Direct current insulation monitoring device

Abstract

The utility model discloses a DC insulation monitoring device. The device comprises a monitoring host, a monitoring expansion module and a current transformer. The monitoring host is in communication connection with the plurality of monitoring expansion modules, and each monitoring expansion module is connected with the plurality of current transformers; the monitoring expansion module comprises an expansion control unit, an expansion communication unit, a current detection unit and a current reference unit; the expansion control unit is in communication connection with the monitoring host through the expansion communication unit, the expansion control unit is connected to the current detection unit, and the expansion control unit is connected to the current reference unit; the current reference unit surrounds the current transformer, and the current detection unit surrounds the current transformer. According to the device, the insulation monitoring performance of the insulation monitoring device can be effectively improved, and the operation and maintenance frequency of operation and maintenance personnel on the insulation monitoring device can be reduced. The utility model relates to the technical field of DC power distribution.

Description

Technical Field

[0001] This utility model relates to the field of DC power distribution technology, and in particular to a DC insulation monitoring device. Background Technology

[0002] DC systems are power supply equipment used in hydroelectric and thermal power plants, various substations, and other users of DC equipment. They provide DC power to signaling equipment, protection systems, automatic devices, emergency lighting, emergency power supplies, and circuit breaker opening and closing operations. To ensure high-quality operation of DC systems, power production units need to regularly inspect and maintain the DC system equipment.

[0003] Currently, existing technologies typically monitor the insulation status of DC systems through insulation monitoring devices. However, due to the wear or aging of the internal electronic components of these devices during long-term operation caused by environmental factors (such as temperature and humidity), the insulation monitoring performance of the devices deteriorates, leading to an increase in the frequency of maintenance required by maintenance personnel.

[0004] Therefore, the problems existing in the current technology still need to be solved and optimized. Utility Model Content

[0005] The purpose of this utility model is to solve, to a certain extent, the technical problems existing in the related technologies.

[0006] Therefore, one objective of this utility model is to provide a DC insulation monitoring device, which can effectively improve the insulation monitoring performance of the insulation monitoring device and help reduce the frequency of maintenance of the insulation monitoring device by maintenance personnel.

[0007] To achieve the above technical objectives, this utility model provides a DC insulation monitoring device, including a monitoring host, a monitoring expansion module, and a current transformer;

[0008] The monitoring host is communicatively connected to several monitoring expansion modules, and each monitoring expansion module is connected to several current transformers;

[0009] The monitoring extension module includes an extension control unit, an extension communication unit, a current detection unit, and a current reference unit;

[0010] The extended control unit is connected to the monitoring host via the extended communication unit, the extended control unit is connected to the first end of the current detection unit, and the extended control unit is connected to the first end of the current reference unit;

[0011] The second end of the current reference unit surrounds the first end of the current transformer, and the second end of the current detection unit surrounds the second end of the current transformer.

[0012] In addition, a DC insulation monitoring device according to an embodiment of the present invention may also have the following additional technical features:

[0013] Optionally, in one embodiment of the present invention, the current reference unit includes a first current reference circuit and a second current reference circuit;

[0014] The first current reference circuit is wrapped around the first end of the current transformer in the forward direction, and the second current reference circuit is wrapped around the first end of the current transformer in the reverse direction.

[0015] Optionally, in one embodiment of the present invention, the current detection unit includes a first amplifier, the output of which is connected to the extended control unit.

[0016] Optionally, in one embodiment of the present invention, the monitoring host includes a host communication unit, a host control unit, a bridge circuit correction unit, and a voltage reference unit;

[0017] The host control unit communicates with the monitoring expansion module through the host communication unit;

[0018] The host control unit is connected to the first terminal of the voltage reference unit, the host control unit is connected to the first terminal of the bridge circuit correction unit, and the second terminal of the voltage reference unit is connected to the second terminal of the bridge circuit correction unit.

