Power grid short circuit fault direction discrimination method based on current change characteristics

Abstract

The invention discloses a power grid short-circuit fault direction discrimination method based on current change characteristics, and the method comprises the following steps: carrying out the adaptive analysis of the influence of the access of a doubly-fed fan / DC feed-in on a positive-sequence component direction element, and obtaining fault characteristics; establishing a new fault criterion which takes the fluctuation amplitude of the calculation result of the phase angle difference delta theta of the memory voltage and the fault current within a certain time after the fault as a main criterion and takes the amplitude change rate d of the short-circuit current as a supplementary criterion; accessing voltage and current sampling data of the protected equipment acquired by the protection device in real time; judging whether a fault occurs or not based on the sampling data, and if so, further judging the fault type; judging the direction of the positive sequence component direction element when the interphase short circuit occurs based on a new criterion; according to the method, the fault direction is judged through the new criterion of the direction element according to the type of the phase-to-phase ungrounded fault, and the reliability of the action of the direction element and line protection in a power grid is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power grid short-circuit fault direction determination, and in particular relates to a power grid short-circuit fault direction determination method based on current variation characteristics. Background Art

[0002] With the connection of new energy power sources to the grid through power electronic equipment and the input of a large amount of DC, the power grid is showing increasingly obvious power electronic characteristics. Its short-circuit current is affected by the control strategy and exhibits characteristics that are completely different from those of synchronous generators, such as limited amplitude, non-industrial frequency, and controlled phase angle. During faults, it has a discrete and nonlinear dynamic response process.

[0003] Among them, whether it is a DC feed-in system or a wind power new energy access system, the zero-sequence grid structure of the system is stable during the fault and is not affected by the DC system or the new energy system. Therefore, in the case of a grounding fault, the zero-sequence directional element can well determine the fault direction. In the case of an ungrounded fault, since there is no zero sequence, the positive-sequence fault component directional element is required to determine the direction. Affected by the transient regulation of the DC and wind power systems, the positive and negative sequence system impedances and current amplitudes are both fluctuating, resulting in unreliable direction determination of the positive-sequence fault analysis element.

[0004] Therefore, in order to solve the above problems, it is necessary to develop a method for determining the direction of power grid short-circuit fault based on current change characteristics. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a method for determining the direction of a short-circuit fault in a power grid based on current change characteristics. For the type of phase-to-phase ungrounded fault, the fault direction is determined by a new directional element criterion, thereby improving the reliability of the directional element action and the line protection in the power grid.

[0006] The object of the present invention is achieved by: a method for determining the direction of a short-circuit fault in a power grid based on current variation characteristics, comprising the following steps:

[0007] S1. Adaptive analysis is performed on the impact of the access of the doubly-fed wind turbine / DC feed-in on the directional element of the positive sequence component, and the fault characteristics when a fault occurs in the wind farm transmission line or the DC feed-in grid line;

[0008] S2. Establish a new fault criterion that takes the fluctuation amplitude of the calculation result of the memory voltage and the fault current phase angle difference Δθ within a certain period of time after the fault as the main criterion, and takes the amplitude change rate d of the short-circuit current as the supplementary criterion;

[0009] S3, access the voltage and current sampling data of the protected equipment collected in real time by the protection device;

[0010] S4. Determine whether a fault occurs based on the sampled data, and if a fault occurs, further determine the fault type;

[0011] S41, if it is a ground fault, the fault direction is determined by a zero-sequence directional element and then the process ends;

[0012] S42, if it is a phase-to-phase ungrounded fault, a new criterion is used for determination;

[0013] S5. Based on the new criterion, the direction of the positive sequence component direction element when a phase-to-phase short circuit occurs is determined; specifically, the following steps are included:

[0014] S51, threshold setting: setting the threshold Δθ of the phase angle difference Δθ set , set the short-circuit current amplitude change rate d threshold d set ;

[0015] S52, when Δθ>Δθ set When the current at the protection installation is provided by the fan / DC side, the fan / DC side is a forward fault, and the system side is a reverse fault;

[0016] S53, when Δθ<Δθ set When Δθ<Δθ, the supplementary criterion of current amplitude change rate and short-circuit current amplitude change rate d is introduced for further judgment. set And d>d set When the current at the protection installation is provided by the fan / DC side, the fan / DC side is a forward fault, and the system side is a reverse fault. When Δθ<Δθ set And d <d set When the current at the protection installation is provided by the system side, the fan / DC side is a reverse fault and the system side is a forward fault.

