CN114019286A - Transformer direct-current magnetic bias tolerance checking field test method and system - Google Patents
Transformer direct-current magnetic bias tolerance checking field test method and system Download PDFInfo
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Abstract
The invention discloses a field test method and a system for checking the DC magnetic bias tolerance of a transformer, wherein the method comprises the following steps: step 1, carrying out direct current magnetic bias tolerance test wiring: one side of the transformer is open-circuited, the other side of the transformer is sequentially connected with a controllable square wave power supply and a current sensor in series, signals of the current sensor are transmitted to a power supply control unit, and the power supply control unit controls the output of the controllable square wave power supply; step 2, initializing the return-to-zero magnetic flux of the transformer core; step 3, detecting the DC magnetic bias tolerance of the transformer: the power supply control unit controls the controllable square wave source to output + U voltage, the current sensor detects current, and a real-time excitation curve of the transformer core is formed by acquiring data and processing the data in real time; pressurizing the transformer to enable the real-time slope of the iron core curve of the transformer to reach a preset value, and stopping pressurizing; and calculating the DC magnetic bias tolerance value of the transformer at the moment. The invention solves the problem that the transformer field has no DC magnetic bias endurance test method.
Description
Technical Field
The invention relates to the technical field of high-voltage test methods, in particular to a method and a system for checking the field test of the direct-current magnetic bias tolerance of a transformer.
Background
At present, extra-high voltage direct current engineering and railway track traffic are built under great force, and direct current magnetic biasing of a transformer is caused by direct current leakage current of an extra-high voltage direct current monopole earth operation and a railway track traffic. The transformer excitation loop tends to be saturated due to the influence of direct-current magnetic biasing, the transformer excitation impedance is greatly reduced, the excitation current is increased, the transformer loss, vibration and heating are aggravated, and the transformer is damaged.
In order to avoid the influence of the direct current magnetic bias on the transformer, the transformer in the area with the direct current magnetic bias condition is required to have the direct current magnetic bias tolerance capability. The existing method for checking the direct current bias magnet tolerance of the transformer is to test by adopting a power frequency injection direct current mode, two tested products of the transformer with consistent capacity and other properties are needed, the capacity of a test power supply is far larger than the no-load capacity of the transformer, the requirement on test conditions is high, and the method is not feasible in field checking. At present, a transformer direct-current magnetic bias tolerance checking test method which is easy to implement on site is lacked.
Disclosure of Invention
The invention aims to solve the technical problem that the existing method for checking the direct-current bias magnet tolerance of the transformer adopts a power frequency injection direct-current mode for testing, needs two tested products of the transformer with consistent capacity and other properties, has the capacity of a test power supply far larger than the no-load capacity of the transformer, has higher requirement on test conditions, and has no feasibility in field checking.
The invention aims to provide a method and a system for checking the field test of the direct current bias magnet tolerance of a transformer. The invention solves the problem that the transformer field has no DC magnetic bias tolerance test method, ensures that the requirement of the excitation magnetic bias tolerance of the transformer is reliably executed, and improves the operation reliability of the transformer.
The invention is realized by the following technical scheme:
in a first aspect, the invention provides a field test method for checking the direct current bias magnet tolerance of a transformer, which comprises the following steps:
step 1, carrying out direct current magnetic bias tolerance test wiring: one side of the transformer is open-circuited, the other side of the transformer is sequentially connected with a controllable square wave power supply and a current sensor in series, signals of the current sensor are transmitted to a power supply control unit, and the power supply control unit controls the output of the controllable square wave power supply;
step 2, initializing the return-to-zero magnetic flux of the transformer core;
step 3, detecting the DC magnetic bias tolerance of the transformer: the power supply control unit controls the controllable square wave source to output + U voltage, the current sensor detects current i, and a real-time excitation curve of the transformer core is formed by acquiring data and processing the data in real time; pressurizing the transformer to enable the real-time slope k of the iron core curve of the transformer to reach a preset value, and stopping pressurizing; and calculating the DC magnetic bias tolerance value of the transformer at the moment.
