A system and method for performing a DC bias test on an AC transformer

Abstract

The present invention belongs to the technical field of AC transformers, and relates to a system for performing a DC bias test on an AC transformer. The zero-phase O1 of the high-voltage coil of the first AC transformer leads out a first test connection line and a second test connection line respectively. The first test connection line is connected to the zero-phase O2 of the high-voltage coil of the second AC transformer after being connected in series with a linearly adjustable DC current output module. The second test connection line is grounded after being connected in series with an AC current measurement module. An emergency stop protection and alarm module, a linearly adjustable gap discharge protection module, an adjustable resistor overvoltage protection module, and an adjustable capacitor AC circulation module are connected in parallel between the first test connection line and the second test connection line. The present invention also relates to a method for performing a DC bias test on an AC transformer. The linearly adjustable DC output module applies a specified AC current to the AC transformer, and the test data of the AC transformer in this state is read by a low-voltage measuring instrument. The present invention can evaluate whether the AC transformer meets the requirements under a specified DC content.

Description

Technical Field

[0001] The invention belongs to the technical field of AC transformers, and particularly relates to a system and method for performing a DC bias test on an AC transformer. Background Art

[0002] With the vigorous development of the national power and high-speed rail industries, the impact of the DC content in the power transmission system on the operation of AC transformers is becoming increasingly significant. How to simulate the operating state of an AC transformer under the condition of containing DC content has become an urgent problem to be solved.

[0003] When the transformer operates normally under AC over-excitation, the magnetic flux density of the iron core will increase, the excitation current will become distorted, the transformer operates in the non-linear region of the magnetization curve, and the excitation current waveform is a peak wave with symmetric positive and negative half-cycles. When a DC component appears in the transformer excitation current, it causes semi-circular magnetic saturation of the transformer iron core, and the transformer is biased to DC. When the DC and AC magnetic fluxes are superimposed, the magnetic core saturation of the half-cycle consistent with the DC bias direction increases, and the magnetic core saturation of the other half-cycle decreases. Accordingly, the excitation current waveform presents an asymmetric shape of positive and negative half-cycles.

[0004] DC bias is an abnormal operating state of the transformer because the primary equivalent impedance of the transformer only exhibits a resistance characteristic to the DC component and the resistance is very small. Therefore, a small DC component will form a large DC magnetization potential in the winding. The combined action of this DC magnetic potential and the AC magnetic potential on the primary side of the transformer causes the working magnetization curve of the transformer iron core to shift, appear near the origin, and be asymmetric, namely the transformer bias phenomenon. When the transformer operates in this state for a long time, the vibration of the transformer intensifies, the operating noise becomes larger, the operating loss becomes larger, the operating current becomes larger, which directly affects the service life of the transformer.

[0005] Currently, each manufacturer conducts relatively few DC bias tests on AC transformers, the test data is not comprehensive, and there is no professional test instrument for this experiment on the market. The test randomness is relatively large. If the operation is improper during the test, the situation of the high-voltage neutral point being suspended will occur. The invention provides a test instrument and has a reliable protection module. Summary of the Invention

[0006] In order to solve the above technical problems, the invention provides a method for performing a DC bias test on an AC transformer. The technical solution adopted by the invention is as follows:

[0007] A system for performing DC bias test on an AC transformer, comprising a first AC transformer and a second AC transformer. The C-phase C1 of the high-voltage coil of the first AC transformer is connected to the C-phase C2 of the high-voltage coil of the second AC transformer. The B-phase B1 of the high-voltage coil of the first AC transformer is connected to the B-phase B2 of the high-voltage coil of the second AC transformer. The A-phase A1 of the high-voltage coil of the first AC transformer is connected to the A-phase A2 of the high-voltage coil of the second AC transformer. The neutral-phase O1 of the high-voltage coil of the first AC transformer respectively leads out a first test connection line and a second test connection line. The first test connection line is connected to the neutral-phase O2 of the high-voltage coil of the second AC transformer after being connected in series with a linearly adjustable DC current output module. The second test connection line is grounded after being connected in series with an AC current measurement module. An emergency stop protection and alarm module, a linearly adjustable gap discharge protection module, an adjustable resistor overvoltage protection module, and an adjustable capacitor AC conduction module are connected in parallel between the first test connection line and the second test connection line. The emergency stop protection and alarm module is located between the neutral-phase O1 of the high-voltage coil of the first AC transformer and the linearly adjustable DC current output module. The linearly adjustable gap discharge protection module, the linearly adjustable resistor overvoltage protection module, and the linearly adjustable capacitor AC conduction module are sequentially located between the linearly adjustable DC current output module and the neutral-phase O2 of the high-voltage coil of the second AC transformer.

