Dry-type air-core reactor turn-to-turn short circuit early warning method

Abstract

The invention belongs to the technical field of power equipment state monitoring and fault diagnosis, and particularly relates to a dry-type air-core reactor turn-to-turn short circuit early warning method, which comprises the following steps of: establishing a circuit model and a voltage equation set of a dry-type air-core reactor in a normal operation state and a turn-to-turn short circuit fault state; acquiring a voltage signal and a current signal of the dry-type air-core reactor in a running process in real time; calculating one or more key electrical parameters of the dry-type air-core reactor based on the voltage signal and the current signal; comparing and analyzing the calculated key electrical parameters with corresponding preset thresholds or reference parameters in a normal state; and when the variable quantity or the absolute value of at least one key electrical parameter exceeds a corresponding preset range, triggering turn-to-turn short circuit early warning. According to the invention, the early and accurate early warning of the turn-to-turn short circuit fault of the dry-type air-core reactor is realized, and the technical bottleneck of slow action of traditional overcurrent protection is fundamentally broken through.

Description

Technical Field

[0001] This invention belongs to the field of power equipment condition monitoring and fault diagnosis technology, specifically relating to a method for early warning of inter-turn short circuits in dry-type air-core reactors. Background Technology

[0002] Dry-type air-core reactors, as key reactive power compensation devices in power systems, are widely used in substations, converter stations, and other fields due to their advantages such as being oil-free, fire-resistant, simple in structure, and having good linearity. However, their inherent cascaded air-core winding structure results in relatively weak mechanical strength, requiring them to withstand enormous transient electrodynamic and thermal stress shocks during switching operations. Operational statistics show that most reactor faults, especially inter-turn insulation damage, occur during the switching process or are caused by cumulative damage generated during this process. Inter-turn short-circuit faults typically manifest as localized, minor changes in electrical characteristics in their initial stages. If they are not detected and warned of in time, the fault point will rapidly expand and generate heat, eventually leading to reactor burnout or even fire, posing a serious threat to the safe and stable operation of the power grid.

[0003] Currently, condition monitoring and fault diagnosis of dry-type air-core reactors mainly rely on the following two types of methods:

[0004] Periodic preventative testing mainly includes offline DC resistance, inductance, and impedance measurements. The limitation of this method is that the equipment must be taken out of service, making it unable to reflect the reactor's dynamic performance changes under actual operating conditions, especially during switching. Furthermore, the testing cycle is long, making it difficult to promptly detect rapidly developing early faults.

[0005] Online live-line testing technologies mainly include infrared thermography, ultraviolet imaging, and vibration and noise detection. Infrared thermography is effective for surface overheating, but inter-turn short circuits occur inside the coil, and by the time heat reaches the surface, the fault has often progressed to a middle or late stage, resulting in detection delays and blind spots. Ultraviolet imaging is mainly used to detect corona discharge, but its direct indication of inter-turn short circuits is not strong. Vibration and noise detection is easily affected by the field environment, and the fault characteristic quantities are not easily distinguishable from vibration signals during normal operation, leading to a high false alarm rate.

[0006] In addition, existing relay protection systems (such as overcurrent protection) are mainly designed for severe short-circuit faults. Their operating settings are relatively high, and they are not very sensitive to early inter-turn short circuits that only cause small current and impedance changes, so they cannot achieve early warning functions. Summary of the Invention

[0007] The purpose of this invention is to provide a method for early warning of inter-turn short circuits in dry-type air-core reactors, so as to solve the problems existing in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for early warning of inter-turn short circuits in a dry-type air-core reactor, comprising the following steps:

[0009] S1: Establish the circuit model and voltage equation set of the dry-type air-core reactor under normal operation and inter-turn short-circuit fault conditions;

[0010] S2: Real-time acquisition of voltage and current signals of the dry-type air-core reactor during operation;

[0011] S3: Based on the voltage and current signals, calculate one or more key electrical parameters of the dry-type air-core reactor, including equivalent resistance, equivalent reactance, total impedance, and loss percentage;

[0012] S4: Compare and analyze the calculated key electrical parameters with their corresponding preset thresholds or reference parameters under normal conditions;

[0013] S5: When the change or absolute value of at least one of the key electrical parameters exceeds its corresponding preset range, an inter-turn short circuit warning is triggered.

[0014] Preferably, in step S1, establishing the circuit model of the dry-type air-core reactor under the inter-turn short-circuit fault state specifically involves:

[0015] The faulty layer coil where an inter-turn short circuit occurs is equivalent to two parallel branches. One branch consists of the short-circuited turns, and the other branch consists of the remaining normal turns of the layer, thus forming an equivalent circuit model containing n+1 branches, where n is the total number of reactor layers.

