A protection method and device for a new energy grid-connected tie line

Abstract

This invention discloses a protection method and device for the continuous disconnection and reclosing of renewable energy grid-connected tie lines, comprising: acquiring and preprocessing basic data of the line and busbar where the device is located in real time; based on the preprocessed data, determining the entire process of renewable energy system tie line fault occurrence, tie line power system side switch tripping, and tie line fault persistence based on a first, second, and third discrimination condition; when all three discrimination conditions are met, outputting a continuous disconnection command for the grid-connected tie line, controlling the switch on the renewable energy system side of the tie line to trip, disconnecting the faulty line; after the faulty line is disconnected, the reclosing system will undergo a fixed delay and monitor the voltage conditions required for reclosing on the renewable energy system side of the tie line; after the voltage conditions are confirmed to be met, the reclosing operation is performed on the renewable energy system tie line. This invention can accurately identify faults and isolate line faults, effectively improving the reliability of renewable energy grid connection.

Description

Technical Field

[0001] This invention relates to the field of electrical engineering, and specifically to a protection method and device for connecting and disconnecting new energy grid-connected interconnection lines. Background Technology

[0002] With the rapid development of the new energy industry, a large number of new energy power plants have been connected to the power grid. During operation, new energy transmission lines are prone to faults due to various factors such as lightning strikes, bird damage, insulation failure, and external forces. Power system operation statistics show that about 70% to 80% of overhead line faults are single-phase grounding faults, and more than 80% of these are transient faults. After the switches on both sides of the transmission line trip, the arc at the fault point is extinguished and the line insulation is restored. At this time, the system power supply can be quickly restored through automatic reclosing.

[0003] However, after new energy sources are connected to the grid, changes in grid fault characteristics may cause adaptation problems in the original protection modes and setting principles. This may result in the transmission line's new energy side being unable to take timely and effective protection measures to disconnect the faulty tie line, and the fault arc will continue to exist. Ultimately, this will cause the main transformer gap overvoltage to activate and the entire station to shut down. This not only reduces the reliability of new energy grid connection but also expands the scope of the power outage and significantly increases the time required for power restoration.

[0004] Therefore, there is an urgent need to develop a new protection method and device for connecting and reconnecting new energy grid-connected lines to solve the above problems. Summary of the Invention

[0005] To address the issues of accurate protection and rapid power restoration during tie line faults after new energy sources are connected to the grid, this invention provides a protection method and device for disconnecting and reconnecting new energy grid-connected tie lines. This method can accurately identify the persistent fault characteristics of tie lines in islanded grid systems after a new energy tie line fault, quickly disconnect the faulty line, and prevent the main transformer gap protection from tripping due to the persistent presence of the fault arc, thus avoiding a complete power outage. This effectively improves the reliability of new energy grid connection, reduces the scope of power outages, and shortens the power restoration time.

[0006] This invention is achieved through the following technical solution:

[0007] In a first aspect, the present invention provides a protection method for connecting and disconnecting new energy grid-connected interconnection lines, the method comprising:

[0008] Real-time acquisition and preprocessing of basic data of the line and busbar where the device is located to obtain preprocessed data;

[0009] Based on the preprocessed data, the entire process of the new energy system tie line fault occurrence, tie line power system side switch tripping, and tie line fault persistence is determined sequentially based on the first, second, and third discrimination conditions.

[0010] When the first, second, and third judgment conditions are all met, a command to disconnect the grid-connected tie line is output to control the switch on the new energy system side of the grid-connected tie line to trip and disconnect the faulty line.

[0011] After the faulty line is disconnected, the reclosing system will wait for a fixed delay and monitor the voltage conditions required for reclosing on the new energy system side of the tie line. Once the voltage conditions are confirmed to be met, the reclosing operation will be performed on the new energy system tie line.

[0012] Furthermore, the basic data of the line and busbar where the device is located are acquired in real time and preprocessed, including:

[0013] The three-phase voltage of the bus and the synchronous voltage of the line are obtained in real time through the voltage transformer element of the line or bus where the device is located. Based on the three-phase voltage and the synchronous voltage, the amplitude and phase angle of each phase voltage, the positive and negative zero sequence components of the three-phase voltage, and the amplitude and phase angle of the synchronous voltage are calculated in real time.

[0014] The three-phase current on the line side is obtained in real time through the current transformer element of the line or bus where the device is located, and the positive and negative zero sequence components of the three-phase current are calculated in real time.

