Method and device for overcurrent protection during start-up of a pumped storage unit

Abstract

The application discloses a method and device for overcurrent protection in a starting process of a pumped storage unit. The method determines that a short-circuit fault occurs outside a generator motor area, and the maximum value of three-phase currents at the neutral point side of the generator motor exceeds a setting value Iset. After a short delay Tset1, the protection is activated. Iset is set according to the maximum normal operating current during the starting process. If it is not determined that a short-circuit fault occurs outside the generator motor area, when the maximum value of three-phase currents at the neutral point side of the generator motor exceeds the setting value Iset, after a long delay Tset2, the protection is activated, and Tset1 < Tset2. When the differential protection condition is not met, the composite voltage condition is met, and the fault component negative sequence power direction points to the unit, it is determined that a short-circuit fault occurs outside the generator motor area. The technical scheme can effectively determine a short-circuit fault on an in-plant starting bus loop outside the stator winding, accelerate the protection action, timely remove the fault, and reduce the risk of unit damage.

Description

A method and device for overcurrent protection during the startup process of a pumped storage unit Technical Field

[0001] This invention belongs to the field of relay protection technology for main equipment in power systems, and specifically relates to a method and device for overcurrent protection during the startup process of a pumped storage unit. Background Technology

[0002] The pump startup process of a pumped storage power station mainly involves two methods: static frequency converter (SFC) startup and back-to-back startup. SFC startup refers to the process where, after the motor is excited, a static frequency converter (SFC) applies a current with a gradually increasing frequency to the motor stator, driving the unit to rotate. Back-to-back startup involves electrically connecting the stators of one generator set and one pump set, with their phase sequence connections being AC, BB, CA. The generator set generates electricity, driving the pump set to rotate. During the pump startup process, the driving unit (or SFC) and the driven pump set are connected to form a circuit.

[0003] Protection devices for pumped-storage power station pump units typically only connect to the electrical quantities of the unit itself. The conventional differential protection range does not include the plant's common drive bus circuit connected to the driven unit during startup. If a phase-to-phase short-circuit fault occurs in this circuit, it falls outside the differential protection zone and does not meet the differential protection's operating criteria. In this case, the backup protection of the pumped-storage power station pump unit protection device must coordinate the operation. However, the low-frequency overcurrent protection used as backup protection has a relatively long operating time setting, typically between 0.5s and 3s. In actual faults, this excessively long operating time may cause serious damage to the unit. Summary of the Invention

[0004] The purpose of this invention is to provide a method and device for overcurrent protection during the startup process of a pumped storage unit, which can effectively identify short-circuit faults on the plant startup bus circuit located outside the stator winding, accelerate protection action, promptly clear the fault, and reduce the risk of unit damage.

[0005] To achieve the above objectives, the solution of the present invention is:

[0006] A method for overcurrent protection during the startup process of a pumped storage unit includes:

[0007] Monitor the three-phase current on the generator terminal side and the three-phase current on the neutral point side of the generator motor to determine whether the differential protection conditions are met.

[0008] Monitor the three-phase voltage and negative sequence voltage at the generator terminals of the generator motor, and determine whether the composite voltage condition is met based on the phase-to-phase voltage amplitude and the negative sequence voltage amplitude.

[0009] Monitor the three-phase voltage at the generator terminals and the three-phase current at the generator terminals, calculate the negative sequence power of the fault component, and determine whether the direction of the negative sequence power of the fault component points towards the generator unit.

[0010] If the differential protection conditions are not met, the composite voltage conditions are met, and the direction of the negative sequence power of the fault component points to the generator unit, it is determined that a short circuit fault has occurred outside the generator motor zone.

[0011] If the differential protection conditions are met, the composite voltage conditions are not met, or the direction of the negative sequence power of the fault component does not point to the generator unit, it is determined that no short circuit fault has occurred outside the generator motor zone.

[0012] When a short-circuit fault occurs outside the generator motor zone and the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset and is continuously delayed for Tset1, the corresponding protection action is executed.

[0013] When no short-circuit fault occurs outside the generator motor zone and the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset and is continuously delayed for Tset2, the corresponding protection action is executed.

[0014] Monitoring the three-phase currents at the generator terminals and the neutral point to determine whether the differential protection conditions are met includes: monitoring the three-phase currents at the generator terminals and the neutral point; calculating the differential current and braking current from the three-phase currents at the generator terminals and the neutral point; and using the ratio braking differential characteristic based on the magnitude of the differential current and braking current to determine whether the differential protection conditions are met.