[0019] Optionally, in one embodiment of the present invention, the voltage reference unit includes a sampling regulator chip, a first resistor, a second resistor, and a third resistor;

[0020] The host control unit is connected to the first terminal of the sampling voltage regulator chip through the first resistor, the first terminal of the sampling voltage regulator chip is connected to the first terminal of the second resistor, and the second terminal of the sampling voltage regulator chip is connected to the first terminal of the second resistor;

[0021] The third terminal of the sampling voltage regulator chip is connected to the second terminal of the third resistor, the first terminal of the third resistor is connected to the second terminal of the second resistor, and the first terminal of the third resistor is connected to the bridge circuit correction unit.

[0022] Optionally, in one embodiment of the present invention, the bridge circuit correction unit includes a bridge and voltage divider circuit and a voltage amplifier circuit;

[0023] The input terminal of the bridge and voltage divider circuit is connected to the DC bus in the DC system, and the output terminal of the bridge and voltage divider circuit is connected to the voltage amplifier circuit.

[0024] Optionally, in one embodiment of the present invention, the bridge and voltage divider circuit includes a first switch, a second switch, a third switch, a fourth switch, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, and an eleventh resistor.

[0025] The first terminal of the first switch is grounded through the fourth resistor, the first terminal of the second switch is grounded through the fifth resistor, the first terminal of the third switch is grounded through the sixth resistor, and the first terminal of the fourth switch is grounded through the seventh resistor.

[0026] The second terminal of the first switch is connected to the second terminal of the third switch, the second terminal of the third switch is connected to the first terminal of the eighth resistor, the second terminal of the eighth resistor is connected to the first terminal of the ninth resistor, the first terminal of the ninth resistor is connected to the first terminal of the voltage amplifier circuit, and the second terminal of the ninth resistor is grounded.

[0027] The second terminal of the second switch is connected to the second terminal of the fourth switch, the second terminal of the fourth switch is connected to the second terminal of the eleventh resistor, the first terminal of the eleventh resistor is connected to the second terminal of the tenth resistor, the second terminal of the tenth resistor is connected to the second terminal of the voltage amplifier circuit, and the first terminal of the tenth resistor is grounded.

[0028] Optionally, in one embodiment of the present invention, the voltage amplification circuit includes an optocoupler isolation chip and a second amplifier, the output terminal of the optocoupler isolation chip is connected to the input terminal of the second amplifier, and the output terminal of the second amplifier is connected to the host control unit.

[0029] Optionally, in one embodiment of the present invention, the monitoring host further includes a display unit, which is communicatively connected to the monitoring host.

[0030] Optionally, in one embodiment of the present invention, the monitoring host further includes an alarm unit connected to the monitoring host.

[0031] The advantages and beneficial effects of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention:

[0032] This application discloses a DC insulation monitoring device, which includes a monitoring host, monitoring expansion modules, and current transformers. The monitoring host is communicatively connected to several monitoring expansion modules, and each monitoring expansion module is connected to several current transformers. Each monitoring expansion module includes an expansion control unit, an expansion communication unit, a current detection unit, and a current reference unit. The expansion control unit is communicatively connected to the monitoring host via the expansion communication unit, and is connected to a first end of the current detection unit and a first end of the current reference unit. A second end of the current reference unit surrounds a first end of the current transformer, and a second end of the current detection unit surrounds a second end of the current transformer. This device, based on the current reference unit and current detection unit respectively surrounding and connected to the current transformer, and detecting the current transformer's inductance current signal under different states through the current detection unit, can effectively improve the insulation monitoring performance of the insulation monitoring device and help reduce the frequency of maintenance by operation and maintenance personnel. Attached Figure Description

[0033] The accompanying drawings are used to provide a further understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0034] Figure 1 A schematic diagram of the frame of a DC insulation detection device provided in one embodiment of this utility model;

[0035] Figure 2 A simplified schematic diagram of a current reference unit and a current transformer provided for one embodiment of this utility model;

[0036] Figure 3 A circuit diagram of a current detection unit provided in one embodiment of the present invention;

