Transformer residual magnetism demagnetization method based on programmable voltage method

Abstract

A transformer remanence demagnetization method based on a programmable voltage method can guarantee rapid magnetization and reduce voltage impact to the maximum extent, sets a programmable excitation power supply to be in a voltage source state and a current source state, and enables the programmable excitation power supply to work in the current source state to generate alternating current signals; the degaussing instrument is used for recording the relation between voltage and current, due to the existence of saturation voltage, the power supply bears the impact higher than the forward saturation voltage, and the current is distorted in the reversal stage; the excitation power supply continuously adjusts the length of the current reversal time, so that the impact voltage is reduced to be below the saturation voltage of the power supply, and the impact on the excitation power supply is avoided; the control module acquires the real-time waveform of the voltage through the voltage sampling module and records the real-time waveform as a control voltage reference waveform in the demagnetization process; the control voltage reference waveform degaussing voltage in the degaussing process is programmed, and the transformer iron core is degaussed by generating periodic voltage with gradually reduced amplitude.

Description

Technical Field

[0001] The invention relates to the field of power transformers, in particular to a transformer residual magnetism demagnetization method based on a programmable voltage method. Background Art

[0002] Power transformers are important components in power transmission systems. Transformers are devices that use electromagnetic conversion to achieve energy transfer. The quality of their iron cores directly affects the stability and safety of transformer operation. In actual use, when the transformer undergoes a DC test or is exposed to a strong magnetic environment for a long time, the transformer's iron core will have residual magnetism. When the residual magnetism reaches a certain level, it will cause a very large electromagnetic surge current at the moment the transformer is powered on, causing the power protection device to operate, resulting in power transmission failure and even damage to other power equipment. Therefore, the power transformer must be demagnetized before it is powered on.

[0003] At present, the main methods for demagnetizing transformers include DC current method, AC current method and AC variable frequency voltage method. The basic principle is to generate an alternating and gradually decreasing magnetic field in the transformer core, thereby eliminating the residual magnetic field.

[0004] The DC degaussing method is to apply a positive and negative alternating DC current to the winding, and the current gradually decreases and finally decreases to zero. Since this degaussing method uses DC for excitation, the excitation effect is relatively good and the residual magnetism can be quickly eliminated. However, since the transformer winding is an inductor device, at the moment of current commutation, due to the effect of inductance, a large impact voltage will be generated. This voltage will not only cause relatively large impact damage to the degaussing equipment, but also threaten the safety of the operator. At the same time, due to the presence of high-order harmonics during the impact process, the residual magnetism of the transformer will increase. Therefore, the DC degaussing method is used less and less.

[0005] The AC demagnetization method is to apply an AC current with a gradually decreasing amplitude to the winding, and finally reduce it to zero. This demagnetization method avoids voltage shock during the commutation process and makes the demagnetization process more stable. However, since the application process of the maximum current is short during the application of the AC current, the excitation effect is not good. This causes the equipment using the AC demagnetization method to require a relatively long demagnetization time and the demagnetization efficiency is relatively low.

[0006] Both of the above methods use current source as the excitation power supply. The development and control of the current source are relatively complicated, and the reliability of the work is not as high as the demagnetization method using a voltage source. In addition, in actual use, the current source always has a saturation voltage limit. Once the saturation voltage is reached, the actual current cannot reach the set value. Therefore, during the current method demagnetization process, the actual current curve is often not the same as the designed one, so the demagnetization effect is greatly reduced.

[0007] In order to reduce the power supply requirements and avoid current saturation, someone proposed the demagnetization method using AC variable frequency voltage.

[0008] The AC variable frequency voltage method uses AC voltage for demagnetization. During the demagnetization process, the frequency of the demagnetization voltage is gradually increased. As the frequency increases, the impedance of the transformer becomes larger, so the applied current becomes smaller and smaller, thereby achieving the demagnetization effect. The advantage of this method is that it uses a fixed amplitude voltage source for demagnetization, the development and control of the power supply are relatively simple, and the work is more reliable, but at the same time, the demagnetization efficiency is relatively low. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a transformer residual magnetism demagnetization method based on a programmable voltage method. The programmable voltage control technology is used to record the magnitude of the impulse voltage in real time during the magnetization process, and then the impulse voltage is controlled within a certain range, thereby ensuring the rapidity of magnetization to the greatest extent, reducing the voltage impact, and protecting the equipment and the test product.

