A cable anti-theft system based on common N line

Abstract

The application provides a cable anti-theft system based on common N line, belonging to the field of cable anti-theft, which comprises a power supply system, a power supply protection switch, a cable, a charging device, an overvoltage relay, a battery pack, a wireless transmitting device, a repeater, a capacitor, an earth, an alarm terminal grounding device and a power supply system grounding device. One end of the charging device is connected with the phase line of the cable, and the other end is connected with the neutral line of the cable. The positive input end of the battery pack is connected with the output end of the charging device through the normally closed contact of the voltage relay. The charging transformer adopts a single-phase autotransformer. Since the common end in the primary side / secondary side of the autotransformer is directly connected and connected with the neutral line of the power cable, the AC / DC loop of the device can directly use the neutral line N line of the power cable as the common conductor, which provides sufficient and necessary conditions for the operation of the device. Meanwhile, the earth is used as another conductor of the device, thereby saving the cost of the system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cable theft prevention, and in particular to a cable theft prevention system based on a shared N line. BACKGROUND

[0002] Most existing cable theft prevention methods include the following: pouring concrete at random points on the cable; locking the street cable manhole cover to prevent theft; assigning staff to patrol the area day and night; and using power line carrier communication to determine whether the cable has been stolen.

[0003] Existing Chinese patent cable theft prevention devices and systems use power carrier communication for electric theft prevention and impedance detection for non-electric theft prevention. In the case of non-electric theft prevention, the relationship between the electrical load and the cable line connection or disconnection is complex, or the relationship between the branch line and the main line connection or disconnection is complex, and the impedance detection is not accurate, which interferes with non-electric theft prevention and makes management more difficult. Therefore, a simple, convenient, and fast cable theft prevention device is needed. SUMMARY

[0004] The present application aims to provide a cable theft prevention system based on a shared N line, which solves the problem of complex structure of existing cable theft prevention devices and inaccurate non-electric theft prevention monitoring.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0006] A cable theft prevention system based on a shared N line includes a power supply system, a power supply protection switch, a power supply cable, a charging device, an overvoltage relay, a battery pack, a wireless transmission alarm device, an intermediate relay, a capacitor, ground, an alarm terminal grounding device, and a power supply system grounding device. The power supply system is connected to the power supply cable through the power supply protection switch. One end of the charging device is connected to the power supply cable, and the other end of the charging device is connected to the neutral line of the power supply cable. The positive electrode of the battery pack is connected to the output end of the charging device, and the negative electrode of the battery pack is connected to the ground wire of the power supply cable. One end of the wireless transmission alarm device is connected to the positive electrode of the battery pack, and the other end of the wireless transmission alarm device is connected to the neutral line of the power supply cable through the intermediate relay. One end of the capacitor is connected to the intermediate relay, and the other end of the capacitor is connected to the alarm terminal grounding device. The neutral point of the power supply system is connected to the power supply system grounding device, and the alarm terminal grounding device and the power supply system grounding device are both connected to the ground.

[0007] Further, the charging device includes a self-coupled transformer and a rectifier diode. The neutral line N of the power supply cable is connected to the low-voltage input end of the primary winding of the self-coupled transformer, and the high-voltage output end of the self-coupled transformer is connected to the anode of the rectifier diode.

[0008] Further, the overvoltage relay comprises an overvoltage relay coil, an overvoltage relay normally closed contact A and an overvoltage relay normally closed contact B, the cathode of the rectifier diode is connected with the positive pole of the battery set, one end of the wireless transmitting alarm device and one end of the intermediate relay coil through the overvoltage relay normally closed contact B respectively, and the other end of the capacitor is connected with the low potential input end of the primary winding of the autotransformer and one end of the overvoltage relay normally closed contact A through the overvoltage relay coil respectively.

