Drop protection device for direct current resistance tester

Abstract

The invention discloses a disconnection protection device for a direct current resistance tester, and relates to the field of direct current resistance measurement and protection of electromagnetic components of a power system. The device comprises a reverse discharge wire, a counting alarm module, a reverse connection alarm module and a self-checking test loop. The reverse discharge wire is composed of a double-tube parallel diode and a discharge current-limiting resistor and discharges magnetic field energy according to the exponential attenuation law. The counting alarm module can quickly trigger alarm and record a discharge event; the reverse connection alarm module is matched with color identification to prevent wiring polarity errors; the self-checking test loop can simulate the function of the power-down scene verification device. Through electromagnetic energy calculation and transient response design, the device adapts to scenes of a main transformer, a plant transformer and the like, equipment damage and personnel safety risks caused by high voltage when a test loop is interrupted can be avoided, dual protection of test personnel and equipment is realized, and the test safety and efficiency are improved.

Description

Technical Field

[0001] This invention relates to the field of power systems, and more specifically, to the field of DC resistance measurement and testing of electromagnetic components such as transformers and motors in power systems. It is a protective device used to ensure test safety and equipment integrity when the DC resistance tester goes offline during the aforementioned DC resistance measurement and testing process. Background Technology

[0002] In the daily operation and maintenance and testing of power systems, testers often need to use a DC resistance meter to measure the DC resistance of electromagnetic components such as transformers and motors. During this test, the test current output by the DC resistance meter charges the magnetic field inside the electromagnetic component, causing the component to store a certain amount of magnetic field energy.

[0003] In actual testing, unexpected situations may occur, such as the measuring line breaking accidentally due to pulling, or the DC resistance meter suddenly losing power. When these situations happen, according to Lenz's law, the magnetic field storing energy inside the electromagnetic component will rapidly release energy, inducing an extremely high voltage in the measuring circuit during this process. This induced high voltage may lead to two serious consequences: first, it may cause a discharge phenomenon inside the electromagnetic component under test, resulting in localized damage to the internal insulation structure of the component, affecting the normal performance and service life of the equipment under test; second, it may cause the measuring circuit to discharge externally, posing a threat to the personal safety of testing personnel near the equipment under test.

[0004] The study found that during the experiment, the magnitude of the test current, the width of the cross-section of the electromagnetic component's core, and the number of turns in the component's winding were all positively correlated with the total energy stored in the magnetic field. That is, the larger the test current, the wider the core cross-section, and the more turns in the winding, the greater the total energy stored in the magnetic field. When the measurement circuit is interrupted, the induced backflash voltage will also be correspondingly higher, and the aforementioned safety hazards and equipment damage risks will also increase accordingly.

[0005] To avoid the high induced voltage problem caused by the interruption of the measurement circuit, and to ensure the personal safety of test personnel and the integrity of the equipment under test, a corresponding protection circuit is urgently needed when performing DC resistance measurement tests. This protection circuit must provide a safe release path for magnetic field energy in the event of an accidental disconnection of the test circuit or a sudden interruption of current. By using methods such as parallel reverse discharge lines, the magnetic field energy can be smoothly released and dissipated, thereby preventing the generation of high induced voltage in the circuit and preventing equipment damage and personnel injury. Summary of the Invention

[0006] (I) Purpose of the Invention

[0007] This invention aims to solve the problem of electromagnetic component magnetic field energy leakage and induced high voltage caused by test circuit interruption (such as disconnection of the measuring line or power failure of the instrument) in DC resistance measurement tests. Specific objectives include:

[0008] (1) Using the characteristics of diodes and Lenz's law, a reverse discharge circuit is designed to safely release and consume magnetic field energy when the current in the measurement circuit is interrupted, so as to prevent equipment damage and personnel injury caused by induced high voltage.

[0009] (2) Configure the protection device with a self-test function to ensure that the protection device is in normal performance before the test and to avoid the protection device losing its protective function due to failure.

[0010] (3) Design discharge counting and disconnection alarm functions to record discharge events, facilitate post-test analysis of the equipment under test, and promptly remind test personnel of abnormal situations.

[0011] (4) Design a reverse connection alarm function to prevent the device from being connected in the wrong direction, ensure that the device is correctly connected to the circuit, and ensure that the protection function is effectively performed.

[0012] (5) Provides comprehensive safety assurance for the operation process of measuring electromagnetic components of DC resistance meter, and improves test safety and efficiency.

