Leakage protection method for mining frequency converter

Abstract

The invention provides an earth leakage protection method for a mining frequency converter, which comprises the following steps of: S1, connecting three rectifier tubes to three phases of a power grid, and connecting the other ends of the rectifier tubes together and grounding; s2, monitoring the ground insulation condition of an underground three-phase three-wire system power supply system with the voltage level of 3.3 kV and below; and S3, current signals are collected, once the current rises to a set value, a protection device acts, and leakage protection is achieved. Protection can be achieved without an additional direct-current power source. Meanwhile, distribution parameters on the two sides of the frequency converter are considered, and when different types of electric leakage faults occur on the input side and the output side, the insulation resistance value can be accurately measured. After an electric leakage fault occurs, the detection direct current can be instantaneously increased, and the action is rapid.

Description

Technical Field

[0001] The invention belongs to the technical field of leakage protection of mine frequency converters, and in particular relates to a leakage protection method for mine frequency converters. Background Art

[0002] In recent years, frequency converters have been increasingly used in underground power supply systems. The rectifier and inverter circuits inside the frequency converter contain a large number of nonlinear power electronic devices, which will generate high-frequency pulses and harmonics when working, causing three-phase asymmetry, so that the system will have zero-sequence components even when there is no leakage, resulting in the original insulation fault line selection method based on the zero-sequence component principle no longer being applicable. In addition, the leakage protection method that uses a three-phase reactor to form an additional DC detection power supply that is considered to be the neutral point will fail when applied to a mine power supply system containing a frequency converter, and even cause a serious accident in which the mine cable has caught fire due to leakage faults but has not tripped.

[0003] The existing secondary leakage protection devices of mobile substations that power mine frequency converters are difficult to operate accurately and quickly, which poses a major safety hazard and cannot meet the safety and reliability requirements of the underground power supply system in the Coal Mine Safety Regulations. The existence of frequency converters has brought new challenges to selective leakage protection. In order to ensure the safety of workers, the safety of power supply lines and electrical equipment, and the normal operation of enterprises, how to reliably implement leakage protection of underground power supply systems with frequency converters has important theoretical and practical significance. Summary of the invention

[0004] The purpose of the present invention is to provide a method for leakage protection of a mine frequency converter, so as to realize ground insulation monitoring and three-phase, two-phase and single-phase leakage protection of a three-phase three-wire power supply system with a voltage level of 3300V or below in a mine.

[0005] The technical solution of the present invention is as follows:

[0006] A mine frequency converter leakage protection method, comprising:

[0007] S1 connects the three rectifier tubes to the three phases of the power grid, and the other ends are connected together and grounded;

[0008] S2 monitors the insulation of the three-phase three-wire power supply system with a voltage level of 3.3kV or below in the mine;

[0009] S3 collects current signals. Once the current rises to the set value, the protection device will be activated to achieve leakage protection.

[0010] Furthermore, the S1 is specifically:

[0011] Connect the three rectifier tubes to the A, B, and C phases of the power grid respectively, and connect the other ends together and grounded through a load resistor.

[0012] Furthermore, the S2 is specifically:

[0013] Calculate the equivalent steady-state effective value of the electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0014] Calculate the transient effective value of electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0015] Analyze the transient spectrum of single-phase leakage current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0016] Monitor the three-phase insulation resistance, two-phase insulation resistance and single-phase insulation resistance of the inverter input and output sides of the mine 3.3kV and below power supply system;

[0017] The waveform shape of the sampled voltage is used to determine whether it is a single-phase insulation drop, a two-phase insulation drop or a three-phase insulation drop;

[0018] Verify the single-phase leakage protection method that is not affected by the inverter output frequency, distributed capacitance, and carrier frequency. Build a simulation model, change the inverter output frequency, distributed capacitance, and carrier frequency, and simulate the leakage on the input and output sides of the inverter.

