Online inspection device for continuity of neutral protection conductor of three-phase five-wire system power supply system

Abstract

The utility model relates to the technical field of three-phase five-wire system power supply system frequency conversion driving elevator neutral protection conductor current detection, and especially relates to a three-phase five-wire system power supply system neutral protection conductor continuity on-line detection device. The current clamp grounding detection circuit comprises a grounding detection circuit and a current clamp, the grounding detection circuit comprises a current transformer and a current signal amplification circuit, and the current signal amplification circuit comprises a first amplification circuit, a second amplification circuit, a third amplification circuit and a fourth amplification circuit. A current signal which is output by the output end of the current transformer and collected by the current clamp sequentially passes through the first amplifying circuit, the second amplifying circuit and the third amplifying circuit and is finally output through the fourth amplifying circuit. In the process, the current signal is amplified step by step, and finally an undistorted current signal is obtained.

Description

Technical Field

[0001] The utility model relates to the technical field of current detection of neutral protection conductors of variable frequency driven elevators in three-phase five-wire power supply systems, in particular to an online detection device for the continuity of neutral protection conductors in three-phase five-wire power supply systems. Background Art

[0002] Grounding is essential for all types of electrical equipment that draws strong current. Typically, conductors are connected to the neutral point of the power system or electrical device, as well as to exposed conductive parts and external conductive parts of the device. Grounding can be categorized as working grounding, lightning protection grounding, and protective grounding.

[0003] For example, special equipment such as elevators require regular inspection, maintenance, and upkeep. One of the important inspection items is to check whether the elevator is safely grounded, whether the grounding conductor is continuous, and whether it has the ability to balance the charge of leakage, static electricity, electromagnetic interference, lightning (surge) and other electrical equipment of the elevator to the ground terminal of the power transformer to prevent electric shock accidents. The current flowing through the grounding conductor is usually harmonics, common mode, leakage and circuit grounding faults, etc. Small currents in the milliampere range that do not do work. When the current elevator is regularly inspected, such as Figure 1The diagram below shows the neutral conductor connection diagram for elevator electrical equipment. Nodes ① and ③ of the elevator system are hundreds of meters away from the elevator machine room at the top of the building. The electrical connections at each conductor end are visually blind, making it impossible to verify the continuity of the conductor. Although measuring the ground resistance at node ③ using a ground resistance meter can also confirm the continuity of the ground conductor, this method is limited by the inability to measure live ground voltage and the short probe lead length of only 20 meters. Therefore, this method is only theoretically feasible. Given the inherent harmonics and common-mode voltages between inverters, motors, and other equipment in variable-frequency drive systems, detecting current flowing through node ③, even under continuous power conditions, indicates that the conductors at nodes ① and ③ are continuous and not disconnected. However, current clamp meters use a current clamp to acquire electrical signals and then amplify them using a traditional operational amplifier. Whenever a traditional operational amplifier changes state (power on, power off, or switches to low-power mode), the output DC blocking capacitor charges and discharges, generating significant noise. Even the moment a chip powers on or off, as well as some possible operations after powering on and stabilizing, can cause transient surges, generating so-called "pop" noise at the device's output. Furthermore, the op amp's inverting and non-inverting inputs and the transistor's base require a fixed DC bias level to ground for proper operation. Therefore, if an op amp or transistor is used as a signal input circuit, capacitors must be used to isolate the DC bias potential. Using capacitive coupling also results in capacitive reactance attenuating AC signals of varying frequencies, leading to signal distortion.

[0004] Therefore, a high-gain, high-fidelity detection device is needed to amplify weak common-mode and harmonic current signals to a level that can be recognized by an oscilloscope. Utility Model Content

[0005] To address the shortcomings of existing technologies, this utility model provides an online device for verifying the continuity of the neutral conductor in a three-phase, five-wire power supply system. By using a multi-stage amplifier to amplify circuit signals, this device addresses the issues of current clamps being bulky, subject to signal distortion, and insufficient amplification. It also addresses the challenge of accurately determining the complete separation of the neutral and ground conductors in a TN-S power supply system without power outages.

