A withstand voltage tester grounding protection circuit and a withstand voltage tester

Abstract

The utility model discloses a kind of grounding protection circuit and withstand voltage tester of withstand voltage tester, and the protection circuit includes: current transformer B1, signal processing circuit and control unit MCU. The primary side of current transformer B1 is connected in series between the high-voltage tail of withstand voltage tester and ground wire, for monitoring ground fault current. Signal processing circuit is connected with the secondary side of current transformer B1, when the ground fault current sensed exceeds preset threshold, output protection trigger signal. After control unit MCU receives the signal, withstand voltage tester is immediately controlled to disconnect high-voltage output. The utility model can reliably detect the ground fault current bypassing conventional sampling resistance by setting independent current monitoring channel on total grounding circuit, and protection response is quickly made, effectively avoid the risk that high-voltage transformer is burnt due to overcurrent, improve the reliability and security of instrument.

Description

Technical Field

[0001] This utility model relates to the field of electrical testing equipment technology, specifically a grounding protection circuit for a withstand voltage tester and a withstand voltage tester. Background Technology

[0002] Withstand voltage testing is a crucial step in testing the insulation performance of various electrical devices and insulating materials. Its basic principle involves applying a high voltage, exceeding the product's normal operating voltage, for a specified period. The reliability of the insulation structure is assessed by monitoring whether the breakdown current remains within a specified range during this process.

[0003] like Figure 1 The diagram shown illustrates a typical withstand voltage tester in the prior art. During testing, the mains power is boosted by a voltage regulator and a high-voltage transformer, and then applied to the product under test through the high-voltage terminal. Current flows through the product under test to the test terminal, and then returns to the high-voltage tail of the high-voltage transformer through the sampling resistor R1. The high-voltage tail is typically connected to the equipment ground wire. The control unit (MCU) calculates the loop current by monitoring the voltage across the sampling resistor R1, thereby achieving overcurrent protection.

[0004] This design works well under normal testing conditions. However, in actual operation, the product under test (DUT) may come into direct contact with the ground due to improper placement or structural issues, or the test terminal of the test fixture may accidentally become grounded. In this case, high-voltage current will flow directly into the ground through the DUT and then return to the high-voltage tail via the ground wire, thus bypassing the sampling resistor R1. This causes the control unit (MCU) to fail to detect the ground fault current, even if the current is already very large. If the ground fault current exceeds the rated load of the high-voltage transformer, and the control unit (MCU) fails to take timely protective action, the high-voltage transformer will burn out due to overcurrent, causing permanent damage to the withstand voltage tester.

[0005] Therefore, how to effectively monitor and protect against fault currents caused by accidental grounding of the tested product is an urgent problem to be solved in existing withstand voltage tester technology. Utility Model Content

[0006] To address the shortcomings of existing technologies, this utility model provides a grounding protection circuit for a withstand voltage tester and a withstand voltage tester, thus solving the aforementioned problems.

[0007] To achieve the above objectives, this utility model provides the following technical solution: a grounding protection circuit for a withstand voltage tester, comprising: Current transformer B1, whose primary side is connected in series between the high voltage tail of the high voltage circuit of the withstand voltage tester and the equipment ground wire, is used to sense the ground fault current flowing from the high voltage tail to the ground wire. The signal processing circuit is connected to the secondary side of the current transformer B1 and is used to convert the ground fault current into a voltage signal and compare the voltage signal with a preset reference voltage. When the voltage signal exceeds the reference voltage, a protection trigger signal is output. The control unit MCU is connected to the output terminal of the signal processing circuit to receive the protection trigger signal and control the withstand voltage tester to disconnect the high voltage output according to the signal.

[0008] Preferably, the signal processing circuit includes: The comparator IC7A has a first input terminal for receiving the voltage signal, a second input terminal for receiving the reference voltage, and an output terminal for outputting the protection trigger signal.

[0009] Preferably, the signal processing circuit further includes a detection and amplification circuit disposed between the secondary side of the current transformer B1 and the first input terminal of the comparator IC7A, for detecting and amplifying the AC signal induced on the secondary side of the current transformer B1 to generate the voltage signal.

