A device and method for testing cumulative strain in transformer coils

Abstract

This invention relates to a device and method for testing the cumulative strain of transformer coils. It constructs a simulation system for the stress characteristics of the coil during a short-circuit impact, fully considering the influence of coil heating, distributed stress on the electromagnetic wire, and the interaction between the electromagnetic wire and the pad on the strain test. A coil cumulative strain testing device is designed to reproduce the transient stress changes during a short-circuit impact, and a method for testing the cumulative strain of the coil is proposed, achieving accurate simulation of the distributed stress on the winding and testing of the cumulative strain. This invention fully considers the influence of the transformer's electromagnetic wire, cardboard structure, and stress distribution on the mechanical stability of the winding, reproduces the transient stress changes during a short circuit, and effectively tests the cumulative strain of the coil under the influence of multiple short-circuit processes. It can accurately reflect the characteristics of a real transformer while controlling test costs, helping to improve the accuracy of transformer post-short-circuit condition assessment and better ensure the safe operation of power equipment.

Description

Technical Field

[0001] This invention belongs to the field of electrical equipment operation testing, and in particular to a device and method for testing the cumulative strain of transformer coils. Background Technology

[0002] With the increase in power grid capacity, the short-circuit current of the power system is constantly increasing, which places higher demands on the mechanical strength of transformers during short circuits. During a transformer short circuit, the internal coils will experience stress and strain under large instantaneous current and electrodynamic forces. The cumulative effect of multiple short circuits will cause the stress and strain of the coils to accumulate continuously, leading to axial and radial instability of the coils. In severe cases, it can cause coil twisting, collapse, and other phenomena, ultimately causing transformer failure and shutdown.

[0003] To evaluate the mechanical state of a transformer coil after multiple short circuits, it is necessary to test the deformation of the coil's electromagnetic wire and cardboard under stress as a function of the number and amplitude of impacts. For large transformers, the method of using external simulated short circuits and internal coil performance testing is costly. Even with scaled-down models, it is difficult to meet the testing requirements of different types of coils while controlling costs. A common testing method involves treating the electromagnetic wire and cardboard as separate test objects and conducting cyclic loading tests on them separately to obtain curves showing the changes in the electromagnetic wire and cardboard as a function of the number and amplitude of artificial loads.

[0004] Cyclic loading tests conducted independently on the electromagnetic wire and cardboard have the following drawbacks. First, the structures of the electromagnetic wire and cardboard specimens differ significantly from those in actual transformers. Different winding structures used when the electromagnetic wire is wound into coils (such as continuous, kinked, and spiral windings) affect the mechanical stability of the coil. The cardboard and pads are compressed by different turns of the coil, affecting the direction of force, all of which are difficult to reflect in cyclic loading tests on regularly shaped specimens. Second, the strain of the electromagnetic wire during a short circuit is caused by distributed stress. Cyclic loading tests conducted through tension and bending reflect the strain of the electromagnetic wire under concentrated stress, but cannot accurately simulate the stress distribution of the coil. Third, rapid stress changes occur during a transformer short circuit; tests conducted under a given static load cannot reflect the impact of stress changes on mechanical stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose a transformer coil cumulative strain testing device and method, which can accurately reflect the real transformer characteristics while controlling the test cost, help improve the accuracy of transformer post-short circuit condition assessment, and better ensure the safe operation of power equipment.

[0006] The technical problem solved by this invention is achieved through the following technical solution:

[0007] A transformer coil cumulative strain testing device, which acts on the transformer coil, includes a pulse magnetic field generating unit, a current boosting unit, and an immersion winding fixing device. The transformer coil is fixed inside the immersion winding fixing device. The current boosting unit is connected to the transformer coil to boost the current of the transformer coil and collect the total current of the transformer coil. The pulse magnetic field generating unit is arranged on the upper and lower sides of the transformer coil to provide a magnetic field.

[0008] Furthermore, the pulsed magnetic field generating unit includes: a pulsed magnetic field generating coil, a damping resistor, a control switch, a capacitor bank, a DC charging power supply, a controller, a magnetic field sensor, and a thermometer. The DC charging power supply, damping resistor, control switch, and capacitor bank constitute two identical RLC oscillation circuits. The output of the controller is connected to the control switch to receive switch time setting parameters and temperature setting parameters. When the actual temperature is within the set range, the switch is controlled to operate according to the given time parameters. The output of each RLC oscillation circuit is connected to a pulsed magnetic field generating coil. One pulsed magnetic field generating coil is positioned above the transformer coil, and the other is positioned below the transformer coil. The magnetic field sensor is positioned around the transformer coil to measure the magnetic field changes generated by the pulsed magnetic field generating coil. The thermometer is positioned inside the immersion winding fixing device. The output of the thermometer is connected to the input of the controller, and the output of the magnetic field sensor is connected to the input of the controller.