The working principle is as follows: the existing method for checking the direct current bias magnet tolerance of the transformer is to test by adopting a power frequency injection direct current mode, two tested products of the transformer with consistent capacity and other properties are needed, the capacity of a test power supply is far larger than the no-load capacity of the transformer, the requirement on test conditions is high, and the method is not feasible in field checking. The invention designs a field test method for checking the direct-current magnetic bias tolerance of a transformer, which is easy to implement on site, and the direct-current magnetic bias tolerance of the transformer is detected on site through controllable square-wave voltage source injection and current detection. The invention solves the problem that the transformer field has no DC magnetic bias tolerance test method, ensures that the requirement of the excitation magnetic bias tolerance of the transformer is reliably executed, and improves the operation reliability of the transformer.
Compared with the prior art, the invention has the beneficial effects that: (1) the method for checking the direct-current magnetic bias tolerance of the transformer by the existing laboratory direct-current superposition power frequency technology is extremely large in required equipment, and the method provided by the invention simplifies test equipment. (2) At present, the power grid puts forward the requirement of direct current magnetic bias tolerance to the transformer, and no method is available on site to carry out the inspection of the requirement of the direct current magnetic bias tolerance. (3) By using the method, the magnetic flux of the transformer core needs to be reset to zero before and after the detection of the DC bias tolerance current value of the transformer, so that the magnetizing inrush current of the transformer during operation can be reduced.
Further, initializing the magnetic flux return-to-zero of the transformer core in step 2 specifically includes:
the controllable square wave power supply is controlled to output + U voltage, and when the current sensor detects that the current reaches 5A (or 10A), the magnetic flux psi of the iron core of the transformermReaching a positive magnetic saturation state;
the controllable square wave power supply is controlled to output-U voltage, and when the current sensor detects that the current reaches-5A (or-10A), the magnetic flux psi of the iron core of the transformermA negative magnetic saturation state is reached;
recording the magnetic flux Ψ of the transformermTime 2T from reaching the positive magnetic saturation state to reaching the negative magnetic saturation state;
and gradually attenuating 50% at the beginning of 1.5T, and applying +/-U to realize the zero return of the magnetic flux of the transformer core.
The square wave controllable source voltage application process is shown in fig. 4, and the magnetic flux change of the transformer core is shown in fig. 5; the process of applying ± U starting at 1.5T with a gradual decay of 50% comprises four steps, as follows:
the first step is as follows: the positive voltage is applied for 1.5T from the negative magnetic saturation state of the transformer, and the magnetic flux point of the transformer reaches +0.5 psim；
The second step is that: from transformer flux +0.5 ΨmThe negative voltage of 0.75T is applied to the beginning, and the magnetic flux point of the transformer reaches-0.25 psim；
The third step: from transformer flux-0.25 psimThe positive voltage of 0.375T is applied to the transformer, and the magnetic flux point of the transformer reaches +0.125 psim；
The fourth step: from transformer flux +0.125 ΨmThe negative voltage is applied at the beginning of 0.1875T, and the magnetic flux point of the transformer reaches-0.0625 psimAnd ending the magnetic return-to-zero of the transformer.
Further, in step 3, the calculation formula of the real-time slope k of the transformer core curve is as follows:
∫Udt＝Ψ (1)
k＝dΨ/di (2)
in the formula, psi refers to a flux linkage and is obtained by integral calculation of controllable square wave power supply output voltage + U to time t; k represents the real-time slope of the transformer core curve and is calculated by the derivative of the flux linkage psi to the current i detected by the current sensor.
Further, the DC bias tolerance value I of the transformer in step 3pThe calculation formula of (2) is as follows:
in the formula IpRepresenting a direct current magnetic bias tolerance value of the transformer; i represents the current value measured by the current sensor when the transformer is pressurized and the real-time slope k of the iron core curve of the transformer reaches a preset value; i is0Representing the rated no-load current value of the transformer.
Further, rated no-load current value I of the transformer0The parameter is obtained by inquiring the parameter of the nameplate of the transformer.
Further, the preset value in step 3 is k0/3 wherein k0And the initial value of the slope of the real-time excitation curve of the transformer core is represented.
