Electric leakage detection equipment for three-phase motor

Abstract

The utility model provides electric leakage detection equipment for a three-phase motor. The electric leakage detection equipment comprises a current transformer, a range switching circuit, an effective value proportional amplifying circuit, an adjusting circuit and an output circuit, the current transformer is used for collecting the phase line current of a measured three-phase motor, the current transformer is connected with the input end of the range switching circuit, and the output end of the range switching circuit is connected with the input end of the effective value proportional amplification circuit; the output end of the effective value proportion amplifying circuit is connected with the input end of the adjusting circuit, and the output end of the adjusting circuit is connected with the input end of the output circuit. According to the utility model, the phase line current of the three-phase motor is collected by adopting the universal straight-through mutual inductor, so that the leakage current detection of the three-phase motor is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of motor fault diagnosis, and particularly to a three-phase motor leakage detection device. Background Art

[0002] As a power source, three-phase motors are widely used in both civilian and industrial fields, and there are corresponding products with power ranging from a few hundred watts to several megawatts. As an electrical equipment, there is undoubtedly a possibility of leakage in three-phase motors, and leakage will undoubtedly pose a great threat to both personal safety and equipment safety.

[0003] In the steel industry, cranes are widely used as the main production equipment, and three-phase motors are usually the only power source for cranes. Each crane usually has several or even dozens of motors. With the progress of technology, voltage regulation speed control and variable frequency speed control technologies are commonly used in the drive technology of three-phase motors. Both of these technologies use silicon-based power components such as thyristors and IGBTs for power output. The advantages of this silicon-based power component are small volume and high power density, but it is sensitive to current, and excessive current will cause it to be quickly damaged. In the drive of three-phase motors, leakage and short circuit are the main reasons for abnormal current, and they are also one of the main reasons for the damage of drive equipment.

[0004] However, at present, the drive equipment on the market basically has reliable protection measures for short circuits, but the protection measures for leakage faults are not perfect, and false actions or insensitivity often occur. If the false actions are too frequent, it will cause the equipment to frequently malfunction and stop running, seriously affecting the operation of the equipment and production efficiency. If it is insensitive, it will cause equipment damage or personal safety accidents when leakage actually occurs. The main reason for this situation is that more computing power of the core processor of the drive equipment is used for the regulation of output voltage and current, which is also the key to whether the drive equipment can ensure that the characteristic curve of the driven motor is smooth and stable. The leakage current is usually sporadic and weak in current, and its characteristics are not obvious. Its detection requires fast floating-point operations and efficient and frequent ADC conversions. Therefore, the detection of leakage current will involve the core computing power of the drive equipment, and because the leakage detection is only an auxiliary function of the drive equipment and accounts for a very low proportion and is not taken seriously, the current situation of unsatisfactory leakage detection of drive equipment has been caused. The short-circuit current usually causes the current to increase sharply in a short time, and its characteristics are obvious, so the short-circuit detection is usually very sensitive and reliable.

[0005] The patent document with the publication number CN211718471U discloses a three-phase leakage current tester for motors, which includes a current tester body. Four bases are fixed at the bottom of the current tester body. On the front of the current tester body, there are a display screen, a test socket operation key, a test socket, a voltage adjustment knob, a power key, and a reset key. A rubber ring is fixed inside the test socket. The current tester body includes an impedance converter, a range converter, an AC / DC converter, a circuit amplifier, and an indicator. All five components are fixed on a support frame. A partition is horizontally arranged below the support frame. However, this patent document still has the defect of being insufficiently sensitive and reliable.

[0006] Therefore, developing a three-phase motor leakage detection device that can ensure the reliability, stability, and accuracy of leakage current detection during the driving process of a three-phase motor, thereby effectively ensuring the safety of the driving device, the motor, and personnel, is an urgent problem to be solved at present. Utility Model Content

[0007] Aiming at the defects in the prior art, the purpose of the present utility model is to provide a three-phase motor leakage detection device.

[0008] According to a three-phase motor leakage detection device provided by the present utility model, it includes: a current transformer, a range switching circuit, an effective value proportional amplification circuit, an adjustment circuit, and an output circuit;

[0009] The current transformer is used to collect the phase current of the measured three-phase motor. The current transformer is connected to the input end of the range switching circuit, and the output end of the range switching circuit is connected to the input end of the effective value proportional amplification circuit;

[0010] The output end of the effective value proportional amplification circuit is connected to the input end of the adjustment circuit, and the output end of the adjustment circuit is connected to the input end of the output circuit.

[0011] Preferably, a sampling resistor is connected between the current transformer and the range switching circuit, and a reference circuit is connected to the adjustment circuit.

[0012] Preferably, the range switching circuit includes a manual range switching circuit, and the adjustment circuit includes a comparison delay circuit.

[0013] Preferably, the manual range switching circuit includes connection terminals CN2, resistors R1, R3, R4, R5, R6, R7, and a multi-position selection switch SW1;

[0014] The connection terminal CN2 serves as the input end of the manual range switching circuit. One end of the resistor R1 is respectively connected to one end of the resistor R3, the first connection end of the multi-position selection switch SW1, and the first connection end of the connection terminal CN2; the other end of the resistor R1 is respectively connected to one end of the resistor R7 and grounded.

[0015] The other end of the resistor R3 is connected to one end of the resistor R4, and the other end of the resistor R4 is respectively connected to one end of the resistor R5 and the second connection end of the multi-position selection switch SW1.

[0016] The other end of the resistor R5 is connected to one end of the resistor R6, and the other end of the resistor R6 is respectively connected to the other end of the resistor R7 and the third connection end of the multi-position selection switch SW1.

[0017] The fourth connection end of the multi-position selection switch SW1 serves as the output end of the manual range switching circuit.

[0018] Preferably, the range switching circuit includes an automatic range switching circuit, the adjustment circuit includes a CPU circuit, and the automatic range switching circuit is connected to the CPU circuit.

[0019] Preferably, the automatic range switching circuit includes a connection terminal CN3, resistors R1, R3, R4, R5, R6, R7, a control chip U4, and an analog switch.

[0020] The connection terminal CN3 serves as the input end of the automatic range switching circuit. One end of the resistor R1 is respectively connected to one end of the resistor R3, the first connection end of the control chip U4, and the first connection end of the connection terminal CN3; the other end of the resistor R1 is respectively connected to one end of the resistor R7 and the second connection end of the connection terminal CN3 and grounded.

[0021] The other end of the resistor R3 is connected to one end of the resistor R4, and the other end of the resistor R4 is respectively connected to one end of the resistor R5 and the second connection end of the control chip U4.

[0022] The other end of the resistor R5 is connected to one end of the resistor R6, and the other end of the resistor R6 is respectively connected to the other end of the resistor R7 and the third connection end of the control chip U4.

[0023] The analog switch is connected to the control chip U4; the fourth connection end of the control chip U4 serves as the output end of the automatic range switching circuit.

