Large generator outlet side PT primary winding turn-to-turn short circuit online monitoring method

Abstract

The invention provides a large-scale generator outlet side PT primary winding turn-to-turn short circuit on-line monitoring method, which comprises the following steps: measuring a primary winding current through a primary current measuring device additionally arranged at a generator terminal voltage transformer PT, and inputting the primary winding current into a protection device; measuring the current of the secondary winding, the current of the open delta winding and the secondary voltage by using a protection device; virtual excitation current and virtual excitation voltage are calculated through a protection device according to measured data, secondary winding resistance detected in an offline mode and the known number of turns of a PT winding, virtual excitation impedance is further calculated, the module value of the virtual excitation impedance is taken, and the module value of the machine end PT virtual excitation impedance is obtained; the impedance module value is used as a monitoring index through the protection device, when the impedance module value is between the low-section fixed value and the high-section fixed value, an alarm is given, stator grounding protection is closed, and when the impedance module value is lower than the low-section fixed value, the stator grounding protection action is allowed. The method effectively improves the sensitivity of PT on-line monitoring, is easy to implement, and can find an insulation fault at the early stage of the fault.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of design and manufacture of large hydro-generator and relay protection of main equipment of power system, and particularly relates to a method and system for online monitoring of turn-to-turn short circuit of PT primary winding at outlet side of large generator. BACKGROUND

[0002] A potential transformer (PT) is a key device for monitoring the voltage of a generator, but a turn-to-turn short circuit fault of the PT is easy to trigger misoperation of stator grounding or over-excitation protection, resulting in unplanned shutdown. In order to reduce the non-stop events caused by the action of the protection of the motor body due to the fault of the measuring device, online monitoring of the turn-to-turn short circuit fault of the potential transformer becomes a possible solution.

[0003] At present, the detection of the turn-to-turn short circuit of the PT is mostly in a power-off detection mode, including DC resistance test, ratio test, no-load current test, and impulse voltage test, etc. However, the power-off detection can only be used as a pre-test or a detection means after an accident occurs, and the confirmation of the fault after the accident has caused serious economic losses. Therefore, compared with the power-off detection, it is particularly important to realize early diagnosis and rapid early warning of the turn-to-turn short circuit fault of the PT primary winding of the generator during operation through technical means.

[0004] The existing online monitoring methods include the current of the primary winding of the potential transformer, comparison of the voltage differences measured by multiple sets of potential transformers at the outlet side, etc. The size of the primary winding current is closely related to the secondary load and the primary side voltage, and cannot completely represent the turn-to-turn short circuit; and the difference in the measured voltage is not obvious enough in the early fault.

[0005] Therefore, in view of the above problems, it is necessary to study the online monitoring method for the turn-to-turn short circuit of the potential transformer of the large hydro-generator. SUMMARY

[0006] The present application aims to at least solve one of the technical problems in the related art to some extent.

[0007] To this end, a first object of the present application is to provide a method for online monitoring of turn-to-turn short circuit of PT primary winding at outlet side of large generator, which solves the problem that the existing method cannot accurately monitor whether the PT at the outlet side of the generator has a turn-to-turn short circuit fault of the primary winding, effectively improves the sensitivity of online monitoring of the PT, is easy to implement, and can find the insulation fault in the early stage.

[0008] A second object of the present application is to provide a system for online monitoring of turn-to-turn short circuit of PT primary winding at outlet side of large generator.

[0009] To achieve the above object, the first aspect of the present application proposes a large generator outlet side PT primary winding inter-turn short circuit online monitoring method, comprising:

[0010] The primary winding current is measured by a primary current measuring device installed on the generator terminal PT, and the measured primary winding current is input into the protection device;

[0011] The secondary winding current, open-delta winding current and secondary voltage are measured by the protection device;

[0012] The virtual excitation current is calculated by the protection device using the measured primary winding current, secondary winding current, open-delta winding current and known PT winding turns, the virtual excitation voltage is calculated using the measured secondary voltage, secondary winding current and offline detected secondary winding resistance, the virtual excitation impedance is calculated based on the virtual excitation current and virtual excitation voltage, and the modulus value of the virtual excitation impedance is obtained to obtain the terminal PT virtual excitation impedance modulus value;

[0013] The calculated impedance modulus value is taken as a monitoring index by the protection device, when it is between the low segment setting value and the high segment setting value, the alarm is acted and the stator ground protection is locked out, and when it is lower than the low segment setting value, the stator ground protection is allowed to act.

