Grounding wire monitoring system and grounding inspection device for the grounding wire of mobile electrical equipment

Abstract

The present invention relates to a ground wire monitoring system and a ground connection inspection device for a mobile electrical equipment ground wire. The device has a terminal +, a terminal -, a reference source, a constant current source circuit, and a voltage detection circuit. The reference source is arranged adjacent to the ground point PE of the mobile electrical equipment, its anode is electrically connected to the ground point PE, and the cathode is connected to the terminal +. The ground point PE is connected to the ground busbar PE of the power grid through a ground wire, and the ground busbar PE is connected to the terminal -. The constant current source circuit includes a constant current source and a resistor R1. The constant current generated by the constant current source is output to the terminal + and flows back to the constant current source from the terminal -. The terminal - is connected to the common terminal COM through the resistor R1. The voltage detection circuit is used to obtain the voltage drop signal between the terminal + and the terminal -. The present invention is used to ensure the true electrical safety of the electrical equipment monitored by the ground wire monitor and prevent leakage accidents from occurring.

Description

Technical Field

[0001] The present invention relates to safety guarantee devices in the field of power electronics, and particularly to a ground wire monitoring system and a ground wire grounding inspection device for a mobile electrical equipment. Background Art

[0002] Large mobile devices such as mining shovels, quay-side cranes, stacker reclaimers, portable conveyors, shore-to-ship, etc. all use drag cables for power supply during operation. During operation, the failure rate of the dragged rubber-sheathed cable is relatively high, and insulation damage occurs frequently. In the light case, the insulation resistance decreases, and in the heavy case, electric leakage occurs. Once electric leakage occurs, the personnel on the mobile device are prone to casualties due to electric shock. Although the metal shell of the device is insulated from the live part and the shell will not be energized, if the insulator inside the electrical appliance ages or is damaged, electricity may be transmitted to the metal shell. If the shell is not grounded, people will get an electric shock when touching it. If the metal shell is grounded, the current will flow into the ground through the ground wire, and people will not get an electric shock when touching the energized metal shell. Grounding is to use a relatively thick wire, connect one end of it to the device shell, and the other end to the grounding busbar PE of the power grid. This connecting wire is called the ground wire. The ground wire is a wire directly connected to the earth, and can also be called a safety return wire. In case of danger, it directly transfers the high voltage to the earth. It is a life-saving wire, as Figure 1 shown.

[0003] The rubber-sheathed cable of the mobile electrical equipment using drag cable for power supply has a relatively high failure rate and is more prone to electric leakage accidents. Moreover, like the drag cable, the ground wire is also moving and dragging, and is prone to disconnection or poor contact. And the disconnection or poor contact of the ground wire is not easy to be found during production operation. Even if it is disconnected, the device can still work normally. Only when electric leakage causes personal injury will the grounding condition of the device be checked. The grounding inspection before and during the operation of the device is often ignored. Therefore, it is necessary to monitor the grounding condition of the ground wire of the mobile electrical equipment using drag cable for power supply in real time. Once it is found that the ground wire is disconnected or has poor contact, an alarm will be given immediately and the power supply of the device will be disconnected, and the device is prohibited from continuing to work when the ground wire is disconnected or has poor contact.

[0004] For on-line monitoring of the ground wire, such as Figure 2The voltage on-off detection method shown in the figure. The +5V power supply of the ground wire monitor is output to the ground point PE of the mobile device through the resistor R1, and the COM terminal of the +5V power supply is connected to the PE of the grounding bar. When the PE point of the mobile device is connected to the PE point of the grounding bar, the voltage value detected by the voltage detection circuit of the ground wire monitor is 0V or a voltage value close to 0V; if the ground wire is disconnected, the voltage value detected by the voltage detection circuit of the ground wire monitor is 5V or a value close to 5V. The MCU in the monitor can judge the on-off situation of the ground connection by sampling the voltage of the ground detection circuit. If a voltage value of 5V or close to 5V is detected, it is judged that the ground wire is disconnected, and the MCU controls KJ1 to disconnect, cutting off the main power circuit of the mobile device.