[0015] The frequency of the new energy system is calculated in real time based on the three-phase voltage, synchronous voltage, and three-phase current.

[0016] Furthermore, the first criterion used to identify the occurrence of a fault refers to the abnormal zero-sequence voltage on the busbar caused by a single-phase transient ground fault on the tie line.

[0017] The second criterion is used to identify the occurrence of islanding, which refers to the frequency change of the new energy islanding system caused by the tripping of the switch on the tie line power system side.

[0018] The third criterion is used to determine the continuity of the fault and execute continuous disconnection. It means that after the new energy system is determined to be in islanded operation, the bus voltage on the new energy system side is monitored. If there is still an abnormality in the zero-sequence voltage of the bus, the fault continues to exist.

[0019] Furthermore, the first criterion includes:

[0020] When the bus zero-sequence voltage exceeds the preset zero-sequence voltage activation threshold, an asymmetrical fault is determined to have occurred in the tie line, and the protection logic is activated. The calculation process for the bus zero-sequence voltage is as follows:

[0021] Calculate the phase voltage at the fault point based on the positive sequence impedance, negative sequence impedance, zero sequence impedance, fault phase-to-ground impedance, and rated phase voltage of the power system.

[0022] If a single-phase ground fault occurs on a line at a predetermined distance from the new energy system side, the fault phase voltage on the new energy system side is calculated based on the phase voltage at the fault point.

[0023] The zero-sequence voltage of the bus is synthesized based on the fault phase voltage on the new energy system side and the voltages of other phases on the bus.

[0024] Furthermore, the formula for calculating the zero-sequence voltage of the bus is:

[0025] ;

[0026] ;

[0027] ;

[0028] In the formula, This is the zero-sequence voltage of the bus. The fault phase voltage on the new energy system side (taking phase A as an example); This refers to the voltage of phase B of the busbar. This refers to the C-phase voltage of the busbar. This is the rated phase voltage; This refers to the zero-sequence current of the line. L is the zero-sequence impedance per unit length of the line; L is the line length from the fault point to the new energy system side. The phase voltage at the fault point; The grounding impedance of the faulty phase. For the positive sequence impedance of the power system, For the negative sequence impedance of the power system, This is the zero-sequence impedance of the power system.

[0029] Furthermore, the second criterion includes:

[0030] When the frequency of the new energy system exceeds the rated allowable range, the switch on the tie line power system side trips, disconnecting the new energy system from the tie line power system side, and the new energy system is determined to be in an isolated grid operation state.

[0031] Furthermore, the third criterion includes:

[0032] If the zero-sequence voltage of the busbar is greater than the preset zero-sequence voltage start threshold, and the effective value of the line current is less than the no-current judgment value, and this state continues for a preset duration, then it is determined that the tie line on the other side has tripped and the fault continues to exist.

[0033] Furthermore, voltage conditions include:

[0034] Busbar undervoltage criterion: If the highest phase voltage of the busbar is less than the first preset value, it is judged that the busbar on this side is undervoltage and has no internal power supply support.

[0035] Line energization criterion: If the synchronous voltage of the line is greater than the second preset value, it is determined that the power system side of the tie line has been successfully reconnected and the line has been restored to power.

[0036] Secondly, the present invention provides a protection device for connecting and disconnecting new energy grid-connected interconnection lines, the device comprising:

[0037] The data acquisition unit is used to acquire basic data of the line and busbar where the device is located in real time and perform preprocessing to obtain preprocessed data.

[0038] The discrimination condition unit is used to determine the entire process of the occurrence of a fault in the new energy system tie line, the tripping of the power system side switch of the tie line, and the continued existence of the tie line fault based on the first discrimination condition, the second discrimination condition, and the third discrimination condition, according to the preprocessed data.

[0039] The fault-cutting control unit is used to output a grid-connected tie line command when the first, second, and third judgment conditions are all met, thereby controlling the switch on the new energy system side of the grid-connected tie line to trip and cut off the faulty line.

[0040] After the faulty line is disconnected, the reclosing system will perform a fixed delay and monitor the voltage conditions required for reclosing on the new energy system side of the tie line. Once the voltage conditions are confirmed to be met, the reclosing operation will be performed on the new energy system tie line.

[0041] Thirdly, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-described method for protecting the connection line between connected and reconnected new energy grid lines.