Further, step 4 is included after step 3 of the method, and the magnetic flux of the transformer core is reset to zero.
In a second aspect, the invention further provides a field test system for checking the direct current bias magnet tolerance of a transformer, which supports the field test method for checking the direct current bias magnet tolerance of the transformer, and comprises the transformer, a controllable square wave power supply, a current sensor and a power supply control unit; one side of the transformer is open-circuited, the other side of the transformer is sequentially connected with a controllable square wave power supply and a current sensor in series, signals of the current sensor are transmitted to a power supply control unit, and the power supply control unit controls the output of the controllable square wave power supply;
the power supply control unit controls the controllable square wave source to output + U voltage, the current sensor detects current i, and a real-time excitation curve of the transformer core is formed by acquiring data and processing the data in real time; pressurizing the transformer to enable the real-time slope k of the iron core curve of the transformer to reach a preset value, and stopping pressurizing; and calculating the DC magnetic bias tolerance value of the transformer at the moment, and detecting the DC magnetic bias tolerance capability of the transformer.
Furthermore, the magnetic flux of the transformer core needs to be reset to zero before and after the detection of the DC bias tolerance of the transformer, so that the magnetizing inrush current of the transformer during operation can be reduced; the execution process of zeroing the magnetic flux of the transformer core comprises the following steps:
the controllable square wave power supply is controlled to output + U voltage, and when the current sensor detects that the current reaches 5A (or 10A), the magnetic flux of the iron core of the transformer reaches a positive magnetic saturation state;
controlling the controllable square wave power supply to output-U voltage, and when the current sensor detects that the current reaches-5A (or-10A), the magnetic flux of the iron core of the transformer reaches a negative magnetic saturation state;
recording the time 2T from the magnetic flux of the transformer to the positive magnetic saturation state to the negative magnetic saturation state;
and gradually attenuating 50% at the beginning of 1.5T, and applying +/-U to realize the zero return of the magnetic flux of the transformer core.
Further, the DC magnetic bias tolerance value I of the transformerpThe calculation formula of (2) is as follows:
in the formula IpRepresenting a direct current magnetic bias tolerance value of the transformer; i represents the current value measured by the current sensor when the transformer is pressurized and the real-time slope k of the iron core curve of the transformer reaches a preset value; i is0The rated no-load current value of the transformer is represented and is obtained by inquiring the parameter of a name plate of the transformer; preset value k0/3，k0And the initial value of the slope of the real-time excitation curve of the transformer core is represented.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the method for checking the direct-current magnetic bias tolerance of the transformer by the existing laboratory direct-current superposition power frequency technology is extremely large in required equipment, and the method provided by the invention simplifies test equipment.
2. At present, the power grid puts forward the requirement of direct current magnetic bias tolerance to the transformer, and no method is available on site to carry out the inspection of the requirement of the direct current magnetic bias tolerance.
3. According to the method and the system, before and after the detection of the DC bias magnet tolerance current value of the transformer, the magnetic flux of the iron core of the transformer needs to be reset to zero, so that the magnetizing inrush current of the transformer during operation can be reduced.
4. The invention designs a field test method and a field test system for checking the direct-current magnetic bias tolerance of a transformer, which are easy to implement on site, and the direct-current magnetic bias tolerance of the transformer is detected on site through controllable square wave voltage source injection and current detection; the invention solves the problem that the transformer field has no DC magnetic bias tolerance test method, ensures that the requirement of the excitation magnetic bias tolerance of the transformer is reliably executed, and improves the operation reliability of the transformer.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a flow chart of a field test method for checking the DC bias tolerance of a transformer according to the present invention.
FIG. 2 is a detailed flowchart of a field test method for checking DC bias tolerance of a transformer according to the present invention.
Fig. 3 is a wiring diagram of a field test system for checking the direct-current magnetic bias tolerance of a transformer according to the invention.
Fig. 4 is a schematic diagram of the square wave controllable source voltage applying process of the present invention.
Fig. 5 is a diagram of the return-to-zero excitation curve path of the magnetic flux of the transformer core according to the invention.
Fig. 6 is a real-time excitation curve of the transformer core of the present invention.