[0014] To achieve the above object, the second aspect of the present application proposes a large generator outlet side PT primary winding inter-turn short circuit online monitoring system, comprising a primary current measuring device and a protection device, wherein,

[0015] The primary current measuring device is installed on the generator terminal PT and is used to measure the primary winding current and input the measured primary winding current into the protection device;

[0016] The protection device is used to:

[0017] measure the secondary winding current, open-delta winding current and secondary voltage;

[0018] calculate the virtual excitation current using the measured primary winding current, secondary winding current, open-delta winding current and known PT winding turns, calculate the virtual excitation voltage using the measured secondary voltage, secondary winding current and offline detected secondary winding resistance, calculate the virtual excitation impedance based on the virtual excitation current and virtual excitation voltage, and obtain the terminal PT virtual excitation impedance modulus value by taking the modulus value of the virtual excitation impedance;

[0019] The calculated impedance modulus value is taken as a monitoring index, when it is between the low segment setting value and the high segment setting value, the alarm is acted and the stator ground protection is locked out, and when it is lower than the low segment setting value, the stator ground protection is allowed to act.

[0020] The large generator outlet side PT primary winding inter-turn short circuit online monitoring method and system of the embodiment of the application, through the installation of a voltage transformer primary side current sensor, and using the voltage and current that can be measured by the protection device and the number of turns of the PT winding, an online monitoring index is constructed, overcoming the shortcomings that the correspondence between the existing method and the fault characteristics is not direct enough, the monitoring method of the embodiment is easy to implement, and the sensitivity of the PT online monitoring is effectively improved, and insulation defects can be found in the early stage of failure.

[0021] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those having ordinary skill in the art upon examination of the following or can be learned from practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0022] The above and / or additional aspects and advantages of the application will become apparent and be readily understood by considering the following detailed description, including the accompanying drawings, in which:

[0023] Figure 1 A flowchart of a large generator outlet side PT primary winding inter-turn short circuit online monitoring method provided by the embodiment of the application is shown in Figure 1.

[0024] Figure 2 An implementation scheme diagram of the large hydro-generator terminal PT inter-turn short circuit online monitoring of the embodiment of the application is shown in Figure 2.

[0025] Figure 3 A diagram of a measurement signal of one phase of the large hydro-generator terminal PT of the embodiment of the application is shown in Figure 3.

[0026] Figure 4 An equivalent circuit diagram of the terminal PT primary winding inter-turn short circuit fault of the embodiment of the application is shown in Figure 4.

[0027] Figure 5 A diagram of simulating the terminal PT inter-turn short circuit, calculating the virtual excitation impedance modulus and other electrical quantity change waveforms of the embodiment of the application is shown in Figure 5. DETAILED DESCRIPTION

[0028] The embodiments of the application are described in detail below, examples of which are shown in the accompanying drawings, in which the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the application, and cannot be understood as a limitation of the application.

[0029] The large generator outlet side PT primary winding inter-turn short circuit online monitoring method and system of the embodiment of the application are described below with reference to the accompanying drawings.

[0030] Figure 1A flowchart of a large generator outlet side PT primary winding inter-turn short circuit online monitoring method provided by Embodiment One of the present application.

[0031] As shown in Figure 1 The large generator outlet side PT primary winding inter-turn short circuit online monitoring method includes the following steps:

[0032] Step 101, measuring the primary winding current through a primary current measuring device installed on the generator terminal PT, and inputting the measured primary winding current into a protection device;

[0033] In this embodiment, Figure 2 An implementation scheme diagram for large hydro-generator terminal PT inter-turn short circuit online monitoring, Figure 3 A diagram of a large hydro-generator terminal PT one-phase measurement signal, Figure 4 An equivalent circuit diagram of a terminal PT primary winding inter-turn short circuit fault.

[0034] Step 102, measuring the secondary winding current, open-delta winding current and secondary voltage using the protection device;

[0035] Step 103, calculating the virtual excitation current by the protection device using the measured primary winding current, secondary winding current, open-delta winding current and known PT winding turns, calculating the virtual excitation voltage using the measured secondary voltage, secondary winding current and offline detected secondary winding resistance, calculating the virtual excitation impedance based on the virtual excitation current and virtual excitation voltage, and taking the modulus value to obtain the terminal PT virtual excitation impedance modulus value;

[0036] Step 104, taking the calculated impedance modulus value as a monitoring index by the protection device, acting on the alarm when it is between the low segment value and the high segment value, and locking the stator ground protection, and allowing the stator ground protection to act when it is lower than the low segment value.

