CN117031353A - Single-phase earth fault transition resistance identification method for resonance grounding system - Google Patents
Single-phase earth fault transition resistance identification method for resonance grounding system Download PDFInfo
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Abstract
The invention discloses a method for identifying a single-phase grounding fault transition resistance of a resonant grounding system, which can realize rapid and accurate transition resistance identification by observing transient waveform characteristics of zero sequence voltage after a pre-adjusting arc suppression coil is adjusted to a full compensation state and has higher detection accuracy and sensitivity in low-resistance and high-resistance grounding faults. The method solves the problem that the conventional transition resistance identification method of the resonance grounding system needs time delay to acquire fault information, so that the arc extinguishing rapidity cannot be ensured. The invention has simple operation and easy realization.
Description
Technical Field
The invention relates to the field of feeder protection of distribution networks, in particular to a single-phase grounding fault transition resistance identification technology of a resonance grounding system.
Background
The single-phase earth fault accounts for more than 80% of the total faults of the power distribution network, the earth current is mainly capacitance current, and in order to prevent the insulation of equipment from breakdown caused by the earth arc due to the overlarge capacitance current, arc extinction measures should be timely taken to promote the recovery of transient faults and prevent the deterioration of permanent faults. The pre-adjusting arc suppression coil is used for detecting the change of the power grid to ground capacitance in real time when the power grid normally operates, adjusting inductance in real time and guaranteeing that inductive current generated by the arc suppression coil counteracts the current of the power grid to ground capacitance. The pre-adjusted arc suppression coil has the main advantages that the arc suppression coil is adjusted to a resonance state before grounding occurs, and the compensation effect can be directly achieved at the moment of grounding, so that the compensation effect is relatively good. Because the arc suppression coil inductance and the distribution capacitance of the distribution network are adjusted to a resonance state before the grounding fault, the potential of a neutral point is easily raised, and the virtual grounding occurs. Therefore, the common pre-adjusting arc suppression coil needs to be connected with a damping resistor in parallel to restrain resonance and limit the offset voltage of a neutral point to be too high, and after a single-phase grounding fault occurs, the damping resistor needs to be cut off or short-circuited as soon as possible in order to ensure that the residual current of the grounding point is minimum.
In practice, the single-phase earth fault of the power distribution network is mainly a transient fault, and the arc extinction process is accompanied by fault recovery to change the transition resistance, such as instability of the transition resistance when a fault such as tree collision occurs. Therefore, if the transient fault is recovered, the arc suppression coil exits from full compensation in time, so that the system can be effectively prevented from running in a resonance overvoltage state; for permanent faults, the arc suppression coil should maintain a fully compensated arc suppression state to prevent fault degradation. Therefore, the key of the arc suppression coil full compensation state scientific switching is to rapidly identify the magnitude of the grounding resistance so as to identify the type of the grounding fault. The current transition resistance identification method cannot adapt to the influence of the rapid full compensation of the arc suppression coil on fault information, and is poor in real-time performance of transition resistance identification.
Through searching in the prior art, the Chinese patent application number is 202211282770.0, the application publication number is CN115629276A, and the patent name is: a method for selecting fault line of resonant grounding system includes utilizing wavelet packet to transform and decompose zero sequence transient signal and extracting multiple fault feature to identify transition resistance by collecting transient signal of zero sequence current and voltage of each line after single-phase grounding fault occurs in small current grounding system.
Chinese patent application number 202110875762.6, grant publication number CN113391236B, patent name: a method for detecting single-phase grounding fault of resonant grounding system and related device are disclosed, which require reserving a certain time to collect transient zero sequence current to identify transition resistance after fault occurs, thereby affecting the rapidity of arc extinction of arc suppression coil.
Disclosure of Invention
Technical problems: the invention aims to solve the technical problem of providing a method for identifying the transition resistance of a single-phase grounding fault of a resonant grounding system, which is used for solving the problem that the existing method for identifying the transition resistance of the resonant grounding system does not consider the interference of full compensation of an arc suppression coil on fault information, thereby influencing the identification accuracy of the transition resistance.
The technical scheme is as follows: in order to solve the technical problems, the invention provides a method for identifying the transition resistance of a single-phase grounding fault of a resonant grounding system, which utilizes the change rule of the zero sequence voltage of the system after a pre-adjusted arc suppression coil is adjusted to a full compensation state to realize quick identification of the transition resistance.
