Transformer field load measuring system

Abstract

The utility model belongs to the technical field of transformer test, and relates to a transformer field load measuring system using a frequency-doubled power supply, which comprises a variable-frequency power supply, an intermediate transformer, a compensating capacitor bank, a current transformer and a power analyzer, the output end of the variable-frequency power source is electrically connected with the low-potential side of the intermediate transformer, the high-potential side of the intermediate transformer is electrically connected with the high-voltage side of the tested transformer, the low-voltage side of the tested transformer is in short circuit through the short-circuit line, and the compensation capacitor bank is connected to the high-potential side of the intermediate transformer in parallel. The current transformer and the power analyzer are connected in series in one branch of the intermediate transformer and the tested transformer, and the compensation capacitor bank is close to the tested transformer. When a load test is carried out under frequency multiplication, the capacitance of the compensation capacitor bank is small, the occupied space of equipment is reduced, a field test loop is simplified, the test space is saved, the workload of testers is reduced, and the test safety coefficient and the work efficiency are improved.

Description

Technical Field

[0001] This utility model belongs to the field of transformer testing technology, specifically relating to a transformer field load measurement system utilizing a frequency multiplier power supply. Background Technology

[0002] Load testing measures the impedance voltage and load loss of the transformer under test, and is one of the important parameter measurement tests in the transformer factory testing program. While this test is not currently required under normal transformer application conditions, with the solid progress made in my country's efforts to achieve its carbon peaking and carbon neutrality commitments, on-site transformer load measurement is becoming increasingly necessary. Currently, the test power sources for transformer load testing are relatively limited, mainly using power frequency generators or voltage regulators. However, directly using power frequency generators or voltage regulators to measure transformer load under on-site conditions would be very costly. Furthermore, as an inductive load, the capacitive load requiring compensation under power frequency conditions would be substantial, inevitably necessitating the deployment of numerous compensation capacitor banks on-site. However, in the limited space of an on-site environment, deploying a large number of compensation capacitor banks is usually impractical. Summary of the Invention

[0003] To solve the above-mentioned technical problems, this utility model provides a transformer field load measurement system. The technical solution adopted by this utility model is as follows:

[0004] The transformer field load measurement system includes: a frequency converter, an intermediate transformer, a compensation capacitor bank, a current transformer, and a power analyzer. The intermediate transformer has three-phase input and single-phase output. The output terminal of the frequency converter is electrically connected to the low-potential side of the intermediate transformer, and the high-potential side of the intermediate transformer is electrically connected to the high-voltage side of the transformer under test. The low-voltage side of the transformer under test is short-circuited by a jumper wire. The compensation capacitor bank is connected in parallel to the high-potential side of the intermediate transformer. The current transformer and the power analyzer are connected in series in one of the branches of the intermediate transformer and the transformer under test. The compensation capacitor bank is located close to the transformer under test.

[0005] Preferably, it also includes a voltage transformer and a frequency meter, wherein the voltage transformer and the frequency meter are connected in parallel between two branches of the intermediate transformer and the transformer under test, the frequency meter is close to the intermediate transformer, and the voltage transformer is close to the compensation capacitor bank and electrically connected to the power analyzer.

[0006] Preferably, the compensation capacitor bank consists of two sets of three-phase compensation capacitors, and the two sets of three-phase compensation capacitors form a capacitor tower.

[0007] The beneficial effects of this utility model are:

[0008] When performing frequency multiplication load tests, this invention features a small compensation capacitor bank, which 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. Attached Figure Description

[0009] The accompanying drawings are provided to further illustrate the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention, but do not constitute a limitation thereof. In the drawings:

[0010] Figure 1 This is a schematic diagram of the transformer field load measurement system according to an embodiment of the present invention;

[0011] In the diagram, 1-frequency converter, 2-intermediate transformer, 3-transformer under test, 4-current transformer, 5-power analyzer, 6-frequency meter, 7-voltage transformer, and 8-compensation capacitor bank. Detailed Implementation

[0012] The technical solution of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this utility model, but not all embodiments.

[0013] like Figure 1 As shown, the transformer field load measurement system mainly includes: a frequency converter 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. Specifically: the output terminal of the frequency converter 1 is electrically connected to the low-potential side of the input terminal of the intermediate transformer 2; the high-potential side of the output terminal of the intermediate transformer 2 is electrically connected to the high-voltage side of the transformer under test 3; the low-voltage side of the transformer under test 3 is short-circuited via a jumper 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 terminal of the intermediate transformer 2; the current transformer 4 and power analyzer 5 are connected in series in one branch of the intermediate transformer 2 and the transformer under test 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.

[0014] The frequency converter 1 is a power supply that outputs a frequency multiple of the load for on-site load measurement and testing. The voltage and current output by the frequency converter 1 are increased to the test voltage and test current required by the test through the intermediate transformer 2, and the compensation capacitor bank 8 performs reactive power compensation.