[0006] The utility model discloses, through an embodiment, an online test device for the continuity of a neutral protective conductor in a three-phase five-wire power supply system. The device comprises a ground detection circuit, the ground detection circuit including a current transformer and a current signal amplification circuit, wherein the current signal amplification circuit includes a first amplification circuit, a second amplification circuit, a third amplification circuit, and a fourth amplification circuit. The output end of the current transformer is connected to the input end of the first amplification circuit, the output end of the first amplification circuit is connected to the input end of the second amplification circuit, the output end of the second amplification circuit is connected to the input end of the third amplification circuit, the output end of the third amplification circuit is connected to the input end of the fourth amplification circuit, and the output end of the fourth amplification circuit serves as the output end of the current signal amplification circuit.

[0007] Furthermore, the output end of the current transformer is also connected to a grounded first capacitor for filtering out harmonic voltages generated by the LED lighting device and the like in the node current.

[0008] Furthermore, the output end of the current transformer is also connected to a grounded bidirectional amplitude limiting circuit, which can effectively prevent the input signal from being overloaded.

[0009] Furthermore, the first amplifier circuit includes a first field-effect transistor and a second field-effect transistor. The gate of the first field-effect transistor is connected to the output terminal of the current transformer and is also connected to a grounded first resistor. The source of the first field-effect transistor serves as the output terminal of the first amplifier circuit and is also connected to a positive power supply via a second resistor. The source of the second field-effect transistor is connected to the positive power supply via a fifth resistor. The drain of the first field-effect transistor and the drain of the second field-effect transistor are connected via two ends of a variable resistor, and the middle end of the variable resistor is grounded via a fourth resistor and a third resistor.

[0010] Furthermore, the second amplifier circuit includes a first NPN-type transistor and a second NPN-type transistor. The base of the first transistor is connected to the source of the first field-effect transistor, and the collector of the first transistor is connected to a positive power supply. The base of the second transistor is connected to the source of the second field-effect transistor, and the collector of the second transistor serves as the output of the second amplifier circuit. The collector of the second transistor is also connected to the positive power supply via an eighth resistor. The emitter of the first transistor is connected to the emitter of the second transistor and then to ground via a seventh resistor.

[0011] Furthermore, the third amplifier circuit includes a third PNP-type transistor. The base of the third transistor is connected to the collector of the second transistor; the collector of the third transistor is connected to the forward power supply via a fifteenth resistor; the collector of the third transistor serves as the output terminal of the third amplifier circuit; the gate of the second field-effect transistor is connected to the collector of the third transistor via a ninth resistor and a thirteenth resistor; the collector of the third transistor is also connected to the collector of a fourth NPN-type transistor, which serves as a constant current source load for the third transistor; the emitter of the fourth transistor is connected to the reverse power supply via a fourteenth resistor, and the base of the fourth transistor is connected to the forward power supply via a sixteenth resistor.

[0012] Furthermore, the fourth amplifier circuit includes an NPN-type fifth transistor, an NPN-type sixth transistor, and a PNP-type seventh transistor. The base of the fifth transistor is connected to the collector of the third transistor via an eighteenth resistor; the collector of the fifth transistor is connected to the positive power supply via a twentieth resistor; the emitter of the fifth transistor is connected to the emitter of the sixth transistor, and the emitter of the fifth transistor is further connected to a grounded twenty-first resistor; the base of the sixth transistor is connected to a grounded twenty-second resistor, and the collector of the sixth transistor is connected to the positive power supply; the emitter of the seventh transistor is connected to the positive power supply; the base of the seventh transistor is connected to the collector of the fifth transistor; a twenty-third resistor is connected between the collector of the seventh transistor and the base of the sixth transistor; and the collector of the seventh transistor serves as the output terminal of the fourth amplifier circuit.

[0013] To achieve the above objectives, the present invention also includes a current clamp for picking up current signals. The ground detection circuit and current clamp together form an online continuity test device for the neutral conductor of a three-phase, five-wire power supply system. This device is used to detect whether the ground wire is grounded successfully and amplify the signal obtained.