[0013] (II) Device Composition

[0014] The DC resistance tester disconnection protection device of this invention mainly consists of four parts: a reverse discharge line, a counting alarm module, a reverse connection alarm module, and a self-test circuit. The structure and function of each part are as follows:

[0015] (1) Core structure design

[0016] A DC resistance tester disconnection protection device, characterized in that it includes a reverse discharge line, a counting alarm module, a reverse connection alarm module, and a self-test circuit;

[0017] The reverse discharge line is connected in parallel with the measurement circuit consisting of a DC resistance tester and the electromagnetic component under test. This is used to discharge the magnetic field energy formula when the measurement circuit is interrupted. (W is the magnetic field energy, L is the inductance of the electromagnetic component under test, and I is the test current output by the DC resistance tester) Discharge magnetic field energy;

[0018] The counting alarm module is connected in parallel with the reverse discharge line. When a reverse discharge occurs in the measurement circuit, the module is used to trigger an alarm and record the discharge event.

[0019] The reverse connection alarm module is connected to the forward and reverse connectors of the measurement circuit to monitor the wiring polarity and alert for errors;

[0020] The self-test circuit is used to simulate a power failure scenario in the measurement circuit and to check whether the disconnection protection device is functioning properly.

[0021] (2) Specific design of the reverse discharge line

[0022] Based on the above core structural design, the reverse discharge line includes a discharge diode and a discharge current-limiting resistor; by utilizing the forward conduction and reverse cutoff characteristics of the diode, the magnetic field energy generated by the test circuit disconnection is consumed on the discharge current-limiting resistor, thus avoiding excessive current from damaging other components.

[0023] The discharge diodes are arranged in parallel. The purpose of this design is to ensure that the reverse discharge line can still conduct and discharge normally when a single diode fails, thus ensuring the reliability of the protection function.

[0024] Furthermore, the discharge diode has a reverse peak voltage of 600V, a forward current of 25A, a maximum inrush current of 200A, a reverse current of 0.5mA, and a forward voltage drop of 0.55V. These parameters are based on the extremely short duration of the peak voltage during magnetic field energy discharge; therefore, component selection is not based on heat capacity, but rather on the maximum inrush current capability (IFSM) as the core indicator. Considering the requirement of a maximum output current of 40A for the DC resistance meter, a dual-tube parallel design is adopted, and the maximum inrush current capability of a single tube must not be less than the output current of the DC resistance meter.

[0025] The discharge current limiting resistor has a resistance of 5Ω and an overcurrent peak voltage of 600V. It can limit the circuit current during the discharge of magnetic field energy, and prevent excessive current from damaging the reverse discharge line and other device components. Together with the discharge diode connected in parallel with the two tubes, it forms a stable and reliable reverse discharge circuit.

[0026] Furthermore, the discharge process of the reverse discharge line follows an exponential decay law, and the formula for the change of discharge current I(t) with time t is: (Where I0 is the initial discharge current, R is the total resistance of the discharge circuit, and L is the inductance of the electromagnetic component under test), peak discharge voltage U peak =I0×R, where discharge duration is defined as the time required for the current to decay to 37% of its initial value, and time constant.

[0027] The energy consumption of discharge follows the formula: (where W) 剩余 (t) represents the remaining energy at time t).

[0028] (3) Specific design of the counting alarm module

[0029] Based on the core structural design, the counting alarm module is assembled from a pre-built electrical pulse counter module. Its starting voltage is 30V, starting time is no more than 0.1s, and starting current is no more than 1A. Manual reset is required after startup. This ensures that the alarm and counting functions are quickly triggered when the reverse discharge line starts discharging energy. Manual reset by the test personnel after startup facilitates complete recording of discharge events in a single test.

[0030] Furthermore, the counting alarm module is connected in parallel with the reverse discharge line. When the reverse discharge line starts working and releases magnetic field energy, the pulse counter starts synchronously, issues an alarm signal, and records the discharge event.

[0031] (4) Specific design of the self-test circuit

[0032] According to the core structural design, the self-test circuit is assembled from a battery boost energy storage discharge circuit module. The discharge energy of this circuit is not less than 200kJ, the discharge current is not less than 20A, and the energy storage voltage is not less than 500V. After the self-test button is pressed and closed, it can be manually disconnected or automatically disconnected after a delay.

[0033] The self-test circuit operates as follows: Before the test circuit is connected, press the self-test button. The boost discharge module and the electromagnetic component under test form a circuit, and the boost discharge module charges the electromagnetic component under test. When the self-test button is disconnected, the disconnection protection circuit formed by the electromagnetic component under test and the reverse discharge line is connected. If the disconnection protection device functions normally, the buzzer in the circuit will sound and the LED will light up, indicating a successful self-test. If the disconnection protection device malfunctions, there will be no alarm, indicating a failed self-test. The wiring and equipment of the disconnection protection device must be rechecked. The DC resistance measurement test can only be started after confirming that the disconnection protection device is functioning normally.

[0034] The self-test circuit can realistically simulate the circuit power failure under different test scenarios (such as high current in the main transformer and low current in the plant transformer), comprehensively test the function of the protection device, and ensure that the self-test results can cover the extreme working conditions in actual tests.

