Transmitting line asymmetric fault distance protection method based on new energy negative sequence voltage suppression

Abstract

The invention discloses a new energy negative sequence voltage suppression-based sending-out line asymmetric fault distance protection method. The method comprises the following steps of 1, detecting a voltage drop abrupt change signal and a negative sequence voltage signal of a new energy sending-out end to start asymmetric fault distance protection; 2, detecting a current break variable and a zero-sequence component of a new energy sending-out end, and carrying out fault type discrimination; 3, reading measured impedance of an impedance relay according to the fault type; 4, calculating an additional impedance phase angle of the measured impedance based on new energy negative sequence voltage suppression; 5, calculating fault distance impedance according to the sine theorem; and 6, carrying out internal and external fault judgment, protection action or locking. According to the method, the fault position can be calculated only by using the single-end measurement quantity of the protected line, and the method is not influenced by transition resistance. Meanwhile, negative sequence voltage suppression of new energy is considered, and a calculation method for measuring an additional impedance angle in impedance is provided. Compared with a traditional distance measurement type distance protection scheme, the method is suitable for a new energy sending-out system, the principle is simple, and practicability is high.

Description

Technical Field

[0001] The present invention belongs to the field of relay protection of power systems, and relates to technical fields such as distance protection of transmission lines, renewable energy power generation and grid connection technology, and power electronic equipment control, and specifically to a method for distance protection of asymmetric faults of transmission lines based on negative sequence voltage suppression of renewable energy. Background Art

[0002] Distance protection can reflect the fault distance, and its protection range and sensitivity are not affected by the system operation mode. It is widely used in transmission line protection. However, when non-metallic short circuit occurs, traditional distance protection is affected by transition resistance, and incorrect protection action often occurs. At the same time, with the access of a large number of new energy sources to the power grid, the power supply form and fault response characteristics of the system have undergone profound changes, and the adaptability of traditional distance protection has been challenged.

[0003] It is generally believed that there are two ways to implement distance protection. One is to accurately measure the fault location and then determine whether it is within the action area. For this type of method, the solutions to improve the ability to withstand transition resistance include: distance protection with adaptive adjustment of the action boundary, distance protection based on impedance compensation, distance protection scheme based on impedance complex plane, and distance protection scheme based on power balance. The protection scheme of adaptively adjusting the protection action boundary can automatically adjust the action area according to the fault characteristics and transition resistance. However, in the system with new energy access, due to the controllability and weak feedback of new energy, it is easy to cause the setting area to be too large, which is easy to cause protection misoperation when there is a fault outside the area. For the distance protection scheme that compensates for the fault impedance, the additional fault impedance caused by the compensation transition resistance is used to make the measured impedance accurately reflect the impedance from the fault point to the protection installation. The distance protection scheme based on the impedance complex plane estimates the additional fault impedance using the fault component and sequence component at the protection installation, and then solves and calculates the actual fault location. This type of scheme will produce errors in scenarios where the impedance of multiple voltage level lines is inconsistent. The distance protection scheme based on power balance analyzes the fault characteristics from the perspective of energy, calculates the transition resistance using the active power at both ends of the transmission line, and directly deducts its influence from the measured impedance by the relay to obtain the accurate location of the fault, but this method requires obtaining information on both ends of the line through instant communication. For the above distance protection schemes that accurately measure the fault location, there are problems such as poor selectivity, large error in fault distance calculation, and the need for communication. Another method is to not accurately measure the fault location, but only indirectly determine whether the fault occurs within the action boundary or outside the action boundary. Based on this idea, a voltage phasor plane distance protection scheme using transition resistance fault characteristics was derived, and the fault characteristics of the internal and external faults were obtained by analyzing the voltage phasor plane. However, this distance protection scheme has the problems of low reliability and poor speed. Summary of the invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to propose a transmission line asymmetric fault distance protection method based on negative sequence voltage suppression of renewable energy. This method is not affected by transition resistance and can effectively operate under various asymmetric faults, and can fully tap the negative sequence voltage suppression capability of renewable energy. The control strategy and fault distance derivation principle are simple and have strong adaptability.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A method for asymmetric fault distance protection of a transmission line based on negative sequence voltage suppression of renewable energy includes the following steps:

[0007] Step 1: Detect the voltage drop mutation signal and negative sequence voltage signal at the renewable energy transmission end to start the distance protection of asymmetric fault

