Method for measuring residual magnetism and demagnetizing transformer iron core by adopting high-voltage oscillation method
By using a high-voltage oscillation method in the transformer, the oscillation current is generated by using external capacitors, efficient measurement and elimination of the residual magnetism of the transformer is solved, and the core saturation and reactive consumption problems caused by residual magnetism are ensured, ensuring the safe and stable operation of the transformer.
Patent Information
- Application Number
- CN202411957065.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-29
- Publication Date
- 2025-06-20
AI Technical Summary
The transformer will produce residual magnetism after DC test, resulting in half-circumference saturation of the iron core, increased reactive power consumption, shortened life, and may cause malfunction of the relay protection device, causing equipment accidents and economic losses. The prior art usually performs residual magnetic measurement and demagnetization separately, and excessive demagnetization current will cause an impact on the equipment, and too small will cause low efficiency.
The high-voltage oscillation method is used to measure and eliminate the residual magnetism of the transformer by a tester composed of a DC power supply, a switching switch and a current sensor. This method records the changes in the oscillation current, calculates the ratio of the current waveform, and adjusts the oscillation period to achieve efficient residual magnetic elimination.
It realizes efficient residual magnetization elimination, improves the intensity of the demagnetization current, shortens the demagnetization time, ensures the safe and stable operation of the transformer, and measures the residual magnetism size in real time to avoid equipment damage.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to the field of power transformers, and in particular to a method for measuring and demagnetizing the residual magnetism of a transformer core using a high-voltage oscillation method. Background Art
[0002] Power transformers are one of the important devices for transmitting electrical energy. The quality and reliability of transformers are directly related to the safe and reliable operation of the power grid. Preventive tests are required after the commissioning and maintenance of power transformers.
[0003] Due to the inherent hysteresis phenomenon of ferromagnetic materials, residual magnetism will be generated in the transformer core after the DC test of the transformer. When the transformer is put into operation, the residual magnetism in the core will cause the transformer core to be saturated in half a cycle, and a large number of harmonics will be generated in the excitation current. This not only increases the reactive power consumption of the transformer, shortens the service life of the transformer, but also may cause misoperation of the relay protection device, resulting in serious equipment accidents and economic losses. Therefore, after the DC test of the transformer, the transformer must be demagnetized to ensure the safe and stable operation of the transformer.
[0004] At present, the methods of demagnetization used at home and abroad generally measure and demagnetize the residual magnetism separately, that is, first measure the residual magnetism, and then use the DC method or AC method to eliminate the residual magnetism. When demagnetizing, if the current is too large, it will cause a great impact on the instrument and equipment. If the demagnetizing current is too small, the demagnetizing efficiency is low and the demagnetizing time is long. Summary of the Invention
[0005] The present invention aims to solve the problems existing in the background art and proposes a method for measuring and demagnetizing the residual magnetism of a transformer using a high-voltage oscillation method, including:
[0006] Step 1: Use a tester composed of a DC power supply, a changeover switch, and a current sensor. The changeover switch, the transformer winding connection terminal, the current transformer, and the external capacitor connection terminal are connected in series between the positive and negative poles of the DC power supply. The transformer winding connection terminal is connected to the winding of the transformer to be tested, and the external capacitor connection terminal is connected to an external capacitor Cx. The capacitor Cx is used to store charge to generate an oscillating current, and can be selected according to the capacity of the transformer;
[0007] Step 2: Switch the changeover switch to position 1, and the DC power supply charges the external capacitor Cx through the transformer winding. At this time, the current magnitude is measured through the current transformer, and the charging is completed;
[0008] Step 3: Switch the changeover switch to position 2. At this time, the capacitor Cx discharges to the transformer winding through the changeover switch and the current transformer, and the transformer winding and the capacitor Cx form a typical CL oscillating circuit;
[0009] Step 4: As time goes by, the peak value of the oscillating current gradually decreases to zero. Record the change of the oscillating current through the current transformer, obtain the typical waveform of the current, and precisely rectify the current signal to obtain the rectified current waveform.