[0024] Preferably, the effective value ratio amplification circuit includes a capacitor C19, a resistor R18, a resistor R20, a resistor R21, a variable resistor R23, a resistor R28, an operational amplifier chip U8.1, a diode D5, a diode D6, a capacitor C28, a resistor R27, an operational amplifier chip U8.2, a resistor R29, and a capacitor C30;

[0025] One end of the capacitor C19 is respectively connected to one end of the resistor R18 and one end of the resistor R22, and serves as the input end of the effective value ratio amplification circuit; the other end of the capacitor C19 is grounded;

[0026] The other end of the resistor R18 is respectively connected to one end of the resistor R21, one end of the diode D5, and the inverting input end of the operational amplifier chip U8.1; the non-inverting input end of the operational amplifier chip U8.1 is connected to one end of the resistor R20, and the other end of the resistor R20 is grounded;

[0027] The other end of the resistor R21 is connected to one end of the variable resistor R23, and the other end of the variable resistor R23 is respectively connected to one end of the resistor R28 and the inverting input end of the operational amplifier chip U8.2;

[0028] The other end of the diode D5 is respectively connected to the output end of the operational amplifier chip U8.1 and one end of the diode D6; the other end of the diode D6 is respectively connected to one end of the capacitor C28 and one end of the resistor R27, and the other end of the capacitor C28 is grounded; the other end of the resistor R27 is respectively connected to the other end of the resistor R22 and the non-inverting input end of the operational amplifier chip U8.2;

[0029] The output end of the operational amplifier chip U8.2 is respectively connected to the other end of the resistor R28 and one end of the resistor R29, and the other end of the resistor R29 is connected to one end of the capacitor C30 and serves as the output end of the effective value ratio amplification circuit; the other end of the capacitor C30 is grounded;

[0030] The positive power supply terminal and the negative power supply terminal of the operational amplifier chip U8.1 are externally connected to a power supply.

[0031] Preferably, the comparison delay circuit includes a variable resistor R16, a resistor R17, a resistor R19, an operational amplifier chip U9.1, a variable resistor R24, a resistor R26, a capacitor C29, an operational amplifier chip U9.2, and a resistor R36;

[0032] The first connection end of the variable resistor R16 is externally connected to a power supply, and the adjustment connection end of the variable resistor R16 is connected to the inverting input end of the operational amplifier chip U9.1;

[0033] One end of the resistor R17 serves as the input end of the comparison delay circuit, and the other end of the resistor R17 is respectively connected to one end of the resistor R19 and the non-inverting input end of the operational amplifier chip U9.1;

[0034] The negative power supply end of the operational amplifier chip U9.1 is externally connected to a power supply; the output end of the operational amplifier chip U9.1 is respectively connected to one end of the resistor R26, the non-inverting input end of the operational amplifier chip U9.2, and one end of the capacitor C29;

[0035] The first connection end of the adjustable resistor R24 is connected to the other end of the resistor R26 and is externally connected to a power supply; the second connection end of the resistor R24 is connected to the other end of the capacitor C29; the adjustable connection end of the resistor R24 is connected to the inverting input end of the operational amplifier chip U9.2;

[0036] The output end of the operational amplifier chip U9.2 is connected to one end of the resistor R36 and serves as the output end of the comparison delay circuit; the other end of the resistor R36 is externally connected to a power supply;

[0037] The second connection end of the resistor R16, the other end of the R19, the positive power supply end of the operational amplifier chip U9.1, and the second connection end of the R24 are equipotential.

[0038] Preferably, the output circuit includes a resistor R30, a resistor R31, a triode Q1, a diode D7, a relay, and a connection terminal CN4;

[0039] One end of the resistor R30 is connected to one end of the resistor R31 and serves as the input end of the output circuit; the other end of the resistor R30 is connected to the emitter of the triode Q1 and is grounded;

[0040] The other end of the resistor R31 is connected to the base of the triode Q1, and the collector of the triode Q1 is respectively connected to the first connection end of the relay and one end of the diode D7;

[0041] The other end of the diode D7 is connected to the second connection end of the relay and is externally connected to a power supply; the third connection end of the relay is connected to the first connection end of the connection terminal CN4, the fourth connection end of the relay is connected to the second connection end of the connection terminal CN4, and the fifth connection end of the relay is connected to the third connection end of the connection terminal CN4.

[0042] Preferably, the reference circuit includes a core chip U6, an adjustable resistor R32, a resistor R33, and a diode D8;

[0043] The first connection terminal of the core chip U6 is externally connected to a power supply. The second connection terminal of the core chip U6 is respectively connected to the first connection terminal of the adjustable resistor R32 and one end of the resistor R33. The third connection terminal of the core chip U6 is connected to the adjustable end of the adjustable resistor R32;

[0044] The other end of the resistor R33 is connected to one end of the diode D8; the other end of the diode D8 is connected to the second connection terminal of the adjustable resistor R32 and grounded.

[0045] Compared with the prior art, the utility model has the following beneficial effects:

[0046] 1. The utility model realizes the leakage current detection of a three-phase motor by using a common through-core current transformer to collect the phase current of the three-phase motor.

[0047] 2. The utility model uses a 10-watt 1-ohm power resistor as a sampling resistor. When sampling the output current of a 5-A current transformer, the sampling voltage will reach a maximum of 5V. Compared with a sampling resistor in the milliohm range, the sampling voltage is higher and less susceptible to electromagnetic interference from the external environment, so the sampling accuracy will be higher.

[0048] 3. The utility model realizes the voltage division of the leakage current through a range selection circuit. Since the range of the leakage current may be from a dozen milliamperes to several hundred or thousands of amperes, which is too large, it must be voltage-divided by a range selection circuit before normal detection can be carried out.

[0049] 4. The utility model rectifies and amplifies the sampling voltage through an effective value proportional amplification circuit. Since the current of the three-phase motor is an alternating current, the sampling voltage will also be an alternating voltage. Therefore, it is necessary to measure the effective value of the sampling voltage to accurately obtain the actual leakage current of the motor. Therefore, the sampled voltage after voltage division needs to pass through an effective value proportional amplification circuit for full-wave rectification and proportional amplification to obtain a DC voltage, which is the effective value of the sampling voltage. The leakage situation of the motor can be obtained by comparing and judging this voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects, and advantages of the utility model will become more apparent:

[0051] Figure 1 It is a schematic structural framework diagram of a leakage detection device for a three-phase motor;

[0052] Figure 2 It is a schematic circuit structure diagram of a manual range switching circuit;

[0053] Figure 3Schematic diagram of the circuit structure of the automatic range switching circuit;

[0054] Figure 4 Schematic diagram of the circuit structure of the RMS proportional amplification circuit;

[0055] Figure 5 Schematic diagram of the circuit structure of the comparison delay circuit;

[0056] Figure 6 Schematic diagram of the circuit structure of the output circuit;

[0057] Figure 7 Schematic diagram of the circuit structure of the CPU circuit;

[0058] Figure 8 Schematic diagram of the circuit structure of the reference circuit;

[0059] Figure 9 Schematic diagram of the circuit structure of the power supply circuit. Detailed implementation manners

[0060] The present utility model will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present utility model, but do not limit the present utility model in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present utility model, several changes and improvements can still be made. These all belong to the protection scope of the present utility model.

