A generator PT slow melting discrimination method and system based on voltage sequence components

Abstract

The present application relates to a kind of generator PT slow melting discrimination method and system based on voltage sequence component, belong to the technical field of voltage mutual inductor, based on the difference of negative sequence component and zero sequence component of voltage, PT slow melting fault can be detected very sensitively, highly accurately and reliably, solve the problem that current relay protection equipment cannot sensitively respond PT slow melting fault, which may lead to misoperation of generator set relay protection equipment, false alarm and other problems, conducive to the safe and stable operation of generator set and power grid.

Description

Technical Field

[0001] This invention relates to a method and system for detecting slow fuses in generator PTs based on voltage sequence components, belonging to the field of voltage transformer technology. Background Technology

[0002] A PT (Potential Transformer) is an important component of relay protection. It transforms high voltage into a standard secondary voltage of 100V or lower according to a proportional relationship, for use by protection, metering, and instrumentation devices. At the same time, using a voltage transformer can isolate high voltage from electrical workers.

[0003] Slow-blowout of a PT fuse refers to the process where the fuse blows at a weak point, the fracture surface begins to arc until the fracture widens, and finally the fuse completely breaks. In the early stages of slow-blowout, the voltage drop in the fault phase is minimal, possibly only around 1V to 3V, which is below the PT disconnection alarm threshold. During this process, the effective value of the fault phase voltage decreases slowly, a zero-sequence voltage appears in the PT's secondary open delta winding, and the amplitude of the third harmonic voltage in the open delta winding increases. Therefore, current relay protection equipment cannot sensitively detect slow-blowout faults in PTs. This can lead to serious consequences such as false tripping and false alarms in generator set relay protection equipment.

[0004] To address the aforementioned issues, existing technologies primarily employ the following two methods to determine PT disconnection at the generator terminal:

[0005] Method 1: Balanced PT open circuit determination method. This method determines whether the primary high-voltage fuse of the PT has blown by taking the difference (|PT1-PT2|) between the effective values ​​of the terminal voltages sampled by the two PTs. When |PT1-PT2| > Uset (Uset is the set PT voltage difference value), it is determined that the PT has slow-blown, and an alarm is triggered after a delay.

[0006] Method 2: Negative sequence voltage determination method. This involves calculating the negative sequence voltage U2 from the collected secondary voltage of the PT. When the negative sequence voltage component U2 > the set value of U2set, it is determined that the PT has experienced slow melting, and an alarm is triggered after a delay.

[0007] However, both of the above methods have their drawbacks. Due to factors such as low measurement accuracy or inaccurate algorithms, to prevent adverse effects caused by PT open circuit malfunctions, the PT voltage difference setting Uset and the negative sequence voltage judgment threshold U2set cannot be set too small; in engineering, they are usually set to 5% of the stator rated voltage. When one or more phases of the PT secondary side experience an open circuit, the effective value of the stator voltage drops significantly, making it relatively easy to identify the PT open circuit fault using the two methods mentioned above. However, in the early stage of a slow-blow PT, the voltage of the faulty phase does not decrease much, possibly only around 1V to 3V, which does not reach the PT open circuit alarm threshold of the relay protection. During this process, the effective value of the faulty phase voltage decreases slowly, a zero-sequence voltage appears in the PT secondary open delta winding, and the amplitude of the third harmonic voltage of the open delta winding increases. Therefore, current relay protection equipment cannot sensitively react to PT slow-blow faults, which may lead to serious consequences such as maloperation and false alarms of the generator set relay protection equipment.

