CN105182157A - Neutral point multi-point grounding detection device based on high-accuracy detection current - Google Patents

Abstract

The invention discloses a neutral point multi-point grounding detection device based on high-precision detection current, including an analyzer, a detector and a clamp meter. When the analyzer and the clamp meter are connected together, they form a fault analysis module. The detector and the clamp meter When the clamp meters are connected together, they form a fault location module. In the analyzer, a detection current generator designed according to the node shunt principle is adopted, and the detection current generator can achieve high linearity, which significantly improves detection accuracy. The present invention has a wide range of applicable scenarios and is easy to apply. For example, it can be used to check the multi-point grounding of the secondary circuit of the current transformer in a substation, and effectively detect the secondary circuit of the current transformer without affecting the normal operation of the protection device. Whether multi-point grounding occurs.

Description

Neutral point multi-point grounding detection device based on high-precision detection current

technical field

The invention discloses a neutral point multi-point grounding detection device based on high-precision detection current, and relates to the technical field of electric power automatic detection.

Background technique

In the field of power technology, equipment that produces, transforms, transmits, and distributes electrical energy (such as generators, transformers, and transmission and distribution power lines, etc.), as well as equipment that uses electrical energy (such as motors, electric furnaces, relay protection and control devices, etc.), Even the same whole composed of energy management system is called power system. The composition of the power system can be divided into a primary system (or primary loop) and a secondary system (or secondary loop) according to functional differences: the former is responsible for the transmission and distribution of electric energy, and the latter is used to monitor the primary system (or primary loop) , control, measurement and protection tasks, the equipment in the primary system is called primary equipment, and the equipment in the secondary system is called secondary equipment.

In the power system, the public circuit plays a very important role in ensuring the safe operation of the system. Under the normal operation of the system, in order to ensure the safety of people and equipment, the "Electrical Work Site Safety Regulations" stipulates that an electrical connection of the common circuit of the transformer must have a reliable grounding point. At the same time, in order to ensure the correct operation of relay protection and automatic devices, one point of the circuit is required to be grounded. However, there are many connected devices in the public circuit of the substation, and the extension range is wide. Often due to man-made wiring errors or some unavoidable natural laws, such as the aging of insulation, etc., multi-point grounding occurs in an electrically connected public circuit, and Most of the public circuits of the system are outdoors, and the probability of insulation damage is high. Multi-point grounding leads to incorrect actions of protection, causing large-scale power outages to occur frequently in the system. For example, in order to ensure the normal operation of the voltage secondary circuit, the neutral network of the voltage secondary circuit must be permanently grounded, and only have this grounding point. If there are other grounding points other than the permanent grounding point, it will be Cause accidents such as line zero-sequence protection reverse direction misoperation, joint transformer protection misoperation and longitudinal protection misoperation, causing major impacts.

At present, the method of on-site multi-point grounding inspection in substations is mainly to remove the original grounding point, and determine whether there is a multi-point grounding phenomenon by measuring the resistance of the circuit to ground.

In the patent application with the application number 201310109898.1, a method and system for detecting multi-point grounding of the neutral line network of the voltage secondary circuit are disclosed. However, in this application, conventional detection current injection equipment is used, and the commonly used three-phase current generator is When generating and outputting various AC and DC three-phase current waveforms required for verification, it is impossible to maintain the stability and accuracy of the output current waveform in the audio range from DC, power frequency to 2kHz at the same time, and there are narrow operating frequency bands, When outputting high-order harmonics, the attenuation is more obvious and the high-frequency components of the waveform are easy to induce self-oscillation and other shortcomings, which obviously do not meet the requirements of the verification of harmonic energy meters.

In the patent application with the application number 201310565336.8, a non-contact current transformer secondary circuit multi-point grounding detection method and system are disclosed, which use Faraday's law of electromagnetic induction to determine whether there is current in the neutral line. The method also has the disadvantage of low detection accuracy.

