Transformer field load measurement method based on frequency multiplication power supply

Abstract

The invention belongs to the field of transformer test, and relates to a transformer field load measurement method based on a frequency-doubled power supply, which comprises the following steps: electrically connecting the output end of a variable-frequency power supply with the low-potential side of an intermediate transformer, electrically connecting the high-potential side of the intermediate transformer with the high-voltage side of a tested transformer, and short-circuiting the low-voltage side of the tested transformer; a compensation capacitor bank is connected in parallel to the high potential side of the intermediate transformer, and a current transformer and a power analyzer are connected in series to one branch of the intermediate transformer and the tested transformer; during testing, multiple frequencies are selected according to parameters of the variable-frequency power source, the load capacity of the whole loop is calculated according to the selected frequencies, the compensation capacitor bank is adjusted to enable the whole loop to be kept in a sub-resonance state, and the load loss converted to the reference temperature under the power frequency is calculated according to rated parameters of the tested transformer. According to the invention, the capacitance of the compensation capacitor bank is small during load test under frequency multiplication, the occupied space of equipment is small, a field test loop is simplified, and the test safety coefficient and the working efficiency are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of transformer testing, and in particular relates to a transformer on-site load measurement method based on a frequency-doubling power supply. Background Art

[0002] The load test can measure the impedance voltage and load loss of the transformer under test and is one of the most important parameter measurement tests in the transformer factory test program. This test is not currently required under field conditions for transformer applications, so on-site transformer load measurement is imperative. Currently, the test power supply for transformer load tests is relatively simple, primarily using a power-frequency generator or voltage regulator. Directly using a power-frequency generator or voltage regulator when measuring transformer load under field conditions is very expensive. Furthermore, as a transformer is an inductive load, the capacitive load that needs to be compensated under power-frequency conditions is very large, necessitating the deployment of a large number of compensation capacitor banks on-site. However, in a limited field environment, deploying a large number of compensation capacitor banks is generally not feasible. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a transformer on-site load measurement method based on a frequency-doubled power supply. The technical solution adopted by the present invention is as follows:

[0004] A method for measuring transformer load on-site based on a frequency-doubled power supply adopts a variable frequency power supply and an intermediate transformer for power supply. The intermediate transformer has a three-phase input and a single-phase output, and includes the following steps:

[0005] The output end of the variable frequency power supply is electrically connected to the low-potential side of the intermediate transformer, the high-potential side of the intermediate transformer is electrically connected to the high-voltage side of the tested transformer, the low-voltage side of the tested transformer is short-circuited by a short-circuit wire, a compensation capacitor group is connected in parallel to the high-potential side of the intermediate transformer, a current transformer and a power analyzer are connected in series in one of the branches between the intermediate transformer and the tested transformer, and the compensation capacitor group is close to the tested transformer;

[0006] During the test, first select a frequency multiplication frequency according to the parameters of the variable frequency power supply, calculate the load capacity of the entire circuit according to the selected frequency, adjust the parameters of the compensation capacitor group so that the entire circuit always maintains a sub-resonant state, adjust the variable frequency power supply boost, and monitor the current amplitude through the current transformer during the test. When the current reaches 20% of the rated current, record the loss measurement value displayed on the power analyzer, and convert it to the loss at the reference temperature, which is called P2; change the test frequency, repeat the above operation, and obtain the loss converted to the reference temperature, which is called P3. Substitute the data P2 and P3 measured at the two times the frequency multiplication frequency to obtain a set of two-variable linear equations, and solve the equation to obtain the stray loss P SE1 and eddy current loss PWE1 , the stray loss P SE1 and eddy current loss P WE1 Substitute into the formula The load loss P1 converted to the reference temperature at the power frequency is calculated based on the rated parameters of the tested transformer.

[0007] Preferably, it also includes a voltage transformer and a frequency meter, which are connected in parallel between the intermediate transformer and the two branches of the tested transformer, the frequency meter is close to the intermediate transformer, and the voltage transformer is close to the compensation capacitor group and electrically connected to the power analyzer.

[0008] Preferably, the compensation capacitor group is two sets of three-phase compensation capacitors, and the two sets of three-phase compensation capacitors form a capacitor tower.

[0009] Beneficial effects of the present invention:

[0010] The present invention has a small capacitance of the compensation capacitor group when performing a load test under double frequency, reduces the space occupied by the equipment, effectively simplifies the on-site test circuit, saves test space, reduces the workload of test personnel, and improves the test safety factor and work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0012] Figure 1 Schematic diagram of a transformer on-site load measurement method based on a frequency-doubled power supply according to an embodiment of the present invention;

[0013] In the figure, 1- variable frequency power supply, 2- intermediate transformer, 3- tested transformer, 4- current transformer, 5- power analyzer, 6- frequency meter, 7- voltage transformer, 8- compensation capacitor bank. DETAILED DESCRIPTION

[0014] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, but not all of the embodiments.