[0014] The technical principle of the utility model is: a weak current signal is collected by a current transformer, and then the signal is amplified step by step through a first amplification circuit, a second amplification circuit, a third amplification circuit and a fourth amplification circuit, and finally an undistorted current signal is obtained.

[0015] Compared with the prior art, the present invention has the following beneficial effects: it can amplify the current signal without distortion and obtain a detection result with higher accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solution of the present invention and facilitate a further understanding of the technical effects, technical features and purposes of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings. The accompanying drawings constitute an essential part of the specification and are used together with the embodiments of the present invention to illustrate the technical solution of the present invention, but do not constitute a limitation to the present invention.

[0017] Figure 1 This is a schematic diagram of the neutral protection conductor connection of the elevator electrical equipment described in the background technology of this utility model;

[0018] Figure 2 A schematic block diagram of a ground detection circuit according to the present invention;

[0019] Figure 3 A circuit diagram of a ground detection circuit according to the present invention;

[0020] Figure 4 This is a schematic diagram of the current clamp described in the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. Of course, the specific embodiments described below are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Furthermore, the portions described in the embodiments or drawings are merely illustrative of the relevant portions of the present invention and are not intended to be exhaustive. All other embodiments derived by those of ordinary skill in the art based on the embodiments of the present invention are intended to fall within the scope of protection of the present invention.

[0022] like Figure 2 、 3 As shown, the present invention provides an online continuity test device for the neutral protective conductor of a three-phase five-wire power supply system through the following embodiments. The device includes a ground detection circuit, which includes a current transformer HL and a current signal amplification circuit. The current signal amplification circuit includes a first amplification circuit, a second amplification circuit, a third amplification circuit, and a fourth amplification circuit. The output end of the current transformer is connected to the input end of the first amplification circuit, the output end of the first amplification circuit is connected to the input end of the second amplification circuit, the output end of the second amplification circuit is connected to the input end of the third amplification circuit, the output end of the third amplification circuit is connected to the input end of the fourth amplification circuit, and the output end of the fourth amplification circuit serves as the output end of the current signal amplification circuit.

[0023] like Figure 3 As shown, in this embodiment, the output end of the current transformer HL is further connected to a grounded first capacitor C1 for filtering out harmonic voltages generated by the LED lighting device and the like in the node current.

[0024] like Figure 3 As shown, in this embodiment, the output end of the current transformer HL is further connected to a grounded bidirectional amplitude limiting circuit, which can effectively prevent the input signal from being overloaded. The bidirectional amplitude limiting circuit is composed of two diodes D1 and D2.

[0025] like Figure 3 As shown, in this embodiment, the first amplifier circuit includes a differential amplifier formed by a first field-effect transistor Q1 and a second field-effect transistor Q2. The gate of the first field-effect transistor Q1 is connected to the output terminal of the current transformer HL and is also connected to a grounded first resistor R1. The source of the first field-effect transistor Q1 serves as the output terminal of the first amplifier circuit and is also connected to a positive power supply via a second resistor R2. The source of the second field-effect transistor Q2 is connected to the positive power supply via a fifth resistor R5. The drain of the first field-effect transistor Q1 and the drain of the second field-effect transistor Q2 are connected via two ends of a varistor W01, and the middle end of the varistor W01 is grounded via a fourth resistor R4 and a third resistor R3.

[0026] like Figure 3 As shown, in this embodiment, the second amplifier circuit includes a differential amplifier formed by a first NPN transistor BG1 and a second NPN transistor BG2, which operates in an extended linear region. The base of the first transistor BG1 is connected to the source of the first field-effect transistor Q1, and the collector of the first transistor BG1 is connected to a positive power supply. The base of the second transistor BG2 is connected to the source of the second field-effect transistor Q2, and the collector of the second transistor BG2 serves as the output of the second amplifier circuit. The collector of the second transistor BG2 is also connected to the positive power supply via an eighth resistor R8. The emitter of the first transistor BG1 is connected to the emitter of the second transistor BG2 and is then grounded via a seventh resistor R7.

