A device and method for accurately detecting a leakage resistance and implementing a lockout

Abstract

This invention belongs to the field of precise leakage resistance detection technology, and discloses a device for accurately detecting leakage resistance and achieving interlocking, comprising: a housing providing protection and providing an interface and a grounding terminal. Leakage resistance is detected using a 0.1% precision resistance network, with a maximum resistance error ≤0.4%; a 12-bit A / D converter is used to calculate the leakage resistance, with the full-scale voltage data value being: [value missing]. The A / D converter reference power supply is 4.096V, and according to the voltage divider formula: V [value missing] L =, when R L When V = ∞, the test point is an open circuit. L The maximum voltage at the point is: V L ==4.096V, minimum voltage resolution is:, when the test point is closed, leakage resistance R L =(7.5469V D (4096-V) D Taking 40KΩ (leakage lockout resistance value for 1140V voltage level in coal mines) as an example, the actual calculated leakage resistance value is 39.997KΩ, with an error rate of 0.0075%.

Description

Technical Field

[0001] This invention belongs to the field of precise leakage resistance detection technology, specifically a device and method for precisely detecting leakage resistance and achieving interlocking. Background Technology

[0002] Leakage current interlock is an electrical safety protection function, typically used in explosive environments such as coal mines or in power distribution systems with high safety requirements. Its principle is to continuously monitor the insulation resistance of the power supply line to ground after the equipment is powered off. If the insulation value is detected to be lower than the safety threshold (i.e., there is a leakage current hazard), the system will forcibly interlock and prevent the circuit from being reconnected, even if the operator attempts to close the circuit. This function eliminates the possibility of electric shock or spark accidents caused by accidental power supply before the hazard is eliminated. It must be used in conjunction with leakage current protection to form multiple layers of protection and is a key technical measure to ensure electrical safety in hazardous work environments.

[0003] Currently, the following four methods are generally used in high-voltage power distribution systems for leakage current monitoring and interlocking: (1) DC injection detection method: The device outputs a DC reference signal and injects it into the circuit under test. By collecting feedback signals, the insulation resistance of the circuit to ground is calculated. If it is lower than the threshold, the interlock is triggered. Its disadvantage is that the detection device is easily damaged by high voltage or residual magnetic voltage. The arc of the equipment when it stops and the residual magnetic potential of the motor will enter the detection circuit, burn out the internal components. The distributed capacitance of the wiring will generate an induced electromotive force, which will interfere with the DC signal, resulting in a decrease in detection accuracy and misjudgment of results. (2) Residual current detection method: The residual current of the line is collected by the current transformer. When the current exceeds the standard, it is judged as leakage and the blocking is triggered. It is low cost and easy to popularize. Its disadvantage is that it cannot distinguish between resistive leakage current and capacitive leakage current. The harmonics of capacitive current increase with the increase of line length, resulting in frequent false alarms. Moreover, the detection accuracy is low and the detection range is small, which cannot meet the requirements of multiple voltages and multiple scenarios in coal mines. (3) Direct insulation resistance testing method: The insulation resistance of the line to ground is measured directly after the power is off. Disadvantages: There is no isolation protection, and the direct contact testing is susceptible to high voltage impact from the circuit under test, resulting in a high failure rate of the device; its disadvantage is that each product requires manual adjustment of the potentiometer to adapt the lockout threshold, resulting in poor versatility; (4) Indirect isolation detection method: The detection circuit is isolated from the circuit under test by a transformer. The primary coil is connected in series with the detection circuit and the secondary coil is connected in series with a resistor. When leakage occurs, the primary current increases and the secondary induced voltage reaches the standard to trigger the lockout. Its disadvantages are that transformer isolation will lose signal strength, the detection accuracy will drop significantly, small current leakage is easy to miss, and the anti-interference is weak. It is easy to malfunction under voltage fluctuation and high frequency harmonics. The response speed is slow and cannot meet the fast lockout requirements of high voltage scenarios.

[0004] In summary, existing technologies have drawbacks such as weak anti-interference capabilities and low detection accuracy, resulting in high false alarm and false negative rates. False alarms can affect equipment power supply and coal mine production, while false alarms or false negatives can easily lead to equipment damage or personal safety accidents. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for accurately detecting leakage resistance and achieving interlocking, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a device for accurately detecting leakage resistance and achieving interlocking, comprising: Housing: Provides protection and provides interfaces and grounding terminals; PCB board: integrates various circuits; The PCB board integrates: Power supply circuit: Provides 24V and 5V DC power to the device; Leakage resistance detection circuit: The leakage resistance value is calculated using a 0.1% precision resistor; High-voltage isolation circuit: Enables the switching on / off function of the detection circuit and high-voltage isolation; CPU circuitry: performs data acquisition, computation, and communication control; 485 communication interface circuit: realizes bidirectional signal conversion; External PLC interface signal circuit: sends switch signals to the external PLC and transmits leakage resistance value information to the external PLC through the 485 communication interface circuit.