[0035] (5) Specific design of the reverse connection alarm module

[0036] Based on the core structural design, the reverse connection alarm module is assembled from finished modules, with a starting current of 1A and a starting delay time of 2s. It alarms via a buzzer when a wiring polarity error is detected. The forward and reverse connectors of the measurement circuit are color-coded, with red for the positive terminal and black for the negative terminal, thus doubly preventing device malfunctions caused by wiring errors.

[0037] (6) Device workflow design

[0038] According to the core structural design, the device's workflow includes five stages: pre-test self-test, device wiring and reverse connection detection, normal test, disconnection protection, test end and reset.

[0039] During the disconnection protection phase, when the measurement circuit is interrupted, the reverse discharge line is activated, and the magnetic field energy is determined according to the formula. The discharge and counting alarm modules are activated synchronously, and energy consumption follows [the specified procedure].

[0040] Furthermore, in the pre-test self-test stage, if the device malfunctions after the self-test circuit is started, the fault must be investigated and the self-test must be repeated until the self-test is successful before proceeding to the next stage.

[0041] Furthermore, during the wiring and reverse connection detection phase of the device, if the reverse connection alarm module detects an incorrect wiring polarity, a buzzer will sound an alarm after a 2-second delay. Only after the staff corrects the wiring can the device enter the test-ready state.

[0042] The specific steps are as follows:

[0043] 1. Pre-test self-check

[0044] The self-test test circuit is activated, simulating a power outage in the test circuit through the battery boost energy storage discharge circuit. This self-test test circuit is assembled using a purchased boost discharge circuit module, which can stably output an energy storage voltage of not less than 500V, a discharge current of not less than 20A, and a discharge energy of not less than 200kJ, ensuring that the simulated scenario is close to the power outage condition of the test circuit in actual testing.

[0045] If the device is functioning normally, the buzzer in the self-test circuit will sound and the LED will light up (self-test successful); if the self-test fails, the fault needs to be checked and the self-test repeated until it succeeds.

[0046] 2. Device wiring and reverse connection test

[0047] After the self-test is successful, connect the device to the measurement circuit between the DC resistance meter and the component under test according to the connector color markings (positive red, negative black).

[0048] The reverse connection alarm module monitors the wiring polarity in real time: if the connection is reversed, a buzzer sounds after a 2-second delay, prompting personnel to correct the wiring; if the wiring is correct, the alarm circuit does not activate, and the device enters the test-ready state. This reverse connection alarm module is assembled from pre-built modules. Its parameters of 1A starting current and 2-second alarm delay avoid false alarms caused by momentary poor wiring contact, while ensuring timely alerts for polarity errors and guaranteeing correct wiring.

[0049] 3. Normal testing phase

[0050] Start the DC resistance tester and begin the measurement test. During normal testing, the diode in the reverse discharge line will not bypass the measurement circuit due to its reverse cutoff characteristic (equivalent to disconnection), ensuring accurate measurement. The DC resistance tester will output the test current normally and accurately measure the DC resistance of the electromagnetic component under test.

[0051] 4. Anomaly Protection Phase

[0052] If the measuring line is disconnected or the instrument is powered off, the current in the test circuit is interrupted, and the magnetic field of the electromagnetic component releases energy. According to Lenz's law, a reverse voltage is induced in the circuit.

[0053] At this time, the diode in the reverse discharge line is forward-biased, and the magnetic field energy is dissipated through the 5Ω discharge current-limiting resistor. Simultaneously, the counting alarm module, triggered by the voltage of the reverse discharge line (starting voltage 30V), activates within 0.1 seconds, the buzzer sounds an alarm signal, and the discharge event is recorded, ensuring that test personnel can promptly detect abnormalities. This counting alarm module uses a purchased electrical pulse counter module, whose starting current is no more than 1A, making it suitable for the energy dissipation scenario of the reverse discharge line and preventing damage to the counting module due to excessive current.

[0054] 5. End of Test and Reset

[0055] After the test is completed normally or an abnormality is resolved, turn off the DC resistance meter and end the test.

[0056] The staff manually reset the counting alarm module, cleared the discharge record, and restored the device to its initial state, preparing it for the next test.