[0008] The working environment of the above system for performing DC bias test on an AC transformer is -5°C to 45°C, and the humidity is <80%; the working frequency is 47 - 60 Hz, and the working voltage is supplied by a 220V ± 10% AC power supply. A set of linearly adjustable DC current output module (Is), whose function is to provide a specified constant DC current to the high-voltage winding of the AC transformer; a set of linearly adjustable gap discharge protection module (J), whose function is to form a grounding discharge protection when the system is overvoltage; a set of adjustable resistor overvoltage protection module (R), whose function is to protect the system against overvoltage; a set of adjustable capacitor AC conduction module (C), whose function is to form a path for AC current and block the flow of DC current, so that the AC transformer is in an AC grounding state; a set of AC current measurement module (A), whose function is to measure the AC current value of the high-voltage neutral phase to ground of the AC transformer under the AC voltage state, so as to select the range of each protection module according to this value; an emergency stop protection and alarm module (D), whose function is to form an instantaneous grounding protection for the system.

[0009] A method for performing DC bias test on an AC transformer, applying the above system for performing DC bias test on an AC transformer, comprising the following steps:

[0010] S1. Modulate the output of the linearly adjustable DC output module to 0. The emergency stop protection and alarm module is in the access state. The linearly adjustable gap discharge protection module is modulated to the maximum spacing state. The linearly adjustable voltage overvoltage protection module is modulated to the off state. The linearly adjustable capacitor AC conduction module is adjusted to the maximum capacitance gear.

[0011] S2. Apply an AC voltage to the second AC transformer to the level that needs to be tested, record the value measured by the AC current measurement module, and then stop applying the AC voltage to the second AC transformer;

[0012] S3. According to the measured value of the AC current measurement module, sequentially select the ranges of the linearly adjustable gap discharge protection module and the linearly adjustable capacitor AC current conduction module;

[0013] S4. Select the range of the linearly adjustable resistor overvoltage protection module according to the resistance values of the first AC transformer and the second AC transformer;

[0014] S5. Connect the linearly adjustable resistor overvoltage protection module, disconnect the emergency stop protection and alarm module, modulate the output of the linearly adjustable DC output module to the DC voltage value that needs to be applied, apply a specified AC current to the AC transformer, and read the no-load loss, no-load current, no-load sound level and vibration test data of the AC transformer recorded by the low-voltage measuring instrument in this state;

[0015] S6. After the test is completed, first connect the emergency stop protection and alarm module and keep it for five minutes. After the capacitor of the linearly adjustable capacitor AC current conduction module is fully discharged, modulate the output of the linearly adjustable DC output module to 0, and sequentially restore the linearly adjustable gap discharge protection module, the adjustable resistor overvoltage protection module and the adjustable capacitor AC current conduction module to the state described in step S1.

[0016] Advantages of the present invention:

[0017] By means of a device that adds a DC current to the coil of the AC transformer, the present invention realizes the simulation of the influence of different DC contents of the system on the operation of the AC transformer, and further examines whether the performance parameters of the AC transformer meet the requirements of standards and relevant agreements under the specified DC content. Description of the drawings

[0018] In order to more clearly illustrate the specific implementation manners of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific implementation manners or the prior art. Obviously, the following drawings are some specific implementation manners of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings within the scope of protection of this application can also be obtained based on these drawings.