Contents of the invention

The technical problem to be solved by the present invention is to provide a neutral point multi-point grounding detection device based on high-precision detection current, which can work normally in the range of DC, AC and audio frequency. The current generators of each phase are independent, that is, they are electrically isolated from each other, and the generated currents are also independent of each other. They can be connected to corresponding potentials as required to accurately detect multi-point grounding problems in the power supply system.

The present invention adopts the following technical solutions for solving the problems of the technologies described above:

A neutral point multi-point grounding detection device based on high-precision detection current, including an analyzer, a detector and a clamp meter. When the analyzer and the clamp meter are connected together, they form a fault analysis module, and the detector and the clamp meter are connected. together constitute the fault location module, where,

The analyzer includes a first digital-to-analog conversion module, a signal analysis module, a signal control module, a detection current generator and a first display module; the clamp meter is connected to the busbar and the ground wire of the secondary circuit main circuit of the power system to be tested, The output end of the clamp meter is connected to the signal control module after passing through the first analog-to-digital conversion module and the signal analysis module in sequence, and the output ends of the signal control module are respectively connected with the detection current generator and the first display module, and the The output end of the detection current generator is connected to the busbar of the main circuit of the secondary circuit of the power system to be tested;

The detector includes a filter module, a second digital-to-analog conversion module, a signal processing module, a fault analysis and positioning module, an acousto-optic alarm module, and a second display module; the clamp meter and the grounding wire of each branch of the secondary circuit of the power system to be tested The output end of the clamp meter is connected to the fault analysis and positioning module after passing through the filter module, the second digital-to-analog conversion module, and the signal processing module in sequence. The output ends of the fault analysis and positioning module are respectively connected with the sound and light alarm module and the second display modules are connected.

The first and second display modules are preferably liquid crystal displays.

As a further preferred solution of the present invention, the specific circuit structure of the detection current generator includes first to thirteenth resistors, first to fourth switches, first and second power amplifiers, wherein,

The input terminals of the circuit are respectively connected to the first resistor and one terminal of the second resistor, the other terminal of the first resistor is connected to the first input terminal of the first switch, and the other terminal of the second resistor is respectively connected to the second terminal of the first switch. The input terminal, one terminal of the third resistor, the second input terminal of the second switch, one terminal of the fourth resistor, the second input terminal of the third switch, one terminal of the fifth resistor, and the second input terminal of the fourth switch are connected; The other end of the third resistor is connected to the first input end of the second switch, the other end of the fourth resistor is connected to the first input end of the third switch, and the other end of the fifth resistor is connected to the first input end of the fourth switch. The first output ends of the first to fourth switches are respectively connected to the first to fourth CPU pins, and the second output ends of the first to fourth switches are respectively connected to one end of the tenth resistor and one end of the eleventh resistor. One end, one end of the twelfth resistor, one end of the thirteenth resistor; One end of the ninth resistor is connected to the positive input end of the first amplifier, the other end of the ninth resistor is connected to the negative input end of the first amplifier and grounded, and the output end of the first amplifier is connected to one end of the sixth resistor, The other end of the sixth resistor is connected to one end of the eighth resistor and the positive input end of the second amplifier, the negative input end of the second amplifier is grounded through the seventh resistor, and the output end of the second amplifier is connected to the other end of the eighth resistor. connected as the output of the circuit.

As a further preferred solution of the present invention, the detection current generator outputs alternating current with a frequency less than 1 Hz.

As a further preferred solution of the present invention, the detection current generator further includes a limit element, and when the output current exceeds a maximum limit, the limit element controls the detection current generator to use the set maximum limit as the output current.

As a further preferred solution of the present invention, the sizes of the tenth to thirteenth resistors are 62 ohms, 120 ohms, 240 ohms, and 480 ohms in sequence.

As a further preferred solution of the present invention, the input voltage of the detection current generator is 5V.

