A detection circuit and evaluation method for power curve of variable frequency power supply for high voltage test

Abstract

The present invention belongs to the technical field of power supply power detection, and specifically relates to a detection circuit and evaluation method for a power curve of a variable frequency power supply for high voltage testing; the technical scheme adopted is: adjusting the load in a variable load device to a maximum value of 10Ω, and making its power factor angle 0°; after adjusting the output frequency of the variable frequency power supply to 50Hz, adjusting the output voltage of the variable frequency power supply with a 5V voltage as a step until the output voltage reaches a maximum of 350V; each voltage node U n By adjusting the variable load device to the maximum current that the variable frequency power supply can output, record the current value I at this time n After the test is completed, the output voltage of the tested variable frequency power supply is reduced to 0 through the variable frequency power supply control box and disconnected; through N groups of data, the I n =K·U n Working straight line, record the proportional coefficient K1 at this time; the present invention is used for the detection circuit of the power curve of the variable frequency power supply.

Description

Technical Field

[0001] The invention belongs to the technical field of power supply detection, and in particular relates to a detection circuit and an evaluation method for a power curve of a variable frequency power supply for a high voltage test. Background Art

[0002] As the main equipment for controlling power supply at high-voltage test site, variable frequency power supply can convert the commonly used 380V maintenance power supply at site into a test power supply with adjustable voltage and frequency, and has almost completely replaced the position of generator in field test; however, compared with the load capacity of generator, the load capacity of variable frequency power supply (usually expressed by power curve, defined as the linear function relationship between output voltage and output current under certain load conditions) is relatively limited, which often places high requirements on the compensation amount on the high-voltage side of field test, and often causes the field test to be unable to be carried out due to insufficient load capacity of variable frequency power supply. At present, there are many types of variable frequency power supplies on the market, and the load capacity varies. The relevant users have not yet had devices and methods for testing the load capacity of variable frequency power supply, so it is very necessary to test the load capacity of variable frequency power supply. Summary of the invention

[0003] The present invention overcomes the shortcomings of the prior art and provides a method and device for testing the load capacity of a variable frequency power supply for high voltage testing. By adjusting the combined parameters of circuit elements (resistance, capacitance, inductance) in a variable load device in a test loop, the operation mode of the variable frequency power supply under representative working conditions is simulated, and the power curves under these working conditions are measured, thereby achieving a comprehensive verification of its load capacity.

[0004] In the test circuit for measuring the power curve of the variable frequency power supply, except for the variable frequency power supply of the equipment under test, other equipment including current transformers, voltage transformers, variable load devices, etc., all use special test equipment that has been inspected by relevant inspection agencies and meets the test accuracy requirements.

[0005] Each test can obtain the power curve under one of the operating conditions, and the proportional coefficient K can be obtained based on the linear relationship between current and voltage. By comparing the K value with the set standard value, the load capacity of the tested variable frequency power supply can be judged, which effectively guarantees the implementation of high-voltage test on-site work.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a detection circuit for a power curve of a variable frequency power supply for high voltage testing, comprising: a variable frequency power supply to be detected, a current transformer and a variable load device;

[0007] The input end of the tested variable frequency power supply is connected to the 380V power supply system through a low voltage input cable, and the output end of the tested variable frequency power supply is connected to the variable load device through a low voltage output cable to form an output circuit;

[0008] The primary side of the voltage transformer is connected in parallel to the output circuit and connected to the output end of the detected variable frequency power supply, the secondary side of the voltage transformer is connected to the voltage terminal of the power analyzer, the current terminal of the power analyzer is connected to the secondary side of the current transformer, and the primary side of the current transformer is connected in series to the output circuit of the detected variable frequency power supply;

[0009] The detected variable frequency power supply is connected with a variable frequency power supply control box.

[0010] The detected variable frequency power supply is connected to the variable frequency power supply control box via a control optical fiber.

[0011] The secondary side of the voltage transformer is connected to the input end of the power analyzer through a secondary test line.

[0012] The above-mentioned evaluation method of the detection circuit of the power curve of the variable frequency power supply for high voltage test comprises the following steps:

[0013] Step 1: The test requires constant ambient temperature and humidity, constant power capacity, and stable output voltage. The following steps should be carried out under the condition that the test environment and power quality data remain unchanged;

[0014] Step 2: Use a low-voltage input cable to connect the 380V power supply system to the input end of the tested variable frequency power supply. The output end of the tested variable frequency power supply is connected to the variable load device through a low-voltage output cable. The tested variable frequency power supply can convert the three-phase power supply into a single-phase power supply with adjustable voltage and frequency.