[0015] Monitor the three-phase terminal voltage and negative sequence voltage of the generator motor, and determine whether the composite voltage condition is met based on the phase-to-phase voltage amplitude and negative sequence voltage amplitude. This includes: monitoring the three-phase terminal voltage of the generator motor and calculating the phase-to-phase voltage amplitude U of the generator motor. ab U bc U ca Simultaneously, the negative sequence voltage of the generator motor is monitored, the negative sequence voltage amplitude U2 is calculated, and max(U ab U bc U ca ) and U ppset Compare U2 with U 2set Compare, if max(U) is satisfied ab U bc U ca ) < U ppset And U2>U 2set If U is constant, then the composite voltage condition is satisfied; where U is constant. ppset =k·U n U n U is the rated value of the phase-to-phase voltage, k is a coefficient;2set This is the negative sequence voltage threshold value.

[0016] The coefficient k takes values ​​of 90% to 95%.

[0017] Monitoring the three-phase voltage at the generator terminals of the generator motor and calculating the phase-to-phase voltage amplitude of the generator motor includes: monitoring the three-phase voltage at the generator terminals of the generator motor, calculating the three-phase voltage phasor values, and then calculating the phase-to-phase voltage amplitude of the generator motor.

[0018] The method for calculating the three-phase voltage phasor values ​​is to adjust the sampling frequency according to the change of the electrical quantity frequency, so that at any current frequency, each electrical quantity cycle has a fixed number of sampling points. Then, the fixed data window Fourier algorithm is used to calculate the real and imaginary parts of the three-phase voltage, thereby obtaining the voltage phasor values.

[0019] Alternatively, the method for calculating the three-phase voltage phasor values ​​is to use a fixed sampling frequency to discretely sample the three-phase voltages to obtain a sequence of sampled values; dynamically adjust the data window of the Fourier algorithm according to the current electrical quantity frequency so that the actual frequency is half of the rated frequency; then use the Fourier algorithm to measure and calculate the real and imaginary parts of the three-phase voltages to obtain the voltage phasor values.

[0020] Monitoring the three-phase voltage at the generator terminals and the three-phase current on the generator side, calculating the negative-sequence power of the fault component, and determining whether the direction of the negative-sequence power of the fault component points towards the generator unit includes: monitoring the three-phase voltage at the generator terminals and the three-phase current on the generator side, calculating the effective value ΔU2 of the negative-sequence voltage fault component of the generator from the three-phase voltage at the generator terminals, calculating the effective value ΔI2 of the negative-sequence current fault component from the three-phase current on the generator side, and then calculating the negative-sequence power ΔP2 of the fault component. When ΔU2, ΔI2, and ΔP2 are all greater than the corresponding threshold values, it is determined that the direction of the negative-sequence power of the fault component points towards the generator unit.

[0021] The above-mentioned setpoint Iset is set to avoid the maximum normal operating current during startup; Tset1 <Tset2。

[0022] A device for overcurrent protection during the startup process of a pumped storage unit, comprising:

[0023] The first judgment module is used to monitor the three-phase current on the generator terminal side and the three-phase current on the neutral point side of the generator motor, determine whether the differential protection conditions are met, and send the judgment result to the short circuit fault discrimination module.

[0024] The second judgment module is used to monitor the three-phase voltage and negative sequence voltage at the generator terminals of the generator motor, and to determine whether the composite voltage condition is met based on the phase-to-phase voltage amplitude and the negative sequence voltage amplitude, and to send the judgment result to the short-circuit fault discrimination module.

[0025] The third judgment module is used to monitor the three-phase voltage at the generator terminal and the three-phase current at the generator terminal, calculate the negative sequence power of the fault component, determine whether the direction of the negative sequence power of the fault component points to the generator unit, and send the judgment result to the short circuit fault discrimination module.

[0026] The short-circuit fault discrimination module is used to determine whether a short-circuit fault has occurred outside the generator motor zone based on the judgment results of the first to third judgment modules, when the differential protection condition is not met, the composite voltage condition is met, and the direction of the negative sequence power of the fault component points to the generator unit. It is also responsible for determining whether a short-circuit fault has occurred outside the generator motor zone. The short-circuit fault discrimination module sends the judgment result of whether a short-circuit fault has occurred or not outside the generator motor zone to the overcurrent protection action module.

[0027] The comparison module is used to compare whether the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset, and sends a timing signal to the timing module when it exceeds the set value.

[0028] The timing module is used to start a delay timing upon receiving a timing signal from the comparison module, and to send the timing result to the overcurrent protection action module; and,

[0029] The overcurrent protection action module is used to execute the corresponding protection action after receiving the judgment result of the short circuit fault judgment module indicating that a short circuit fault has occurred outside the generator motor area and after receiving the time delay Tset1 from the timing module; or, after receiving the judgment result of the short circuit fault judgment module indicating that no short circuit fault has occurred outside the generator motor area and after receiving the time delay Tset2 from the timing module, the corresponding protection action is executed.