[0057] (III) Calculation Principles

[0058] The protection device of this invention is designed based on electromagnetic energy theory and circuit transient response principles. By calculating magnetic field energy, inductance parameters, and discharge duration, it ensures rapid and safe energy dissipation in DC resistance test disconnection scenarios. The specific calculation principle is as follows:

[0059] (1) Inductance value calculation method

[0060] Based on the core structural design, the inductance value L of the electromagnetic component under test is calculated using the no-load characteristics, including the following steps:

[0061] Step 1: Calculate the inductive component of the no-load current I L The no-load current includes the inductive component I. L and resistive component I R The no-load current percentage is 0.1%, therefore the no-load current amplitude I no-load =I n ×0.1%; No-load loss P no-load (Three-phase total), phase voltage (V is the rated voltage, I) n (Rated current); Resistance component I R (per phase): Inductance component I L (per phase):

[0062] Step 2: Calculate the inductance L: inductive reactance per phase inductance

[0063] (2) Calculation of magnetic field energy

[0064] The magnetic field energy W stored by the electromagnetic component (such as a transformer or motor) during the test is calculated using the following formula: Where: W is the magnetic field energy (unit: joule J); L is the inductance of the electromagnetic component under test (unit: henry, H); I is the test current output by the DC resistance tester (unit: ampere, A).

[0065] (3) Discharge duration and current decay model

[0066] Step 1: The discharge process of the reverse discharge line follows an exponential decay law, and the change of the discharge current I(t) with time t is expressed as: Where: I0 is the initial discharge current (i.e., test current, unit: A); R is the total resistance of the discharge circuit (including current limiting resistor and line resistance, unit: ohm, Ω); L is the inductance value of the electromagnetic component (unit: H).

[0067] The discharge duration is determined by the time it takes for the current to decay to a safe threshold, ensuring that the peak value of the induced voltage does not exceed the device's tolerance limit.

[0068] Step 2: Peak voltage (moment of disconnection):

[0069] U peak =I0×R

[0070] Step 3: Definition and Calculation Standard of Discharge Duration

[0071] Discharge duration is typically defined as the current decaying to 37% of its initial value (i.e., e). -1 The time required, the time constant τ is: Therefore: I(τ)=I0e -1 .

[0072] Step 4: Calculation of the complete discharge process

[0073] To comprehensively evaluate discharge performance, current values ​​at multiple time points were calculated. The complete discharge process calculation included time t (s) and attenuation coefficient. Current I(t)(A).

[0074] (4) Discharge energy consumption process

[0075] Initial total energy: Formula for energy decay during discharge:

[0076] (5) Discharge voltage change process

[0077] Discharge circuit voltage formula: Initial peak voltage: U0 = I0 × R; Voltage at time constant τ: U(τ) = U0 × e -1 .

[0078] (iv) Beneficial effects

[0079] Significant safety protection effect: Through the design of the reverse discharge line, the magnetic field energy can be quickly released and consumed when the test circuit is interrupted, avoiding internal discharge (insulation damage) and external discharge (personnel injury) caused by induced high voltage, thus achieving dual protection for test personnel and equipment.

[0080] High device reliability: The reverse discharge line adopts a dual-tube parallel design to prevent single-tube failure from causing protection failure; the self-test function ensures that the device is in normal performance before the test, providing double protection for device reliability from the design and process, and reducing the probability of risks caused by device failure.

[0081] Facilitates test traceability and analysis: The counting alarm module can record discharge events. After the test, staff can use the records to confirm whether a disconnection discharge has occurred, providing data support for analyzing changes in the magnetic field energy of the tested equipment, potential faults, etc., and assisting in equipment operation and maintenance.

[0082] Easy to operate and highly fault-tolerant: The reverse connection alarm module, in conjunction with color-coded indicators, prevents device failure due to wiring errors; self-test, alarm, and other functions are intuitively indicated by a buzzer and LEDs, reducing operational difficulty and improving testing efficiency.

[0083] Wide adaptability: The maximum inrush current of a single diode in the reverse discharge line is not less than the output current of the DC resistance meter, which can be adapted to different test current scenarios and meet the test protection needs of various electromagnetic components such as transformers and motors. Attached Figure Description

[0084] Figure 1 This is a schematic diagram of the structure of the present invention.

[0085] Figure 2 This is a flowchart illustrating the working principle of the present invention.

[0086] Figure 3 This is a flowchart illustrating the working principle of the self-testing circuit of the present invention.

[0087] Figure 4 This is a flowchart illustrating the working principle of the reverse connection alarm module of the present invention.

[0088] Figure 5 This is a flowchart illustrating the working principle of the disconnection protection function of the present invention.

[0089] Figure 6 This is a flowchart illustrating the working principle of the boost discharge module of the present invention. Detailed Implementation

[0090] To make the technical solution, purpose and advantages of the present invention clearer, the following examples of main transformers and plant transformers will be used to explain in detail the application process, parameter calculation and function verification of the DC resistance tester disconnection protection device.

