CN103605041A - Non-contact multi-point grounding detection method and system for secondary circuit of current transformer - Google Patents

Abstract

The invention relates to a non-contact current transformer secondary circuit multi-point grounding detection method and its system. By applying a changing magnetic field in the neutral line of the secondary circuit, based on Faraday's law of electromagnetic induction, it is possible to determine the grounding of the neutral line. Whether there is current generation, only when there are two points grounded in the secondary circuit, the current will be generated in the neutral line, if only one point of the circuit is grounded, no current will be formed; the device includes a device for applying a force perpendicular to the neutral line to the neutral line The signal injection system for the changing magnetic field of the neutral line, the signal acquisition device for collecting the neutral line current, and the data processing and grounding criterion system for judging whether it is multi-site wiring. The invention can be conveniently used in substations to check the multi-point grounding of the secondary circuit of the current transformer, and effectively detect whether the secondary circuit of the current transformer is multi-point grounded under the premise that the normal operation of the protection device is not affected.

Description

Non-contact current transformer secondary circuit multi-point grounding detection method and system

technical field

The invention relates to a non-contact method and system for detecting the multi-point grounding of a secondary circuit of a current transformer of a substation, belonging to the technical field of electric power automation.

Background technique

In the power system, the secondary circuit plays a very important role in ensuring the safe and stable operation of the system. In the normal operation mode of the system, in order to ensure the safety of people and equipment, "Eighteen Major Power Grid Anti-Accident Measures of the State Grid Corporation", " The Electric Work Site Safety Regulations stipulates that an electrical connection of the secondary circuit of the current transformer must have a reliable grounding point. At the same time, in order to ensure the correct operation of relay protection and safety automatic devices, only one grounding point is required in the current loop. However, since the current secondary circuit of the substation is often connected to multiple devices and has a wide range of extension, often due to human wiring errors or secondary circuit insulation aging, there are multiple grounding points in an electrically connected current secondary circuit, and multi-point grounding causes Accidents of busbar protection, main transformer protection, and line protection incorrect action occurred frequently.

There are two situations for multi-point grounding of the secondary circuit of the current transformer: 1) multi-point grounding of the neutral line; 2) multi-point grounding on both sides of the protection device, multi-point grounding method (as shown in Figure 1).

As shown in Figure 1, R1, R2, and R3 are the equivalent resistances of the ABC three-phase sampling circuit of the protection device respectively. Under normal circumstances, there is one and only one grounding point of the TA secondary circuit, which is at the root of the CT or in the protection room. In Figure 1, there is a wiring method in which the grounding point is connected to the protection screen. ① and ② respectively simulate the two grounding situations of the neutral line multi-point grounding of the current loop and the multi-point grounding on both sides of the protection.

For the case where the neutral line is grounded at two points, since the grounding network of the substation is not the actual equipotential surface, a certain potential difference will appear at different points, and the potential difference will enter the secondary circuit of the current transformer, especially when there is a short-circuit current or When the lightning strikes the current, the potential of different points on the cable shielding layer is different, so that the current flows through the shielding layer, which may burn the shielding layer and cause interference to the secondary circuit.

For the case of multiple grounding points on both sides of the protection device, if the grounding network of the substation is an equipotential network (that is, there is no potential difference between the grounding points), the parallel circuit formed by the two grounding points and the grounding network will cause the secondary circuit current to shunt, making the flow The sampling loop current of the over-protection device is greatly reduced. If the grounding network of the substation is a non-equal potential network, and there is a potential difference between the grounding points on both sides of the protection device, the current caused by the potential difference will flow through the protection device, making the sampling of the protection device incorrect.

The above analysis shows that the multi-point grounding of the secondary circuit of the current transformer will affect the sampling of the protection device or the safety automatic device, and then affect the action behavior of the protection device.