[0042] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0043] 1. This invention provides a protection method and device for connecting and reconnecting new energy grid-connected tie lines. Based on a first, second, and third discrimination condition, it sequentially determines the entire process of a new energy system tie line fault occurrence, the tripping of the tie line power system side switch, and the continued existence of the tie line fault. It can accurately identify the continuous fault characteristics of the tie line under the islanded grid system after a new energy tie line fault, quickly connect and disconnect the faulty line, and avoid the main transformer gap protection action causing a station-wide power outage due to the continued existence of the fault arc. This effectively improves the reliability of new energy grid connection, reduces the scope of power outage, and shortens the power restoration time.

[0044] 2. The present invention provides a protection method and device for connecting and disconnecting new energy grid-connected interconnection lines. The fault identification is reliable. By comprehensively considering multiple dimensions such as zero-sequence voltage, voltage frequency deviation, and no-current characteristics, the fault can be accurately identified and the line fault can be isolated.

[0045] 3. This invention provides a protection method and device for the continuous switching and reconnection of renewable energy grid-connected tie lines, which helps to isolate fault points in a renewable energy islanded grid system in a timely manner and effectively prevents the expansion of the power outage area due to overvoltage action at the transformer neutral point. In addition, the continuous switching operation on the renewable energy system side of the tie line can also create arc-extinguishing conditions for transient faults.

[0046] 4. The present invention provides a protection method and device for disconnecting and reconnecting new energy grid connection lines. By automatically reconnecting disconnected grid connection lines, the reliability of new energy grid connection can be effectively improved. Attached Figure Description

[0047] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0048] Figure 1 This is a flowchart of a protection method for connecting and overlapping new energy grid-connected interconnection lines according to the present invention;

[0049] Figure 2 This is a topology diagram of a new energy grid-connected transmission line provided in Embodiment 2 of the present invention;

[0050] Figure 3(a) shows the simulation results after the failure without using this method;

[0051] Figure 3(b) shows the simulation results after the fault using this method;

[0052] Figure 4 This is a structural block diagram of a protection device for connecting and disconnecting new energy grid-connected lines according to the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0054] This invention effectively solves the practical problems of protection failure on the renewable energy side and difficulty in quickly clearing faults after tie line faults, thus causing the power outage area to expand. The fault discrimination logic of this invention is reliable, which can effectively reduce the impact range of power outages, significantly improve the stability of renewable energy grid-connected operation, and can be widely adapted to various relay protection application scenarios of renewable energy grid-connected tie lines.

[0055] Example 1

[0056] like Figure 1 As shown, the present invention provides a protection method for connecting and disconnecting new energy grid-connected interconnection lines, the method comprising:

[0057] Step 1: The basic data of the line and busbar where the device is located is acquired in real time through the acquisition unit and preprocessed to obtain preprocessed data;

[0058] Specifically, step 1 includes:

[0059] Step 11: Obtain the three-phase bus voltage in real time through the voltage transformer (PT) element of the line or bus where the device is located. , , Synchronous voltage of the line Based on the three-phase voltage and the synchronous voltage, the amplitude and phase angle of each phase voltage, the positive and negative zero sequence components of the three-phase voltage, and the amplitude and phase angle of the synchronous voltage are calculated in real time.

[0060] Step 12: Obtain the three-phase current on this side of the line in real time through the current transformer (CT) element of the line or bus where the device is located. , , And calculate the positive and negative zero sequence components of the three-phase current in real time;

[0061] Step 13: Calculate the frequency of the new energy system side in real time based on the three-phase voltage, synchronous voltage, and three-phase current.

[0062] Step 2: Based on the preprocessed data, determine the entire process of the new energy system tie line fault occurrence, tie line power system side switch tripping, and tie line fault persistence based on the first, second, and third discrimination conditions. Among them, the abnormal zero-sequence voltage of the bus after a single-phase instantaneous ground fault occurs in the tie line is used as the first discrimination condition; the frequency change of the new energy islanded grid system caused by the tripping of the tie line power system side switch is used as the second discrimination condition; after the new energy system is determined to be in islanded operation, continue to monitor the bus voltage on the new energy system side. If the bus zero-sequence voltage abnormality still exists, the fault persists as the third discrimination condition.

[0063] Specifically, the three discrimination conditions are as follows:

[0064] First criterion (fault identification): A single-phase transient ground fault on the new energy interconnection line will generate zero-sequence voltage. When the bus zero-sequence voltage... greater than zero-sequence voltage start-up threshold This allows us to determine if a fault has occurred.

