CN106990327A - High voltage single-core cable short trouble point detecting method - Google Patents

Abstract

The invention relates to a method for detecting a short-circuit fault point of a high-voltage single-core cable, which is used for determining the specific location of a fault point in a cable where a short-circuit fault occurs. Assume that a short-circuit fault occurs at each sampling point and perform simulation, respectively calculate the phase difference of the sheath current at both ends of the cable when the short-circuit fault occurs at each sampling point, and perform fitting according to the calculated phase differences to obtain the corresponding short-circuit fault of the cable The relationship between the location of the fault point and the phase difference; when a short-circuit fault occurs in the cable, the specific location of the fault point where the short-circuit fault occurs is determined by solving the relationship between the location of the fault point where the short-circuit fault occurs and the phase difference. The invention can quickly and accurately determine the specific location of a short-circuit fault in a section of cable, can realize more accurate positioning, and can realize on-line monitoring, and can find out the fault point in time after a fault occurs.

Description

Detection method of short-circuit fault point of high-voltage single-core cable

technical field

The invention relates to a method for detecting a short-circuit fault point of a high-voltage single-core cable for determining the specific location of a short-circuit fault in a section of cable in a cable cross-connection section.

Background technique

There are two main modes of cable fault location at present: one is the protection distance measurement using the distance protection device, and the other is the fault location mode of the traveling wave method using the electronic sensor. 1) The principle of distance protection based on parameter identification uses the parameters that change in the system after a fault to form the protection criterion. However, the distribution parameters of power cables have obvious characteristics, include multiple complete cross-connection sections, and the environment of line channels is complex, which will significantly affect distance protection. Algorithm performance. Since the measured impedance is no longer proportional to the fault distance, the protection range of the traditional distance protection algorithm will be reduced. In practical applications, the distance protection using line impedance still has inaccurate line impedance calculation and incomplete line length information, so it is impossible to determine the specific location of the short-circuit fault in the cable. 2) The traveling wave method performs fault location by detecting the propagation time of the transient traveling wave on the fault line between the busbar and the fault point. Since the propagation speed of the transient traveling wave is close to the speed of light, the fault location mode based on the traveling wave method exists The problem of noise elimination and wave head time extraction. In addition, multiple cross-connection sections and complex line channel environments cause the wave velocity of long cable lines to be inconsistent and wave impedance to be discontinuous. This method is difficult to apply to actual long cable lines. Accurate location of the fault location.

The invention patent with the application number of 201611128521.0 "Short-circuit fault location method and device for high-voltage single-core cable cross-connection structure" discloses a method for locating short-circuit faults based on the direction of the current signal. Which section of the cable in the cable cross-connection structure the fault occurs in, but the specific fault point in the cable cannot be determined.

Contents of the invention

The purpose of the present invention is to provide a high-voltage single-core cable short-circuit fault point detection method that can quickly and accurately determine the specific location of the short-circuit fault in the cable.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A method for detecting a short-circuit fault point of a high-voltage single-core cable, which is used to determine the specific location of a fault point in a cable where a short-circuit fault occurs. The method for detecting a short-circuit fault point of a high-voltage single-core cable is: taking n sampling points in the cable , respectively assuming that a short-circuit fault occurs at each of the sampling points and performing simulation, respectively calculating the phase difference of the sheath current at both ends of the cable when the short-circuit fault occurs at each of the sampling points, and fitting according to the calculated phase differences , to obtain the relational expression of the fault point position and the phase difference corresponding to the short-circuit fault of the cable; The specific location of the fault point of the short circuit fault.

Preferably, one end of the cable is taken as the origin, and the distance between the fault point and the origin is used to characterize the location of the fault point where the short-circuit fault occurs.

Preferably, the distance between the fault point and the origin has a linear relationship with the phase difference.

Preferably, the origin is taken as the end of the cable close to the power supply.

Preferably, the sampling points are selected at equal intervals on the cable.