[0030] The aforementioned first judgment module monitors the three-phase current on the generator terminal side and the three-phase current on the neutral point side of the generator motor, and determines whether the differential protection conditions are met. This includes: the first judgment module monitors the three-phase current on the generator terminal side and the three-phase current on the neutral point side of the generator motor, calculates the differential current and braking current from the three-phase current on the generator terminal side and the three-phase current on the neutral point side, and determines whether the differential protection conditions are met based on the magnitude of the differential current and the braking current and the ratio braking differential characteristic.

[0031] The aforementioned second judgment module monitors the three-phase voltage and negative sequence voltage at the generator terminals of the generator motor, and determines whether the composite voltage condition is met based on the phase-to-phase voltage amplitude and the negative sequence voltage amplitude. This includes: the second judgment module monitors the three-phase voltage at the generator terminals of the generator motor and calculates the phase-to-phase voltage amplitude U of the generator motor. ab U bc U ca Simultaneously, the negative sequence voltage of the generator motor is monitored, the negative sequence voltage amplitude U2 is calculated, and max(U ab U bc U ca) and U ppset Compare U2 with U 2set Compare, if max(U) is satisfied ab U bc U ca ) < U ppset ] and U2>U 2set If U is constant, then the composite voltage condition is satisfied; where U is constant. ppset =k·U n U n U is the rated value of the phase-to-phase voltage, k is a coefficient; 2set This is the negative sequence voltage threshold value.

[0032] The coefficient k takes values ​​of 90% to 95%.

[0033] The second judgment module mentioned above monitors the three-phase voltage at the generator terminals of the generator motor and calculates the phase-to-phase voltage amplitude of the generator motor, including: monitoring the three-phase voltage at the generator terminals of the generator motor, calculating the three-phase voltage phasor values, and then calculating the phase-to-phase voltage amplitude of the generator motor.

[0034] The method for calculating the three-phase voltage phasor values ​​is to adjust the sampling frequency according to the change of the electrical quantity frequency, so that at any current frequency, each electrical quantity cycle has a fixed number of sampling points. Then, the fixed data window Fourier algorithm is used to calculate the real and imaginary parts of the three-phase voltage, thereby obtaining the voltage phasor values.

[0035] Alternatively, the method for calculating the three-phase voltage phasor values ​​is to use a fixed sampling frequency to discretely sample the three-phase voltages to obtain a sequence of sampled values; dynamically adjust the data window of the Fourier algorithm according to the current electrical quantity frequency so that the actual frequency is half of the rated frequency; then use the Fourier algorithm to measure and calculate the real and imaginary parts of the three-phase voltages to obtain the voltage phasor values.

[0036] The aforementioned third judgment module monitors the three-phase voltage at the generator terminals and the three-phase current on the generator side, calculates the fault component negative sequence power, and determines whether the direction of the fault component negative sequence power points towards the generator unit. This includes: the third judgment module monitors the three-phase voltage at the generator terminals and the three-phase current on the generator side, calculates the effective value ΔU2 of the fault component negative sequence voltage of the generator from the three-phase voltage at the generator terminals, calculates the effective value ΔI2 of the fault component negative sequence current from the three-phase current on the generator side, and then calculates the fault component negative sequence power ΔP2. When ΔU2, ΔI2, and ΔP2 are all greater than the corresponding threshold values, it is determined that the direction of the fault component negative sequence power points towards the generator unit.

[0037] The above-mentioned set value Iset is set to avoid the maximum normal operating current during the startup process; Tset1 < Tset2.

[0038] After adopting the above solution, the beneficial effects of the present invention are: to determine whether the short circuit fault is located on the plant start-up bus circuit outside the stator winding; if so, to shorten the backup overcurrent protection delay, accelerate the protection action, and clear the fault in time, thereby reducing the risk of unit damage. Attached Figure Description

[0039] Figure 1 is a schematic diagram illustrating the application principle of the present invention;

[0040] Wherein, 1 to n are the unit numbers, GS101 to GSn01 are the terminal circuit breakers of the 1st to nth units respectively, GS111 to GSn11 are the drive switches of the 1st to nth units respectively, GS112 to GSn12 are the driven switches of the 1st to nth units respectively, GS121 to GSn21 are the phase-changing generator switches of the 1st to nth units respectively, GS122 to GSn22 are the phase-changing water pump switches of the 1st to nth units respectively, GS001 is the SFC drive switch, F is the phase-to-phase short-circuit fault location of the drive circuit, CT11 to CTn1 are the terminal current transformers of the 1st to nth units respectively, PT01 is the terminal voltage transformer of Unit 1, and the label 51G indicates the node electrical quantity association of the overcurrent protection during the startup process of Unit 1;