[0037] Figure 4 A circuit diagram of a voltage reference unit provided in one embodiment of the present invention;

[0038] Figure 5 A circuit diagram of a voltage amplifier circuit provided for one embodiment of the present invention;

[0039] Figure 6 A circuit diagram of a bridge and voltage divider circuit is provided as an embodiment of this utility model. Detailed Implementation

[0040] The embodiments of this utility model are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0041] In the description of this utility model, it should be understood that the terms "length," "upper," "lower," "front," "rear," "left," "right," "top," "inner," "outer," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, features defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, unless otherwise stated, "a plurality of" means two or more.

[0042] Currently, existing technologies typically monitor the insulation status of DC systems using insulation monitoring devices. However, the internal electronic components of these devices may wear out or age due to environmental factors (such as temperature and humidity) during long-term operation, leading to a decline in their insulation monitoring performance. Specifically, this decline applies to the insulation monitoring performance of feeder branches and DC buses within the DC system. To ensure the long-term monitoring performance (such as monitoring accuracy and stability) of the DC insulation devices, maintenance personnel need to perform more frequent maintenance and calibration work on the insulation monitoring devices, thus increasing the frequency of maintenance work.

[0043] In view of this, the present invention provides a DC insulation monitoring device. This device is based on a current reference unit and a current detection unit respectively connected around a current transformer. The current detection unit detects the inductance current signal of the current transformer under different states. This effectively improves the insulation monitoring performance of the insulation monitoring device for feeder branches in DC systems, thus reducing the frequency of maintenance required by operators. Furthermore, the device provides a reference voltage to the bridge circuit correction unit based on a voltage reference unit, which effectively improves the insulation monitoring performance of the insulation monitoring device for bridge circuits in DC systems, further reducing the frequency of maintenance required by operators.

[0044] Reference Figure 1 Specifically, a DC insulation monitoring device in this application embodiment includes a monitoring host, a monitoring expansion module, and a current transformer;

[0045] The monitoring host is communicatively connected to several monitoring expansion modules, and each monitoring expansion module is connected to several current transformers;

[0046] The monitoring extension module includes an extension control unit, an extension communication unit, a current detection unit, and a current reference unit;

[0047] The extended control unit is connected to the monitoring host via the extended communication unit, the extended control unit is connected to the first end of the current detection unit, and the extended control unit is connected to the first end of the current reference unit;

[0048] The second end of the current reference unit surrounds the first end of the current transformer, and the second end of the current detection unit surrounds the second end of the current transformer.

[0049] In this embodiment, the monitoring host is used to exchange data with the monitoring expansion module. Specifically, the data interaction between the monitoring host and the monitoring expansion module can be realized based on a bus-type communication method. For example, based on RS485 communication, the data interaction between the monitoring host and several monitoring expansion modules can be realized through multiple RS485 communication circuits. Each monitoring expansion module can correspond to one RS485 communication circuit. There are many ways to implement the RS485 communication circuit, which will not be described in detail here.

[0050] Understandably, each current transformer is used to monitor the current of a corresponding feeder branch in the DC system, thereby monitoring the insulation status of the feeder branch in the DC system; the extended control unit is used to process communication data with the monitoring data; the extended communication unit is used to realize data interaction between the monitoring host and the monitoring extension module; the current monitoring unit is used to collect the induced current generated by the current transformer; and the current reference unit is used to provide a reference current to the current transformer.

[0051] For example, for a certain current transformer, the working principle of a DC insulation monitoring device provided in this application embodiment is as follows:

[0052] When the current reference unit does not provide a reference current to the current transformer, the current transformer generates an induced current related to the corresponding feeder branch of the DC system based on the principle of electromagnetic induction. This induced current is recorded as the first mutual inductance current signal and is transmitted to the current detection unit. After receiving the first mutual inductance current signal, the current detection unit amplifies and performs analog-to-digital conversion on the first mutual inductance current signal, and then transmits the processed first mutual inductance current signal to the extended control unit.