[0009] Further, the intermediate relay comprises an intermediate relay coil and an intermediate relay normally closed contact, the other end of the intermediate relay coil is connected with the alarm grounding device and one end of the capacitor respectively, the other end of the overvoltage relay normally closed contact A is connected with the negative pole of the battery set and one end of the intermediate relay normally closed contact respectively, and the other end of the intermediate relay normally closed contact is connected with the other end of the wireless transmitting device.

[0010] Further, the phase line output end of the power supply system is connected with the phase line of the power supply cable through the power supply protection switch, the autotransformer adopts the connection mode of high voltage input and low voltage output, any phase line of the power supply cable is connected with the high potential input end of the primary winding of the autotransformer, the alarm grounding device is connected with the power supply system grounding device through the ground, and the power supply system grounding device is connected with the neutral point of the power supply system and the neutral line N of the power supply cable respectively.

[0011] Further, when the power supply protection switch is closed and the power supply cable is in the non-disconnected state, the power supply system is charged by the charging device and supplies power to the battery set and the intermediate relay coil, all working currents of the intermediate relay coil flow out from the cathode of the rectifier diode, flow to the intermediate relay coil through the overvoltage relay normally closed contact B, flow into the ground through the alarm grounding device, flow into the neutral point of the power supply system from the ground through the power supply system grounding device, part of the currents flow to the low potential input end of the autotransformer through the neutral line N of the power supply cable, flow into the anode of the rectifier diode through the high potential output end of the autotransformer, and part of the currents flow to the power supply protection switch through the internal part of the power supply system, then flow into the high potential input end of the autotransformer through the phase line of the power supply cable, and flow into the anode of the rectifier diode through the high potential output end of the autotransformer.

[0012] Further, when the power supply protection switch is opened and the power supply cable is in the non-disconnected state, the battery set supplies power to the intermediate relay coil, all working currents of the intermediate relay coil flow out from the positive pole of the battery set, flow into the intermediate relay coil, flow into the ground through the alarm grounding device, flow into the neutral point of the power supply system from the ground through the power supply system grounding device, flow to the overvoltage relay normally closed contact A through the neutral line N of the power supply cable, and then flow into the negative pole of the battery set.

[0013] Further, when the power supply switch is closed and the neutral line N of the power supply cable is disconnected before the phase line connecting the charging device, the phase line voltage is introduced into the overvoltage relay coil through the primary winding of the autotransformer, the overvoltage relay coil is actuated by overvoltage, the overvoltage relay normally closed contact A and the overvoltage relay normally closed contact B are disconnected, the holding current of the intermediate relay coil is cut off, the intermediate relay coil loses power, the intermediate relay normally closed contact is closed, the wireless transmission alarm device is powered on, and a cable theft signal is sent. After the overvoltage relay normally closed contact A and the overvoltage relay normally closed contact B are disconnected, high voltage is prevented from being introduced into the battery pack, the wireless transmission alarm device and the intermediate relay coil, and the devices are prevented from being burned out.

[0014] Further, when the power supply switch is closed and the neutral line N of the power supply cable is disconnected after the phase line connecting the charging device, the overvoltage relay coil will not have an overvoltage phenomenon, the overvoltage relay normally closed contact A and the overvoltage relay normally closed contact B are still in the closed state, and after the neutral line N is disconnected, the relay coil current cannot pass through the capacitor (9), the overvoltage relay coil (15) and the overvoltage relay normally closed contact A (16) to reach the negative electrode of the battery pack (6) due to the blocking effect of the capacitor on direct current, the holding current of the intermediate relay coil is cut off, the intermediate relay coil loses power, the intermediate relay normally closed contact is closed, the wireless transmission alarm device is powered on, and a cable theft signal is sent.

[0015] Further, in the open state of the power supply switch, the overvoltage relay coil will not have an overvoltage phenomenon, the overvoltage relay normally closed contact A and the overvoltage relay normally closed contact B are still in the closed state, and after the neutral line N of the power supply cable is disconnected, the relay coil current cannot pass through the capacitor (9), the overvoltage relay coil (15) and the overvoltage relay normally closed contact A (16) to reach the negative electrode of the battery pack (6) due to the blocking effect of the capacitor on direct current, the holding current of the intermediate relay coil is cut off, the intermediate relay coil loses power, the intermediate relay normally closed contact is closed, the wireless transmission alarm device is powered on, and a cable theft signal is sent.