[0041] Figure 2 is a flowchart of this method;

[0042] Figure 3 is a diagram of the bilinear ratio braking characteristics, where I r For braking current, I d For differential current, I cdqd For the differential protection starting current, I t Where is the inflection point current, and k is the ratio braking coefficient;

[0043] Figure 4 shows the variable slope ratio braking characteristic diagram, where k′1 and k′2 are the initial slope and maximum slope, respectively, and the curve between the initial slope and the maximum slope is the variable slope fitting curve. Detailed Implementation

[0044] The technical solution and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0045] As shown in Figure 2, this invention provides a method for overcurrent protection during the startup process of a pumped storage unit. In conjunction with Figure 1, the method introduces the three-phase current at the turbine terminals and the secondary current of the neutral point three-phase current transformer, and simultaneously introduces the three-phase voltage of the turbine terminal PT, to enable the judgment and handling of external faults. The method includes the following steps:

[0046] Step 1: The three-phase current on the generator terminal side and the three-phase current on the neutral point side constitute a phase-separated differential protection. Determine whether the differential protection conditions are met. If they are met, the differential protection will operate.

[0047] Step 2: First, calculate the phasor values ​​of the three-phase voltages from the three-phase voltages at the generator terminals, and then calculate the phase-to-phase voltage amplitude and the negative sequence voltage amplitude to determine whether the composite voltage condition is met.

[0048] In step 2, the calculation of the three-phase voltage phasor values ​​from the three-phase terminal voltage can be performed using either of the following two methods:

[0049] The first method involves adjusting the hardware sampling frequency based on the changes in the electrical quantity frequency, so that at any given frequency, each electrical quantity cycle has a fixed number of sampling points, for example, 24 sampling points per cycle. Then, a fixed data window Fourier algorithm is used to calculate the real and imaginary parts of the three-phase voltage, thereby obtaining the voltage phasor values.

[0050] The second method involves using a fixed sampling frequency to discretely sample the three-phase voltages, obtaining a sequence of sampled values. Based on the current electrical frequency, the data window (number of sampling points) of the Fourier algorithm is dynamically adjusted. For example, at the rated frequency, the data window takes 24 sampling points, and when the actual frequency is half of the rated frequency, the data window becomes 48 sampling points. Then, the Fourier algorithm is used to measure and calculate the real and imaginary parts of the current and voltage, thereby obtaining the voltage phasor values.

[0051] In step 2, the composite voltage condition is: max(U ab U bc U ca ) < U ppset And U2>U 2set , among which, U ppset =k·U n U n For the rated value of the phase-to-phase voltage, k is taken as 90% to 95%; U 2set U1 is the negative sequence voltage threshold, ranging from 0.5 to 3V; U2 is the negative sequence voltage amplitude.

[0052] Step 3: Calculate the negative sequence voltage fault component of the generator motor from the three-phase voltage at the generator terminal, calculate the negative sequence current fault component from the three-phase current at the generator terminal, then calculate the negative sequence power of the fault component, and determine whether the direction of the negative sequence power of the fault component points to the generator unit.

[0053] In step 3, the negative sequence power ΔP2 of the fault component is calculated from the three-phase voltage at the generator terminal and the three-phase current on the generator terminal side. in This is a negative sequence voltage fault component. e is the conjugate of the negative sequence current fault component. jΦ Φ is the phase shift factor, and Φ is the negative sequence impedance sensitivity angle, which can be taken as 78°.

[0054] In step 3, the basis for determining whether the direction of the negative sequence power of the fault component points towards the unit is:

[0055]

[0056] Where ΔP2 is the negative sequence power of the fault component, ΔU2 is the effective value of the negative sequence voltage fault component, and ΔI2 is the effective value of the negative sequence current fault component; ε p The negative sequence power threshold is set to 0.0001–0.01; ε u The threshold for the negative sequence voltage fault component is set to 0.1V to 1V; ε i The threshold for the negative sequence current fault component is set at 0.01 to 0.1 times the secondary rated current of the generator motor.

[0057] Step 4: When the differential protection in step 1 does not operate, the composite voltage condition in step 2 is met, and the negative sequence power direction of the fault component in step 3 points to the generator unit, it is considered that a short circuit fault has occurred outside the generator motor zone.