[0005] In this detection method, the ground detection line and the ground wire are regarded as resistor R, which is connected in series with resistor R1. The +5V power supply is applied to the series resistor of R1 and R. Assuming that resistor R does not exceed 100Ω and resistor R1 in the monitor is 1000Ω, a measured voltage U≤1V of the voltage detection circuit indicates that the ground wire is grounded normally.

[0006] This detection method has both advantages and disadvantages.

[0007] Advantages:

[0008] Simple and easy to implement.

[0009] Disadvantages:

[0010] 1) When the ground detection line is short-circuited, it creates an illusion that the mobile device is reliably grounded, so that the monitor MCU always thinks that the ground wire is well grounded. Because both a short-circuited ground detection line and a well-grounded ground wire will cause the voltage detection circuit of the monitor to detect a voltage value of 0V or ≤1V. As shown in the figure. Using the constant voltage source method, after the peripheral circuit resistance is short-circuited, the voltage across resistor R1 in the monitor increases, the loss increases, resulting in a temperature rise, and even catches fire and burns, damaging the monitor. Figure 3 As shown. Using the constant voltage source method, after the peripheral circuit resistance is short-circuited, the voltage across resistor R1 in the monitor increases, the loss increases, resulting in a temperature rise, and even catches fire and burns, damaging the monitor.

[0011] 2) Using the method of resistance voltage division for detection, the larger the line resistance R, the smaller the current in the line. Coupled with a long detection line, the detection circuit is easily affected by electromagnetic interference. That is to say, the distance between the monitor and the mobile device cannot be too long. If it is too long, it will cause a large resistance of the ground detection line, a small current in the line, and be easily affected by electromagnetic interference, causing the MCU to misreport the ground wire fault and reducing the reliability of the ground wire monitor.

[0012] In response to this, the present invention adopts the constant current source + reference source method, which not only increases the detection distance, but also can accurately detect whether the ground wire is well grounded and whether the ground detection line is short-circuited. Summary of the Invention

[0013] The object of the present invention is to enable the electrical equipment monitored by the earthing wire monitor to be truly safe in power use and prevent electric leakage accidents from occurring.

[0014] To achieve the above object, a grounding inspection device for the earthing wire of a mobile electrical equipment is provided, which includes a terminal +, a terminal -, a reference source, a constant current source circuit, and a voltage detection circuit;

[0015] The reference source is arranged adjacent to the earthing point PE of the mobile electrical equipment, its anode is electrically connected to the earthing point PE, and its cathode is connected to the terminal + through a first earthing detection wire. The earthing point PE is connected to the earthing busbar PE of the power grid through an earthing wire, and the earthing busbar PE is connected to the terminal - through a second earthing detection wire;

[0016] The constant current source circuit includes a constant current source and a resistor R1. The constant current generated by the constant current source is output to the terminal + and flows back to the constant current source from the terminal -. The terminal - is connected to the common terminal COM through the resistor R1;

[0017] The voltage detection circuit is used to obtain the voltage drop signal between the terminal + and the terminal -.

[0018] Further, the constant current source circuit further includes a triode Q1, a resistor R2, and a resistor R3. The collector of the triode Q1 is connected to the terminal -, the emitter is connected to the common terminal COM through the resistor R1, and the base is used to obtain the voltage drop of the resistor R3 in the voltage dividing branch composed of the resistor R2 and the resistor R3.

[0019] Further, the constant current output by the constant current source

[0020] Further, the reference source is a reference diode.

[0021] Further, the voltage detection circuit includes an operational amplifier U2A, a resistor R5, a resistor R11, a capacitor C1, and a capacitor C5. The positive input terminal of the operational amplifier U2A is connected to the terminal - and is connected to the common terminal COM through the resistor R5. The negative input terminal of the operational amplifier U2A is connected to the terminal + and is connected to its output terminal through the resistor R11. The capacitor C1 is connected in parallel with the resistor R11, and the capacitor C5 is connected in parallel with the resistor R5.

[0022] Further, the voltage detection circuit further includes a follower U2B, and the operational amplifier U2A outputs through the follower U2B.

