Transformer no-load current and no-load loss measurement system and method

Abstract

The present invention discloses a measurement system and method for no-load current and no-load loss of a transformer, wherein the measurement system comprises a circuit breaker, a bypass switch, a closing resistor, a current transformer, a voltage transformer, a collection module and a processing module. When the circuit breaker performs a closing operation on the transformer, the excitation surge current is rapidly reduced to a stable state by the closing resistor, the no-load current signal of the transformer is measured by the current transformer, and the voltage signal of the transformer is measured by the voltage transformer, and the current signal and the voltage signal are collected by the collection module and sent to the processing module for processing, and the no-load current and no-load voltage of the transformer after interference removal and synchronous processing are extracted, and then the no-load loss is calculated according to the no-load current and no-load voltage, which can realize the online and accurate measurement of the no-load current and no-load loss of the transformer, thereby providing data support for the evaluation of the excitation characteristics and equipment quality of the transformer.

Description

Technical Field

[0001] The present invention relates to the technical field of power equipment monitoring, and in particular to a system and method for measuring no-load current and no-load loss of a transformer. Background Art

[0002] Large transformers are one of the most important and expensive equipment in AC and DC power transmission systems, and their equipment quality is related to the safe and reliable operation of the power system. The no-load current and no-load loss of the transformer are important and intuitive indicators that reflect the state of the transformer core and the quality of the equipment. The measurement of the no-load characteristics of the transformer can not only reflect whether the transformer magnetic circuit design, silicon steel sheet material selection, and manufacturing process meet the requirements, but also can inspect the transportation and installation quality of the equipment. There have been many cases of abnormal transformer no-load characteristics and equipment failures caused by the quality of silicon steel sheets, multi-point grounding of the core, short circuit of silicon steel sheets caused by foreign objects, and reduced insulation of silicon steel sheets due to moisture at home and abroad.

[0003] At present, the main means of detecting the no-load characteristics of transformers is no-load testing, which is generally carried out during factory tests and on-site handover tests. The purpose of the handover test is to check whether there are quality risks after long-distance transportation and on-site installation of the equipment. Due to the constraints of on-site test power supply, construction period and other conditions, the on-site no-load test generally adopts the valve side low voltage (380V) pressurization method, and the measured results are compared with the no-load test results under low voltage in the factory. However, since the no-load current under low voltage is very small, generally at the milliampere level, the measurement results are greatly affected by the on-site environment, resulting in a large error in the test results, and the current standards lack clear test criteria for on-site no-load tests, resulting in this test being unable to effectively assess the excitation characteristics of the transformer and the quality of the equipment. In addition, at present, the winding current of large transformers is mostly measured through bushing CT, which has poor anti-interference and measurement accuracy under low current, and cannot accurately measure the transformer no-load current waveform; the no-load voltage is generally measured through the busbar CVT, and its frequency response characteristics are poor. These have become technical bottlenecks for the accurate measurement and evaluation of the no-load characteristics of large transformers.

[0004] Therefore, in order to achieve the purpose of effectively evaluating the excitation characteristics and equipment quality of the transformer, it is necessary to provide a measurement device for the no-load current and no-load loss of the transformer, so as to provide data support for the evaluation of the no-load characteristics of the transformer. Summary of the invention

[0005] The embodiment of the present invention provides a system and method for measuring no-load current and no-load loss of a transformer, which can perform online monitoring of the no-load current and no-load loss of the transformer, thereby providing data support for the evaluation of the excitation characteristics and equipment quality of the transformer.

[0006] A measurement system for no-load current and no-load loss of a transformer provided in an embodiment of the present invention comprises a measurement module, a collection module and a processing module, wherein the measurement module comprises a circuit breaker, a bypass switch, a closing resistor, a current transformer and a voltage transformer, a first end of the circuit breaker is connected to a power supply, a second end of the circuit breaker is connected to a first end of the closing resistor, a second end of the closing resistor is connected to a first end of the current transformer, a second end of the current transformer is connected to a first end of the voltage transformer, and a second end of the voltage transformer is connected to a grid side of a transformer to be measured; the first end of the closing resistor is also connected to a first end of the bypass switch, and the second end of the current transformer is also connected to a second end of the bypass switch;

[0007] The acquisition module is connected to the measurement module and is used to send the acquired current signal and voltage signal to the processing module;

[0008] The processing module is connected to the acquisition module, and is used to remove interference and perform clock synchronization processing on the received current signal and voltage signal to obtain current data and voltage data, and calculate the no-load loss of the transformer based on the current data and voltage data.