[0007] As a preferred embodiment of the present invention, the power supply circuit includes: a P1 terminal; a fuse F1; a varistor R5; a safety capacitor C1; an AC / DC power module U2; a DC / DC power module U1; relays K1, K2, and K3; an inductor L3; and filter capacitors C2, C3, and C5.

[0008] As a preferred embodiment of the present invention, the P1 terminal is connected to an external 220V AC power supply, and the filter capacitor C5 is a 5V filter capacitor.

[0009] As a preferred embodiment of the present invention, the leakage resistance detection circuit includes: 0.1% precision resistors R10, R11, R12, and R13, wherein the 0.1% precision resistor R13 and the leakage resistance R L The leakage resistor R is connected in parallel. L The formula for calculating the resistance is: R L =(7.5469 V D ) (4096-V D ) Where V D For V L The voltage is converted into a decimal voltage data value after being converted by an A / D converter.

[0010] As a preferred embodiment of the present invention, the high-voltage isolation circuit includes: relays K2 and K3; transistors Q2 and Q3; diodes D2 and D3; and resistors R6, R7, R8, R14, R15, and R16.

[0011] In a preferred embodiment of the present invention, the CPU circuit comprises a CPU chip, an A / D reference power supply circuit, a crystal oscillator circuit, a reset circuit, a baud rate selection circuit, and an address DIP switch circuit. The A / D reference power supply circuit comprises U4 and R3, and the reset circuit comprises R25 and C8.

[0012] As a preferred embodiment of the present invention, the 485 communication interface circuit is composed of components U3, L2, R26, R27, R24, R29, D4, R28, C4, R21, R22, and R23.

[0013] A method for accurately detecting leakage resistance and achieving interlocking, comprising the following specific steps: Step 1: First, power on the controlled device. Then, connect the device to the external PLC control contactor and power it with the 1140V / 220V isolation transformer to complete the device's power-on initialization. Step 2: The CPU controls the high-voltage relay K2 and the ground isolation relay K3 to engage, forming a closed circuit between the device, the busbar under test, and the grounding terminal of the chassis. The leakage resistance R... L The parallel connection with R13 changes V L Point voltage; Step 3: V L After the point voltage signal enters the CPU, it undergoes ten A / D conversions, and after mean filtering and conversion calculations, the leakage resistance R is obtained. L value; Step 4: The CPU will R L The value is compared with the threshold. If R L If the value is less than the threshold, the CPU controls the relay K1 coil to have no output signal, K1 output has no action, and at the same time sends the resistance value and detection abnormality information through the 485 communication interface. The external PLC detects the abnormal leakage resistance, issues a main circuit prohibition closing command, and publishes leakage lockout alarm information to the system background until the RL value is greater than or equal to 1.5 times the threshold. The CPU controls the relay K1 to output a normally open or normally closed signal and sends information to the external PLC through the 485 communication interface. The CPU outputs a low-level signal to control the high-voltage relay K2 and the ground isolation relay K3 to release, cutting off the detection circuit.

[0014] As a preferred embodiment of the present invention, the threshold is determined by the voltage level of the leakage resistor. When the voltage level of the leakage resistor is 1140V, the threshold is 40KΩ, and when the voltage level of the leakage resistor is 660V, the threshold is 22KΩ.

