A method for protecting against symmetrical loss of excitation fault of variable speed pumping and storage unit

Abstract

The application discloses a variable-speed pumped storage unit symmetrical loss-of-field fault protection method, and belongs to the technical field of generator motor relay protection, and comprises the following steps: S1. collecting the stator-side current and voltage, reactive power and unit active power of a variable-speed pumped storage unit, and calculating the unit equivalent internal potential and the per-unit value of the stator voltage; S2. identifying the unit steady-state operation interval and the abnormal working condition starting moment according to the unit active power, and determining the equivalent internal potential reference value, the stator voltage reference value, the reactive power reference value and the unit active power reference value based on the steady-state operation interval; S3. constructing a main loss-of-field detection index and an auxiliary loss-of-field detection index; S4. after the abnormal working condition starting moment, determining the unit symmetrical loss-of-field fault according to the main and auxiliary loss-of-field detection indexes. The application realizes accurate and reliable identification of the symmetrical loss-of-field fault of the variable-speed pumped storage unit and improves the anti-interference capability of the loss-of-field protection.

Description

Technical Field

[0001] This invention relates to the field of relay protection technology for generator motors, and specifically to a method for protecting against symmetrical loss of excitation faults in variable speed pumped storage units. Background Technology

[0002] With the large-scale grid connection of new energy sources and the continuous advancement of the construction of new power systems, the role of variable-speed pumped-storage units in peak shaving, frequency regulation, phase regulation, and backup support in power systems is becoming increasingly significant. Compared with constant-speed pumped-storage units, variable-speed pumped-storage units have advantages such as a wider operating range, faster dynamic response, and more flexible operating condition adjustment, enabling them to better adapt to the power grid's demand for flexible resource regulation. Therefore, variable-speed pumped-storage units have become one of the important development directions of pumped-storage technology.

[0003] Existing research indicates that rotor circuit faults account for a significant proportion of electrical faults in generating units, and faults in different rotor components can lead to partial or complete demagnetization. Complete demagnetization faults, in particular, cause more severe operational consequences, including abnormal active power, reactive power variations, and deterioration of the unit's electrical operating conditions. Therefore, it is necessary to conduct specialized protection research for symmetrical demagnetization faults on the rotor side.

[0004] Existing research often constructs protection criteria based on port electrical quantities, DC bus voltage, and flux linkage. However, existing methods are prone to malfunction under power system disturbances or power fluctuations. Therefore, a symmetrical loss-of-excitation fault protection method is needed that combines the dual-condition characteristics of variable-speed generators and the coordinated changes of multiple electrical quantities, to balance the sensitivity, reliability, and anti-interference capability of fault identification. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for protecting variable speed pumped storage units against symmetrical loss of excitation faults, so as to achieve accurate and reliable identification of symmetrical loss of excitation faults in variable speed pumped storage units and effectively distinguish between loss of excitation faults and non-loss of excitation disturbances, thereby improving the anti-interference capability of loss of excitation protection.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows.

[0007] A method for protecting a variable-speed pumped-storage unit against symmetrical loss-of-excitation faults includes the following steps: S1. Collect the stator and rotor side current and voltage, reactive power and active power of the variable speed pumped storage unit, and calculate the per-unit value of the equivalent internal potential and stator voltage of the unit. S2. Identify the steady-state operating range and the start time of abnormal operating conditions of the unit based on the active power of the unit, and determine the equivalent internal potential reference value, stator voltage reference value, reactive power reference value and active power reference value of the unit based on the steady-state operating range; S3. Construct the main demagnetization detection index and auxiliary demagnetization detection index; S4. After the start time of the abnormal operating condition, when the main demagnetization detection index and the auxiliary demagnetization detection index simultaneously and continuously meet the preset judgment conditions and continue for a preset time, it is determined that the variable speed pumped storage unit has a symmetrical demagnetization fault, and a protection action signal is output.

[0008] Preferably, in step S1, the stator and rotor side electrical parameters are transformed to the dq coordinate system using the Park transformation, and the equivalent internal potential vector is:

[0009] in, E dq Let be the equivalent internal potential of the pumped-storage unit in the dq coordinate system. E d for E dq d-axis component, E q for E dq The q-axis component, equivalent internal potential amplitude ; Synchronous angular velocity; L m The mutual inductance of the main magnetic flux between the stator and rotor; L r For rotor inductance; For rotor flux linkage; It is the imaginary unit.

[0010] Preferably, in step S2, the method for identifying the steady-state operating range includes: When the active power of the variable speed pumped storage unit is in the range of [0.3, 0.9] per unit and the duration reaches the first preset time, the unit is determined to be in the steady-state operation range of the power generation condition. When the active power of the variable speed pumped storage unit is in the per-unit value range of [-0.98, -0.7] and the duration reaches the first preset time, the unit is determined to be in the steady-state operation range of pumping operation.

[0011] Preferably, in step S2, the identification of the start time of the abnormal operating condition includes any of the following situations: Scenario 1: The active power of the unit deviates from the steady-state operating range of the corresponding operating condition and continues to reach the second preset time. Scenario 2: The deviation of the unit's active power from the reference value of the unit's active power under the corresponding operating condition exceeds the preset ratio and continues to reach the second preset time.