[0008] Chinese invention patent application CN107271836A discloses a method for detecting PT (potential transformer) open circuit when the primary fuse at the generator terminal blows slowly. The method includes the following steps: First, data acquisition; second, determining the criteria for whether the first and second voltage transformers are open circuit; third, if the generator primary fuse blows slowly and criteria one and two in step two are not met, then measuring the actual operating current of the fuse connected to the generator. The measured current of the fuse is I. 熔 The rated current of the fuse is I 熔e Let the excitation voltage change be ΔU fd The third judgment condition is determined; the fourth step is that if either the first voltage transformer or the second voltage transformer at the generator terminal is disconnected, an alarm will be triggered, and the process will end. Clearly, directly comparing the phase voltage amplitude or current-voltage ratio of a single PT with a fixed threshold lacks a redundant differential reference and fails to utilize the zero-sequence amplification effect, negative-sequence information, or neutral-point zero-sequence voltage. This makes it almost undetectable for early-stage slow-blowout (minor imbalance) events with a voltage drop of only 1-3V. Furthermore, its instantaneous threshold criterion lacks delay filtering, making it prone to malfunctions due to excitation regulation, switch closing, or instantaneous harmonic impacts. Moreover, without comparison between dual PT differential and neutral-point zero-sequence voltages, it is impossible to determine whether the PT itself is blown or if the system as a whole is unbalanced. The threshold is also not calibrated with an operating reference, making it difficult to adapt to different unit and load conditions. Summary of the Invention

[0009] The purpose of this invention is to provide a generator PT slow fuse detection method and system based on voltage sequence components, in order to solve the problem that the current relay protection equipment cannot sensitively detect PT slow fuse faults, which may lead to false tripping and false alarms of the generator set relay protection equipment.

[0010] To address the aforementioned technical problems, the first aspect of this invention proposes a method for identifying slow-blowout generator PTs based on voltage sequence components, comprising the following steps:

[0011] 1) Calculate the negative sequence voltage component, zero sequence voltage component, and open delta zero sequence voltage of the three-phase voltage of the first voltage transformer connected to the generator under test; calculate the negative sequence voltage component and zero sequence voltage component of the three-phase voltage of the second voltage transformer connected to the generator under test.

[0012] 2) Determine whether the voltage transformer has experienced slow PT melting based on the negative sequence voltage and zero sequence voltage.

[0013] In one possible implementation, the following method is used to determine whether a voltage transformer (PT) has experienced a slow fuse, based on the negative-sequence voltage and the zero-sequence voltage:

[0014] Based on the negative sequence voltage and a pre-defined negative sequence voltage criterion, determine whether the voltage transformer has experienced a slow-blowout PT; or,

[0015] Based on the zero-sequence voltage and a pre-defined zero-sequence voltage criterion, a determination is made as to whether the voltage transformer has experienced a slow-blowout PT.

[0016] In one possible implementation, the discrimination formula for the negative sequence voltage criterion is:

[0017] or ;

[0018] in, This is the effective value of the negative sequence voltage of the first voltage transformer; This is the effective value of the negative sequence voltage of the second voltage transformer; This is the threshold setting value for negative sequence voltage difference.

[0019] In one possible implementation, the The value is (1% U) N 3% U N ); where U N This is the rated line voltage on the secondary side of the voltage transformer.

[0020] In one possible implementation, the zero-sequence voltage of the neutral-grounded transformer connected to the generator under test is calculated; wherein,

[0021] The discrimination formula for the zero-sequence voltage criterion is as follows:

[0022] ;

[0023] Among them, among them, This is the effective value of the zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the second voltage transformer; The effective value of the open delta zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the neutral-point grounded transformer; is the zero-sequence voltage difference threshold setting value; K is the neutral point zero-sequence voltage balance coefficient.

[0024] In one possible implementation, the The value is (1% U) N 3% U N ); where U N This is the rated line voltage on the secondary side of the voltage transformer.

[0025] In one possible implementation, when the negative sequence voltage criterion is met, it is determined that either the first voltage transformer or the second voltage transformer has experienced a slow PT fuse.

[0026] When the first criterion in the zero-sequence voltage criterion is met, it is determined that the first voltage transformer or the second voltage transformer has experienced a slow PT fuse.

[0027] When the second criterion in the zero-sequence voltage criterion is satisfied, it is determined that the first voltage transformer has experienced a slow PT melt.

[0028] In one possible implementation, the method further includes: generating an alarm signal in response to a slow fuse of the voltage transformer (PT), and issuing the alarm signal upon the arrival of a set delay time to perform a blocking protection.

[0029] To address the aforementioned technical problems, a second aspect of the present invention provides a generator PT slow fuse discrimination system based on voltage sequence components, comprising a processor that executes a computer program to perform the following steps:

[0030] 1) Calculate the negative sequence voltage component, zero sequence voltage component, and open delta zero sequence voltage of the three-phase voltage of the first voltage transformer connected to the generator under test; calculate the negative sequence voltage component and zero sequence voltage component of the three-phase voltage of the second voltage transformer connected to the generator under test.