[0019] Furthermore, the calculation of the equivalent steady-state effective value of the electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below is specifically:

[0020] When a single-phase grounding fault or electric shock accident occurs in the variable frequency power supply system, the ground distribution parameters of the input and output sides of the inverter are considered, and the electric shock occurs on the input side of the inverter and on the output side of the inverter respectively. The equivalent circuit diagram is drawn according to the principle of the PLM algorithm; each time period ΔT n The effective value of the electric shock current I rms(n) The size is:

[0021]

[0022] Assume that within one power frequency cycle, the PWM control signal is divided into n time periods; the effective value of the electric shock current within one power frequency cycle is I R for:

[0023]

[0024] in,

[0025] Furthermore, the calculation of the transient effective value of the electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below is specifically:

[0026] Based on the inverter equivalent voltage source model, the equivalent circuit diagram at this time is drawn, and the waveform of the human electric shock current at this time is calculated; under the same parameters, MATLAB / Simulink is used for simulation to obtain the simulation waveform of the human electric shock current, and the differential equations are solved to obtain the transient effective value of the human electric shock current.

[0027] Furthermore, the analysis of the transient spectrum of single-phase leakage current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below is specifically as follows:

[0028] Matlab is used to simulate the leakage current corresponding to the spectrum analysis diagram when a single-phase leakage of 50kΩ occurs on the output side, and the spectrum analysis diagram is used to further analyze the characteristics of the leakage current.

[0029] Furthermore, the monitoring of the three-phase to ground insulation resistance, two-phase to ground insulation resistance and single-phase to ground insulation resistance of the inverter input and output sides of the mine 3.3kV and below power supply system includes:

[0030] Monitor the DC component of the current:

[0031]

[0032] In the formula, r Σ =r A / / r B / / r C , E is the average value of the voltage after three-phase half-wave rectification;

[0033]

[0034] Among them, E is a fixed value, R y is a fixed value, I y Direct reflection ∑ As long as the insulation of the power supply system decreases, whether it is single-phase, two-phase or three-phase leakage, it is equivalent to r ∑ Changes in value;

[0035] By detecting the flow through R y The size of the DC current is compared with the set value to determine whether the power grid is in a leakage fault.

[0036] Further, judging whether the single-phase insulation decreases, the two-phase insulation decreases or the three-phase insulation decreases by sampling the waveform shape of the voltage includes:

[0037] Under different insulation drop conditions, it was observed that the waveform shapes were different when single-phase insulation drop, two-phase insulation drop and three-phase insulation drop occurred. The insulation resistance drop condition was judged by the waveform shape.

[0038] Furthermore, the construction of the simulation model is specifically as follows:

[0039] A simulation model was built. The model used a three-phase power supply module as a 3300V power supply and a motor as a load. The sampling resistance Ry was set to 100kΩ, the distributed capacitance per phase to ground was 0.1μF, the insulation resistance of the cable per phase to ground was 100MΩ, the carrier frequency was 2000Hz, and the inverter output frequency was 50Hz.

[0040] Furthermore, the changing of the inverter output frequency, distributed capacitance, and carrier frequency to simulate the inverter input and output leakage is specifically as follows:

[0041] Change the inverter output frequency and simulate the inverter input and output leakage at 40Hz and 60Hz respectively;

[0042] Change the size of the distributed capacitance on the input and output sides of the inverter and set r A =r B =r C =150kΩ, simulate the leakage on the input and output sides of the inverter;

[0043] Change the size of the inverter carrier frequency, set r A =r B =r C =150kΩ, simulate the leakage on the input and output sides of the inverter.

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] 1) In view of the problems of complex structure and unreliable operation of existing leakage protection devices, the corresponding leakage protection device of the present invention has a simple structure, does not require an additional DC power supply to obtain protection, and has a higher DC detection voltage, which can better reflect the actual insulation level of the power grid.

[0046] 2) In view of the fact that the existing leakage protection method has inaccurate insulation detection after adding the frequency converter, and is prone to false operation and refusal to operate, the leakage protection method of the present invention can accurately measure the insulation resistance value when different types of leakage faults (single-phase, two-phase, three-phase) occur on the input side and the output side while considering the distributed parameters on both sides of the frequency converter.

[0047] 3) In view of the slow action speed of the existing leakage protection method, the leakage protection method of the present invention can make the detected DC current rise instantly after the leakage fault occurs, and the action is fast. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings generally illustrate various embodiments by way of example and not limitation, and together with the description and claims, serve to illustrate the embodiments of the invention. Where appropriate, the same reference numerals are used throughout the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be exhaustive or exclusive embodiments of the present apparatus or method.