[0037] The large generator outlet side PT primary winding inter-turn short circuit online monitoring method of the present application installs a voltage transformer primary side current sensor, and uses the voltage and current that can be measured by the protection device and the PT winding turns to construct an online monitoring index, overcoming the shortcomings that the correspondence between the existing method and the fault characteristics is not direct enough. The monitoring method of the present embodiment is easy to implement, effectively improves the sensitivity of PT online monitoring, and can find insulation defects in the early stage of failure.

[0038] This embodiment takes the inter-turn short circuit experiment of a custom PT as an example to illustrate the large generator outlet side PT primary winding inter-turn short circuit online monitoring method of the present embodiment.

[0039] The basic parameters of the PT are shown in Table 1.

[0040] Table 1 Subscribed with fault lead PT

[0041]

[0042] The self-coupling voltage regulator output side is connected to the primary side of the fault PT, the PT internal coil lead is connected to the terminal row, the two ends are connected in series through the air switch, and the secondary side of the voltage transformer and the open delta winding side are open circuit. The voltage signal measured by the voltage probe and the current signal measured by the current amplifier are connected to the oscilloscope.

[0043] The steps of the embodiment are as follows:

[0044] Step 1: A primary current measurement probe and a current amplifier are added to the test PT, the measured primary current is input to the oscilloscope, and the voltage quantity is measured at the corresponding port.

[0045] Step 2: The virtual excitation current is calculated using the measured primary winding current, secondary current, and open delta winding current, and the virtual excitation voltage is calculated using the secondary voltage, secondary current, and offline detected secondary winding resistance, thereby obtaining the virtual excitation impedance, taking the modulus value,

[0046]

[0047] Symbol explanation: signal quantity is the measured primary current, signal quantity are the secondary winding current, open delta winding current, and secondary voltage measured by the protection device. The parameter r2 is the secondary winding resistance, N1 is the primary winding number of turns, N2 is the secondary winding number of turns, and N4 is the open delta winding number of turns. The number of turns is provided by the transformer manufacturer, is the virtual excitation voltage, is the virtual excitation current. The value of the resistance parameter is obtained in advance through field measurement test. The calculated is the virtual excitation impedance value of the short-circuit branch in parallel with the excitation branch through the conversion resistance, viewed from the secondary side.

[0048] Step 3: The calculated impedance value is used as a monitoring index, which is divided into high and low segments. When the index is lower than the high segment value but higher than the low segment value, the alarm is acted and the stator ground protection is locked out; when the index is lower than the low segment value, the stator ground protection is allowed to act.

[0049] The inter-turn short circuit fault of the simulation PT (short-circuit turn number 3 turns, accounting for about 0.4% of the primary winding number of turns) is measured by the oscilloscope, and the corresponding virtual excitation impedance modulus value is calculated, and the waveform is as Figure 5 shown.

[0050] The results show that the virtual excitation impedance as an online monitoring index changes obviously after the inter-turn fault, thereby realizing accurate and sensitive identification of the PT inter-turn short-circuit fault.

[0051] In order to realize the above-mentioned embodiments, the application further provides a large generator outlet side PT primary winding inter-turn short-circuit online monitoring system.

[0052] The large generator outlet side PT primary winding inter-turn short-circuit online monitoring system comprises a primary current measuring device and a protection device, wherein,

[0053] The primary current measuring device is installed on the generator terminal PT, is used for measuring the primary winding current, and inputs the measured primary winding current into the protection device;

[0054] The protection device is used for:

[0055] measuring the secondary winding current, the open-delta winding current and the secondary voltage;

[0056] calculating the virtual excitation current by using the measured primary winding current, secondary winding current, open-delta winding current and known PT winding turns, calculating the virtual excitation voltage by using the measured secondary voltage, secondary winding current and offline detected secondary winding resistance, calculating the virtual excitation impedance based on the virtual excitation current and the virtual excitation voltage, and obtaining the terminal PT virtual excitation impedance modulus value by taking the modulus value of the virtual excitation impedance;

[0057] The calculated impedance modulus value is taken as a monitoring index, when it is between a low segment value and a high segment value, the alarm is acted and the stator ground protection is locked out, and when it is lower than the low segment value, the stator ground protection is allowed to act.

[0058] Further, in the embodiments of the application, the primary current measuring device comprises a primary current measuring probe and a current amplifier.