[0061] Example 1:

[0062] As Figures 1 to 9 shown, this embodiment provides a three-phase motor leakage detection device, including: a current transformer, a range switching circuit, an RMS proportional amplification circuit, an adjustment circuit, and an output circuit; the current transformer is used to collect the phase current of the three-phase motor to be measured, the current transformer is connected to the input end of the range switching circuit, and the output end of the range switching circuit is connected to the input end of the RMS proportional amplification circuit; the output end of the RMS proportional amplification circuit is connected to the input end of the adjustment circuit, and the output end of the adjustment circuit is connected to the input end of the output circuit.

[0063] A sampling resistor is connected between the current transformer and the range switching circuit, and a reference circuit is connected to the adjustment circuit. The reference circuit includes a core chip U6, a variable resistor R32, a resistor R33, and a diode D8; the first connection end of the core chip U6 is externally connected to a power supply, the second connection end of the core chip U6 is respectively connected to the first connection end of the variable resistor R32 and one end of the resistor R33, the third connection end of the core chip U6 is connected to the adjustable end of the variable resistor R32; the other end of the resistor R33 is connected to one end of the diode D8; the other end of the diode D8 is connected to the second connection end of the variable resistor R32 and grounded.

[0064] The range switching circuit includes a manual range switching circuit, and the adjustment circuit includes a comparison delay circuit. The manual range switching circuit includes connection terminal CN2, resistor R1, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, and multi-position selection switch SW1; connection terminal CN2 serves as the input end of the manual range switching circuit, and one end of resistor R1 is respectively connected to one end of resistor R3, the first connection end of multi-position selection switch SW1, and the first connection end of connection terminal CN2; the other end of resistor R1 is respectively connected to one end of resistor R7 and grounded; the other end of resistor R3 is connected to one end of resistor R4, and the other end of resistor R4 is respectively connected to one end of resistor R5 and the second connection end of multi-position selection switch SW1; the other end of resistor R5 is connected to one end of resistor R6, and the other end of resistor R6 is respectively connected to the other end of resistor R7 and the third connection end of multi-position selection switch SW1; the fourth connection end of multi-position selection switch SW1 serves as the output end of the manual range switching circuit.

[0065] The comparison delay circuit includes adjustable resistor R16, resistor R17, resistor R19, operational amplifier chip U9.1, adjustable resistor R24, resistor R26, capacitor C29, operational amplifier chip U9.2, and resistor R36; the first connection end of adjustable resistor R16 is externally connected to the power supply, and the adjustment connection end of adjustable resistor R16 is connected to the inverting input end of operational amplifier chip U9.1; one end of resistor R17 serves as the input end of the comparison delay circuit, and the other end of resistor R17 is respectively connected to one end of resistor R19 and the non-inverting input end of operational amplifier chip U9.1; the negative power supply end of operational amplifier chip U9.1 is externally connected to the power supply; the output end of operational amplifier chip U9.1 is respectively connected to one end of resistor R26, the non-inverting input end of operational amplifier chip U9.2, and one end of capacitor C29; the first connection end of adjustable resistor R24 is connected to the other end of resistor R26 and is externally connected to the power supply; the second connection end of adjustable resistor R24 is connected to the other end of capacitor C29; the adjustable connection end of adjustable resistor R24 is connected to the inverting input end of operational amplifier chip U9.2; the output end of operational amplifier chip U9.2 is connected to one end of resistor R36 and serves as the output end of the comparison delay circuit; the other end of resistor R36 is externally connected to the power supply; the second connection end of resistor R16, the other end of R19, the positive power supply end of operational amplifier chip U9.1, and the second connection end of R24 are equipotential.

[0066] The effective value ratio amplification circuit includes capacitor C19, resistor R18, resistor R20, resistor R21, adjustable resistor R23, resistor R28, operational amplifier chip U8.1, diode D5, diode D6, capacitor C28, resistor R27, operational amplifier chip U8.2, resistor R29, and capacitor C30; one end of capacitor C19 is respectively connected to one end of resistor R18 and one end of resistor R22, and serves as the input end of the effective value ratio amplification circuit; the other end of capacitor C19 is grounded; the other end of resistor R18 is respectively connected to one end of resistor R21, one end of diode D5, and the inverting input end of operational amplifier chip U8.1; the non-inverting input end of operational amplifier chip U8.1 is connected to one end of resistor R20, and the other end of resistor R20 is grounded; the other end of resistor R21 is connected to one end of adjustable resistor R23, and the other end of adjustable resistor R23 is respectively connected to one end of resistor R28 and the inverting input end of operational amplifier chip U8.2; the other end of diode D5 is respectively connected to the output end of operational amplifier chip U8.1 and one end of diode D6; the other end of diode D6 is respectively connected to one end of capacitor C28 and one end of resistor R27, and the other end of capacitor C28 is grounded; the other end of resistor R27 is respectively connected to the other end of resistor R22 and the non-inverting input end of operational amplifier chip U8.2; the output end of operational amplifier chip U8.2 is respectively connected to the other end of resistor R28 and one end of resistor R29, the other end of resistor R29 is connected to one end of capacitor C30, and serves as the output end of the effective value ratio amplification circuit; the other end of capacitor C30 is grounded; the positive power supply terminal and the negative power supply terminal of operational amplifier chip U8.1 are externally connected to a power supply.

[0067] The output circuit includes resistor R30, resistor R31, triode Q1, diode D7, relay, and connection terminal CN4; one end of resistor R30 is connected to one end of resistor R31, and serves as the input end of the output circuit; the other end of resistor R30 is connected to the emitter of triode Q1 and is grounded; the other end of resistor R31 is connected to the base of triode Q1, and the collector of triode Q1 is respectively connected to the first connection end of the relay and one end of diode D7; the other end of diode D7 is connected to the second connection end of the relay and is externally connected to a power supply; the third connection end of the relay is connected to the first connection end of connection terminal CN4, the fourth connection end of the relay is connected to the second connection end of connection terminal CN4, and the fifth connection end of the relay is connected to the third connection end of connection terminal CN4.

[0068] In other embodiments, the range switching circuit further includes an automatic range switching circuit, and the adjustment circuit further includes a CPU circuit. It can be switched to or select other range switching circuits and adjustment circuits. The range switching circuit is an automatic range switching circuit, and the adjustment circuit is a CPU circuit. The automatic range switching circuit is connected to the CPU circuit. The automatic range switching circuit includes a connection terminal CN3, a resistor R1, a resistor R3, a resistor R4, a resistor R5, a resistor R6, a resistor R7, a control chip U4, and an analog switch; the connection terminal CN3 serves as the input end of the automatic range switching circuit. One end of the resistor R1 is respectively connected to one end of the resistor R3, the first connection end of the control chip U4, and the first connection end of the connection terminal CN3; the other end of the resistor R1 is respectively connected to one end of the resistor R7 and the second connection end of the connection terminal CN3, and is grounded; the other end of the resistor R3 is connected to one end of the resistor R4, and the other end of the resistor R4 is respectively connected to one end of the resistor R5 and the second connection end of the control chip U4; the other end of the resistor R5 is connected to one end of the resistor R6, and the other end of the resistor R6 is respectively connected to the other end of the resistor R7 and the third connection end of the control chip U4; the analog switch is connected to the control chip U4; the fourth connection end of the control chip U4 serves as the output end of the automatic range switching circuit. As Figure 1 shown, Figure 1 The circuit shown by the dashed box is an optional circuit in different embodiments.