[0031] 2) Determine whether the voltage transformer has experienced slow PT melting based on the negative sequence voltage and zero sequence voltage.

[0032] In one possible implementation, the following method is used to determine whether a voltage transformer (PT) has experienced a slow fuse, based on the negative-sequence voltage and the zero-sequence voltage:

[0033] Based on the negative sequence voltage and a pre-defined negative sequence voltage criterion, determine whether the voltage transformer has experienced a slow-blowout PT; or,

[0034] Based on the zero-sequence voltage and a pre-defined zero-sequence voltage criterion, a determination is made as to whether the voltage transformer has experienced a slow-blowout PT.

[0035] In one possible implementation, the discrimination formula for the negative sequence voltage criterion is:

[0036] or ;

[0037] in, This is the effective value of the negative sequence voltage of the first voltage transformer; This is the effective value of the negative sequence voltage of the second voltage transformer; This is the threshold setting value for negative sequence voltage difference.

[0038] In one possible implementation, the The value is (1% U) N 3% U N ); where U N This is the rated line voltage on the secondary side of the voltage transformer.

[0039] In one possible implementation, the zero-sequence voltage of the neutral-grounded transformer connected to the generator under test is calculated; wherein,

[0040] The discrimination formula for the zero-sequence voltage criterion is as follows:

[0041] ;

[0042] Among them, among them, This is the effective value of the zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the second voltage transformer; The effective value of the open delta zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the neutral-point grounded transformer; is the zero-sequence voltage difference threshold setting value; K is the neutral point zero-sequence voltage balance coefficient.

[0043] In one possible implementation, the The value is (1% U) N 3% U N ); where U N This is the rated line voltage on the secondary side of the voltage transformer.

[0044] In one possible implementation, when the negative sequence voltage criterion is met, it is determined that either the first voltage transformer or the second voltage transformer has experienced a slow PT fuse.

[0045] When the first criterion in the zero-sequence voltage criterion is met, it is determined that the first voltage transformer or the second voltage transformer has experienced a slow PT fuse.

[0046] When the second criterion in the zero-sequence voltage criterion is satisfied, it is determined that the first voltage transformer has experienced a slow PT melt.

[0047] In one possible implementation, the method further includes: generating an alarm signal in response to a slow fuse of the voltage transformer (PT), and issuing the alarm signal upon the arrival of a set delay time to perform a blocking protection.

[0048] The beneficial effects of this invention are as follows: Based on the difference between the negative sequence component and the zero sequence component of voltage, it can detect PT slow fuse faults with high sensitivity, accuracy and reliability, solving the problems that current relay protection equipment cannot sensitively respond to PT slow fuse faults, which may lead to false tripping and false alarms of generator set relay protection equipment, thus facilitating the safe and stable operation of generator sets and power grids. Attached Figure Description

[0049] Figure 1 This is a flowchart of a generator PT slow fuse discrimination method based on voltage sequence components proposed in this invention;

[0050] Figure 2 This is a schematic diagram of the electrical main wiring of a typical application of the generator PT slow fuse discrimination method based on voltage sequence components proposed in this invention in a practical application scenario.

[0051] Figure 3 This is a logic diagram for judging PT slow fuse faults in a practical application scenario of a generator PT slow fuse discrimination method based on voltage sequence components proposed in this invention;

[0052] Figure 4 This is a logic diagram for PT3 slow fuse fault identification in a practical application scenario of a generator PT slow fuse identification method based on voltage sequence components proposed in this invention.

[0053] Figure 5 This is a structural diagram of a generator PT slow fuse discrimination system based on voltage sequence components proposed in this invention. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0055] The inventive concept of this invention is as follows: Based on the difference between the negative sequence component and the zero sequence component of voltage, this invention can detect PT slow fuse faults with high sensitivity, accuracy and reliability, solving the problems that current relay protection equipment cannot sensitively detect PT slow fuse faults, which may lead to false tripping and false alarms of generator set relay protection equipment, thus benefiting the safe and stable operation of generator sets and power grids.