[0027] like Figure 3 As shown, in this embodiment, the third amplifier circuit includes a single-tube Class A amplifier formed by a third PNP transistor BG3, which can output signals with low impedance, achieving high dynamic range and gain. The base of the third transistor BG3 is connected to the collector of the second transistor BG2; the collector of the third transistor BG3 is connected to the forward power supply via a fifteenth resistor R15; the collector of the third transistor BG3 serves as the output terminal of the third amplifier circuit; the gate of the second field-effect transistor Q2 is connected to the collector of the third transistor BG3 via a ninth resistor R9 and a thirteenth resistor R13; the collector of the third transistor BG3 is also connected to the collector of a fourth NPN transistor BG4, which serves as a constant current source load for the third transistor BG3; the emitter of the fourth transistor BG4 is connected to the reverse power supply via a fourteenth resistor R14, and the base of the fourth transistor BG4 is connected to the forward power supply via a sixteenth resistor R16.

[0028] like Figure 3 As shown, in this embodiment, the fourth amplifying circuit includes a differential amplifier consisting of an NPN fifth transistor BG5, an NPN sixth transistor BG6 and a PNP seventh transistor BG7, and outputs the electrical signal in the form of low impedance. The base of the fifth transistor BG5 is connected to the collector of the third transistor BG3 via an eighteenth resistor R18; the collector of the fifth transistor BG5 is connected to the forward power supply via a twentieth resistor R20; the emitter of the fifth transistor BG5 is connected to the emitter of the sixth transistor BG6, and the emitter of the fifth transistor BG5 is further connected to a grounded twenty-first resistor R21; the base of the sixth transistor BG6 is connected to a grounded twenty-second resistor R22, and the collector of the sixth transistor BG6 is connected to the forward power supply; the emitter of the seventh transistor BG7 is connected to the forward power supply; the base of the seventh transistor BG7 is connected to the collector of the fifth transistor BG5; a twenty-third resistor R23 is connected between the collector of the seventh transistor BG7 and the base of the sixth transistor BG6; the collector of the seventh transistor BG7 serves as the output end of the fourth amplifier circuit. Use an oscilloscope to observe the output signal waveform, and judge whether the ground and neutral wires of the three-phase five-wire TN-S power supply system are completely separated based on the difference that the neutral wire waveform is a sine wave and the ground wire waveform is a non-sinusoidal wave (if the waveforms of the ground wire and neutral wire are the same, it means that the ground and neutral wires are mixed and not separated).

[0029] like Figure 3 As shown, in the circuit diagram of this embodiment, there are also components such as capacitor C3, capacitor C4, resistor R1, etc. that play the role of isolation and interference reduction in the circuit. They belong to the existing technology and are not described in detail in this embodiment.

[0030] like Figure 4 As shown, the present invention also includes a current clamp for picking up current signals. It features a wide opening and a small-section clamp arm. The ground detection circuit and current clamp together form an online device for verifying the continuity of the neutral conductor in a three-phase, five-wire power supply system. The current transformer is located in the clamp head (1) and the current signal amplifier is located in the clamp handle (2). These devices are used to detect the continuity of the ground wire and amplify the signal picked up by the current clamp.

[0031] It should be noted that the above embodiments are only for more clearly illustrating the technical solutions of the present invention. Those skilled in the art will understand that the implementation methods of the present invention are not limited to the above contents, and obvious changes, replacements or substitutions based on the above contents do not exceed the scope covered by the technical solutions of the present invention; without departing from the concept of the present invention, other implementation methods will naturally fall within the scope of the present invention.