[0015] Step 3: The primary winding of the current transformer is connected in series to the output circuit of the variable frequency power supply, the primary winding of the voltage transformer is connected in parallel to the output circuit of the variable frequency power supply, the voltage input terminal of the power analyzer is connected to the secondary winding of the voltage transformer through the secondary test line, and the current input terminal is connected to the secondary winding of the current transformer;

[0016] Step 4: Connect the control optical fiber to the variable frequency power supply control box 5 to achieve complete isolation between low voltage and high voltage while realizing remote control of output voltage and frequency;

[0017] Step 5: Adjust the load in the variable load device to a maximum value of 10Ω and make its power factor angle 0°;

[0018] Step 6: Start the test circuit, adjust the output frequency of the variable frequency power supply to 50Hz, and then adjust the output voltage of the variable frequency power supply in steps of 5V until the output voltage reaches the maximum of 350V;

[0019] Step 7: At each voltage node U nAt this point (a total of 70 voltage nodes), by adjusting the variable load device (keeping the power factor angle at 0°) until the current that the variable-frequency power supply can output reaches the maximum, the output display interface of the variable-frequency power supply will flash. Record the current value I at this time. n ;

[0020] Step 8: After the entire test is completed, lower the output voltage of the variable-frequency power supply under test to 0 through the variable-frequency power supply control box and disconnect it.

[0021] Step 9: Through 70 groups of (I n , U n ) data, fit the I n = K1·U n working straight line under this working condition, and record the proportionality coefficient K1 at this time.

[0022] Step 10: Adjust the resistance-capacitance-inductance ratio of the load in the variable load device so that R = X L = 10Ω, X L = 10Ω, R = X C = 10Ω, X C = 10Ω, that is, the power factor angles of the variable load device are 45°, 90°, -45°, -90° respectively at this time.

[0023] Step 11: Repeat the operations from Step 6 to Step 9, and keep the power factor angle under this working condition when adjusting the variable load device to obtain the proportionality coefficients K2, K3, K4, K5 under each working condition.

[0024] Step 12: Define K = average[K1, K2, K3, K4, K5], which is the final assessment index for the load-carrying capacity of the variable-frequency power supply under test.

[0025] Step 13: Rate the variable-frequency power supply under test:

[0026] If Q ≤ 2, define the unqualified grade for the variable-frequency power supply under test;

[0027] If 2 < Q ≤ 3, define the qualified grade for the variable-frequency power supply under test;

[0028] If 3 < Q ≤ 4, define the good grade for the variable-frequency power supply under test;

[0029] If Q > 4, define the excellent grade for the variable-frequency power supply under test.

[0030] The beneficial effects of the present invention compared with the prior art are:

[0031] The method of the present invention is simple, practical and efficient, and the results are reliable. By evaluating the power curves of the variable-frequency power supply under various working conditions, the load-carrying capacity of the variable-frequency power supply is tested, thereby improving the reliability level of the equipment and realizing the quality control of the test equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be further described below in conjunction with the accompanying drawings.

[0033] Figure 1 The figure is a detection circuit diagram of the power curve of the variable frequency power supply of the present invention.

[0034] In the figure: 1 is the variable frequency power supply to be tested, 2 is the voltage transformer, 3 is the variable load device, 4 is the low voltage input cable, 5 is the 380V power supply system, 6 is the low voltage output cable, 7 is the power analyzer, 8 is the current transformer, 9 is the variable frequency power supply control box, 10 is the control optical fiber, and 11 is the secondary test line. DETAILED DESCRIPTION

[0035] As shown in the figure, a detection circuit for a power curve of a variable frequency power supply for high voltage testing includes: a variable frequency power supply to be detected 1, a voltage transformer 2 and a variable load device 3;

[0036] The input end of the tested variable frequency power supply 1 is connected to a 380V power supply system 5 through a low voltage input cable 4, and the output end of the tested variable frequency power supply 1 is connected to a variable load device 3 through a low voltage output cable 6 to form an output circuit;

[0037] The primary side of the voltage transformer 2 is connected in parallel to the output circuit and connected to the output end of the detected variable frequency power supply 1, the secondary side of the voltage transformer 2 is connected to the voltage terminal of the power analyzer 7, the current terminal of the power analyzer 7 is connected to the secondary side of the current transformer 8, and the primary side of the current transformer 8 is connected in series to the output circuit of the detected variable frequency power supply;

[0038] The detected variable frequency power supply 1 is connected to a variable frequency power supply control box 9 .