[0058] Step 5: If step 4 determines that a short circuit fault has occurred outside the generator motor zone, and the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset, the protection will operate after a short delay Tset1. Iset is set to avoid the maximum normal operating current during the startup process, generally 0.3Ie to 0.7Ie. Conversely, if step 4 does not determine that a short circuit fault has occurred outside the generator motor zone, and the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset, the protection will operate after a longer delay Tset2. Tset1 is 0.1s to 0.2s; Tset2 is 0.5s to 3s.

[0059] This invention also provides an overcurrent protection device for the startup process of a pumped storage unit, which is connected to the three-phase current on the neutral point side of the generator motor, the three-phase current on the generator terminal side, and the three-phase voltage on the generator terminal side, including,

[0060] The short-circuit fault detection module is used to determine whether a short-circuit fault has occurred outside the generator motor zone when the differential protection conditions are not met, the composite voltage conditions are met, and the negative sequence power direction of the fault component points to the generator unit.

[0061] The comparison module is used to compare whether the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset;

[0062] The timing module is used to perform a delay timing after the comparison module obtains the comparison result; and,

[0063] The overcurrent protection action module is used to perform protection action when the short-circuit fault detection module determines that a short-circuit fault has occurred outside the generator motor zone, the comparison module obtains that the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset, and the timing module counts for Tset1; or when the short-circuit fault detection module does not determine that a short-circuit fault has occurred outside the generator motor zone, the comparison module obtains that the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset, and the timing module counts for Tset2.

[0064] Where Tset1 < Tset2.

[0065] Specifically, the short-circuit fault discrimination module includes a first judgment module for judging whether the differential protection conditions are met. The first judgment module calculates the differential current and braking current from the three-phase current on the generator side and the three-phase current on the neutral point side. Based on the magnitude of the differential current and braking current, the ratio braking differential characteristic is used to judge whether the differential protection conditions are met.

[0066] Specifically, the short-circuit fault detection module includes a second detection module for determining whether the composite voltage condition is met. The basis for the second detection module's determination is max(U ab U bc U ca ) < U ppset And U2>U 2set , among which, U ppset =k·U n U n For the rated value of the line voltage, k is taken as 90% to 95%; U 2set For negative sequence voltage threshold; U ab U bc U ca This represents the phase-to-phase voltage amplitude.

[0067] Specifically, the method for the second judgment module to calculate the phase-to-phase voltage amplitude is to first calculate the three-phase voltage phasor values ​​from the three-phase voltage at the generator terminals, and then calculate the phase-to-phase voltage amplitude of the generator motor.

[0068] Specifically, the three-phase voltage phasor values ​​can be calculated using either of the following two methods:

[0069] The first method is to adjust the sampling frequency according to the change of electrical quantity frequency, so that at any current frequency, each electrical quantity cycle has a fixed number of sampling points. Then, the fixed data window Fourier algorithm is used to calculate the real and imaginary parts of the three-phase voltage, thereby obtaining the voltage phasor value.

[0070] The second method is to use a fixed sampling frequency to discretely sample the three-phase voltage to obtain a sequence of sampled values; dynamically adjust the data window of the Fourier algorithm according to the current electrical quantity frequency; and then use the Fourier algorithm to measure and calculate the real and imaginary parts of the current and voltage to obtain the voltage phasor values.

[0071] Specifically, the short-circuit fault discrimination module includes a third judgment module for determining whether the direction of the negative sequence power of the fault component points to the generator unit. The third judgment module calculates the negative sequence voltage fault component of the generator motor from the three-phase voltage at the generator terminal, calculates the negative sequence current fault component from the three-phase current at the generator terminal, and then calculates the negative sequence power of the fault component to determine whether the direction of the negative sequence power of the fault component points to the generator unit.

[0072] Specifically, the third judgment module determines whether the direction of the negative sequence power of the fault component points to the unit based on the following:

[0073]

[0074] Where ΔP2 is the negative sequence power of the fault component, ΔU2 is the effective value of the negative sequence voltage fault component, and ΔI2 is the effective value of the negative sequence current fault component; ε p For negative sequence power threshold, ε u ε is the threshold for negative sequence voltage fault components. i Negative sequence current fault component threshold.

[0075] As a preferred embodiment of the method of the present invention, the method includes the following steps:

[0076] (1) The phase-separated differential protection is composed of the three-phase current on the generator terminal side and the three-phase current on the neutral point side. For each phase current, the generator terminal current of that phase is used to determine the phase current. and neutral point current Calculate the differential current I d and braking current I r The formula is as follows:

[0077]

[0078] A mature and widely used start-stop protection algorithm, unaffected by frequency, such as the zero-crossing integral algorithm, is employed to calculate the amplitudes of the differential current and braking current. Based on the magnitudes of the differential current and braking current, a ratio braking differential characteristic is used to implement differential protection during the pump start-up process of the pumped storage power station.

