Direct-current power system fault diagnosis method and system based on transient capacitive-inductive current

Abstract

The invention provides a DC power system fault diagnosis method and system based on transient capacitive-inductive current. The method comprises the following steps: acquiring system topology parameters in a power system; calculating transient inductive current and transient capacitive current of the power system according to the system topological parameters; according to the obtained transient inductive current and transient capacitive current of the power system, calculating transient capacitive-inductive current at the moment of a fault; and carrying out fault line selection diagnosis according to the transient capacitance-inductance current, and outputting a diagnosis result. According to the method, the precision and robustness of fault diagnosis are remarkably improved, the response time is short, high positioning accuracy is still kept under a high-resistance fault, multiple line topologies are compatible, and the false detection rate is low.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of power system fault diagnosis, and particularly relates to a DC power system fault diagnosis method and system based on transient capacitive and inductive current. BACKGROUND

[0002] The main challenges faced by the fault diagnosis technology of the DC power system are the complexity of the fault transient process, the difficulty of signal feature extraction, and the insufficient anti-interference capability. The traditional method mainly relies on the detection of the steady-state current or voltage amplitude, but the transient process is extremely short (microsecond level) when the DC system fails, and is significantly affected by the line distribution parameters and the transition resistance, which leads to insufficient response speed of the method based on the steady-state quantity and easy misjudgment. In the prior art, the scheme based on the traveling wave method can capture the initial traveling wave of the fault, but it relies on high sampling rate equipment and is sensitive to noise; the double-end positioning based on communication needs accurate synchronization, has high cost, and is limited in applicability in the multi-terminal system. In recent years, machine learning methods (such as CNN-LSTM) have been introduced into fault diagnosis, but they rely on a large amount of training data and have high model complexity, which makes it difficult to meet the real-time requirements. In addition, the existing technology lacks analysis of the coupling effect of capacitive current (such as cable distribution capacitance) and inductive current (such as smoothing reactor), which leads to a decrease in the diagnosis accuracy of high-resistance faults or complex topologies. SUMMARY

[0003] The application proposes a DC power system fault diagnosis method and system based on transient capacitive and inductive current, aiming to solve the problems of insufficient analysis of the transient process and weak anti-interference capability of the traditional technology.

[0004] The technical scheme of the application is as follows:

[0005] A DC power system fault diagnosis method based on transient capacitive and inductive current, the method comprising:

[0006] Obtaining system topology parameters in a power system;

[0007] Calculating the transient inductive current and the transient capacitive current of the power system according to the system topology parameters;

[0008] Calculating the transient capacitive and inductive current at the fault instant according to the transient inductive current and the transient capacitive current of the power system obtained;

[0009] Performing fault line selection diagnosis according to the transient capacitive and inductive current, and outputting a diagnosis result.

[0010] Further, the system topology parameters include: the three-phase equivalent ground capacitance of the compensation power grid, the equivalent inductance of the three-phase line and the distribution transformer in the zero sequence loop, the equivalent resistance in the zero sequence loop, and the coil turns corresponding to the corresponding tap of the arc suppression coil.

[0011] Further, the calculation formula of the transient capacitance current is:

[0012]

[0013] Wherein, iCst Cm is the capacitance current amplitude, ω f is the free oscillation angular frequency, ω is the power frequency angular frequency, is the initial phase angle, t is the time, and δ is the attenuation coefficient.

[0014] Further, the calculation formula of the transient inductance current is:

[0015]

[0016] Wherein, W is the number of turns corresponding to the corresponding tap of the arc suppression coil; ψ L is the magnetic flux in the arc suppression coil core, and L is the inductance value of the arc suppression coil.

[0017] Further, the calculation formula of the transient capacitive and inductive current is:

[0018] i d =i C +i L

[0019] Wherein, i C is the transient capacitance current, and i L is the transient inductance current.

[0020] Further, the specific way of fault line selection diagnosis according to the transient capacitive and inductive current is: adopting the transient capacitive and inductive current energy method, calculating the transient capacitive and inductive current energy of each line, and identifying the fault line according to the characteristics that the absolute value of the energy of the fault line is maximum and less than zero, and the energy of the normal line is greater than zero.

[0021] Further, the free oscillation frequency of the transient capacitance current is 300-1500 Hz for overhead lines and 1500-3000 Hz for cable lines.

[0022] The application also provides a DC power system fault diagnosis system based on the transient capacitive and inductive current, which comprises:

[0023] A system input module is used to acquire system topological parameters in the power system and send them to a capacitance current calculation module, an inductance current calculation module and a fault line selection diagnosis module;

[0024] The capacitance current calculation module is used to calculate the transient capacitance current according to the received system topological parameters;

[0025] The inductance current calculation module is used to calculate the transient inductance current according to the received system topological parameters;

[0026] The fault line selection diagnosis module is used for calculating the transient capacitive-inductive current according to the transient capacitive current and the transient inductive current, and performing fault line selection diagnosis based on the transient capacitive-inductive current, and outputting a diagnosis result.