[0009] Furthermore, the control switch includes a first control switch S1 and a second control switch S2. The first control switch S1 and the second control switch S2 each include a normally closed node and a normally open node. The normally closed node is located on the line between the capacitor bank and the positive terminal of the power supply, and the normally open node is located on the line between the capacitor bank and the damping resistor.

[0010] Moreover, the pulsed magnetic field generating coil is wound with a high mechanical strength copper alloy and epoxy cast.

[0011] Furthermore, the current boosting unit includes a DC current booster, a limit switch, a current acquisition unit, and an emergency stop control switch. The output terminal of the DC current booster is connected to the transformer coil through the current acquisition unit. The limit switch is located around the transformer coil and is connected to the control terminal of the DC current booster through the emergency stop control switch.

[0012] Furthermore, the immersion winding fixing device includes an oil chamber, insulating oil, a clamping mechanism, an insulating pressure plate and pressure nails, an iron core, and a magnetic shield. The oil tank contains insulating oil capable of immersing the transformer coil. The transformer coil is placed in the middle of the clamping mechanism. The clamping mechanism fixes the transformer coil from both above and below by means of the insulating pressure plate and pressure nails. The iron core is located at the center of the transformer coil to enhance the magnetic field. The magnetic shield is located on the inner surface of the oil chamber to reduce external magnetic leakage.

[0013] Moreover, the clamping mechanism is made of high-strength material, and the iron core and magnetic shield are made of stacked silicon steel sheets.

[0014] A test method for a transformer coil cumulative strain testing device includes the following steps:

[0015] Step 1: Based on the rated current parameters of the transformer coil, set different levels of inrush current i. imp (t);

[0016] Step 2, based on the impact current i imp (t) Magnitude, calculate the parameters of each component of the pulse magnetic field generating unit, and adjust the device parameters by adjusting the DC charging power supply voltage, capacitor bank value, damping resistor value, and switch closing time;

[0017] Step 3: Conduct multiple impacts, calculate the distributed force F per unit length of the transformer coil electromagnetic wire, and measure the cumulative strain Δs of the transformer coil to obtain the relationship between F and Δs.

[0018] Furthermore, the specific implementation method of step 2 is as follows: the number of turns of the upper and lower pulse magnetic field generating coils are N1 and N2, the equivalent inductances are L1 and L2, and the currents passing through them are i1 and i2, respectively. In the two RLC oscillation circuits with the same structure, the initial voltages are U1 and U2, the capacitances are C1 and C2, and the resistances are R1 and R2, respectively. The two RLC oscillation circuits are connected at times t1 and t2, respectively. The number of turns of the transformer coil is denoted as N, and the output current of the current booster is I. d Test the impact current i imp When the cumulative strain is at (t), the current in the coil is made close to the desired impact current. Calculate the test circuit parameters R1, R2, L1, L2, C1, C2, t1, t2:

[0019]

[0020] in:

[0021] After the test circuit parameters are calculated, U k C k R k By directly adjusting the DC charging power supply voltage, capacitor bank value, and damping resistor value, L k The distance between the pulse magnetic field generating coil and the iron core is adjusted; the smaller the distance, the more L... k The larger the value, the greater the distance, L k The smaller t k The settings are configured via the controller, from 0 to t. kAt that moment, the DC charging power supply passes through switch S k The normally closed switch charges the capacitor bank, t k At any given time, under the action of the controller, switch S k When the normally closed switch is opened and the normally open switch is closed, the capacitor bank discharges in units to the pulsed magnetic field, forming a pulsed magnetic field that passes through the tested winding, causing current changes and distributed stress in the tested winding.

[0022] Furthermore, the specific implementation method of step 3 is as follows: control switch S through the controller. k Multiple capacitor bank charging and pulsed magnetic field discharge processes were completed. The magnetic induction intensity b(t) and the current i(t) through the tested winding were recorded by the magnetic field sensor during each discharge process. The force F = ∫b(t)i(t)dt per unit length of the winding was calculated. After the discharge process, the accumulated strain Δs of the tested winding in the horizontal direction was measured at multiple points, with different impact currents i... imp (t), calculate and adjust the parameters of the coil cumulative strain test circuit, and measure the relationship between the distributed force F per unit length and the coil cumulative strain Δs under the corresponding impact level.