[0010] Step 5: Calculate the ratio of the difference between the two peak values corresponding to the intersection points of the extension lines of the envelope of the odd-numbered peaks and the extension line of the envelope of the even-numbered peaks of the rectified current waveform and the vertical coordinate axis to the sum of the two peak values.
[0011] Step 6: When the ratio > 5%, repeat Step 2, Step 3, Step 4, and Step 5; when the ratio ≤ 5%, it indicates that there is no residual magnetism in the transformer core and the demagnetization is completed.
[0012] Furthermore, the translational offset generated by the envelope of the odd-numbered peaks and the envelope of the even-numbered peaks gradually decreases during the demagnetization process.
[0013] Furthermore, during the demagnetization process, adjust the elimination effect of the residual magnetism by adjusting the number of oscillation periods.
[0014] Furthermore, when the charging is completed, the current measured by the current transformer ≤ 1 mA.
[0015] The beneficial effects of the present invention are as follows: Since the high-voltage oscillation method is adopted, a very high demagnetizing current can be generated, and the demagnetization efficiency is higher. At the same time, due to the adoption of the oscillation method, the magnitude of the current and the positive and negative symmetry of the current can be measured in real time during the demagnetization process, so that the magnitude of the residual magnetism of the transformer can be measured, and the measurement and elimination of the residual magnetism are realized simultaneously. The external capacitor can be adjusted according to the size of the transformer. Description of the Drawings
[0016] Figure 1 is the circuit schematic diagram of the tester of the present invention;
[0017] Figure 2 is the schematic diagram of the shaped current waveform during the demagnetization process;
[0018] Figure 3 is the schematic diagram of the typical waveform of the current when there is no residual magnetism after demagnetization;
[0019] Figure 4 is Figure 3 the schematic diagram of the shaped current waveform of the waveform in Detailed Embodiment
[0020] A method for measuring and demagnetizing the residual magnetism of a transformer using the high-voltage oscillation method, including:
[0021] Step 1: As shown in Figure 1As shown in the figure, a tester using a DC power supply 1, a switching switch 2, and a current sensor 3 is adopted. The switching switch 2, the transformer winding access terminal 4, the current transformer 3, and the external capacitor access terminal 5 are connected in series between the positive and negative poles of the DC power supply. The transformer winding access terminal 5 is connected to the transformer winding 4 to be measured, and the external capacitor access terminal 6 is connected to the external capacitor Cx. The external capacitor Cx is used to store charges to generate an oscillating current, and can be selected according to the capacity of the transformer;
[0022] Step 2: Switch the change-over switch 2 to position "1", and the DC power supply charges the external capacitor Cx through the transformer winding. At this time, the current magnitude is measured through the current transformer 3 until the current is less than 1 mA, and the charging is completed;
[0023] Step 3: Switch the change-over switch 2 to position "2". At this time, the capacitor Cx discharges to the transformer winding 4 through the change-over switch 2 and the current transformer 3, and the transformer winding and the capacitor Cx form a typical CL oscillating circuit;
[0024] Step 4: As time goes by, the peak value of the oscillating current will gradually decrease to zero. The change of the oscillating current is recorded through the current transformer, and the typical waveform of the current is obtained. The current signal is precisely rectified to obtain the rectified current waveform, as Figure 2 shown; Figure 2 In the figure, ① is the envelope line of the odd-numbered wave peaks, and ② is the envelope line of the even-numbered wave peaks. It can be seen from the figure that when there is residual magnetism, the two envelope lines will produce vertical translation. The greater the residual magnetism, the greater the translation distance of the envelope line;
[0025] Step 5: Calculate the ratio of the difference between the two peak values corresponding to the intersection points of the extension lines of the envelope lines of the odd-numbered wave peaks and the envelope lines of the even-numbered wave peaks of the rectified current waveform and the sum of the two peak values with the vertical coordinate axis;
[0026] Step 6: When the ratio > 5%, repeat Step 2, Step 3, Step 4, and Step 5; when the ratio ≤
[0027] 5%, the typical waveform of the corresponding current and the current waveform after precisely rectifying the current signal are respectively as Figure 3 , Figure 4 shown, indicating that there is no residual magnetism in the transformer core and the demagnetization is completed.