[0091] Example 1: Application of protection device based on main transformer (rated voltage 235.9kV, rated current 929.9A)

[0092] 1.1 Adaptation of main transformer basic parameters and device components

[0093] In this embodiment, the rated parameters of the main transformer are: rated voltage (V = 235.9kV), rated current (I0). n =929.9A), no-load loss (P) no-load =163.75kW (total three-phase);

[0094] Reverse discharge line: The discharge diode is model MUR2560 (reverse peak voltage 600V, forward current 25A, maximum inrush current 200A, reverse current 0.5mA, forward voltage drop 0.55V), and adopts a dual-diode parallel design to prevent single-diode failure; the discharge current limiting resistor (R1=5Ω, overcurrent peak voltage 600V) is adapted to the main transformer test current carrying requirements.

[0095] Counting Alarm Module: The counting alarm module has a startup voltage of 30V, a startup time of ≤0.1s, and a startup current of ≤1A. It requires manual reset after startup to ensure rapid response and recording of discharge events. This counting alarm module is assembled using a purchased pre-built electrical pulse counter module, simplifying the device setup process while ensuring the stability of the counting and alarm functions.

[0096] The self-test circuit employs a battery boost energy storage and discharge circuit with a discharge energy ≥200kJ, discharge current ≥20A, and energy storage voltage ≥500V, simulating the magnetic field energy discharge scenario during main transformer testing. This circuit is assembled using a pre-purchased boost discharge circuit module, eliminating the need for designing the energy storage and discharge circuits independently, reducing development complexity, and ensuring that the parameters meet the self-test requirements for high-energy scenarios of the main transformer.

[0097] Reverse connection alarm module: 1A starting current, 2s starting delay time. An alarm sounds when reverse connection is detected. Color coding on the main transformer wiring (red for positive, black for negative) helps prevent incorrect polarity connection. This circuit uses pre-assembled modules, ensuring precise compatibility with high-voltage main transformer wiring scenarios and preventing device failure or main transformer damage due to incorrect polarity.

[0098] 1.2 Calculation of Inductance and Magnetic Field Energy of Main Transformer

[0099] (1) Inductance calculation steps

[0100] Step 1: Calculate the no-load current I no-load

[0101] According to Formula I no-load =I n ×0.1%, substitute into I n =929.9A, therefore:

[0102] I no-load =929.9A×0.001=0.9299A≈0.93A.

[0103] Step 2: Calculate the phase voltage U phase

[0104] According to the formula Substituting V = 235900V, we get

[0105] Step 3: Calculate the resistance component of the no-load current I R (per phase)

[0106] According to the formula Substitute P no-load =163750W, therefore

[0107] Step 4: Calculate the inductance component of the no-load current I L (per phase)

[0108] According to the formula Substitute I no-load ≈0.93A, I R =0.4A, therefore:

[0109]

[0110] Step 5: Calculate the inductive reactance X L With inductor L

[0111] ①Inductive reactance formula Substituting the parameters, we get:

[0112] ②Inductance formula Substituting, we get:

[0113] (2) Calculation of magnetic field energy

[0114] According to the formula for magnetic field energy Calculate the magnetic field energy based on the test currents of the main transformer (10A, 20A, 40A):

[0115] 1. When the test current I = 10A:

[0116]

[0117] 2. When the test current I = 20A:

[0118]

[0119] 3. When the test current I = 40A:

[0120]

[0121] 1.3 Verification of the operation process of the protection device

[0122] (1) Self-test phase: Start the self-test test circuit, the battery boost energy storage discharge circuit releases energy ≥200kJ and current ≥20A, simulating a power outage in the main transformer test circuit (e.g., ...). Figure 3 (As shown); This self-test circuit is assembled using a purchased boost discharge circuit module, eliminating the need for designing complex circuits and reducing the difficulty of device development. At the same time, it ensures that the energy storage voltage is ≥500V, meeting the self-test requirements of the main transformer in high-energy scenarios. At this time, the buzzer of the self-test circuit sounds and the LED lights up, confirming that the reverse discharge line and the counting alarm module are functioning normally. Only after the self-test is successful can the test proceed.

[0123] (2) Wiring and Reverse Connection Detection: Connect the device between the main transformer and the DC resistance meter according to the color coding (positive red, negative black) (connect the device to the positive terminal on the high-voltage side of the main transformer and the negative terminal on the low-voltage side); the reverse connection alarm module monitors the polarity in real time (e.g., Figure 4 As shown in the diagram, due to correct wiring, the circuit does not operate, and the device enters the test-ready state. The reverse connection alarm module is assembled using finished modules, meeting the requirements of a 1A starting current and a 2s delay for buzzer alarm. Its stable parameter performance can prevent false triggering or failure of the alarm module due to the high voltage environment of the main transformer, ensuring the accuracy of wiring detection.

[0124] (3) Normal testing and abnormal protection

[0125] Normal test: Start the DC resistance meter and output the test current (taking 40A as an example). Due to its reverse cutoff characteristic, the diode in the reverse discharge line does not bypass the measurement circuit (e.g., Figure 1 As shown in the figure, ensure that the DC resistance meter accurately measures the DC resistance of the main transformer.