[0065] When a single-phase transient ground fault occurs on the tie line of the new energy system, the symmetrical component method is used for analysis: Assume the rated line voltage is... The grounding impedance of the faulty phase is The positive sequence impedance of the power circuit system is Negative sequence impedance of power circuit system Zero-sequence impedance of power circuit system Phase voltage at the fault point It can be represented as:

[0066]

[0067] in, (Rated phase voltage).

[0068] If a single-phase ground fault occurs on a line a certain distance from the new energy system side, the voltage of the faulty phase on this side will be... for:

[0069]

[0070] in, This is the zero-sequence current of the line. Let L be the zero-sequence impedance per unit length of the line, and L be the line length from the fault point to the new energy system side.

[0071] Assuming an asymmetrical ground fault occurs in phase A, since the renewable energy transmission system is a directly grounded neutral system, the neutral point potential is clamped, and the voltage amplitude and phase of the non-faulty phases B and C remain essentially unchanged. In this case, the zero-sequence voltage of the renewable energy transmission system can be obtained by synthesizing the three-phase voltages:

[0072]

[0073] In the formula, This is the zero-sequence voltage of the bus. The fault phase voltage of the new energy system (taking phase A as an example). This refers to the voltage of phase B of the busbar. This refers to the C-phase voltage of the busbar.

[0074] At this time, the zero-sequence component of the three-phase voltage is dominated by the voltage offset of the faulted phase. When a single-phase ground fault occurs in the system, Significant changes will occur, therefore this can be observed through the bus zero-sequence voltage. .

[0075] The second criterion (isolated grid state): After the tie-line power system side switch trips, the new energy source will form a regional isolated grid system. Because the new energy isolated grid system has no inertial power supply support, its frequency will deviate rapidly from the rated value. That is, when the frequency on the new energy system side exceeds the frequency deviation threshold ±0.2Hz, after the tie-line power system side switch trips, the new energy system side is disconnected from the tie-line power system side, and it is determined that the new energy system has switched to isolated grid operation state.

[0076] The frequency deviation threshold is set based on the following: the rotor motion equation of a traditional synchronous generator is:

[0077]

[0078] in, The moment of inertia is (kg·m²). The rated frequency is 50Hz. The actual measured frequency (Hz). Mechanical power (W). Electromagnetic power (W). The frequency change rate is Hz / s.

[0079] However, the power sources in new energy systems (photovoltaic inverters, wind power converters) have no mechanical rotors, and their "equivalent inertia" is usually much smaller than that of synchronous machines. In this case, the active power imbalance in the isolated grid system of new energy will directly lead to a sharp increase in the rate of frequency change, and the equation can be simplified to:

[0080]

[0081] in The equivalent inertia of a new energy isolated grid system. It contributes power to new energy sources and has poor power output for isolated grid loads.

[0082] when Even a tiny ΔP (power deviation before and after a line fault) can cause the frequency of the isolated renewable energy grid system to deviate from its rated value within a few to tens of milliseconds. Considering that the normal grid frequency deviation is allowed to be ±0.2Hz, i.e., the operating range of 49.8~50.2Hz, setting the frequency action threshold to ±0.2Hz is derived from a comprehensive derivation of the grid's normal operating frequency limit and the critical condition for active power balance in isolated grids. Once the frequency exceeds the limit, it can be determined that the renewable energy area grid has been affected by a fault and disconnected from the main grid, entering an isolated grid operation state.

[0083] Third criterion (fault persistence): Continuously monitor bus voltage and line current; when the bus zero-sequence voltage... Threshold greater than zero-sequence voltage start-up threshold Furthermore, at least one phase current of the line satisfies the no-current criterion, i.e., the effective value of the line current. Less than the no-flow determination value If this state lasts for 100ms, it is determined that the other side of the tie line has tripped and the fault persists.

[0084] To avoid the impact of reactive power during line charging, the no-current determination value should be set according to the following principles:

[0085]

[0086] in, This is the reliability coefficient (generally taken as 1.2~1.3). The effective value of the line charging capacitor current (which can be calculated from the line's positive sequence capacitance). The third discrimination condition effectively prevents misjudgments when faults occur outside the designated area.

[0087] Step 3: When the first, second, and third judgment conditions are all met, output the command to disconnect the grid connection tie line, control the switch on the new energy system side of the grid connection tie line to trip, and disconnect the faulty line.