[0015] like Figure 1As shown, a method for measuring transformer load on-site based on a frequency-doubling power supply mainly includes: a variable frequency power supply 1, an intermediate transformer 2, a compensation capacitor bank 8, a current transformer 4, a voltage transformer 7, a frequency meter 6, and a power analyzer 5. The output end of the variable frequency power supply 1 is electrically connected to the low-potential side of the input end of the intermediate transformer 2, the high-potential side of the output end of the intermediate transformer 2 is electrically connected to the high-voltage side of the tested transformer 3, and the low-voltage side of the tested transformer 3 is short-circuited by a shorting wire K. The frequency meter 6, voltage transformer 7, and compensation capacitor bank 8 are sequentially connected in parallel to the high-potential side of the output end of the intermediate transformer 2, respectively. The current transformer 4 and power analyzer 5 are connected in series in one of the branches between the intermediate transformer 2 and the tested transformer 3, the voltage transformer 7 is electrically connected to the power analyzer 5, and the current transformer 4 and power analyzer 5 are located between the frequency meter 6 and the voltage transformer 7.

[0016] The variable frequency power supply 1 is a power supply that outputs a double frequency for the on-site load measurement test. The voltage and current output by the variable frequency power supply 1 are increased to the test voltage and test current required by the test through the intermediate transformer 2, and the compensation capacitor group 8 performs reactive power compensation.

[0017] Based on the current maximum capacity and voltage level of transformers used in power grids, the compensation capacitor bank 8 in the embodiment of the present invention is designed as two sets of three-phase compensation capacitors, one of which is a three-phase design with two stages per phase, each stage including one 25kvar (kilovar), one 50kvar, one 100kvar, one 200kvar, and one 400kvar single-phase capacitor, for a total of five 9.0kV single-phase capacitors, each of which is switched in a separate group, with a stage capacity of 775kvar, a phase capacity of 1550kvar, and a total capacity of 4650kvar. The other set is a three-phase design with two stages per phase, each stage including four 9.0kV 400kvar single-phase capacitors, each grouped in two, with a stage capacity of 1600kvar, a phase capacity of 3200kvar, and a total capacity of 9600kvar. Two sets of three-phase compensation capacitors form a capacitor tower. The tower supports three-phase, two-stage parallel / series connections, as well as Y / △ connections, for a total of four voltage combinations, meeting diverse application requirements. The tower has a rated voltage of 31.176 kV and a maximum rated output phase current of 50 Hz / 800 A. Pneumatic single-pole switches are used for grouping, interstage series / parallel connections, single-phase / three-phase conversion, and output. All switch opening and closing operations, as well as signal feedback, are handled within the solenoid valve cabinet and signal feedback cabinet. To facilitate equipment transportation, the two sets of three-phase compensation capacitors are integrated and installed in two identical 20-inch high-top capacitor containers. If the test voltage requirement is low, testers can quickly connect the capacitor containers to the electrical equipment container using three prefabricated high-voltage cables. All electrical connections and disconnect switches of the compensation capacitor bank 8 fully consider the overcurrent requirements and the mechanical strength of the wires, with ample margins left. This design effectively addresses the existing technical challenge of arranging large numbers of compensation capacitor banks on-site.

[0018] Considering that most of the large-capacity variable frequency power supplies 1 currently used on site are single-phase, the embodiment of the present invention adopts a single-phase load connection method, with the intermediate transformer 2 having three-phase input and single-phase output. Figure 1 Only the AC phase loss P of the tested transformer 3 is shown. AC Similarly, by changing different wiring methods, the AB phase loss P of the tested transformer 3 is measured respectively. AB and BC phase loss P BC The three-phase loss of the tested transformer 3 is calculated by three single-phase losses. The calculation formula is: (P AB +P AC +P BC ) / 3.

[0019] The output frequency of the variable frequency power supply 1 is selectable and adjustable, and is an integer multiple of 50 Hz. During the test, the input frequency of the variable frequency power supply 1 is 50 Hz. First, a multiple frequency (such as 150 Hz, 200 Hz, 250 Hz, etc.) is selected based on the parameters of the variable frequency power supply 1. The load capacity of the entire circuit is calculated based on the selected frequency. The parameters of the compensation capacitor bank 8 are adjusted so that the entire circuit always maintains a sub-resonant state. The variable frequency power supply 1 is adjusted to slowly increase the voltage. During the test, the current amplitude is monitored through the current transformer 4. When the current reaches 20% of the rated current, the loss measurement value displayed on the power analyzer 5 is recorded. The loss converted to the reference temperature is called P2. The test frequency is changed and the above operation is repeated. The loss converted to the reference temperature is called P3. The formula is as follows:

[0020]

[0021] Where: R-equivalent resistance of resistance loss, unit is Ω; P1-loss when converted to reference temperature at power frequency, unit is kW; I1-rated current at power frequency, unit is A; f1-power frequency, unit is Hz; P x -x frequency is the loss when converted to 85℃, in kW; I x - Applied current at frequency x, in A; f x -x frequency, in Hz; P SE1 - stray losses, in kW; P WE1 - Eddy current losses in kW.

