insulation performance are determined by detecting the traveling wave caused by corona discharge or partial discharge that occurs at the position.

If the insulation layer of the transmission line is damaged, corona discharge or partial discharge will occur in this part.

The resulting discharge causes the generation of a traveling wave that travels from the damaged site in both directions along the line. Therefore, by detecting the presence or absence of such traveling waves, it is possible to determine the condition of the transmission line whose insulation performance has deteriorated. As a method for detecting the direction of the above-mentioned traveling wave, for example, the phase of the traveling wave at a specific (reference) point of the common bus as an electrical reference point is compared with the phase of the traveling wave in each transmission line obtained from the common bus , so that the location of the damage can be determined. That is, if the direction of the traveling wave is measured at multiple places, the point where the traveling wave occurs (deterioration position) can be identified.

Now illustrate according to Figure 6, first assume that the insulation of point P has deteriorated, and the resulting traveling wave current passes through all sensors. Here, with the direction of the traveling wave passing through the sensor SF near the capacitor C installed on the first common bus LF as a reference, if you observe the traveling wave current passing through the sensor (S) installed on each cable (L), you will find Only the sensor (S1) on this cable (L1) with deteriorated insulation can detect traveling waves in the opposite direction.

Similarly, if we observe the traveling wave current passing through the sensor (S) installed on each cable (L) based on the direction of the traveling wave passing through the sensor SG located between the second common bus LG and the ground GND, we will find Only the sensor (S4) on this cable (L1) with deteriorated insulation can detect the traveling wave in the opposite direction.

Therefore, the signal detected by these sensors S is measured by the measuring section 53, and the position of the insulation failure can be known.

Examples of sensors for detecting traveling waves are as follows.

That is, the magnetomotive force is approximately proportional to the magnetic flux density, the BH characteristic is approximately linear, and the magnetic permeability is approximately constant from the low frequency region to the high frequency region. A sensor (signal discriminator) is formed by winding the first coil M1 with both ends short-circuited and the second coil M2 for detecting signals.

The aforementioned annular core K may be made of, for example, an amorphous metal having cobalt as a main component.

Also, as shown in FIG. 8(A), a cable L serving as a signal line to be detected is wound around the ring core K. As shown in FIG. The low-frequency current and the high-frequency current flow through the cable L, so that a magnetomotive force is generated in the core K.

With respect to the cable L (primary coil), the first coil M1 and the second coil M2 function as secondary coils, so an electromotive force is generated in the first coil M1 corresponding to the above-mentioned magnetomotive force, but due to the Both ends are short-circuited, so a current that cancels the change in magnetic flux is generated in the ring core K. Therefore, the magnetic permeability of the annular core K here is high, the magnetic permeability from the low frequency region to the high frequency region is roughly stable, the remanence and coercive force are very small, and the magnetomotive force is approximately proportional to the magnetic flux density. Since it has a linear BH characteristic, the inductance of the first coil M1 is small for low frequencies and large for high frequencies.

Therefore, the low frequency components are cancelled, and only the high frequency components can be obtained from the second coil M2.

Furthermore, as shown in FIG. 8(B), in fact, the detected line (L) only needs to pass through the core K.

As an example, the material of the above-mentioned annular core K is composed of cobalt (Co), iron (Fe), silicon (Si), boron (B), molybdenum (Mo), and nickel (Ni), and the following formula can be used

(Co)a(Fe)b(Si)c(B))d(Mo)e(Ni)f said.

(where a～f represent the percentage of each element composition, a=50～90, b=1～10, c=5～20, d=0～20, e=0～20, f=1～5, and The sum of a~f is 100)

In addition, the toroidal core K is made of, for example, a cobalt-based amorphous alloy ribbon. Since the toroidal core is heat-treated at a temperature of 150 to 450°C for 5 to 180 minutes, the desired magnetic permeability can be obtained. It is best to perform heat treatment in a DC magnetic field or an AC magnetic field to make the properties uniform. Furthermore, if the treatment is carried out in a nitrogen environment, the performance can be made more stable.

In addition, the first coil M1 and the second coil M2 may be wound separately, or a part of the first coil M1 and the second coil M2 may be shared.

In addition, if the core K is formed as an annular core using, for example, a cobalt-based amorphous alloy ribbon 6025F manufactured by Bacum Schumacher Co., Ltd., desired magnetic permeability can be obtained.

Next, an embodiment of the present invention will be described with reference to FIGS. 6 to 14 .

First, the present applicant has confirmed that when insulation failure occurs in a power transmission line, corona discharge or partial discharge occurs in that portion, and traveling waves are generated in the power transmission line accompanying this discharge.

Next, when describing the method of detecting the insulation state, we will start with the device for detecting the part of the insulation failure in the transmission line based on the above-mentioned traveling wave.

The AC power source A first supplies power to the substation 51. In the substation 51, after the transmission line passes through the transformer T1 and the circuit breaker B1 It is used as the first common bus LF, and the first common bus LF is grounded (GND) through the capacitor C.

On the line between the capacitor C and the ground portion, a ring sensor SF is installed around the line, and the signal output by the sensor SF becomes the signal at the reference point provided on the common bus.