[0023] The advantages and positive effects of this invention are:

[0024] This invention constructs a simulation system for the stress characteristics of a coil during a short-circuit impact. It fully considers the influence of coil heating, distributed stress on the electromagnetic wire, and the interaction between the electromagnetic wire and the pad on strain testing. A coil cumulative strain testing device is designed to recreate the transient stress changes during a short-circuit impact, and a method for testing coil cumulative strain is proposed, achieving accurate simulation of distributed stress on the winding and testing of cumulative strain. This invention fully considers the influence of the transformer's electromagnetic wire, cardboard structure, and stress distribution on the mechanical stability of the winding, recreates the transient stress changes during a short circuit, and effectively tests the cumulative strain of the coil under the influence of multiple short-circuit processes. Applied to the mechanical condition assessment of transformers after multiple short circuits, it can accurately reflect the characteristics of real transformers while controlling test costs, helping to improve the accuracy of transformer post-short-circuit condition assessment and better ensure the safe operation of power equipment. Attached Figure Description

[0025] Figure 1 This is a system structure diagram of the present invention.

[0026] 1-Pulse magnetic field generating unit; 2-Damping resistor; 3-Control switch; 4-Current acquisition unit; 5-Capacitor bank; 6-DC charging power supply; 7-Limit switch; 8-Transformer coil; 9-Oil chamber; 10-Insulating pressure plate; 11-Iron core; 12-Magnetic shield; 13-Thermometer; 14-Emergency stop control switch; 15-Magnetic field sensor; Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings.

[0028] A transformer coil cumulative strain testing device is applied to the transformer coil, such as... Figure 1 As shown, it includes a pulse magnetic field generating unit 1, a current boosting unit, and an immersion winding fixing device. The transformer coil 8 is fixed inside the immersion winding fixing device. The current boosting unit is connected to the transformer coil to boost the current of the transformer coil and collect the total current of the transformer coil. The pulse magnetic field generating unit is set on the upper and lower sides of the transformer coil to provide a magnetic field.

[0029] The pulse magnetic field generating unit includes: a pulse magnetic field generating coil, a damping resistor 2, a control switch 3, a capacitor bank 5, a DC charging power supply 6, a controller, a magnetic field sensor 15, and a thermometer 13. The DC charging power supply, damping resistor, control switch, and capacitor bank constitute two identical RLC oscillation circuits. The output of the controller is connected to the control switch to receive the switch time setting parameters and temperature setting parameters. When the actual temperature is within the set range, the switch is controlled to operate according to the given time parameters. The output of each RLC oscillation circuit is connected to a pulse magnetic field generating coil. One pulse magnetic field generating coil is located above the transformer coil, and the other is located below the transformer coil. The magnetic field sensor is located around the transformer coil to measure the magnetic field changes generated by the pulse magnetic field generating coil. The thermometer is located inside the immersion winding fixing device. The output of the thermometer is connected to the input of the controller, and the output of the magnetic field sensor is connected to the input of the controller.

[0030] The control switches include a first control switch S1 and a second control switch S2. The first control switch S1 and the second control switch S2 each contain a normally closed node and a normally open node. The normally closed node is set on the line between the capacitor bank and the positive terminal of the power supply, and the normally open node is set on the line between the capacitor bank and the damping resistor. After receiving a signal from the controller, the state is reversed (the normally closed node opens and the normally open node closes). The controller receives the switch time setting parameters and temperature setting parameters. When the actual temperature is within the set range, the controller controls the operation of switches S1 and S2 according to the given time parameters.

[0031] The pulsed magnetic field generating coil is wound with a high mechanical strength copper alloy and then epoxy cast.

[0032] The current booster unit includes a DC current booster, a limit switch 7, a current acquisition unit 4, and an emergency stop control switch 14. The output terminal of the DC current booster is connected to the transformer coil through the current acquisition unit. The limit switch is set around the transformer coil and is connected to the control terminal of the DC current booster through the emergency stop control switch. When the tested transformer winding triggers the limit switch, it immediately triggers the emergency stop of the current booster and cuts off the output of the DC current booster. The current acquisition unit acquires the total current passing through the winding through an electronic current transformer.

[0033] The submerged winding fixing device includes an oil chamber 9, insulating oil, a clamping mechanism, an insulating pressure plate 10 and pressure nails, an iron core 11, and a magnetic shield 12. The oil tank contains insulating oil that can submerge the transformer coil. The transformer coil is placed in the middle of the clamping mechanism. The clamping mechanism fixes the transformer coil from both above and below by the insulating pressure plate and pressure nails. The iron core is set at the center of the transformer coil to enhance the magnetic field. The magnetic shield is set on the inner surface of the oil chamber to reduce external magnetic leakage.