[0022] According to formula (2), by substituting the data P2 and P3 measured at twice the frequency, a set of two-variable linear equations can be obtained. Solving the equations, the stray loss P is obtained. SE1 and eddy current loss P WE1 , substituting both into formula (1), the load loss P1 converted to the reference temperature at the power frequency can be obtained according to the rated parameters of the tested transformer 3.

[0023] During the measurement process, the frequency meter 6 is used to monitor the test voltage frequency in the test circuit, and the voltage transformer 7 is used to monitor the voltage value in the test circuit.

[0024] The embodiment of the present invention utilizes the fact that the capacitance of the compensation capacitor group 8 is small during the load test under double frequency, the space occupied by the equipment is reduced, and the power supply capacity can also be appropriately reduced. Through two double frequency load tests, the stray loss P under power frequency is obtained using the calculation formula in the standard. SE1 and eddy current loss P WE1The present invention adopts variable frequency power supply 1 for power supply. Unlike the traditional transformer load, the power supply frequency is selected as an integer multiple of 50Hz to change the test system environment and reduce the capacity of the compensation capacitor group 8 to 1 / n of the capacity required for the power frequency test. 2 (n is the test frequency / power frequency). During the test, two double-frequency currents of different frequencies are applied to obtain two loss results. The stray loss P is calculated based on the two measurement results. SE1 and eddy current loss P WE1 , and then calculate the load loss of the tested transformer 3 at 50Hz through the formula. This method can effectively simplify the on-site test circuit, save test space, reduce the workload of test personnel, and improve the test safety factor and work efficiency.

[0025] In the embodiments of the present invention, technical features not described in detail are all existing technologies or conventional technical means and will not be described in detail here.

[0026] Finally, it should be noted that the above embodiments are only specific implementation methods of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them, and the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any person skilled in the art can modify or easily think of changes to the technical solutions described in the above embodiments within the technical scope disclosed by the present invention, or make equivalent replacements for some of the technical features therein; and these modifications, changes or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A transformer on-site load measurement method based on a frequency-doubled power supply, which uses a variable frequency power supply (1) and an intermediate transformer (2) for power supply, wherein the intermediate transformer (2) has a three-phase input and a single-phase output, and is characterized in that: The following steps are involved: The output end of the variable frequency power supply (1) is electrically connected to the low potential side of the intermediate transformer (2), the high potential side of the intermediate transformer (2) is electrically connected to the high voltage side of the tested transformer (3), the low voltage side of the tested transformer (3) is short-circuited by a short-circuit wire, a compensation capacitor group (8) is connected in parallel to the high potential side of the intermediate transformer (2), a current transformer (4) and a power analyzer (5) are connected in series to one of the branches between the intermediate transformer (2) and the tested transformer (3), and the compensation capacitor group (8) is close to the tested transformer (3); During the test, a multiplication frequency is first selected according to the parameters of the variable frequency power supply (1), the load capacity of the entire circuit is calculated according to the selected frequency, the parameters of the compensation capacitor group (8) are adjusted so that the entire circuit always maintains a sub-resonant state, and the variable frequency power supply (1) is adjusted to increase the voltage. During the test, the current amplitude is monitored by the current transformer (4). When the current reaches 20% of the rated current, the loss measurement value displayed on the power analyzer (5) is recorded, and the loss converted to the reference temperature is called P2; the test frequency is changed, and the above operation is repeated to obtain the loss converted to the reference temperature, which is called P3. The data P2 and P3 measured at the two multiplication frequencies are substituted into a set of two-variable linear equations, and the equation is solved to obtain the stray loss P SE1 and eddy current loss P WE1 , the stray loss P SE1 and eddy current loss P WE1 Substitute into the formula The load loss P1 converted to the reference temperature at the power frequency is calculated based on the rated parameters of the tested transformer (3).

2. The transformer on-site load measurement method based on a frequency-doubled power supply according to claim 1, characterized in that: The invention also includes a voltage transformer (7) and a frequency meter (6), which are connected in parallel between the intermediate transformer (2) and the two branches of the tested transformer (3), the frequency meter (6) being close to the intermediate transformer (2), and the voltage transformer (7) being close to the compensation capacitor bank (8) and electrically connected to the power analyzer (5).

3. The transformer on-site load measurement method based on a frequency-doubled power supply according to claim 2, characterized in that: The compensation capacitor group (8) is two sets of three-phase compensation capacitors, and the two sets of three-phase compensation capacitors form a capacitor tower.

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