[0010] Preferably, the signal processing circuit further includes: The switching transistor is a PNP transistor, and its control terminal is connected to the output terminal of the comparator IC7A. The input terminal of the optocoupler U1 is connected in series with the output circuit of the PNP switching transistor; The output terminal of the optocoupler U1 is connected to the control unit MCU, and is used to transmit the protection trigger signal to the control unit MCU after electrical isolation.

[0011] Preferably, the signal processing circuit further includes a reference voltage adjustment unit VAC0, used to adjust the magnitude of the reference voltage to set the current threshold for grounding protection.

[0012] This utility model also provides a withstand voltage tester, including the grounding protection circuit of the withstand voltage tester described in any of the above claims.

[0013] Beneficial effects This utility model provides a grounding protection circuit for a withstand voltage tester and a withstand voltage tester. Compared with the prior art, it has the following advantages: (1) The grounding protection circuit and the withstand voltage tester of this withstand voltage tester can effectively monitor the grounding fault current that bypasses the conventional test circuit by connecting the current transformer B1 in series on the main grounding circuit. This makes up for the blind spot of the traditional protection circuit and avoids the risk of the high voltage transformer burning out due to the accidental grounding of the tested product. Once a grounding fault occurs, the protection circuit can quickly sense the current and compare it with the set threshold, triggering the control unit MCU to immediately cut off the high voltage. The protection action is timely and reliable, effectively protecting the core components of the instrument. The optocoupler U1 is used to isolate the protection signal of the high voltage part from the control unit MCU of the low voltage part, avoiding interference from the high voltage side to the core control system, and improving the stability and safety of the whole machine.

[0014] (2) The grounding protection circuit and the circuit structure of the withstand voltage tester are simple, the added components have low cost, and it is easy to integrate into the existing withstand voltage tester design. It has high economic and practical value. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the principle of an existing pressure resistance tester in the background technology of this utility model; Figure 2 This is a schematic diagram of the principle of the pressure resistance tester of this utility model; Figure 3 This is a circuit diagram of the grounding protection circuit of the withstand voltage tester of this utility model. Detailed Implementation

[0016] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0017] Example: Please see Figure 2-3 This invention provides a grounding protection circuit for a withstand voltage tester, used in the tester to provide protection when the product under test is accidentally grounded. This protection circuit adds a bypass protection system specifically for monitoring grounding fault current to the original high-voltage circuit of the withstand voltage tester. Specifically, the circuit includes a current transformer B1, a signal processing circuit, and a control unit (MCU).

[0018] The primary side of current transformer B1 is connected in series between the high-voltage tail of the withstand voltage tester's high-voltage transformer and the equipment ground (GND). During normal testing, the current flows from the test terminal back to the high-voltage tail via the sampling resistor R1, theoretically bypassing the ground; therefore, virtually no current flows through current transformer B1. However, when the product under test or the test terminal is accidentally grounded, the high-voltage current will bypass the sampling resistor R1 and flow directly back to the high-voltage tail through the ground. In this case, the ground fault current will inevitably flow through the primary side of current transformer B1.

[0019] The signal processing circuit is connected to the secondary side of current transformer B1. When a ground fault current flows through the primary side of current transformer B1, an AC current is induced on its secondary side according to the turns ratio. This AC current first flows through a sampling resistor (R1 between B1-1 and B1-2 in the figure), generating an AC voltage signal across it.

[0020] Subsequently, the AC voltage signal is fed into a detector amplifier circuit (consisting of IC5A, IC5B, and their peripheral components as shown in the figure). The detector amplifier circuit performs, for example, half-wave or full-wave detection on the signal and amplifies it, converting it into a DC or pulsating DC voltage signal proportional to the amplitude of the ground fault current.

[0021] The voltage signal is sent to one input (e.g., the non-inverting input) of comparator IC7A (as shown in the figure, model LM393). The other input (e.g., the inverting input) of comparator IC7A is connected to an adjustable reference voltage. This reference voltage is provided by the reference voltage adjustment unit VAC0 (as shown by potentiometer VAC0 in the figure). By adjusting this potentiometer, the current threshold for protection operation can be easily set. For example, this threshold can be set slightly below the rated maximum current of the high-voltage transformer.