[0009] As an improvement of the above solution, the current transformer is an all-optical current transformer, and the current transformer is connected to the acquisition module through a polarization-maintaining optical fiber.

[0010] As an improvement of the above solution, the voltage transformer is an electronic voltage transformer, and the voltage transformer is connected to the acquisition module through a polarization-maintaining optical fiber.

[0011] As an improvement of the above solution, the measurement system further includes a storage module, and the storage module is connected to the processing module.

[0012] As an improvement of the above solution, the storage module is an EEPROM memory.

[0013] As an improvement of the above solution, the measurement system further includes a monitoring module, and the monitoring module is connected to the processing module through communication.

[0014] The embodiment of the present invention further provides a method for measuring no-load current and no-load loss of a transformer, and the measuring system for no-load current and no-load loss of the transformer based on the above-mentioned method comprises:

[0015] Execute the circuit breaker closing operation, measure the current signal of the transformer when it is running at no-load through the current transformer, and analyze and process the collected current signal to obtain the no-load current of the transformer after steady state;

[0016] The no-load voltage of the transformer during no-load operation is measured by a voltage transformer;

[0017] The no-load loss of the transformer in a steady state is obtained according to the no-load voltage and the no-load current.

[0018] As an improvement of the above solution, before the circuit breaker closing operation is performed, the method further includes:

[0019] Calculate and set the closing resistor value and the closing time of the bypass switch, including:

[0020] The resistance value of the closing resistor is set by calculating the quantitative relationship between the closing current inrush amplitude and inrush current decay time and the closing resistor value;

[0021] The time for the no-load closing current to reach a steady state is determined according to the calculated closing current inrush decay time, and the closing time of the bypass switch is set, wherein the closing time of the bypass switch is greater than the closing current steady-state time.

[0022] As an improvement of the above solution, obtaining the no-load loss of the transformer after steady state according to the no-load voltage and the no-load current specifically includes:

[0023] The no-load loss of the transformer is calculated according to the following formula:

[0024]

[0025] Among them, u is the no-load voltage, i is the no-load current, t is the time, P is the no-load loss, and T is a time period.

[0026] Compared with the prior art, the measurement system and method for no-load current and no-load loss of a transformer provided by the embodiment of the present invention have the following beneficial effects:

[0027] The no-load current and no-load loss measurement system provided by the embodiment of the present invention includes a circuit breaker, a bypass switch, a closing resistor, a current transformer, a voltage transformer, an acquisition module and a processing module. During operation, when the circuit breaker closes the transformer, the excitation surge current is quickly reduced to a stable state by the closing resistor, the no-load current signal of the transformer is measured by the current transformer, and the voltage signal of the transformer is measured by the voltage transformer. The current signal and the voltage signal are collected by the acquisition module and sent to the processing module for processing, and the no-load current and no-load voltage of the transformer after interference removal and synchronous processing are extracted, and then the no-load loss is calculated according to the no-load current and no-load voltage. It can realize the online and accurate measurement of the no-load current and no-load loss of the transformer, thereby providing data support for the evaluation of the excitation characteristics and equipment quality of the transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1It is a structural block diagram of an implementation of a no-load current and no-load loss measurement system provided by an embodiment of the present invention;

[0029] Figure 2 It is a structural block diagram of another implementation of a no-load current and no-load loss measurement system provided in an embodiment of the invention;

[0030] Figure 3 It is a flow chart of a method for measuring no-load current and no-load loss provided by an embodiment of the present invention;

[0031] Figure 4 It is a detailed flow chart of the no-load current and no-load loss measurement method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] See also Figure 1 , Figure 1 It is a structural block diagram of an implementation of a no-load current and no-load loss measurement system provided in an embodiment of the present invention.