Fig. 7 is a schematic diagram of the square wave controllable source voltage applying process of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
As shown in fig. 1 to 7, the field test method for checking the dc bias tolerance of the transformer according to the present invention includes the following steps:
step 1, carrying out direct current magnetic bias tolerance test wiring: as shown in fig. 3, one side of the transformer is open-circuited, the other side of the transformer is connected in series with the controllable square wave power supply and the current sensor in sequence, the signal of the current sensor is transmitted to the power supply control unit, and the power supply control unit controls the output of the controllable square wave power supply;
step 2, initializing the return-to-zero magnetic flux of the transformer core; the method considers that the initial magnetic flux of the transformer core is not at a zero position due to residual magnetism, and the magnetic flux of the transformer core needs to be returned to zero in a direct-current magnetic bias endurance detection test. The implementation specifically comprises:
the controllable square wave power supply is controlled to output + U voltage, and when the current sensor detects that the current reaches 5A, the magnetic flux psi of the iron core of the transformermReaching a positive magnetic saturation state;
the controllable square wave power supply is controlled to output-U voltage, and when the current sensor detects that the current reaches-5A, the magnetic flux psi of the iron core of the transformermA negative magnetic saturation state is reached;
recording the magnetic flux Ψ of the transformermTime 2T from reaching the positive magnetic saturation state to reaching the negative magnetic saturation state;
and gradually attenuating 50% at the beginning of 1.5T, and applying +/-U to realize the zero return of the magnetic flux of the transformer core.
The process of applying ± U starting at 1.5T with a gradual decay of 50% comprises four steps, as follows:
the first step is as follows: the positive voltage is applied for 1.5T from the negative magnetic saturation state of the transformer, and the magnetic flux point of the transformer reaches +0.5 psim；
The second step is that: from transformer flux +0.5 ΨmThe negative voltage of 0.75T is applied to the beginning, and the magnetic flux point of the transformer reaches-0.25 psim；
The third step: from transformer flux-0.25 psimThe positive voltage of 0.375T is applied to the transformer, and the magnetic flux point of the transformer reaches +0.125 psim；
The fourth step: from transformer flux +0.125 ΨmThe negative voltage is applied at the beginning of 0.1875T, and the magnetic flux point of the transformer reaches-0.0625 psimAnd ending the magnetic return-to-zero of the transformer.
The square wave controllable source voltage application process is shown in fig. 4, and the transformer core flux change is shown in fig. 5.
Step 3, detecting the DC magnetic bias tolerance of the transformer: the power supply control unit controls the controllable square wave source to output + U voltage, the current sensor detects current i, and a real-time excitation curve of the transformer core is formed by acquiring data and processing the data in real time, as shown in fig. 6; the slope of the initial point of the transformer core excitation curve is k0Pressurizing the transformer, and in the pressurizing process, the real-time slope k and the initial k of the iron core curve of the transformer are used0By comparison, where k is k0At/3, the current value I is recorded, and the pressurization is stopped, the pressurization process is shown in FIG. 7. And calculating the DC magnetic bias tolerance value of the transformer at the moment.
Specifically, the method comprises the following steps: the direct-current bias magnet endurance test wiring is shown in fig. 3, one side of the transformer with an open circuit is connected with a controllable square-wave power supply and a current sensor in series, signals of the current sensor are transmitted to a power supply control unit, and the power supply control unit controls the controllable square-wave power supply to output.
The calculation formula of the real-time slope k of the transformer core curve is as follows:
∫Udt＝Ψ (1)
k＝dΨ/di (2)
in the formula, psi refers to a flux linkage and is obtained by integral calculation of controllable square wave power supply output voltage + U to time t; k represents the real-time slope of the transformer core curve and is calculated by the derivative of the flux linkage psi to the current i detected by the current sensor.
Specifically, the method comprises the following steps: the DC bias tolerance value I of the transformerpThe calculation formula of (2) is as follows:
in the formula IpRepresenting a direct current magnetic bias tolerance value of the transformer; i represents that the transformer is pressurized to enable the real-time slope k of the iron core curve of the transformer to reach a preset value k0The current value measured by the current sensor at the time of/3; i is0Representing the rated no-load current value of the transformer.