[0069] Example 2:

[0070] Those skilled in the art can understand this embodiment as a more specific illustration of Embodiment 1.

[0071] The abnormal current in the three-phase power supply line includes zero-sequence current and leakage current in addition to the short-circuit current. The zero-sequence current refers to the vector sum of the three-phase phase currents, and its formula is: i0 = i u + i v + i w , and the zero-sequence current is zero under the condition of balanced three-phase power supply. The leakage current is the sum of the zero-sequence current and the N-line current, and its formula is: i = i u + i v + i w + i n .

[0072] Currently, industrial three-phase motors, especially those three-phase motors using drive equipment for speed regulation, are all three-phase powered and do not have an N line. Therefore, for these three-phase motors, the zero-sequence current and the leakage current are the same, and the three-phase currents of the three-phase motor are balanced. So under normal circumstances, the zero-sequence current is the leakage current and should be 0. Therefore, by collecting the data of the zero-sequence current of the motor, the leakage situation of the motor can be judged. This embodiment will be implemented based on this theory.

[0073] Zero-sequence current detection is currently usually achieved by using a through-core zero-sequence current transformer. All phase lines are passed through the zero-sequence current transformer to detect the zero-sequence current. There are already mature through-core zero-sequence current transformer products on the market for sale. This method is the mainstream design solution and is widely used in building electrical fire prevention. Most products on the market are in specifications of 500 mA and 1000 mA. This design generally rarely considers the overload multiple. The AD digital acquisition range is narrow, and the measurement accuracy is relatively high. A 10 mA current can also be accurately and reliably calculated, meeting the personal safety standards and being suitable for civil buildings. Therefore, in theory, using a through-core zero-sequence current transformer can also detect the leakage current of a three-phase motor. However, because the leakage current detection range is relatively narrow, the maximum leakage current is just over 1 A. It is obviously not suitable for industrial electrical applications. Industrial equipment all has large loads. Generally, when there is a leakage current, it is dozens of amperes, hundreds of amperes, and even thousands of amperes may occur. At this time, the zero-sequence current transformer will have the situation of core saturation, and the current value cannot be detected, and it may even be damaged.

[0074] The general current detection transformer has a large overload capacity. When there is a leakage current of thousands of amperes, the core will not saturate, and the calculation is accurate and reliable. Therefore, it is more appropriate to use a general current transformer as the sampling sensor. However, because the current measurement range is wide, especially for small currents in the milliampere level, the calculation error is relatively large. However, for three-phase motor-driven equipment, it usually already has complete protection functions (such as overcurrent protection), and the leakage current in the milliampere level can usually be ignored. If there is a need, a microprocessor can be used to perform curve fitting on the measurement data of the transformer to improve the detection accuracy and ensure that the current in the milliampere level can also be reliably detected.

[0075] In this embodiment, by using a general through-core transformer to collect the phase currents of a three-phase motor, the leakage current detection of the three-phase motor is realized. For a motor with a small driving current, one transformer can be used, and the three phase lines of the motor are all passed through the transformer for leakage current detection. For a motor with a large current, the phase lines are thicker, and even multiple cables need to be connected in parallel for power supply. At this time, it is impossible to implement the leakage current collection by passing all the phase lines through one transformer because the aperture of the transformer is too small. At this time, the three-phase lines of the motor can be passed through independent transformers respectively, and then the output ends of the three transformers are connected in series in turn. The leakage current detection is realized by detecting the current after the three transformers are connected in series. However, at this time, attention needs to be paid to the polarity of the output ends of the transformers. If the polarity is reversed, the detection result will be incorrect.

[0076] In this embodiment, a 10-watt 1-ohm power resistor is used as the sampling resistor. When sampling the current output of a 5-A current transformer, the highest sampling voltage will reach 5V. Compared with a sampling resistor in the milliohm range, the sampling voltage is higher and less susceptible to electromagnetic interference from the external environment. Therefore, the sampling accuracy will be higher. The disadvantage is that the power consumption is greater, which causes the sampling resistor to heat up, resulting in an increase in the resistance value, and thus a decrease in sampling accuracy. However, since the current when the sampling resistor heats up has reached the ampere level, the loss of accuracy at this time will no longer affect the leakage judgment. In addition, the resistance value accuracy of power resistors is generally not high, but this can be compensated by measuring its accurate resistance value through a bridge during implementation and then adjusting the proportional coefficient of the subsequent circuit, without affecting the accuracy.

[0077] Since the range of leakage current may be from a dozen milliamperes to hundreds or thousands of amperes, which is too large, it must pass through a range selection circuit for voltage division before normal detection can be carried out. Since the current of a three-phase motor is an alternating current, the sampling voltage will also be an alternating voltage. Therefore, it is necessary to measure the effective value of the sampling voltage to accurately obtain the actual leakage current of the motor. So the sampled voltage after voltage division needs to pass through an effective value proportional amplification circuit for full-wave rectification and proportional amplification to obtain a DC voltage, which is the effective value of the sampling voltage. By comparing and judging this voltage, the leakage situation of the motor can be obtained.

[0078] This voltage can be judged whether it exceeds the threshold through a comparison circuit with adjustable threshold, and then through a delay circuit with adjustable time to drive a relay for status output. This is the simplest solution. This solution is simple, reliable, and low-cost, and has good accuracy for motors operating at 50Hz power frequency. However, in the case of a motor with variable-frequency drive, especially when the motor operates at low frequency, the leakage current detection error is relatively large.

[0079] The output load of the effective value proportional amplification circuit in this embodiment is an RC circuit with a time constant of about 27 milliseconds. For a working frequency of 50Hz, the true effective value can be collected with high accuracy. For working frequencies lower than 50Hz, since the current period will be greater than 27 milliseconds, even reaching several hundred milliseconds, the sampled voltage of this circuit is actually a pulsating voltage at this time. This voltage is only the instantaneous effective value, not the true effective value. If directly compared and judged, the accuracy will seriously decline.

