CN106443293A - Direct current ground fault online detection and alarm device - Google Patents

Abstract

The invention discloses an on-line detection and alarm device for DC grounding faults, which belongs to the field of fault detection and includes a leakage current detection module, an A/D conversion circuit, a microprocessor, an alarm threshold control module, an audio and sound control circuit, and an acousto-optic Alarm circuit; the input end of the leakage current detection module is installed on the DC power supply inlet end of the load, and the output end of the leakage current detection module is connected to the microprocessor through the A/D conversion circuit, and the microprocessor It is bidirectionally connected with the alarm threshold control module, and the output end of the microprocessor is connected to the input end of the sound and light alarm circuit through the audio and sound control circuit. The invention can accurately locate the grounding fault branch and the grounding fault under the condition that the equipment in operation is not powered off.

Description

A DC ground fault online detection and alarm device

technical field

The invention relates to an on-line detection and alarm device for a DC grounding fault, which belongs to the field of fault detection.

Background technique

The DC system is an important part of power plants, substations and communication base stations. It is a complex multi-branch network. Provide working power. The working condition of the DC system will directly affect the safe, reliable and efficient operation of the power system and communication system. The DC ground fault is the most common fault in the DC system, which may cause misoperation, refusal to operate, burnout of relay contacts and fuses of the control circuit and relay protection devices, resulting in serious accidents. For power plants, especially hydropower plants, the DC system is not well insulated from the ground due to the humid environment of the plant. The DC circuit cables are widely distributed and there are many components, making it more difficult to find fault points. When the DC system insulation drops, it will affect the safe operation of the generator set control system.

The traditional way to find DC grounding faults is the method of "tracking and looking for segmented processing", that is, follow the steps of first signal and then operation part, first outdoor and then indoor part to find the DC system, and step by step to determine which branch line There is a method of manually unplugging the ground fault to find out the fault point. When the circuit power supply is pulled for a short time, the relay protection device or the automatic device may cause false tripping due to the problem of anti-interference performance or fault criterion due to DC power loss. The damage caused by the fault point is detected by the pull-up DC branch method. is very serious. Therefore, the State Power Corporation issued the transmission comprehensive letter [2001] No. 238, "Several Regulations on Unattended Hydropower Plants", Article 7.6.1 pointed out: It is strictly forbidden to adopt the method of cutting DC loads during equipment operation to find and deal with DC grounding faults. When testing the insulation with a 500V megger, all the weak current circuits should be withdrawn to prevent damage. This method cannot accurately locate the fault point, and it takes time and effort to troubleshoot the fault, making the on-site personnel feel at a loss when searching for the DC grounding, and there are many difficulties.

In addition, the disadvantage of the old-fashioned insulation monitoring device using the principle of bridge balance is that it cannot truly reflect the insulation of the DC bus, but can only reflect the imbalance of the insulation resistance of the positive and negative buses. The ground monitoring relay in the ground detection circuit limits the insulation resistance of the bus. at the 30kΩ level.

In recent years, there is also a method of using a clamp ammeter to search by branch. Because the detection sensitivity of the clamp ammeter is not high, it is difficult to detect ground faults at the milliampere level.

The method of externally injecting low-frequency signals is gradually not recommended because the injected AC component will pass through the battery of the DC power system and be affected by the distributed capacitance of the secondary circuit.

Contents of the invention

The technical problem to be solved by the present invention is to provide an on-line detection and alarm device for direct current grounding faults that can realize non-stop power failure of electrical equipment during operation and can accurately locate.

The present invention adopts following technical scheme:

An on-line detection and alarm device for a DC grounding fault, which includes a leakage current detection module, an A/D conversion circuit, a microprocessor, an alarm threshold control module, an audio and sound control circuit, and an acousto-optic alarm circuit; the leakage current detection module The input end of the load is installed at the DC power supply inlet end of the load, the output end of the leakage current detection module is connected to the microprocessor through the A/D conversion circuit, and the microprocessor is bidirectionally connected with the alarm threshold control module, so The output end of the microprocessor is connected to the input end of the sound and light alarm circuit through the audio frequency and sound control circuit.

Further, the leakage current detection module includes an induction coil and an electromagnetic conversion circuit, and the induction coil is correspondingly installed at the DC power inlet end of each secondary circuit load, and the output of the induction coil is connected to the input end of the electromagnetic conversion circuit , the output terminal of the electromagnetic conversion circuit is connected to the input terminal of the A/D conversion circuit.