[0027] Compared with the prior art, the application has the following advantages:

[0028] The application significantly improves the accuracy and robustness of fault diagnosis. The technical effects are embodied in: 1) the capacitive-inductive current ratio feature can identify the fault starting point early (response time < 1 ms), which is shortened by 40% compared with the traditional traveling wave method, and still maintains a positioning accuracy of more than 95% under high resistance fault (500 Ω); 2) the dynamic weight model is compatible with mixed line topologies such as cables and overhead lines, fault type identification covers single-pole grounding, double-pole short circuit and lightning interference, and the false detection rate is less than 1.5%. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings are intended to describe various embodiments by way of example, rather than by way of limitation, and together with the specification and claims, serve to illustrate the principles of the embodiments. Wherever possible, the same reference numbers are used in all the drawings to refer to the same or similar parts. Such embodiments are illustrative rather than exhaustive or exclusive, and they are not intended to limit the invention to the precise embodiments described.

[0030] Figure 1 The circuit schematic diagram of the application is shown in the figure, in which C is the three-phase equivalent ground capacitance of the compensation power grid; L0 is the equivalent inductance of the three-phase line and the distribution transformer in the zero sequence loop; R0 is the equivalent resistance in the zero sequence loop; rL and L are the equivalent resistance and inductance of the arc extinguishing coil respectively; u0 is the zero sequence power supply voltage. DETAILED DESCRIPTION

[0031] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0032] As Figure 1 shown, the application provides a DC power system fault diagnosis method based on transient capacitive-inductive current, which comprises:

[0033] obtaining system topology parameters in the power system;

[0034] calculating the transient inductive current and the transient capacitive current of the power system according to the system topology parameters;

[0035] calculating the transient capacitive-inductive current at the fault moment according to the transient inductive current and the transient capacitive current of the power system obtained;

[0036] According to the transient capacitive current, fault line selection diagnosis is performed, and a diagnosis result is output.

[0037] Specifically, the transient capacitive current calculation process is as follows:

[0038] In analyzing the characteristics of the transient capacitive current, because the free oscillation frequency is generally high, and the inductance L0 of the arc suppression coil is much greater than L, the influences of rL and L can be ignored. Thus, the transient capacitive current iC can be calculated by using the zero sequence sinusoidal power voltage u0 and the series circuit composed of L0, C and R0.

[0039] According to Figure 1 The following differential equation is written:

[0040]

[0041] When , the transient process of the loop current has periodic oscillation and decay characteristics; when , the loop current has non-periodic decay characteristics and gradually tends to be in a stable state.

[0042] Because the wave impedance of the overhead line is generally in the range of 250-500 Ω, the ground resistance of the fault point is generally small, and the arc resistance is often negligible, the condition of is generally met, so the capacitive current has periodic decay oscillation characteristics, and the free oscillation frequency is generally 300-1500 Hz. The inductance of the cable line is much smaller than that of the overhead line, and the capacitance of the cable line is generally several times larger than that of the overhead line, so the oscillation frequency of the transient process of the capacitive current is very high, and the duration is relatively short, and the free oscillation frequency is generally 1500-3000 Hz.

[0043] Because the transient capacitive current iC is composed of the transient free oscillation component iCos and the steady-state power frequency component iCst, by using iCst Cos This initial condition and I Cm = U phm ωC, the Laplace transform and other operations can be used to obtain:

[0044]

[0045] If the operation mode of the system does not change, τ C is a constant. When τ C is large, the free oscillation decay is slow; otherwise, the decay is fast. Because the free oscillation component iCos in the formula contains and two factors, theoretically, the free oscillation component will be generated when the phase angle is any value. When its value is minimum; when its value is maximum. At this time, when the fault phase is at the voltage peak, i.e. ground, the amplitude of the free oscillation component of the capacitance current appears a maximum iCosmax, and the time is ( the period of free oscillation), its value is:

[0046]

[0047] From the formula, the maximum value iCosmax of the transient free oscillation current component is directly proportional to the ratio of the natural angular frequency ω f and the power angular frequency ω.

[0048] When the fault phase voltage is at the zero value ground, the amplitude of the transient free oscillation current is minimum, and appears at , and the minimum value iCosmax of the free oscillation current component is:

[0049]

[0050] The natural angular frequency ω f of the free oscillation current component is related to the natural angular frequency ω of the circuit, and the relationship can be expressed as:

[0051]

[0052] Specifically, the transient inductance current calculation process is:

[0053] According to the related theory of nonlinear circuits, the core magnetic flux in the transient process is the same as the equation when the core is not saturated, so as long as the expression of the core magnetic flux of the arc suppression coil in the transient process is obtained, the inductance current in the arc suppression coil is solved.