[0056] Detailed implementation method 1:

[0057] like Figure 1 The diagram shows a flowchart of a generator PT slow fuse detection method based on voltage sequence components proposed in this invention, which includes steps S11 and S12, specifically:

[0058] Step S11: Calculate the negative sequence voltage component, zero sequence voltage component, and open delta zero sequence voltage of the three-phase voltage of the first voltage transformer connected to the generator under test; calculate the negative sequence voltage component and zero sequence voltage component of the three-phase voltage of the second voltage transformer connected to the generator under test.

[0059] Step S12: Determine whether the voltage transformer has experienced slow PT melting based on the negative sequence voltage and zero sequence voltage. It should be noted that: the determination of whether the voltage transformer has experienced slow PT melting is based on the negative sequence voltage and a pre-defined negative sequence voltage criterion; or, the determination of whether the voltage transformer has experienced slow PT melting is based on the zero sequence voltage and a pre-defined zero sequence voltage criterion.

[0060] Preferably, the formula for the negative sequence voltage criterion is:

[0061] or ;

[0062] in, This is the effective value of the negative sequence voltage of the first voltage transformer; This is the effective value of the negative sequence voltage of the second voltage transformer; This is the threshold setting value for negative sequence voltage difference.

[0063] Calculate the zero-sequence voltage of the neutral-grounded transformer connected to the generator under test; the formula for the zero-sequence voltage criterion is:

[0064] ;

[0065] Among them, among them, This is the effective value of the zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the second voltage transformer; The effective value of the open delta zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the neutral-point grounded transformer; is the zero-sequence voltage difference threshold setting value; K is the neutral point zero-sequence voltage balance coefficient.

[0066] When the negative sequence voltage criterion is satisfied (that is, when the negative sequence voltage criterion is satisfied), or When the condition is met, it is determined that either the first voltage transformer or the second voltage transformer has experienced a slow PT fuse.

[0067] When the first criterion in the zero-sequence voltage criterion is satisfied (that is, ... When the condition is met, it is determined that either the first voltage transformer or the second voltage transformer has experienced a slow PT fuse.

[0068] When the second criterion in the zero-sequence voltage criterion is satisfied (that is, ... When the condition is met, it is determined that the first voltage transformer has experienced a slow PT melt.

[0069] Through the above steps S11-S12, the difference between the negative sequence component and the zero sequence component based on voltage is realized, which can detect PT slow fuse faults with high sensitivity, accuracy and reliability. This solves the problem that the current relay protection equipment cannot sensitively respond to PT slow fuse faults, which may cause the generator set relay protection equipment to malfunction and false alarm, thus benefiting the safe and stable operation of the generator set and the power grid.

[0070] Method Detailed Implementation 2:

[0071] The following explanation, in conjunction with practical applications, details a generator PT slow-blow detection method based on voltage sequence components proposed in this invention. This method includes steps 1-3, wherein two sets of voltage transformers with the same rated voltage (a first voltage transformer and a second voltage transformer, respectively) are connected to the generator terminals under test. The second side of the first voltage transformer has an open delta winding. Specifically:

[0072] Step 1: Collect the three-phase voltage and open delta zero-sequence voltage of the first voltage transformer; collect the three-phase voltage of the second voltage transformer; collect the zero-sequence voltage of the neutral-point grounded transformer of the generator under test.

[0073] Here, the three-phase voltages of the two voltage transformers are the voltages of phases A, B, and C; the open delta zero-sequence voltage refers to the voltage formed by connecting the three auxiliary secondary windings (usually rated voltage of 100 / 3 V) of the voltage transformer in series end to end, but leaving the two ends (usually da and dn) of the last winding open. The voltage at both ends of this opening is numerically equal to the vector sum of the voltages of the three windings; the zero-sequence voltage of the neutral point grounding transformer of the generator under test refers to the voltage between the neutral point of the generator under test and the ground.

[0074] In actual data acquisition, when the two voltage transformers are connected in a three-phase four-wire configuration, the secondary side star winding of the PT (Power Transformer) leads out three phase voltage terminals (A, B, C) and one common neutral point terminal (N). The acquisition device connects to three pairs of signals: AN, BN, and CN. Each pair of signals directly measures the phase voltage phasor to ground (to the neutral point). The auxiliary winding of the first voltage transformer is connected in an open delta configuration, and its output terminals are usually marked as da (or L) and dn (or N). The acquisition device directly acquires the instantaneous voltage value between these two terminals. The voltage across the L and N terminals of the single-phase grounding transformer or arc suppression coil on the neutral point side of the generator under test is directly acquired by the acquisition device.