[0080] Another solution is that after the output voltage of the effective value ratio amplification circuit is collected by an embedded CPU and undergoes analog-to-digital conversion, complex statistics and operations can be performed on this voltage. Curve fitting can be carried out on the coefficients of the current transformer, sampling resistor, and effective value ratio amplification circuit in this embodiment, thereby improving the sampling accuracy. At the same time, time-domain analysis can be performed on the sampling data to obtain the true effective value data of the leakage current, making the judgment more accurate and reliable. A human-machine interaction interface can also be implemented through the cooperation of a keyboard input and a display device, thereby realizing adjustment functions for multiple data such as threshold adjustment, delay adjustment, range adjustment, and system parameters. At the same time, the detection result can also be output to the display device, enabling the user to more intuitively observe the specific data of the leakage current of the motor. The embedded CPU can accurately judge whether the leakage current is abnormal based on the above series of parameter settings and the calculated true effective value data, making the output result more stable and reliable.

[0081] This embodiment is implemented through two design solutions, which can meet the leakage current detection of motors with and without drive devices, motors operating at power frequency and variable frequency under all working conditions, and can perform stable, accurate, and reliable leakage current judgment, thus solving the current situation of the lack or unreliability of leakage detection means for three-phase motors in the industrial field, and effectively realizing the safety protection of various aspects such as the three-phase motor body, drive device, and personnel. It also indirectly guarantees production efficiency, stable production, and safe production.

[0082] Figure 2 It is a manual range switching circuit. The switching action is achieved through a multi-position selection switch (SW1). CN2 is the connection terminal of the current transformer, and the output terminal of the current transformer is connected to the manual range switching circuit through this terminal. R1 is a sampling resistor with a resistance value of 1 ohm and a power of 10 watts. The current of the current transformer flows through the sampling resistor to form a sampling voltage. R3 to R7 form a voltage division circuit, which is the core circuit of the manual range switching circuit. The series resistance of R3 and R4 is 9 kΩ, the series resistance of R5 and R6 is 900 Ω, the resistance value of R7 is 100 Ω, and the total resistance of R3 to R7 is 10 kΩ. Therefore, the voltage division at the upper end of R7 is 1% of the sampling voltage, the voltage division at the upper end of R5 is 10% of the sampling voltage, and the voltage at the upper end of R3 is equal to the sampling voltage. The voltage division circuit composed of R3 to R7 is actually in parallel with the sampling resistor R1. In theory, it should shunt a part of the sampling current, but because the total resistance of R3 to R7 is 10 kΩ, which is 10,000 times that of the sampling resistor, the shunted current can be ignored.

[0083] Figure 3 It is an automatic range switching circuit. The core part of the automatic range switching circuit is the same as that of the manual switching circuit, only Figure 2The manual switch in it is replaced with an analog switch CD4066, that is, SW1 is replaced with U4. Since an analog switch is adopted, all range switching can be controlled through the CPU circuit, thereby realizing the automatic range switching function.

[0084] Figure 4 It is an effective value proportional amplification circuit, implemented by using the dual operational amplifier chip LM358. This circuit is a composite input asymmetric full-wave small-signal precision full-wave rectification circuit, and it is required that R21 + R23 = R18. The advantage is that the dual functions of full-wave rectification and proportional amplification can be realized by one dual operational amplifier, with a simple structure and easy adjustment. R28 can be used to adjust the proportional gain, and the proportional gain is equal to 1 + R28 / (R21 + R23). If R28 = 0, the proportional gain is equal to 1. The disadvantage is that the input impedances of the positive and negative half-waves are not equal, and the output waveform is asymmetric. However, this problem can be solved by appropriately adjusting R23 to make the positive and negative waveforms basically symmetric, and a little deviation can be ignored for this utility model. R29 and C30 are the RC loads of this circuit, and the time constant τ = RC is approximately equal to 27 milliseconds. For a working frequency of 50Hz, the period is 20 milliseconds, so the true effective value can be collected with high precision. For the case of variable frequency drive, the frequency may be as low as below 10Hz. Since the period of the current will be greater than 27 milliseconds and may reach several hundred milliseconds, the sampled voltage of this circuit is actually a pulsating voltage at this time. This voltage is only the instantaneous effective value, not the true effective value, and the CPU circuit needs to perform time-domain analysis to obtain the true effective value data.

[0085] Figure 5 It is a comparison delay circuit, implemented by using the dual comparator chip LM393. The whole circuit is divided into two parts: threshold comparison and output delay. R16 is an adjustable potentiometer, with a reference voltage of 5V as the reference (by Figure 8The reference circuit provides a voltage divider circuit, and its output voltage serves as the threshold voltage. The voltage output by the above-mentioned effective value proportional amplification circuit serves as the comparison voltage. Since the output of the effective value proportional amplification circuit is approximately 0 - 10V and the reference voltage is 5V, the output voltage of the effective value proportional amplification circuit needs to be attenuated through a 1 / 2 voltage divider circuit composed of R17 and R19 to make its voltage variation range fall within the interval of 0 - 5V, so as to realize the data comparison of the full range. When the comparison voltage is greater than the threshold voltage, the output of U9.1 will become a high-impedance state. At this time, the RC circuit composed of R26 and C29 will be in a charging state, and the voltage at the upper end of the capacitor C29 will serve as the comparison voltage. R24 is an adjustable potentiometer, which also realizes a voltage divider circuit based on the 5V reference voltage, and its output voltage serves as the threshold voltage. When the comparison voltage is greater than the threshold voltage, the output of U9.2 will become a high-impedance state, and due to the pull-up of R36, the delay circuit will output a high level. When the comparison voltage is less than the threshold voltage, the output of U9.1 will become a low level. At this time, the charge on C29 will be quickly released through U9.1, and the voltage becomes 0. Then the output of U9.2 will become a low level.

[0086] The time constant τ = RC of the RC circuit composed of R26 and C29 is equal to 10 seconds. According to the characteristics of the RC circuit, the voltage at the upper end of its capacitor C will increase with the increase of time. When the time t is equal to 2τ, the voltage is about 86% of the power supply voltage. When the time t is equal to 3τ, the voltage is about 95% of the power supply voltage. When the time t is equal to 4τ, the voltage is about 98% of the power supply voltage. When the time t is equal to 5τ, the voltage is about 99% of the power supply voltage. Therefore, the theoretically maximum delay time is about 50 seconds. However, in fact, the adjustment range of the potentiometer R24 after more than 10 seconds is very small, and its slight change will cause a large increase in the delay time, so it is extremely difficult to adjust and has little practical significance. Therefore, the normal adjustment time range of this circuit is still within the interval of 0 - 10 seconds.

[0087] Figure 6 is the output circuit. The output circuit is a triode drive circuit that drives a relay with a working voltage of 5V to act. In the initial stage when the circuit is powered on, there is an unstable time. At this time, R30 pulls down the base of the triode Q1 to a low level to ensure that the relay will not malfunction in the initial stage of power-on. And R31 is the base resistor of the triode Q1 and is the action control input terminal of the output circuit. When a high level (greater than 1V) is input, the triode will conduct, thereby driving the relay to pull in, and the action status information can be provided to external devices through the relay contacts.

[0088] Figure 7It is a CPU circuit. The CPU uses a domestic embedded CPU, with the model number STC32F12K54-64I-LQFP48. This CPU has 32-bit computing power, a hardware floating-point arithmetic processor, and 12-bit resolution ADC conversion ability. Therefore, it has strong capabilities in processing analog quantities. This model of CPU is an industrial-grade CPU and can work normally in the environment of -40°C to 85°C.