[0034] The clamping mechanism is made of high-strength materials, and the iron core and magnetic shield are made of stacked silicon steel sheets. Pressure is applied to the winding from both the top and bottom directions through insulating pressure plates and multiple pressure pins.

[0035] A test method for a transformer coil cumulative strain testing device includes the following steps:

[0036] Step 1: Based on the rated current parameters of the transformer coil, set different levels of inrush current i. imp (t).

[0037] Step 2, based on the impact current i imp (t) Calculate the parameters of each component in the pulse magnetic field generating unit, and adjust the device parameters by adjusting the DC charging power supply voltage, capacitor bank value, damping resistor value, and switch closing time.

[0038] The number of turns of the upper and lower pulse magnetic field generating coils are N1 and N2, respectively, and their equivalent inductances are L1 and L2, respectively. The currents passing through them are i1 and i2, respectively. In two identical RLC resonant circuits, the initial voltages are U1 and U2, the capacitances are C1 and C2, and the resistances are R1 and R2, respectively. The two RLC resonant circuits are connected at times t1 and t2, respectively. The number of turns of the transformer coil is denoted as N, and the output current of the current booster is I. d Test the impact current i imp When the cumulative strain is at (t), the current in the coil is made close to the desired impact current. Calculate the test circuit parameters R1, R2, L1, L2, C1, C2, t1, t2:

[0039]

[0040] in:

[0041] After the test circuit parameters are calculated, U k C k R k By directly adjusting the DC charging power supply voltage, capacitor bank value, and damping resistor value, L k The distance between the pulse magnetic field generating coil and the iron core is adjusted; the smaller the distance, the more L... k The larger the value, the greater the distance, L k The smaller t k The settings are configured via the controller, from 0 to t. k At that moment, the DC charging power supply passes through switch S k The normally closed switch charges the capacitor bank, t k At any given time, under the action of the controller, switch S k When the normally closed switch is opened and the normally open switch is closed, the capacitor bank discharges in units to the pulsed magnetic field, forming a pulsed magnetic field that passes through the tested winding, causing current changes and distributed stress in the tested winding.

[0042] Step 3: Conduct multiple impacts, calculate the distributed force F per unit length of the transformer coil electromagnetic wire, and measure the cumulative strain Δs of the coil to obtain the relationship between F and Δs.

[0043] Switch S is controlled by the controller. k Multiple capacitor bank charging and pulsed magnetic field discharge processes were completed. The magnetic induction intensity b(t) and the current i(t) through the tested winding were recorded by the magnetic field sensor during each discharge process. The force F = ∫b(t)i(t)dt per unit length of the winding was calculated. After the discharge process, the accumulated strain Δs of the tested winding in the horizontal direction was measured at multiple points, with different impact currents i... imp (t), calculate and adjust the parameters of the coil cumulative strain test circuit, and measure the relationship between the distributed force F per unit length and the coil cumulative strain Δs under the corresponding impact level.

[0044] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention includes, but is not limited to, the embodiments described in the specific implementation. Any other implementations derived by those skilled in the art based on the technical solutions of this invention are also within the scope of protection of this invention.

Claims

1. A transformer coil cumulative strain testing device, applied to a transformer coil, characterized in that: It includes a pulse magnetic field generating unit, a current boosting unit, and an immersion winding fixing device. The transformer coil is fixed inside the immersion winding fixing device. The current boosting unit is connected to the transformer coil to boost the current of the transformer coil and collect the total current of the transformer coil. The pulse magnetic field generating unit is set on the upper and lower sides of the transformer coil to provide a magnetic field. The pulsed magnetic field generating unit includes: a pulsed magnetic field generating coil, a damping resistor, a control switch, a capacitor bank, a DC charging power supply, a controller, a magnetic field sensor, and a thermometer. The DC charging power supply, damping resistor, control switch, and capacitor bank constitute two identical RLC oscillation circuits. The output of the controller is connected to the control switch to receive switch time setting parameters and temperature setting parameters. When the actual temperature is within the set range, the switch is controlled to operate according to the given time parameters. The output of each RLC oscillation circuit is connected to a pulsed magnetic field generating coil. One pulsed magnetic field generating coil is positioned above the transformer coil, and the other is positioned below the transformer coil. The magnetic field sensor is positioned around the transformer coil to measure the magnetic field changes generated by the pulsed magnetic field generating coil. The thermometer is positioned inside the immersion winding fixing device. The output of the thermometer is connected to the input of the controller, and the output of the magnetic field sensor is also connected to the input of the controller. The current boosting unit includes a DC current booster, limit switches, a current acquisition unit, and an emergency stop control switch. The output terminal of the DC current booster is connected to the transformer coil through the current acquisition unit. The limit switches are arranged around the transformer coil and are connected to the control terminal of the DC current booster through the emergency stop control switch. The submerged winding fixing device includes an oil chamber, insulating oil, a clamping mechanism, insulating pressure plates and pressure nails, an iron core, and a magnetic shield. The oil tank contains insulating oil sufficient to submerge the transformer coil. The transformer coil is placed in the middle of the clamping mechanism. The clamping mechanism fixes the transformer coil from both above and below by means of insulating pressure plates and pressure nails. The iron core is located at the center of the transformer coil to enhance the magnetic field. The magnetic shield is located on the inner surface of the oil chamber to reduce external magnetic leakage.