Wherein, the rated no-load current value I of the transformer0The parameter is obtained by inquiring the parameter of the nameplate of the transformer.
And 4, carrying out the magnetic flux return to zero of the transformer core, namely repeating the step 2.
The working principle is as follows: the existing method for checking the direct current bias magnet tolerance of the transformer is to test by adopting a power frequency injection direct current mode, two tested products of the transformer with consistent capacity and other properties are needed, the capacity of a test power supply is far larger than the no-load capacity of the transformer, the requirement on test conditions is high, and the method is not feasible in field checking. The invention designs a field test method for checking the direct-current magnetic bias tolerance of a transformer, which is easy to implement on site, and the direct-current magnetic bias tolerance of the transformer is detected on site through controllable square-wave voltage source injection and current detection. The invention solves the problem that the transformer field has no DC magnetic bias tolerance test method, ensures that the requirement of the excitation magnetic bias tolerance of the transformer is reliably executed, and improves the operation reliability of the transformer.
Compared with the prior art, the invention has the beneficial effects that:
(1) the method for checking the direct-current magnetic bias tolerance of the transformer by the existing laboratory direct-current superposition power frequency technology is extremely large in required equipment, and the method provided by the invention simplifies test equipment.
(2) At present, the power grid puts forward the requirement of direct current magnetic bias tolerance to the transformer, and no method is available on site to carry out the inspection of the requirement of the direct current magnetic bias tolerance.
(3) By using the method, the magnetic flux of the transformer core needs to be reset to zero before and after the detection of the DC bias tolerance current value of the transformer, so that the magnetizing inrush current of the transformer during operation can be reduced.
Example 2
As shown in fig. 3, the present embodiment is different from embodiment 1 in that the present embodiment provides a field test system for checking dc bias tolerance of a transformer, which supports the field test method for checking dc bias tolerance of a transformer described in embodiment 1, and the system includes a transformer, a controllable square wave power supply, a current sensor, and a power supply control unit; one side of the transformer is open-circuited, the other side of the transformer is sequentially connected with a controllable square wave power supply and a current sensor in series, signals of the current sensor are transmitted to a power supply control unit, and the power supply control unit controls the output of the controllable square wave power supply;
the power supply control unit controls the controllable square wave source to output + U voltage, the current sensor detects current i, and a real-time excitation curve of the transformer core is formed by acquiring data and processing the data in real time; pressurizing the transformer to enable the real-time slope k of the iron core curve of the transformer to reach a preset value, and stopping pressurizing; and calculating the DC magnetic bias tolerance value of the transformer at the moment, and detecting the DC magnetic bias tolerance capability of the transformer.
In the embodiment, the magnetic flux of the transformer core needs to be reset to zero before and after the detection of the DC bias tolerance of the transformer, so that the magnetizing inrush current of the transformer during operation can be reduced; the execution process of zeroing the magnetic flux of the transformer core comprises the following steps:
the controllable square wave power supply is controlled to output + U voltage, and when the current sensor detects that the current reaches 5A, the magnetic flux psi of the iron core of the transformermReaching a positive magnetic saturation state;
the controllable square wave power supply is controlled to output-U voltage, and when the current sensor detects that the current reaches-5A, the magnetic flux psi of the iron core of the transformermA negative magnetic saturation state is reached;
recording the magnetic flux Ψ of the transformermTime 2T from reaching the positive magnetic saturation state to reaching the negative magnetic saturation state;
and gradually attenuating 50% at the beginning of 1.5T, and applying +/-U to realize the zero return of the magnetic flux of the transformer core.
The process of applying ± U starting at 1.5T with a gradual decay of 50% comprises four phases, as follows:
in the first stage: the positive voltage is applied for 1.5T from the negative magnetic saturation state of the transformer, and the magnetic flux point of the transformer reaches +0.5 psim；
The second stage is as follows: from transformer flux +0.5 ΨmThe negative voltage of 0.75T is applied to the beginning, and the magnetic flux point of the transformer reaches-0.25 psim；
The third stage: from transformer flux-0.25 psimStarting to apply the positive voltage of 0.375T, and reaching the flux point of the transformer to +0.125 psi m;
the fourth stage: from transformer flux +0.125 ΨmThe negative voltage is applied at the beginning of 0.1875T, and the magnetic flux point of the transformer reaches-0.0625 psimAnd ending the magnetic return-to-zero of the transformer.