[0126] Abnormal protection: If the measuring line is accidentally disconnected or the instrument is powered off, the main transformer's magnetic field releases energy according to Lenz's law, inducing a reverse voltage in the circuit, causing the diode to conduct in the forward direction, and the magnetic field energy is dissipated through the 5Ω current-limiting resistor (e.g., Figure 5 (As shown); simultaneously, the counting alarm module is triggered by the voltage of the reverse discharge line (starting voltage 30V), the buzzer sounds an alarm and records the discharge event. Test personnel can promptly disconnect the relevant power supply to prevent the danger from escalating. This counting alarm module uses a purchased electrical pulse counter module, whose starting current is no greater than 1A, and can safely adapt to the energy discharge scenario of the reverse discharge line, ensuring that the alarm and counting functions are implemented synchronously.

[0127] (4) Test Reset: After the test ends (or after handling the abnormality), manually reset the counting alarm module, clear the discharge record, and restore the device to its initial state to prepare for the next test (e.g., Figure 2 (As shown).

[0128] 1.4 Calculation of the complete discharge process

[0129] (1) Discharge process analysis: Based on the discharge duration and current decay model, the total resistance of the discharge circuit is selected as R = 10Ω (including R1 = 5Ω (current limiting resistor), and the initial current is I0 = 40A.

[0130] ① Current decay formula:

[0131] ②Time constant The current decays to its initial value in 1 second. The time corresponding to 37% of the initial current (approximately 14.8A) is approximately τ≈51.64s;

[0132] ③ Peak voltage: U peak =I0×R=40A×10Ω=400V.

[0133]

[0134]

[0135] (2) Calculation of main transformer discharge energy consumption

[0136] (a) Calculation of energy consumption during discharge of the main transformer at a test current of 40A

[0137] 1. The law of change of discharge current and voltage

[0138] The total resistance of the discharge circuit is R = 10Ω (including the discharge current limiting resistor R1 = 5Ω), the inductance is L = 516.4H, and the initial test current is I0 = 40A.

[0139] Formula for discharge current changing with time:

[0140]

[0141] Formula for discharge voltage changing with time: (When t = 0, U(0) = 400V, the device components meet the voltage requirements).

[0142]

[0143]

[0144] 2. Discharge energy consumption process

[0145] Energy consumption follows the formula Initial energy

[0146]

[0147] time constant

[0148] Energy decay formula:

[0149]

[0150]

[0151] (b) Calculation of energy consumption during discharge of the main transformer at a test current of 20A

[0152] 1. The law of change of discharge current and voltage

[0153] The total resistance of the discharge circuit is R = 10Ω (including the discharge current limiting resistor R1 = 5Ω), the inductance is L = 516.4H, and the initial test current is I0 = 20A.

[0154] Formula for discharge current changing with time:

[0155]

[0156] Formula for discharge voltage changing with time:

[0157] Time t(s) Voltage value (V) Voltage attenuation percentage 0 200.0 0.0 15 148.7 25.7 51.64 73.6 63.2 90 33.1 83.5 150 8.8 95.6

[0158] 2. Calculation of energy consumption process

[0159] Initial energy

[0160]

[0161] time constant

[0162] Energy decay formula:

[0163]

[0164]

[0165]

[0166] (c) Calculation of energy consumption during discharge of 10A test current of main transformer

[0167] 1. The law of change of discharge current and voltage

[0168] The total resistance of the discharge circuit is R = 10Ω (including the discharge current limiting resistor R1 = 5Ω), the inductance is L = 516.4H, and the initial test current is I0 = 10A.

[0169] Formula for discharge current changing with time:

[0170]

[0171] Formula for discharge voltage changing with time:

[0172] Time t(s) Voltage value (V) Voltage attenuation ratio 0 100.0 0.0 25 61.7 38.33 51.64 36.8 63.22 100 16.5 83.5 150 7.4 92.6

[0173] 2. Calculation of energy consumption process

[0174] Initial energy

[0175]

[0176] time constant

[0177] Energy decay formula:

[0178]

[0179]

[0180] In all test scenarios of Example 1, the device met the protection requirements:

[0181] Response time: ≤0.1s to activate protection

[0182] Voltage safety: Peak voltage ≤ 600V, lower than the device's withstand voltage.

[0183] Energy processing: Capable of handling energy ranges from 25.82 to 413.12 kJ. Complete discharge: 99.9% energy consumption completed within 200 seconds.