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. Related articles have also proposed other detection methods for multi-point grounding of current loops, such as a method of using low-voltage AC signal injection to detect multi-point grounding of loops. This method is simple and effective, and can quickly and accurately detect multi-point grounding phenomena, but it needs to be connected in series with a low-voltage signal generator in the original circuit, which is not suitable for large-scale promotion, especially for substations that have already been put into operation. Therefore, it is necessary to study a non-contact multi-point grounding detection method that does not change the original current loop.

Contents of the invention

In view of the deficiencies in the prior art, the purpose of the present invention is to provide a non-contact substation current transformer secondary circuit multi-point grounding detection method based on Faraday's law of electromagnetic induction, and to construct a non-contact current loop multi-point grounding detection system , using this detection method can effectively detect whether the secondary circuit of the current transformer is multi-point grounded under the premise of ensuring that the normal operation of the protection device is not affected.

In order to achieve the above object, the present invention is achieved through the following technical solutions:

A non-contact current transformer secondary circuit multi-point grounding detection method, based on Faraday's law of electromagnetic induction, the method is: (1) non-contact signal injection; apply a vertical and The changing magnetic field of the neutral wire causes changing magnetic flux in the neutral wire to realize non-contact signal injection;

(2) Judging whether there is current on the neutral line, if there is current, it is multi-point grounding; otherwise, it is one-point grounding.

In the above step (1), a signal injection system is installed on the neutral line, and a changing magnetic field perpendicular to the neutral line is generated through the signal injection system.

The signal injection system includes a pliers core that can be opened and closed, a coil disposed on the pliers core, and an AC current source connected to the coil. The coil is connected to an AC current source, and the alternating current passing through the coil will excite alternating The magnetic flux, the pliers iron core is vertically clamped on the neutral line, so that the neutral line is applied with a magnetic field that varies vertically with the neutral line.

In the above step (1), before clamping the iron core of the pliers vertically on the neutral line, confirm that the signal output of the AC current source is zero, and the frequency is set to a value M, 0<M≤50 Hz; then clamp the iron core vertically On the neutral line, gradually increase the output current of the AC current source to generate magnetic flux in the neutral line.

In the above step (2), it is used to judge whether the current is generated on the neutral line by observing the change of the current value of the current acquisition device. If the current value is always zero, further increase the output current of the AC current source to a value of N, where , 0<N<5 amperes, at the same time increase the current frequency to a value of L, where L≤150Hz, if the current is not detected, it is judged that there is no multi-point grounding phenomenon in the secondary circuit;

If the current acquisition device detects an increase in current as the output current of the current source increases, then continue to increase the output current of the AC current source until the current value measured by the data processing and multi-point grounding criterion system is greater than or equal to 10mA . After that, Use data processing and multi-point grounding criterion system to detect that the measured current frequency should be M ( on the contrary, re-test) . At this time, gradually reduce the output current of the AC current source, and increase the value of the current frequency to 2M at the same time. Then use data processing and multi-point grounding criterion system to detect that the value of the measured current frequency should be 2M ( on the contrary, re-test), then it is determined that there is a multi-point grounding phenomenon in the loop, and through data processing and multi-point grounding criterion system Send out a warning signal.

Preferably, the signal acquisition device actually adopts a high-precision current clamp meter, which is easy to use and improves the accuracy of acquisition.

A non-contact current transformer secondary circuit multi-point grounding detection system, which includes:

The signal injection system is set on the neutral line of the secondary circuit of the current transformer in the substation, and is used to apply the changing magnetic field of the vertical and neutral lines to the neutral line;

The signal acquisition device is set on the neutral line of the secondary circuit of the current transformer in the substation, and is used to collect whether current is generated on the neutral line;

The data processing and multi-point grounding criterion system is connected with the signal acquisition device, used to receive the acquisition information sent by the signal acquisition device, and perform data analysis and multi-point grounding discrimination according to the acquisition information, according to the criterion logic set in the system Determine whether multi-point grounding occurs with the fixed value, and send an alarm signal to determine whether multi-point grounding occurs in the secondary circuit of the current transformer.