The square wave controllable source voltage application process is shown in fig. 4, and the transformer core flux change is shown in fig. 5.
In this embodiment, the power control unit controls the controllable square wave source to output + U voltage, the current sensor detects current i, and a real-time excitation curve of the transformer core is formed by collecting data and processing in real time, as shown in fig. 6; the slope of the initial point of the transformer core excitation curve is k0Pressurizing the transformer to make the real-time slope k of the iron core curve of the transformer reach the preset value k0And/3, where k is k0At the time of/3, recording the current value I at the time, and stopping pressurizing, wherein the pressurizing process is shown in figure 7; and calculating the DC magnetic bias tolerance value of the transformer at the moment, and detecting the DC magnetic bias tolerance capability of the transformer.
The DC bias tolerance value I of the transformerpThe calculation formula of (2) is as follows:
in the formula IpRepresenting a direct current magnetic bias tolerance value of the transformer; i represents the current value measured by the current sensor when the transformer is pressurized and the real-time slope k of the iron core curve of the transformer reaches a preset value; i is0Representing a voltage transformationThe rated no-load current value of the transformer is obtained by inquiring the parameters of a name plate of the transformer; preset value k0/3，k0And the initial value of the slope of the real-time excitation curve of the transformer core is represented.
The field test system for checking the direct-current magnetic bias tolerance of the transformer is easy to implement on site, and test equipment is simplified; and the direct-current magnetic bias tolerance of the transformer is detected on site through controllable square wave voltage source injection and current detection. The invention solves the problem that the transformer field has no DC magnetic bias tolerance test method, ensures that the requirement of the excitation magnetic bias tolerance of the transformer is reliably executed, and improves the operation reliability of the transformer. The invention solves the problem that the needed equipment is huge in the existing method for checking the DC magnetic bias tolerance of the transformer by the laboratory DC superimposed power frequency technology. In addition, the system of the invention needs to return the magnetic flux of the transformer core to zero before and after the detection of the DC bias tolerance current value of the transformer, thereby reducing the excitation inrush current of the transformer during operation.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. A field test method for checking the DC bias magnet tolerance capability of a transformer is characterized by comprising the following steps:
step 1, carrying out direct current magnetic bias tolerance test wiring: one side of the transformer is open-circuited, the other side of the transformer is sequentially connected with a controllable square wave power supply and a current sensor in series, signals of the current sensor are transmitted to a power supply control unit, and the power supply control unit controls the output of the controllable square wave power supply;
step 2, initializing the return-to-zero magnetic flux of the transformer core;
step 3, detecting the DC magnetic bias tolerance of the transformer: the power supply control unit controls the controllable square wave source to output + U voltage, the current sensor detects current, and a real-time excitation curve of the transformer core is formed by acquiring data and processing the data in real time; pressurizing the transformer to enable the real-time slope of the iron core curve of the transformer to reach a preset value, and stopping pressurizing; and calculating the DC magnetic bias tolerance value of the transformer at the moment.
2. The field test method for checking the direct-current bias magnet tolerance of the transformer according to claim 1, wherein the step 2 of initializing the zero return of the magnetic flux of the iron core of the transformer specifically comprises the following steps:
the controllable square wave power supply is controlled to output + U voltage, and when the current sensor detects that the current reaches 5A or 10A, the magnetic flux of the iron core of the transformer reaches a positive magnetic saturation state;
controlling the controllable square wave power supply to output-U voltage, and when the current sensor detects that the current reaches-5A or-10A, enabling the magnetic flux of the iron core of the transformer to reach a negative magnetic saturation state;
recording the time 2T from the magnetic flux of the transformer to the positive magnetic saturation state to the negative magnetic saturation state;
and gradually attenuating 50% at the beginning of 1.5T, and applying +/-U to realize the zero return of the magnetic flux of the transformer core.