[0079] The ratio braking characteristic can be selected from either the double-segment ratio braking method shown in Figure 3 or the variable slope braking method shown in Figure 4. Taking the double-segment ratio braking characteristic shown in Figure 3 as an example, the differential protection action criterion is:

[0080]

[0081] (2) The three-phase voltage phasor values ​​are calculated from the three-phase voltage at the generator terminals using the variable data window Fourier algorithm. First, the current frequency is obtained using a frequency measurement algorithm (see "Li Yiquan, He Benteng. A high-precision frequency measurement method based on Fourier algorithm [J]. Proceedings of the CSEE. 2006 26(2). 78-81"). Based on the current sampling frequency f s Current frequency f of terminal voltage e Calculate the number of sampling points N for each current wave, which is also the length of the real-time data window.

[0082]

[0083] [] indicates rounding down or up.

[0084] Assuming the sampling frequency is 1200Hz and the current voltage and current frequency is 48.8Hz, then N can be 24 or 25.

[0085] Once the data window length N of the Fourier algorithm is determined, calculate the sine and cosine coefficient table of the Fourier algorithm.

[0086]

[0087] Ksin(k) is the sine coefficient at point k, and Kcos(k) is the cosine coefficient at point k.

[0088] The variable data window Fourier algorithm is used to calculate the three-phase voltage phasor values ​​from the three-phase voltage at the generator terminals. Let the real part of phase X be U. Xr and the imaginary part U Xi Phase X represents any one of phases A, B, and C. The Fourier algorithm formula for matching is:

[0089]

[0090] Among them, u x (n) represents the X-phase electrical quantity data sequence.

[0091] Thus, electrical phasors are obtained. as follows:

[0092]

[0093] As mentioned earlier, U ar U br U cr U represents the real parts of phases A, B, and C, respectively. ai Ubi U ci These represent the imaginary parts of phases A, B, and C, respectively.

[0094] Then, the phase-to-phase voltage amplitude of the generator motor is calculated using the following formula:

[0095]

[0096] In the formula, U represents the phasor value of the three-phase voltage. ab U bc U ca This represents the phase-to-phase voltage amplitude.

[0097] The negative sequence voltage amplitude of the generator motor is calculated using the following formula:

[0098]

[0099] Where α is e j120° U2 is the negative sequence voltage amplitude.

[0100] (3) Calculate the negative sequence voltage fault component of the generator motor from the three-phase voltage at the generator terminals, calculate the negative sequence current fault component from the three-phase current at the generator terminals, and calculate the negative sequence power ΔP2 of the fault component. in This is a negative sequence voltage fault component. It is the conjugate of the negative sequence current fault component.

[0101] The method for determining whether the negative sequence power direction element of the fault component points to the unit is as follows:

[0102]

[0103] Where, ε p Take 0.002, ε u Take 0.5V, ε i Take 0.02 times the secondary rated current of the generator motor.

[0104] (4) When the differential protection in step (1) does not operate, the composite voltage condition in step (2) is met, and the negative sequence power direction of the fault component in step (3) points to the generator unit, it is considered that a short circuit fault has occurred outside the generator motor area.

[0105] (5) If step (4) determines that a short circuit fault has occurred outside the generator motor zone and the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset, the protection will operate after a short delay Tset1. Iset is set to avoid the maximum operating current during the startup process, and Tset1 is set to 0.15s. Conversely, if step (4) does not determine that a short circuit fault has occurred outside the generator motor zone, the protection will operate after a long delay Tset2 when the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset. Iset is also set to avoid the maximum operating current during the startup process, and Tset2 is set to 0.5s.

[0106] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for overcurrent protection during the startup process of a pumped storage unit, characterized in that: Monitor the three-phase currents at the generator terminals and the three-phase currents at the neutral point of the generator motor to determine if the differential protection conditions are met; monitor the three-phase voltages and negative sequence voltages at the generator terminals, and determine if the composite voltage conditions are met based on the phase-to-phase voltage amplitude and the negative sequence voltage amplitude; monitor the three-phase voltages at the generator terminals and the three-phase currents at the generator terminals, calculate the negative sequence power of the fault component, and determine if the direction of the negative sequence power of the fault component points towards the generator unit; if the differential protection conditions are not met, the composite voltage conditions are met, and the direction of the negative sequence power of the fault component points towards the generator unit, a short-circuit fault is determined to have occurred outside the generator motor zone; if the differential protection conditions are met, the composite voltage conditions are not met, or the direction of the negative sequence power of the fault component does not point towards the generator unit, ... The system determines whether a short-circuit fault has occurred outside the generator motor zone. If a short-circuit fault occurs outside the generator motor zone and the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset while being continuously delayed for Tset1, the corresponding protection action is executed. If no short-circuit fault occurs outside the generator motor zone and the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset while being continuously delayed for Tset2, the corresponding protection action is executed. This includes monitoring the three-phase voltage and negative sequence voltage at the generator motor terminals, and determining whether the composite voltage condition is met based on the phase-to-phase voltage amplitude and the negative sequence voltage amplitude. This includes monitoring the three-phase voltage at the generator motor terminals and calculating the phase-to-phase voltage amplitude of the generator motor. Simultaneously, the negative sequence voltage of the generator motor is monitored, and the amplitude of the negative sequence voltage is calculated. and will and Compare, and Compare, if satisfied and If , then it is determined that the composite voltage condition is met; where, ， This is the rated value of the phase-to-phase voltage. For coefficients; This is the negative sequence voltage threshold value.