Further, the data processing and multi-point grounding criterion system judges whether multi-point grounding occurs according to the criterion logic and fixed value set in the system, and sends out an alarm signal if it is multi-point grounding.

According to the criterion logic and fixed value judgment set in the data processing and multi-point grounding criterion system, that is, when the output current of the AC current source is 5A, and the output current frequency increases to 150Hz at the same time, if the data processing and multi-point grounding criterion If the neutral wire current value measured by the system detection is still less than 10mA, it is judged that there is no multi-point grounding. If the value of the neutral wire current measured by the data processing and multi-point grounding criterion system detection reaches If it exceeds 10mA, it is judged that multi-point grounding has occurred, and an alarm signal is sent; the data processing and multi-point grounding criterion function is exactly the controller of the function of current collection and current size discrimination, and its realization is a prior art.

The signal injection system includes a pliers core that can be opened and closed, a coil disposed on the pliers core, and an AC current source connected to the coil. The coil is connected to an AC current source, and the alternating current passing through the coil will excite alternating The magnetic flux, the pliers iron core is vertically clamped on the neutral line, so that the neutral line is applied with a magnetic field that varies vertically with the neutral line.

As a preference, the AC current source is a single-phase relay protection tester.

，若回路只有一点接地，不会形成电流，可方便用于变电站检查电流互感器二次回路多点接地的判断，保证对保护装置正常运行不产生影响的前提下，有效地检测出电流互感器二次回路是否发生多点接地。 The construction of the multi-point grounding detection method and detection platform of the non-contact current secondary circuit of the present invention, by applying a changing magnetic field in the neutral line of the secondary circuit, based on Faraday's law of electromagnetic induction, determines whether there is current in the neutral line, Only when there are two points grounded in the secondary circuit, the current will flow in the neutral wire

, if only one point of the circuit is grounded, no current will be formed. It can be conveniently used in the substation to check the multi-point grounding of the secondary circuit of the current transformer, and effectively detect the current transformer without affecting the normal operation of the protection device. Whether there is multi-point grounding in the secondary circuit.

Description of drawings

The present invention is described in detail below in conjunction with accompanying drawing and specific embodiment;

Fig. 1 is the multi-point grounding schematic diagram of existing current transformer;

Fig. 2 is the schematic diagram of neutral line multi-point grounding of the present invention;

Fig. 3 is a schematic diagram of multi-point grounding on both sides of the protection of the present invention;

Fig. 4 is the multi-point grounding detection system of the non-contact current secondary circuit of the present invention;

Fig. 5 is the equivalent circuit of the multi-point grounding detection system of the non-contact current secondary circuit of the present invention;

Fig. 6 is a flow chart of multi-point grounding detection of the non-contact current secondary circuit of the present invention.

Detailed ways

In order to make the technical means, creative features, goals and effects achieved by the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

Referring to Fig. 2-Fig. 6, the non-contact current secondary circuit multi-point grounding detection method of the present embodiment, and constructs the non-contact current circuit multi-point grounding detection system; it is Faraday's law of electromagnetic induction, in the current transformer two Apply a changing magnetic field perpendicular to the neutral line in the neutral line of the secondary circuit, so that a changing magnetic flux is generated in the neutral line to realize non-contact signal injection; then judge whether a current is generated on the neutral line, and if there is a current, it is multi-point Grounding; otherwise, it is one-point grounding. The concrete implementation of this embodiment is as follows:

1. Non-contact signal injection method based on electromagnetic induction;

Referring to Figure 2 and Figure 3, according to Faraday's law of electromagnetic induction, the change of magnetic flux in the wire loop will generate an induced electromotive force in the wire loop, and the faster the magnetic flux changes, the greater the induced electromotive force.

 ，实现交流信号注入。式中，

为感应电动势，

为变化的磁通量，

 为回路等值电阻，

为回路电流。 The secondary multi-point grounding loop of the current transformer TA can be regarded as a wire loop, and a changing magnetic field is applied in the loop, which will generate an induced electromotive force

, to achieve AC signal injection. In the formula,

is the induced electromotive force,

is the changing magnetic flux,

is the equivalent resistance of the loop,

is the loop current.