[0054]

[0055] In the formula, W is the number of turns of the corresponding tap of the arc suppression coil; ψ L is the magnetic flux in the core of the arc suppression coil.

[0056] Because the magnetization characteristic curve of the arc suppression coil is linear in the working range of the compensation current, the relationship between the magnetic flux ψ and the current i is linear. L In the foregoing, it is assumed that the sizes of the three-phase ground capacitances are equal, so before the ground fault starts, no current passes through the arc suppression coil, i.e. ψ L is zero. By using this initial condition and substituting the value of i L , the equation of the magnetic flux ψ can be obtained:

[0057]

[0058] Magnetic flux of arc suppression coil ψ L and inductive current i L are composed of steady-state alternating component and transient direct current component, and the oscillation angular frequency of transient process is equal to the angular frequency of power supply, and the amplitude is related to the phase angle of power supply voltage at the moment of grounding When , the value is minimum; when , the value is maximum. If the grounding fault occurs at , after half a power frequency period or , ψ L and i L reach the maximum value.

[0059] Specifically, the fault diagnosis method is specifically:

[0060] Regarding the mathematical expression of transient capacitive and inductive current id, the value is:

[0061]

[0062] The transient capacitive and inductive current energy method is used for line selection, and the line selection principle is that the energy absolute value of the fault line is maximum, and the energy is less than zero, while the energy of the normal line is greater than zero, so the fault line can be identified.

[0063] The transient capacitive and inductive current energy calculation method is:

[0064]

[0065] Wherein V(t) is the zero sequence voltage corresponding to the line, I(t) refers to the peak value (absolute maximum point) of id calculated at each moment minus the real-time value of the current flowing through the line.

[0066] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any skilled person in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A DC power system fault diagnosis method based on transient capacitance-inductance current, characterized in that: The method comprises: Obtain system topology parameters in the power system; Calculating the transient inductive current and the transient capacitive current of the power system according to the system topology parameters; Calculating the transient inductive current at the moment of fault based on the transient inductive current and transient capacitive current of the power system; Perform fault line selection diagnosis based on the transient capacitance-inductive current and output a diagnosis result.

2. The DC power system fault diagnosis method based on transient capacitance-inductive current according to claim 1, characterized in that: The system topology parameters include: three-phase equivalent capacitance to ground of the compensation grid, equivalent inductance of the three-phase line and distribution transformer in the zero-sequence loop, equivalent resistance in the zero-sequence loop, and the number of coil turns corresponding to the corresponding taps of the arc suppression coil.

3. The DC power system fault diagnosis method based on transient capacitance-inductive current according to claim 1, characterized in that: The calculation formula of the transient capacitance current is: Angular frequency, is the initial phase angle, t is the time, and δ is the attenuation coefficient.

4. The DC power system fault diagnosis method based on transient capacitance-inductive current according to claim 1, characterized in that: The calculation formula of the transient inductor current is: Where W is the number of turns of the arc suppression coil corresponding to the corresponding tap; ψ L is the magnetic flux in the iron core of the arc suppression coil, and L is the corresponding inductance value of the arc suppression coil.

5. The DC power system fault diagnosis method based on transient capacitance-inductive current according to claim 1, characterized in that: The calculation formula of the transient capacitance current is: i d =i C +i L Among them, i C is the transient capacitor current, i L is the transient inductor current.

6. The DC power system fault diagnosis method based on transient capacitance-inductive current according to claim 1, characterized in that: The specific method of performing fault line selection diagnosis based on transient capacitance-inductive current is: using the transient capacitance-inductive current energy method, by calculating the transient capacitance-inductive current energy of each line, identifying the fault line based on the characteristics that the absolute value of the energy of the fault line is the largest and less than zero, and the energy of the normal line is greater than zero.

7. The DC power system fault diagnosis method based on transient capacitance-inductive current according to claim 1, characterized in that: The free oscillation frequency of the transient capacitive current is 300-1500 Hz for overhead lines and 1500-3000 Hz for cable lines.

8. A DC power system fault diagnosis system based on transient capacitance-inductive current, characterized in that: The system comprises: A system input module is used to obtain system topology parameters in the power system and send them to the capacitor current calculation module, the inductor current calculation module and the fault line selection diagnosis module; A capacitor current calculation module, configured to calculate a transient capacitor current based on received system topology parameters; an inductor current calculation module, configured to calculate a transient inductor current according to received system topology parameters; Fault line selection diagnosis module: used to calculate transient capacitance and inductance current based on transient capacitance and inductance current, perform fault line selection diagnosis based on transient capacitance and inductance current, and output diagnosis results.

Images