[0088] Step 4: After the faulty line is disconnected, the reclosing system will undergo a fixed delay and monitor the voltage conditions required for reclosing on the new energy system side of the tie line; once the voltage conditions are confirmed to be met, the reclosing operation will be performed on the new energy system tie line.

[0089] Specifically, in step 4, after a fault occurs in the grid connection tie line of the new energy system and the new energy side of the tie line is successfully disconnected using the method of this invention, the reclosing system will automatically enter a fixed delay phase, the duration of which is [duration missing]. It can be pre-set according to line parameters, new energy anti-islanding protection and power supply reliability, usually set to 1 to 3 seconds, to ensure that the arc at the fault point is fully extinguished and to avoid overlapping with permanent faults.

[0090] Prior to this, the reclosing condition of the power transmission line of the new energy system is that the system bus meets the no-voltage condition, that is, the maximum phase voltage. Less than the system no-pressure judgment value And the line synchronous voltage is present, that is, the line synchronous voltage Greater than the circuit voltage detection value The device will issue a command to perform a reclosing operation on the grid connection line of the new energy system. If the reclosing is successful, the line will resume normal power supply; if the fault is still detected after reclosing, the system will immediately lock the reclosing function, trip the new energy side of the connection line again, and issue an alarm.

[0091] Example 2

[0092] This embodiment is applied to a 110kV photovoltaic power generation grid-connected system. For example... Figure 2 As shown, the system includes a photovoltaic station, a step-up transformer, a data connection line, a grid-connected tie line, and the power system on the opposite side. The protection device of this invention is installed on the renewable energy system side of the grid-connected tie line. The specific execution process according to the method flow of Embodiment 1 is as follows:

[0093] Step 1: Data Acquisition and Preprocessing

[0094] The protection device acquires the three-phase voltage in real time at a sampling rate of 24 points per cycle through voltage transformers (PTs) installed on the 110kV bus, voltage transformers (PTs) on the tie lines, and current transformers (CTs) on the tie lines. , and three-phase current The internal processor of the protection device uses a full-cycle Fourier transform algorithm to calculate the effective values ​​and phases of voltage and current, including three-phase voltage. , , synchronous voltage Three-phase current , , The positive and negative zero-sequence components of voltage and current are calculated in real time using the symmetrical component method, as shown below:

[0095]

[0096]

[0097] Where a is the rotation operator, , ;

[0098] This represents the positive-sequence component of the voltage. It is the negative-sequence component of voltage. This is the zero-sequence component of the voltage. This represents the positive sequence component of the current. This represents the negative sequence component of the current. This represents the zero-sequence component of the current.

[0099] Meanwhile, the protection device can use mature frequency calculation methods to monitor the frequency on the renewable energy side in real time based on the collected bus three-phase voltage, line synchronous voltage, and line three-phase current, thus obtaining the renewable energy side frequency. .

[0100] Step 2: Comprehensive Fault Diagnosis and Connection Switching Logic

[0101] Assuming a transient ground fault occurs in phase A of the power transmission line of the new energy system, the protection device will operate according to the following logic:

[0102] Phase 1: Identifying the Fault Occurrence (First Decision Criterion)

[0103] At the moment the fault occurred, the three-phase voltage of the system was unbalanced, and the protection device detected the zero-sequence voltage on the bus. mutation.

[0104] Set zero-sequence voltage start-up threshold .

[0105] When measured When an asymmetrical fault is detected in the tie line, the protection logic is activated.

[0106] Phase Two: Identifying Isolated Network Formations (Second Decision Criterion)

[0107] After a fault occurs, the tie-line power system-side protection device can accurately identify the fault and operate reliably, tripping the tie-line power system-side switch. However, due to the weak electrical characteristics and insignificant fault quantity on the renewable energy side, it cannot be effectively identified, and the tie-line power system-side protection device cannot operate reliably. After the tie-line power system-side switch trips, the renewable energy system is disconnected from the power system and enters islanded operation.

[0108] The protection device monitors the system frequency of the new energy system in real time. When the system frequency is detected to exceed the rated allowable range, i.e., the frequency is higher than 50.2Hz or lower than 49.8Hz, the new energy system is determined to switch to islanded operation.

[0109] Phase 3: Determine if the fault persists and execute a continuous shutdown (third judgment condition).

[0110] After the renewable energy system switches to islanded operation, if the arc at the fault point is not extinguished, the renewable energy system will continue to supply short-circuit current to maintain arc combustion, and the protection device will continue to perform real-time status monitoring. A no-current judgment value is set. This setting must be greater than the line's no-charge current, and a dedicated discrimination time window of 100ms must be set.