[0015] The beneficial effects of this invention are as follows: Leakage resistance was detected using a 0.1% precision resistor network, with a maximum resistance error ≤0.4%; the leakage resistance was calculated using a 12-bit A / D converter, and the full-scale voltage data value was: The A / D converter's reference power supply is 4.096V. According to the voltage divider formula: V L = When R L When V = ∞, that is, the test point is an open circuit, V L The maximum voltage at the point is: V L = =4.096V, minimum voltage resolution is: When the test point is closed, the leakage resistance R L =(7.5469 V D ) (4096-V D Taking 40KΩ (leakage blocking resistance value of 1140V voltage level in coal mines) as an example, the actual calculated leakage resistance value is 39.997KΩ, with a calculation error rate of 0.0075%. Considering the 1% error of the reference power supply and sampling error, the overall system error is ≤2%, which has the advantages of small overall error, high accuracy and high anti-interference. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the power supply circuit structure of the present invention; Figure 2 This is a schematic diagram of the external PLC interface signal circuit of the present invention; Figure 3 This is a schematic diagram of the leakage resistance detection circuit and high-voltage isolation circuit of the present invention; Figure 4 This is a schematic diagram of the 485 communication interface circuit of the present invention; Figure 5 This is a schematic diagram of the CPU circuit of the present invention; Figure 6 This is a flowchart illustrating the steps involved in using this invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] like Figures 1 to 6 As shown, this embodiment of the invention provides a device for accurately detecting leakage resistance and achieving interlocking, comprising: Housing: Provides protection and provides interfaces and grounding terminals; PCB board: integrates various circuits; The PCB board integrates: Power supply circuit: Provides 24V and 5V DC power to the device; Leakage resistance detection circuit: The leakage resistance value is calculated using a 0.1% precision resistor; High-voltage isolation circuit: Enables the switching on / off function of the detection circuit and high-voltage isolation; CPU circuitry: performs data acquisition, computation, and communication control; 485 communication interface circuit: realizes bidirectional signal conversion; External PLC interface signal circuit: sends switch signals to the external PLC and transmits leakage resistance value information to the external PLC through the 485 communication interface circuit.

[0019] Employing a 0.1% precision resistor network and a 12-bit A / D converter, it achieves lower overall error. High-voltage isolation design, 485 communication anti-interference circuit, and common-mode filter inductor suppress external interference. It is compatible with both 1140V and 660V voltage levels. The precision resistor network and A / D converter ensure measurement accuracy without manual adjustment. It accurately distinguishes between leakage resistance and distributed capacitance. The unlock threshold is set by software at 1.5 times the latching threshold, ensuring high accuracy.

[0020] The power supply circuit includes: terminal P1; fuse F1; varistor R5; safety capacitor C1; AC / DC power module U2; DC / DC power module U1; relays K1, K2, K3; inductor L3; and filter capacitors C2, C3, C5.

[0021] F1 provides overcurrent protection, R5 provides overvoltage protection, C1 suppresses differential-mode interference, L3 suppresses common-mode interference, and R2 and LED1 are 5V power indicators.

[0022] Terminal P1 is connected to an external 220V AC power supply, and capacitor C5 is a 5V filter capacitor.

[0023] The power supply circuit is supplied with external AC 220V and connected to terminal P1. It connects to fuse F1, varistor R5, and safety capacitor C1, and enters AC / DC power module U2 to be converted to DC 24V voltage. The 24V mainly powers the coils of relays K1, K2, and K3. The 24V is connected to filter capacitors C2 and C3 through inductor L3 and enters DC / DC power module U1 to be converted to 5V, which powers the CPU circuit, 485 communication circuit, and other circuits.

[0024] The leakage resistance detection circuit includes: 0.1% precision resistors R10, R11, R12, and R13, with the 0.1% precision resistor R13 and the leakage resistance R... L Parallel connection, leakage resistance R L The formula for calculating the resistance is: R L =(7.5469 V D ) (4096-V D ) Where V D For V L The decimal voltage data value of the point voltage after A / D conversion.

[0025] When the leakage resistance R L After being incorporated into the resistor sampling circuit, R L The change in resistance will cause V L The point voltage changes.

[0026] The high-voltage isolation circuit includes: relays K2 and K3; transistors Q2 and Q3; diodes D2 and D3; and resistors R6, R7, R8, R14, R15, and R16.

[0027] K2 connects to the high-voltage busbar, enabling the on / off switching of the detection circuit and high-voltage isolation. K3 isolates the chassis grounding terminal from the device PCB ground potential. R8 is the base current limiting resistor for transistor Q2, and R6 is the collector current limiting resistor for transistor Q2. R7 is the pull-up resistor for the relay2_cntrl_out signal. R14 is a varistor for overvoltage protection. Diodes D2 and D3 protect the K2 and K3 coils. Transistor Q2 amplifies the current, providing drive current to the K2 coil. The CPU controls the relay2_cntrl_out signal to be high, turning on transistors Q2 / Q3, energizing the relays K2 / K3 coils, and connecting the external leakage resistor to the measurement circuit. When the external equipment is operating normally, the device is not energized, the K2 / K3 coils are not energized, and the K2 / K3 contacts are in a normally open state, isolating the external 1140V / 660V voltage.