2. The method for overcurrent protection during the startup process of a pumped storage unit as described in claim 1, characterized in that: Monitoring the three-phase currents at the generator terminals and the neutral point to determine whether the differential protection conditions are met includes: monitoring the three-phase currents at the generator terminals and the neutral point; calculating the differential current and braking current from the three-phase currents at the generator terminals and the neutral point; and using the ratio braking differential characteristic based on the magnitude of the differential current and braking current to determine whether the differential protection conditions are met.

3. The method for overcurrent protection during the startup process of a pumped storage unit as described in claim 1, characterized in that: coefficient The value ranges from 90% to 95%.

4. The method for overcurrent protection during the startup process of a pumped storage unit as described in claim 1, characterized in that: Monitoring the three-phase terminal voltage of a generator motor and calculating the phase-to-phase voltage amplitude includes: monitoring the three-phase terminal voltage of the generator motor, calculating the three-phase voltage phasor values, and then calculating the phase-to-phase voltage amplitude. The method for calculating the three-phase voltage phasor values ​​involves adjusting the sampling frequency according to the frequency changes of the electrical quantity, ensuring a fixed number of sampling points within each electrical quantity cycle at any given frequency. Then, a fixed data window Fourier algorithm is used to calculate the real and imaginary parts of the three-phase voltage, thus obtaining the voltage phasor values. Alternatively, the method involves discretely sampling the three-phase voltage at a fixed sampling frequency to obtain a sequence of sampled values. The data window of the Fourier algorithm is dynamically adjusted according to the current electrical quantity frequency, ensuring the actual frequency is half the rated frequency. Then, the Fourier algorithm is used to measure and calculate the real and imaginary parts of the three-phase voltage, thus obtaining the voltage phasor values.

5. The method for overcurrent protection during the startup process of a pumped storage unit as described in claim 1, characterized in that: Monitoring the three-phase voltage at the generator terminals and the three-phase current on the generator side, calculating the negative-sequence power of the fault component, and determining whether the direction of the negative-sequence power of the fault component points towards the generator unit includes: monitoring the three-phase voltage at the generator terminals and the three-phase current on the generator side, and calculating the effective value of the negative-sequence voltage fault component of the generator from the three-phase voltage at the generator terminals. The effective value of the negative sequence current fault component is calculated from the three-phase current at the generator terminal. Then, the negative sequence power of the fault component is calculated. ,when ， ， When all values ​​are greater than the corresponding threshold, the fault component is judged to have a negative sequence power direction pointing towards the unit.