[0012] Preferably, in step S2, the equivalent internal potential reference value, stator voltage reference value, reactive power reference value, and unit active power reference value are the average values ​​of the corresponding electrical quantities when the unit is in the steady-state operating range.

[0013] Preferably, in step S3, the main demagnetization detection index is:

[0014] in, LFDI The main indicator for loss of magnetization detection; E g,pre This is the reference value of the equivalent internal potential of the unit when it is in the steady-state operating range; U This refers to the real-time stator voltage. U pre This is the reference value for the stator voltage.

[0015] Preferably, in step S3, the auxiliary demagnetization detection index is:

[0016] in, This refers to the change in reactive power of the generator unit. Real-time reactive power; This is the reference value for reactive power when the unit is in the steady-state operating range.

[0017] Preferably, in step S4, the preset judgment condition is: when the main demagnetization detection index is less than 1 and the auxiliary demagnetization detection index is less than 0, and this continues for a third preset time, the unit is judged to have a symmetrical demagnetization fault and a protection action signal is output.

[0018] Due to the adoption of the above technical solutions, the technical progress achieved by this invention is as follows.

[0019] The invention has high reliability: By combining steady-state reference values, main demagnetization detection indicators and auxiliary demagnetization detection indicators to form a "dual-indicator collaborative judgment" protection logic, the invention can reliably identify symmetrical demagnetization faults in variable-speed pumped storage units and avoid the risk of misjudgment that may exist with a single criterion.

[0020] This invention has strong anti-interference capabilities: By setting multiple constraints such as abnormal operating condition start conditions, simultaneous judgment of dual indicators, and continuous delay confirmation, this invention can effectively distinguish between symmetrical demagnetization faults and non-demagnetization disturbances (such as system oscillation, reactive power step, active power exceeding limits, etc.), which significantly improves the anti-interference capability of the protection.

[0021] This invention features adaptability to dual operating conditions of variable speed units: It sets up different steady-state operating range identification methods for the two operating conditions of power generation and pumping of variable speed pumped storage units, and determines electrical quantity reference values ​​based on the corresponding operating conditions, which can cover the entire operating range of the unit.

[0022] The physical significance of this invention is clear: the main loss-of-excitation detection index adopted in this invention is based on the ratio of equivalent internal potential to stator voltage, which directly reflects the change in rotor excitation level. When a symmetrical loss-of-excitation fault occurs, the equivalent internal potential is significantly reduced. The physical mechanism is clear and the detection principle is reliable. Attached Figure Description