The above-mentioned first public bus LF is respectively connected to the cables L1, L2 and L3 for power transmission through the circuit breaker B2, the circuit breaker B3 and the circuit breaker B4, and ring sensors S1, S2 and S3 are installed on these cables to surround the cables. , and the above-mentioned cable L1 is extended to the place 52 where power supply is required.

In the field 52 that needs power supply, a sensor S4 is installed on the cable L1, and is connected to the second common bus LG through a circuit breaker B5.

The second common bus line LG is grounded (GND) through a capacitor C. A sensor SG is installed on the line between the capacitor C and the ground, and surrounds the line, and a signal output from the sensor SG becomes a signal at a reference point on the second common bus.

The cables L4 and L5 for power transmission are respectively connected to the above-mentioned second common bus LG through circuit breakers B6 and B7, and ring sensors S5 and S6 are respectively installed on these cables to surround the cables.

Further, the cable L4 is connected to the motor M, and the cable L5 is connected to the transformer T2.

The output signals of the above sensors S1, S2, S3 are input to the scanning circuit 60, and after time series decomposition, are input to the direction comparison circuit 61 for comparison with the signal from the above sensor SF. The comparison result is input to the data transfer circuit 62 .

On the other hand, the output signals of the sensors S5 and S6 are input to the scanning circuit 70, after time-series analysis, input to the direction comparison circuit 71, and compared with the signal from the sensor SG. The comparison result is input to the data transfer circuit 72 .

The respective signals of the above-mentioned data transmission circuit 62 and data transmission circuit 72 are input to the measuring part 53, and these signals are first input to the scanning circuit 81, and after being decomposed into time series, are input to the fast data storage circuit 82, and are also input to the alarm-display circuit 83 at the same time. . Fast data storage circuit 82 is connected with personal computer 84, carries out the access of data, and personal computer 84 is connected with display 86 and printer 87, can show the inspection result, the specific hardware of above-mentioned fast data storage circuit 82 can be added according to Fig. 12 Explanation, as shown in the figure, the circuit is composed of a sensor S, a buffer BU connected to the next stage of the sensor S, amplifying the signal amplifier AP from the buffer BU, and connected to the next stage of the amplifier AP to detect the output The peak detection part PS of the maximum value of the signal, the 20 MHz A/D converter AD connected in parallel with the peak detection part PS, and the output signals of the peak detection part PS and the A/D converter AD can be stored respectively A memory board MB with a capacity of two thousand bytes, a personal computer 84 storing signals to the memory board MB, and a printer 85 serving as an output device are connected.

Next, the working principle of the above-mentioned sensor S and the working principle of the circuit will be described.

The above-mentioned sensor S is constructed by winding a coil around an iron core K made of cobalt-based amorphous metal. The magnetic permeability of the iron core K is approximately constant from low frequency to high frequency as shown in FIG. 10 . The coercive force is very small, and the B-H characteristic is linear, as shown in Figure 9, and as shown in Figure 8, the coil is composed of a short-circuited first coil M1 wound on the core K and a second coil with both ends open. Made of M2. The core K has a width of 10 mm, a thickness of 3 mm, and an inner diameter of 150 mm. The number of turns of the first coil M1 is 3, and the number of turns of the second coil M2 is 10.

With such a structure, the low-frequency current of the power frequency and its high-order harmonics and the traveling wave current accompanying the above-mentioned corona discharge or partial discharge can be distinguished. The experimental results show that the sensitivity of the sensor S with this structure can detect 20 ps Coulomb-sized amount of corona discharge charge.

Fig. 7 shows the embodiment on the three-phase AC transmission line, where the traveling speed V of the traveling wave is

V=[(magnetic permeability×permittivity)1/2] ¹

In the formula, because the dielectric constant of the polyethylene insulator is 4 times that of air, the propagation speed of the traveling wave in the transmission line is about 1/2 of the speed of light, so the magnitude of V is 150 m/μs. The high speed passes through the iron core, so a strong pulse magnetomotive force is generated. The low-frequency current of the power frequency and its higher harmonics, and the traveling wave current accompanying the above-mentioned corona discharge or partial discharge are induced in each coil, but the inductance of the first coil M1 is very small for low frequencies, and it is not suitable for pulses. It is said to be very large, so the change of magnetic flux produced by the magnetomotive force of the low-frequency current iE can be almost completely offset, and the change of magnetic flux produced by the magnetomotive potential of the pulse current generated by the passing of the traveling wave current iP will not be offset and stay.

Therefore, from the two terminals of the second coil M2, only signals passing through with the traveling wave can be obtained.

In addition, due to the fact that each phase bus with capacitor CT The sensor SR used to judge the insulation deterioration is inserted in the LM, so it is judged which item the traveling wave passes through, and the discrimination signal of the insulation deterioration phase can be obtained. Furthermore, no matter which phase is degraded or which part of the system is degraded, the traveling wave passes through the sensor SF provided on the common line of the capacitor CT in the same direction, so a signal serving as a reference for the direction of the traveling wave can be obtained.