，若回路只有一点接地，不会形成电流

，可以据此判断回路是否存在多点接地。 In Fig. 2 and Fig. 3, it shows a schematic diagram of a method for realizing signal injection by using Faraday's law of electromagnetic induction under two kinds of multi-point grounding conditions of the TA secondary circuit. It can be seen from the figure that only when there are two points grounded in the secondary circuit, the current will be generated in the neutral line

, if only one point of the loop is grounded, no current will form

, it can be judged whether there is multi-point grounding in the circuit.

Applying a changing magnetic field in the neutral line of the secondary circuit can realize non-contact signal injection. Based on the working principle of the power transformer, the alternating current of the primary coil will excite the alternating magnetic flux in the iron core, and the iron core of the current transformer is made into a pliers that can be opened and closed, that is, a pliers-type iron core is formed, and the pliers-type iron core The core is clamped on the neutral wire of the TA secondary circuit, which can generate a changing magnetic flux in the neutral wire, thereby realizing non-contact signal injection in the multi-point grounding circuit.

2. Implementation method of non-contact multi-point grounding detection;

As shown in Figure 4, realizing multi-point grounding circuit non-contact signal source injection is the premise of multi-point grounding detection. This embodiment provides an electromagnetic induction non-contact current loop multi-point grounding detection system, including three parts : Signal injection system, signal acquisition device, data processing and grounding criterion system.

，该电流回路作为钳式铁芯的原边线圈缠绕n圈，钳式铁芯在原边线圈电流作用下产生稳定变化的磁通量

。TA二次回路中性线与其他接地点构成闭合回路，作为钳式铁芯的副边线圈，根据法拉第电磁感应定律，副边线圈中会产生感应电动势，并流过电流

。 The signal injection system consists of a clamp-type iron core and an AC current source. A coil is arranged on the clamp-type iron core. The coil and the AC current source pass through the coil. The AC current source in this embodiment uses a single-phase relay protection tester. This AC current source produces a current with a constant and adjustable frequency

, the current loop is wound around n turns as the primary coil of the clamp-type iron core, and the clamp-type iron core produces a stable and changing magnetic flux under the action of the primary coil current

. The neutral line of the TA secondary circuit and other grounding points form a closed loop, which is used as the secondary coil of the clamp iron core. According to Faraday's law of electromagnetic induction, an induced electromotive force will be generated in the secondary coil, and current will flow

.

，并送入数据处理及多点接地判据系统进行数据分析和多点接地判别，根据系统中设置的判据逻辑和定值判别是否发生多点接地，若发生多点接地则发出告警信号。 In this implementation, the signal acquisition device uses a high-precision current clamp meter, which collects the current in the neutral line

, and sent to the data processing and multi-point grounding criterion system for data analysis and multi-point grounding discrimination, according to the criterion logic and setting value set in the system to determine whether multi-point grounding occurs, and if multi-point grounding occurs, an alarm signal will be issued.

In this embodiment, according to the criterion logic and fixed value discrimination set in the data processing and multi-point grounding criterion system, the discrimination method is as follows: when the output current of the AC current source is 5A, and the output current frequency increases to 150Hz at the same time, If the measured neutral line current value detected by the data processing and multi-point grounding criterion system is still less than 10mA, it is judged that multi-point grounding has not occurred. If the output current and current frequency of the AC current source increase, the data processing and multi-point The point grounding criterion system detects that the measured neutral line current value reaches 10mA or above, then it is judged that multi-point grounding has occurred and an alarm signal is issued; the functions of data processing and multi-point grounding criterion are current collection and current size discrimination The controller of the function, its realization is prior art, does not now carry on the burden.