[0016] The application has the following beneficial effects due to the adoption of the above technical solutions:

[0017] The charging transformer adopts single-phase autotransformer, and the primary / secondary winding of the autotransformer is directly connected at one end and connected to zero, so that the AC / DC circuit of the device can directly use the neutral line N of the power cable as the common conductor, and the device provides sufficient and necessary conditions for operation, and uses the earth as the other conductor of the device, greatly saving the cost of the system, and the battery pack adopts the floating charging mode, when the power grid is powered, the repeater is powered by the power grid, when the power grid is powered off, the repeater is powered by the battery pack, and the device can realize monitoring at different time periods, when the cable is stolen or cut off, the wireless alarm transmitter is powered by the battery pack and enters the alarm working state, and the device will not stop working due to power grid interruption, the device has the advantages of simple structure, accurate alarm and low maintenance cost. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the structural diagram of the present application;

[0019] Figure 2 is the working current path diagram of the intermediate relay in the power grid power supply state of the present application (in the figure, I1 = I2 + I3);

[0020] Figure 3 is the working current path diagram of the intermediate relay in the power grid power supply state of the present application;

[0021] Figure 4 is the working current path diagram of the wireless transmitting alarm device in the alarm state of the present application.

[0022] In the drawings, 1 is a power supply system, 2 is a power supply protection switch, 3 is a power supply cable, 4 is a charging device, 5 is an overvoltage relay, 6 is a battery pack, 7 is a wireless transmitting alarm device, 8 is an intermediate relay, 9 is a capacitor, 10 is the earth, 11 is an alarm grounding device, 12 is a power supply system grounding device, 13 is an autotransformer, 14 is a rectifier diode, 15 is an overvoltage relay coil, 16 is an overvoltage relay normally closed contact A, 17 is an overvoltage relay normally closed contact B, 18 is an intermediate relay coil, and 19 is an intermediate relay normally closed contact. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear and obvious, the present application is further described in detail below with reference to the drawings and preferred embodiments. However, it should be noted that many details in the description are only for the reader to have a thorough understanding of one or more aspects of the present application, and the aspects of the present application can be realized without these specific details.

[0024] As Figures 1-4As shown in the figure, a cable anti-theft system based on common N line includes power supply system 1, power supply protection switch 2, power supply cable 3, charging device 4, overvoltage relay 5, battery pack 6, wireless transmission alarm device 7, intermediate relay 8, capacitor 9, ground 10, alarm terminal grounding device 11 and power supply system grounding device 12, power supply system 1 is connected with power supply cable 3 through power supply protection switch 2, one end of charging device 4 is connected with any phase line of power supply cable 3, the other end of charging device 4 is connected with neutral line of power supply cable 3, the positive pole of battery pack 6 is connected with the output end of charging device 4, the negative pole of battery pack 6 is connected with neutral line of power supply cable 3 through overvoltage relay 5, one end of wireless transmission alarm device 7 is connected with the positive pole of battery pack 10, the other end of wireless transmission alarm device 7 is connected with neutral line of power supply cable 3 through intermediate relay 8, one end of capacitor 9 is connected with intermediate relay 8, and the other end of capacitor 9 is connected with alarm terminal grounding device 11, the neutral point of power supply system 1 is connected with power supply system grounding device 12, and alarm terminal grounding device 11 and power supply system grounding device 12 are both connected with ground 10.

[0025] In the embodiment of the present application, as shown in the figure, Figure 1 charging device 4 includes autotransformer 13 and rectifier diode 14, neutral line N of power supply cable 3 is connected with the low potential input end of primary winding of autotransformer 13, and the high potential output end of autotransformer 13 is connected with the anode of rectifier diode 14.