[0028] The CPU circuit consists of a CPU chip, an A / D reference power supply circuit, a crystal oscillator circuit, a reset circuit, a baud rate selection circuit, and an address DIP switch circuit. The A / D reference power supply circuit consists of U4 and R3, and the reset circuit consists of R25 and C8.

[0029] The main functions of the CPU chip U8 are data acquisition, processing, and communication control; the A / D reference power supply is responsible for providing a precise 4.096V power supply to the A / D converter; the reset circuit provides a low-level reset signal when the CPU is powered on.

[0030] The 485 communication interface circuit consists of components U3, L2, R26, R27, R24, R29, D4, R28, C4, R21, R22, and R23.

[0031] U3 is the 485 chip, whose core function is to realize bidirectional conversion between differential signals and TTL logic signals, thereby enabling communication between the CPU and external PLCs or other terminals; L2 is a common-mode filter to eliminate common-mode signal interference; R26 / R27 are 485 bus matching resistors to eliminate echo interference; R24 / R29 are bias resistors to provide bias voltage for the 485 bus; D4 is an ESD protection device to prevent static electricity; R28 is a termination matching resistor; C4 is a 485 chip filter capacitor; R21 / R22 / R23 are pull-up resistors to ensure signal level accuracy.

[0032] A method for accurately detecting leakage resistance and achieving interlocking, comprising the following specific steps: Step 1: First, power on the controlled device. Then, connect the device to the external PLC control contactor and power it with the 1140V / 220V isolation transformer to complete the device's power-on initialization. Step 2: The CPU controls the high-voltage relay K2 and the ground isolation relay K3 to engage, forming a closed circuit between the device, the busbar under test, and the grounding terminal of the chassis. The leakage resistance R... L The parallel connection with R13 changes V L Point voltage; Step 3: V L After the point voltage signal enters the CPU, it undergoes ten A / D conversions, and after mean filtering and conversion calculations, the leakage resistance R is obtained. L value; Step 4: The CPU will R L The value is compared with the threshold. If R LIf the value is less than the threshold, the CPU controls the relay K1 coil to have no output signal, K1 output has no action, and at the same time sends the resistance value and detection abnormality information through the 485 communication interface. The external PLC detects the abnormal leakage resistance, issues a main circuit prohibition closing command, and publishes leakage lockout alarm information to the system background until the RL value is greater than or equal to 1.5 times the threshold. The CPU controls the relay K1 to output a normally open or normally closed signal and sends information to the external PLC through the 485 communication interface. The CPU outputs a low-level signal to control the high-voltage relay K2 and the ground isolation relay K3 to release, cutting off the detection circuit.

[0033] The single threshold is the locking value, and 1.5 times the threshold is the unlocking value. If the detection result is abnormal, the controlled equipment needs to be repaired and powered off. After the power supply is restored, the entire detection process is repeated.

[0034] The threshold value is determined by the voltage level of the leakage resistance. When the voltage level of the leakage resistance is 1140V, the threshold value is 40KΩ, and when the voltage level of the leakage resistance is 660V, the threshold value is 22KΩ.

[0035] Depending on the different leakage resistance thresholds, it can adapt to dual voltage levels of 1140V / 660V without manual adjustment.

[0036] Working principle and usage process: When the controlled equipment is initially powered on, the main circuit is in the open state; the external PLC controls the contactor to engage, supplying power to the device through the 1140V / 220V isolation transformer. After the device is powered on, the CPU controls the high-voltage relay K2 and the ground isolation relay K3 to engage, forming a closed circuit between the device, the busbar under test, and the grounding terminal of the casing. The leakage resistor RL is connected in parallel with R13 to change the voltage. L The point voltage signal enters the CPU, where it undergoes A / D conversion and the leakage resistance RL value is calculated.

[0037] If R L If the value is greater than or equal to the threshold, the CPU controls relay K1 to output a normally open or normally closed signal, and simultaneously sends the resistance value information to the external PLC via the 485 communication interface. The PLC detects that the leakage resistance is normal, cuts off the power to the leakage current interlock device, and closes the main circuit; if R... L If the value is less than the threshold, the CPU controls the relay K1 coil to have no output signal, K1 output has no action, and at the same time sends the resistance value and abnormal detection information through the 485 communication interface. The external PLC detects the abnormal leakage resistance, issues a main circuit prohibition closing command, and publishes leakage current interlocking alarm information to the system background, until R... LIf the value is ≥1.5 times the threshold, the CPU controls relay K1 to output a normally open or normally closed signal and sends a notification to the external PLC via the 485 communication interface. The CPU outputs a low-level signal to control the high-voltage relay K2 and the ground isolation relay K3 to release, cutting off the detection circuit. If the detection result is abnormal, the controlled equipment needs to be repaired and powered off. After power is restored, the above detection process is repeated.