[0075] Step 2: Based on the parameters collected in Step 1, calculate in real time the negative sequence voltage component, zero sequence voltage component, and open delta zero sequence voltage of the three-phase voltage of the first voltage transformer; the negative sequence voltage component and zero sequence voltage component of the three-phase voltage of the second voltage transformer; and the effective value of the zero sequence voltage of the neutral point grounding transformer of the generator under test.

[0076] Here, the parameters of the first voltage transformer are calculated as follows: the negative sequence voltage component is obtained through the following formula:

[0077] ;

[0078] in, It is a negative sequence voltage component; This refers to the voltage of phase A. This is the voltage of phase B; This refers to the voltage of phase C. is the rotation factor.

[0079] The zero-sequence voltage component is obtained through the following formula:

[0080] ;

[0081] in, It is the zero-sequence voltage component; This refers to the voltage of phase A. This is the voltage of phase B; This is the voltage of phase C.

[0082] The open-delta zero-sequence voltage is obtained directly from the open-delta zero-sequence voltage (L, N) channel of the first voltage transformer. .

[0083] The negative-sequence voltage component and the zero-sequence voltage component of the second voltage transformer are calculated, which are obtained by calculating the negative-sequence voltage component formula and the zero-sequence voltage component formula of the first voltage transformer.

[0084] The effective value of the zero-sequence voltage of the neutral-point grounded transformer of the generator under test is calculated by directly collecting the neutral-point zero-sequence voltage.

[0085] Step 3: Determine whether a PT slow fuse has occurred based on the negative sequence voltage difference and the zero sequence voltage difference; when a PT slow fuse fault is determined to have occurred, issue an alarm signal and lock out the relevant protection after a set delay; the set delay value range is 0.1s to 100s.

[0086] It should be noted that the determination of whether a slow-blow PT fault has occurred based on the negative-sequence voltage difference and the zero-sequence voltage difference includes both negative-sequence voltage difference criteria and zero-sequence voltage difference criteria. When either the negative-sequence voltage difference criterion or the zero-sequence voltage difference criterion meets its corresponding set value, a slow-blow PT fault is determined to have occurred. The determination formula is as follows:

[0087] The formula for determining the negative sequence voltage difference is as follows:

[0088] or (1)

[0089] in, This is the effective value of the negative sequence voltage of the first voltage transformer; This is the effective value of the negative sequence voltage of the second voltage transformer; The threshold setting value for negative sequence voltage difference is preferred in this application. The value is (1%, 3%)U N .

[0090] The formula for the zero-sequence voltage difference criterion is as follows:

[0091] or (2)

[0092] (3)

[0093] in, This is the effective value of the zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the second voltage transformer; The effective value of the open delta zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage at the neutral point; The preferred value in this application is the zero-sequence voltage difference threshold setting. The value is (1%, 3%)U N K is the neutral point zero-sequence voltage balance coefficient. In this application, the value of K is determined by the zero-sequence voltage transformation ratio n of the first voltage transformer open delta. vg0 and generator neutral point zero-sequence voltage transformation ratio n v0 Decision, K= .

[0094] When equation (1) is true, the slow-blow condition of the first voltage transformer or the second voltage transformer is met, and the slow-blow fault of the first voltage transformer or the second voltage transformer is determined.

[0095] When equation (2) is true, the slow-blow condition of the first voltage transformer or the second voltage transformer is met, and the slow-blow fault of the first voltage transformer or the second voltage transformer is determined.

[0096] When equation (3) is true, the slow-blow condition of the first voltage transformer is met, and the slow-blow fault of the first voltage transformer is determined.