[0022] When the ground fault current is small and the voltage signal after detection and amplification is lower than the reference voltage, comparator IC7A outputs a stable level (e.g., low level). When the ground fault current exceeds the set threshold and the voltage signal after detection and amplification is higher than the reference voltage, the output level of comparator IC7A flips (e.g., becomes high level), and outputs a protection trigger signal.

[0023] The protection trigger signal drives a PNP switching transistor (as shown in the figure, PNP transistor 9012). When the comparator IC7A outputs a high level, the PNP switching transistor is turned on.

[0024] The input terminal (i.e., light-emitting diode) of an optocoupler U1 is connected in series in the collector circuit of the PNP switching transistor. When the PNP switching transistor is turned on, current flows through the light-emitting diode of the optocoupler U1, causing it to emit light.

[0025] The output terminal (i.e., phototransistor) of optocoupler U1 is connected to an I / O port of the control unit MCU. When its input terminal emits light, the phototransistor at its output terminal conducts, outputting a signal (e.g., low level) to the control unit MCU.

[0026] The control unit MCU continuously monitors the level of this I / O port. Once a valid protection signal (e.g., low level) is received from the optocoupler U1, the control unit MCU immediately executes the preset protection program, such as immediately disconnecting the relay JK4 that drives the primary of the high-voltage transformer, thereby instantly cutting off the high-voltage output, and simultaneously driving the buzzer or display screen to issue an audible and visual alarm, prompting the operator that the equipment has a grounding fault.

[0027] Through the above structure, this invention constructs a ground fault protection channel independent of conventional test circuits. Regardless of where the ground fault occurs, as long as a large current path to ground is formed, the current transformer B1 can capture the current and drive the subsequent circuit to respond rapidly within microseconds or milliseconds. The control unit MCU then cuts off the high voltage, thereby effectively protecting the safety of the expensive high-voltage transformer and the entire equipment.

[0028] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0029] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0030] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A grounding protection circuit for a withstand voltage tester, characterized in that, include: Current transformer B1, whose primary side is connected in series between the high voltage tail of the high voltage circuit of the withstand voltage tester and the equipment ground wire, is used to sense the ground fault current flowing from the high voltage tail to the ground wire. The signal processing circuit is connected to the secondary side of the current transformer B1 and is used to convert the ground fault current into a voltage signal and compare the voltage signal with a preset reference voltage. When the voltage signal exceeds the reference voltage, a protection trigger signal is output. The control unit MCU is connected to the output terminal of the signal processing circuit to receive the protection trigger signal and control the withstand voltage tester to disconnect the high voltage output according to the signal.

2. The grounding protection circuit for a withstand voltage tester according to claim 1, characterized in that, The signal processing circuit includes: The comparator IC7A has a first input terminal for receiving the voltage signal, a second input terminal for receiving the reference voltage, and an output terminal for outputting the protection trigger signal.

3. The grounding protection circuit for a withstand voltage tester according to claim 2, characterized in that, The signal processing circuit further includes a detection and amplification circuit located between the secondary side of the current transformer B1 and the first input terminal of the comparator IC7A, for detecting and amplifying the AC signal induced on the secondary side of the current transformer B1 to generate the voltage signal.

4. The grounding protection circuit for a withstand voltage tester according to claim 3, characterized in that, The signal processing circuit further includes: The switching transistor is a PNP transistor, and its control terminal is connected to the output terminal of the comparator IC7A. The input terminal of the optocoupler U1 is connected in series with the output circuit of the PNP switching transistor; The output terminal of the optocoupler U1 is connected to the control unit MCU, and is used to transmit the protection trigger signal to the control unit MCU after electrical isolation.

5. A grounding protection circuit for a withstand voltage tester according to claim 4, characterized in that, The signal processing circuit also includes a reference voltage adjustment unit VAC0, which is used to adjust the magnitude of the reference voltage to set the current threshold for grounding protection.

6. A withstand voltage tester, characterized in that, The grounding protection circuit for the withstand voltage tester includes any one of claims 1 to 5.

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