[0089] KEY1 to KEY4 form a keyboard input circuit, which is connected to the P2.0 to P2.3 input interfaces of the CPU, providing a manual input interface for the human-machine interface of the CPU circuit. KEY1 is a parameter setting function key, KEY2 is a data increment function key, KEY3 is a data decrement function key, and KEY4 is a cursor shift function key.

[0090] LED1 is a 4-digit LED digital tube, forming a display circuit, and has a colon clock separator. This separator can blink to give a prompt when the utility model detects that the leakage current exceeds the threshold and starts timing. When working, it displays the currently detected leakage current, and when setting parameters, it displays the setting menu and setting data. The CPU connects to the segment pins of LED1 through ports P4.0 to P4.7 to achieve segment driving, and connects to the bit pins of LED1 through ports P5.0 to P5.3 to achieve bit switching, and drives LED1 to display through the dynamic scanning method.

[0091] The keyboard input circuit and the display circuit cooperate to implement a human-machine interaction interface, thereby realizing the adjustment functions of multiple data such as trigger threshold, trigger delay time, range, and system parameters.

[0092] The output voltage of the RMS proportional amplification circuit is connected to the analog quantity acquisition port ADC14 of the CPU. Since the output of the RMS proportional amplification circuit is approximately 0 to 10V, and the reference voltage is 5V, it is necessary to attenuate the output voltage of the RMS proportional amplification circuit through a 1 / 2 voltage division circuit composed of R34 and R35 so that its voltage change range falls within the interval of 0 to 5V to achieve full-range data detection.

[0093] The CPU circuit also needs to perform a range judgment to implement the automatic range switching function. Because the range of the entire leakage current is very wide, it may be from a few milliamperes to thousands of amperes. The utility model is divided into three ranges, and each range is set with an upper limit threshold and a lower limit threshold. If the quantified data is greater than the upper limit threshold, the gear is raised; conversely, if the quantified data is less than the lower limit threshold, the gear is lowered. The gear switching function is realized by controlling the analog switch CD4066 in the automatic range switching circuit through ports P0.0 to P0.2.

[0094] The analog-to-digital conversion of the CPU requires a stable reference voltage, which needs to be provided by a reference circuit ( Figure 8 ), and the reference voltage is connected to the reference voltage interface REF+ of the CPU.

[0095] Figure 8 The reference circuit has a core chip of AD586, which can provide a reference voltage of 5V. Since this utility model is applied to the industrial field and the electromagnetic interference in the working environment is very strong, a relatively high voltage needs to be selected for the reference voltage source to improve the resistance to electromagnetic interference. Therefore, 5V voltage is selected as the reference voltage of this utility model. The detection accuracy and reliability of this utility model both require a stable, reliable, and accurate voltage as reference data. Therefore, the performance of the reference voltage source is of decisive significance for whether the detection of this utility model is stable, reliable, and accurate.

[0096] The performance of AD586 is significantly higher than that of most other 5V reference voltage sources. AD586 represents a major advancement in the field of advanced single-chip reference voltage sources. It uses a proprietary ion-implanted buried zener diode and laser wafer trimming of highly stable thin-film resistors, enabling it to provide excellent performance at a relatively low cost. The model selected for this utility model is AD586A, whose operating temperature is -40°C to +85°C, and it is an industrial-grade chip.

[0097] Figure 9 For the power supply circuit, this utility model is an industrial instrument product, and its working stability and reliability require a high-quality power supply for guarantee. Most of the DC power supplies in industrial products are 24V. Therefore, this utility model uses a 24V DC power supply as the power source. However, the CPU circuit and output circuit of this utility model require a 5V power supply, the effective value ratio amplification circuit requires a ±12V power supply, the comparison delay circuit requires 12V and 5V power supplies, and the reference circuit requires a power supply greater than 6V. Considering comprehensively, this utility model needs to set up a 5VDC power supply circuit and a ±12VDC power supply circuit. The 5VDC power supply circuit supplies power to the CPU circuit and the output circuit, the ±12VDC power supply circuit supplies power to the effective value ratio amplification circuit, and the comparison delay circuit and the reference circuit are powered by the +12VDC power supply in the ±12VDC power supply circuit and the 5V power supply in the 5VDC power supply circuit. To improve the stability and reliability of this utility model, the ±12VDC power supply circuit uses linear LDO chips 78L12 and 79L12 to achieve +12VDC and -12VDC regulated power supplies respectively. And the input voltage of 78L12 and 79L12 needs to be greater than the output voltage. Moreover, since they are LDO chips, the greater the difference between the input voltage and the output voltage, the greater their own power consumption. To reduce power consumption, this utility model uses a ±15VDC power supply circuit to supply power to the ±12VDC power supply circuit, thereby achieving a stable and reliable ±12VDC power output.

[0098] Since the power supply is a unipolar power supply, the ±15VDC power supply must be implemented through a circuit capable of changing the power supply polarity. The present utility model uses the SX1308 chip to achieve power supply polarity conversion. SX1308 is a fixed-frequency, current-mode boost converter in an SOT23-6 package. The operating frequency of up to 1.2MHz allows for smaller specifications of the peripheral inductors and capacitors. The built-in soft-start function reduces the inrush current during startup. SX1308 automatically switches to the PFM mode under light load. SX1308 includes input undervoltage lockout, current limit, and thermal protection functions. However, since SX1308 is a boost chip, the supply voltage must be less than 12V. Therefore, the ±15VDC power supply circuit is powered by a 5VDC power supply circuit.

[0099] The 5VDC power supply circuit of the present utility model is implemented using the LM2576T-5.0 chip. The LM2576T series voltage regulators are monolithic integrated circuits and are step-down switching voltage regulators. They can drive a 3A load with excellent line and load regulation. Compared with LDO voltage regulator chips, the switching voltage regulator will not have a significant increase in power consumption due to a large difference between the input voltage and the output voltage. The switching voltage regulator can greatly reduce the size of the heat sink and in some cases, no heat sink is required. The input voltage range of the LM2576T-5.0 chip is 4V to 40V, the output voltage is 5V, the output current can reach 3A, the switching frequency is 52kHz, the operating efficiency is as high as 80%, and the operating temperature range is -40°C to 125°C, fully meeting the requirements of the present utility model.

[0100] Therefore, the power supply structure of the present utility model is that the 24VDC power supply first passes through the C5 and C8 capacitors for filtering and then powers the 5VDC power supply circuit. Its output voltage is 5V DC voltage. After passing through the C11 and C14 capacitors for filtering, it powers the CPU circuit, the output circuit, and the ±15VDC power supply circuit. The ±15VDC power supply circuit converts the 5VDC power supply into a ±15VDC power supply. Among them, the +15V power supply passes through a series of capacitor banks for filtering and then outputs to the input terminal of the 78L12 chip in the ±12VDC power supply circuit, and then is converted into a stable and reliable +12VDC power supply to power the effective value ratio amplification circuit, the comparison delay circuit, and the reference circuit. The -15V power supply passes through a series of capacitor banks for filtering and then outputs to the input terminal of the 79L12 chip in the ±12VDC power supply circuit, and then is converted into a stable and reliable -12VDC power supply to power the effective value ratio amplification circuit.