[0026] In the embodiment of the present application, as shown in the figure, Figure 1 overvoltage relay 5 includes overvoltage relay coil 15, overvoltage relay normally closed contact A 16 and overvoltage relay normally closed contact B 17, the cathode of rectifier diode 14 is connected with the positive pole of battery pack 6, one end of wireless transmission alarm device 7 and one end of intermediate relay coil 18 through overvoltage relay normally closed contact B 17, respectively, the other end of capacitor 9 is connected with the low potential input end of primary winding of autotransformer 13 and one end of overvoltage relay normally closed contact A 16 through overvoltage relay coil 15, respectively.

[0027] In the embodiment of the present application, as shown in the figure, Figure 1 intermediate relay 8 includes intermediate relay coil 18 and intermediate relay normally closed contact 19, the other end of intermediate relay coil 18 is connected with alarm terminal grounding device 11 and one end of capacitor 9, respectively, the other end of overvoltage relay normally closed contact A 16 is connected with the negative pole of battery pack 6 and one end of intermediate relay normally closed contact 19, respectively, the other end of intermediate relay normally closed contact 19 is connected with the other end of wireless transmission device 7.

[0028] When the cable 3 is in the power supply state, the charging device 4 charges the battery group 6 and supplies power to the relay coil 18, the relay coil 18 generates magnetic attraction to open the relay normally closed contact 19, the wireless transmitting device 7 is powered off, and no alarm occurs. When the power supply cable 3 is in the power-off state, the negative pole of the battery group 6 is connected to the other end of the relay coil 18 through the voltage relay normally closed contact A16, the neutral line of the power supply cable 3, the power supply system grounding device 12, the ground 10 and the alarm terminal grounding device 11. Since the positive pole of the battery group 6 is connected to one end of the relay coil 18, the battery group 6 supplies power to the relay coil 18, the relay coil 18 generates magnetic attraction to open the relay normally closed contact 19, the wireless transmitting device 7 is powered off, and no alarm occurs. When the power supply cable 3 is cut off, the charging device 4 cannot supply power, the negative pole of the battery group 6 cannot be connected to the other end of the relay coil 18 through the neutral line of the power supply cable 3, the battery group 6 cannot supply power to the relay coil 18, the relay coil 18 does not generate magnetic attraction, the relay normally closed contact 19 is closed, the wireless transmitting device 7 forms a closed loop with the battery group 6, the wireless transmitting device 7 is powered on, and an alarm signal is sent

[0029] In the embodiment of the present application, as shown in Figure 1 the phase line output end of the power supply system 1 is connected to the phase line of the power supply cable 3 through the power supply protection switch 2, the autotransformer 13 adopts a connection mode of high-voltage input and low-voltage output, any phase line of the power supply cable 3 is connected to the high-voltage input end of the primary winding of the autotransformer 13, the alarm terminal grounding device 11 is connected to the power supply system grounding device 12 through the ground 10, and the power supply system grounding device 12 is connected to the neutral line N of the power supply cable 3 and the neutral point of the power supply system 1.

[0030] In the embodiment of the present application, as shown in Figure 1 the power supply protection switch 2 is closed and the power supply cable 3 is in the non-disconnected state, the power supply system 1 charges the battery group 6 and supplies power to the intermediate relay coil 18 through the charging device 4, all working currents of the intermediate relay coil 18 flow out from the cathode of the rectifier diode 14, flow to the intermediate relay coil 18 through the voltage relay normally closed contact B17, flow into the ground 10 through the alarm terminal grounding device 11, flow into the neutral point of the power supply system 1 through the power supply system grounding device 12 from the ground 10, part of the currents flow to the low-voltage input end of the autotransformer 13 through the neutral line N of the power supply cable 3, flow into the anode of the rectifier diode 14 through the high-voltage output end of the autotransformer 13, and part of the currents flow to the power supply protection switch 2 through the inside of the power supply system 1, then flow into the high-voltage input end of the autotransformer 13 through the phase line of the power supply cable 3, and finally flow into the anode of the rectifier diode 14 through the high-voltage output end of the autotransformer 13.