[0028] Furthermore, the translation offset generated by the envelope line of the odd-numbered wave peaks and the envelope line of the even-numbered wave peaks gradually becomes smaller during the demagnetization process.
[0029] Furthermore, during the demagnetization process, the elimination effect of the residual magnetism is adjusted by adjusting the number of oscillation periods.
[0030] Test results:
[0031] Tests were carried out on a power transformer. DC measurements were made on the power transformer using a DC resistance tester, with a measurement current of 20 A and a measurement time ranging from 10 minutes to 30 minutes. Then, tests were conducted using a residual magnetism measurement and elimination device, and the test results are shown in the following table:
[0032] DC measurement time Initial remanence Demagnetization oscillation period Final remanence 10 15％ 10 3％ 10 16％ 5 12％ 20 25％ 10 6％ 20 28％ 5 18％ 30 31％ 10 8％ 30 33％ 5 21％
[0033] It can be seen that through this method, the residual magnetism in the transformer core generated due to DC test items can be effectively eliminated, and there is a certain positive correlation between the demagnetization effect and the demagnetization current, which is in line with general knowledge.
[0034] The above are only specific embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A method for measuring and demagnetizing residual magnetism of a transformer using a high voltage oscillation method, characterized in that: include: Step 1: Use a tester consisting of a DC power supply, a switching switch, and a current sensor. The switching switch, a transformer winding access terminal, a current transformer, and an external capacitor access terminal are connected in series between the positive and negative electrodes of the DC power supply. The transformer winding access terminal is connected to the transformer winding to be tested, and the external capacitor access terminal is connected to an external capacitor Cx. The capacitor Cx is used to store charge to generate an oscillating current and can be selected according to the capacity of the transformer. Step 2: Switch the conversion switch to position 1, and the DC power supply charges the external capacitor Cx through the transformer winding. At this time, the current is measured by the current transformer until the charging is completed; Step 3: Switch the conversion switch to position 2. At this time, the capacitor Cx discharges to the transformer winding through the conversion switch and the current transformer. The transformer winding and the capacitor Cx form a typical CL oscillation circuit. Step 4: As time changes, the peak value of the oscillating current gradually decreases to zero. The change of the oscillating current is recorded by a current transformer, and a typical waveform of the current is obtained. The current signal is precisely rectified to obtain a rectified current waveform. Step 5, calculating the ratio of the difference between two peak values corresponding to the intersection of the extended line of the envelope of the odd-numbered peaks and the extended line of the envelope of the even-numbered peaks corresponding to the rectified current waveform and the ordinate axis to the sum of the two peak values; Step 6: When the ratio is greater than 5%, repeat steps 2, 3, 4 and 5; when the ratio is less than or equal to 5%, it indicates that there is no residual magnetism in the transformer core and demagnetization is completed.
2. The method for measuring and demagnetizing residual magnetism of a transformer using a high voltage oscillation method according to claim 1, characterized in that: The translation offset generated by the envelope of the odd-numbered peaks and the envelope of the even-numbered peaks gradually decreases during the demagnetization process.
3. The method for measuring and demagnetizing residual magnetism of a transformer using a high voltage oscillation method according to claim 1, characterized in that: During the demagnetization process, the residual magnetism elimination effect is adjusted by adjusting the number of oscillation cycles.
4. The method for measuring and demagnetizing residual magnetism of a transformer using a high voltage oscillation method according to claim 1, characterized in that: When charging is complete, the current measured by the current transformer is ≤1mA.