[0010] The technical solution of the present invention is: a method for demagnetizing residual magnetism of a transformer based on a programmable voltage method, comprising:

[0011] Step 1, using a demagnetizer composed of a programmable excitation power supply, a control module, a current sampling circuit and a voltage sampling circuit, wherein the current sampling circuit, the voltage sampling circuit and the programmable excitation power supply are all controlled by the control module, and the programmable excitation power supply is connected to the winding outside the transformer core;

[0012] Step 2, setting the programmable excitation power supply to two working states, namely, voltage source state and current source state; the voltage source state is used to generate a programmable variable voltage, which is used as a working power supply during the demagnetization process; the current source state is used to generate a programmable current in the pre-magnetization stage, which is used to determine the waveform of the demagnetization control voltage and provide a voltage design curve for the demagnetization process;

[0013] Step 3, make the programmable excitation power supply work in the current source state, generate an alternating current signal, the current change is divided into a current reverse continuous stage, a forward reversal stage, a forward current continuous stage and a reverse reversal stage; the reversal stage is a partial sine wave; perform pre-magnetization, the pre-magnetization stage is used to determine the voltage waveform of the demagnetization stage;

[0014] Step 4, using the demagnetizer to record the relationship between voltage and current, the voltage change includes reverse stable voltage, forward impulse voltage, forward saturation voltage and forward stable voltage; due to the existence of saturation voltage, the power supply is subjected to an impact higher than the forward saturation voltage, and the current is distorted in the reversal stage; the programmable excitation power supply continuously adjusts the length of the current reversal time to reduce the impulse voltage to below the saturation voltage of the power supply, thereby ensuring that the voltage will not exceed the saturation voltage of the power supply during the entire demagnetization process, avoiding the impact on the excitation power supply; the control module collects the real-time waveform of the voltage through the voltage sampling module and records it as the control voltage reference waveform in the demagnetization process;

[0015] Step 5: Program the control voltage reference waveform demagnetization voltage during the demagnetization process, and achieve demagnetization of the transformer core by generating a periodic voltage with a gradually decreasing amplitude.

[0016] Furthermore, the amplitude in step 5) decreases linearly.

[0017] Furthermore, the sampling rate of the current acquisition circuit and the voltage acquisition circuit is not less than 100KS / s.

[0018] The beneficial effects of the present invention are as follows: using programmable voltage control technology, the programmable excitation power supply is operated in the current source state to determine the optimal demagnetization voltage curve. In the second step, the power supply operates in the voltage source state, and the transformer core is demagnetized using the optimal demagnetization voltage. During the magnetization process, the magnitude of the impulse voltage is recorded in real time, and then the impulse voltage is controlled within a certain range, which ensures the rapidity of magnetization to the maximum extent, reduces the voltage impact, and protects the equipment and the test product. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a circuit block diagram of the degaussing device of the present invention;

[0020] Figure 2 It is a circuit schematic diagram of the programmable excitation power supply of the present invention;

[0021] Figure 3 It is the waveform diagram of the pre-charge magnetization current of the present invention;

[0022] Figure 4 It is the voltage and current waveform diagram of the pre-magnetization stage of the present invention;

[0023] Figure 5 It is the voltage and current waveform after adjustment;

[0024] Figure 6 It is the waveform of the demagnetization voltage. DETAILED DESCRIPTION

[0025] A method for demagnetizing residual magnetism of a transformer based on a programmable voltage method, comprising:

[0026] Step 1: Figure 1 As shown, a demagnetizer consisting of a programmable excitation power supply, a control module, a current sampling circuit and a voltage sampling circuit is used. The current sampling circuit, the voltage sampling circuit and the programmable excitation power supply are all controlled by the control module, and the programmable excitation power supply is connected to the winding outside the transformer core;

[0027] like Figure 2 As shown, the programmable excitation power supply includes an operational amplifier UA, resistors RA1~RA4 and RSA, a relay and a contact RL1. In the figure, ① is the function control terminal. When ① is at a high level, the operational amplifier works in a voltage source state. When ① is at a low level, the operational amplifier works in a current source state. ② is the voltage / current programming terminal, ③ is the operational amplifier, and OPA549 is used as the amplifier device. Four devices are used in parallel, and the maximum output current can reach 30A, while the maximum voltage can reach ±30V. When the instrument is actually developed, the maximum current is 10A and the maximum voltage is ±24V. ④ is the output terminal, which connects the transformer winding to excite the winding.