[0008] When the voltage drop mutation signal and negative sequence voltage signal at the renewable energy transmission end are detected, it is determined that an asymmetric fault has occurred in the system and the asymmetric fault distance protection is activated;

[0009] Step 2: Detect the phase current difference mutation and zero-sequence component at the renewable energy transmission end to identify the fault type

[0010] According to whether the measured current at the renewable energy transmission end contains a zero-sequence component, determine whether the asymmetric fault is a ground short circuit fault or an unground short circuit fault, and select the phase for the asymmetric fault according to the phase current difference mutation at the renewable energy transmission end;

[0011] Step 3: Read the measured impedance of the impedance relay according to the fault type

[0012] Step 4: Calculate the additional impedance phase angle of the measured impedance based on the negative sequence voltage suppression of the new energy source

[0013] According to the fault type, based on the negative sequence voltage suppression of renewable energy, the negative sequence current output by renewable energy is controlled during asymmetric faults, the phase of reactive current is adjusted, the negative sequence network is reshaped, and a constant proportional relationship between the negative sequence current at the renewable energy output end and the negative sequence current at the fault point is established. The additional impedance phase angle of the measured impedance is calculated only through the measurement information of the single end of the line; Step 5: According to the sine theorem, the fault distance impedance is calculated

[0014] Based on the phasor relationship among the fault distance impedance, the measured impedance and the additional impedance, the asymmetric short-circuit fault distance impedance which is not affected by the transition resistance is calculated according to the sine theorem.

[0015] Step 6: Identify faults inside and outside the zone, and activate or lock protection

[0016] When the calculated fault distance impedance is less than the set value, it is considered to be an internal fault and the protection is activated; when the calculated fault distance impedance is greater than the set value, it is considered to be an external fault and the protection of the line is locked.

[0017] The additional impedance angle of the measured impedance is determined by using the single-ended sequence component of the protected line. According to the sine theorem, a unified expression for calculating the fault distance impedance is established, as shown in equation (6). This method is not affected by transition resistance and can adapt to various asymmetric fault conditions.

[0018]

[0019] Among them, |Z M | is the fault distance impedance, |Z fm |Measure the impedance, is the absolute value of the additional impedance phase angle, is the impedance angle of the transmission line.

[0020] Asymmetric faults include single-phase ground short circuit fault, two-phase short circuit fault, and two-phase ground short circuit fault.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] Applicable to distance protection of new energy transmission lines. Since the present invention constructs a new relationship of protection measurement quantity based on the negative sequence voltage suppression capability during the fault of the new energy power station, no other control links need to be added, the principle is simple, and the feasibility is strong; at the same time, the derivation process of the unified expression of the fault distance impedance is simple, and the result is not affected by the transition resistance, and can adapt to various asymmetric fault conditions, and has strong applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method of the present invention;

[0024] Figure 2 is a topological diagram of an embodiment. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0026] like Figure 1 As shown, the embodiment of the present invention provides a method for asymmetric fault distance protection of a transmission line based on negative sequence voltage suppression of renewable energy, and the specific steps are as follows:

[0027] Step 1: When a voltage drop is detected at the renewable energy transmission end, it is considered that a short circuit fault has occurred on the line. If a negative sequence voltage signal is detected at the renewable energy transmission end at the same time, it is determined that an asymmetric fault has occurred in the system, and the asymmetric fault distance protection will be activated.

[0028] Step 2: Detect the current mutation and zero-sequence component at the renewable energy transmission end to identify the fault type

[0029] According to whether the measured current at the renewable energy transmission end contains a zero-sequence component, it is determined whether the asymmetric fault is a ground short-circuit fault or an unground short-circuit fault. The asymmetric fault phase is selected according to the sudden change in the phase current difference. Asymmetric faults include single-phase ground short-circuit fault, two-phase short-circuit fault, and two-phase ground short-circuit fault.

[0030] Step 3: Read the measured impedance of the impedance relay according to the fault type.

[0031] According to the fault type identified in step 2, calculate the measured impedance of the impedance relay.

[0032] The measured impedance for single-phase ground short circuit fault and two-phase ground short circuit fault can be expressed as:

[0033]

[0034] Among them, Z fm Measure the impedance for the fault, are the voltage and current of the fault phase respectively, K0 is the zero-sequence current compensation coefficient, is the zero sequence current.