[0017] Furthermore, the adaptive analysis of the influence of the access of the doubly-fed wind turbine / DC feed-in on the positive-sequence component directional element in step S1 specifically includes: setting AG, BC, BCG and ABCG faults at the midpoint of the doubly-fed wind power transmission line / the midpoint of the AC / DC hybrid system line, and simulating and verifying the performance of the positive-sequence directional element in the doubly-fed wind turbine wind power grid-connected system / DC feed-in system.

[0018] Furthermore, the fault characteristics include the characteristics of the positive-sequence impedance phase angle changing with time. For the AC system transmission line with double-fed wind turbine / DC feed, the positive-sequence impedance phase angle on the system side is stable or fluctuates with time, and the positive-sequence impedance phase angle on the wind turbine side / DC side decreases with time.

[0019] Furthermore, the calculation process of the phase angle difference Δθ between the memory voltage and the fault current in step S2 is as follows: the phase angle difference θ between the memory voltage and the fault current is defined as follows:

[0020] ,

[0021] In the formula, is the BC phase voltage phasor, is the BC phase current phasor; then the phase angle difference Δθ between the memory voltage and the fault current is:

[0022] Δθ=max(θ)-min(θ),

[0023] Where max(θ) and min(θ) are the minimum and maximum memorized voltage and fault current phase angle difference calculated within 20ms to 30ms after the forward fault of the fan / DC side protection.

[0024] Furthermore, the amplitude change rate d of the short-circuit current in step S2 is represented by a current attenuation rate.

[0025] Furthermore, the amplitude change rate d, i.e., the current attenuation rate, is expressed as follows:

[0026] ,

[0027] In the formula, I k (t0) is the initial current amplitude calculated using the full-cycle Fourier algorithm, I k (t T / 2 ) is the current amplitude calculated after half a sampling period.

[0028] Due to the adoption of the above technical scheme, the beneficial effects of the present invention are as follows: adaptive analysis is performed on the influence of the access of the doubly-fed wind turbine / DC feed-in on the positive-sequence component directional element, and the fault characteristics when the wind farm transmission line or the DC feed-in grid line fails are obtained. Based on the fault characteristics, a new fault judgment criterion is adopted, which uses the fluctuation amplitude of the calculation result of the difference Δθ of the memory voltage and the fault current phase angle difference within a certain period of time after the fault as the main judgment criterion, and uses the amplitude change rate d of the short-circuit current as the supplementary judgment criterion, to judge the direction of the positive-sequence component directional element when a phase-to-phase short circuit occurs, thereby improving the reliability of the directional action of the positive-sequence component directional element and the line protection in the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flow chart of the present invention.

[0030] Figure 2 It is a simulation diagram of the positive sequence impedance phase angle on the system side and the wind turbine side when the midpoint AG fault occurs in the doubly-fed wind power transmission line of the present invention.

[0031] Figure 3 It is a simulation diagram of the positive sequence impedance phase angle on the system side and the wind turbine side when the midpoint BC of the doubly-fed wind power transmission line in the present invention fails.

[0032] Figure 4It is a simulation diagram of the positive sequence impedance phase angle on the system side and the wind turbine side when a BCG fault occurs at the midpoint of the doubly-fed wind power transmission line in the present invention.

[0033] Figure 5 It is a simulation diagram of the positive sequence impedance phase angle on the system side and the wind turbine side when the midpoint ABCG of the doubly-fed wind power transmission line in the present invention fails.

[0034] Figure 6 It is a simulation diagram of the positive sequence impedance phase angle on the system side and the DC side when the midpoint AG fault occurs in the AC / DC hybrid system line in the present invention.

[0035] Figure 7 It is a simulation diagram of the positive sequence impedance phase angle on the system side and the DC side when the midpoint BC of the AC / DC hybrid system line fails in the present invention.