[0184] Example 2: Application of protection device based on plant transformer (no-load current 1A)

[0185] In this embodiment, the transformer's basic parameters and device compatibility are as follows: no-load current 1A, rated voltage 35kV, and test current 3A. The protection device uses the same component selection as in Embodiment 1—the MUR2560 diode has a maximum inrush current of 200A, and the 5Ω current-limiting resistor can cover the 1A no-load current. Its self-test is fully matched to the transformer's low-energy scenario. The alarm circuit parameters use a starting voltage of 30V. The alarm counting circuit is assembled using purchased pulse counter modules, meeting the functional requirements of starting time ≤0.1s and starting current ≤1A. It also supports manual reset, adapting to the transformer's low-current testing scenario and avoiding functional failures due to module parameter mismatch.

[0186] 2.1 Calculation of Inductance and Magnetic Field Energy of Plant Substation

[0187] (1) Inductance calculation steps

[0188] Step 1: Calculate the phase voltage U phase

[0189] According to the formula Substituting V = 35000V, we get:

[0190] Step 2: Calculate inductive reactance

[0191] Assuming the no-load current is mainly composed of inductive components (the resistive component can be ignored because the no-load loss is relatively small):

[0192] I R ≈I no-load =1A

[0193]

[0194] Step 3: Calculate the inductance

[0195] Substituting, we get:

[0196] (2) Calculation of magnetic field energy when the test current is 3A

[0197] According to the formula for magnetic field energy Calculate the magnetic field energy based on the main transformer's test current of 3A:

[0198] When the test current I = 3A:

[0199]

[0200] 2.2 Calculation of discharge energy consumption of the plant transformer (total resistance is taken as 10Ω)

[0201] Calculate the process of discharging residual energy when the transformer has an unloaded current of 1A:

[0202] Initial energy

[0203]

[0204] time constant

[0205] Energy decay formula:

[0206]

[0207]

[0208] Formula for discharge current changing with time:

[0209]

[0210] Formula for discharge voltage changing with time: U peak =30V,

[0211]

[0212]

[0213] 2.3 Verification of the operation process of the protection device

[0214] 1. Self-test phase: The self-test circuit is activated, releasing energy ≥200kJ and current ≥20A (redundant coverage for low-energy scenarios in transformer substations). The buzzer and LED respond normally, indicating a successful self-test (e.g., ...). Figure 3 (As shown). The battery boost energy storage discharge circuit of the self-test circuit is assembled by purchasing finished modules. It can stably output an energy storage voltage of not less than 500V and a discharge current of not less than 20A, which is compatible with the self-test requirements of the plant transformer. There is no need to adjust the self-test module due to changes in equipment parameters, thus improving the versatility of the device.

[0215] 2. Wiring and Reverse Connection Test: Connect the wires according to the color coding (red connector for the positive terminal of the transformer). If the reverse connection alarm module does not alarm, the wiring is correct (e.g., ...). Figure 4(As shown). This reverse connection alarm module is assembled from finished modules. Its parameters of 1A start-up current and 2s alarm delay are suitable for low-voltage wiring scenarios in plant transformers, avoiding the alarm module failing to start due to low equipment voltage and ensuring effective wiring detection.

[0216] 3. Normal testing and abnormal protection:

[0217] Normal test: When the transformer is unloaded, start the DC resistance meter to output a 3A test current. The MUR2560 diode in the reverse discharge line is reverse cut off, which does not affect the measurement accuracy (e.g., Figure 1 As shown in the figure, the DC resistance meter completed the test normally.

[0218] Abnormal protection: If the circuit is interrupted, the magnetic field energy (289.49J) is released through the reverse discharge line, the diode conducts in the forward direction, and the energy is consumed through the 5Ω current-limiting resistor (e.g., Figure 5 (As shown); simultaneously, the counting alarm module starts within ≤0.1s, sounds an alarm, and records the event, posing no safety risk. The counting alarm module uses a purchased electrical pulse counter module with a starting voltage of 30V, which can trigger the module to start, ensuring the alarm and counting functions are implemented.

[0219] 4. Test Reset: Manually reset the counting alarm module; the device returns to its initial state (e.g., ...). Figure 2 (As shown).

[0220] 2.4 Verification of the protection performance of the device in Example 2

[0221] Maximum peak voltage: 30V << 600V (diode withstand voltage);

[0222] Maximum current: 1A << 200A (maximum inrush current of the diode);

[0223] Energy handling capacity: 289.49J << 200kJ (self-testing circuit capability);

[0224] Response time: Starts within 0.1 seconds;

[0225] Alarm function: An alarm can be triggered when the voltage fluctuates, ensuring that abnormality alerts are effective;

[0226] Recording function: Fully records discharge events;

[0227] Complete discharge: 99.9% of energy is consumed within 20 seconds.