[0023] Figure 1 This is a flowchart of the present invention; Figure 2 This is a simulation result diagram of the protection system when the generating unit experiences symmetrical total loss of excitation under the power generation condition in an embodiment of the present invention. Figure 2 (a) is a simulation result of the equivalent internal potential amplitude. Figure 2 (b) is a simulation result of the stator voltage. Figure 2 (c) is a simulation result diagram of the unit's active power. Figure 2 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 2 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 2 (f) is a simulation result diagram of the protection action tripping; Figure 3 This is a simulation result diagram of the protection system when the unit experiences symmetrical total loss of excitation under pumping conditions, as shown in the embodiment of the present invention. Figure 3 (a) is a simulation result of the equivalent internal potential amplitude. Figure 3 (b) is a simulation result of the stator voltage. Figure 3 (c) is a simulation result diagram of the unit's active power. Figure 3 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 3 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 3 (f) is a simulation result diagram of the protection action tripping; Figure 4 This is a simulation result diagram of the protection system oscillation induced after the clearing of a three-phase short-circuit fault at the generator port in an embodiment of the present invention. Figure 4 (a) is a simulation result of the equivalent internal potential amplitude. Figure 4 (b) is a simulation result of the stator voltage. Figure 4 (c) is a simulation result diagram of the unit's active power. Figure 4 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 4 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 4 (f) is a simulation result diagram of the protection action tripping; Figure 5 This is a simulation result diagram of the protection system when the generator unit experiences system oscillation induced by the clearing of a three-phase short-circuit fault on the stator side under the power generation operating conditions, as shown in the embodiment of the present invention. Figure 5(a) is a simulation result of the equivalent internal potential amplitude. Figure 5 (b) is a simulation result of the stator voltage. Figure 5 (c) is a simulation result diagram of the unit's active power. Figure 5 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 5 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 5 (f) is a simulation result diagram of the protection action tripping; Figure 6 This is a simulation result diagram of the protection system when the system oscillates and subsequently experiences a loss of excitation fault after the three-phase short-circuit fault at the generator port is cleared under the power generation operating condition in this embodiment of the invention. Figure 6 (a) is a simulation result of the equivalent internal potential amplitude. Figure 6 (b) is a simulation result of the stator voltage. Figure 6 (c) is a simulation result diagram of the unit's active power. Figure 6 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 6 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 6 (f) is a simulation result diagram of the protection action tripping; Figure 7 This is a simulation result diagram of the protection system during the event of system oscillation and subsequent loss of excitation after the clearing of a three-phase short-circuit fault in the stator of the generator unit under the power generation operating condition, as described in this embodiment of the invention. Figure 7 (a) is a simulation result of the equivalent internal potential amplitude. Figure 7 (b) is a simulation result of the stator voltage. Figure 7 (c) is a simulation result diagram of the unit's active power. Figure 7 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 7 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 7 (f) is a simulation result diagram of the protection action tripping; Figure 8 This is a simulation result diagram of the protection system when a reactive power step occurs in the generating unit under the power generation condition in an embodiment of the present invention. Figure 8 (a) is a simulation result of the equivalent internal potential amplitude. Figure 8 (b) is a simulation result of the stator voltage. Figure 8 (c) is a simulation result diagram of the unit's active power. Figure 8 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 8 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 8 (f) is a simulation result diagram of the protection action tripping; Figure 9 This is a simulation result diagram of the protection when the active power exceeds the limit of the generating unit under the power generation condition in an embodiment of the present invention. Figure 9 (a) is a simulation result of the equivalent internal potential amplitude. Figure 9 (b) is a simulation result of the stator voltage. Figure 9 (c) is a simulation result diagram of the unit's active power. Figure 9 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 9 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 9 (f) is a simulation result diagram of the protection action tripping; Figure 10 This is a simulation result diagram of the protection system when a step increase in active power occurs in the generating unit under the power generation condition in an embodiment of the present invention. Figure 10 (a) is a simulation result of the equivalent internal potential amplitude. Figure 10 (b) is a simulation result of the stator voltage. Figure 10 (c) is a simulation result diagram of the unit's active power. Figure 10 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 10 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 10 (f) is a simulation result diagram of the protection action tripping; Figure 11 This is a simulation result diagram of the protection system oscillation induced by the clearing of a three-phase short-circuit fault at the unit port under the pumping operation condition in an embodiment of the present invention. Figure 11 (a) is a simulation result of the equivalent internal potential amplitude. Figure 11 (b) is a simulation result of the stator voltage. Figure 11 (c) is a simulation result diagram of the unit's active power. Figure 11 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 11 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 11 (f) is a simulation result diagram of the protection action tripping; Figure 12 This is a simulation result diagram of the protection system oscillation induced after the three-phase short-circuit fault in the stator of the unit is cleared under pumping conditions, as shown in the embodiment of the present invention. Figure 12 (a) is a simulation result of the equivalent internal potential amplitude. Figure 12 (b) is a simulation result of the stator voltage. Figure 12 (c) is a simulation result diagram of the unit's active power. Figure 12 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 12 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 12 (f) is a simulation result diagram of the protection action tripping; Figure 13 This is a simulation result diagram of the protection system when the three-phase short-circuit fault at the unit port is cleared and the system oscillates and subsequently experiences a loss-of-excitation fault under the pumping operation condition in this embodiment of the invention. Figure 13 (a) is a simulation result of the equivalent internal potential amplitude. Figure 13(b) is a simulation result of the stator voltage. Figure 13 (c) is a simulation result diagram of the unit's active power. Figure 13 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 13 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 13 (f) is a simulation result diagram of the protection action tripping; Figure 14 This is a simulation result diagram of the protection system when the system oscillates and subsequently experiences a loss of excitation fault after the three-phase short-circuit fault of the unit stator is cleared under pumping conditions, as described in this embodiment of the invention. Figure 14 (a) is a simulation result of the equivalent internal potential amplitude. Figure 14 (b) is a simulation result of the stator voltage. Figure 14 (c) is a simulation result diagram of the unit's active power. Figure 14 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 14 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 14 (f) is a simulation result diagram of the protection action tripping; Figure 15 This is a simulation result diagram of the protection system when a reactive power step occurs in the pumping operation of the unit according to an embodiment of the present invention. Figure 15 (a) is a simulation result of the equivalent internal potential amplitude. Figure 15 (b) is a simulation result of the stator voltage. Figure 15 (c) is a simulation result diagram of the unit's active power. Figure 15 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 15 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 15 (f) is a simulation result diagram of the protection action tripping; Figure 16 This is a simulation result diagram of the protection system when the active power exceeds the limit under the pumping operation condition in an embodiment of the present invention. Figure 16 (a) is a simulation result of the equivalent internal potential amplitude. Figure 16 (b) is a simulation result of the stator voltage. Figure 16 (c) is a simulation result diagram of the unit's active power. Figure 16 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 16 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 16 (f) is a simulation result diagram of the protection action tripping; Figure 17 This is a simulation result diagram of the protection system when the unit experiences a step increase in active power during pumping operation, as shown in the embodiment of the present invention. Figure 17 (a) is a simulation result of the equivalent internal potential amplitude. Figure 17 (b) is a simulation result of the stator voltage. Figure 17(c) is a simulation result diagram of the unit's active power. Figure 17 (d) is a simulation result diagram of auxiliary loss of magnetization detection indicators. Figure 17 (e) is a simulation result diagram of the main loss of excitation detection index. Figure 17 (f) is a simulation result diagram of the protection action tripping. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] A method for protecting symmetrical loss-of-excitation faults in variable-speed pumped-storage units, combined with Figure 1 As shown, it includes the following steps: S1. Collect the stator and rotor side currents and voltages, reactive power and active power of the variable speed pumped storage unit, and calculate the per-unit values ​​of the unit's equivalent internal potential and stator voltage.