Due to the application of the above-mentioned technical solutions, the present invention has the following advantages compared with the prior art: the present invention can quickly and accurately determine the specific location of a short-circuit fault in a section of cable, can realize more accurate positioning, and can realize on-line monitoring, fault After the occurrence, the fault point can be found in time.

Description of drawings

Figure 1 is a schematic diagram of a simple power system.

Figure 2 is a schematic diagram of fault current flow in the cross-connection section of a high-voltage single-core cable.

Figure 3 is a schematic diagram of the equivalent circuit of the induced voltage and the sheath current of the metal sheath of the high-voltage cable in the cross-connection section of the high-voltage single-core cable.

detailed description

The present invention will be further described below in conjunction with the embodiments shown in the accompanying drawings.

Embodiment 1: Figure 1 shows a single-order power system, which consists of a power supply-transmission line-load, wherein the transmission line part uses a high-voltage cable. The transmission line in Figure 1 adopts a complete cable cross-connection section, which is connected between the first grounding box G1 and the second grounding box G2, which includes three-phase lines, which are A-phase line and B-phase line and C-phase line. Each phase line includes three sections of single-core cables numbered from 1 to 3 in sequence, then the three sections of single-core cables in the A-phase line are A1, A2, and A3 respectively; the three sections of single-core cables in the B-phase line are respectively B1 , B2, B3; the three sections of single-core cables in the C-phase line are respectively C1, C2, and C3. The cores of each section of single-core cables contained in each phase line are directly connected in sequence to form each phase line. Each single-core cable has two ends, a front end and a rear end, respectively. The first section of single-core cables in the three-phase lines, that is, the front ends of the metal sheaths of A1, B1, and C1 are respectively connected to the first grounding box G1, and the first and second sections of single-core cables A1, A2 in the A-phase line The back end of the metal sheath of the cable is connected to the front end of the metal sheath of the second and third sections of single-core cables B2 and B3 in the B-phase line through the cross-connection boxes J1 and J2 respectively, and the first and second sections of the single-core cables in the B-phase line The back ends of the metal sheaths of cables B1 and B2 are respectively connected to the front ends of the metal sheaths of the second and third sections of single-core cables C2 and C3 in the C-phase line through cross-connection boxes J1 and J2. The back ends of the metal sheaths of the two sections of single-core cables C1 and C2 are respectively connected to the front ends of the metal sheaths of the second and third sections of single-core cables A2 and A3 in the A-phase line through cross-connection boxes J1 and J2. The metal sheath rear ends of the third section single-core cables A3, B3, and C3 in the three-phase lines are respectively connected to the second grounding box G2. The "front end" mentioned here refers to the end of each single-core cable that is close to the first grounding box G1, that is, the end close to the power supply, and the end close to the second grounding box G2, that is, the end that is close to the load is called the "back end". ".