Claims

1. An online device for testing the continuity of the neutral protective conductor of a three-phase five-wire power supply system, comprising a ground detection circuit, the ground detection circuit including a current transformer and a current signal amplification circuit, and characterized by: The current signal amplifying circuit includes a first amplifying circuit, a second amplifying circuit, a third amplifying circuit and a fourth amplifying circuit; The output end of the current transformer is connected to the input end of the first amplifier circuit, the output end of the first amplifier circuit is connected to the input end of the second amplifier circuit, the output end of the second amplifier circuit is connected to the input end of the third amplifier circuit, the output end of the third amplifier circuit is connected to the input end of the fourth amplifier circuit, and the output end of the fourth amplifier circuit serves as the output end of the current signal amplifier circuit.

2. The online test device for the continuity of the neutral protective conductor of a three-phase five-wire power supply system according to claim 1, characterized in that: The output end of the current transformer is further connected to a first grounded capacitor.

3. The online continuity test device for the neutral protective conductor of a three-phase five-wire power supply system according to claim 1, characterized in that: The output end of the current transformer is also connected to a grounded bidirectional amplitude limiting circuit.

4. The online continuity test device for the neutral protective conductor of a three-phase five-wire power supply system according to claim 1, characterized in that: The first amplifying circuit includes a first field effect transistor and a second field effect transistor; The gate of the first field effect transistor is connected to the output end of the current transformer, and the gate of the first field effect transistor is also connected to a grounded first resistor; the source of the first field effect transistor serves as the output end of the first amplifier circuit, and the source of the first field effect transistor is also connected to a positive power supply through a second resistor; The source of the second field effect transistor is connected to the positive power supply through a fifth resistor; The drain of the first field effect transistor and the drain of the second field effect transistor are connected through two ends of a varistor, and a middle end of the varistor is grounded through a fourth resistor and a third resistor.

5. The online continuity test device for the neutral protective conductor of a three-phase five-wire power supply system according to claim 4, characterized in that: The second amplifying circuit includes a first NPN transistor and a second NPN transistor; The base of the first transistor is connected to the source of the first field effect transistor, and the collector of the first transistor is connected to a positive power supply; The base of the second transistor is connected to the source of the second field effect transistor, the collector of the second transistor serves as the output end of the second amplifier circuit, and the collector of the second transistor is further connected to the positive power supply via an eighth resistor; The emitter of the first transistor and the emitter of the second transistor are connected to ground via a seventh resistor.

6. The online continuity test device for the neutral protective conductor of a three-phase five-wire power supply system according to claim 5, characterized in that: The third amplifying circuit includes a third PNP transistor; The base of the third transistor is connected to the collector of the second transistor; The collector of the third transistor is connected to the positive power supply through the fifteenth resistor; The collector of the third triode serves as the output end of the third amplifier circuit; The gate of the second field effect transistor is connected to the collector of the third transistor through a ninth resistor and a thirteenth resistor; The collector of the third transistor is also connected to the collector of an NPN-type fourth transistor, and the fourth transistor serves as a constant current source load for the third transistor; the emitter of the fourth transistor is connected to a reverse power supply through a fourteenth resistor, and the base of the fourth transistor is connected to a forward power supply through a sixteenth resistor.

7. The online continuity test device for the neutral protective conductor of a three-phase five-wire power supply system according to claim 6, characterized in that: The fourth amplifying circuit includes an NPN-type fifth transistor, an NPN-type sixth transistor, and a PNP-type seventh transistor; The base of the fifth transistor is connected to the collector of the third transistor via an eighteenth resistor; The collector of the fifth transistor is connected to the positive power supply via the twentieth resistor; The emitter of the fifth transistor is connected to the emitter of the sixth transistor, and the emitter of the fifth transistor is further connected to a twenty-first resistor connected to ground; The base of the sixth transistor is connected to a grounded twenty-second resistor, and the collector of the sixth transistor is connected to a positive power supply; The emitter of the seventh transistor is connected to the forward power supply; The base of the seventh transistor is connected to the collector of the fifth transistor; A twenty-third resistor is connected between the collector of the seventh transistor and the base of the sixth transistor; The collector of the seventh transistor serves as the output end of the fourth amplifier circuit.

8. The online continuity test device for the neutral protective conductor of a three-phase five-wire power supply system according to claim 1, characterized in that: A current clamp is also included for collecting current signals.

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