[0111] When the protection device detects the zero-sequence voltage on the bus... This indicates that the grounding fault still exists; at the same time, the current in any one of the three phases of the line is less than the threshold for determining no current. This confirms that the switch on the other side of the tie line has been disconnected, and the station is operating in an isolated network with a fault. If the above operating condition remains stable for 100ms, it is determined that the switch on the other side of the tie line has tripped and the fault persists.

[0112] Step 3: Fault clearance and arc suppression

[0113] If the first, second, and third discrimination conditions in step 2 are all met, execute the command to disconnect the new energy system side of the tie line, control the switch on the new energy system side of the tie line to trip, and disconnect the switches on both sides of the tie line, thus creating conditions for the arc at the fault point to be extinguished.

[0114] Step 4: Automatic Reclosing Logic

[0115] The system enters a fixed delay timer; in this embodiment, the fixed delay time is set to... This time is sufficient to ensure that the arc of a transient fault is completely extinguished and to avoid the influence of residual current, while simultaneously matching the anti-islanding protection of the renewable energy system side to complete its operation. After the delay, the device collects the voltage status of the renewable energy side bus and line, executes the reclosing logic for checking line voltage and bus voltage, and waits for the main grid switch on the opposite side to successfully reclose first.

[0116] Busbar no-voltage criterion: highest phase voltage of the busbar The busbar on this side was deemed to be undervoltage and lacking internal power supply support.

[0117] Criterion for determining line voltage: Synchronous voltage of the line It was determined that the power system side of the tie line had been successfully reconnected and the line had been restored to power.

[0118] When the above conditions are met, the device sends a closing pulse to close the new energy side switch.

[0119] Scenario A (Successful Reclosing): After closing, the voltage and current return to normal, and grid connection is restored.

[0120] Scenario B (Reclosing to a permanent fault): If the device detects fault characteristics again after closing, it will immediately trip the switch, block reclosing, issue an alarm signal, and wait for manual handling.

[0121] To verify the practical effectiveness of the present invention, a simulation model as shown in Figure 2 was built based on the PSCAD / EMTDC simulation platform. Comparative simulations were carried out using the method of the present invention and without any optimization method. The relevant comparative verification results are shown in Figure 3(a) and Figure 3(b). Figure 3(a) shows the simulation results after failure without using the present method, and Figure 3(b) shows the simulation results after failure using the present method.

[0122] Using the method of this invention:

[0123] The simulated single-phase ground fault on the tie line triggered a sudden rise in the zero-sequence voltage of the bus to 60V, with obvious fault characteristics.

[0124] (0.06s after the fault) The protection on the tie line system side reliably trips the switch, the new energy power station is disconnected from the main grid and forms an isolated grid. At this time, the frequency on the new energy side changes on the field, which meets the isolated grid criterion.

[0125] (0.16s after the fault) The device continuously detects the presence of zero-sequence voltage and the current of the non-faulty phase drops to a low level, meeting the 100ms delay setting condition, and immediately issues a command to disconnect the new energy side of the interconnection line.

[0126] (0.20s after the fault) The new energy side switch completes the tripping, the fault is effectively isolated, and conditions are created for the arc at the fault point to be extinguished; the subsequent device can perform the reclosing operation on this side and restore operation by detecting that the reclosing of the power system side switch of the tie line has successfully met the line voltage condition and that the photovoltaic anti-islanding protection on this side has been activated to meet the bus voltage condition.

[0127] The method of this invention was not used:

[0128] When a single-phase ground fault is triggered on the proposed tie line, the zero-sequence voltage of the bus also rises instantaneously to 60V, and the initial state of the fault is the same as that of the method used.

[0129] (0.06s after the fault) The protection on the tie line system side reliably tripped the switch, and the new energy power station was disconnected from the main grid, forming an isolated grid operation.

[0130] In the subsequent period, the switch on the renewable energy side of the tie line remained closed and did not operate. The arc at the fault point could not be extinguished on its own, and the zero-sequence voltage of the bus remained abnormally high for a long time, preventing effective isolation of the fault. Affected by the continuous burning of the fault arc, the system-side switch on the tie line could not complete the normal reclosing operation, resulting in long-term abnormal distortion of the line voltage. The renewable energy area remained in an isolated grid operation state, and the regional system frequency and voltage gradually deviated from the rated operating range. The long-term single-phase grounding fault caused the zero-sequence voltage to remain high, which triggered the neutral point gap overvoltage protection of the main transformer, causing the main transformer to trip and the entire substation to lose power. In addition, the electrical equipment in the substation was operating under overcurrent and overvoltage conditions for a long time, which easily caused insulation aging and damage, inducing various equipment failures.