[0016] Preferably, in step S3, the calculation of the equivalent resistance and equivalent reactance is specifically achieved through the following formulas:

[0017] Total current:

[0018] Equivalent resistance:

[0019] Equivalent reactance:

[0020] in, U is the total current flowing through the reactor, U is the applied voltage, and δ is the loss angle.

[0021] Preferably, in step S3, the total impedance Z is determined by the formula: The percentage of loss is calculated using the formula. Obtained through calculation.

[0022] Preferably, in step S3, the calculation process of the key electrical parameters further considers the ambient temperature factor, and the variation law of the key electrical parameters under different temperature conditions is calculated by numerical analysis method.

[0023] Preferably, in step S2, the voltage and current signals are obtained from existing voltage and current transformers on site, without the need for additional installation of dedicated electrical sensors.

[0024] Preferably, in step S4, the preset threshold or reference parameter is established by learning from the historical operating data of the dry-type air-core reactor under normal fault-free conditions or by calculating through its theoretical circuit model.

[0025] Preferably, in step S5, the triggering of the warning includes warning signals of different levels. The warning level is divided according to the number or degree of electrical parameters exceeding the preset range, so as to indicate the severity of the fault.

[0026] A dry-type air-core reactor inter-turn short-circuit early warning system is provided for implementing the method described above. The system includes:

[0027] The data acquisition module is used to acquire voltage and current signals from voltage transformers and current transformers in real time.

[0028] The data processing and calculation module is used to calculate at least one key electrical parameter among the equivalent resistance, equivalent reactance, total impedance, and loss percentage based on the voltage signal and current signal.

[0029] The analysis and judgment module is used to compare the calculated key electrical parameters with preset thresholds or benchmark parameters;

[0030] The early warning output module is used to output an early warning signal when it is determined that there is a risk of inter-turn short circuit.

[0031] Preferably, the system includes a lower-level computer unit with the ground as the reference potential and an upper-level computer unit with the control room ground as the reference potential. The lower-level computer unit and the upper-level computer unit exchange data and are electrically isolated from each other through optical fiber communication.

[0032] The beneficial effects of this invention are as follows: This invention achieves early and accurate warning of inter-turn short-circuit faults in dry-type air-core reactors, fundamentally breaking through the technical bottleneck of slow operation of traditional overcurrent protection. By establishing an accurate fault equivalent circuit model and monitoring and analyzing key electrical parameters that can sensitively reflect the inter-turn insulation state, such as total impedance and loss percentage, in real time, this method can accurately capture abnormal signs at the fault initiation stage, that is, before the short-circuit circulating current reaches the traditional protection setting value. This effectively avoids serious accidents such as equipment burnout or even fire caused by the expansion of the fault, and significantly improves the operational safety and reliability of the reactor itself and the power grid. Attached Figure Description

[0033] Figure 1 This is the circuit schematic diagram of the present invention;

[0034] Figure 2 This is a schematic diagram of the structure of the present invention;

[0035] Figure 3 This is a flowchart of the present invention;

[0036] Figure 4 The equivalent circuit diagram established by the unit in this invention;

[0037] Figure 5 This is the equivalent circuit diagram of the dry-type hollow parallel reactor in this invention, which is based on layers. Detailed Implementation

[0038] like Figure 1 and Figure 2 As shown, the implementation of this invention relies on an online monitoring system, and the implementation process is as follows:

[0039] The online monitoring device does not change the primary main wiring of the reactor, and directly obtains the three-phase voltage signal U from the secondary circuit of the existing voltage transformer (PT) and current transformer (CT) serving the reactor line. SA U SB and U SC Three-phase current signal I SA I SB and I SC This avoids the need to install expensive and complex new sensors.

[0040] The online monitoring device (lower-level unit) is installed in the protection room of the substation. This device integrates signal conditioning circuitry, a high-precision A / D converter, an embedded microprocessor, and the first fiber optic converter. All these components operate with earth as the reference potential.

[0041] To ensure reliable data transmission and electrical isolation in environments with strong electromagnetic interference, fiber optic communication is used between the lower-level computer and the upper-level computer located in the main control room. Data is processed by the lower-level computer and then sent to fiber optic converter 1, where it is converted into an optical signal and transmitted via fiber optic cable to fiber optic converter 2 in the main control room. The signal is then converted back into an electrical signal and sent to the upper-level computer. The upper-level computer and its components use the control room ground as the reference potential.