The method for identifying the single-phase earth fault transition resistance of the resonant grounding system comprises the following steps:
step a: after a single-phase grounding fault occurs in the resonant grounding system, the preset arc suppression coil is adjusted to a full compensation state from a state far away from resonance, a damping resistor connected in parallel with an equivalent inductance of the arc suppression coil is required to be cut off, and a zero sequence voltage waveform after the damping resistor is cut off is recorded;
step b: c, observing and decomposing the zero sequence voltage waveform recorded in the step a, if the zero sequence voltage waveform contains an attenuated direct current component, indicating that the power distribution network has a low-resistance ground fault, and entering the step c when the system is in an over-damping state; if the power distribution network contains an attenuated alternating current component, indicating that the power distribution network has a high-resistance ground fault, wherein the system is in an underdamped state, and entering a step d;
step c: the system attenuates the direct current component u in zero sequence voltage under the over-damping state S0 (t) can be expressed as:
in the above, L is the inductance value corresponding to the full compensation state of the arc suppression coil, t 0 Time for adjusting arc suppression coil to full compensation stateWherein A is 1 、A 2 、P 1 、P 2 The method meets the following conditions:
in the formulas 2 and 3, omega is the angular frequency of the system, C Σ To total capacitance to ground G Σ Is the total conductance to ground; g E Is transition conductive and has a transition resistance R E ＝1/G E ；E A Is the electromotive force of the A-phase power supply, p and theta are the amplitude and the phase of unbalanced voltage of the fault phase respectively, T y1 、V y1 The current value and the voltage value on the arc extinguishing coil at the full compensation moment of the arc extinguishing coil are respectively;
reading the horizontal and vertical coordinate values of any point on the DC component curve of zero sequence voltage attenuation, and introducing the coordinate values into the corresponding transition resistance R calculated in the process 1 E ；
Step d: in the underdamped state of the system, the zero sequence voltage has attenuated alternating current components, the zero sequence voltage envelope is extracted, the time constant gamma corresponding to the envelope is read, and the corresponding transition resistance R is calculated by using the formula 4 E 。
Further, T in formula (3) of step c y1 、V y1 The method comprises the following steps:
in formula 5, i 2 (t 0 )、u 0 (y 0 ) The method comprises the following steps of:
in formula 6, k ∑ ＝Y A +α 2 Y B +αY C ，Y A 、Y B 、Y C In turn, A, B, C relative total admittance, G X The conductance corresponding to the parallel damping of the preset arc suppression coil is realized.
Further, the method for extracting the attenuated direct current component curve in the step c comprises the following steps: and (3) solving the upper and lower envelopes of the zero-sequence voltage after the pre-adjusting arc suppression coil is adjusted to the full compensation state by using a Hilbert transformation method, wherein the vertical bisectors of the upper and lower envelopes are the direct-current components of the zero-sequence voltage attenuation, namely the attenuated direct-current component curves are the symmetry axes of the zero-sequence voltage curves.
Further, in the step d, the upper envelope curve and the lower envelope curve of the zero-sequence voltage attenuation alternating current curve change exponentially along with time, and the zero-sequence voltage transient component value corresponding to the arc suppression coil full compensation moment is recorded as an initial value, so that the time required for the zero-sequence voltage change to 1.632 times of the initial value is the time constant gamma.
Drawings
FIG. 1 is a flow chart for identifying the transition resistance of a single-phase ground fault of a resonant grounding system;
FIG. 2 is a schematic diagram of the recognition of the transition resistance in the over-damped condition;
FIG. 3 is a schematic diagram of underdamped transition resistance identification;
FIG. 4 is a diagram of a topology of a simulation system;
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
FIG. 1 is a flow chart for identifying the transition resistance of a single-phase ground fault of a resonant grounding system.