[0035] The measured impedance of a two-phase short-circuit fault can be expressed as:

[0036]

[0037] in, is the phase-to-phase voltage of the fault phases f1 and f2, is the phase-to-phase current of the fault phases f1 and f2.

[0038] Step 4: Based on the negative sequence voltage suppression of the new energy, the additional impedance phase angle of the measured impedance is calculated according to the fault type.

[0039] Since the phase of the output current of the new energy is controlled, the present invention is based on the suppression of the negative sequence voltage of the new energy, controls the negative sequence current output by the new energy during the asymmetric fault, adjusts the phase of the reactive current, reshapes the negative sequence network, and establishes a constant proportional relationship between the negative sequence current at the new energy sending end and the negative sequence current at the fault point, controls the negative sequence current output by the new energy and the negative sequence current at the fault point to be in phase, and realizes a constant proportional relationship between the negative sequence current at the single end of the line and the negative sequence current at the fault point. According to the asymmetric fault type determined in step 2, the additional impedance angle of the measurement impedance can be calculated only through the measurement information of the single end of the line.

[0040] (1) Single-phase ground short circuit

[0041] For phase A ground short circuit, the additional impedance phase angle φΔ Expressed as

[0042]

[0043] in, is the negative sequence current of phase A at the new energy transmission end, is the A-phase current at the new energy transmission end, K0 is the zero-sequence current compensation coefficient, is the zero sequence current.

[0044] (2) Two-phase short circuit

[0045] For AB phase short circuit, the phase angle of the additional impedance is φ Δ Expressed as:

[0046]

[0047] in, is the negative sequence current of phase A at the new energy transmission end, is the A-phase current at the new energy output end, It is the B-phase current at the new energy sending end.

[0048] (3) Two-phase ground short circuit

[0049] For AB phase ground short circuit, the phase angle of the additional impedance is φ Δ Expressed as:

[0050]

[0051] in, is the zero-sequence current of phase A at the new energy transmission end, is the A-phase current at the new energy output end, is the B-phase current at the new energy transmission end, K0 is the zero-sequence current compensation coefficient, is the zero sequence current.

[0052] Step 5: Combine the measured impedance from step 3 and the additional impedance angle from step 4 and calculate the fault distance impedance according to the law of sines.

[0053] According to the law of sines, the fault distance impedance can be expressed as:

[0054]

[0055] Among them, |Z M | is the fault distance impedance, |Z fm |Measure the impedance, is the absolute value of the additional impedance phase angle, is the impedance angle of the transmission line.

[0056] Step 6: Identify faults inside and outside the zone, and activate or lock protection

[0057] The fault distance impedance less than the setting value is used as the protection criterion:

[0058]

[0059] Among them, |Z set | is the value of the set impedance, |Z L | is the positive sequence impedance of the protected line, K rel The reliability coefficient is 0.8 to 0.85, and the reliability coefficient is 0.85 in general.

[0060] When the calculated fault distance impedance |Z M | Smaller than the setting value of the distance protection of this line | Z set |, it is considered that a fault occurs in the area and the distance protection is activated; when the calculated fault distance impedance |Z M |Greater than the setting value of the distance protection of this line|Z set |, it is considered that a fault occurs outside the zone, and the distance protection is locked. The effect of the present invention is described below through a specific embodiment:

[0061] The topology diagram of the embodiment is as follows Figure 2 As shown, the new energy power station is connected to the grid through the transmission lines L1 and L2, and the control strategy of new energy during the fault meets the requirements of the new energy grid connection standard (GB / T 19963.1-2021). The positive and negative sequence impedances of the transmission line are 0.17+j0.395Ω / km, and the zero sequence impedance is 0.51+j1.185Ω / km. The length of line L1 is 100km, and the length of line L2 is 60km. Line L1 is used as the research object to verify the effectiveness of the distance protection of the present invention, and F represents the fault point.

[0062] The calculated fault distance impedance values ​​and protection action conditions obtained by the method of the present invention when different transition resistance faults occur at point F of line L1 in the topology of the embodiment are shown in Table 1-3.

[0063] In the table, the distances between point F and the new energy transmission end are 10km (0.1pu), 20km (0.2pu), 50km (0.5pu), 80km (0.8pu), 110km (1.1pu), and 130km (1.3pu), respectively; the calculated value of the fault location impedance is obtained by formula (6) according to different fault types. √ indicates that the fault distance impedance calculated by the method of the present invention can correctly reflect the actual fault distance, and the distance protection can operate correctly.