[0038] 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.

[0039] Although embodiments of the 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 invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A device for accurately detecting leakage resistance and achieving interlocking, characterized in that, include: Housing: Provides protection and provides interfaces and grounding terminals; PCB board: integrates various circuits; The PCB board integrates: Power supply circuit: Provides 24V and 5V DC power to the device; Leakage resistance detection circuit: The leakage resistance value is calculated using a 0.1% precision resistor; High-voltage isolation circuit: Enables the switching on / off function of the detection circuit and high-voltage isolation; CPU circuitry: performs data acquisition, computation, and communication control; 485 communication interface circuit: realizes bidirectional signal conversion; External PLC interface signal circuit: sends switch signals to the external PLC and transmits leakage resistance value information to the external PLC through the 485 communication interface circuit.

2. The device for accurately detecting leakage resistance and achieving interlocking according to claim 1, characterized in that: The power supply circuit includes: terminal P1; fuse F1; varistor R5; safety capacitor C1; AC / DC power module U2; DC / DC power module U1; relays K1, K2, and K3; inductor L3; and filter capacitors C2, C3, and C5.

3. The device for accurately detecting leakage resistance and achieving interlocking according to claim 2, characterized in that: The P1 terminal is connected to an external 220V AC power supply, and C5 is a 5V filter capacitor.

4. The device for accurately detecting leakage resistance and achieving interlocking according to claim 1, characterized in that: The leakage resistance detection circuit includes: 0.1% precision resistors R10, R11, R12, and R13, wherein the 0.1% precision resistor R13 is connected to the leakage resistance R... L The leakage resistor R is connected in parallel. L The formula for calculating the resistance is: R L =(7.5469 V D ) (4096-V D ) Where V D For V L The voltage is converted into a decimal voltage data value after being converted by an A / D converter.

5. The device for accurately detecting leakage resistance and achieving interlocking according to claim 1, characterized in that: The high-voltage isolation circuit includes: relays K2 and K3; transistors Q2 and Q3; diodes D2 and D3; and resistors R6, R7, R8, R14, R15, and R16.

6. The device for accurately detecting leakage resistance and achieving interlocking according to claim 1, characterized in that: The CPU circuit consists of a CPU chip, an A / D reference power supply circuit, a crystal oscillator circuit, a reset circuit, a baud rate selection circuit, and an address DIP switch circuit. The A / D reference power supply circuit consists of U4 and R3, and the reset circuit consists of R25 and C8.

7. The device for accurately detecting leakage resistance and achieving interlocking according to claim 1, characterized in that: The 485 communication interface circuit consists of components U3, L2, R26, R27, R24, R29, D4, R28, C4, R21, R22, and R23.

8. A method for accurately detecting leakage resistance and achieving interlocking, characterized in that, The specific steps are as follows: Step 1: First, power on the controlled device. Then, connect the device to the external PLC control contactor and power it with the 1140V / 220V isolation transformer to complete the device's power-on initialization. Step 2: The CPU controls the high-voltage relay K2 and the ground isolation relay K3 to engage, forming a closed circuit between the device, the busbar under test, and the grounding terminal of the chassis. The leakage resistance R... L The parallel connection with R13 changes V L Point voltage; Step 3: V L After the point voltage signal enters the CPU, it undergoes ten A / D conversions, and after mean filtering and conversion calculations, the leakage resistance R is obtained. L value; Step 4: The CPU will R L The value is compared with the threshold. If R L If the value is less than the threshold, the CPU controls the relay K1 coil to have no output signal, K1 output has no action, and at the same time sends the resistance value and detection abnormality information through the 485 communication interface. The external PLC detects the abnormal leakage resistance, issues a main circuit prohibition closing command, and publishes leakage lockout alarm information to the system background until the RL value is greater than or equal to 1.5 times the threshold. The CPU controls the relay K1 to output a normally open or normally closed signal and sends information to the external PLC through the 485 communication interface. The CPU outputs a low-level signal to control the high-voltage relay K2 and the ground isolation relay K3 to release, cutting off the detection circuit.

9. The method for accurately detecting leakage resistance and achieving interlocking according to claim 8, characterized in that, include: The threshold value is determined by the voltage level of the leakage resistance. When the voltage level of the leakage resistance is 1140V, the threshold value is 40KΩ, and when the voltage level of the leakage resistance is 660V, the threshold value is 22KΩ.

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