Assuming that a certain power distribution network has n lines, taking an example that a single-phase ground fault occurs in an A phase of an h line of the power distribution network as an example, the method for identifying the single-phase ground fault transition resistance of the resonant grounding system is specifically introduced, and comprises the following steps:
step a: after a single-phase grounding fault occurs in the resonant grounding system, the preset arc suppression coil is adjusted to a full compensation state from a state far away from resonance, a damping resistor connected in parallel with an equivalent inductance of the arc suppression coil is required to be cut off, and a zero sequence voltage waveform after the damping resistor is cut off is recorded;
step b: c, observing and decomposing the zero sequence voltage waveform recorded in the step a, if the zero sequence voltage waveform contains an attenuated direct current component, indicating that the power distribution network has a low-resistance ground fault, and entering the step c when the system is in an over-damping state; if the power distribution network contains an attenuated alternating current component, indicating that the power distribution network has a high-resistance ground fault, wherein the system is in an underdamped state, and entering a step d;
step c: FIG. 2 illustrates the principle of the method for identifying the transition resistance in the over-damped state. The system attenuates the direct current component u in zero sequence voltage under the over-damping state S0 (t) can be expressed as:
in the above, L is the inductance value corresponding to the full compensation state of the arc suppression coil, t 0 For adjusting the arc suppression coil to the full compensation state, wherein A 1 、A 2 、P 1 、P 2 The method meets the following conditions:
in the formulas 2 and 3, omega is the angular frequency of the system, C Σ To total capacitance to ground G Σ Is the total conductance to ground; g E For the purpose of the transition electrical conductance,and transition resistance R E ＝1/G E ；E A Is the electromotive force of the A-phase power supply, p and theta are the amplitude and the phase of unbalanced voltage of the fault phase respectively, T y1 、V y1 The current value and the voltage value on the arc extinguishing coil at the full compensation moment of the arc extinguishing coil are respectively; t in (3) y1 、V y1 The method comprises the following steps:
in formula 4, i 2 (t 0 )、u 0 (t 0 ) The method comprises the following steps of:
in formula 5, k ∑ ＝Y A +α 2 Y B +αY C ，Y A 、Y B 、Y C In turn, A, B, C relative total admittance, G X The conductance corresponding to the parallel damping of the preset arc suppression coil is realized.
As can be seen from FIG. 2, the value of the abscissa of any point on the DC component curve of the zero sequence voltage decay is read and taken into the corresponding transition resistance R calculated in FIG. 1 E . The method for extracting the attenuated direct current component curve specifically comprises the following steps: and (3) solving the upper and lower envelopes of the zero-sequence voltage after the pre-adjusting arc suppression coil is adjusted to the full compensation state by using a Hilbert transformation method, wherein the vertical bisectors of the upper and lower envelopes are the direct-current components of the zero-sequence voltage attenuation, namely the attenuated direct-current component curves are the symmetry axes of the zero-sequence voltage curves.
Step d: in the underdamped state, the system has attenuated alternating current component in the zero sequence voltage, extracts the zero sequence voltage envelope curve, and reads the time constant gamma corresponding to the envelope curve. The specific method for reading the time constant gamma is as follows: the upper and lower envelopes of the zero-sequence voltage attenuation AC curve change exponentially with time, the zero-sequence voltage transient component value corresponding to the arc suppression coil full compensation time is recorded as an initial value, and when the zero-sequence voltage changes to 1.632 times of the initial value (corresponding to the point O1 of figure 3Should be shown at point O in FIG. 3 2 ) The required time is the time constant gamma.
Calculating the corresponding transition resistance R by using the method 6 E 。
The transition resistance identification method of the resonant grounding system based on the transient zero sequence voltage change rule after the pre-adjustment arc suppression coil is adjusted to be fully compensated is verified by utilizing MATLAB/Simulink simulation. Fig. 4 is a topological structure diagram of a simulation system, wherein the simulation system is a 10kV power distribution network with three feeder lines, and specific parameters are shown in table 1. The total capacitance current of the simulation system is 72.770A, the total active current is 1.316A, the asymmetry of the system is 1.750%, and the total damping rate is 1.809%.
Table 1 simulation system zero sequence parameter settings
And (3) verifying a transition resistance identification method: in practice, the power distribution network is mainly based on transient faults, and because the arc suppression coil can suppress arc overvoltage and compensate grounding current, when the arc suppression device reduces the grounding current or the fault phase voltage to decay to a limit value for maintaining arc combustion, the transient arc is rapidly suppressed, and the transition resistance is changed. In order to verify the accuracy of the transition resistance identification method, an A-phase grounding fault with the transition resistance of 10Ω, 20Ω, 30Ω, 1000Ω, 2000 Ω, 5000 Ω and 10kΩ is set in a MATLAB/Simulink simulation system, so that a fault occurs at the time of t=0s, and the full compensation is adjusted to a full compensation state at the time of t=0.142 s. Table 2 shows the calculation results of the transition resistance and the error thereof.