As a further preferred solution of the present invention, the second resistor is an adjustable resistor.

As a further preferred solution of the present invention, the clamp meter is a high-precision current clamp meter.

The invention also discloses a detection method of a neutral point multi-point grounding detection device based on high-precision detection current, and the specific steps include:

Step 1, the detection current generator injects the first current into the bus bar of the main circuit of the secondary circuit of the power system to be tested, and the clamp meter detects the second current from the grounding wire of the main circuit of the secondary circuit of the power system to be tested;

Step 2: Comparing the difference between the second current and the first current with a preset threshold, if the difference is within the preset threshold, it is determined that there are many point grounding;

Step 3. The clamp meter detects the grounding current of the branch circuit from the grounding wire of each branch circuit of the secondary circuit of the power system to be tested. According to the difference between the grounding current of the branch circuit and the first current, determine the specific grounding point of the multi-point grounding. Location.

As a further preferred solution of the present invention, in the third step, each grounding point is located according to the topology structure of the neutral line network of the secondary circuit.

Compared with the prior art, the present invention adopts the above technical scheme and has the following technical effects:

1. Through the magnitude of the grounding loop current, it can be judged whether there is a multi-point grounding fault in the neutral point of the secondary public loop, which is simple and convenient, and the judgment speed is fast.

2. It can display the specific size and waveform of signal current, secondary public loop current and other loop currents.

3. Direction display function, when the detector detects that the system has multi-point grounding, it will display the search direction of the ground fault point.

4. The size of the signal current can be adjusted. Depending on the site conditions, different signal current selections can be made to facilitate the location of the fault point. The detection current signal is generated based on the principle of node shunting, which is more accurate and has the function of realizing a high-precision ammeter.

Description of drawings

Fig. 1 is the connection schematic diagram of system structure module of the present invention;

Fig. 2 is a schematic diagram of the electrical structure connection of the detection current generator in the present invention;

Figure 3 is a schematic diagram of the working principle of judging the system's multi-point grounding;

Fig. 4 is a schematic diagram of a multi-point grounding detection circuit for a voltage secondary circuit neutral line network in a specific embodiment;

Wherein, R1 to R13 are the first to the thirteenth resistors respectively, P1.0 to P1.3 are the first to the fourth CPU pins respectively, and A1 and A2 are the first and the second power amplifiers respectively.

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

Below in conjunction with accompanying drawing, technical scheme of the present invention is described in further detail:

In a specific embodiment of the present invention, taking the multi-point grounding of the neutral line network of the voltage secondary circuit as an example, the schematic diagram of the detection circuit is shown in FIG. 4 : this figure shows the schematic diagram of the multi-point grounding detection. In this figure, A, B, C, and D are several contacts in a branch of the neutral network, r1, r2, and r3 are the resistances of the three wires in the branch, D is the permanent grounding point, and r is Ground the resistor at the second ground point. Normally, the neutral wires of the substation voltage secondary circuit form an interconnected network, which is grounded at one point in the control room. When there is one and only one grounding point in the neutral network, a current is injected from any point of the neutral network to the ground. According to Kirchhoff's current law, the current flowing into the permanent grounding point should be the same as the value of the injected current , if there is a difference, it means that there is a parasitic ground point somewhere in the middle (that is, a ground point other than the permanent ground point) causing the shunt. Based on this principle, the parasitic grounding point can be found by detecting the injection current distribution of the relevant neutral line loop according to the neutral line network structure.

For example: a small current I is injected from point A to the ground (grounding point). Under normal circumstances (single point grounding), the currents flowing through the grounding wire segment AB, BC segment and CD segment are equal to the injected current I. But there is a grounding point C other than the permanent grounding point D in the branch. In this case, the grounding resistance r existing between C and the ground will act as a shunt, so that the current flowing through the CD section of the grounding wire must be smaller than the injected current I. Therefore, as long as the current flowing through the AB, BC, and CD segments is detected and compared with the injected current, the non-permanent grounding point can be found.