[0015] Based on the current maximum capacity and voltage level of transformers used in power grids, the compensation capacitor bank 8 in this embodiment is designed as two sets of three-phase compensation capacitors. One set is a three-phase design, with each phase divided into two levels. Each level includes one 25kvar, one 50kvar, one 100kvar, one 200kvar, and one 400kvar single-phase capacitor, totaling five 9.0kV single-phase capacitors. Each capacitor is switched in a separate group, with a level capacity of 775kvar, a phase capacity of 1550kvar, and a total capacity of 4650kvar. The other set is a three-phase design, with each phase divided into two levels. Each level includes four 9.0kV 400kvar single-phase capacitors, switched in groups of two, with a level 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, which can realize three-phase two-stage parallel / series and Y / Δ connection combinations, for a total of four voltage combinations to meet various application requirements. The rated voltage of the capacitor tower is 31.176kV, and the maximum rated output phase current is designed for 50Hz / 800A. Grouping, inter-stage series and parallel connection, single / three-phase conversion, and output all adopt pneumatic single-pole switches. All switch opening and closing operations and signal feedback are realized in the solenoid valve cabinet and signal feedback cabinet. For easy equipment transportation, the two sets of three-phase compensation capacitors are integrated and installed in two identical 20-inch high-roof capacitor containers. If the test voltage requirement is not high, the test personnel can use three prefabricated high-voltage cables to quickly connect the capacitor container to the electrical equipment container. All electrical connections and disconnecting switches of the compensation capacitor group 8 fully consider their overcurrent requirements and the mechanical strength of the conductors, and leave sufficient margin. Through the above design, the technical problem of not being able to deploy a large number of compensation capacitor groups on site in the existing technology is effectively solved.

[0016] Considering that most high-capacity frequency converters used in the field are currently single-phase, this embodiment of the invention adopts a single-phase load wiring method, with the intermediate transformer 2 having three-phase input and single-phase output, and an attached... Figure 1 Only the AC phase loss P of the transformer under test 3 is shown. AC Similarly, by changing the wiring method, the AB phase loss P of the transformer under test 3 was measured respectively. AB and BC phase loss P BC The three-phase losses of the tested transformer 3 were calculated from the three single-phase losses, and the calculation formula is: (P AB +P AC +P BC ) / 3.

[0017] The output frequency of the frequency converter 1 is selectable and adjustable, and is an integer multiple of 50Hz. During the test, the input frequency of the frequency converter 1 is 50Hz. First, select a frequency multiple (such as 150Hz, 200Hz, 250Hz, etc.) according to the parameters of the frequency converter 1. Calculate the load capacity of the entire circuit based on the selected frequency. Adjust the parameters of the compensation capacitor bank 8 to keep the entire circuit in a sub-resonant state. Slowly increase the voltage of the frequency converter 1. During the test, monitor the current amplitude through the current transformer 4. When the current reaches 20% of the rated current, record the loss measurement value displayed on the power analyzer 5. The loss converted to the reference temperature is called P2. Change the test frequency and repeat the above operation to obtain the loss converted to the reference temperature, called P3. The formula is as follows:

[0018]

[0019] Where: R - equivalent resistance of the resistance loss, in Ω; P1 - loss converted to reference temperature at power frequency, in kW; I1 - rated current at power frequency, in A; f1 - power frequency, in Hz; P x -x frequency converted to 85℃ loss, unit is kW; I x The applied current at frequency -x, in amperes (A); f x -x Frequency, unit: Hz; P SE1 - Stray losses, in kW; P WE1 - Eddy current loss, in kW.

[0020] According to formula (2), substituting the data P2 and P3 measured at the two harmonic frequencies, we can obtain a system of two linear equations. Solving the equations yields the stray loss P. SE1 and eddy current loss P WE1 Substituting both into formula (1), the load loss P1 at the reference temperature under power frequency can be obtained based on the rated parameters of the transformer under test 3.

[0021] During the measurement process, frequency meter 6 is used to monitor the frequency of the test voltage in the test circuit, and voltage transformer 7 is used to monitor the voltage value in the test circuit.

[0022] This embodiment of the invention utilizes the small capacitance of the compensation capacitor bank 8 during frequency doubling load testing, which reduces the space occupied by the equipment and allows for a suitable reduction in power supply capacity. Through two frequency doubling load tests, the stray loss P at the power frequency is obtained using the calculation formula in the standard. SE1 and eddy current loss P WE1The numerical values ​​are then used to obtain the overall load loss at the power frequency. This invention uses a frequency converter 1 for power supply. Unlike traditional transformer loads, the applied power frequency is selected as an integer multiple of 50Hz to alter the test system environment, reducing the capacity of the compensation capacitor bank 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 frequency-harmonic currents of different frequencies are applied to obtain two loss results. The stray loss P is calculated from the two measurement results. SE1 and eddy current loss P WE1 Then, the load loss of the transformer under test 3 at 50Hz is calculated using a 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.

[0023] In this embodiment of the utility model, all technical features not described in detail are existing technologies or conventional technical means, and will not be repeated here.

[0024] Finally, it should be noted that the above embodiments are merely specific implementations of this utility model, used to illustrate the technical solution of this utility model, and not to limit it. The protection scope of this utility model is not limited thereto. Those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the technical scope disclosed in this utility model; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this utility model, and should all be covered within the protection scope of this utility model.

Claims

1. Transformer field load measurement system, including: The variable frequency power supply (1), intermediate transformer (2), compensation capacitor bank (8), current transformer (4) and power analyzer (5) are characterized in that the intermediate transformer (2) has three-phase input and single-phase output, the output terminal 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 potential side of the transformer under test (3), the low potential side of the transformer under test (3) is short-circuited by a shorting wire, the compensation capacitor bank (8) is connected in parallel to the high potential side of the intermediate transformer (2), the current transformer (4) and the power analyzer (5) are connected in series in one of the branches of the intermediate transformer (2) and the transformer under test (3), and the compensation capacitor bank (8) is close to the transformer under test (3).

2. The transformer field load measurement system according to claim 1, characterized in that, It also includes a voltage transformer (7) and a frequency meter (6), which are connected in parallel between two branches of the intermediate transformer (2) and the transformer under test (3). The frequency meter (6) is close to the intermediate transformer (2), and the voltage transformer (7) is close to the compensation capacitor bank (8) and electrically connected to the power analyzer (5).

3. The transformer field load measurement system according to claim 2, characterized in that, The compensation capacitor bank (8) consists of two sets of three-phase compensation capacitors, which together form a capacitor tower.

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