The hottest leakage protection system based on two

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Leakage protection system based on two bus

Abstract: This paper expounds the application of two bus in underground leakage protection device. Through the real-time monitoring of underground insulation resistance by the microcomputer of the general protection and the bus communication between the general protection and branch outlet protection, the fault line can be quickly judged and the fault can be isolated in time, so as to comprehensively improve the safety of underground work

key words: leakage from the definition, we can see the protection of two bus zero sequence current 1 underground leakage protection status

most mine electricity in China has been using the neutral point ungrounded mode. With the extension of underground power supply line and the increase of capacitive current, single-phase grounding current will be greater than 20A in case of fault, and some even exceed 70A. However, measures should be taken to reduce it to below 20A in accordance with the coal mine safety regulations, Therefore, the neutral point through arc suppression coil and resistance grounding system are widely used

in system protection, according to the operation of low-voltage power underground in China, it is generally considered that "two-level protection" is implemented for low-voltage power distribution, and further increase in the number of levels will have no use significance. The purpose of implementing hierarchical protection is to ensure reliable action and cut off the power supply from the perspective of personal and equipment safety and normal power consumption, and to limit the power outage caused by this action trip to the minimum. Most of the commonly used leakage protection devices are additional DC power supply type protection and zero sequence current protection devices. An additional DC power supply protection is installed at the general protection, which can operate reliably regardless of symmetrical or asymmetrical leakage of the system. Zero sequence current protection is installed at the branch outlet as the main protection of horizontal selective protection

the leakage system generally establishes two-level backup protection, with additional DC power protection and leakage locking as the primary and secondary backup of the branch leakage protection unit [1]. In the low-voltage power supply with hierarchical protection, the condition for determining the classification is that the rated action time of the next level protector (including the tripping time of the main switch breaking circuit) must be less than the limit non action time of the previous level protector. For the lower level protection, its rated action time is required to reach the fastest, so as to quickly remove the fault. For the upper protection, a certain time delay is required to ensure selectivity, so as to avoid the time required for particles with different components to show different colors when the lower protection trips. According to the field investigation, the zero sequence current leakage protection action makes the total tripping time of the branch switch action reach 200ms, so the action time of the additional DC power protection needs to be added with a fixed delay of 200ms to ensure selectivity. Therefore, in case of symmetrical leakage (branches cannot be detected), branch protection failure or switch failure, the total protection action time is up to 400ms. At this time, the electric shock current will increase, which can not only ensure personal safety, but also prevent biogas and coal dust explosion

with the popularization of vacuum circuit breaker, although due to the differential protection action time Δ The reduction of T reduces the loss caused by short circuit to the minimum, but does not fundamentally solve the problem caused by time difference

2 improvement scheme

in the improvement scheme, communication is established between the total leakage protection unit and the branch unit to ensure that the fault point is cut off in the shortest time and eliminate the dead zone existing in the existing leakage protection system

2 then cover the front cover of the panel 1. Two bus technology

in this paper, the communication bus adopts two bus technology. Two bus is a highly reliable and automatic synchronous coding and decoding communication, which can convert multiple analog quantities of field nodes into digital quantities and carry out long-distance serial transmission. Its features are as follows:

A. intelligent tracking and automatic coding

b. remote monitoring, with a monitoring distance of 2km

c. transmit signal and power at the same time, and the node does not need to supply power independently

d. the number of loop nodes can be increased or decreased according to the scale, up to 64

the two bus is very suitable for the current situation that there are many outlets of underground distribution feeders and the feeder lines are gradually growing, and can resist the influence of various underground interferences. The two buses communicate. The voltage between the two buses is 24V. The two bus communication chip at the sending end outputs the digital quantity to be transmitted in the form of current in serial to the two buses; The receiving end receives the signal while obtaining power from the bus, realizing the requirements of the common bus for power and signal [2]

2.2 communication realization

common bus interfaces include qa840159, which provides the interface between MCU and bus, and exchanges data with CPU through handshake circuit and data bus. The bus interface obtains the coded address, control code and other information from the CPU and sends the standard serial code to the bus loop, including address segment, address verification segment, control segment and analog quantity return segment. The address segment and address verification segment are exactly the same to ensure the reliability of communication. The two bus communication codec chip is located at the branch outlet, which can automatically synchronize the codec and on-chip a/d conversion. It does not need to adjust the frequency and synchronization. It can intelligently analyze the encoded data of the total protection and automatically track and align the bits. The on-chip high-speed a/d conversion circuit is powered up only when the address matches, which greatly reduces the total current of the system, and can easily realize analog acquisition and two bus communication

3 design of intelligent leakage protection

the system is composed of three parts: general protection, branch protection and two bus communication interface. The real-time underground data detected by each branch protection can be communicated through two buses. The number of underground feeder branch outlets is set as N, and its structure diagram is shown in Figure 1

the general protection office is a single chip microcomputer 8051 system with high cost performance, which is composed of a/d converter, input/output interface, flash memory, output execution circuit, etc. The general protection is equipped with additional DC power leakage protection, which can detect the total insulation of the electricity. At the same time, through the sampling of the leakage DC detection circuit, the change of the insulation resistance of the underground electricity a, B, C three phases is monitored and displayed by the circuit, so it is easy to find and deal with the fault phase. During normal operation, the working parameters of electricity and the insulation level to the ground are displayed circularly, and after fault tripping, the parameters and status of fault are displayed circularly, which greatly improves the efficiency of fault judgment. If different given values are set and stored in the microcomputer, the microcomputer can judge whether the fault is a ground fault, a personal electric shock accident or a insulation resistance drop fault

the general protection is connected to the second bus through the bus interface

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