Signals from these detection coils can be sequentially output by the scanning circuit as in the above-mentioned embodiment, and can be processed in parallel if there is room in the signal transmission capacity.

The above-mentioned traveling waves have the same spectrum as discharge noise, are distributed over a wide frequency range, and have a certain amount of energy. However, there may be a frequency distribution unique to corona discharge accompanying poor insulation. At the same time, in order to limit the unnecessary frequency band , improve the signal-to-noise ratio (S/N) relative to the external noise, and use the band-pass filter to limit the frequency band, which has a very good effect.

In this way, when using a band-pass filter for experiments, set the detected frequency range from 20 kHz to 200 MHz, preferably from 300 kHz to 50 MHz, and if it is set at 300 kHz to 50 MHz, it will be fine. Even better, this gives good results. The specific frequency to be passed must be determined using a spectrum analyzer or the like which is most suitable for the situation. As for the filter, of course, the above-mentioned single-tuned type can be used, and in addition, a series-type filter with multi-point tuning can also be used.

Next, in the circuit shown in FIG. 6 , the experimental results of detecting traveling waves caused by corona discharge accompanying insulation degradation of cables using the sensor shown in FIG. 8 will be described together with FIG. 11 . In the graph, J is the signal characteristic curve of the sensor S1 arranged on the cable, and Q is the signal characteristic curve of the sensor SF arranged on the bus. When there is damage on the cable, the traveling wave travels in two directions, and the traveling wave current passes through the sensor SF and the sensor S1 in opposite directions respectively, so the phases of J and Q are roughly opposite, so it can be seen that there is a traveling wave, that is, on the cable There is damage.

Next, actual measurement waveforms will be described with reference to FIGS. 13 and 14 .

FIG. 13 shows the situation when a traveling wave is generated at a distance from a measurement point, and the traveling wave reflected by an end load such as a motor periodically appears.

However, it is still possible to observe the pulse generated with the corona discharge, but because this pulse only appears in a very short time, it is often difficult to capture it, so a resonant circuit is inserted in the pulse detection circuit, which is It makes it easy to capture the pulse. Figure 14 shows the waveform obtained when this circuit is used. J1 is a pulse accompanied by corona discharge. After this pulse excites the resonant circuit, it presents a decay waveform J2 of a specific frequency.

Furthermore, the above-mentioned embodiments do not limit the size, shape and material of the core K, which can be appropriately changed according to the detection conditions.

As described above, according to the present invention, it is possible to monitor the insulation state of electrical equipment and cables under normal electrification.

In addition, when the insulation state is abnormal, the location of the abnormal state can be determined.

Therefore, it can be detected in the slight stage of poor insulation, and accidents caused by poor insulation can be prevented before they happen.

Claims (6)

1, a kind of detection has the method for two or more state of insulation from the electric power system of the transmission line of electricity of the public expenditure of common bus, comprise when having a bar insulation performance to descend in the transmission line of electricity, traveling-wave phase by relatively being located at the datum of ground connection side on the common bus of capacity earth and comprise each locational traveling-wave phase a plurality of positions in a transformer station and an electricity consumption district from each transmission line of electricity that common bus branch comes out, detect the capable ripple direction that the corona discharge that produced by the detection position of described this transmission line of electricity or shelf depreciation cause in described electric power system, and determine that transmission line of electricity of decreasing insulating and the position of decreasing insulating from detected above line ripple direction.

2, method according to claim 1, wherein, the described traveling-wave phase signal on each bar transmission line of electricity that will come out from common bus branch is imported arithmetic unit with time-sharing format, carries out calculation process.

3, method according to claim 1, wherein, the described traveling-wave phase signal on each bar transmission line of electricity that will come out from common bus branch is imported arithmetic unit with parallel mode, carries out calculation process.

4, the detection method of state of insulation according to claim 1, wherein, corona discharge or the caused capable ripple of shelf depreciation that a position of the transmission line of electricity that has descended in a certain insulating property with the sensor that is installed in respectively on electric reference point and each transmission line of electricity produces, above-mentioned each sensor by the 2nd coil on ring-shaped core and two terminal shortcircuits the 1st coil constitute, described ring-shaped core has the BH characteristic that is linear approximately, to the high frequency region constant, described each sensor provides the measuring-signal from the 2nd coil to its magnetic permeability from low frequency range.

5, a kind of detection has the device of state of insulation the electric power system of two or more transmission line of electricity that branches out from common bus, comprise from individual sensor, be used for detecting the capable ripple that corona discharge that the position produced of transmission line of electricity that insulating property have descended or shelf depreciation cause, in described a plurality of sensor each all with in corresponding transmission line of electricity or the described common bus work is associated, determination part divides to be imported thus from described signal of sensor, and the described signal of the sensor output that will link by each and transmission line of electricity and carry out corresponding comparison by the signal of the sensor output that links with described common bus, each sensor is made of the 1st coil of the 2nd coil on ring-shaped core and two terminal shortcircuits, and the described annular heart has the BH characteristic that is linear approximately, and magnetic permeability from low frequency range to the high frequency region constant.

6, device according to claim 5, wherein, described iron core is to be that the amorphous metal alloy of principal ingredient is made in order to cobalt.

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