[0042] The core diagnostic logic of this invention is implemented by specialized software in a host computer, and its program flowchart can be found here. Figure 3 The specific execution steps are as follows:

[0043] Model Establishment: First, an equivalent circuit model of the dry-type air-core reactor under normal conditions is established. This reactor has an axisymmetric structure, and each layer of coils is equivalent to the conductor resistance, self-inductance, and mutual inductance; these parameters are determined by the reactor's design structural parameters. The equivalent circuit established layer by layer is as follows: Figure 4 As shown, its voltage equations are as follows:

[0044]

[0045] Where n is the number of coil layers. By solving this system of equations, the current in each layer can be obtained, and the total current flowing through the reactor is:

[0046]

[0047] Fault Modeling: When an inter-turn short circuit occurs in the i-th layer, the fault layer is equivalent to two parallel branches: one composed of short-circuited turns, and the other composed of the remaining normal turns in the layer. Therefore, an equivalent circuit model of an inter-turn short-circuit fault containing n+1 branches is established. The equivalent circuit including the parallel reactor for the inter-turn short-circuit fault is as follows: Figure 5 The voltage equations are as follows:

[0048]

[0049] Equation (1-3) forms a system of equations with a current variable. Solving the system of equations yields the values ​​of each current. The total current of the reactor at this point is:

[0050] Parameter Calculation: Based on the real-time acquired voltage U and the calculated total current I, a set of key electrical parameters are further calculated. These parameters are extremely sensitive to inter-turn short circuits.

[0051] The total current consists of resistive and inductive components:

[0052]

[0053] The total current is:

[0054]

[0055] The equivalent resistance and equivalent reactance are respectively:

[0056]

[0057] The total impedance is:

[0058]

[0059] Percentage of loss:

[0060]

[0061] Early warning judgment: The calculated key electrical parameters (equivalent resistance, equivalent reactance, total impedance, and loss percentage) are compared with preset normal reference values ​​or thresholds. When any parameter or combination of parameters deviates abnormally (such as a significant increase in loss percentage or a decrease in total impedance), an inter-turn short circuit early warning signal is triggered.

[0062] It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention.

Claims

1. A method for early warning of inter-turn short circuits in a dry-type air-core reactor, characterized in that, Includes the following steps: S1: Establish the circuit model and voltage equation set of the dry-type air-core reactor under normal operation and inter-turn short-circuit fault conditions; S2: Real-time acquisition of voltage and current signals of the dry-type air-core reactor during operation; S3: Based on the voltage and current signals, calculate one or more key electrical parameters of the dry-type air-core reactor, including equivalent resistance, equivalent reactance, total impedance, and loss percentage; S4: Compare and analyze the calculated key electrical parameters with their corresponding preset thresholds or reference parameters under normal conditions; S5: When the change or absolute value of at least one of the key electrical parameters exceeds its corresponding preset range, an inter-turn short circuit warning is triggered.

2. The method according to claim 1, characterized in that, In step S1, establishing the circuit model of the dry-type air-core reactor under the inter-turn short-circuit fault state specifically involves: The faulty layer coil where an inter-turn short circuit occurs is equivalent to two parallel branches. One branch consists of the short-circuited turns, and the other branch consists of the remaining normal turns of the layer, thus forming an equivalent circuit model containing n+1 branches, where n is the total number of reactor layers.

3. The method according to claim 1 or 2, characterized in that, In step S3, the calculation of equivalent resistance and equivalent reactance is specifically achieved through the following formulas: Total current: Equivalent resistance: Equivalent reactance: in, U is the total current flowing through the reactor, U is the applied voltage, and δ is the loss angle.

4. The method according to claim 3, characterized in that, In step S3, the total impedance Z is determined by the formula: The percentage of loss is calculated using the formula. Obtained through calculation.

5. The method according to claim 1, characterized in that, In step S3, the calculation process of the key electrical parameters further considers the ambient temperature factor, and calculates the variation law of the key electrical parameters under different temperature conditions through numerical analysis methods.

6. The method according to claim 1, characterized in that, In step S2, the voltage and current signals are obtained from the existing voltage and current transformers on site, without the need to install additional dedicated electrical sensors.

7. The method according to claim 1, characterized in that, In step S4, the preset threshold or reference parameter is established by learning from the historical operating data of the dry-type air-core reactor under normal fault-free conditions or by calculating it through its theoretical circuit model.

8. The method according to claim 1, characterized in that, In step S5, the triggering of the warning includes warning signals of different levels. The warning level is divided according to the number or degree of electrical parameters exceeding the preset range to indicate the severity of the fault.

9. A dry-type air-core reactor inter-turn short-circuit early warning system, used to implement the method as described in any one of claims 1-8, characterized in that, The system includes: The data acquisition module is used to acquire voltage and current signals from voltage transformers and current transformers in real time. The data processing and calculation module is used to calculate at least one key electrical parameter among the equivalent resistance, equivalent reactance, total impedance, and loss percentage based on the voltage signal and current signal. The analysis and judgment module is used to compare the calculated key electrical parameters with preset thresholds or benchmark parameters; The early warning output module is used to output an early warning signal when it is determined that there is a risk of inter-turn short circuit.

10. The system according to claim 9, characterized in that, The system includes a lower-level computer unit with the ground as the reference potential and an upper-level computer unit with the control room ground as the reference potential. The lower-level computer unit and the upper-level computer unit exchange data and are electrically isolated from each other through optical fiber communication.

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