[0053] When the current reference unit provides a reference current to the current transformer, the current transformer generates an induced current related to the corresponding feeder branch of the DC system based on the principle of electromagnetic induction. This induced current is recorded as the second mutual inductance current signal and is transmitted to the current detection unit. After receiving the second mutual inductance current signal, the current detection unit amplifies and performs analog-to-digital conversion on the second mutual inductance current signal, and then transmits the processed second mutual inductance current signal to the expansion control unit.

[0054] After receiving the processed first mutual inductance current signal and second mutual inductance current signal, the extended control unit can detect and correct the insulation monitoring performance of the feeder branch based on the processed first mutual inductance current signal and second mutual inductance current signal. At the same time, it generates communication data corresponding to the first mutual inductance current signal and second mutual inductance current signal, and transmits the communication data to the monitoring host through the extended communication unit.

[0055] It should be noted that for insulation detection of a DC system feeder branch by a certain current transformer, the extended control unit, after receiving the first current transformer signal, generates corresponding communication data based on the first current transformer signal, and transmits this communication data to the monitoring host through the extended communication unit. Furthermore, this DC insulation detection device does not involve any software improvements; the software aspects can be easily derived from existing technologies.

[0056] Reference Figure 2 In some embodiments, the current reference unit includes a first current reference circuit and a second current reference circuit;

[0057] The first current reference circuit is forward-facing around the first end of the current transformer 100, and the second current reference circuit is reverse-facing around the first end of the current transformer 100.

[0058] Reference Figure 3 In some embodiments, the current detection unit includes a first amplifier U31, the output of which is connected to the extended control unit.

[0059] In this embodiment, the first current reference circuit may include a voltage regulator chip U21, a reference switch K21, and a resistor R21. The voltage regulator chip U21 may be any one of the TL431 chip, LM399 chip, etc. The second current reference circuit is similar to the first current reference circuit and can be easily deduced by analogy.

[0060] Understandably, for the insulation monitoring performance of the feeder branch by the insulation detection device, the first mutual inductance current signal can be obtained in the current detection unit, and the first mutual inductance current can be amplified and converted from analog to digital to obtain the processed first mutual inductance current signal; and, by closing any one of the reference switches in the first current reference circuit or the second current reference circuit, the processed second mutual inductance current signal can be obtained through the current detection unit; if the processed second mutual inductance current signal is the same as or similar to the first mutual inductance current signal, it indicates that the current transformer 100 is damaged.

[0061] It should be noted that, for the calibration of the insulation monitoring performance of the feeder branch by the insulation detection device, the first mutual inductance current signal can be obtained through the current detection unit; at the same time, by closing the reference switch in the first current reference circuit or the second current reference circuit respectively, the first type of second mutual inductance current signal corresponding to the first current reference circuit and the second type of mutual inductance current signal corresponding to the second current reference circuit can be obtained; then, based on the first type of second mutual inductance current signal, the second type of second mutual inductance current signal and the first mutual inductance current signal, the zero point of the current transformer 100 can be calculated, and the zero point calculated can be used to calibrate the insulation monitoring performance of the feeder branch by the insulation detection device.

[0062] In some embodiments, the monitoring host includes a host communication unit, a host control unit, a bridge circuit correction unit, and a voltage reference unit;

[0063] The host control unit communicates with the monitoring expansion module through the host communication unit;

[0064] The host control unit is connected to the first terminal of the voltage reference unit, the host control unit is connected to the first terminal of the bridge circuit correction unit, and the second terminal of the voltage reference unit is connected to the second terminal of the bridge circuit correction unit.

[0065] In this embodiment, the host control unit is used to control whether the voltage reference unit outputs a reference voltage to the bridge circuit correction unit; the voltage reference unit is used to provide a reference voltage to the bridge circuit correction unit; and the bridge circuit correction unit is used to realize the detection and correction of the insulation monitoring performance of the DC bus by the insulation detection device.