[0228] Example verification conclusions

[0229] As can be seen from the above embodiments, this protection device meets the requirements of the invention in both main transformer (high current, high energy) and plant transformer (low current, low energy) scenarios:

[0230] The device composition and component selection are adapted to different equipment parameters. Core components such as dual-transistor parallel diodes and current-limiting resistors can safely withstand magnetic field energy (e.g., Figure 1 (as shown);

[0231] The calculation of discharge energy consumption can accurately reflect the energy consumption process over time, ensuring the safety of the experiment;

[0232] The working process fully covers the "self-test - wiring - test - protection - reset" procedure (e.g.) Figure 2 As shown in the figure, each functional module is accurately triggered, achieving dual protection for test personnel and equipment.

Claims

1. A DC resistance tester disconnection protection device, characterized in that, Includes reverse discharge line, counting alarm module, reverse connection alarm module and self-test circuit; The reverse discharge line is connected in parallel with the measurement circuit consisting of a DC resistance tester and the electromagnetic component under test. The counting alarm module is connected in parallel with the reverse discharge line. When a reverse discharge occurs in the measurement circuit, the module is used to trigger an alarm and record the discharge event. The reverse connection alarm module is connected to the forward and reverse connectors of the measurement circuit to monitor the wiring polarity and alert for errors; The self-test circuit is used to simulate a power failure scenario in the measurement circuit and to check whether the disconnection protection device is functioning properly.

2. The DC resistance tester disconnection protection device according to claim 1, characterized in that, The reverse discharge line includes a discharge diode and a discharge current-limiting resistor; The discharge diode is a dual-diode parallel configuration, with a reverse peak voltage of 600V, a forward current of 25A, a maximum inrush current of 200A, a reverse current of 0.5mA, and a forward voltage drop of 0.55V. The discharge current limiting resistor has a resistance of 5Ω and an overcurrent peak voltage of 600V.

3. The DC resistance tester disconnection protection device according to claim 2, characterized in that, The discharge process of the reverse discharge line follows an exponential decay law, and the formula for the change of discharge current I(t) with time t is: (Where I0 is the initial discharge current, R is the total resistance of the discharge circuit, and L is the inductance of the electromagnetic component under test), peak discharge voltage U peak =I0×R, where discharge duration is defined as the time required for the current to decay to 37% of its initial value, and time constant. The energy consumption of discharge follows the formula: (where W) 剩余 (t) represents the remaining energy at time t).

4. The DC resistance tester disconnection protection device according to claim 1, characterized in that, The counting alarm module is assembled from a finished electrical pulse counter module. Its starting voltage is 30V, the starting time is no more than 0.1s, the starting current is no more than 1A, and it needs to be manually reset after starting.

5. The DC resistance tester disconnection protection device according to claim 1, characterized in that, The self-test circuit is assembled using a battery boost energy storage discharge circuit module. The discharge energy of this circuit is not less than 200kJ, the discharge current is not less than 20A, and the energy storage voltage is not less than 500V. When the self-test circuit detection device functions normally, the buzzer in the circuit will sound and the LED will light up.

6. The DC resistance tester disconnection protection device according to claim 1, characterized in that, The reverse connection alarm module is assembled from finished modules. Its starting current is 1A and the starting delay time is 2s. When a wiring polarity error is detected, an alarm is triggered by a buzzer. The forward and reverse connectors of the measurement circuit are color-coded, with red for the positive terminal and black for the negative terminal.

7. The DC resistance tester disconnection protection device according to claim 1, characterized in that, The inductance value L of the electromagnetic component under test is calculated based on its no-load characteristics, including the following steps: Step 1: Calculate the inductive component of the no-load current I L The no-load current includes the inductive component I. L and resistive component I R The no-load current percentage is 0.1%, therefore the no-load current amplitude I no-load =I n ×0.1%; No-load loss P no-load (Three-phase total), phase voltage (V is the rated voltage, I) n (Rated current); Resistance component I R (per phase): Inductance component I L (per phase): Step 2: Calculate the inductance L: inductive reactance per phase inductance 8. The DC resistance tester disconnection protection device according to claim 1, characterized in that, The device's workflow includes five stages: pre-test self-test, device wiring and reverse connection detection, normal test, disconnection protection, and test end and reset. During the disconnection protection phase, when the measurement circuit is interrupted, the reverse discharge line is activated, and the magnetic field energy is determined according to the formula. The energy is released, and the counting alarm module is activated simultaneously, with energy consumption following...

9. The DC resistance tester disconnection protection device according to claim 8, characterized in that, During the pre-test self-test phase, if the device malfunctions after the self-test circuit is started, the fault must be investigated and the self-test repeated until the self-test is successful before proceeding to the next phase.

10. The DC resistance tester disconnection protection device according to claim 8, characterized in that, During the wiring and reverse connection detection phase of the device, if the reverse connection alarm module detects an incorrect wiring polarity, the buzzer will sound an alarm after a 2-second delay. Only after the staff corrects the wiring can the device enter the test-ready state.

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