[0097] Steps S11-S13 achieve highly sensitive, accurate, and reliable detection of PT slow-blow faults based on the difference between the negative-sequence and zero-sequence voltage components. This solves the problem of current relay protection equipment's inability to sensitively detect PT slow-blow faults, which may lead to maloperation and false alarms in generator relay protection equipment. Specifically, the system uses the three-phase voltage of the first voltage transformer at the generator terminal, the open-delta zero-sequence voltage, the three-phase voltage of the second voltage transformer at the generator terminal, and the zero-sequence voltage of the generator neutral point. When the difference between the negative-sequence and zero-sequence voltage components meets the PT slow-blow fault criterion, a PT slow-blow fault is determined to have occurred. After a delay, an alarm signal is issued and relevant protection is blocked, notifying operators to handle the situation promptly, thus facilitating the safe and stable operation of the generator unit and the power grid.

[0098] Method Detailed Implementation 3:

[0099] The following section explains the generator PT slow fuse discrimination method based on voltage sequence components proposed in this application, using practical application scenarios as examples.

[0100] This invention collects the three-phase voltage and open delta zero-sequence voltage of PT1 (i.e., the first voltage transformer) at the generator terminal; collects the three-phase voltage of PT3 (i.e., the second voltage transformer) at the generator terminal; and collects the zero-sequence voltage of the generator neutral point grounding transformer.

[0101] Based on the collected three-phase voltage and open-delta zero-sequence voltage of PT1, the negative-sequence voltage component, zero-sequence voltage component, and open-delta zero-sequence voltage of PT1 are calculated in real time. Based on the collected three-phase voltage of PT3, the negative-sequence voltage component and zero-sequence voltage component of PT3 are calculated in real time. Based on the collected zero-sequence voltage of the generator neutral point contact transformer, the effective value of the generator neutral point zero-sequence voltage is calculated in real time.

[0102] When the negative sequence voltage difference criterion or the zero sequence voltage difference criterion meets the set value, it is determined to be a PT slow fuse fault, and an alarm signal is given after a delay and the relevant protection is blocked.

[0103] The specific implementation of this method is illustrated using a 600MW generator system of a power plant as an example. For the main electrical wiring diagram and the wiring diagram for the PT slow-blow detection method, please refer to [link / reference]. Figure 2 As shown.

[0104] The preferred PT1 ratio is or or kV and PT3 transformer ratios are: or or kV, generator neutral point zero-sequence voltage grounding transformer voltage ratio is Or 0.1kV, the specific steps for implementing a generator PT slow fuse discrimination method based on voltage sequence components are as follows:

[0105] 1. Collect the three-phase voltage and open delta zero-sequence voltage of PT1 at the generator terminal; collect the three-phase voltage of PT3 at the generator terminal; collect the zero-sequence voltage of the generator neutral point grounding transformer.

[0106] 2. Real-time calculation of the negative sequence voltage component of the three-phase voltage of PT1 Zero-sequence voltage component PT1 open delta zero-sequence voltage Negative sequence voltage component of PT3 three-phase voltage Zero-sequence voltage component Effective value of generator neutral point zero-sequence voltage .

[0107] 3. The typical value is (1% to 3%)U N , The typical value is (1% to 3%)U N K is the neutral point zero-sequence voltage balance coefficient, and its value is determined by the zero-sequence voltage transformation ratio n of PT1 open delta. vg0 and generator neutral point zero-sequence voltage transformation ratio n v0 Decision, K= .

[0108] 4. Negative sequence voltage difference criterion and zero sequence voltage difference criterion: When either the negative sequence voltage difference criterion or the zero sequence voltage difference criterion meets the set value, it is determined to be a slow-blow PT. The discrimination formula is as follows:

[0109] The formula for determining the negative sequence voltage difference is as follows:

[0110] or (1)

[0111] The formula for the zero-sequence voltage difference criterion is as follows:

[0112] or (2)

[0113] (3)

[0114] When equation (1) is true, the slow melting condition of PT1 or PT3 is met, and the slow melting fault of PT1 or PT2 is determined.

[0115] When equation (2) is true, the slow melting condition of PT1 or PT3 is met, and the slow melting fault of PT1 or PT3 is determined.

[0116] When equation (3) is true, the corresponding PT1 slow-blow condition is met, and the PT1 slow-blow fault is determined.

[0117] 5. When formula (1) or (2) or (3) is true, the corresponding PT slow-blow condition is met, the corresponding PT slow-blow fault is determined, and after a set delay, a PT slow-blow fault alarm is issued and the relevant protection is locked.