3. The field test method for checking the direct-current bias magnet tolerance of the transformer according to claim 1, wherein the calculation formula of the real-time slope k of the transformer core curve in the step 3 is as follows:
∫Udt＝Ψ
k＝dΨ/di
in the formula, psi refers to a flux linkage and is obtained by integral calculation of controllable square wave power supply output voltage + U to time t; k represents the real-time slope of the transformer core curve and is calculated by the derivative of the flux linkage psi to the current i detected by the current sensor.
4. The field test method for checking DC bias magnet tolerance of transformer according to claim 3, wherein in step 3, the DC bias magnet tolerance value I of transformerpThe calculation formula of (2) is as follows:
in the formula IpRepresenting a direct current magnetic bias tolerance value of the transformer; i represents the current value measured by the current sensor when the transformer is pressurized and the real-time slope k of the iron core curve of the transformer reaches a preset value; i is0Representing the rated no-load current value of the transformer.
5. The field test method for checking DC bias magnet endurance of transformer as claimed in claim 4, wherein rated no-load current value of transformer is I0The parameter is obtained by inquiring the parameter of the nameplate of the transformer.
6. The field test method for checking direct-current bias magnet tolerance of transformer according to claim 1, wherein the preset value in step 3 is k0/3 wherein k0And the initial value of the slope of the real-time excitation curve of the transformer core is represented.
7. The field test method for checking the direct-current bias magnet endurance of the transformer according to claim 1, wherein the method further comprises a step 4 after the step 3, wherein the step 4 is performed to return the magnetic flux of the transformer core to zero.
8. A transformer dc bias tolerance checking field test system, wherein the system supports a transformer dc bias tolerance checking field test method according to any one of claims 1 to 7, the system comprises a transformer, a controllable square wave power supply, a current sensor and a power supply control unit; one side of the transformer is open-circuited, the other side of the transformer is sequentially connected with a controllable square wave power supply and a current sensor in series, signals of the current sensor are transmitted to a power supply control unit, and the power supply control unit controls the output of the controllable square wave power supply;
the power supply control unit controls the controllable square wave source to output + U voltage, the current sensor detects current i, and a real-time excitation curve of the transformer core is formed by acquiring data and processing the data in real time; pressurizing the transformer to enable the real-time slope k of the iron core curve of the transformer to reach a preset value, and stopping pressurizing; and calculating the DC magnetic bias tolerance value of the transformer at the moment, and detecting the DC magnetic bias tolerance capability of the transformer.
9. The field test system for checking the direct-current bias magnet tolerance of the transformer according to claim 8, wherein the magnetic flux of the transformer core needs to be zeroed before and after the detection of the direct-current bias magnet tolerance of the transformer; the execution process of zeroing the magnetic flux of the transformer core comprises the following steps:
the controllable square wave power supply is controlled to output + U voltage, and when the current sensor detects that the current reaches 5A or 10A, the magnetic flux of the iron core of the transformer reaches a positive magnetic saturation state;
controlling the controllable square wave power supply to output-U voltage, and when the current sensor detects that the current reaches-5A or-10A, enabling the magnetic flux of the iron core of the transformer to reach a negative magnetic saturation state;
recording the time 2T from the magnetic flux of the transformer to the positive magnetic saturation state to the negative magnetic saturation state;
and gradually attenuating 50% at the beginning of 1.5T, and applying +/-U to realize the zero return of the magnetic flux of the transformer core.
10. The field test system for checking DC bias tolerance of transformer according to claim 8, wherein the DC bias tolerance value I of transformer ispThe calculation formula of (2) is as follows:
in the formula IpRepresenting a direct current magnetic bias tolerance value of the transformer; i represents the current value measured by the current sensor when the transformer is pressurized and the real-time slope k of the iron core curve of the transformer reaches a preset value; i is0The rated no-load current value of the transformer is represented and inquired by a transformer nameplateObtaining parameters; preset value k0/3，k0And the initial value of the slope of the real-time excitation curve of the transformer core is represented.
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