[0131] As can be seen from the comparison, the method of this invention can quickly isolate faults, ensure successful reclosing on the other side, and restore power supply to the entire network. Without this method, faults cannot be effectively handled, leading to prolonged system anomalies. This fully verifies the effectiveness and necessity of the method of this invention.

[0132] Through the above steps, this embodiment achieves rapid connection switching on the local side after a fault occurs in the tie line and the other side trips, utilizing the islanded frequency characteristics of the new energy system and the voltage / current composite criterion, thus avoiding a station-wide power outage caused by the overvoltage protection action of the main transformer gap. By verifying the reclosing strategy with energized lines, the grid connection is automatically restored after confirming that the fault has been eliminated and the main grid has been restored, significantly improving the power supply reliability of the new energy power station.

[0133] Example 3

[0134] like Figure 4 As shown, the difference between this embodiment and Embodiment 1 is that this embodiment provides a protection device for the continuous switching and re-closing of new energy grid connection lines. This device corresponds one-to-one with the protection method for the continuous switching and re-closing of new energy grid connection lines in Embodiment 1. The device includes:

[0135] The data acquisition unit is used to acquire basic data of the line and busbar where the device is located in real time and perform preprocessing to obtain preprocessed data.

[0136] The discrimination condition unit is used to determine the entire process of the occurrence of a fault in the new energy system tie line, the tripping of the power system side switch of the tie line, and the continued existence of the tie line fault based on the first discrimination condition, the second discrimination condition, and the third discrimination condition, according to the preprocessed data.

[0137] The fault-cutting control unit is used to output a grid-connected tie line command when the first, second, and third judgment conditions are all met, thereby controlling the switch on the new energy system side of the grid-connected tie line to trip and cut off the faulty line.

[0138] After the faulty line is disconnected, the reclosing system will perform a fixed delay and monitor the voltage conditions required for reclosing on the new energy system side of the tie line. Once the voltage conditions are confirmed to be met, the reclosing operation will be performed on the new energy system tie line.

[0139] The execution process of each unit can be carried out according to the protection method of connecting and reconnecting new energy grid interconnection lines in Embodiment 1, and will not be described in detail in this embodiment.

[0140] Meanwhile, the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the above-mentioned method for protecting the connection line between new energy grid-connected and overlapping new energy sources.

[0141] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0142] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0143] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0144] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0145] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A protection method for connecting and reconnecting new energy grid-connected interconnect lines, characterized in that, The method includes: Real-time acquisition and preprocessing of basic data of the line and busbar where the device is located to obtain preprocessed data; Based on the preprocessed data, the entire process of the new energy system tie line fault occurrence, tie line power system side switch tripping, and tie line fault persistence is determined sequentially based on the first discrimination condition, the second discrimination condition, and the third discrimination condition. When the first, second, and third judgment conditions are all met, a command to disconnect the grid-connected tie line is output to control the switch on the new energy system side of the grid-connected tie line to trip and disconnect the faulty line. After the faulty line is disconnected, the reclosing system will wait for a fixed delay and monitor the voltage conditions required for reclosing on the new energy system side of the tie line; once the voltage conditions are confirmed to be met, the reclosing operation will be performed on the new energy system tie line.

2. The protection method for a new energy grid connection line that is connected to and disconnected from the grid as described in claim 1, characterized in that, Real-time acquisition and preprocessing of basic data of the line and busbar where the device is located, including: The three-phase voltage of the bus and the synchronous voltage of the line are obtained in real time by the voltage transformer element of the line or bus where the device is located. Based on the three-phase voltage and the synchronous voltage, the amplitude and phase angle of each phase voltage, the positive and negative zero sequence components of the three-phase voltage, and the amplitude and phase angle of the synchronous voltage are calculated in real time. The device obtains the three-phase current on the line side in real time through the current transformer element of the line or bus where the device is located, and calculates the positive and negative zero sequence components of the three-phase current in real time. The frequency of the new energy system is calculated in real time based on the three-phase voltage, the synchronous voltage, and the three-phase current.