[0101] Example 3:

[0102] Those skilled in the art can understand this embodiment as a more specific description of Embodiment 1 and Embodiment 2.

[0103] In this embodiment, the phase line current of the three-phase motor under test is collected by a current transformer, and the output of the current transformer is connected to a sampling resistor ( Figure 2 The sampling voltage is connected to the manual range switching circuit ( Figure 2 ), realize range switching and obtain the measured voltage. The manual range switching circuit is mainly a voltage divider circuit with three ranges of 1%, 10%, and 100% of the sampled data, which are switched through a multi-position selection switch. The measured voltage is connected to the effective value proportional amplifier circuit ( Figure 4 ) input end, the effective value proportional amplifier circuit will first perform full-wave rectification on the measured voltage, then perform proportional amplification, and then obtain a comparison voltage on an RC load. The comparison voltage is the voltage after the effective value of the measured voltage is proportionally amplified. This voltage is connected to the comparison delay circuit ( Figure 5 ), the comparison delay circuit is divided into a comparison circuit and a delay circuit. The comparison voltage is connected to the input end of the comparison circuit, the output end of the comparison circuit is connected to the input end of the delay circuit, and the output end of the delay circuit is connected to the input end of the output circuit.

[0104] The comparison circuit compares the comparison voltage with the threshold voltage. If it exceeds the threshold, it will output a high level, and then output it to the delay circuit. After a certain delay, the output state is connected to the output circuit ( Figure 6 ), the status output is carried out through the relay, and the delay time can be manually adjusted through the potentiometer. Figure 8 ) provides a reference voltage for the threshold of the comparison circuit, and the threshold is manually adjusted through a potentiometer.

[0105] Example 4:

[0106] Those skilled in the art may understand this embodiment as a more specific description of Embodiment 1 and Embodiment 2.

[0107] In this embodiment, the phase line current of the three-phase motor under test is collected by a current transformer, and the output of the current transformer is connected to a sampling resistor ( Figure 3 R1 in the circuit) to obtain the sampling voltage, which is then connected to the automatic range switching circuit ( Figure 3 ), realize range switching and obtain the measured voltage. The automatic range switching circuit is mainly a voltage divider circuit with three ranges of 1%, 10%, and 100% of the sampled data, which are switched by the CD4066 electronic switch. The measured voltage is connected to the effective value proportional amplifier circuit ( Figure 4) At the input end, the effective value proportional amplification circuit will first perform full-wave rectification on the measured voltage, then perform proportional amplification, and then obtain a comparison voltage on an RC load. The comparison voltage is the voltage after proportional amplification of the effective value of the measured voltage, and this voltage is connected to the ADC analog-to-digital conversion port of the CPU circuit ( Figure 7 ), and the CPU performs analog-to-digital conversion on this signal to obtain a quantization data of the comparison voltage.

[0108] The CPU can perform complex statistics and operations on the quantization data of the comparison voltage. Before the product leaves the factory, a series of calibration operations need to be carried out in this embodiment, including curve fitting for the mutual inductor, sampling resistor, automatic range switching circuit, and effective value proportional amplification circuit in the present utility model to obtain a discretized fitting data set. This data set will be interval-corresponded with the collected quantization data of the comparison voltage and the current range, thereby greatly improving the calculation accuracy. At the same time, it is also necessary to perform time-domain analysis on the quantization data of the comparison voltage. Usually, data acquisition can be carried out every 10 milliseconds, and then time-domain calculation can be carried out every 200 milliseconds. The true effective value data of the leakage current is calculated in the form of root mean square. The true effective value data is compared with the set trigger threshold. If it is greater than the trigger threshold, the timing starts. If the timing time is greater than the set trigger delay time, a trigger status signal is output through the IO interface. The trigger status signal is connected to the input end of the output circuit ( Figure 6 ), and the status is output through a relay. If it is detected during the timing process that the quantization data drops and is less than the trigger threshold, the timing stops and the timer is cleared.

[0109] The 200-millisecond time-domain calculation period can cover the motor drive frequencies from 5 Hz to 50 Hz, and basically can cover all working conditions of the motors in the crane application field, so that the judgment can be more accurate and reliable.

[0110] In addition, a human-machine interaction interface can be realized through the cooperation of the keyboard input and the display device, so as to realize the adjustment functions of multiple data such as trigger threshold adjustment, trigger delay time adjustment, range adjustment, and system parameters. It can be set to a fixed range or an automatic range. The fixed range means selecting a fixed range through the software interface, that is, the CPU will control the analog switch chip of the automatic range circuit to select a fixed path to conduct. In the case of automatic range, the CPU will automatically switch the range according to the value of the quantization data of the comparison voltage.

[0111] For the automatic range, usually an upper limit threshold of this range is set. If the quantization data is greater than this threshold, the gear is raised. On the contrary, a lower limit threshold of this range also needs to be set. If the quantization data is less than this threshold, the gear is lowered to realize the automatic range switching function.

[0112] At the same time, the CPU circuit can output the test results to the display device, so that the user can more intuitively observe the specific data of the motor leakage current. The CPU performs accurate calculations based on the above series of parameters, combined with the calculated true effective value data and the adjusted fitting curve data, so that the leakage current can be accurately calculated, thereby accurately judging whether the leakage current is abnormal, making the output result more stable and reliable.

[0113] The analog-to-digital conversion of the CPU requires a stable reference voltage, which requires a reference circuit ( Figure 8 ) is provided.

[0114] The utility model adopts a universal core-penetrating mutual inductor to collect the phase line current of the three-phase motor, thereby realizing leakage current detection of the three-phase motor.

[0115] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0116] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other at will.

Claims

1. A three-phase motor leakage detection device, characterized in that Including: Current transformer, range switching circuit, RMS proportional amplification circuit, adjustment circuit, and output circuit; The current transformer is used to collect the phase current of the three-phase motor to be measured. The current transformer is connected to the input end of the range switching circuit, and the output end of the range switching circuit is connected to the input end of the RMS proportional amplification circuit; The output end of the RMS proportional amplification circuit is connected to the input end of the adjustment circuit, and the output end of the adjustment circuit is connected to the input end of the output circuit.

2. The three-phase motor leakage detection device according to claim 1, wherein, A sampling resistor is connected between the current transformer and the range switching circuit, and a reference circuit is connected to the adjustment circuit.

3. The three-phase motor leakage detection device according to claim 1, characterized in that, The range switching circuit includes a manual range switching circuit, and the adjustment circuit includes a comparison delay circuit.