When a short-circuit fault occurs in the cross-connection section of the above cables, the following method can be used to determine which section of the single-core cable the short-circuit fault occurs in: set current transformers I _1a and I _1b at the front ends of the metal sheaths of A1, B1, and C1 respectively , I _1c , and then install current transformers at the back end of the metal sheath of each section of single-core cable, respectively I _2a , I _2b , I _2c , I _3a , I _3b , I _3c , I _4a , I _4b , I _4c . When no fault occurs, affected by the cross interconnection, the metal sheath of each single-core cable is wired by the current induced by the core. When any section of single-core cable has a cable line breakdown fault, its core forms a short circuit to the metal sheath, and the core current directly passes through the metal sheath and flows into the ground from the grounding points at both ends, causing single-core cables in the faulty section and crossover faults. The metal sheath current of the interconnected single-core cable increases, and the sheath current is close to the fault current. At the same time, due to the electromagnetic coupling effect, the lines adjacent to the faulty line will also induce a large current. Take the A1-B2-C3 interconnection section as an example, as shown in Figure 2, assuming that the fault occurs in the B2 section of the single-core cable, the fault current flows from the fault point along the metal sheath to both ends of B2, and at the front end of B2, the current The current flows into the metal sheath of A1 through the cross interconnection box J1 and the current transformer I _2a and then enters the ground. At the rear end of B2, the current flows into the metal sheath of C3 through the current transformer I _3b and the cross interconnection box J2 and then enters the ground. Then the current directions in the two current transformers I _2a and I _3b flowing through the two ends of the single-core cable B2 section are opposite. And for the non-fault segment, such as C3, the current directions in the two current transformers I _3b and I _4c at its two ends are the same. But for the single-core cable A1 of the first section, due to the setting position of the current transformer I _1a at the front end, its current reference direction is opposite to that of other current transformers, so the two ends of the single-core cable A1 section The current directions in the two current transformers I _1a and I _2b are the same. Based on the above characteristics, firstly, for the first section of single-core cables A1, B1, and C1 in the three-phase line, the reverse signal of the current signal directly detected by the front end of the metal sheath is defined as the first section of single-core cable A1 , B1, and C1 respectively the front-end current of the sheath; for the first and second single-core cables A1, B1, C1, A2, B2, and C2 in the three-phase line, define the current directly detected by the back end of the metal sheath The current is the back-end current of the sheath of the first and second single-core cables and the front-end current of the sheath of the second and third single-core cables connected to it; for the third single-core cable A3 in the three-phase line , B3, C3, define the current directly detected by the rear end of the metal sheath as the current at the rear end of the sheath of the third single-core cable. That is, in the structure shown in Figure 1, the reverse signal of the current signal I _1a directly detected by the front end of the metal sheath of A1 is the current of the front end of the sheath of A1, and the current signal I _1b directly detected by the front end of the metal sheath of B1 The reverse signal of the reverse signal is the front-end current of the sheath of B1, and the reverse signal of the current signal I _1c detected directly by the front-end of the metal sheath of C1 is the front-end current of the sheath of C1; I _2a is the back-end current of the sheath of A1 and The front-end current of the sheath of B2, I _3b is the back-end current of B2 and the front-end current of the sheath of C3 at the same time, I _2b is the back-end current of B1 and the front-end current of the sheath of C2 at the same time, and I _3c is the current of C2 at the same time The back-end current of the sheath and the front-end current of the sheath of A3, I _2c is the back-end current of the sheath of C1 and the front-end current of the A2 sheath at the same time, and I _3a is the back-end current of the sheath of A2 and the front-end of the sheath of B3 Current; I _4a is the back-end current of the sheath of A3, I _4b is the back-end current of the sheath of B3, and I _4c is the back-end current of the sheath of C3. Then judge whether a short circuit fault occurs in each section of single-core cable according to whether the current at the back end of the sheath of each section of single-core cable is in the opposite direction to the current at the front end of the sheath; If the current direction is opposite, a short circuit fault occurs in this section of single-core cable. Usually directly detect the current signal at the front end of the metal sheath of the first section of single-core cable in the three-phase line, and invert the power frequency phase of the directly detected current signal to obtain the sheath of the first section of single-core cable The power frequency phase of the front-end current; directly detect the current signal at the back end of the metal sheath of the first and second single-core cables in the three-phase line, and use the power frequency phase of the directly detected current signal as the first and second The power frequency phase of the back-end current of the sheath of a single-core cable and the power-frequency phase of the front-end current of the sheath of the second and third single-core cables connected to it; directly detect the third single-core in the three-phase line The current signal at the back end of the metal sheath of the cable, and the power frequency phase of the directly detected current signal is used as the power frequency phase of the current at the back end of the sheath of the third single-core cable. In the above process, fast Fourier transform is performed on each directly detected current signal to obtain its power frequency phase. The opposite direction of the current is reflected by the phase. Therefore, the rear end of the sheath of each section of single-core cable can be judged according to the difference between the power frequency phase of the current at the back end of the sheath of each section of single-core cable and the power frequency phase of the current at the front end of the sheath. Whether the direction of the current is opposite to that of the current at the front end of the sheath. When the current direction is opposite, the phase difference of the current signal is about 180°. In the following, B(I) is used to represent the power frequency phase of the current signal I (unit is angle), and P(section) represents the difference between the power frequency phase of the current at the back end of the sheath of the corresponding single-core cable and the power frequency phase of the current at the front end of the sheath. difference(section ∈ ["A1", "B1", "C1", "A2", "B2", "C2", "A3", "B3", "C3"]), then:

P(A1)=B(I _2a )-[B(I _1a )+180]

P(B1)=B(I _2b )-[B(I _1b )+180]

P(C1)=B(I _2c )-[B(I _1c )+180]

P(A2)=B(I _3a )-B(I _2c )

P(B2)=B(I _3b )-B(I _2a ) (1)

P(C2)=B(I _3c )-B(I _2b )

P(A3)=B(I _4a )-B(I _3c )

P(B3)=B(I _4b )-B(I _3a )

P(C3)=B(I _4c )-B(I _3b )

If the difference P(section) between the power frequency phase of the current at the back end of the sheath of any single-core cable and the power frequency phase of the current at the front end of the sheath is within the allowable range of the phase centered at ±180°, then the section is judged The direction of the current at the back end of the sheath of the single-core cable is opposite to that at the front end of the sheath. Since the cable line in a cross interconnection section generally does not exceed 500m, the phase difference of the sheath current signal at both ends of the fault will not be significantly different due to the unequal length of the fault point from both ends, while the phase of the faulty section and the non-faulty section The difference is relatively large, so a large margin can be left in formulating the fault section criterion. For example, the phase allowable range is (120°, 240°)∪(-240°, -120°), when the phase difference is in When the above range is exceeded, it is considered that a short circuit fault has occurred. The phase difference between the two ends of the non-faulty single-core cable end is very small, within ±30°, so the above method can be used to determine the cable section where the short-circuit fault is located.

After determining the cable segment where the short-circuit fault occurs, it is necessary to further determine the specific location of the fault point in the cable segment. Still taking the above-mentioned A1-B2-C3 interconnection section as an example, the equivalent circuit diagram of the induced voltage and the sheath current of the high-voltage cable metal sheath is shown in Figure 3, where the sheath current I _m1 is:

In the case of no fault, the sheath current I _m1 can sometimes reach several amps or even tens of amps, the induced voltage is not large, but the sheath impedance is very small. And Z _ma1 , Z _mb2 and Z _mc3 are all perceptual. The grounding resistance R _g is purely resistive. Therefore, the magnitude of the grounding resistance _Rg can affect the nature of the impedance. If the grounding resistance R _g is small, the inductive components of Z _ma1 , Z _mb2 and Z _mc3 are relatively large, and the induced voltage has a greater influence on the sheath current, so the inductive components have a greater influence on the phase difference. If the grounding resistance R _g is large, the inductive components of Z _ma1 , Z _mb2 and Z _mc3 are small, and the overall resistive component of the sheath impedance loop is relatively large, so the inductive component has little influence on the phase difference. The grounding resistance under normal operating conditions generally does not exceed 0.5Ω, and is under 0.5Ω.

A high-voltage single-core cable short-circuit fault point detection method for determining the specific location of the fault point in the cable where the short-circuit fault occurs is: for each section of cable, first take n sampling points in the cable, assuming that each sampling point occurs The short-circuit fault is simulated, and the phase difference of the sheath current at both ends of the cable is calculated when the short-circuit fault occurs at each sampling point, and is fitted according to the calculated phase differences to obtain the corresponding fault point position and The relation of phase difference. When a short-circuit fault occurs in the cable, the specific position of the fault point where the short-circuit fault occurs is determined by solving the relational expression between the position of the fault point where the short-circuit fault occurs and the phase difference.