3. The protection method for a new energy grid connection line that is switched on and over-connected according to claim 1, characterized in that, The first discrimination condition is used to identify the occurrence of a fault, which refers to the abnormal zero-sequence voltage of the busbar caused by a single-phase instantaneous ground fault in the tie line. The second discrimination condition is used to identify the occurrence of islanding, which refers to the frequency change of the new energy islanding system caused by the tripping of the tie-line power system side switch; The third discrimination condition is used to determine the persistence of the fault. It means that after the new energy system is determined to be in islanded operation, the bus voltage on the new energy system side is monitored. If there is still an abnormality in the zero-sequence voltage of the bus, the fault persists.

4. The protection method for a new energy grid connection line that is switched on and over-connected according to claim 3, characterized in that, The first discrimination condition includes: When the bus zero-sequence voltage exceeds the preset zero-sequence voltage activation threshold, an asymmetrical fault is determined to have occurred in the tie line, and the protection logic is activated. The calculation process for the bus zero-sequence voltage is as follows: Calculate the phase voltage at the fault point based on the positive sequence impedance, negative sequence impedance, zero sequence impedance, fault phase-to-ground impedance, and rated phase voltage of the power system. If a single-phase ground fault occurs on a line within a set distance from the new energy system side, the fault phase voltage on the new energy system side is calculated based on the phase voltage at the fault point. The zero-sequence voltage of the bus is synthesized based on the fault phase voltage on the new energy system side and the voltages of other phases on the bus.

5. The protection method for a new energy grid connection line that is switched on and over-connected according to claim 4, characterized in that, The formula for calculating the zero-sequence voltage of the bus is: ； ； ； In the formula, This is the zero-sequence voltage of the bus. The voltage of phase A is a fault on the new energy system side. This refers to the voltage of phase B of the busbar. This refers to the C-phase voltage of the busbar. This is the rated phase voltage; This refers to the zero-sequence current of the line. L is the zero-sequence impedance per unit length of the line; L is the line length from the fault point to the new energy system side. The phase voltage at the fault point; The grounding impedance of the faulty phase. For the positive sequence impedance of the power system, For the negative sequence impedance of the power system, This is the zero-sequence impedance of the power system.

6. The protection method for a new energy grid connection line that is switched on and over-connected according to claim 3, characterized in that, The second discrimination condition includes: When the frequency of the new energy system exceeds the rated allowable range, the switch on the tie line power system side trips, disconnecting the new energy system from the tie line power system side, and the new energy system is determined to be in an isolated grid operation state.

7. The protection method for a new energy grid connection line that is connected to and disconnected from the grid as described in claim 3, characterized in that, The third discrimination condition includes: If the zero-sequence voltage of the busbar is greater than the preset zero-sequence voltage start threshold, and the effective value of the line current is less than the no-current judgment value, and this state continues for a preset duration, then it is determined that the tie line on the other side has tripped and the fault continues to exist.

8. The protection method for a new energy grid connection line that is switched on and over-connected according to claim 1, characterized in that, The voltage conditions include: Busbar undervoltage criterion: If the highest phase voltage of the busbar is less than the first preset value, it is judged that the busbar on this side is undervoltage and has no internal power supply support. Line energization criterion: If the synchronous voltage of the line is greater than the second preset value, it is determined that the power system side of the tie line has been successfully reconnected and the line has been restored to power.

9. A protection device for connecting and disconnecting new energy grid-connected transmission lines, characterized in that, The device includes: The data acquisition unit is used to acquire basic data of the line and busbar where the device is located in real time and perform preprocessing to obtain preprocessed data. The discrimination condition unit is used to determine the entire process of the occurrence of a fault in the new energy system tie line, the tripping of the tie line power system side switch, and the continued existence of the tie line fault based on the preprocessed data, according to the first discrimination condition, the second discrimination condition, and the third discrimination condition. The fault-cutting control unit is used to output a grid-connected tie line command when the first, second, and third judgment conditions are all met, thereby controlling the switch on the new energy system side of the grid-connected tie line to trip and cut off the faulty line. After the faulty line is disconnected, the reclosing system will perform a fixed delay and monitor the voltage conditions required for reclosing on the new energy system side of the tie line. Once the voltage conditions are confirmed to be met, the reclosing operation will be performed on the new energy system tie line.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements a protection method for connecting and reconnecting new energy grid-connected interconnecting lines as described in any one of claims 1 to 8.

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