[0028] Step 2, setting the programmable excitation power supply to two working states, namely, voltage source state and current source state; the voltage source state is used to generate a programmable variable voltage, which is used as a working power supply during the demagnetization process; the current source state is used to generate a programmable current in the pre-magnetization stage, which is used to determine the waveform of the demagnetization control voltage and provide a voltage design curve for the demagnetization process;

[0029] Step 3: Make the programmable excitation power supply work in the current source state to generate an alternating current signal, such as Figure 3 As shown, the current change is divided into a current reverse continuation stage t1, a forward reversal stage t2, a forward current continuation stage t3 and a reverse reversal stage t4; the reversal stages t2 and t4 are partial sine waves; pre-magnetization is performed, and the pre-magnetization stage is used to determine the voltage waveform of the demagnetization stage;

[0030] Step 4: Use the degaussing instrument to record the relationship between voltage and current, such as Figure 4 As shown in the figure, the voltage changes include reverse stable voltage, forward impulse voltage, forward saturation voltage and forward stable voltage. In the figure, ① is the reverse stable voltage, ② is the forward saturation voltage, ③ is the forward stable voltage, and ④ is the reverse saturation voltage. Due to the existence of saturation voltage, the power supply is subjected to an impact higher than the forward saturation voltage, and the current is distorted in the reversal stage.

[0031] Step 5: Figure 5As shown, the programmable excitation power supply continuously adjusts the length of the current reversal time t2 and t4 to reduce the impact voltage to below the saturation voltage of the power supply, thereby ensuring that the voltage will not exceed the saturation voltage of the power supply during the entire demagnetization process, avoiding the impact on the excitation power supply; the control module collects the real-time waveform of the voltage through the voltage sampling module and records it as the control voltage reference waveform during the demagnetization process;

[0032] Step 6: Program the control voltage reference waveform demagnetization voltage during the demagnetization process, such as Figure 6 As shown, demagnetization of the transformer core is achieved by generating a periodic voltage with a gradually decreasing amplitude.

[0033] Furthermore, the amplitude in step 5 decreases linearly.

[0034] Furthermore, the sampling rate of the current acquisition circuit and the voltage acquisition circuit is not less than 100KS / s.

[0035] Test results:

[0036] The test was carried out on the power transformer. The DC resistance tester was used to measure the DC on the power transformer. The measuring current was 20A and the measuring time was from 10 minutes to 30 minutes. Then the residual magnetism of the transformer was measured with the residual magnetism measuring equipment. The measurement was made once before and after demagnetization. The demagnetization current was 5A and 1A. The test results are as follows:

[0037] DC measurement time Initial remanence Degaussing current Final remanence 10 15％ 5 3％ 10 16％ 1 10％ 20 25％ 5 4％ 20 28％ 1 15％ 30 31％ 5 6％ 30 33％ 1 20％

[0038] The above are only specific embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for demagnetizing residual magnetism of a transformer based on a programmable voltage method, characterized in that: include: Step 1, using a demagnetizer composed of a programmable excitation power supply, a control module, a current sampling circuit and a voltage sampling circuit, wherein the current sampling circuit, the voltage sampling circuit and the programmable excitation power supply are all controlled by the control module, and the programmable excitation power supply is connected to the winding outside the transformer core; Step 2, setting the programmable excitation power supply to two working states, namely, a voltage source state and a current source state; The voltage source state is used to generate a programmable variable voltage, which is used as a working power supply during the demagnetization process; the current source state is used to generate a programmable current in the pre-magnetization stage, which is used to determine the waveform of the demagnetization control voltage and provide a voltage design curve for the demagnetization process; Step 3, make the programmable excitation power supply work in the current source state to generate an alternating current signal, and the current change is divided into a current reverse continuous stage, a forward reversal stage, a forward current continuous stage and a reverse reversal stage; The reversal stage is a partial sine wave; pre-magnetization is performed, and the pre-magnetization stage is used to determine the voltage waveform of the demagnetization stage; Step 4, using the demagnetizer to record the relationship between voltage and current, the voltage change includes reverse stable voltage, forward impulse voltage, forward saturation voltage and forward stable voltage; due to the existence of saturation voltage, the power supply is subjected to an impact higher than the forward saturation voltage, and the current is distorted in the reversal stage; the programmable excitation power supply continuously adjusts the length of the current reversal time to reduce the impulse voltage to below the saturation voltage of the power supply, thereby ensuring that the voltage will not exceed the saturation voltage of the power supply during the entire demagnetization process, avoiding the impact on the excitation power supply; the control module collects the real-time waveform of the voltage through the voltage sampling module and records it as the control voltage reference waveform in the demagnetization process; Step 5: Program the control voltage reference waveform demagnetization voltage during the demagnetization process, and achieve demagnetization of the transformer core by generating a periodic voltage with a gradually decreasing amplitude.

2. The method for demagnetizing residual magnetism of a transformer based on a programmable voltage method according to claim 1, characterized in that: The amplitude in step 5) decreases linearly.

3. The method for demagnetizing residual magnetism of a transformer based on a programmable voltage method according to claim 1, characterized in that: The sampling rate of the current acquisition circuit and the voltage acquisition circuit is not less than 100KS / s.

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