[0026] Step S1 specifically includes: S11. Transform the stator and rotor side electrical parameters into the dq coordinate system using the Park transformation. The equivalent internal potential vector is:

[0027] in, E dq Let be the equivalent internal potential of the pumped-storage unit in the dq coordinate system. E d for E dq d-axis component, E q for E dq The q-axis component, equivalent internal potential amplitude Equivalent internal potential amplitude E g Reference value for equivalent internal potential used to determine the steady-state operating range. E g,pre And further used to construct the main demagnetization detection index. LFDI ; Synchronous angular velocity; L m The mutual inductance of the main magnetic flux between the stator and rotor; L r For rotor inductance; The rotor flux linkage can be represented by the stator and rotor voltages and currents. It is the imaginary unit.

[0028] S12. The stator voltage is calculated from the stator dq-axis voltage. To reduce the impact of sampling noise on the protection criteria, the equivalent internal potential, stator voltage, and reactive power are smoothed.

[0029] S2. Identify the steady-state operating range and the start time of abnormal operating conditions of the unit based on the unit's active power, and determine the equivalent internal potential reference value, stator voltage reference value, reactive power reference value, and unit active power reference value based on the steady-state operating range.

[0030] Specifically, the methods for identifying the steady-state operating range include: When the active power of the variable speed pumped storage unit is in the range of [0.3, 0.9] per unit and the duration reaches the first preset time, the unit is determined to be in the steady-state operation range of the power generation condition. When the active power of the variable speed pumped storage unit is in the per-unit value range of [-0.98, -0.7] and the duration reaches the first preset time, the unit is determined to be in the steady-state operation range of pumping operation.

[0031] Based on the identified steady-state operating range, the equivalent internal potential reference values ​​are obtained respectively. E g,pre Stator voltage reference value U pre Reactive power reference value and active power reference value P grid,pre In this embodiment, each reference value is the average value of the corresponding electrical quantity when the unit is in the steady-state operating range; the first preset time is 1.5s.

[0032] Specifically, the identification of the start time of abnormal operating conditions includes any of the following scenarios: Scenario 1: Active power of the unit P grid It deviates from the steady-state operating range of the corresponding working condition and continues to reach the second preset time; Scenario 2: Active power of the unit P grid Compared to the reference value of the unit's active power under the corresponding operating conditions P grid,pre The deviation exceeds the preset ratio and continues to reach the second preset time.

[0033] When any of the above conditions are met, the unit is determined to have entered an abnormal operating condition. In this embodiment, the preset ratio is 10%; the second preset time is 100ms.

[0034] S3. Construct the main loss-of-magnetism detection index and the auxiliary loss-of-magnetism detection index.

[0035] Specifically, the main demagnetization detection index is composed of the ratio of the real-time equivalent internal potential to the equivalent internal potential reference value and the ratio of the stator voltage reference value to the real-time stator voltage. That is, the main demagnetization detection index is:

[0036] in, LFDI The main indicator for loss of magnetization detection; E g Calculated by step S11; E g,pre This is the reference value of the equivalent internal potential of the unit when it is in the steady-state operating range; U This refers to the real-time stator voltage. U pre This is the reference value for the stator voltage.

[0037] Specifically, the auxiliary loss of excitation detection index is composed of the deviation between the real-time reactive power and the reactive power reference value, that is, the auxiliary loss of excitation detection index is:

[0038] in, This refers to the change in reactive power of the generator unit. Real-time reactive power; This is the reference value for reactive power when the unit is in the steady-state operating range.

[0039] S4. Determine the symmetrical loss of excitation fault of the unit based on the main and auxiliary loss of excitation detection indicators.

[0040] Continuous monitoring of the main demagnetization detection index after the onset of the abnormal operating condition. LFDI The main and auxiliary loss-of-excitation detection indicators are used. When the main and auxiliary loss-of-excitation detection indicators simultaneously and continuously meet the preset judgment conditions and continue for a preset time, it is determined that the variable-speed pumped-storage unit has a symmetrical loss-of-excitation fault, and a protection action signal is output.

[0041] The preset judgment condition is: when the main demagnetization detection index LFDI When the value is less than the first preset threshold and the auxiliary loss-of-excitation detection index is less than the second preset threshold, and continues to reach the third preset time, it is determined that the unit has a symmetrical loss-of-excitation fault, and a protection action signal is output.

[0042] In this embodiment, the first preset threshold is 1, the second preset threshold is 0, and the third preset time is 1.5s. That is, when the main demagnetization detection index is less than 1 and the auxiliary demagnetization detection index is less than 0, and this continues for 1.5s, the unit is determined to have a symmetrical demagnetization fault and a protection action signal is output.