The connection schematic diagram of the system structure module of the present invention is shown in Figure 1, and the neutral point multi-point grounding detection device based on high-precision detection current includes an analyzer, a detector and a clamp meter, and the analyzer and the clamp meter are connected When the fault analysis module is jointly formed, the detector and the clamp meter are connected together to form a fault location module, and the analyzer includes a first digital-to-analog conversion module, a signal analysis module, a signal control module, a detection current generator and a first display module; the clamp meter is connected to the bus bar and the grounding wire of the secondary circuit main circuit of the power system to be tested, and the output end of the clamp meter passes through the first analog-to-digital conversion module and the signal analysis module successively and then accesses the signal control module. The output ends of the signal control module are respectively connected to the detection current generator and the first display module, and the output ends of the detection current generator are connected to the busbar of the main circuit of the secondary circuit of the power system to be tested; the detector includes a filter module, the second digital-to-analog conversion module, the signal processing module, the fault analysis and location module, the sound and light alarm module and the second display module; The output end passes through the filter module, the second digital-to-analog conversion module, and the signal processing module in turn, and then connects to the fault analysis and location module. The output ends of the fault analysis and location module are respectively connected to the sound and light alarm module and the second display module.

In a specific embodiment of the present invention, the analyzer uses AC220V commercial power as the working power supply, and one end of the power cord is connected to the power interface of the analyzer, and the other end is connected to the power socket; the clamp meter and the signal wire are connected to the analyzer , Use the red clip of the signal line to connect to the terminal block, and the black clip to the ground point, and clamp the clamp connected to the analyzer to the public circuit and signal line. Confirm that all wires are connected correctly, turn on the power switch of the analyzer, and the analyzer will apply a low frequency and small current signal suitable for system detection. Adaptively output signals according to different grounding degrees, the analyzer will automatically calculate the signal data, when there is only one grounding point in the public circuit, the LCD screen will display the signal current, public circuit current, other circuit shunt current, and the grounding method is Single-point or multi-point grounding.

The detector is powered by 4 AA batteries. If there are multiple ground faults in the system to be detected, use the detector to locate the ground fault point. When using the detector, first remove the clamp meter from the analyzer, connect it to the detector, pay attention to the docking of the plug, beware of misalignment, keep the analysis signal mode unchanged, and the power is on; put 4 AA batteries into the detector battery After confirming that all operations are correct, turn on the power switch of the detector; the power indicator light of the detector is on, clamp the meter to the ground wire under test, press the "multi-point grounding" function, and then press the "test" button to perform grounding detection.

In the present invention, the electrical structure connection diagram of the detection current generator is shown in Figure 2. The specific circuit structure of the detection current generator includes first to thirteenth resistors, first to fourth switches, first, second Power amplifier; the input end of the circuit is connected to the first resistor and one end of the second resistor respectively, the other end of the first resistor is connected to the first input end of the first switch, and the other end of the second resistor is respectively connected to the first switch The second input end of the third resistor, the second input end of the second switch, one end of the fourth resistor, the second input end of the third switch, one end of the fifth resistor, the second input end of the fourth switch The other end of the third resistor is connected with the first input end of the second switch, the other end of the fourth resistor is connected with the first input end of the third switch, the other end of the fifth resistor is connected with the fourth switch The first input ends are connected; the first output ends of the first to fourth switches are respectively connected to the first to fourth CPU pins, and the second output ends of the first to fourth switches are respectively connected to one end of the tenth resistor, the tenth One end of the first resistor, one end of the twelfth resistor, and one end of the thirteenth resistor are connected; the other end of the tenth resistor is connected with the other end of the eleventh resistor, the other end of the twelfth resistor, and the thirteenth resistor The other end, one end of the ninth resistor, and the positive input end of the first amplifier are connected, the other end of the ninth resistor is connected to the negative input end of the first amplifier and grounded, and the output end of the first amplifier is connected to one end of the sixth resistor The other end of the sixth resistor is respectively connected to one end of the eighth resistor and the positive input end of the second amplifier, the negative input end of the second amplifier is grounded through the seventh resistor, and the output end of the second amplifier is connected to the eighth resistor The other end is connected as the output end of the circuit.