[0118] 6. To avoid voltage fluctuations and various transient interferences from system faults, the delay setting can be set to 5.0s.

[0119] Method Detailed Implementation 4:

[0120] Based on the specific implementation method 3 of the present invention described above, and in conjunction with the accompanying drawings... Figure 3 and Figure 4 The methods for judging PT1 slow melting faults and PT2 slow melting faults are explained respectively.

[0121] like Figure 3 The diagram shows the logic diagram for PT1 slow-blow fault detection in a practical application scenario of the generator PT slow-blow detection method based on voltage sequence components proposed in this invention. Based on the collected three-phase voltage and open-delta zero-sequence voltage of PT1, the negative-sequence voltage component, zero-sequence voltage component, and open-delta zero-sequence voltage of PT1 are calculated in real time. Based on the collected three-phase voltage of PT3, the negative-sequence voltage component and zero-sequence voltage component of PT3 are calculated in real time. Based on the collected zero-sequence voltage of the generator neutral-point grounding transformer, the effective value of the generator neutral-point zero-sequence voltage is calculated in real time.

[0122] when or or When the PT1 slow melt fault is detected, a PT1 slow melt fault alarm is issued after a delay of time t.

[0123] like Figure 4The diagram shows the logic diagram for PT3 slow-blow fault detection in a practical application scenario using the generator PT slow-blow detection method based on voltage sequence components proposed in this invention. Based on the collected three-phase voltage and open-delta zero-sequence voltage of PT1, the negative-sequence voltage component, zero-sequence voltage component, and open-delta zero-sequence voltage of PT1 are calculated in real time. Similarly, based on the collected three-phase voltage of PT3, the negative-sequence voltage component and zero-sequence voltage component of PT3 are calculated in real time. Finally, based on the collected generator neutral point zero-sequence voltage, the effective value of the generator neutral point zero-sequence voltage is calculated in real time.

[0124] when or When the PT3 is confirmed to have a slow-melting fault, a PT3 slow-melting fault alarm is issued after a delay of time t.

[0125] System implementation details:

[0126] A generator PT slow fuse detection system based on voltage sequence component according to the present invention is shown in the schematic diagram below. Figure 5 As shown, the system includes a memory, a processor, a system bus, and a computer program stored in the memory. The processor and memory communicate and exchange data via the system bus. The processor executes the computer program to implement the steps of the generator PT slow fuse detection method based on voltage sequence components according to the present invention. The processor can be a microprocessor (MCU) or other processing device; the memory can be any type of memory that stores information using electrical energy, such as non-volatile storage media (including computer programs, databases), or other types of memory.

[0127] This system offers high deployment flexibility. It can be deployed on cloud servers, leveraging their powerful computing and storage resources to process large-scale voltage data and enable PT fault detection and remote operation and maintenance on generators. Alternatively, it can be deployed on edge computing nodes or industrial control computers on generators to achieve local real-time data processing and low-latency discrimination, reducing reliance on network bandwidth and ensuring data privacy and security. Furthermore, the system can be provided as a software-as-a-service, allowing users to view the discrimination results through terminals, effectively reducing hardware investment and maintenance costs on the generator side.

[0128] In summary, the beneficial effects of this invention are that it provides a generator PT slow-blow fault detection method and system based on voltage sequence components. Based on the difference between the negative-sequence and zero-sequence voltage components, it can detect PT slow-blow faults with high sensitivity, accuracy, and reliability, solving the problems of current relay protection equipment's inability to sensitively detect PT slow-blow faults, which may lead to false tripping and false alarms in generator relay protection equipment. This invention uses the three-phase voltage of PT1 at the generator terminal, the open-delta zero-sequence voltage, the three-phase voltage of PT3 at the generator terminal, and the zero-sequence voltage of the generator neutral-point grounding transformer. When the difference between the negative-sequence and zero-sequence voltage components meets the PT slow-blow fault criterion, a PT slow-blow fault is determined to have occurred. After a delay, an alarm signal is issued and relevant protection is blocked, notifying operators to handle the situation promptly, which is beneficial to the safe and stable operation of the generator unit and the power grid.