[0023] A ground wire monitoring system is also provided, which includes a power supply, a mobile electrical device, a grounding bar PE of the power grid, an MCU, and a relay KJ1. The power supply supplies power to the mobile electrical device through the contacts of the relay KJ1. The grounding point PE of the mobile electrical device is connected to the grounding bar PE through a ground wire. The MCU is used to control the energization or de-energization of the coil in the relay KJ1. For the above-mentioned grounding inspection device for the ground wire of the mobile electrical device, the voltage detection circuit in the grounding inspection device for the ground wire of the mobile electrical device outputs the voltage drop signal to the MCU.

[0024] Further, taking the voltage drop of the reference source as A1 and the preset upper limit of the voltage value as A2;

[0025] When the MCU detects that A1 ≤ the voltage value U of the voltage drop signal ≤ A2, it is determined that the ground wire is normal;

[0026] When the MCU detects that the voltage value U of the voltage drop signal < A1, it is determined that the ground detection line is short-circuited;

[0027] When the MCU detects that the voltage value U of the voltage drop signal > A2, it is determined that the contact resistance value between the ground wire and the ground detection line exceeds the standard;

[0028] When it is determined that the ground detection line is short-circuited and / or the contact resistance value exceeds the standard, the relay KJ1 is disconnected.

[0029] Further, A2 is 4.3V.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] 1. By adopting constant current detection, the detection distance of the ground wire can be effectively increased and the anti-interference ability can be improved.

[0032] 2. By adopting constant current source detection, even if the peripheral circuit such as the ground detection line is short-circuited, the current remains constant, and the temperature of the internal circuit of the monitor is the same as that during normal operation.

[0033] 3. By installing the reference source on the mobile electrical device, the monitor can correctly judge whether the output ground detection line is short-circuited. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It shows a schematic diagram of the grounding of the metal shell of the mobile electrical device.

[0035] Figure 2 It shows a topology diagram of the common monitoring method of the ground wire.

[0036] Figure 3 It shows a schematic diagram of the short circuit of two ground detection lines.

[0037] Figure 4 The topology diagram of the ground wire monitoring system of the present invention is shown.

[0038] Figure 5 The main implementation circuit of the ground wire grounding inspection device for mobile electrical equipment of the present invention is shown. Specific embodiments

[0039] The technical solution of the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0040] The ground wire grounding inspection device of the present invention, as Figure 5 shown, includes terminal +, terminal -, a reference source, a constant current source circuit, and a voltage detection circuit; the reference source is arranged adjacent to the ground point PE of the mobile electrical equipment, its anode is electrically connected to the ground point PE, the cathode is connected to terminal + through a first ground detection line, the ground point PE is connected to the ground busbar PE of the power grid through a ground wire, and the ground busbar PE is connected to terminal - through a second ground detection line; the constant current source circuit includes a constant current source and a resistor R1, the constant current generated by the constant current source is output to terminal + and flows back to the constant current source from terminal -, and terminal - is connected to the common terminal COM through resistor R1; the voltage detection circuit is used to obtain the voltage drop signal between terminal + and terminal -.

[0041] Among them, for implementing the switch control of the constant current circuit, the constant current source circuit is provided with a triode Q1, a resistor R2, and a resistor R3. The collector of the triode Q1 is connected to terminal -, the emitter is connected to the common terminal COM through resistor R1, and the base is used to obtain the voltage drop of resistor R3 in the voltage dividing branch composed of resistor R2 and resistor R3. On this basis, to ensure the stability of the circuit, the constant current I output by the constant current source is configured as

[0042] As Figure 5 shown, the ground wire monitoring system of the present invention is composed of a ground wire grounding inspection device, a power supply, a mobile electrical equipment, the ground busbar PE of the power grid, an MCU, a relay KJ1, etc. The power supply supplies power to the mobile electrical equipment through the contacts of the relay KJ1, the ground point PE of the mobile electrical equipment is connected to the ground busbar PE through a ground wire, the MCU is used to control the energization or de-energization of the coil in the relay KJ1, and the voltage detection circuit in the ground wire grounding inspection device for mobile electrical equipment outputs a voltage drop signal to the MCU.