P1.0, P1.1, P1.2, and P1.3 are CPU control pins, switches 1, 2, 3, and 4 are control switches, and the CPU pins output control signals to control the switch state.

According to the node shunt principle, when a switch is in the open state, the 5v DC voltage will produce a voltage drop in the corresponding output resistance (62Ω, 120Ω, 240Ω, 480Ω). According to Ohm’s law, the corresponding output current (10mA, 20mA, 40mA, 80mA). When it is necessary to generate a signal current of 150mA, only the corresponding control switch needs to be in the open state.

The schematic diagram of the working principle of judging the multi-point grounding of the system is shown in Figure 3. The device analyzer will apply a low-frequency DC current signal to the public circuit system under test. When single-point grounding, the current signal can only flow through the N600 grounding wire. The magnitude of the current is equal to the magnitude of the applied signal source; when there is a multi-point ground fault, the current of the signal source will flow through other grounding wires besides the N600 grounding wire, so through the test of the known signal source and the N600 grounding wire The comparison of the signal size can realize the judgment of multi-point grounding or not.

As shown in Figure 3, when the system is single-electric grounding, C and D are disconnected, I1=I2, and the current measured by the current clamp meter is 0; when there is multi-point grounding in the system, the multi-point grounding point occurs at C and D, then I1=I2+I3, the current measured by the current clamp meter is I1-I2=I3, and the frequency of this current change is consistent with the frequency of the signal current. According to this characteristic, it can be judged that there is multi-point grounding in the system.

When a multi-point ground fault occurs in the system, the detector can be used to detect other ground wires one by one. For the branch without multi-point ground fault, the signal current cannot be detected, as shown in the figure 1 and 2; For the branch circuit with multi-point ground fault, the detector detects the signal current I3, such as the branch circuit n in the figure, and the location of the ground fault point is realized by analyzing this current.

The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments, and can also be made without departing from the gist of the present invention within the scope of knowledge possessed by those of ordinary skill in the art. Variations. The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this field Those skilled in the art, without departing from the scope of the technical solution of the present invention, may use the technical content disclosed above to make some changes or modify equivalent embodiments with equivalent changes, but as long as they do not depart from the technical solution of the present invention, according to the technical content of the present invention Within the spirit and principles of the present invention, any simple modifications, equivalent replacements and improvements made to the above embodiments still fall within the scope of protection of the technical solutions of the present invention.

Claims (10)