[0049] Figure 1 It is a flow chart of the leakage protection method of the mine frequency converter of the present invention;

[0050] Figure 2 This is a schematic diagram of the electric shock principle when the distributed parameters on both sides of the inverter are considered in the present invention;

[0051] Figure 3 It is the PLM model of electric shock on the input side of the frequency converter of the present invention; wherein (a) is an equivalent model, and (b) is a simplified model;

[0052] Figure 4 It is a Laplace transform calculation circuit for electric shock to human body at the input side of the frequency converter of the present invention;

[0053] Figure 5 It is the PLM model of electric shock on the output side of the inverter of the present invention; wherein (a) is an equivalent model and (b) is a simplified model;

[0054] Figure 6 It is a Lagrangian operation circuit for preventing electric shock to human body at the output side of the frequency converter of the present invention;

[0055] Figure 7 This is a visual diagram of electric shock to a person when the parameters of the front and rear ends of the inverter are considered in the present invention;

[0056] Figure 8 This is an equivalent circuit diagram of electric shock to a person when the parameters before and after the inverter are considered in the present invention;

[0057] Fig. 9 The present invention is a human body electric shock current waveform diagram obtained by two methods when considering the ground parameters before and after the inverter; wherein (a) is the calculated waveform, and (b) is the simulated waveform;

[0058] Fig.10 This is a single-phase leakage spectrum analysis diagram at the output side of the present invention;

[0059] Fig.11 1 is a sampling voltage waveform diagram corresponding to different insulation degradation conditions of the present invention; wherein (a) is a single-phase insulation degradation, (b) is a two-phase insulation degradation, and (c) is a three-phase insulation degradation;

[0060] Fig.12 This is a schematic diagram of the leakage protection principle composed of three rectifier tubes of the present invention;

[0061] Fig.13It is the leakage protection equivalent circuit diagram composed of three rectifier tubes of the present invention;

[0062] Fig.14 It is the working principle diagram of the frequency converter of the present invention;

[0063] Fig.15 is the internal topology diagram of the frequency converter of the present invention;

[0064] Fig.16 It is the electrical connection diagram of the sensor of the present invention. DETAILED DESCRIPTION

[0065] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0066] Ginseng Figure 1 As shown, this embodiment provides a method for protecting a mine frequency converter from leakage, including:

[0067] Step 1: Connect the three rectifier tubes V1, V2, and V3 to the A, B, and C phases of the power grid respectively, and connect the other ends together through the load resistor R l0 Grounding;

[0068] Step 2: monitor the insulation of the three-phase three-wire power supply system with a voltage level of 3300V or below in the mine, and consider the distributed parameters on both sides of the inverter to ensure accurate measurement of the insulation resistance value and instantaneous increase of the detection DC current when different types of leakage faults occur on the input side and the output side;

[0069] Step 3: DC current flows through R l0 , earth, grid to ground insulation resistance r A , r B , r C Return to the power supply. If the equivalent resistance decreases, the detection current increases, and the current transformer detects that the current increases to the set value, the protection device is activated to complete the leakage protection.

[0070] Wherein, the step 2 comprises:

[0071] Calculate the equivalent steady-state effective value of the electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0072] Calculate the transient effective value of electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0073] Analyze the transient spectrum of single-phase leakage current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0074] Monitor the three-phase insulation resistance between the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0075] Monitor the insulation resistance between the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0076] Monitor the single-phase insulation resistance between the input and output sides of the inverter of the mine power supply system of 3.3kV and below;

[0077] The waveform shape of the sampled voltage is used to determine whether it is a single-phase insulation drop, a two-phase insulation drop or a three-phase insulation drop;

[0078] Single-phase leakage protection method for the input and output sides of the inverter of the mine 3.3kV and below power supply system, which is not affected by the inverter output frequency;

[0079] Single-phase leakage protection method for the input and output sides of the inverter of the mine 3.3kV and below power supply system without being affected by distributed capacitance;

[0080] A single-phase leakage protection method for the inverter input and output sides of the mine 3.3kV and below power supply system is not affected by the inverter carrier frequency.

[0081] The mine inverter leakage protection method monitors the insulation of the three-phase three-wire power supply system with a voltage level of 3300V and below to the ground, and takes into account the three-phase, two-phase and single-phase leakage protection on the input and output sides. The leakage protection device has a simple structure and can be protected without an additional DC power supply. It has a high DC detection voltage and can better reflect the actual insulation level of the power grid. After a leakage fault occurs, the leakage protection method can make the detected DC current rise instantly, and it acts quickly to quickly respond to leakage faults.