Table 2 calculation results of transition resistance and error thereof
As can be seen from Table 2, the transition resistance identification method provided by the invention has higher measurement accuracy. The accurate and rapid transition resistance identification method has important significance for identifying and tracking the grounding fault degree and judging the fault type, so that the scientific switching of the full compensation state of the arc suppression coil is realized, and the system resonance overvoltage is avoided.
Claims (4)
1. The identification method of the transition resistance of the single-phase grounding fault of the resonant grounding system is characterized by comprising the following steps of:
step a: after a single-phase grounding fault occurs in the resonant grounding system, the preset arc suppression coil is adjusted to a full compensation state from a state far away from resonance, a damping resistor connected in parallel with an equivalent inductance of the arc suppression coil is required to be cut off, and a zero sequence voltage waveform after the damping resistor is cut off is recorded;
step b: c, observing and decomposing the zero sequence voltage waveform recorded in the step a, if the zero sequence voltage waveform contains an attenuated direct current component, indicating that the power distribution network has a low-resistance ground fault, and entering the step c when the system is in an over-damping state; if the power distribution network contains an attenuated alternating current component, indicating that the power distribution network has a high-resistance ground fault, wherein the system is in an underdamped state, and entering a step d;
step c: the system attenuates the direct current component u in zero sequence voltage under the over-damping state S0 (t) can be expressed as:
in the above, L is the inductance value corresponding to the full compensation state of the arc suppression coil, t 0 For adjusting the arc suppression coil to the full compensation state, wherein A 1 、A 2 、P 1 、P 2 The method meets the following conditions:
in the formulas 2 and 3, omega is the angular frequency of the system, C Σ To total capacitance to ground G Σ Is the total conductance to ground; g E Is transition conductive and has a transition resistance R E ＝1/G E ；E A Is the electromotive force of the A-phase power supply, p and theta are the amplitude and the phase of unbalanced voltage of the fault phase respectively, T y1 、V y1 The current value and the voltage value on the arc extinguishing coil at the full compensation moment of the arc extinguishing coil are respectively;
reading the horizontal and vertical coordinate values of any point on the DC component curve of zero sequence voltage attenuation, and introducing the coordinate values into the corresponding transition resistance R calculated in the process 1 E ；
Step d: in the underdamped state of the system, the zero sequence voltage has attenuated alternating current components, the zero sequence voltage envelope is extracted, the time constant gamma corresponding to the envelope is read, and the corresponding transition resistance R is calculated by using the formula 4 E 。
2. The method for identifying single-phase earth fault transition resistance of resonant grounding system according to claim 1, wherein T in formula (3) is y1 、V y1 The method comprises the following steps:
in formula 5, i 2 (t 0 )、u 0 (t 0 ) The method comprises the following steps of:
in formula 6, k ∑ ＝Y A +α 2 Y B +αY C ，Y A 、Y B 、Y C In turn, A, B, C relative total admittance, G X The conductance corresponding to the parallel damping of the preset arc suppression coil is realized.
3. The method for identifying the transition resistance of the single-phase ground fault of the resonant grounding system according to claim 1, wherein the method for extracting the attenuated direct-current component curve in the step c is as follows: and (3) solving the upper and lower envelopes of the zero-sequence voltage after the pre-adjusting arc suppression coil is adjusted to the full compensation state by using a Hilbert transformation method, wherein the vertical bisectors of the upper and lower envelopes are the direct-current components of the zero-sequence voltage attenuation, namely the attenuated direct-current component curves are the symmetry axes of the zero-sequence voltage curves.
4. The method for identifying the single-phase grounding fault transition resistance of the resonant grounding system according to claim 1, wherein in the step d, the upper envelope curve and the lower envelope curve of the zero-sequence voltage attenuation alternating current curve change exponentially along with time, and the time required for the zero-sequence voltage to change to 1.632 times of the initial value is the time constant gamma when the zero-sequence voltage transient component value corresponding to the arc suppression coil full compensation moment is recorded as the initial value.
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