[0129] Using the above method, based on the difference between the negative sequence component and the zero sequence component of the voltage, when the difference between the negative sequence component and the zero sequence component of the voltage meets the PT slow fuse criterion, it is determined that a PT slow fuse fault has occurred. After a delay, an alarm signal is given and the relevant protection is blocked, notifying the operator to handle it in time, which is conducive to the safe and stable operation of the generator unit and the power grid.

[0130] This invention proposes a generator PT slow fuse detection method and system based on voltage sequence components. Based on the difference between the negative sequence component and the zero sequence component of voltage, it can detect PT slow fuse faults with high sensitivity, accuracy and reliability. It solves the problems that current relay protection equipment cannot sensitively detect PT slow fuse faults, which may lead to false tripping and false alarms of generator set relay protection equipment, and is conducive to the safe and stable operation of generator sets and power grid.

Claims

1. A method for detecting slow fuses in generator PTs based on voltage sequence components, characterized in that, Includes the following steps: 1) Calculate the negative sequence voltage component, zero sequence voltage component, and open delta zero sequence voltage of the three-phase voltage of the first voltage transformer connected to the generator under test; calculate the negative sequence voltage component and zero sequence voltage component of the three-phase voltage of the second voltage transformer connected to the generator under test. 2) Determine whether the voltage transformer has experienced slow PT melting based on the negative sequence voltage and zero sequence voltage.

2. The generator PT slow fuse discrimination method based on voltage sequence component according to claim 1, characterized in that, Based on the negative sequence voltage and zero sequence voltage, determine whether the voltage transformer has experienced a slow-blowout PT (potential transformer) fuse using the following method: The determination of whether a voltage transformer has experienced slow PT melting is made based on the negative sequence voltage and a pre-defined negative sequence voltage criterion; or, the determination of whether a voltage transformer has experienced slow PT melting is made based on the zero sequence voltage and a pre-defined zero sequence voltage criterion.

3. The generator PT slow fuse discrimination method based on voltage sequence component according to claim 2, characterized in that, The discrimination formula for the negative sequence voltage criterion is as follows: or ; in, This is the effective value of the negative sequence voltage of the first voltage transformer; This is the effective value of the negative sequence voltage of the second voltage transformer; This is the threshold setting value for negative sequence voltage difference.

4. The generator PT slow fuse discrimination method based on voltage sequence component according to claim 3, characterized in that, The The value is (1% U) N 3% U N ); Among them, U N This is the rated line voltage on the secondary side of the voltage transformer.

5. The generator PT slow fuse discrimination method based on voltage sequence component according to claim 2, characterized in that, Calculate the zero-sequence voltage of the neutral-grounded transformer connected to the generator under test; where, The discrimination formula for the zero-sequence voltage criterion is as follows: ； in, This is the effective value of the zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the second voltage transformer; The effective value of the open delta zero-sequence voltage of the first voltage transformer; This is the effective value of the zero-sequence voltage of the neutral-point grounded transformer; is the zero-sequence voltage difference threshold setting value; K is the neutral point zero-sequence voltage balance coefficient.

6. The generator PT slow fuse discrimination method based on voltage sequence component according to claim 5, characterized in that, The The value is (1% U) N 3% U N ); Among them, U N This is the rated line voltage on the secondary side of the voltage transformer.

7. The generator PT slow fuse discrimination method based on voltage sequence component according to claim 2, characterized in that, When the negative sequence voltage criterion is met, it is determined that the first voltage transformer or the second voltage transformer has experienced a slow PT fuse. When the first criterion in the zero-sequence voltage criterion is met, it is determined that the first voltage transformer or the second voltage transformer has experienced a slow PT fuse. When the second criterion in the zero-sequence voltage criterion is satisfied, it is determined that the first voltage transformer has experienced a slow PT melt.

8. The generator PT slow fuse discrimination method based on voltage sequence component according to claim 1, characterized in that, Also includes: In response to a slow fuse of the voltage transformer (PT), an alarm signal is generated, and when the set delay time is reached, the alarm signal is issued to perform the lockout protection.

9. A generator PT slow fuse discrimination system based on voltage sequence components, comprising a processor, characterized in that, The processor executes a computer program to implement the steps of the method according to any one of claims 1 to 8.

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