[0064] Table 1 Calculated values ​​of fault distance impedance and distance protection action of the method of the present invention under different transition resistance conditions when phase A is short-circuited to ground

[0065]

[0066]

[0067] Table 2 Calculated fault distance impedance and distance protection action of the method of the present invention under different transition resistance conditions when AB phase short circuit occurs

[0068]

[0069] Table 3 Calculated fault distance impedance and distance protection action of the method of the present invention under different transition resistance conditions when two phases AB are short-circuited to ground

[0070]

[0071]

[0072] It can be seen from Tables 1-3 that the calculated fault distance impedance value obtained by the method of the present invention has a smaller error than the actual fault distance impedance, and can effectively reflect the actual fault distance impedance under different transition resistances, and the distance protection can operate correctly.

[0073] In summary, the present invention discloses a method for asymmetric fault distance protection of transmission lines based on negative sequence voltage suppression of renewable energy. The present invention establishes a proportional relationship between the negative sequence current of renewable energy output and the negative sequence current of the fault during the fault period and applies it to the derivation of the fault distance impedance. The distance protection method proposed in the present invention uses the single-ended quantity of the protected line to determine the additional impedance angle of the measured impedance, and establishes a unified expression for calculating the fault distance impedance based on the sine theorem. This method is not affected by transition resistance and can adapt to various asymmetric fault conditions.

[0074] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for asymmetric fault distance protection of transmission lines based on negative sequence voltage suppression of renewable energy, characterized in that: The following steps are involved: Step 1: Detect the voltage drop mutation signal and negative sequence voltage signal at the renewable energy transmission end to start the distance protection of asymmetric fault When the voltage drop mutation signal and negative sequence voltage signal at the renewable energy transmission end are detected, it is determined that an asymmetric fault has occurred in the system and the asymmetric fault distance protection is activated; Step 2: Detect the phase current difference mutation and zero-sequence component at the renewable energy sending end to distinguish the fault type. Determine whether the asymmetric fault is a ground short circuit fault or an unground short circuit fault based on whether the measured current at the renewable energy sending end contains a zero-sequence component. Select the asymmetric fault phase based on the phase current difference mutation at the renewable energy sending end. Step 3: Read the measured impedance of the impedance relay according to the fault type Step 4: Calculate the additional impedance phase angle of the measured impedance based on the negative sequence voltage suppression of the new energy source According to the fault type, based on the negative sequence voltage suppression of renewable energy, the negative sequence current output by renewable energy is controlled during the asymmetric fault period, the phase of reactive current is adjusted, the negative sequence network is reshaped, and a constant proportional relationship between the negative sequence current at the renewable energy output end and the negative sequence current at the fault point is established. The additional impedance phase angle of the measured impedance is calculated only through the measurement information of the single end of the line; Step 5: According to the sine theorem, the fault distance impedance is calculated Based on the phasor relationship among the fault distance impedance, the measured impedance and the additional impedance, the asymmetric short-circuit fault distance impedance which is not affected by the transition resistance is calculated according to the sine theorem. Step 6: Identify faults inside and outside the zone, and activate or lock protection When the calculated fault distance impedance is less than the set value, it is considered to be an internal fault and the protection is activated; when the calculated fault distance impedance is greater than the set value, it is considered to be an external fault and the protection of the line is locked.

2. A method for asymmetric fault distance protection of transmission lines based on negative sequence voltage suppression of renewable energy as claimed in claim 1, characterized in that: The additional impedance angle of the measured impedance is determined by using the single-ended sequence component of the protected line. According to the sine theorem, a unified expression for calculating the fault distance impedance is established, as shown in equation (6). This method is not affected by transition resistance and can adapt to various asymmetric fault conditions. in, | Z M| is the fault distance impedance, | Z fm| Measure the impedance. is the absolute value of the additional impedance phase angle, is the impedance angle of the transmission line.

3. The method for asymmetric fault distance protection of transmission lines based on negative sequence voltage suppression of renewable energy as claimed in claim 1, characterized in that: Asymmetric faults include single-phase ground short circuit fault, two-phase short circuit fault, and two-phase ground short circuit fault.

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