4. The three-phase motor leakage detection device according to claim 3, characterized in that, The manual range switching circuit includes connection terminal CN2, resistor R1, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, and multi-position selection switch SW1; The connection terminal CN2 serves as the input end of the manual range switching circuit. One end of the resistor R1 is respectively connected to one end of the resistor R3, the first connection end of the multi-position selection switch SW1, and the first connection end of the connection terminal CN2; the other end of the resistor R1 is respectively connected to one end of the resistor R7 and grounded; The other end of the resistor R3 is connected to one end of the resistor R4, and the other end of the resistor R4 is respectively connected to one end of the resistor R5 and the second connection end of the multi-position selection switch SW1; The other end of the resistor R5 is connected to one end of the resistor R6, and the other end of the resistor R6 is respectively connected to the other end of the resistor R7 and the third connection end of the multi-position selection switch SW1; The fourth connection end of the multi-position selection switch SW1 serves as the output end of the manual range switching circuit.

5. The three-phase motor leakage detection device according to claim 1, characterized in that, The range switching circuit includes an automatic range switching circuit, the adjustment circuit includes a CPU circuit, and the automatic range switching circuit is connected to the CPU circuit.

6. The three-phase motor leakage detection device according to claim 5, characterized in that, The automatic range switching circuit includes connection terminal CN3, resistor R1, resistor R3, resistor R4, resistor R5, resistor R6, resistor R7, control chip U4, and analog switch; The connection terminal CN3 serves as the input end of the automatic range switching circuit. One end of the resistor R1 is respectively connected to one end of the resistor R3, the first connection end of the control chip U4, and the first connection end of the connection terminal CN3; the other end of the resistor R1 is respectively connected to one end of the resistor R7 and the second connection end of the connection terminal CN3 and grounded; The other end of the resistor R3 is connected to one end of the resistor R4, and the other end of the resistor R4 is respectively connected to one end of the resistor R5 and the second connection end of the control chip U4; The other end of the resistor R5 is connected to one end of the resistor R6, and the other end of the resistor R6 is respectively connected to the other end of the resistor R7 and the third connection end of the control chip U4; The analog switch is connected to the control chip U4; the fourth connection end of the control chip U4 serves as the output end of the automatic range switching circuit.

7. The three-phase motor leakage detection device according to claim 1, characterized in that, The effective value proportional amplification circuit includes capacitor C19, resistor R18, resistor R20, resistor R21, adjustable resistor R23, resistor R28, operational amplifier chip U8.1, diode D5, diode D6, capacitor C28, resistor R27, operational amplifier chip U8.2, resistor R29, and capacitor C30; One end of the capacitor C19 is respectively connected to one end of the resistor R18 and one end of the resistor R22 and serves as the input end of the effective value proportional amplification circuit; the other end of the capacitor C19 is grounded; The other end of the resistor R18 is respectively connected to one end of the resistor R21, one end of the diode D5, and the inverting input end of the operational amplifier chip U8.1; the non-inverting input end of the operational amplifier chip U8.1 is connected to one end of the resistor R20, and the other end of the resistor R20 is grounded; The other end of the resistor R21 is connected to one end of the adjustable resistor R23, and the other end of the adjustable resistor R23 is respectively connected to one end of the resistor R28 and the inverting input end of the operational amplifier chip U8.2; The other end of the diode D5 is respectively connected to the output end of the operational amplifier chip U8.1 and one end of the diode D6; the other end of the diode D6 is respectively connected to one end of the capacitor C28 and one end of the resistor R27, and the other end of the capacitor C28 is grounded; the other end of the resistor R27 is respectively connected to the other end of the resistor R22 and the non-inverting input end of the operational amplifier chip U8.2; The output end of the operational amplifier chip U8.2 is respectively connected to the other end of the resistor R28 and one end of the resistor R29, and the other end of the resistor R29 is connected to one end of the capacitor C30 and serves as the output end of the effective value proportional amplification circuit; the other end of the capacitor C30 is grounded; The positive power supply terminal and the negative power supply terminal of the operational amplifier chip U8.1 are externally connected to a power supply.

8. The three-phase motor leakage detection device according to claim 3, characterized in that, The comparison delay circuit includes adjustable resistor R16, resistor R17, resistor R19, operational amplifier chip U9.1, adjustable resistor R24, resistor R26, capacitor C29, operational amplifier chip U9.2, and resistor R36; The first connection end of the adjustable resistor R16 is externally connected to a power supply, and the adjustment connection end of the adjustable resistor R16 is connected to the inverting input end of the operational amplifier chip U9.1; One end of the resistor R17 serves as the input end of the comparison delay circuit, and the other end of the resistor R17 is respectively connected to one end of the resistor R19 and the non-inverting input end of the operational amplifier chip U9.1; The negative power supply terminal of the operational amplifier chip U9.1 is externally connected to a power supply; the output end of the operational amplifier chip U9.1 is respectively connected to one end of the resistor R26, the non-inverting input end of the operational amplifier chip U9.2, and one end of the capacitor C29; The first connection end of the adjustable resistor R24 is connected to the other end of the resistor R26 and is externally connected to a power supply; the second connection end of the resistor R24 is connected to the other end of the capacitor C29; the adjustable connection end of the resistor R24 is connected to the inverting input end of the operational amplifier chip U9.2; The output terminal of the operational amplifier chip U9.2 is connected to one end of the resistor R36 and serves as the output terminal of the comparison delay circuit; the other end of the resistor R36 is externally connected to a power supply; The second connection terminal of the resistor R16, the other end of the R19, the positive power supply terminal of the operational amplifier chip U9.1, and the second connection terminal of the R24 are equipotential.

9. The three-phase motor leakage detection device according to claim 1, characterized in that, The output circuit includes a resistor R30, a resistor R31, a triode Q1, a diode D7, a relay, and a connection terminal CN4; One end of the resistor R30 is connected to one end of the resistor R31 and serves as the input terminal of the output circuit; the other end of the resistor R30 is connected to the emitter of the triode Q1 and is grounded; The other end of the resistor R31 is connected to the base of the triode Q1, and the collector of the triode Q1 is respectively connected to the first connection terminal of the relay and one end of the diode D7; The other end of the diode D7 is connected to the second connection terminal of the relay and is externally connected to a power supply; the third connection terminal of the relay is connected to the first connection terminal of the connection terminal CN4, the fourth connection terminal of the relay is connected to the second connection terminal of the connection terminal CN4, and the fifth connection terminal of the relay is connected to the third connection terminal of the connection terminal CN4.

10. The three-phase motor leakage detection device according to claim 1, characterized in that, The reference circuit includes a core chip U6, a variable resistor R32, a resistor R33, and a diode D8; The first connection terminal of the core chip U6 is externally connected to a power supply, the second connection terminal of the core chip U6 is respectively connected to the first connection terminal of the variable resistor R32 and one end of the resistor R33, and the third connection terminal of the core chip U6 is connected to the adjustable end of the variable resistor R32; The other end of the resistor R33 is connected to one end of the diode D8; the other end of the diode D8 is connected to the second connection terminal of the variable resistor R32 and is grounded.

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