In the above-mentioned high-voltage single-core cable short-circuit fault point detection method, one end of the cable (the end close to the power supply) is usually taken as the origin, and the distance l between the fault point and the origin is used to characterize the position of the fault point where the short-circuit fault occurs. When selecting sampling points, select sampling points at equal intervals on the cable. It is necessary to select sampling points for each section of cable in advance and calculate and fit them. Thus it can be concluded that the distance between the fault point and the origin has a linear relationship with the phase difference.

For example, the present invention has carried out simulation calculation for a 110kV cable line, the line is laid horizontally with three-phase direct burial, the cable model is YJLW03, the three-phase balanced load, each section of cable is 500m, and the total length of the line is 1500m. Starting from the front end of the first section of the cable, a sampling point is taken every 50m and used as a fault point for a simulation. The P value at different positions of the fault point is calculated, and finally the P value is fitted to obtain the relationship between the fault point location and the P value. relationship, as shown in equation (3). Among them, l represents the distance from the fault point to the power end (front end) of the cable segment (0<l<500).

P(A1,l)=-0.02265l+143.8

P(B1,l)=-0.02271l+143.8

P(C1,l)=-0.02278l+143.9

P(A2,l)=-0.05034l+184.8

P(B2,l)=-0.04848l+176.6 (3)

P(C 2,l)＝-0.04581l+168.7

P(A3,l)=-0.06439l+191.3

P(B3,l)=-0.06434l+190.1

P(C3,l)=-0.06444l+191.3

Then, when a fault actually occurs, the distance l between the fault point and the front end of the cable where the fault point is located can be calculated according to a relational expression in the above equation (3), so as to determine the location of the fault point.

The invention utilizes the sheath current of the high-voltage single-core cable to locate the short-circuit fault. According to the characteristics of cross-connection of high-voltage single-core cables and the characteristics of current flow under short-circuit faults, by monitoring the sheath current of high-voltage cables, extracting the amplitude and phase information of the power frequency component of the sheath current signal, and judging the flow direction of the sheath current, first determine Faulty section of high voltage cable. Then, the phase difference of the sheath current at both ends of each cross-connection section is related to the grounding resistance, the location of the fault point, and the load current. The location of the fault point can be more accurately judged according to the phase difference between the grounding resistance, load current, and the sheath current.

The above-mentioned embodiments are only for illustrating the technical conception and characteristics of the present invention, and its purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and not to limit the protection scope of the present invention. All equivalent changes or modifications made according to the spirit of the present invention shall fall within the protection scope of the present invention.

Claims (5)

1. A high-voltage single-core cable short-circuit fault point detection method, used to determine the specific location of the fault point in the cable where the short-circuit fault occurs, is characterized in that: the high-voltage single-core cable short-circuit fault point detection method is: in the cable Take n sampling points, respectively assume that a short-circuit fault occurs at each of the sampling points and perform simulation, respectively calculate the phase difference of the sheath current at the two ends of the cable when the short-circuit fault occurs at each of the sampling points, and according to the calculated Each phase difference is fitted to obtain the relationship between the fault point position and the phase difference corresponding to the short-circuit fault of the cable; when a short-circuit fault occurs in the cable, according to the fault point position and phase difference of the short-circuit fault Solve the relational expression to determine the specific location of the fault point where the short-circuit fault occurs. 2. The method for detecting a short-circuit fault point of a high-voltage single-core cable according to claim 1, wherein: taking one end of the cable as the origin, representing the point where the short-circuit fault occurs with the distance between the fault point and the origin The location of the point of failure. 3. The method for detecting a short-circuit fault point of a high-voltage single-core cable according to claim 2, wherein the distance between the fault point and the origin is in a linear relationship with the phase difference. 4. The method for detecting a short-circuit fault point of a high-voltage single-core cable according to claim 2, wherein the origin is set at the end of the cable close to the power supply. 5. The method for detecting a short-circuit fault point of a high-voltage single-core cable according to claim 1, 2, 3, or 4, wherein the sampling points are selected at equal intervals on the cable.