[0019] Figure 1 is a schematic diagram of the DC bias test principle of the three-phase AC transformer according to the embodiment of the present invention;

[0020] Figure 2 is a schematic diagram of the DC bias test principle of the single-phase AC transformer according to the embodiment of the present invention.

[0021] In the figure: 1 is the first AC transformer, 2 is the second AC transformer, 3 is the linearly adjustable DC current output module, 4 is the emergency stop protection and alarm module, 5 is the linearly adjustable gap discharge protection module, 6 is the linearly adjustable resistor overvoltage protection module, 7 is the linearly adjustable capacitor AC circulation module, and 8 is the AC current measurement module. Specific embodiments

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments.

[0023] As Figure 1 shown, it is a schematic diagram of the DC bias test principle of the three-phase AC transformer in the embodiment of the present invention; as Figure 2 shown, it is a schematic diagram of the DC bias test principle of the single-phase AC transformer in the embodiment of the present invention. A system for performing a DC bias test on an AC transformer. During the test, a 50Hz, 220V AC power supply is used. It includes the first AC transformer 1 and the second AC transformer 2. The C phase C1 of the high-voltage coil of the first AC transformer 1 is connected to the C phase C2 of the high-voltage coil of the second AC transformer 2. The B phase B1 of the high-voltage coil of the first AC transformer 1 is connected to the B phase B2 of the high-voltage coil of the second AC transformer 2. The A phase A1 of the high-voltage coil of the first AC transformer 1 is connected to the A phase A2 of the high-voltage coil of the second AC transformer 2. The neutral phase O1 of the high-voltage coil of the first AC transformer 1 respectively leads out the first test connection line and the second test connection line. The first test connection line is connected to the neutral phase O2 of the high-voltage coil of the second AC transformer 2 after being connected in series with the linearly adjustable DC current output module 3. The second test connection line is grounded after being connected in series with the AC current measurement module 8. The emergency stop protection and alarm module 4, the linearly adjustable gap discharge protection module 5, the adjustable resistor overvoltage protection module 6, and the adjustable capacitor AC circulation module 7 are connected in parallel between the first test connection line and the second test connection line. The emergency stop protection and alarm module 4 is located between the neutral phase O1 of the high-voltage coil of the first AC transformer 1 and the linearly adjustable DC current output module 3. The linearly adjustable gap discharge protection module 5, the linearly adjustable resistor overvoltage protection module 6, and the linearly adjustable capacitor AC circulation module 7 are sequentially located between the linearly adjustable DC current output module 3 and the neutral phase O2 of the high-voltage coil of the second AC transformer 2.

[0024] When a DC current is applied to the neutral phase O1 of the first AC transformer 1, this DC current passes through the coils O1 - A1, O1 - A2, O1 - A3 and enters A2 - O2, B2 - O2, C2 - O2. The DC current converges at the O2 of the second AC transformer 2 and forms a closed-loop circuit with O1. Therefore, the first AC transformer 1 and the second AC transformer 2 are simultaneously subjected to the assessment of the DC bias test.

[0025] The modules used in the above tests are all existing products or existing technologies. The linearly adjustable DC current output module 3, for example, of the Maisheng brand, model MP5030D; the linearly adjustable gap discharge protection module 5, for example, optional models of the FHJ series products or gas discharge tubes, etc.; the linearly adjustable resistor overvoltage protection module 6, for example, the RX20T series 2-watt, 1M - 3MΩ rheostat; the linearly adjustable capacitor AC circulation module 7, for example, formed by paralleling several capacitors of model CJ41 - 2, 30uF ± 5%, 630V to form adjustable gears such as 30uF, 60uF, 90uF, 120uF, 150uF, 180uF, 210uF, 240uF, 270uF, 300uF, 330uF, etc.; the AC current measurement module 8, for example, the FLUK clamp ammeter, etc.