[0039] Preferably, the detected variable frequency power supply 1 is connected to the variable frequency power supply control box 9 via a control optical fiber 10 .

[0040] Preferably, the secondary side of the voltage transformer 2 is connected to the input end of the power analyzer 7 via a secondary test line 11 .

[0041] The above-mentioned evaluation method of the detection circuit of the power curve of the variable frequency power supply for high voltage test comprises the following steps:

[0042] Step 1: The test requires constant ambient temperature and humidity, constant power capacity, and stable output voltage. The following steps should be carried out under the condition that the test environment and power quality data remain unchanged;

[0043] Step 2: Use the low-voltage input cable 4 to connect the 380V power supply system 5 to the input end of the tested variable frequency power supply 1, and the output end of the tested variable frequency power supply 1 is connected to the variable load device 3 through the low-voltage output cable 6. The tested variable frequency power supply 1 can convert the three-phase power supply into a single-phase power supply with adjustable voltage and frequency;

[0044] Step 3: The primary winding of the current transformer 8 is connected in series to the output circuit of the tested variable frequency power supply 1, the primary winding of the voltage transformer 2 is connected in parallel to the output circuit of the tested variable frequency power supply 1, the voltage input terminal of the power analyzer 7 is connected to the secondary winding of the voltage transformer 2 through the secondary test line 11, and the current input terminal is connected to the secondary winding of the current transformer 8;

[0045] Step 4: Connect the control optical fiber 10 to the variable frequency power supply control box 9 to achieve complete isolation between low voltage and high voltage while realizing remote control of output voltage and frequency;

[0046] Step 5: Adjust the load in the variable load device 3 to a maximum value of 10Ω and make its power factor angle 0°;

[0047] Step 6: Start the test circuit, adjust the output frequency of the tested variable frequency power supply 1 to 50Hz, and then adjust the output voltage of the tested variable frequency power supply 1 in steps of 5V until the output voltage reaches the maximum of 350V;

[0048] Step 7: At each voltage node U n At 70 voltage nodes in total, adjust the variable load device 3 (keep the power factor angle at 0°) to the maximum current that the variable frequency power supply can output. At this time, the output display interface of the variable frequency power supply will flash, and record the current value I at this time. n ;

[0049] Step 8: After the entire test is completed, the output voltage of the tested variable frequency power supply 1 is reduced to 0 through the variable frequency power supply control box 9 and disconnected;

[0050] Step 9: Pass 70 groups (I n , U n ) data, fitting the I n =K1·U n Working straight line, record the proportional coefficient K1 at this time;

[0051] Step 10: Adjust the load resistance, capacitance and inductance ratios in the variable load device 3 to R=X L =10Ω、X L =10Ω、R=X C =10Ω、X C =10Ω, that is, the power factor angles of the variable load device are 45°, 90°, -45°, and -90° respectively;

[0052] The eleventh step: Repeat the operations in the sixth step to the ninth step. When adjusting the variable load device, maintain the power factor angle under this working condition to obtain the proportionality coefficients K2, K3, K4, and K5 under each working condition.

[0053] The twelfth step: Define K = average[K1, K2, K3, K4, K5], which is the final assessment index for the load-carrying capacity of the tested variable-frequency power supply 1.

[0054] The thirteenth step: Rate the tested variable-frequency power supply 1:

[0055] If Q ≤ 2, define the unqualified grade for the tested variable-frequency power supply 1;

[0056] If 2 < Q ≤ 3, define the qualified grade for the tested variable-frequency power supply 1;

[0057] If 3 < Q ≤ 4, define the good grade for the tested variable-frequency power supply 1;

[0058] If Q > 4, define the excellent grade for the tested variable-frequency power supply 1.

[0059] The operation process of the present invention:

[0060] After starting the test circuit, simulate the operation modes of the tested variable-frequency power supply 1 under different working conditions by adjusting various ratio combinations of the internal resistance, inductance, and capacitance in the variable load device 3. Select the five most representative operation conditions to obtain the power curves under various operation modes, and classify and judge the power curves of the tested variable-frequency power supply according to the judgment criteria, effectively carrying out the load performance detection work for the variable-frequency power supply.