[0031] In the embodiment of the present application, as shown in Figures 2-4As shown, the power supply protection switch 2 is off and the neutral line of the power supply cable 3 is in the non-disconnected state. The battery pack 6 supplies power to the intermediate relay coil 18, all the working current of the intermediate relay coil 18 flows out of the positive pole of the battery pack 6, flows into the intermediate relay coil 18, flows into the ground 10 through the alarm grounding device 11, flows into the neutral point of the power supply system 1 through the power supply system grounding device 12 from the ground 10, flows to the overvoltage relay normally closed contact A16 through the neutral line N of the power supply cable 3, and then flows into the negative pole of the battery pack 6.

[0032] In the embodiment of the present application, as shown in Figures 2-4 As shown, when the power supply switch 2 is closed and the neutral line N of the power supply cable 3 is disconnected before the phase line connected to the charging device 4, the phase line voltage is introduced into the overvoltage relay coil 15 through the primary winding of the autotransformer 13. The overvoltage relay coil 15 operates due to overvoltage, the overvoltage relay normally closed contact A16 and the overvoltage relay normally closed contact B17 are disconnected, the holding current of the intermediate relay coil 18 is cut off, the intermediate relay coil 18 loses power, the intermediate relay normally closed contact 19 is connected, the wireless transmission alarm device 7 is powered, and a cable stolen signal is sent. After the overvoltage relay normally closed contact A16 and the overvoltage relay normally closed contact B17 are disconnected, high voltage is prevented from being introduced into the battery pack 6, the wireless transmission alarm device 7 and the intermediate relay coil 18, and the devices are prevented from being burned out.

[0033] In the embodiment of the present application, as shown in Figures 2-4 As shown, when the power supply switch 2 is closed and the neutral line N of the power supply cable 3 is disconnected after the phase line connected to the charging device 4, the overvoltage relay coil 15 does not appear overvoltage phenomenon, the overvoltage relay normally closed contact A16 and the overvoltage relay normally closed contact B17 are still in the closed state. After the neutral line N is disconnected, due to the blocking effect of the capacitor 9 on direct current, the other end of the relay coil 18 cannot connect the negative pole of the battery pack through the capacitor 9, the overvoltage coil 15 and the overvoltage relay normally closed contact A16, the holding current of the intermediate relay coil 18 is cut off, the intermediate relay coil 18 loses power, the intermediate relay normally closed contact 19 is closed, the wireless transmission alarm device 7 is powered, and a cable stolen signal is sent.

[0034] In the embodiment of the present application, as shown in Figures 2-4As shown, in the off state of the power supply switch 2, the overvoltage relay coil 15 will not appear overvoltage phenomenon, the overvoltage relay normally closed contact A 16, the overvoltage relay normally closed contact B 17 is still in the closed state, after the neutral line N of the power cable 3 is disconnected, due to the blocking effect of the capacitor 9 on the direct current, the other end of the relay coil 18 cannot pass through the capacitor 9, the overvoltage coil 15, the overvoltage relay normally closed contact A 16 to connect the negative pole of the battery, cutting off the holding current of the intermediate relay coil 18, the intermediate relay coil 18 loses power, the intermediate relay normally closed contact 19 is closed, the wireless transmission alarm device 7 is powered on, and the cable theft signal is sent.