[0066] Reference Figure 4 In some embodiments, the voltage reference unit includes a sampling regulator chip U41, a first resistor R41, a second resistor R42, and a third resistor R43;

[0067] The host control unit is connected to the first terminal of the sampling voltage regulator chip U41 through the first resistor R41, the first terminal of the sampling voltage regulator chip U41 is connected to the first terminal of the second resistor R42, and the second terminal of the sampling voltage regulator chip U41 is connected to the first terminal of the second resistor R42.

[0068] The third terminal of the sampling voltage regulator chip U41 is connected to the second terminal of the third resistor R43, the first terminal of the third resistor R43 is connected to the second terminal of the second resistor R42, and the first terminal of the third resistor R43 is connected to the bridge circuit correction unit.

[0069] In this embodiment, the sampling voltage regulator chip U41 can be any one of a TL431 voltage regulator chip or an LM399 voltage regulator chip, etc. This embodiment uses a TL431 voltage regulator chip as an example. Specifically, when the host control unit provides an output signal to the TL431 voltage regulator chip, the TL431 regulated signal can convert the output signal provided by the host control unit into a stable voltage signal. Based on the voltage division of this voltage signal using the second resistor R42 and the third resistor R43, a reference voltage (i.e., ...) is obtained for output to the bridge circuit correction unit. Figure 4 The reference voltage (Vb) is specifically output to the voltage amplifier circuit.

[0070] In some embodiments, the bridge circuit correction unit includes a bridge and voltage divider circuit and a voltage amplifier circuit;

[0071] The input terminal of the bridge and voltage divider circuit is connected to the DC bus in the DC system, and the output terminal of the bridge and voltage divider circuit is connected to the voltage amplifier circuit.

[0072] Reference Figure 5 In some embodiments, the voltage amplification circuit includes an optocoupler isolation chip U51 and a second amplifier U52, the output terminal of the optocoupler isolation chip U51 is connected to the input terminal of the second amplifier U52, and the output terminal of the second amplifier U52 is connected to the host control unit.

[0073] In this embodiment, the voltage amplifier circuit, bridge and voltage divider circuit, and voltage reference unit can be connected via a double-throw switch. The output of the voltage reference unit can be connected to the first input of the double-throw switch, the output of the bridge and voltage divider circuit can be connected to the second input of the double-throw switch, and the voltage amplifier circuit is connected to the output of the double-throw switch. Specifically, for insulation monitoring of the bridge circuit by the insulation detection device, the switching state of the double-throw switch can be switched so that the first input to the output of the double-throw switch is conducting, while the second input to the output of the double-throw switch is not conducting. For detection and correction of sampling deviation in the bridge circuit by the insulation detection device, the switching state of the double-throw switch can be switched so that the second input to the output of the double-throw switch is conducting, while the first input to the output of the double-throw switch is not conducting.

[0074] It is understood that the optocoupler isolation chip U51 in this embodiment of the application can be an AMC1200 chip. For the detection and correction of the voltage sampling deviation of the bridge circuit by the insulation detection device, the reference voltage can be input to the voltage amplification circuit through a double-throw switch, and the amplified reference voltage can be transmitted to the host control unit so that the host control unit can obtain and correct the circuit coefficient of the voltage amplification circuit, thereby realizing the detection and correction of the voltage sampling deviation of the bridge circuit by the insulation detection device.

[0075] It should be noted that, for Figure 5 The positive voltage V+ input is the voltage when the connection between the first input terminal and the output terminal of the double-throw switch is open, but the connection between the second input terminal and the output terminal is closed. Figure 5 The input voltage can also be the reference voltage provided by the voltage reference unit; additionally, when the input voltage is the negative voltage divider V-, it can be used for... Figure 5 The resistor R51 can be adjusted in a simple way. For example, the input port of the negative voltage divider V- can be connected to the first end of the resistor R51, the second end of the resistor R51 can be connected to the second pin of the optocoupler isolation chip U51, the first end of the resistor R52 can be connected to the GND port, and the second end of the resistor R52 can be connected to the first end of the resistor R51. This example is only for illustration.