6. The method for overcurrent protection during the startup process of a pumped storage unit as described in claim 1, characterized in that: The set value Iset is set to avoid the maximum normal operating current during the startup process; Tset1 <Tset2。 7. A device for overcurrent protection during the startup process of a pumped storage unit, characterized in that: It includes a first judgment module, used to monitor the three-phase current on the generator terminal side and the three-phase current on the neutral point side of the generator motor, determine whether the differential protection conditions are met, and send the judgment result to the short-circuit fault discrimination module; and a second judgment module, used to monitor the three-phase voltage and negative sequence voltage at the generator terminal of the generator motor, and determine whether the composite voltage conditions are met based on the phase-to-phase voltage amplitude and the negative sequence voltage amplitude, and send the judgment result to the short-circuit fault discrimination module. The third judgment module is used to monitor the three-phase voltage at the generator terminal and the three-phase current at the generator terminal, calculate the negative sequence power of the fault component, determine whether the direction of the negative sequence power of the fault component points to the generator unit, and send the judgment result to the short circuit fault discrimination module. The short-circuit fault detection module is used to determine whether a short-circuit fault has occurred outside the generator motor zone based on the judgment results of the first to third judgment modules, when the differential protection condition is not met, the composite voltage condition is met, and the direction of the negative sequence power of the fault component points to the generator unit. It is also responsible for determining whether a short-circuit fault has occurred outside the generator motor zone. The short-circuit fault detection module sends the judgment result of whether a short-circuit fault has occurred outside the generator motor zone to the overcurrent protection action module. The comparison module is used to compare whether the maximum value of the three-phase current on the neutral point side of the generator motor exceeds the set value Iset, and sends a timing signal to the timing module when it exceeds it. The timing module is used to start a delayed timing upon receiving the timing signal from the comparison module and sends the timing result to the overcurrent protection action module. And, an overcurrent protection action module, used to execute the corresponding protection action after receiving the judgment result of a short circuit fault occurring outside the generator motor area sent by the short circuit fault judgment module, and after receiving a continuous delay Tset1 from the timing module; or, after receiving the judgment result of no short circuit fault occurring outside the generator motor area sent by the short circuit fault judgment module, and after receiving a continuous delay Tset2 from the timing module; wherein, the second judgment module monitors the three-phase voltage and negative sequence voltage at the generator motor terminals, and determines whether the composite voltage condition is met based on the phase-to-phase voltage amplitude and the negative sequence voltage amplitude, including: the second judgment module monitors the three-phase voltage at the generator motor terminals and calculates the phase-to-phase voltage amplitude of the generator motor. Simultaneously, the negative sequence voltage of the generator motor is monitored, and the amplitude of the negative sequence voltage is calculated. and will and Compare, and Compare, if satisfied and If , then it is determined that the composite voltage condition is met; where, ， This is the rated value of the phase-to-phase voltage. For coefficients; This is the negative sequence voltage threshold value.

8. The device for overcurrent protection during the startup process of a pumped storage unit as described in claim 7, characterized in that: The first judgment module monitors the three-phase current on the generator terminal side and the three-phase current on the neutral point side of the generator motor, and determines whether the differential protection conditions are met. This includes: the first judgment module monitors the three-phase current on the generator terminal side and the three-phase current on the neutral point side of the generator motor, calculates the differential current and braking current from the three-phase current on the generator terminal side and the three-phase current on the neutral point side, and determines whether the differential protection conditions are met based on the magnitude of the differential current and the braking current and the ratio braking differential characteristic.

9. The device for overcurrent protection during the startup process of a pumped storage unit as described in claim 7, characterized in that: coefficient The value ranges from 90% to 95%.

10. The device for overcurrent protection during the startup process of a pumped storage unit as described in claim 7, characterized in that: The second judgment module monitors the three-phase voltage at the generator terminals of the generator motor and calculates the phase-to-phase voltage amplitude of the generator motor. This includes: monitoring the three-phase voltage at the generator terminals of the generator motor, calculating the three-phase voltage phasor values, and then calculating the phase-to-phase voltage amplitude of the generator motor. The method for calculating the three-phase voltage phasor values ​​is to adjust the sampling frequency according to the change of the electrical quantity frequency, so that each electrical quantity cycle has a fixed number of sampling points at any current frequency. Then, a fixed data window Fourier algorithm is used to calculate the real and imaginary parts of the three-phase voltage, thereby obtaining the voltage phasor values. Alternatively, the method for calculating the three-phase voltage phasor values ​​is to use a fixed sampling frequency to discretely sample the three-phase voltage to obtain a sequence of sampled values. According to the current electrical quantity frequency, the data window of the Fourier algorithm is dynamically adjusted so that the actual frequency is half of the rated frequency. Then, the Fourier algorithm is used to measure and calculate the real and imaginary parts of the three-phase voltage, thereby obtaining the voltage phasor values.

11. The device for overcurrent protection during the startup process of a pumped storage unit as described in claim 7, characterized in that: The third judgment module monitors the three-phase voltage at the generator terminals and the three-phase current on the generator side, calculates the fault component negative sequence power, and determines whether the direction of the fault component negative sequence power points towards the generator unit. This includes: the third judgment module monitors the three-phase voltage at the generator terminals and the three-phase current on the generator side, and calculates the effective value of the fault component negative sequence voltage of the generator from the three-phase voltage at the generator terminals. The effective value of the negative sequence current fault component is calculated from the three-phase current at the generator terminal. Then, the negative sequence power of the fault component is calculated. ,when ， ， When all values ​​are greater than the corresponding threshold, the fault component is judged to have a negative sequence power direction pointing towards the unit.

12. The device for overcurrent protection during the startup process of a pumped storage unit as described in claim 7, characterized in that: The set value Iset is set to avoid the maximum normal operating current during the startup process; Tset1 <Tset2。

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