[0035] Whether in power supply or power failure, when the power cable is stolen or cut off, the N line is disconnected, the current It is interrupted, the alarm relay coil loses power, the normally closed contact is driven to be connected, and the alarm relay coil is powered on. And send an alarm signal to the security center. The charging transformer uses a single-phase autotransformer, and because one end of the primary / secondary winding of the autotransformer is directly connected and connected to zero, the AC / DC loop of the device can directly use the neutral line N of the power cable as a common conductor, providing sufficient and necessary conditions for the operation of the device. Using the earth as the other conductor of the device greatly saves the cost of the system. The battery uses a floating charging method, and when the power grid is powered, the relay is powered by the power grid, and when the power grid is powered off, the relay is powered by the battery, which can realize different break detection. When the cable is stolen or cut off, the wireless alarm transmitter is powered by the battery and enters the alarm working state, and will not stop working due to power grid break.

[0036] The device is suitable for the theft protection of ~220V / 380V outdoor cable lines with TT or TN-S system grounding mode.

[0037] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the art, some improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A cable anti-theft system based on common N-wire, characterized in that: The utility model provides a kind of power supply system, including power supply system (1), power supply protection switch (2), power supply cable (3), charging device (4), overvoltage relay (5), battery pack (6), wireless transmission alarm device (7), intermediate relay (8), capacitor (9), ground (10), alarm end grounding device (11) and power supply system grounding device (12), power supply system (1) is connected with power supply cable (3) by power supply protection switch (2), one end of charging device (4) is connected with power supply cable (3), the other end of charging device (4) is connected with the neutral line of power supply cable (3), the positive pole of battery pack (6) is connected with the output end of charging device (4), the negative pole of battery pack (6) is connected with the neutral line of power supply cable (3), one end of wireless transmission alarm device (7) is connected with the positive pole output end of battery pack (10), the other end of wireless transmission alarm device (7) is connected with the neutral line of power supply cable (3) by intermediate relay (8), one end of capacitor (9) is connected with intermediate relay (8), and alarm end grounding device (11) is connected, the neutral point of power supply system (1) is connected with power supply system grounding device (12), and alarm end grounding device (11) and power supply system grounding device (12) are buried in ground (10); Charging device (4) includes autotransformer (13) and rectifier diode (14), the neutral line N line of power supply cable (3) is connected with the low potential input end of the primary winding of autotransformer (13), and the high potential output end of autotransformer (13) is connected with the anode of rectifier diode (14); Overvoltage relay (5) includes overvoltage relay coil (15), overvoltage relay normally closed contact A (16) and overvoltage relay normally closed contact B (17), the cathode of rectifier diode (14) is connected with the positive pole of battery pack (6), one end of wireless transmission alarm device (7), one end of intermediate relay coil (18) respectively through overvoltage relay normally closed contact B (17), the other end of capacitor (9) is connected with the low potential input end of the primary winding of autotransformer (13) and one end of overvoltage relay normally closed contact A (16) respectively through overvoltage relay coil (15); The phase line output end of power supply system (1) is connected with the phase line of power supply cable (3) by power supply protection switch (2), autotransformer (13) adopts the wiring mode of high voltage input low voltage output, and any phase line of power supply cable (3) is connected with the high potential input end of the primary winding of autotransformer (13), alarm end grounding device (11) is connected with power supply system grounding device (12) through ground (10), and power supply system grounding device (12) is connected with the neutral point of power supply system (1) and the neutral line N line of power supply cable (3) respectively. When the power supply protection switch (2) is closed and the power supply cable (3) is in the non-disconnected state, the power supply system (1) charges the battery pack (6) through the charging device (4) and supplies power to the intermediate relay coil (18). The entire working current of the intermediate relay coil (18) flows out from the cathode of the rectifier diode (14), flows to the intermediate relay coil (18) through the normally closed contact B (17) of the voltage relay, flows into the ground (10) through the alarm grounding device (11), flows into the neutral point of the power supply system (1) from the ground (10) through the power supply system grounding device (12), part of the current flows to the low potential input end of the autotransformer (13) through the neutral line N of the power supply cable (3), flows into the anode of the rectifier diode (14) through the high potential output end of the autotransformer (13), and part of the current flows to the power supply protection switch (2) through the internal part of the power supply system (1), then flows into the high potential input end of the autotransformer (13) through the phase line of the power supply cable (3), and flows into the anode of the rectifier diode (14) through the high potential output end of the autotransformer (13).