[0076] Reference Figure 6 In some embodiments, the bridge and voltage divider circuit includes a first switch K61, a second switch K62, a third switch K63, a fourth switch K64, a fourth resistor R61, a fifth resistor R62, a sixth resistor R63, a seventh resistor R64, an eighth resistor R65, a ninth resistor R66, a tenth resistor R67, and an eleventh resistor R68.

[0077] The first terminal of the first switch K61 is grounded through the fourth resistor R61, the first terminal of the second switch K62 is grounded through the fifth resistor R62, the first terminal of the third switch K63 is grounded through the sixth resistor R63, and the first terminal of the fourth switch K64 is grounded through the seventh resistor R64.

[0078] The second terminal of the first switch K61 is connected to the second terminal of the third switch K63, the second terminal of the third switch K63 is connected to the first terminal of the eighth resistor R65, the second terminal of the eighth resistor R65 is connected to the first terminal of the ninth resistor R66, the first terminal of the ninth resistor R66 is connected to the first terminal of the voltage amplifier circuit, and the second terminal of the ninth resistor R66 is grounded.

[0079] The second terminal of the second switch K62 is connected to the second terminal of the fourth switch K64, the second terminal of the fourth switch K64 is connected to the second terminal of the eleventh resistor R68, the first terminal of the eleventh resistor R68 is connected to the second terminal of the tenth resistor R67, the second terminal of the tenth resistor R67 is connected to the second terminal of the voltage amplifier circuit, and the first terminal of the tenth resistor R67 is grounded.

[0080] In this embodiment, the bridge and voltage divider circuit includes a first switch K61 and a second switch K62 as balancing bridge switches, a fourth resistor R61 and a fifth resistor R62 as balancing bridge resistors, a third switch K63 and a fourth switch K64 as detection bridge switches, a sixth resistor R63 and a seventh resistor R64 as detection bridge resistors, an eighth resistor R65 and a ninth resistor R66 as a positive-to-ground voltage divider, and a tenth resistor R67 and an eleventh resistor R68 as a negative-to-ground voltage divider. Specifically, for the balancing bridge portion of the bridge and voltage divider circuit, the corresponding positive voltage divider voltage V+ and negative voltage divider voltage V- can be obtained by switching the switching states of the first switch K61 and the second switch K62. The operating states of the fourth resistor R61 and the fifth resistor R62 can be analyzed using the positive voltage divider voltage V+ and the negative voltage divider voltage V-. Various specific analysis methods exist, which will not be elaborated here.

[0081] It is understandable that the detection bridge part in the bridge and voltage divider circuit is similar to the content about the balanced bridge part mentioned above. It can be simply deduced that the detection of the DC system bridge circuit can be achieved by detecting the operating status of each resistor in the balanced bridge and the detection bridge. This application will not elaborate further here.

[0082] In some embodiments, the monitoring host further includes a display unit, which is communicatively connected to the monitoring host.

[0083] In some embodiments, the monitoring host further includes an alarm unit connected to the monitoring host.

[0084] In this embodiment, the display unit can be a touchscreen with display and signal input functions, which is used to meet the human-machine interaction needs between maintenance personnel and the monitoring host; the alarm unit is used to send a normal alarm signal to the outside world or external devices when an insulation fault occurs in the DC system or when the insulation monitoring device itself malfunctions. There are various specific implementation methods for the display unit and the alarm unit, which will not be described in detail here.

[0085] In the description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0086] Although embodiments of the present invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A DC insulation monitoring device, characterized in that, Includes the monitoring host, monitoring expansion module, and current transformer; The monitoring host is communicatively connected to several monitoring expansion modules, and each monitoring expansion module is connected to several current transformers; The monitoring extension module includes an extension control unit, an extension communication unit, a current detection unit, and a current reference unit; The extended control unit is connected to the monitoring host via the extended communication unit, the extended control unit is connected to the first end of the current detection unit, and the extended control unit is connected to the first end of the current reference unit; The second end of the current reference unit surrounds the first end of the current transformer, and the second end of the current detection unit surrounds the second end of the current transformer.