[0061] The above embodiments only exemplarily illustrate the principles and effects of the present invention, rather than limiting the present invention. Those familiar with this technology can modify or improve the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field described above without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. An evaluation method for a detection circuit based on a power curve of a variable frequency power supply for a high voltage test, the detection circuit comprising: The variable-frequency power supply under test (1), voltage transformer (2), and variable load device (3); The input end of the variable-frequency power supply under test (1) is connected to the 380V power supply system (5) through a low-voltage input cable (4), and the output end of the variable-frequency power supply under test (1) is connected to the variable load device (3) through a low-voltage output cable (6) to form an output loop; The primary side of the voltage transformer (2) is connected in parallel to the output loop and is connected to the output end of the variable-frequency power supply under test (1). The secondary side of the voltage transformer (2) is connected to the voltage terminal of the power analyzer (7). The current terminal of the power analyzer (7) is connected to the secondary side of the current transformer (8), and the primary side of the current transformer (8) is connected in series to the output loop of the variable-frequency power supply under test; A variable-frequency power supply control box (9) is connected to the variable-frequency power supply under test (1); It is characterized by including the following steps: The first step: It is required that the ambient temperature and humidity are constant, the power supply capacity is constant, the output voltage is stable, and the following steps are carried out under the condition that the ambient and power quality data of previous tests remain unchanged; The second step: Use the low-voltage input cable (4) to connect the 380V power supply system (5) to the input end of the variable-frequency power supply under test (1). The output end of the variable-frequency power supply under test (1) is connected to the variable load device (3) through the low-voltage output cable (6). The variable-frequency power supply under test (1) can convert a three-phase power supply into a single-phase power supply with adjustable voltage and frequency; The third step: The primary winding of the current transformer (8) is connected in series to the output loop of the variable-frequency power supply under test (1). The primary winding of the voltage transformer (2) is connected in parallel to the output loop of the variable-frequency power supply under test (1). The voltage input terminal of the power analyzer (7) is connected to the secondary winding of the voltage transformer (2) through a secondary test line (11), and the current input terminal is connected to the secondary winding of the current transformer (8); The fourth step: Connect to the variable-frequency power supply control box (9) through a control optical fiber (10) to achieve complete isolation between low voltage and high voltage while remotely controlling the output voltage and frequency; The fifth step: Adjust the load in the variable load device (3) to the maximum value of 10Ω and make its power factor angle 0°; The sixth step: Start the test loop. After adjusting the output frequency of the variable-frequency power supply under test (1) to 50Hz, adjust the output voltage of the variable-frequency power supply under test (1) in steps of 5V until the output voltage reaches the maximum of 350V; Step 7: At each voltage node U n By adjusting the variable load device (3) to the maximum current that the variable frequency power supply can output, the output display interface of the variable frequency power supply will flash, and the current value I at this time will be recorded. n ; The eighth step: After the entire test is completed, lower the output voltage of the variable-frequency power supply under test (1) to 0 and disconnect it through the variable-frequency power supply control box (9); Step 9: Through N Group (I n , U n ) data, fitting the I n =K1·U n Working straight line, record the proportional coefficient K1 at this time; Step 10: Adjust the load resistance, capacitance and inductance ratios in the variable load device (3) to R = X L =10Ω、X L =10Ω、R=X C =10Ω、X C =10Ω, that is, the power factor angles of the variable load device are 45°, 90°, -45°, and -90° respectively; The eleventh step: Repeat the operations in the sixth step to the ninth step. When adjusting the variable load device, keep the power factor angle under this working condition to obtain the proportionality coefficients K2, K3, K4, and K5 under each working condition; The twelfth step: Define K = average[K1, K2, K3, K4, K5], which is the final assessment index for the load-carrying capacity of the variable-frequency power supply under test (1); The thirteenth step: Rate the variable-frequency power supply under test (1): If Q ≤ 2, define the unqualified grade of the variable-frequency power supply under test (1); If 2 < Q ≤ 3, define the qualified grade of the variable-frequency power supply under test (1); If 3 < Q ≤ 4, then define the good level of the power frequency converter under test (1); If Q > 4, then define the excellent level of the power frequency converter under test (1).

2. The evaluation method of the detection circuit based on the power curve of the variable frequency power supply for high voltage test according to claim 1 is characterized in that: The power frequency converter under test (1) is connected to the power frequency converter control box (9) through a control optical fiber (10).

3. The evaluation method of the detection circuit based on the power curve of the variable frequency power supply for high voltage test according to claim 2 is characterized in that: The secondary side of the voltage transformer (2) is connected to the input end of the power analyzer (7) through a secondary test line (11).

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