1. The neutral point multi-point grounding detection device based on high-precision detection current is characterized in that: it comprises analyzer, detector and clamp meter, and when said analyzer and clamp meter are connected together, it forms a fault analysis module, and said detector When the meter and the clamp meter are connected together to form a fault location module, wherein, The analyzer includes a first digital-to-analog conversion module, a signal analysis module, a signal control module, a detection current generator and a first display module; the clamp meter is connected to the busbar and the ground wire of the secondary circuit main circuit of the power system to be tested, The output end of the clamp meter is connected to the signal control module after passing through the first analog-to-digital conversion module and the signal analysis module in sequence, and the output ends of the signal control module are respectively connected with the detection current generator and the first display module, and the The output end of the detection current generator is connected to the busbar of the main circuit of the secondary circuit of the power system to be tested; The detector includes a filter module, a second digital-to-analog conversion module, a signal processing module, a fault analysis and positioning module, an acousto-optic alarm module, and a second display module; the clamp meter and the grounding wire of each branch of the secondary circuit of the power system to be tested The output end of the clamp meter is connected to the fault analysis and positioning module after passing through the filter module, the second digital-to-analog conversion module, and the signal processing module in sequence. The output ends of the fault analysis and positioning module are respectively connected with the sound and light alarm module and the second display modules are connected. 2. The neutral point multi-point grounding detection device based on high-precision detection current as claimed in claim 1, characterized in that: the specific circuit structure of the detection current generator includes first to thirteenth resistors, first to thirteenth resistors, The fourth switch, the first and second power amplifiers, wherein, The input terminals of the circuit are respectively connected to the first resistor and one terminal of the second resistor, the other terminal of the first resistor is connected to the first input terminal of the first switch, and the other terminal of the second resistor is respectively connected to the second terminal of the first switch. The input terminal, one terminal of the third resistor, the second input terminal of the second switch, one terminal of the fourth resistor, the second input terminal of the third switch, one terminal of the fifth resistor, and the second input terminal of the fourth switch are connected; The other end of the third resistor is connected to the first input end of the second switch, the other end of the fourth resistor is connected to the first input end of the third switch, and the other end of the fifth resistor is connected to the first input end of the fourth switch. The first output ends of the first to fourth switches are respectively connected to the first to fourth CPU pins, and the second output ends of the first to fourth switches are respectively connected to one end of the tenth resistor and one end of the eleventh resistor. One end, one end of the twelfth resistor, one end of the thirteenth resistor; One end of the ninth resistor is connected to the positive input end of the first amplifier, the other end of the ninth resistor is connected to the negative input end of the first amplifier and grounded, and the output end of the first amplifier is connected to one end of the sixth resistor, The other end of the sixth resistor is connected to one end of the eighth resistor and the positive input end of the second amplifier, the negative input end of the second amplifier is grounded through the seventh resistor, and the output end of the second amplifier is connected to the other end of the eighth resistor. connected as the output of the circuit. 3. The neutral point multi-point grounding detection device based on high-precision detection current according to claim 1 or 2, wherein the detection current generator outputs an alternating current with a frequency less than 1 Hz. 4. The neutral point multi-point grounding detection device based on high-precision detection current as claimed in claim 1 or 2, characterized in that: the detection current generator also includes a limit value element, when the output current exceeds the maximum limit value , the limit element controls the detection current generator to set the maximum limit as the output current. 5. The neutral point multi-point grounding detection device based on high-precision current detection as claimed in claim 2, characterized in that: the sizes of the tenth to thirteenth resistors are 62 ohms, 120 ohms, 240 ohms, 480 ohms. 6. The neutral point multi-point grounding detection device based on high-precision detection current according to claim 2, characterized in that: the input voltage of the detection current generator is 5V. 7. The neutral point multi-point grounding detection device based on high-precision current detection according to claim 2, characterized in that: the second resistor is an adjustable resistor. 8. The neutral point multi-point grounding detection device based on high-precision current detection according to claim 1 or 2, wherein the clamp meter is a high-precision current clamp meter. 9. A detection method of a neutral point multi-point grounding detection device based on high-precision detection current, characterized in that, the specific steps include: Step 1, the detection current generator injects the first current into the bus bar of the main circuit of the secondary circuit of the power system to be tested, and the clamp meter detects the second current from the grounding wire of the main circuit of the secondary circuit of the power system to be tested; Step 2: Comparing the difference between the second current and the first current with a preset threshold, if the difference is within the preset threshold, it is determined that there are many point grounding; Step 3. The clamp meter detects the grounding current of the branch circuit from the grounding wire of each branch circuit of the secondary circuit of the power system to be tested. According to the difference between the grounding current of the branch circuit and the first current, determine the specific grounding point of the multi-point grounding. Location. 10. The detection method of a neutral point multi-point grounding detection device based on high-precision detection current as claimed in claim 8, characterized in that: in said step 3, according to the topology structure of the neutral line network of the secondary circuit Locate each ground point.