[0043] To verify the effectiveness of the method proposed in this invention, a simulation model of a variable-speed pumped-storage unit was established, and simulation verification was conducted under symmetrical demagnetization fault and non-demagnetization disturbance conditions. Since the variable-speed pumped-storage unit has two operating conditions—power generation and pumping—and can operate in subsynchronous and supersynchronous states, to avoid excessive figures and highlight the core technical solution of this invention, this embodiment selects the supersynchronous operating state under both power generation and pumping conditions for simulation verification.

[0044] Taking a specific variable-speed pumped-storage unit as an example, the basic parameters of the unit are shown in Table 1.

[0045] Table 1. Basic parameters of a certain variable-speed pumped-storage unit

[0046] After the system is running stably, t A rotor-side symmetrical demagnetization fault is applied for 10 seconds, and the simulation results are as follows: Figures 2 to 3 As shown.

[0047] Figure 2 This is a simulation result of the protection system when the unit experiences symmetrical total loss of excitation under power generation conditions. The active power of the unit after the fault occurs is... P difg The voltage drops rapidly and deviates from the steady-state operating range, triggering the start-up criterion, and the equivalent internal potential amplitude... E g The voltage drops rapidly, while the stator voltage... U Only a small amplitude change occurred, and its value remained close to 1. The main loss-of-excitation detection index rapidly dropped below 1 after the fault occurred and continued to meet the operation requirements. The auxiliary loss-of-excitation detection index rapidly decreased to less than 0 after the fault and remained stable, ensuring reliable protection operation with an operation time of 1.60 seconds after the fault.

[0048] Figure 3 This presents the protection simulation results for a symmetrical total loss of excitation of the unit under pumping operation. The response pattern is largely consistent with that under generating operation; after the fault occurs, the active power amplitude at the port decreases rapidly and deviates from the steady-state operating range, triggering the start-up criterion; simultaneously, the equivalent internal potential amplitude... E g The stator voltage decreased significantly, with a small fluctuation, close to 1. The auxiliary loss-excitation detection index remained below zero, while the main loss-excitation detection index rapidly dropped below 1. The protection system reliably activated 1.61 seconds after the fault. The results demonstrate that the proposed method can reliably detect symmetrical loss-excitation faults and exhibits good speed of activation.

[0049] To verify the reliability of the loss-of-excitation protection of this invention, various non-loss-of-excitation disturbance conditions were designed under power generation and pumping operation conditions, including: system oscillation after rapid clearing of a three-phase short-circuit fault at the unit port; system oscillation after rapid clearing of a three-phase short-circuit fault on the stator side; system oscillation followed by a loss-of-excitation fault after rapid clearing of a three-phase short-circuit fault at the unit port; system oscillation followed by a loss-of-excitation fault after rapid clearing of a three-phase short-circuit fault on the stator side; reactive power step disturbance when the unit switches from lagging phase operation to leading phase operation; active power exceeding the limit disturbance when the unit's active power enters the non-steady-state operation range from the steady-state operating range; and active power step disturbance when the unit's active power drops to 0.9 times the steady-state reference value. After the system stabilizes,t =10s sets the corresponding abnormal operating condition, and the corresponding simulation results are as follows: Figures 4 to 17 As shown.

[0050] Figure 4 This presents the protection simulation results for system oscillation induced after the clearing of a three-phase short-circuit fault at the unit port under power generation conditions. As shown in the figure, during the transient process after the clearing of the three-phase short-circuit fault at the port, the unit's active power... P difg The deviation from the original steady-state operating range of power generation triggers the start-up criterion, initiating the subsequent loss-of-excitation detection process. After the system oscillation occurs, the equivalent internal potential amplitude... E g and stator voltage U Transient fluctuations occurred in all cases. While the amplitude of the equivalent internal potential changed significantly, it generally increased and did not decrease rapidly and remain in a low range as in a loss-of-excitation fault. The stator voltage also experienced a brief drop under the short-circuit fault but subsequently recovered to near steady state. The main loss-of-excitation detection index also fluctuated significantly during system oscillation, but did not remain consistently below 1. The auxiliary loss-of-excitation detection index showed a short-term negative fluctuation in the early stages of system oscillation, but did not remain consistently below zero, indicating that reactive power under this condition only exhibited transient oscillation deviations and did not show the characteristic of continuous reactive power absorption under a loss-of-excitation fault. Throughout the entire system oscillation process, the protection remained reliably locked.

[0051] Figure 5 This presents the protection simulation results for system oscillation induced by the clearing of a three-phase short-circuit fault on the stator side of the generating unit under power generation conditions. During the transient process after the clearing of the three-phase short-circuit fault on the stator side, the unit's active power... P difg The deviation from the original steady-state operating range of power generation triggers the start-up criterion. Equivalent internal potential amplitude. E g The system initially exhibited a general upward trend followed by a downward trend, eventually stabilizing near its initial steady-state value. The stator voltage showed a short-term decrease, dropping to around 0.5 pu, but then gradually recovered to near its steady-state value. The main loss-of-excitation detection index, during system oscillation, failed to consistently meet the operational requirements due to its value being greater than 1. Similarly, the auxiliary loss-of-excitation detection index, during the initial stage of system oscillation, showed a short-term negative fluctuation and also failed to consistently meet the operational requirements, resulting in reliable locking of the protection device.