[0036] Figure 8 It is a simulation diagram of the positive sequence impedance phase angle on the system side and the DC side when the midpoint ABCG of the AC / DC hybrid system line fails in the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0038] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 As shown, a method for determining the direction of a power grid short-circuit fault based on current change characteristics comprises the following steps:

[0039] S1. Adaptive analysis is performed on the influence of the access of the doubly-fed wind turbine / DC feed-in on the positive-sequence component directional element, and the fault characteristics when the wind farm transmission line or the DC feed-in grid line fails are obtained; specifically, AG, BC, BCG and ABCG faults are set at the midpoint of the doubly-fed wind power transmission line / the midpoint of the AC / DC hybrid system line, and the performance of the positive-sequence directional element in the doubly-fed wind turbine wind power grid-connected system / DC feed-in system is simulated and verified; the fault characteristics include the characteristics of the positive-sequence impedance phase angle changing with time. For the AC system transmission line of the doubly-fed wind turbine / DC feed-in, the positive-sequence impedance phase angle on the system side is stable or fluctuates with time, and the positive-sequence impedance phase angle on the wind turbine side / DC side decreases with time. According to the simulation verification analysis results, when the wind farm transmission line or the DC feed-in grid line fails, the fault characteristics have similar characteristics, such as positive and negative sequence system impedance fluctuations, fault current amplitude changes, etc. Therefore, the new criterion proposed in the present invention is applicable to both the wind power new energy access system and the DC feed-in system.

[0040] S2. Establish a new fault criterion that takes the fluctuation amplitude of the calculation result of the memory voltage and the fault current phase angle difference Δθ within a certain period of time after the fault as the main criterion, and the amplitude change rate d of the short-circuit current as the supplementary criterion.

[0041] Specifically, the calculation process of the phase angle difference Δθ between the memory voltage and the fault current in step S2 is as follows: the phase angle difference θ between the memory voltage and the fault current is defined as follows:

[0042] ,

[0043] In the formula, BC phase voltage phasor, is the BC phase current phasor; then the phase angle difference Δθ between the memory voltage and the fault current is:

[0044] Δθ=max(θ)-min(θ),

[0045] Where max(θ) and min(θ) are the minimum and maximum memorized voltage and fault current phase angle difference calculated within 20ms to 30ms after the forward fault of the fan / DC side protection.

[0046] Specifically, the amplitude change rate d of the short-circuit current in step S2 is represented by the current decay rate; the amplitude change rate d, i.e., the current decay rate, is shown in the following formula:

[0047] ,

[0048] In the formula, I k (t0) is the initial current amplitude calculated using the full-cycle Fourier algorithm, I k (t T / 2 ) is the current amplitude calculated after half a sampling period.

[0049] S3. Access the voltage and current sampling data of the protected equipment collected in real time by the protection device.

[0050] S4. Determine whether a fault occurs based on the sampled data, and if a fault occurs, further determine the type of fault.

[0051] S41, if it is a ground fault, the fault direction is determined by a zero-sequence directional element and then the process ends;

[0052] S42. If it is a phase-to-phase ungrounded fault, a new criterion is used to determine it.

[0053] S5. Based on the new criterion, the direction of the positive sequence component direction element when a phase-to-phase short circuit occurs is determined; specifically, the following steps are included:

[0054] S51, threshold setting: setting the threshold Δθ of the phase angle difference Δθset , set the short-circuit current amplitude change rate d threshold d set ;

[0055] S52, when Δθ>Δθ set When the current at the protection installation is provided by the fan / DC side, the fan / DC side is a forward fault, and the system side is a reverse fault;