[0082] Example 1

[0083] When a single-phase grounding fault or electric shock accident occurs in the variable frequency power supply system, the ground distribution parameters of the input and output sides of the inverter should be considered. The electrical schematic diagram is as follows: Figure 2 shown.

[0084] (1) Electric shock occurs on the inverter input side

[0085] According to the principle of PLM algorithm, draw its equivalent circuit diagram as follows Figure 3 As shown, the Laplace transform operation circuit is as follows Figure 4 shown.

[0086] According to the node voltage method, we can get:

[0087]

[0088] Among them, U b (s) is R rThe voltage across the terminals is:

[0089]

[0090] Depend on Figure 4 We can get:

[0091]

[0092] According to the above calculation results, we can get:

[0093]

[0094] Where n = 2, 3, 4...

[0095] The initial values ​​of the circuit are:

[0096]

[0097] (2) Electric shock occurs on the inverter output side

[0098] According to the principle of PLM algorithm, draw its equivalent circuit diagram as follows Figure 5 As shown, the Laplace transform operation circuit is as follows Figure 6 shown.

[0099] According to the node voltage method, let the node voltage be U b1 (s), the following equation can be listed:

[0100]

[0101] Among them, U b1 (s) is the voltage across the human body resistance.

[0102] Solving the equation yields:

[0103]

[0104] The expression of the electric shock current is:

[0105]

[0106] And by Figure 6 We can get:

[0107]

[0108] According to the above calculation results, we can get:

[0109]

[0110] Where n = 2, 3, 4...

[0111] The initial values ​​of the circuit are:

[0112]

[0113] Each time period ΔT n The effective value of the electric shock current I rms(n) The size is:

[0114]

[0115] Assume that within one power frequency cycle, the PWM control signal is divided into n time periods. The effective value of the electric shock current in one power frequency cycle is I R for:

[0116]

[0117] Example 2

[0118] If the effects of the insulation resistance and distributed capacitance at both ends of the inverter are taken into consideration, when an electric shock occurs, the intuitive diagram of the system is as follows: Figure 7 Based on the inverter equivalent voltage source model, the equivalent circuit diagram can be drawn at this time, as shown in Figure 8 As shown. Since the three-phase voltage u of the inverter equivalent voltage source model A2 、u B2 、u C2 There are moments of sudden change, but the voltage on capacitors C1 and C2 cannot change suddenly. Therefore, the small resistance in the circuit, such as the on-resistance of the rectifier bridge diode and the inverter IGBT, needs to be considered in the equivalent circuit diagram as the internal resistance R of the equivalent voltage source model. s .

[0119] Depend on Figure 8 The equivalent circuit diagram shown and the reference direction indicated in the figure, according to Kirchhoff's law, can be listed as follows:

[0120] i L +i1+i 2C +i 2B +i 2A =0

[0121]

[0122] And because:

[0123]

[0124] Arranging the above formula, we can get the following formula:

[0125]

[0126] The current of electric shock to human body is:

[0127]

[0128] Combining the above formulas, the standard form differential equation system is as follows:

[0129]

[0130] Solving the differential equations, we can get u C2A The waveform of the electric shock current can be calculated by using the changing waveform of the electric shock current. Under the same parameters, MATLAB / Simulink is used to simulate and obtain the simulation waveform of the electric shock current. The current waveforms obtained in the two ways are as follows Fig. 9 As shown. It can be seen that the current waveforms obtained by the two methods are almost completely consistent with each other, and the error is very small, which proves that Figure 8 If an electric shock accident occurs at the front end of the inverter, the transient analysis of the electric shock current is the same as the above analysis method.

[0131] Example 3

[0132] Fig.10 This is the corresponding spectrum analysis diagram of the leakage current when a single-phase leakage of 50kΩ occurs on the output side. The spectrum analysis diagram can be used to further analyze the characteristics of the leakage current.

[0133] Embodiment 4, 5, 6

[0134] According to the above description, the magnitude of the DC component of the measured current can be known:

[0135]

[0136] In the formula, r ∑ =r A / / r B / / r C , E is the average value of the voltage after three-phase half-wave rectification.

[0137]

[0138] Among them, E is a fixed value, R y is a fixed value, so I y Directly reflects ∑ As long as the insulation of the power supply system decreases, whether it is single-phase, two-phase or three-phase leakage, it can be equivalent to r ∑ Therefore, the change of the value can be detected by y The size of the DC current is compared with the set value to determine whether the power grid is in a leakage fault.