The clamp-type iron core of the whole set of non-contact multi-point grounding detection system needs to be conveniently clamped on the neutral wire of the current loop, so that the magnetic field generated by the AC current source in the clamp-type iron core can pass through the neutral wire, and has good magnetic properties. The data processing and grounding criterion system analyzes and calculates the collected secondary current (neutral line current), and judges whether there is a multi-point grounding phenomenon according to the set current value criterion.

3. Theoretical analysis of multi-point grounding detection method

Establish a corresponding mathematical model to strictly analyze the reliability and feasibility of the non-contact multi-point grounding detection method. The grounding loop resistance, the excitation characteristics of the iron core, the position of the clamp iron core and the neutral wire will all affect the final detection result .

The working principle of the non-contact multi-point grounding detection system is similar to that of an ideal transformer. The clamp-type iron core can be regarded as the excitation core of the ideal transformer, and the current loop wound by the AC current source is regarded as the primary coil, and the neutral line and other grounding points form The grounding circuit of the circuit is regarded as the secondary side coil, and its equivalent circuit is shown in Figure 4.

，即原副边电流比值与线圈匝数成反比。 According to the working principle of the transformer, when the iron core loss and magnetic flux leakage are not considered,

, that is, the ratio of the primary and secondary currents is inversely proportional to the number of coil turns.

Although the equivalent diagram of the non-contact multi-point grounding detection system shown in Figure 4 is similar to the transformer structure, the above formula cannot be used. The main reasons are: 1) The clamp-type iron core is not a completely closed iron core, and its magnetic permeability is worse than that of the transformer iron core; 2) The secondary circuit formed by the neutral line grounding point and other grounding points may have a large area. The side coil is greatly disturbed by the space magnetic field.

，

为铁芯中主磁通的有效值，假设钳式铁芯垂直夹在中性线上，则副边线圈中感应电压为： The secondary current of the non-contact multi-point grounding detection system can be calculated according to Faraday's law of electromagnetic induction. The secondary coil is regarded as a wire loop plane, and the primary current generates a changing magnetic flux in the iron core. , an induced electromotive force will be generated in the secondary coil . set up

,

is the effective value of the main magnetic flux in the iron core, assuming that the clamp-type iron core is clamped vertically on the neutral line, the induced voltage in the secondary coil is:

(1)

The secondary coil current is:

          （2）

(2)

，其中

为铁芯的磁导率，

为原边线圈中电流，

为原边圆线圈的半径。设

， Magnetic flux in the core It is generated by the primary current-carrying coil. For the convenience of analysis, it is assumed that the primary coil is a circular coil, and the magnetic field strength of the current-carrying circular coil at the center of the circle is

,in

is the magnetic permeability of the core,

is the current in the primary coil,

is the radius of the primary circle. set up

,

        （3） but

(3)

in is the cross-sectional area of the clamp core, is the effective value of the primary current, and substituting formula (3) into (2), the current of the secondary coil can be obtained as:

      （4）

(4)

大小与铁芯磁导率

、原边电流频率

、原边电流有效值

、铁芯截面积

成正比，而与接地回路电阻

和原边线圈半径成反比。当TA二次回路只有一点接地时，，

；多点接地时，

，检测

大小即可判别是否存在多点接地现象。 It can be seen from formula (4) that when multi-point grounding, the secondary coil is the current in the neutral line loop

Size and Core Permeability

, primary current frequency

, RMS value of primary current

, core cross-sectional area

proportional to the ground loop resistance

and primary coil radius Inversely proportional. When only one point of TA secondary circuit is grounded, ,

; When multi-point grounding,

, detect

The size can determine whether there is a multi-point grounding phenomenon.

4. The specific implementation method of non-contact current transformer secondary circuit multi-point grounding detection is as follows:

When there is multi-point grounding in the loop, through the method of non-contact signal injection, there is indeed current in the neutral line, and the basic method of non-contact current loop multi-point grounding detection is to detect the presence or absence of current in the neutral line loop Determine whether there is multi-point grounding.