[0043] During operation, as Figure 4As shown in the figure, the reference source is installed near the ground point PE of the mobile device and plays a role in a certain voltage drop. The voltage drop here is 2.5V (also known as A1). Ignoring the line resistance of the ground detection line and the ground wire, when the ground detection line is short-circuited, the voltage value measured by the monitor voltage detection circuit is 0V; when the ground wire is well-connected and the ground detection line is not short-circuited, the voltage detected by the monitor voltage detection circuit is 2.5V. In this way, the MCU can distinguish whether the ground detection line is short-circuited or the ground wire is well-grounded. If the detected voltage is 0V, it means that the ground detection line is short-circuited, and the monitor immediately gives an alarm prompt and controls KJ1 to disconnect.

[0044] The monitor ground wire check is powered by a 15V constant current I, and the constant current In the formula, 0.7 is the junction voltage of the triode Q1. Taking R2 = R3 = 1kΩ and R1 = 100Ω, then I = 18mA. When both the ground wire and the ground detection line are normal, the current I passes through the ground detection line, flows through the reference source, and then is output from the reference source to the ground wire, then through the ground wire to the ground row PE, and then back to the collector terminal of the triode Q1 in the ground monitor through the ground detection line, and then is output from the emitter terminal of Q1 to the resistor R1, and then output from the resistor R1 to the COM terminal, forming a complete current loop. When the current passes through the reference source, the current magnitude remains unchanged, still 18mA, but a voltage drop of 2.5V is generated. If the line resistance (ground wire and ground detection line) is ignored, the voltage detection circuit of the monitor will detect a voltage value of 2.5V. At this time, the MCU judges that the ground wire is grounded normally. In fact, both the ground wire and the ground detection line have resistance and cannot be ignored. Assuming the total resistance of their lines is R, then the voltage value U detected by the monitor voltage detection circuit at this time is U = R * I + 2.5V. Assuming the line resistance R = 20Ω, then the detected voltage value U = 20Ω * 0.018A + 2.5V = 2.86V. In order to detect the grounding situation more accurately, considering the maximum line resistance brought by the actual line length, the line resistance value here does not exceed 100Ω. Calculated according to 100Ω, the voltage value U = 4.3V (also known as the voltage value upper limit A2). That is to say, when the voltage value U detected by the monitor satisfies 2.5V ≤ U ≤ 4.3V, the ground wire is grounded normally; when U < 2.5V, the ground detection line is short-circuited, and KJ1 is immediately alarmed and disconnected; when U > 4.3V, it means that the line resistance is too large. If the line length is within the specified range, it means that the contact resistance value of the ground wire and the ground detection line is too large, and KJ1 must be immediately alarmed and disconnected.

[0045] The monitor uses constant current detection, which can greatly improve the detection distance and anti-interference ability. The line resistance is taken as 100Ω, and according to L is the length of the copper wire, ρ is the resistivity of copper, S is the cross-sectional area of the copper wire, and R is the resistance. For standard copper wire, ρ = 0.0165Ω·mm 2 / m, S = 1mm2 , L can reach 6060.6 meters. It can be seen from this that by adopting the constant current + reference source method, the detection line can be laid very long. If necessary, by increasing the voltage drop of the reference source, the detection distance of the grounding detection line can be further extended. In other words, a higher upper limit of the wire length with greater freedom can be obtained.

[0046] Compared with the prior art, the advantages of the present invention are as follows:

[0047] 1. By adopting constant current detection, the detection distance of the grounding wire can be effectively increased and the anti-interference ability can be improved.

[0048] 2. By adopting constant current source detection, even if the peripheral circuits such as the grounding detection line are short-circuited, the current remains constant, and the temperature of the internal circuit of the monitor is the same as that during normal operation.

[0049] 3. Installing the reference source on the mobile electrical equipment enables the monitor to correctly judge whether the output grounding detection line is short-circuited.

[0050] In the present invention, the reference source is configured as a reference diode.