2. The transformer coil cumulative strain testing device according to claim 1, characterized in that: The control switch includes a first control switch S1 and a second control switch S2. The first control switch S1 and the second control switch S2 each include a normally closed node and a normally open node. The normally closed node is located on the line between the capacitor bank and the positive terminal of the power supply, and the normally open node is located on the line between the capacitor bank and the damping resistor.

3. The transformer coil cumulative strain testing device according to claim 1, characterized in that: The pulsed magnetic field generating coil is wound with a high mechanical strength copper alloy and then epoxy cast.

4. The transformer coil cumulative strain testing device according to claim 1, characterized in that: The clamping mechanism is made of high-strength material, and the iron core and magnetic shield are made of stacked silicon steel sheets.

5. A testing method for a transformer coil cumulative strain testing device as described in claims 1 to 4, characterized in that: Includes the following steps: Step 1: Based on the rated current parameters of the transformer coil, set different levels of inrush current i. imp (t); Step 2, based on the impact current i imp (t) Magnitude, calculate the parameters of each component of the pulse magnetic field generating unit, and adjust the device parameters by adjusting the DC charging power supply voltage, capacitor bank value, damping resistor value, and switch closing time; Step 3: Conduct multiple impacts, calculate the distributed force F per unit length of the transformer coil electromagnetic wire, and measure the cumulative strain Δs of the coil to obtain the relationship between F and Δs.

6. The testing method of the transformer coil cumulative strain testing device according to claim 5, characterized in that: The specific implementation method of step 2 is as follows: the number of turns of the upper and lower pulse magnetic field generating coils are N1 and N2, respectively, the equivalent inductances are L1 and L2, and the currents passing through them are i1 and i2, respectively. In the two RLC oscillation circuits with the same structure, the initial voltages are U1 and U2, the capacitances are C1 and C2, and the resistances are R1 and R2, respectively. The two RLC oscillation circuits are connected at times t1 and t2, respectively. The number of turns of the transformer coil is denoted as N, and the output current of the current booster is I. d Test the impact current i imp When the cumulative strain is at (t), the current in the coil is made close to the desired impact current. Calculate the test circuit parameters R1, R2, L1, L2, C1, C2, t1, t2: in: After the test circuit parameters are calculated, U k C k R k By directly adjusting the DC charging power supply voltage, capacitor bank value, and damping resistor value, L k The distance between the pulse magnetic field generating coil and the iron core is adjusted; the smaller the distance, the more L... k The larger the value, the greater the distance, L k The smaller t k The settings are configured via the controller, from 0 to t. k At that moment, the DC charging power supply passes through switch S k The normally closed switch charges the capacitor bank, t k At any given time, under the action of the controller, switch S k When the normally closed switch is opened and the normally open switch is closed, the capacitor bank discharges in units to the pulsed magnetic field, forming a pulsed magnetic field that passes through the tested winding, causing current changes and distributed stress in the tested winding.

7. The testing method of the transformer coil cumulative strain testing device according to claim 5, characterized in that: The specific implementation method of step 3 is as follows: control switch S through the controller. k Multiple capacitor bank charging and pulsed magnetic field discharge processes were completed. The magnetic induction intensity b(t) and the current i(t) through the tested winding were recorded by the magnetic field sensor during each discharge process. The force F = ∫b(t)i(t)dt per unit length of the winding was calculated. After the discharge process, the accumulated strain Δs of the tested winding in the horizontal direction was measured at multiple points, with different impact currents i... imp (t), calculate and adjust the parameters of the coil cumulative strain test circuit, and measure the relationship between the distributed force F per unit length and the coil cumulative strain Δs under the corresponding impact level.

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