[0026] A method for performing a DC bias test on an AC transformer, applying the system for performing a DC bias test on an AC transformer described above, includes the following steps:

[0027] S1. Modulate the output of the linearly adjustable DC output module 3 to 0, the emergency stop protection and alarm module 4 is in the connected state, the linearly adjustable gap discharge protection module 5 is modulated to the maximum gap state, the linearly adjustable voltage overvoltage protection module 6 is modulated to the off state, and the linearly adjustable capacitor AC circulation module 7 is adjusted to the maximum capacitor gear.

[0028] S2. Apply an AC voltage to the second AC transformer 2 that needs to be tested, for example, Ur, record the value of the AC current measurement module 8, and then stop applying the AC voltage to the second AC transformer 2.

[0029] S3. According to the measured value of the AC current measurement module 8, sequentially select the ranges of the linearly adjustable gap discharge protection module 5 and the linearly adjustable capacitor AC circulation module 7.

[0030] For the capacitor gear of the linearly adjustable capacitor AC circulation module 7, according to the current I measured by the AC current measurement module 8, make where ω = 2 * π * f, U = 630V; (f is the power supply frequency, which can be measured by a power analyzer)

[0031] For the range selection of the linearly adjustable gap discharge protection module 5, assuming the range of the linearly adjustable capacitor AC circulation module 7 is C1, then U = I * ω * C1. According to the value of U, select the gap range, recommended as:

[0032] When 0 < U < 200V, 0 < J < 1mm;

[0033] When 0 < U < 400V, 0 < J < 2mm;

[0034] When 0 < U < 600V, 0 < J < 3mm;

[0035] The above content can be referred to in Sections 4 and 13 of GB8898.

[0036] S4. Range selection of the linear adjustable resistor overvoltage protection module 6, according to the resistance values of the first AC transformer 1 and the second AC transformer 2: R O1A1 , R O1B1 , R O1C1 , R O2A2 , R O2B2 , R O2C2 , (this value can be measured or can be based on the design value at the test temperature),

[0037] S5. Connect the linear adjustable resistor overvoltage protection module 6, disconnect the emergency stop protection and alarm module 4, modulate the output of the linear adjustable DC output module 3 to the DC voltage value to be applied, and the linear adjustable DC output module 3 will be in the working state. Apply a specified AC current to the AC transformer, and read the no-load loss, no-load current and other data of the AC transformer recorded by the low-voltage measuring instrument (power analyzer) in this state. If necessary, the test data such as the no-load sound level and vibration under the DC bias state can also be measured.

[0038] S6. After the test, first connect the emergency stop protection and alarm module 4 and keep it for five minutes. After the capacitor of the linear adjustable capacitor AC circulation module 7 is fully discharged, modulate the output of the linear adjustable DC output module 3 to 0, and restore the linear adjustable gap discharge protection module 5, the adjustable resistor overvoltage protection module 6 and the adjustable capacitor AC circulation module 7 to the states described in step S1 in sequence.

[0039] Precautions:

[0040] (1) During the process of applying DC voltage to the second AC transformer 2, do not adjust the linear adjustable gap discharge protection module 5, the adjustable resistor overvoltage protection module 6 and the adjustable capacitor AC circulation module 7;

[0041] (2) In case of an emergency, press the emergency button of the emergency stop protection and alarm module 4;

[0042] (3) If the applied voltage value of the second AC transformer 2 is changed during the test, it is necessary to re-perform the operation steps S1, S2, S3, S4, S5.

[0043] Finally, it should be noted that the above embodiments are only specific implementation manners of the present invention, used to illustrate the technical solutions of the present invention, rather than limiting it. The protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any person skilled in the technical field can modify the technical solutions described in the foregoing embodiments, or can easily think of changes, or perform equivalent replacements on some of the technical features; and these modifications, changes or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered by the protection scope of the present invention.