[0056] S53, when Δθ<Δθ set When Δθ<Δθ, the supplementary criterion of current amplitude change rate and short-circuit current amplitude change rate d is introduced for further judgment. set And d>d set When the current at the protection installation is provided by the fan / DC side, the fan / DC side is a forward fault, and the system side is a reverse fault. When Δθ<Δθ set And d <d set When the current at the protection installation is provided by the system side, the fan / DC side is a reverse fault and the system side is a forward fault.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the specific implementation modes of the present invention can still be modified or replaced by equivalents, and any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for determining the direction of a power grid short-circuit fault based on current variation characteristics, characterized in that: The following steps are involved: S1. Adaptive analysis is performed on the impact of the access of the doubly-fed wind turbine / DC feed-in on the directional element of the positive sequence component, and the fault characteristics when a fault occurs in the wind farm transmission line or the DC feed-in grid line; S2. Establish a new fault criterion that takes the fluctuation amplitude of the calculation result of the memory voltage and the fault current phase angle difference Δθ within a certain period of time after the fault as the main criterion, and takes the amplitude change rate d of the short-circuit current as the supplementary criterion; S3, access the voltage and current sampling data of the protected equipment collected in real time by the protection device; S4. Determine whether a fault occurs based on the sampled data, and if a fault occurs, further determine the fault type; S41, if it is a ground fault, the fault direction is determined by a zero-sequence directional element and then the process ends; S42, if it is a phase-to-phase ungrounded fault, a new criterion is used for determination; S5. Based on the new criterion, the direction of the positive sequence component direction element when a phase-to-phase short circuit occurs is determined; specifically, the following steps are performed: S51, threshold setting; Set the threshold Δθ of the phase angle difference Δθ set , set the short-circuit current amplitude change rate d threshold d set ; S52, when Δθ>Δθ set When the current at the protection installation is provided by the fan / DC side, the fan / DC side is a forward fault, and the system side is a reverse fault; S53, when Δθ<Δθ set When Δθ<Δθ, the supplementary criterion of current amplitude change rate and short-circuit current amplitude change rate d is introduced for further judgment. set And d>d set When the current at the protection installation is provided by the fan / DC side, the fan / DC side is a forward fault, and the system side is a reverse fault. When Δθ<Δθ set And d <d set When the current at the protection installation is provided by the system side, the fan / DC side is a reverse fault and the system side is a forward fault.

2. A method for determining the direction of a power grid short-circuit fault based on current variation characteristics according to claim 1, characterized in that: The adaptive analysis of the influence of the connection of the doubly-fed wind turbine / DC feed-in on the positive-sequence component directional element in the step S1 specifically includes: setting AG, BC, BCG and ABCG faults at the midpoint of the doubly-fed wind power transmission line / the midpoint of the AC / DC hybrid system line, and simulating and verifying the performance of the positive-sequence directional element in the doubly-fed wind turbine wind power grid-connected system / DC feed-in system.

3. A method for determining the direction of a short-circuit fault in a power grid based on current variation characteristics according to claim 2, characterized in that: The fault characteristics include the characteristics of the positive sequence impedance phase angle changing with time. For the AC system transmission line with double-fed wind turbine / DC feed, the positive sequence impedance phase angle on the system side is stable or fluctuates with time, and the positive sequence impedance phase angle on the wind turbine side / DC side decreases with time.

4. A method for determining the direction of a short-circuit fault in a power grid based on current variation characteristics according to claim 1, characterized in that: The calculation process of the phase angle difference Δθ between the memory voltage and the fault current in step S2 is as follows: the phase angle difference θ between the memory voltage and the fault current is defined as follows: ， In the formula, is the BC phase voltage phasor, is the BC phase current phasor; then the phase angle difference Δθ between the memory voltage and the fault current is: Δθ=max(θ)-min(θ), Where max(θ) and min(θ) are the minimum and maximum memorized voltage and fault current phase angle difference calculated within 20ms to 30ms after the forward fault of the fan / DC side protection.

5. A method for determining the direction of a power grid short-circuit fault based on current variation characteristics according to claim 1, characterized in that: The amplitude change rate d of the short-circuit current in step S2 is represented by the current decay rate.

6. A method for determining the direction of a power grid short-circuit fault based on current variation characteristics according to claim 5, characterized in that: The amplitude change rate d, i.e., the current attenuation rate, is shown in the following formula: ， In the formula, I k (t0) is the initial current amplitude calculated using the full-cycle Fourier algorithm, I k (t T / 2 ) is the current amplitude calculated after half a sampling period.

Images