The method of judging multi-point grounding is simple, but it is still necessary to consider how to determine the current setting value as the criterion in actual operation. Comprehensively considering the accuracy of the current clamp meter and the impact on the protection device, the current setting value is set to 10mA in this embodiment. At present, most high-precision current clamp meters can accurately measure the current of 10mA, and at the same time, the current will not have a great impact on the protection sampling.

过大引起保护装置误动。经研究，如图5所示，非接触式电流互感器二次回路多点接地检测方法，具体步骤如下： Since it is not known whether there are multiple points of grounding in the loop before the test, and the resistance of the grounding loop is unknown, it is not possible to directly inject a large current and high frequency signal, in case there are multiple points of grounding and the loop resistance is small,

If it is too large, it will cause the protection device to malfunction. After research, as shown in Figure 5, the non-contact current transformer secondary circuit multi-point grounding detection method, the specific steps are as follows:

(1) Before clamping the iron core of the pliers vertically on the neutral wire, confirm that the signal output of the AC current source is 0, and the frequency is set to a value of 50Hz;

变化；若

=0，即电流数值一直为零，进一步增加交流电流源的输出电流至数值为5A，同时增加电流频率最高至150Hz,若仍未检测到电流，即中性线电流仍为零，则判断二次回路中不存在多点接地现象；若

，则进入步骤（3）。 (2) Then clamp the pliers iron core vertically on the neutral wire, gradually increase the output current of the AC current source to generate magnetic flux in the neutral wire, and always pay attention to the current clamp meter clamped on the neutral wire, that is, the signal acquisition device The current value of

change; if

=0, that is, the current value is always zero, further increase the output current of the AC current source to a value of 5A, and at the same time increase the current frequency up to 150Hz, if the current is still not detected, that is, the neutral current is still zero, then judge two There is no multi-point grounding phenomenon in the secondary circuit; if

, then go to step (3).

频率应为50Hz；第一判断可基本判定回路存在多点接地现象。 (3) If the current acquisition device detects an increase in current as the output current of the current source increases, continue to increase the output current of the AC current source until the value is greater than 10MA. At this time, use data processing and multi-point grounding criterion system to detect the measured current

The frequency should be 50Hz; the first judgment can basically determine that there is a multi-point grounding phenomenon in the circuit.

不大于20mA），最后再利用数据处理及多点接地判据系统检测所检测频率应为100Hz（若不是则重新检测），则确定回路存在多点接地现象，并通过数据处理及多点接地判据系统发出告警信号。结合电流幅值判据和频率判据可以确定回路中有多点接地现象存在。 (4) On the basis of the above, appropriately and gradually reduce the output current amplitude of the AC current source, and at the same time increase the output current frequency value to 100Hz (ensure

not greater than 20mA), and finally detected by data processing and multi-point grounding criterion system detection The frequency should be 100Hz (if not, re-test), then it is determined that there is a multi-point grounding phenomenon in the circuit, and an alarm signal is sent out through data processing and multi-point grounding criterion system. Combining the current amplitude criterion and the frequency criterion, it can be determined that there are multiple grounding points in the circuit.

Application

The non-contact current loop multi-point grounding detection method proposed in this embodiment has been tested and verified in the laboratory. The test shown in Figure 5 is carried out in the laboratory. The current source is provided by a single-phase relay protection tester, and the iron core is The iron core used in the current transformer, the secondary winding adopts the cable circuit with adjustable resistance in series. The feasibility of the above method and the correctness of the theoretical analysis are verified by experiments. The test results show that the use of this detection method can effectively detect whether the secondary circuit of the current transformer has occurred without affecting the normal operation of the protection device. Multi-point grounding can be conveniently used for substation inspection and judgment of multi-point grounding of the secondary circuit of the current transformer.