[0034] The measurement system of no-load current and no-load loss of a transformer provided in an embodiment of the present invention comprises a measurement module 1, an acquisition module 2 and a processing module 3, wherein the measurement module 1 comprises a circuit breaker Q, a bypass switch S, a closing resistor R, a current transformer Io and a voltage transformer Uo, a first end of the circuit breaker Q is connected to a power supply, a second end of the circuit breaker Q is connected to a first end of the closing resistor R, a second end of the closing resistor R is connected to a first end of the current transformer Io, a second end of the current transformer Io is connected to a first end of the voltage transformer Uo, and a second end of the voltage transformer Uo is connected to a grid side of a transformer to be measured; the first end of the closing resistor R is also connected to a first end of the bypass switch S, and the second end of the current transformer Io is also connected to a second end of the bypass switch S;

[0035] The acquisition module 2 is connected to the measurement module 1 and is used to send the acquired current signal and voltage signal to the processing module 3;

[0036] The processing module 3 is connected to the acquisition module 2, and is used for removing interference and performing clock synchronization processing on the received current signal and voltage signal to obtain current data and voltage data, and calculating the no-load loss of the transformer based on the current data and voltage data.

[0037] It is understandable that at the moment of no-load closing of the transformer, since the back electromotive force has not yet been established, the magnetic flux in the coil cannot change instantaneously, and a non-periodic component of magnetic flux will be generated in the iron core and superimposed on the steady-state magnetic flux, resulting in a large closing excitation surge current in the transformer. This surge current may generally reach 6 to 8 times or even higher than the rated current of the transformer. Therefore, the embodiment of the present invention limits the amplitude and duration of this closing surge current by connecting a closing resistor R in series. After the closing is completed and the no-load current reaches a steady state, the closing resistor R is short-circuited to put the transformer into normal operation.

[0038] In the embodiment of the present invention, the acquisition module 2 includes two acquisition branches, namely, a acquisition branch for acquiring the current signal output by the current transformer Io and a acquisition branch for acquiring the voltage signal output by the voltage transformer Uo. The current waveform and voltage waveform of the transformer when it is running at no load can be obtained through the acquisition module 2. In specific implementation, when the transformer is closed, the first current peak will appear, which is the amplitude of the closing excitation inrush current, and then the current will gradually decay until it drops to a stable no-load current.

[0039] The no-load current and no-load loss measurement system provided by the embodiment of the present invention includes a circuit breaker Q, a bypass switch S, a closing resistor R, a current transformer Io, a voltage transformer Uo, an acquisition module 2 and a processing module 3. When the circuit breaker Q performs a closing operation on the transformer, the closing resistor R quickly reduces the excitation surge current to a stable state, and the no-load current signal of the transformer is measured by the current transformer Io, and the voltage signal of the transformer is measured by the voltage transformer Uo. The current signal and the voltage signal are collected by the acquisition module 2 and sent to the processing module for processing, and the no-load current and no-load voltage of the transformer after interference removal and synchronous processing are extracted, and then the no-load loss is calculated according to the no-load current and no-load voltage. It can realize the online and accurate measurement of the no-load current and no-load loss of the transformer, thereby providing data support for the evaluation of the excitation characteristics and equipment quality of the transformer.

[0040] In an optional implementation, the current transformer Io is an all-optical current transformer, and the current transformer Io is connected to the acquisition module 2 via a polarization-maintaining optical fiber.

[0041] It is understandable that in the on-site no-load test of the transformer, due to limited conditions, most of the no-load current tests are carried out under low voltage. Because the no-load current under low voltage is very small, generally at the milliampere level, the measurement results are greatly affected by the on-site environment, resulting in large errors in the test results. The measured values ​​of the factory test and the on-site handover test differ by more than an order of magnitude. Therefore, it is necessary to provide a device suitable for measuring currents with small amplitudes and harmonic components, so that the final measured no-load current data is more real and accurate.

[0042] The all-fiber current transformer is a device that uses the interaction between the electromagnetic field and the polarization state of light to detect current. Its theoretical basis is Faraday's magneto-optical effect and Ampere's loop law. Compared with traditional current measuring instruments, it has a large measurement range, small delay, and good frequency response. It can accurately measure currents from a few amperes to several thousand amperes, and can measure tens of thousands or even hundreds of thousands of amperes of current under fault conditions. Therefore, in an embodiment of the present invention, an all-fiber current transformer is preferably selected as a measuring instrument for the no-load current of the transformer, which can achieve a higher measurement accuracy. In addition, the all-fiber current transformer also supports direct output of digital signals, and does not require an additional conversion module to convert it, thereby simplifying the circuit structure and lines.