[0052] Figure 6 This presents the protection simulation results for a system oscillation followed by a loss-of-excitation fault after the clearing of a three-phase short-circuit fault at the unit's ports during power generation. The active power of the unit is [data missing - likely related to power generation]. P difgThe active power decreases rapidly, deviating from the original steady-state operating range, thus triggering the start-up criterion. After the fault is cleared, its value returns to near the steady-state value; when the loss-of-excitation fault further occurs, the active power decreases and stabilizes, deviating from the original steady-state operating range. In the early stage of system oscillation, the equivalent internal potential amplitude... E g and stator voltage U Change and Figure 4 The system oscillation conditions change similarly; however, after a loss of excitation fault occurs, the equivalent internal potential amplitude drops rapidly and remains at a low level, close to 0, while the stator voltage only shows a slight decrease. The main loss of excitation detection index and the auxiliary loss of excitation protection criterion change similarly in the initial stage of system oscillation. Figure 4 The system oscillation conditions are similar; however, after a loss of excitation fault occurs, the main loss of excitation detection index rapidly drops below 1 and continues to meet the operating conditions. The auxiliary loss of excitation detection index rapidly decreases and remains below 0. After a loss of excitation fault occurs, both the main and auxiliary loss of excitation detection indices simultaneously meet the operating requirements, and after a 1.5s delay, the protection reliably operates, with the operating time being 2.43s after the fault.

[0053] Figure 7 This is a simulation result of the protection system during power generation, specifically when the system oscillates and subsequently experiences a loss-of-excitation fault after the stator three-phase short-circuit fault is cleared. The active power of the unit is shown in the transient process following the clearing of the stator three-phase short-circuit fault. P difg The active power decreases rapidly, deviating from the original steady-state operating range, triggering the start-up criterion; subsequently, when a loss-of-excitation fault occurs, the active power continues to decrease from the steady-state recovery value after the fault is cleared. In the initial stage of system oscillation, the equivalent internal potential amplitude... E g and stator voltage U and the performance of the main loss-of-magnetism detection index and auxiliary loss-of-magnetism detection index. Figure 5 The system exhibited similar oscillation conditions, both showing significant transient fluctuations. However, after a loss of excitation fault occurred, the equivalent internal potential amplitude rapidly decreased and remained at a low level, approaching 0, while the stator voltage only showed some amplitude fluctuations and a slight decrease, hovering around 0.9 pu. The main loss of excitation detection index rapidly decreased to below 1 and consistently met the operating conditions. The auxiliary loss of excitation detection index rapidly decreased and remained below 0. After the loss of excitation fault occurred, both the main and auxiliary loss of excitation detection indices simultaneously met the operating requirements, and after a 1.5s delay, the protection reliably operated, with an operating time of 2.49s after the fault.

[0054] Figure 8 This presents the protection simulation results for a generating unit experiencing a reactive power step disturbance under power generation conditions. Under the reactive power step disturbance, the unit's active power... P difgThe voltage remained relatively stable near its steady-state value, failing to meet the activation criteria. Therefore, the protection system did not enter the subsequent action judgment process, and the main and auxiliary loss-of-excitation detection indicators did not undergo corresponding judgments, maintaining their initial state. Simultaneously, the stator voltage decreased, and the equivalent internal potential amplitude... E g It only fluctuated briefly and did not exhibit the characteristic of a continuous decline and maintenance of low values ​​under demagnetization faults.

[0055] Figure 9 This is a simulation result diagram of the protection system when the active power exceeds the limit under power generation conditions. Under the active power exceeding the limit disturbance, the active power of the unit... P difg The change in [the value] meets the trigger condition of the activation criterion, thus activating the activation criterion; simultaneously, the equivalent internal potential amplitude [is affected]. E g Stator voltage drops U The voltage remained relatively stable, hovering around 1 p.u. Under this condition, the internal potential change trend was similar to that of a loss-of-excitation fault, thus triggering the main loss-of-excitation detection index. The auxiliary loss-of-excitation detection index, however, did not show a continuously decreasing trend. Therefore, the protection was reliably locked out.

[0056] Figure 10 This is a simulation result diagram of the protection system when the active power of the generating unit experiences a step disturbance during power generation. Under the active power step disturbance, the active power of the unit... P difg The start-up criterion trigger condition is met, thus initiating the start-up criterion; simultaneously, the stator voltage... U Both the auxiliary demagnetization detection indicators and the equivalent internal potential amplitude remained basically stable. E g A decrease similar to that observed during a loss of excitation fault occurred, causing the main loss of excitation detection index to activate. However, under this condition, the reactive power did not exhibit the characteristic of a continuous decrease under a loss of excitation fault. Therefore, the protection ultimately did not activate.