Claims

1. A method for performing a DC bias test on an AC transformer, which is applied to a system for performing a DC bias test on an AC transformer, including a first AC transformer (1) and a second AC transformer (2). The C-phase C1 of the high-voltage coil of the first AC transformer (1) is connected to the C-phase C2 of the high-voltage coil of the second AC transformer (2). The B-phase B1 of the high-voltage coil of the first AC transformer (1) is connected to the B-phase B2 of the high-voltage coil of the second AC transformer (2). The A-phase A1 of the high-voltage coil of the first AC transformer (1) is connected to the A-phase A2 of the high-voltage coil of the second AC transformer (2). The neutral phase O1 of the high-voltage coil of the first AC transformer (1) respectively leads out a first test connection wire and a second test connection wire. The first test connection wire is connected to the neutral phase O2 of the high-voltage coil of the second AC transformer (2) after being connected in series with a linearly adjustable DC current output module (3). The second test connection wire is grounded after being connected in series with an AC current measurement module (8). An emergency stop protection and alarm module (4), a linearly adjustable gap discharge protection module (5), a linearly adjustable resistor overvoltage protection module (6), and a linearly adjustable capacitor AC circulation module (7) are connected in parallel between the first test connection wire and the second test connection wire. The emergency stop protection and alarm module (4) is located between the neutral phase O1 of the high-voltage coil of the first AC transformer (1) and the linearly adjustable DC current output module (3). The linearly adjustable gap discharge protection module (5), the linearly adjustable resistor overvoltage protection module (6), and the linearly adjustable capacitor AC circulation module (7) are sequentially located between the linearly adjustable DC current output module (3) and the neutral phase O2 of the high-voltage coil of the second AC transformer (2). It is characterized in that The method includes the following steps: S1. Modulate the output of the linearly adjustable DC current output module (3) to 0. The emergency stop protection and alarm module (4) is in the connected state. The linearly adjustable gap discharge protection module (5) is modulated to the state with the maximum spacing. The linearly adjustable resistor overvoltage protection module (6) is modulated to the disconnected state. The linearly adjustable capacitor AC circulation module (7) is adjusted to the maximum capacitance gear. S2. Apply an AC voltage to the second AC transformer (2) up to the AC voltage to be tested. Record the value of the AC current measurement module (8), and then stop applying the AC voltage to the second AC transformer (2). S3. According to the measured value of the AC current measurement module (8), sequentially select the ranges of the linearly adjustable gap discharge protection module (5) and the linearly adjustable capacitor AC circulation module (7). S4. Select the range of the linearly adjustable resistor overvoltage protection module (6) according to the resistance values of the first AC transformer (1) and the second AC transformer (2). S5. Connect the linearly adjustable resistor overvoltage protection module (6), disconnect the emergency stop protection and alarm module (4). Modulate the output of the linearly adjustable DC current output module (3) to the value of the DC current to be applied. Then apply the rated voltage to the low voltage of the AC transformer, and read the no-load loss, no-load current, no-load sound level, and vibration test data of the AC transformer recorded by the low-voltage measuring instrument in this state. After the test, first connect the emergency stop protection and alarm module (4) and keep it for five minutes. After the capacitor of the linearly adjustable capacitor AC circulation module (7) is fully discharged, modulate the output of the linearly adjustable DC current output module (3) to 0, and restore the linearly adjustable gap discharge protection module (5), the linearly adjustable resistor overvoltage protection module (6), and the linearly adjustable capacitor AC circulation module (7) to the states described in step S1 in sequence.

2. The method for performing a DC bias test on an AC transformer according to claim 1, characterized in that, The linearly adjustable gap discharge protection module (5) uses a gas discharge tube, the linearly adjustable resistor overvoltage protection module (6) uses a rheostat, the linearly adjustable capacitor AC circulation module (7) is formed by connecting several capacitors in parallel to form a series of adjustable gears, and the AC current measurement module (8) uses a clamp ammeter.

3. A method for performing a DC bias test on an AC transformer according to claim 1, characterized in that, In step S4, according to the resistance values of the first AC transformer (1) and the second AC transformer (2): R O1A1， R O1B1， R O1C1， R O2A2， R O2B2， R O2C2 , the range of the linearly adjustable resistor overvoltage protection module (6) > 1000 .

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