Further, the DC ground fault online detection and alarm devices are respectively installed at the DC power inlet end of each load, and each of the DC ground fault online detection and alarm devices is independent of each other, and the number thereof depends on the number of loads. Corresponding configuration.

Further, the alarm threshold control module includes a dual operational amplifier LM4558 and its peripheral components, which are logic circuits for microprocessor operations.

Further, the audio and sound control circuit includes a stereo integrated circuit chip LM4610 and its peripheral components.

Further, the present invention also includes an energy-saving power supply, which supplies power to the microprocessor.

Further, the loads include switch cabinets, protective screens and any other DC power equipment of control and communication systems.

The beneficial effects of the present invention are as follows:

The invention is an intelligent, high-precision on-line detection and alarm device for DC grounding faults, which can accurately locate the grounding fault branch and the grounding fault without power failure of the equipment during operation. It is different from other distributed monitoring systems. This device does not need to be equipped with complex communication and processing systems. It is directly installed at the DC power inlet end of the secondary circuit load, and can realize real-time online monitoring of the DC insulation of the load circuit. Through reasonable Arranging this device can conveniently realize the precise positioning function of the DC grounding fault, so as to realize the rapid fault finding and avoid the fault hazard caused by the pull-circuit investigation.

Based on the real-time on-line uninterrupted monitoring function, the invention realizes the real-time on-line monitoring on the DC grounding fault of the power circuit of the electrical equipment.

The loads detected by the present invention can be switch cabinets, protective screens, and any DC electrical equipment in other control and communication systems; each DC ground fault online detection and alarm device is independent of each other and can be configured according to the number of loads. The installation and configuration are flexible, and it can timely reflect whether there is a short circuit or ground fault in the DC circuit, and can provide reliable and timely troubleshooting basis for professionals.

The invention realizes the setting of the threshold value and the sound and light alarm of the fault through the built-in microprocessor, and has the characteristics of simplicity, high precision and intelligence.

Description of drawings

Fig. 1 is a structural block diagram of the present invention.

Fig. 2 is a logical diagram of the present invention.

Fig. 3 is a working principle diagram of the present invention.

Among them, 1 DC ground fault online detection and alarm device.

detailed description

In order to make the purpose, technical solution and advantages of the present invention clearer, the invention will be clearly and completely described below in conjunction with FIGS. 1 to 3 and specific embodiments.

The invention designs an intelligent, high-precision on-line detection and alarm device for DC grounding faults, the detection sensitivity can reach 0.2 mA, and it is suitable for DC secondary circuits such as power plants and substations. It can be widely used in the power supply, distribution and consumption systems of power system substations, thermal power plants, hydropower stations, and industrial and mining enterprises such as coal mines, steel, metallurgy, and chemical industry.

The invention is applicable to 220V and 110V DC power supply systems and 48V and 36V DC power supply systems for communication equipment.

As shown in Figures 1 to 3, the present embodiment includes a leakage current detection module, an A/D conversion circuit, a microprocessor, an alarm threshold control module, an audio and sound control circuit, and an acousto-optic alarm circuit; the leakage current detection module The input end of the load is installed at the DC power supply inlet end of the load, the output end of the leakage current detection module is connected to the microprocessor through the A/D conversion circuit, and the microprocessor is bidirectionally connected with the alarm threshold control module, so The output end of the microprocessor is connected to the input end of the sound and light alarm circuit through the audio frequency and sound control circuit.

Further, the leakage current detection module includes an induction coil and an electromagnetic conversion circuit, and the induction coil is correspondingly installed at the DC power inlet end of each secondary circuit load, and the output of the induction coil is connected to the input end of the electromagnetic conversion circuit , the output terminal of the electromagnetic conversion circuit is connected to the input terminal of the A/D conversion circuit.

Further, the DC ground fault online detection and alarm devices are respectively installed at the DC power inlet end of each load, and each of the DC ground fault online detection and alarm devices is independent of each other, and the number thereof depends on the number of loads. Corresponding configuration.

Further, the alarm threshold control module includes a dual operational amplifier LM4558 and its peripheral components.

Further, the audio and sound control circuit includes a stereo integrated circuit chip LM4610 and its peripheral components.