[0059] Specifically, in the embodiments of the application, the calculation formula of the virtual excitation current is:

[0060]

[0061] wherein, is the primary winding current, N1 is the primary winding turns, is the secondary winding current, N2 is the secondary winding turns, is the open-delta winding current, N4 is the open-delta winding turns;

[0062] the calculation formula of the virtual excitation voltage is:

[0063]

[0064] in, R1 is the voltage of the secondary winding, and R2 is the resistance of the secondary winding.

[0065] The formula for calculating virtual excitation impedance is:

[0066]

[0067] The formula for calculating the magnitude of the virtual excitation impedance of the generator terminal PT is:

[0068]

[0069] It should be noted that the foregoing explanation of the embodiment of the online monitoring method for inter-turn short circuit of primary winding of PT on the outlet side of a large generator also applies to the online monitoring device for inter-turn short circuit of primary winding of PT on the outlet side of the large generator in this embodiment, and will not be repeated here.

[0070] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0071] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0072] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing custom logic functions or processes, and the scope of the preferred embodiments of this application includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as should be understood by those skilled in the art to which embodiments of this application pertain.

[0073] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0074] It should be understood that various parts of this application can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0075] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0076] Furthermore, the functional units in the various embodiments of this application can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0077] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A method for online monitoring of inter-turn short circuits in the primary winding of a PT on the outlet side of a large generator, characterized in that, include: The primary winding current is measured by a primary current measuring device installed at the generator terminal PT, and the measured primary winding current is input into the protection device. Use the protection device to measure the secondary winding current, open delta winding current and secondary voltage; The protection device uses the measured primary winding current, secondary winding current, open delta winding current, and known PT winding turns to calculate the virtual excitation current. It also uses the measured secondary voltage, secondary winding current, and offline detection secondary winding resistance to calculate the virtual excitation voltage. Based on the virtual excitation current and virtual excitation voltage, the virtual excitation impedance is calculated, and its magnitude is taken to obtain the virtual excitation impedance magnitude of the PT at the generator terminal. The calculated impedance modulus is used as a monitoring indicator by the protection device. When it is between the low-level setting value and the high-level setting value, the device will activate an alarm and lock the stator grounding protection. When it is below the low-level setting value, the stator grounding protection will be allowed to operate.

2. The method as described in claim 1, characterized in that, The primary current measuring device includes a primary current measuring probe and a current amplifier.

3. The method as described in claim 1, characterized in that, The formula for calculating the virtual excitation current is: in, N1 represents the primary winding current, and N1 represents the number of turns in the primary winding. N1 is the secondary winding current, and N2 is the number of turns in the secondary winding. N4 represents the open delta winding current, and N4 represents the number of turns in the open delta winding. The formula for calculating the virtual excitation voltage is: in, R1 is the voltage of the secondary winding, and R2 is the resistance of the secondary winding. The formula for calculating the virtual excitation impedance is: The formula for calculating the virtual excitation impedance modulus of the PT at the generator terminal is as follows: 。 4. An online monitoring system for inter-turn short circuits in the primary winding of a large generator's output side PT, characterized in that, Includes a primary current measuring device and a protection device, wherein, The primary current measuring device is installed on the generator terminal PT to measure the primary winding current and input the measured primary winding current into the protection device. The protective device is used for: Measure the secondary winding current, open delta winding current, and secondary voltage; The virtual excitation current is calculated using the measured primary winding current, secondary winding current, open delta winding current, and known number of turns of the PT winding. The virtual excitation voltage is calculated using the measured secondary voltage, secondary winding current, and secondary winding resistance obtained from offline detection. The virtual excitation impedance is calculated based on the virtual excitation current and virtual excitation voltage, and its magnitude is taken to obtain the magnitude of the virtual excitation impedance of the PT at the generator terminal. The calculated impedance modulus is used as a monitoring indicator. When it is between the low-level setting value and the high-level setting value, an alarm is triggered and the stator grounding protection is locked. When it is below the low-level setting value, the stator grounding protection is allowed to operate.

5. The system as described in claim 4, characterized in that, The primary current measuring device includes a primary current measuring probe and a current amplifier.

6. The system as described in claim 4, characterized in that, The formula for calculating the virtual excitation current is: in, N1 represents the primary winding current, and N1 represents the number of turns in the primary winding. N1 is the secondary winding current, and N2 is the number of turns in the secondary winding. N4 represents the open delta winding current, and N4 represents the number of turns in the open delta winding. The formula for calculating the virtual excitation voltage is: in, R1 is the voltage of the secondary winding, and R2 is the resistance of the secondary winding. The formula for calculating the virtual excitation impedance is: in, for, for; The formula for calculating the virtual excitation impedance modulus of the PT at the generator terminal is as follows: 。

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