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Variations and improvements all fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents. the

Claims (9)

1. A non-contact current transformer secondary circuit multi-point grounding detection method, based on Faraday's law of electromagnetic induction, the method is: (1) non-contact signal injection; applied in the neutral line of the current transformer secondary circuit The changing magnetic field perpendicular to the neutral line causes changing magnetic flux in the neutral line to realize non-contact signal injection; (2) Judging whether there is current on the neutral line, if there is current, it is multi-point grounding; otherwise, it is one-point grounding. 2. The non-contact substation current transformer secondary circuit multi-point grounding detection method according to claim 1, characterized in that, in the above step (1), a signal injection system is installed on the neutral line, through which the signal Injection into the system causes it to generate a changing magnetic field perpendicular to the neutral line. 3. The non-contact current transformer secondary circuit multi-point grounding detection method according to claim 2, characterized in that the signal injection system includes a pliers core that can be opened and closed, a coil arranged on the pliers core And the AC current source connected to the coil, the coil is connected to the AC current source, the alternating current passing through the coil will excite the alternating magnetic flux in the iron core, and the iron core of the pliers is vertically clamped on the neutral wire, so that the neutral wire Apply a magnetic field that varies perpendicular to the neutral line. 4. The non-contact current transformer secondary circuit multi-point grounding detection method according to claim 3, characterized in that, in the above step (1), before the pliers iron core is vertically clamped on the neutral line, it is confirmed that the AC The signal output of the current source is zero, the frequency is set to the value M, 0<M≤50 Hz; then clamp the iron core of the pliers vertically on the neutral line, and gradually increase the output current of the AC current source to generate magnetic flux in the neutral line. 5. The non-contact substation current transformer secondary circuit multi-point grounding detection method according to claim 4, characterized in that in the above step (2), the method for judging whether a current is generated on the neutral line is by observing the current Changes in the current value of the acquisition device, if the current value is always zero, further increase the output current of the AC current source to a value of N, where 0<N<5 amperes, and increase the current frequency to a value of L, where L≤ 150Hz, if the current is still not detected, it is judged that there is no multi-point grounding phenomenon in the secondary circuit; If the current acquisition device detects an increase in current as the output current of the current source increases, then continue to increase the output current of the AC current source until the current value measured by the data processing and multi-point grounding criterion system is greater than or equal to 10mA. At this time, Use data processing and multi-point grounding criterion system to detect the measured current frequency as M, then gradually reduce the output current of the AC current source, and increase the current frequency value to 2M at the same time, then use data processing and multi-point grounding to judge According to the system detection, if the value of the measured current frequency is 2M, it is determined that there is a multi-point grounding phenomenon in the circuit, and an alarm signal is sent out through data processing and multi-point grounding criterion system. 6. A non-contact current transformer secondary circuit multi-point grounding detection system, which includes: The signal injection system is set on the neutral line of the secondary circuit of the current transformer in the substation, and is used to apply the changing magnetic field of the vertical and neutral lines to the neutral line; The signal acquisition device is set on the neutral line of the secondary circuit of the current transformer in the substation, and is used to collect whether current is generated on the neutral line; Data processing and multi-point grounding criterion system, connected with the signal acquisition device, used to receive the acquisition information sent by the signal acquisition device, and perform data analysis and multi-point grounding discrimination according to the acquisition information, and judge according to the criterion logic and fixed value Whether there is multi-point grounding in the secondary circuit of the current transformer, if it is multi-point grounding, an alarm signal is issued to judge. 7. The non-contact current transformer secondary circuit multi-point grounding detection system according to claim 6, characterized in that the signal acquisition device actually uses a high-precision current clamp meter. 8. The non-contact current transformer secondary circuit multi-point grounding detection system according to claim 6, characterized in that, the signal injection system includes a pliers core that can be opened and closed, a coil arranged on the pliers core And the AC current source connected to the coil, the coil is connected to the AC current source, the alternating current passing through the coil will excite the alternating magnetic flux in the iron core, and the iron core of the pliers is vertically clamped on the neutral wire, so that the neutral wire Apply a magnetic field that varies vertically and neutrally. 9 . The non-contact current transformer secondary circuit multi-point grounding detection system according to claim 6 , wherein the AC current source is a single-phase relay protection tester.

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