Further, the present invention also includes an energy-saving power supply, which supplies power to the microprocessor.

Further, the loads include switch cabinets, protective screens and any other DC power equipment of control and communication systems.

As shown in Figure 3, this device adopts the principle of differential current detection. For the current I+ flowing out of any branch from the positive pole of the power supply, after flowing through all the loads of this branch, the current I- returned to the negative pole of the power supply. When the branch is not grounded When fault occurs, I+ = I-, the current passing through the device is equal, and the device has no signal output. When the grounding resistance is Rd, the grounding current is Ir grounding fault, I+ =I- + Ir, the current flowing through the device is not equal, the device outputs a signal reflecting the difference, which is the leakage current signal.

The main functions of this embodiment are as follows:

1) Real-time monitoring and accurate positioning.

Real-time monitoring of the DC leakage current of the DC branch circuit where it is located, based on which the DC-to-ground insulation status of the circuit and ground fault conditions are monitored, and the fault branch circuit is accurately located.

2) Over-limit alarm, according to different equipment and operating conditions, set the over-limit alarm value through the dial switch;

3) With multi-channel alarm function, the indicator light flashes and the buzzer sounds when alarming, which is convenient for operation and maintenance personnel to quickly find the grounding point;

4) Signal memory reset function, when the current exceeds the limit alarm, even if the current decreases to below the limit value, the alarm light and buzzer will not be turned off, and the signal will be turned off after manual reset.

The advantage of this embodiment is as follows:

(1) It can realize the non-stop power supply of the equipment, and accurately locate the ground fault branch circuit and the ground fault device.

(2) It saves the manpower and time to find the fault, and effectively prevents the road from being pulled by mistake.

(3) High safety and reliability. There is no electrical connection between the DC grounding positioning device and the external system, and it will not have any impact on the DC power supply circuit;

(4) It can detect the simultaneous grounding of multiple branch circuits and multiple devices.

(5) There is no need to inject AC signals into the DC system, and it will not increase the voltage ripple coefficient of the DC system, which has no effect on the safe operation of the DC system. The detected ground resistance is not affected by the distributed capacitance of the branch to ground. It does not affect the normal operation of the original insulation monitoring of the DC system.

(6) Small size, simple structure and easy installation. The DC grounding indicator uses a built-in single-chip microcomputer to realize state detection and alarm, and does not require external complicated monitoring systems and wiring; it adopts standard rail-mounted installation, which is fast and simple;

(7) Each DC grounding indicator is independent of each other and can be flexibly configured according to the different requirements of the system and the increase or decrease of the load of the DC system;

(8) Large-scale integrated chip design is adopted, the structure is sealed and moisture-proof, the anti-interference performance is strong, and the environment adaptability is strong.

(9) High sensitivity. The detection sensitivity of this ground indicator can reach 0.1 mA, which is more accurate than the hand-held clamp leakage current search method, and can find high-impedance grounding and insulation drop;

(10) Find the grounding point quickly. Since there are instructions for the grounding components, there is no need to search for each circuit one by one, which greatly saves the time for fault finding.

(11) Quick and easy installation. Through the transition of two jumper wires, the indicator can be quickly installed without power failure, and has no effect on secondary equipment and circuits.

(12) By connecting the communication equipment, the data of the indicator can also be transmitted to the server of the centralized control center, so as to realize the online remote monitoring of the DC grounding and insulation status of the DC system of multiple substations, and provide a basis for the status maintenance and fault handling of the DC system. in accordance with.

The main reasons for the grounding of the DC system are: insulation aging, moisture, damage of cables or equipment components, and damage to the power supply board of the device. The DC systems of power plants and substations mostly use 110V or 220V power supply, and the positive and negative bus bars are floating to the ground. When a ground fault occurs, the DC system can still maintain normal operation because no ground loop is formed, and the ground fault is not easy to detect. However, if it is accompanied by other one or more grounding points, it will cause the relay protection device and the control device to malfunction or refuse to operate. In order to avoid this situation, the current common practice is to use a distributed monitoring system to monitor the insulation situation online in real time, but this method has the disadvantages of large investment, complicated wiring and susceptibility to interference.