[0043] In an optional implementation, the voltage transformer Uo is an electronic voltage transformer, and the voltage transformer Uo is connected to the acquisition module 2 via a polarization-maintaining optical fiber.

[0044] An electronic voltage transformer is a voltage sensor that utilizes the Pockels effect. When a light wave passes through a crystal, the phase difference between the light waves on two axes changes with the voltage or electric field. By monitoring the change in light intensity, the corresponding voltage can be measured. Similarly, the electronic voltage transformer has the same advantages as the all-fiber current transformer. Therefore, in the embodiment of the present invention, the electronic voltage transformer is preferably selected as the instrument for measuring voltage.

[0045] In an alternative embodiment, see Figure 2 The measurement system further comprises a storage module 4, which is connected to the processing module 3. Specifically, the storage module is an EEPROM memory.

[0046] In the embodiment of the present invention, since the purpose of its measurement system is to study the no-load characteristics of the transformer, a storage module 4 is provided to be connected to the processing module 3, so that the no-load current data and no-load voltage data measured by the measurement system can be stored, so as to facilitate the subsequent evaluation of the transformer excitation characteristics and equipment quality based on the no-load current data and no-load voltage data.

[0047] In an alternative embodiment, see Figure 2 The measurement system further includes a monitoring module 5, and the monitoring module 5 is connected to the processing module 3 via communication.

[0048] In an embodiment of the present invention, a monitoring module 5 is provided, which can receive no-load current data and no-load voltage data sent by the processing module 3. Specifically, the monitoring module 5 can be connected to the processing module 3 via wireless, GPRS, 5G and other communication methods.

[0049] Accordingly, see Figure 3 , Figure 3 The flowchart of the no-load current and no-load loss measurement method provided in the embodiment of the present invention is as follows. The no-load current and no-load loss measurement method of the transformer in the embodiment of the present invention is based on the no-load current and no-load loss measurement system of the transformer provided in the above embodiment, and includes steps S11 to S13:

[0050] Step S11, executing the operation of closing the circuit breaker Q, measuring the current signal of the transformer when it is running at no-load through the current transformer Io, and analyzing and processing the collected current signal to obtain the no-load current of the transformer after steady state;

[0051] Step S12, measuring the no-load voltage of the transformer when it is running at no-load by means of the voltage transformer Uo;

[0052] Step S13, obtaining the no-load loss of the transformer after steady state according to the no-load voltage and the no-load current.

[0053] It is understandable that at the moment of no-load closing of the transformer, because the back electromotive force has not been established, the magnetic flux in the coil cannot change instantaneously, and a non-periodic component of magnetic flux will be generated in the iron core and superimposed on the steady-state magnetic flux, resulting in a large closing excitation surge current in the transformer. Therefore, the current signal collected by the current transformer Io will fluctuate greatly in a short period of time. After the first current peak appears, the current will gradually decay until it drops to a stable current. At this time, the transformer is in a steady-state state, and the stable current is the no-load current of the transformer after steady-state.

[0054] In an optional implementation, before the step S11 of "performing the operation of closing the circuit breaker Q", the method further includes:

[0055] Calculate and set the closing resistor value and the closing time of the bypass switch, including:

[0056] The resistance value of the closing resistor is set by calculating the quantitative relationship between the closing current inrush amplitude and inrush current decay time and the closing resistor value;

[0057] The time for the no-load closing current to reach a steady state is determined according to the calculated closing current inrush decay time, and the closing time of the bypass switch is set, wherein the closing time of the bypass switch is greater than the closing current steady-state time.

[0058] In the embodiment of the present invention, before the no-load current measurement operation, the resistance value of the closing resistor and the closing time of the bypass switch are reasonably set to ensure that the current transformer can accurately measure the stabilized no-load current.

[0059] In order to explain the measuring method of the embodiment of the present invention more clearly and in detail, see Figure 4 , Figure 4 The flowchart of the method for measuring no-load current and no-load loss in an embodiment of the present invention is shown. In this embodiment, the measuring method includes steps S1 to S3:

[0060] Step S1, installing a closing resistor, a bypass switch, an electronic voltage transformer and an all-optical current transformer on the grid side of the transformer;

[0061] Step S2, setting the resistance value of the closing resistor and the closing time of the bypass switch (for specific settings, see the above specific process);

[0062] Step S3, executing the circuit breaker closing operation, the closing resistor quickly reduces the excitation inrush current to a stable state, and the no-load current and no-load voltage of the transformer after the steady state are measured by the current transformer and the voltage transformer;

[0063] Step S4, obtaining the no-load loss of the transformer after steady state according to the no-load voltage and the no-load current.