2. The cable anti-theft system based on common N-wire according to claim 1, characterized in that: The intermediate relay (8) includes an intermediate relay coil (18) and an intermediate relay normally closed contact (19). The other end of the intermediate relay coil (18) is connected to the alarm terminal grounding device (11) and one end of the capacitor (9), respectively. The other end of the overvoltage relay normally closed contact A (16) is connected to the negative electrode of the battery pack (6) and one end of the intermediate relay normally closed contact (19), respectively. The other end of the intermediate relay normally closed contact (19) is connected to the other end of the wireless transmission device (7).

3. The common N-wire based cable theft prevention system according to claim 1, wherein: When the power supply protection switch (2) is opened and the power supply cable (3) is in the non-disconnected state, the battery pack (6) supplies power to the intermediate relay coil (18). The entire working current of the intermediate relay coil (18) flows out from the positive electrode of the battery pack (6), flows into the intermediate relay coil (18), flows into the ground (10) through the alarm grounding device (11), and flows into the neutral point of the power supply system (1) from the ground (10) through the power supply system grounding device (12). The neutral line N of the power supply cable (3) flows to the overvoltage relay normally closed contact A (16), and then flows into the negative electrode of the battery pack (6).

4. The common N-wire based cable theft prevention system according to claim 1, wherein: When the power supply switch (2) is closed and the neutral line N of the power supply cable (3) is disconnected before the phase line connected to the charging device (4), the phase line voltage is introduced into the overvoltage relay coil (15) through the primary winding of the autotransformer (13). The overvoltage relay coil (15) operates due to overvoltage, the overvoltage relay normally closed contact A (16) and the overvoltage relay normally closed contact B (17) are opened, the holding current of the intermediate relay coil (18) is cut off, the intermediate relay coil (18) loses power, the intermediate relay normally closed contact (19) is connected, the wireless transmission alarm device (7) is powered, and a cable stolen signal is sent. At the same time, after the overvoltage relay normally closed contact A (16) and the overvoltage relay normally closed contact B (17) are opened, high voltage is prevented from being introduced into the battery pack (6), the wireless transmission alarm device (7), and the intermediate relay coil (18), and the equipment is not burned out.

5. The common N-wire based cable theft prevention system according to claim 1, wherein: When the power supply switch (2) is closed and the neutral line N of the power supply cable (3) is disconnected after connecting the charging device (4), the overvoltage relay coil (15) will not have an overvoltage phenomenon, and the overvoltage relay normally closed contact A (16) and the overvoltage relay normally closed contact B (17) will still be in a closed state. After the neutral line N is disconnected, due to the blocking effect of the capacitor (9) on direct current, the relay coil current cannot pass through the capacitor (9), the overvoltage relay coil (15), and the overvoltage relay normally closed contact A (16) to reach the negative pole of the battery pack (6), cutting off the holding current of the intermediate relay coil (18), the intermediate relay coil (18) loses power, the intermediate relay normally closed contact (19) is closed, the wireless transmission alarm device (7) is powered on, and a cable theft signal is sent.

6. The common N-wire based cable theft prevention system according to claim 1, wherein: In the open state of the power supply switch (2), the overvoltage relay coil (15) will not have an overvoltage phenomenon, and the overvoltage relay normally closed contact A (16) and the overvoltage relay normally closed contact B (17) will still be in a closed state. After the neutral line N of the power supply cable (3) is disconnected, due to the blocking effect of the capacitor (9) on direct current, the relay coil current cannot pass through the capacitor (9), the overvoltage relay coil (15), and the overvoltage relay normally closed contact A (16) to reach the negative pole of the battery pack (6), cutting off the holding current of the intermediate relay coil (18), the intermediate relay coil (18) loses power, the intermediate relay normally closed contact (19) is closed, the wireless transmission alarm device (7) is powered on, and a cable theft signal is sent.

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