2. The DC insulation monitoring device according to claim 1, characterized in that, The current reference unit includes a first current reference circuit and a second current reference circuit. The first current reference circuit is wrapped around the first end of the current transformer in the forward direction, and the second current reference circuit is wrapped around the first end of the current transformer in the reverse direction.

3. The DC insulation monitoring device according to claim 1, characterized in that, The current detection unit includes a first amplifier, the output of which is connected to the extended control unit.

4. The DC insulation monitoring device according to claim 1, characterized in that, The monitoring host includes a host communication unit, a host control unit, a bridge circuit correction unit, and a voltage reference unit; The host control unit communicates with the monitoring expansion module through the host communication unit; The host control unit is connected to the first terminal of the voltage reference unit, the host control unit is connected to the first terminal of the bridge circuit correction unit, and the second terminal of the voltage reference unit is connected to the second terminal of the bridge circuit correction unit.

5. The DC insulation monitoring device according to claim 4, characterized in that, The voltage reference unit includes a sampling regulator chip, a first resistor, a second resistor, and a third resistor; The host control unit is connected to the first terminal of the sampling voltage regulator chip through the first resistor, the first terminal of the sampling voltage regulator chip is connected to the first terminal of the second resistor, and the second terminal of the sampling voltage regulator chip is connected to the first terminal of the second resistor; The third terminal of the sampling voltage regulator chip is connected to the second terminal of the third resistor, the first terminal of the third resistor is connected to the second terminal of the second resistor, and the first terminal of the third resistor is connected to the bridge circuit correction unit.

6. The DC insulation monitoring device according to claim 4, characterized in that, The bridge circuit correction unit includes a bridge and voltage divider circuit and a voltage amplifier circuit. The input terminal of the bridge and voltage divider circuit is connected to the DC bus in the DC system, and the output terminal of the bridge and voltage divider circuit is connected to the voltage amplifier circuit.

7. The DC insulation monitoring device according to claim 6, characterized in that, The bridge and voltage divider circuit includes a first switch, a second switch, a third switch, a fourth switch, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, and an eleventh resistor; The first terminal of the first switch is grounded through the fourth resistor, the first terminal of the second switch is grounded through the fifth resistor, the first terminal of the third switch is grounded through the sixth resistor, and the first terminal of the fourth switch is grounded through the seventh resistor. The second terminal of the first switch is connected to the second terminal of the third switch, the second terminal of the third switch is connected to the first terminal of the eighth resistor, the second terminal of the eighth resistor is connected to the first terminal of the ninth resistor, the first terminal of the ninth resistor is connected to the first terminal of the voltage amplifier circuit, and the second terminal of the ninth resistor is grounded. The second terminal of the second switch is connected to the second terminal of the fourth switch, the second terminal of the fourth switch is connected to the second terminal of the eleventh resistor, the first terminal of the eleventh resistor is connected to the second terminal of the tenth resistor, the second terminal of the tenth resistor is connected to the second terminal of the voltage amplifier circuit, and the first terminal of the tenth resistor is grounded.

8. The DC insulation monitoring device according to claim 6, characterized in that, The voltage amplification circuit includes an optocoupler isolation chip and a second amplifier. The output terminal of the optocoupler isolation chip is connected to the input terminal of the second amplifier, and the output terminal of the second amplifier is connected to the host control unit.

9. The DC insulation monitoring device according to claim 4, characterized in that, The monitoring host also includes a display unit, which is communicatively connected to the monitoring host.

10. The DC insulation monitoring device according to claim 4, characterized in that, The monitoring host also includes an alarm unit, which is connected to the monitoring host.

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