Microcomputer protection and intelligent interface (IED) have been widely used in the existing secondary system. The starting current of the internal drive relay is generally milliamp level current. Therefore, even a high resistance grounding of tens of kiloohms may generate a The current of the secondary circuit leads to malfunction or refusal to operate, which is potentially harmful.

As a result of the microelectronics and miniaturization of the secondary system, the DC grounding detection device is required to be sensitive to the leakage current as low as 0.1 mA.

In this embodiment, leakage current detection technology is used to detect whether there is a ground fault in the DC circuit, and the device is small in size, about the size of a palm. This embodiment is an intelligent high-precision direct-current grounding detection and indication device with a detection sensitivity of up to 0.2 milliamps, and is suitable for direct-current secondary circuits such as power plants and substations. Different from other distributed monitoring systems, the DC grounding positioning device in this embodiment does not need to be equipped with complex communication and processing systems. It is directly installed at the DC power inlet end of the secondary circuit load, which can realize the DC insulation of the load circuit. Real-time online monitoring, and through the built-in single-chip microcomputer to realize threshold setting and fault sound and light alarm; it has the characteristics of simplicity, high precision and intelligence. By rationally arranging the device, it is convenient to realize the precise positioning function of the DC grounding fault, so as to realize the rapid fault finding and avoid the fault hazard caused by the pull-circuit investigation, which is of great significance for improving the safety, stability and high-efficiency operation of the power grid.

The device is respectively connected to multiple loads, which are independent of each other. Through online detection of the leakage current of the DC load circuit, that is, the unbalanced current, the judgment of whether the load is DC grounded or not is realized.

During normal operation, if there is no DC grounding, the leakage current passing through the DC ground fault online detection and alarm device is zero or less than the set alarm threshold, and the DC grounding indicator does not alarm.

When the load equipment or circuit powered by the device is DC grounded or the insulation is reduced, the leakage current passing through the device will exceed the alarm threshold, and the buzzer and light flashing will alarm at this time.

In this embodiment, the ground fault branch and the ground fault can be accurately located without power failure of the equipment in operation.

This embodiment is realized by the following methods:

1. Use leakage current detection technology to detect whether there is leakage current in the DC circuit, and the detection sensitivity can reach 0.1~0.2 mA.

2. The microprocessor detects the leakage current of the circuit and compares it with the set alarm threshold of the device. If the leakage current is zero or less than the set alarm threshold, no alarm will be given. When the load equipment or circuit of the DC ground fault online detection and alarm device is DC grounded or the insulation is reduced, the leakage current passing through the device will exceed the alarm threshold, and the buzzer and light flashing will alarm at this time.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (6)

1. A DC grounding fault online detection and alarm device is characterized in that: it comprises leakage current detection module, A/D conversion circuit, microprocessor, alarm threshold control module, audio frequency and sound control circuit and sound and light alarm circuit; The input end of the leakage current detection module is installed on the DC power inlet end of the load, the output end of the leakage current detection module is connected to the microprocessor through the A/D conversion circuit, and the microprocessor and the alarm threshold The control module is bidirectionally connected, and the output end of the microprocessor is connected to the input end of the sound and light alarm circuit through the audio frequency and sound control circuit. 2. The DC ground fault online detection and alarm device according to claim 1, characterized in that: the leakage current detection module includes an induction coil and an electromagnetic conversion circuit, and the induction coil corresponds to the DC current installed in each secondary circuit load. The power input terminal, the output of the induction coil is connected to the input terminal of the electromagnetic conversion circuit, and the output terminal of the electromagnetic conversion circuit is connected to the input terminal of the A/D conversion circuit. 3. The DC ground fault online detection and alarm device according to claim 1 or 2, characterized in that: the DC ground fault online detection and alarm device is respectively installed at the DC power inlet end of each load, and each The above-mentioned DC ground fault online detection and alarm devices are independent of each other, and the number thereof is correspondingly configured according to the number of loads. 4. The on-line detection and alarm device for DC ground fault according to claim 1, characterized in that: the alarm threshold control module includes a dual operational amplifier LM4558 and its peripheral components. 5. The on-line detection and alarm device for DC ground fault according to claim 1, characterized in that: the audio and sound control circuit includes a stereo integrated circuit chip LM4610 and its peripheral components. 6. The on-line detection and alarm device for DC grounding fault according to claim 1, characterized in that it also includes an energy-saving power supply, and the energy-saving power supply supplies power to the microprocessor.