[0057] Figure 11 This is a simulation result of the protection system oscillation induced after the clearing of a three-phase short-circuit fault at the unit port during pumping operation. After the system oscillation occurs, the active power fluctuation deviates from the original steady-state operating range, thus triggering the start-up criterion. At the same time, the equivalent internal potential amplitude, stator voltage, and auxiliary loss-of-excitation detection index all show significant transient fluctuations, but none of them exhibit the characteristics of the internal potential being continuously lower than the steady-state value or the reactive power being continuously lower than the steady-state value under the loss-of-excitation fault. As a result, the main loss-of-excitation detection index does not continuously meet the action condition of being less than 1, and therefore the protection ultimately does not operate.

[0058] Figure 12This is a simulation result of the protection system oscillation induced by the clearing of a three-phase short-circuit fault in the stator of the unit under pumping operation. The response pattern is basically consistent with that under generating operation. After the clearing of the three-phase short-circuit fault on the stator side, the active power... P difg The amplitude fluctuated significantly, deviating from the original steady-state operating range of the pumping system, further triggering the abnormal operating condition start-up criterion; at the same time, the equivalent internal potential amplitude... E g Stator voltage U Both the auxiliary demagnetization detection index and the equivalent internal potential amplitude showed transient fluctuations. E g The stator voltage is greater than the initial steady-state value. U The brief drop caused the main loss-of-excitation detection index to fail to consistently meet the operating condition of being less than 1. Subsequently, the internal potential and stator voltage tended to approach their initial steady-state values, and the main loss-of-excitation detection index did not show significant changes. The auxiliary loss-of-excitation detection index fluctuated briefly before stabilizing at its initial steady-state value. Therefore, the protection ultimately did not activate.

[0059] Figure 13 This figure shows the simulation results of the protection system during system oscillation and subsequent loss-of-excitation fault after the clearing of a three-phase short-circuit fault at the pumping station. During the system oscillation phase after the clearing of the three-phase short-circuit fault, active power, equivalent internal potential amplitude, stator voltage, and auxiliary loss-of-excitation detection indicators all exhibit transient fluctuations. The main and auxiliary loss-of-excitation detection indicators also change significantly, but none consistently meet the loss-of-excitation protection operation conditions. When the subsequent loss-of-excitation fault occurs, the active power continuously deviates from the original steady-state pumping operating range, the equivalent internal potential amplitude decreases significantly and approaches 0, and the stator voltage... U With a slight decrease in magnitude, the auxiliary loss-of-excitation detection index remained below zero, while the main loss-of-excitation detection index rapidly dropped below 1 and met the operational requirements. After a 1.5s delay, the protection reliably operated 2.50s after the fault.

[0060] Figure 14 This figure shows the simulation results of the protection system during system oscillation and subsequent loss-of-excitation fault after the clearing of a three-phase stator short-circuit fault in pumping operation. During the system oscillation phase after the stator three-phase short-circuit fault is cleared, the active power meets the trigger condition of the start-up criterion, and the start-up criterion is activated. Simultaneously, the equivalent internal potential amplitude, stator voltage, and auxiliary loss-of-excitation detection index all exhibit transient fluctuations, and the main loss-of-excitation detection index also changes significantly, but its amplitude generally increases, thus failing to continuously meet the loss-of-excitation protection operation conditions. When the subsequent loss-of-excitation fault occurs, the equivalent internal potential amplitude drops significantly and rapidly, and the stator voltage... U It also showed a slight decrease, with the auxiliary loss-of-excitation detection index remaining below 0, while the main loss-of-excitation detection index rapidly dropped below 1 and met the operation requirements. After a 1.5s delay, the protection reliably operated 2.49s after the fault.

[0061] Figure 15 This presents the protection simulation results for the unit under pumping operation when a reactive power step disturbance occurs. Under the reactive power step disturbance, the unit's active power... P difg No significant changes occurred, therefore the activation criterion was not triggered, and the protection did not enter the subsequent action criterion judgment process. The main loss-of-excitation detection index and the auxiliary loss-of-excitation detection index remained in their initial states. Therefore, the protection ultimately did not operate. Meanwhile, the equivalent internal potential amplitude... E g Stator voltage U There have been some changes, but the equivalent internal potential amplitude remains the same. E g It did not exhibit a response characteristic of continuously being less than the steady-state value under demagnetization fault.

[0062] Figure 16 This presents the protection simulation results for the unit under pumping operation when the active power exceeds the limit. Under the active power exceedance disturbance, the unit's active power... P difg The trigger condition of the activation criterion is met, thus initiating the activation criterion; simultaneously, the equivalent internal potential amplitude... E g Although some changes occur, their magnitude is limited. However, the trend of internal potential change under this operating condition is similar to that of a loss-of-excitation fault, thereby triggering the main loss-of-excitation detection index and the stator voltage. U The system remained relatively stable, but the auxiliary demagnetization detection indicators did not meet the activation requirements. Therefore, the protection system ultimately did not activate.

[0063] Figure 17 This is a simulation result diagram of the protection system when the unit experiences a step increase in active power during pumping operation. Under the step power condition, the unit's active power... P difg The start-up criterion trigger condition is met, thus initiating the start-up criterion; simultaneously, the stator voltage... U Both the auxiliary demagnetization detection indicators and the equivalent internal potential amplitude remained basically stable. E g A decrease similar to that observed during a loss of excitation fault occurred, causing the main loss of excitation detection index to activate. However, under this condition, the reactive power did not exhibit the characteristic of a continuous decrease under a loss of excitation fault. Therefore, the protection ultimately did not activate.