[0064] In an optional implementation, the step S13 of "obtaining the no-load loss of the transformer after steady state according to the no-load voltage and the no-load current" specifically includes:

[0065] The no-load loss of the transformer is calculated according to the following formula:

[0066]

[0067] Among them, u is the no-load voltage, i is the no-load current, t is the time, P is the no-load loss, and T is a time period.

[0068] In an embodiment of the present invention, the no-load loss is calculated by the no-load voltage and no-load current on the grid side of the transformer according to an integration method within one cycle. After that, the no-load loss measured on site can be compared with the no-load loss test value in the factory to judge the equipment quality and working status of the transformer after transportation and installation, thereby achieving the purpose of evaluating the excitation characteristics and equipment quality of the transformer.

[0069] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A measurement system for no-load current and no-load loss of a transformer, characterized in that: The device comprises a measuring module, a collecting module and a processing module, wherein the measuring module comprises a circuit breaker, a bypass switch, a closing resistor, a current transformer and a voltage transformer, the first end of the circuit breaker is connected to a power supply, the second end of the circuit breaker is connected to the first end of the closing resistor, the second end of the closing resistor is connected to the first end of the current transformer, the second end of the current transformer is connected to the first end of the voltage transformer, and the second end of the voltage transformer is connected to the grid side of the transformer to be measured; the first end of the closing resistor is also connected to the first end of the bypass switch, and the second end of the current transformer is also connected to the second end of the bypass switch; The acquisition module is connected to the measurement module and is used to send the acquired current signal and voltage signal to the processing module; The processing module is connected to the acquisition module, and is used to remove interference and perform clock synchronization processing on the received current signal and voltage signal to obtain current data and voltage data, and calculate the no-load loss of the transformer according to the current data and voltage data; The current transformer is an all-fiber current transformer, and the current transformer is connected to the acquisition module through a polarization-maintaining optical fiber; the voltage transformer is an electronic voltage transformer, and the voltage transformer is connected to the acquisition module through a polarization-maintaining optical fiber.

2. The measuring system for no-load current and no-load loss of a transformer according to claim 1, characterized in that: It also includes a storage module, which is connected to the processing module.

3. The measuring system for no-load current and no-load loss of a transformer according to claim 2, characterized in that: The storage module is an EEPROM memory.

4. A transformer no-load current and no-load loss measurement system as claimed in claim 1, characterized in that: It also includes a monitoring module, which is communicatively connected with the processing module.

5. A method for measuring no-load current and no-load loss of a transformer, characterized in that: The measuring system of no-load current and no-load loss of the transformer according to claim 1 comprises: Execute the circuit breaker closing operation, measure the current signal of the transformer when it is running at no-load through the current transformer, and analyze and process the collected current signal to obtain the no-load current of the transformer after steady state; The no-load voltage of the transformer during no-load operation is measured by a voltage transformer; The no-load loss of the transformer in a steady state is obtained according to the no-load voltage and the no-load current.

6. The method for measuring no-load current and no-load loss of a transformer according to claim 5, characterized in that: Before the circuit breaker closing operation is performed, the method further includes: Calculate and set the closing resistor value and the closing time of the bypass switch, including: The resistance value of the closing resistor is set by calculating the quantitative relationship between the closing current inrush amplitude and inrush current decay time and the closing resistor value; The time for the no-load closing current to reach a steady state is determined according to the calculated closing current inrush decay time, and the closing time of the bypass switch is set, wherein the closing time of the bypass switch is greater than the closing current steady-state time.

7. The method for measuring no-load current and no-load loss of a transformer according to claim 5, characterized in that: The step of obtaining the no-load loss of the transformer after steady state according to the no-load voltage and the no-load current specifically includes: The no-load loss of the transformer is calculated according to the following formula: Among them, u is the no-load voltage, i is the no-load current, t is the time, P is the no-load loss, and T is a time period.

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