[0139] Example 7

[0140] Under different insulation drop conditions, it is observed that the waveforms of the sampling voltage are different. The waveforms of the sampling voltage corresponding to the single-phase, two-phase and three-phase insulation drop are as follows Fig.11 .pass Fig.11 From the waveform diagram, we can see that the waveform shapes are different when single-phase insulation drop, two-phase insulation drop and three-phase insulation drop occur, so the insulation resistance drop can be judged by the waveform shape.

[0141] Embodiment 8, 9, 10

[0142] A simulation model was built for verification. The model uses a three-phase power module as a 3300V power supply and a motor as a load. The sampling resistance Ry is set to 100kΩ, the distributed capacitance per phase to ground is 0.1μF, the insulation resistance of the cable per phase to ground is 100MΩ, the carrier frequency is 2000Hz, and the inverter output frequency is 50Hz.

[0143] ① The output frequency of the inverter is changed, and the leakage on the input and output sides of the inverter is simulated at 40Hz and 60Hz respectively. The experimental results are shown in Table 1 and Table 2.

[0144] Table 1 Influence of inverter output frequency on sampling value when output side leakage occurs

[0145]

[0146] It can be seen from Table 1 that when the distributed parameters on both sides of the inverter are considered at the same time, the output frequency of the inverter is changed when the output side leaks, the sampling current changes slightly, and the error is within 0.6%.

[0147] Table 2 Influence of inverter output frequency on sampling value when input side leakage occurs

[0148]

[0149] It can be seen from Table 2 that when the distributed parameters on both sides of the inverter are considered at the same time, the output frequency of the inverter is changed when the input side leaks, the sampling current changes slightly, and the error is within 0.6%.

[0150] ②Change the size of the distributed capacitance on the input and output sides of the inverter and set r A =r B =r C =150kΩ, the experimental results are shown in Table 3.

[0151] Table 3 Effect of distributed capacitance to ground on sampling value during leakage

[0152]

[0153] It can be seen from Table 3 that when the distributed parameters on both sides of the inverter are considered and the distributed capacitance is changed, the error does not exceed 6%, which meets the requirement that the action error is less than 20%.

[0154] ③Change the size of the inverter carrier frequency and set r A =r B =r C =150kΩ, the experimental results are shown in Table 4.

[0155] Table 4 Influence of inverter carrier frequency on sampling value during leakage

[0156]

[0157]

[0158] It can be seen from Table 4 that when the distributed parameters on both sides of the inverter are considered at the same time, the carrier frequency of the inverter is changed when there is leakage on the input and output sides, and the sampling current changes slightly, with the error within 2%.

[0159] The mine inverter leakage protection method has the following technical effects:

[0160] 1) In view of the problems of complex structure and unreliable operation of existing leakage protection devices, the corresponding leakage protection device of the present invention has a simple structure, does not require an additional DC power supply to obtain protection, and has a higher DC detection voltage, which can better reflect the actual insulation level of the power grid.

[0161] 2) In view of the fact that the existing leakage protection method has inaccurate insulation detection after adding the frequency converter, and is prone to false operation and refusal to operate, the leakage protection method of the present invention can accurately measure the insulation resistance value when different types of leakage faults (single-phase, two-phase, three-phase) occur on the input side and the output side while considering the distributed parameters on both sides of the frequency converter.

[0162] 3) In view of the slow action speed of the existing leakage protection method, the leakage protection method of the present invention can make the detected DC current rise instantly after the leakage fault occurs, and the action is fast.

[0163] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for leakage protection of a mine frequency converter, characterized in that: include: S1 connects the three rectifier tubes to the three phases of the power grid, and the other ends are connected together and grounded; S2 monitors the insulation of the three-phase three-wire power supply system with a voltage level of 3.3kV or below in the mine; S3 collects current signals. Once the current rises to the set value, the protection device will be activated to achieve leakage protection.

2. The method for protecting a mine frequency converter from leakage according to claim 1, characterized in that: The S1 is specifically: Connect the three rectifier tubes to the A, B, and C phases of the power grid respectively, and connect the other ends together and grounded through a load resistor.