[0051] As an improved scheme, as Figure 5 shown, the voltage detection circuit is set to include an operational amplifier U2A, a resistor R5, a resistor R11, a capacitor C1, a capacitor C5, and a follower U2B. The positive input terminal of the operational amplifier U2A is connected to the terminal - and is connected to the common terminal COM through the resistor R5. The negative input terminal of the operational amplifier U2A is connected to the terminal + and is connected to its output terminal through the resistor R11. The capacitor C1 is connected in parallel with the resistor R11, and the capacitor C5 is connected in parallel with the resistor R5. The operational amplifier U2A outputs to the AD conversion channel of the MCU through the follower U2B. In this scheme, the voltage detection circuit samples in a differential manner, is connected to the "+" and "-" terminals of the constant current source circuit, completes the differential amplification processing of the voltage signal, and the processed voltage waveform is linearly isolated and then sent to the AD conversion channel for conversion. The converted digital signal is given to the MCU, and the MCU can judge the grounding condition of the grounding wire according to the sampled voltage data.

[0052] The above specific embodiments are only several preferred embodiments of the present invention. Based on the technical solution of the present invention and the relevant revelations of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A grounding inspection device for a mobile electrical device's grounding wire, characterized in that: It includes terminal +, terminal -, a reference source, a constant current source circuit, and a voltage detection circuit; The reference source is arranged adjacent to the grounding point PE of the mobile electrical device, its anode is electrically connected to the grounding point PE, and its cathode is connected to terminal + through a first grounding detection wire. The grounding point PE is connected to the grounding busbar PE of the power grid through a grounding wire, and the grounding busbar PE is connected to terminal - through a second grounding detection wire; The constant current source circuit includes a constant current source and resistor R1. The constant current generated by the constant current source is output to terminal + and flows back to the constant current source from terminal -. Terminal - is connected to the common terminal COM through resistor R1; The voltage detection circuit is used to obtain the voltage drop signal between terminal + and terminal -; The constant current source circuit further includes triode Q1, resistor R2, and resistor R3. The collector of triode Q1 is connected to terminal -, the emitter is connected to the common terminal COM through resistor R1, and the base is used to obtain the voltage drop of resistor R3 in the voltage dividing branch composed of resistor R2 and resistor R3; The constant current output by the constant current source 2. The ground wire grounding inspection device for mobile electrical equipment according to claim 1, characterized in that: The reference source is a reference diode.

3. The grounding inspection device for a mobile electrical device's grounding wire according to claim 1, characterized in that: The voltage detection circuit includes operational amplifier U2A, resistor R5, resistor R11, capacitor C1, and capacitor C5. The positive input terminal of operational amplifier U2A is connected to terminal - and is connected to the common terminal COM through resistor R5. The negative input terminal of operational amplifier U2A is connected to terminal + and is connected to its output terminal through resistor R11. Capacitor C1 is in parallel with resistor R11, and capacitor C5 is in parallel with resistor R5.

4. The ground wire grounding inspection device for mobile electrical equipment according to claim 3, characterized in that: The voltage detection circuit further includes follower U2B, and the output of operational amplifier U2A is through follower U2B.

5. A ground wire monitoring system, comprising a power supply, a mobile electrical device, a grounding bar PE of the power grid, an MCU, and a relay KJ1. The power supply supplies power to the mobile electrical device through the contacts of the relay KJ1. The grounding point PE of the mobile electrical device is connected to the grounding bar PE through a ground wire. The MCU is used to control the energization or de-energization of the coil in the relay KJ1, and is characterized in that, It further includes the grounding inspection device for a mobile electrical device's grounding wire according to any one of claims 1 - 4. The voltage detection circuit in the grounding inspection device for a mobile electrical device's grounding wire outputs the voltage drop signal to the MCU.

6. The grounding wire monitoring system according to claim 5, characterized in that: Taking the voltage drop of the reference source as A1 and the preset upper limit of the voltage value as A2; When the MCU detects that A1 ≤ the voltage value U of the voltage drop signal ≤ A2, it determines that the grounding wire is normal; When the MCU detects that the voltage value U of the voltage drop signal < A1, it determines that the grounding detection wire is short - circuited; When the MCU detects that the voltage value U of the voltage drop signal > A2, it determines that the contact resistance value of the grounding wire and the grounding detection wire exceeds the standard.

7. The ground wire monitoring system according to claim 6, characterized in that: A2 is 4.3V.

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