[0064] Simulation results show that although non-loss-of-excitation disturbances also cause changes in the unit's active power and some electrical quantities, the main loss-of-excitation detection index... LFDIThe auxiliary loss-of-excitation detection indicators will not continuously meet the operating conditions simultaneously, preventing maloperation of the protection system. However, loss-of-excitation faults occurring after system oscillations can still be reliably detected, ensuring protection operation. The simulation results show that the symmetrical loss-of-excitation fault protection method proposed in this invention can effectively distinguish between symmetrical loss-of-excitation faults and non-loss-of-excitation disturbances on the unit side, exhibiting good identification accuracy and anti-interference capability.

[0065] The supplementary simulation results for the other operating conditions are shown in Table 2.

[0066] Table 2 Simulation results under various operating conditions

[0067] Further analysis shows that the protection method proposed in this invention can effectively identify symmetrical demagnetization faults in both subsynchronous and supersynchronous operating states. Therefore, it is no longer necessary to describe all operating conditions in detail.

Claims

1. A method for protecting a variable-speed pumped-storage unit against symmetrical loss-of-excitation faults, characterized in that: Includes the following steps: S1. Collect the stator and rotor side current and voltage, reactive power and active power of the variable speed pumped storage unit, and calculate the per-unit value of the equivalent internal potential and stator voltage of the unit. S2. Identify the steady-state operating range and the start time of abnormal operating conditions of the unit based on the active power of the unit, and determine the equivalent internal potential reference value, stator voltage reference value, reactive power reference value and active power reference value of the unit based on the steady-state operating range; S3. Construct the main demagnetization detection index and auxiliary demagnetization detection index; In step S3, the main demagnetization detection index is: in, LFDI The main indicator for loss of magnetization detection; E g,pre This is the reference value of the equivalent internal potential of the unit when it is in the steady-state operating range; U This refers to the real-time stator voltage. U pre This is the reference value for the stator voltage; E g This is the equivalent internal potential amplitude; In step S3, the auxiliary demagnetization detection index is: in, This refers to the change in reactive power of the generator unit. Real-time reactive power; This is a reference value for reactive power when the unit is in the steady-state operating range; S4. After the start time of the abnormal operating condition, when the main demagnetization detection index and the auxiliary demagnetization detection index simultaneously and continuously meet the preset judgment conditions and continue for a preset time, it is determined that the variable speed pumped storage unit has a symmetrical demagnetization fault, and a protection action signal is output.

2. The method for protecting a variable-speed pumped-storage unit against symmetrical loss-of-excitation faults according to claim 1, characterized in that: In step S1, the stator and rotor side electrical parameters are transformed to the dq coordinate system using the Park transformation, and the equivalent internal potential vector is: in, E dq Let be the equivalent internal potential of the pumped-storage unit in the dq coordinate system. E d for E dq d-axis component, E q for E dq The q-axis component, equivalent internal potential amplitude ; Synchronous angular velocity; L m The mutual inductance of the main magnetic flux between the stator and rotor; L r For rotor inductance; For rotor flux linkage; It is the imaginary unit.

3. The method for protecting a variable-speed pumped-storage unit against symmetrical loss-of-excitation faults according to claim 2, characterized in that: In step S2, the method for identifying the steady-state operating range includes: When the active power of the variable speed pumped storage unit is in the range of [0.3, 0.9] per unit and the duration reaches the first preset time, the unit is determined to be in the steady-state operation range of the power generation condition. When the active power of the variable speed pumped storage unit is in the per-unit value range of [-0.98, -0.7] and the duration reaches the first preset time, the unit is determined to be in the steady-state operation range of pumping operation.

4. The method for protecting a variable-speed pumped-storage unit against symmetrical loss-of-excitation faults according to claim 2, characterized in that: In step S2, the identification of the start time of the abnormal operating condition includes any of the following situations: Scenario 1: The active power of the unit deviates from the steady-state operating range of the corresponding operating condition and continues to reach the second preset time. Scenario 2: The deviation of the unit's active power from the reference value of the unit's active power under the corresponding operating condition exceeds the preset ratio and continues to reach the second preset time.

5. A method for protecting a variable-speed pumped-storage unit against symmetrical loss-of-excitation faults according to claim 2, characterized in that: In step S2, the equivalent internal potential reference value, stator voltage reference value, reactive power reference value, and unit active power reference value are the average values ​​of the corresponding electrical quantities when the unit is in the steady-state operating range.

6. The method for protecting a variable-speed pumped-storage unit against symmetrical loss-of-excitation faults according to claim 1, characterized in that: In step S4, the preset judgment condition is: when the main demagnetization detection index is less than 1 and the auxiliary demagnetization detection index is less than 0, and this continues for a third preset time, the unit is judged to have a symmetrical demagnetization fault and a protection action signal is output.

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