3. The mine inverter leakage protection method according to claim 1, characterized in that: The S2 is specifically: Calculate the equivalent steady-state effective value of the electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below; Calculate the transient effective value of electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below; Analyze the transient spectrum of single-phase leakage current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below; Monitor the three-phase insulation resistance, two-phase insulation resistance and single-phase insulation resistance of the inverter input and output sides of the mine 3.3kV and below power supply system; The waveform shape of the sampled voltage is used to determine whether it is a single-phase insulation drop, a two-phase insulation drop or a three-phase insulation drop; Verify the single-phase leakage protection method that is not affected by the inverter output frequency, distributed capacitance, and carrier frequency. Build a simulation model, change the inverter output frequency, distributed capacitance, and carrier frequency, and simulate the leakage on the input and output sides of the inverter.

4. The method for protecting a mine frequency converter from leakage according to claim 3, characterized in that: The calculation of the equivalent steady-state effective value of the electric shock current on the input and output sides of the frequency converter of the mine power supply system of 3.3kV and below is specifically: When a single-phase grounding fault or electric shock accident occurs in the variable frequency power supply system, the ground distribution parameters of the input and output sides of the inverter are considered, and the electric shock occurs on the input side of the inverter and on the output side of the inverter respectively. The equivalent circuit diagram is drawn according to the principle of the PLM algorithm; each time period ΔT n The effective value of the electric shock current I rms(n) The size is: Assume that within one power frequency cycle, the PWM control signal is divided into n time periods; the effective value of the electric shock current within one power frequency cycle is I R for: in, 5. The mine inverter leakage protection method according to claim 2, characterized in that: The calculation of the transient effective value of the electric shock current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below is specifically: Based on the inverter equivalent voltage source model, the equivalent circuit diagram at this time is drawn, and the waveform of the human electric shock current at this time is calculated; under the same parameters, MATLAB / Simulink is used for simulation to obtain the simulation waveform of the human electric shock current, and the differential equations are solved to obtain the transient effective value of the human electric shock current.

6. The mine inverter leakage protection method according to claim 3, characterized in that: The analysis of the transient spectrum of single-phase leakage current on the input and output sides of the inverter of the mine power supply system of 3.3kV and below is specifically as follows: Matlab is used to simulate the leakage current corresponding to the spectrum analysis diagram when a single-phase leakage of 50kΩ occurs on the output side, and the spectrum analysis diagram is used to further analyze the characteristics of the leakage current.

7. The method for protecting a mine frequency converter from leakage according to claim 3, characterized in that: The monitoring of the three-phase to ground insulation resistance, two-phase to ground insulation resistance and single-phase to ground insulation resistance of the inverter input and output sides of the mine 3.3kV and below power supply system includes: Monitor the DC component of the current: In the formula, r ∑ =r A / / r B / / r C , E is the average value of the voltage after three-phase half-wave rectification; Among them, E is a fixed value, R y is a fixed value, I y Direct reflection ∑ As long as the insulation of the power supply system decreases, whether it is single-phase, two-phase or three-phase leakage, it is equivalent to r ∑ Change of value; By detecting the flow through R y The size of the DC current is compared with the set value to determine whether the power grid is in a leakage fault.

8. The method for protecting a mine frequency converter from leakage according to claim 3, characterized in that: The determining of single-phase insulation drop, two-phase insulation drop or three-phase insulation drop by sampling the waveform shape of the voltage includes: Under different insulation drop conditions, it was observed that the waveform shapes were different when single-phase insulation drop, two-phase insulation drop and three-phase insulation drop occurred. The insulation resistance drop condition was judged by the waveform shape.

9. The method for protecting a mine frequency converter from leakage according to claim 3, characterized in that: The construction of the simulation model is specifically as follows: A simulation model was built. The model used a three-phase power supply module as a 3300V power supply and a motor as a load. The sampling resistance Ry was set to 100kΩ, the distributed capacitance per phase to ground was 0.1μF, the insulation resistance of the cable per phase to ground was 100MΩ, the carrier frequency was 2000Hz, and the inverter output frequency was 50Hz.

10. The method for protecting a mine frequency converter from leakage according to claim 3, characterized in that: The specific steps of changing the inverter output frequency, distributed capacitance, and carrier frequency to simulate the inverter input and output leakage are as follows: Change the inverter output frequency and simulate the inverter input and output leakage at 40Hz and 60Hz respectively; Change the size of the distributed capacitance on the input and output sides of the inverter and set r A =r B =r C =150kΩ, simulate the leakage on the input and output sides of the inverter; Change the size of the inverter carrier frequency, set r A =r B =r C =150kΩ, simulate the leakage on the input and output sides of the inverter.

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