Analysis of the protection of coal mine electrical equipment and power supply system Qu Yanfang (Shun Coal Group Sima Coal Industry Co., Ltd., Changzhi 047105, Shanxi) The components and principles of the protection device, and the development of coal mine electrical equipment and power supply system protection. The working environment in coal mines is harsh, the load fluctuates greatly, the working conditions are very unstable, and the phenomenon of gas accumulation and dripping will gradually reduce the insulation strength, and there will often be leakage and other faults. Therefore, in the safe production of coal mines, the protection of electrical equipment and power supply systems in underground coal mines plays an important role. At present, most of the protection of coal mine electrical equipment and power supply system adopts relay protection device. With the continuous development of computer control technology, microelectronic technology, information technology and network communication technology, the intelligent protection system has been successfully developed to make the reliability of the whole system. There is a big improvement to ensure the quality of production. 1 Common types of protection in underground mines are divided into general electrical equipment for mine use and electrical equipment for mine explosion-proof. The former does not have explosion-proof performance, and the latter has explosion-proof and explosion-proof performance. At the same time, according to the working voltage, electrical equipment can be divided into low-voltage electrical equipment and high-voltage electrical equipment. Most of the underground electrical equipment belongs to a type of load and a second type of load. The current and voltage during operation are large, and the protection is guaranteed. The key to reliability. Over-current protection, leakage protection and grounding protection are the three major protections in the well. Other protections include loss of voltage protection, under-voltage protection, over-voltage protection, etc. 2.1.1 Leakage protection The leakage of underground wells will further damage the equipment and form a short-circuit accident. It can also cause personal electric shock and electric sparks to trigger the danger of gas and coal dust. The stray current also corrodes adjacent metal pipes and armored cable metal skin, shortening the service life of metal pipes and armored cables. It may also cause an early explosion of electric detonators, threatening personnel safety. Therefore, a leakage protection device must be installed in the underground power supply system to achieve insulation monitoring, leakage protection, and compensation of the capacitive current flowing through the body. According to its protection function, it is divided into non-selective leakage protection and selective leakage protection. 1.1.1 Selective leakage protection uses the principle of zero-sequence current protection. The zero sequence current signal is obtained by a zero sequence current transformer. When no leakage occurs, the primary side three-phase current is symmetrical, its current phasor sum is 0, and the secondary side has no current output; when leakage occurs, the primary side three-phase current is asymmetrical, and its current phasor is not 0. There is current output on the secondary side. The device is used in conjunction with a shunt switch, which has the advantages of reducing the power outage range and making it easy to find faulty lines, and thus is widely used. 1.1.2 Non-selective leakage protection The protection principle of the additional DC power supply. The additional power supply, also called the auxiliary power supply, adds (auxiliary) DC power to the detection circuit including the insulation resistance to ground, and monitors the change of its direct current. If the voltage is discharged to the ground after the leakage, there will be voltage at the ground and voltage terminals. The voltage drop and current exist. If the direction of the voltage drop, the direction of the current, and the direction of the unbalanced voltage signal detected by the three-phase reactor are the same, the leakage trip is judged, thereby achieving the purpose of monitoring the insulation resistance. The device needs to be used with a low voltage automatic feed master switch. The shortcoming is that the power outage range is large, and it is difficult to judge the leakage line, but the structure is simple and the work is reliable, so it is still in use. 1.2 Overcurrent protection The main cause of electric fire is the overcurrent of the power grid, and the overcurrent is caused by short circuit, overload and phase failure. Therefore, the method of preventing electric fire is to prevent the occurrence of overcurrent. Therefore, overcurrent protection includes short circuit protection, overload protection and phase failure protection. 1.2.1 Overload protection Overload refers to the operating current of the motor or the operating current of the electrical equipment is greater than its rated current, but less than a multiple of the rated current, usually less than 1.5 times the rated current. There are many reasons for overloading motors or electrical equipment, such as sudden increases in load, phase-failure operation, and grid voltage reduction. The action time of the overload protection is related to the magnitude of the overload current, and the action value setting is smaller than the action value of the short circuit protection. The action delay depends on the degree of overload. The greater the degree of overload, the shorter the delay. The smaller the overload, the longer the delay. This characteristic is called the inverse time characteristic. The delay link consists of a time relay. When overloaded, the current relay operates, and the contact turns on the relay coil. After the delay, the time relay contact acts to make the actuator act, cut off the main loop power supply, and simultaneously send an overload signal. Overload protection can be achieved by electromagnetic relays, electronic relays and thermal relays. 1.2.2 Short-circuit protection The instantaneous current generated by the short-circuit can reach ten to several tens of times of the rated current, causing electrical damage to the electrical equipment or distribution lines due to overcurrent, and even fire caused by the arc. The short-circuit protection has a short operating time, and its action value is set to a large value, and the power is turned off in a short period of time. Both electromagnetic relays and electronic relays provide short circuit protection. 1.3 Phase-failed protection motor During operation, due to grid fault or fuse of one-phase fuse, the symmetrical three-phase power supply lacks one phase. After phase loss, the motor will run at low speed or block, the stator current is very large, and it is easy to cause motor insulation and The winding is damaged. Phase-failure protection is a way of protecting the power supply from being applied to the protected device by relying on the disappearance of current in the phase conductor of the multi-phase circuit to disconnect the protected device or relying on phase or phase loss of the multi-phase system. . Phase failure protection adopts the principle of negative sequence protection, and electronic relays and thermal relays can realize phase failure protection. 1.4 Grounding Protection Grounding protection can limit the current through the human body to within the limiting current. The key to protective grounding is to reduce the grounding resistance of the protective earthing device to within the specified range. The coal mine safety regulations stipulate that the grounding resistance of any protective earthing point on the grounding network shall not exceed 2a. The distance between the main grounding pole and the auxiliary grounding pole shall not be less than 5m. 2 Relay protection device relay protection device is protected by one or more The components and logic components are combined to respond to a specific protection function in the power system fault and act in time on the circuit breaker tripping or signaling the automation equipment. Fuse, relay and contactor can be used to protect the device. However, due to the increasing working current and short-circuit current in the coal mine system, the fuse can not meet the requirements of selectivity and rapidity. Relays and contactors are currently used. A wider range of protection devices. The main components are 4: the on-site signal input part. The live signal is sent to the relay protection device to perform necessary pre-processing, such as photoelectric isolation technology to eliminate interference signals; level conversion circuit makes low signal into strong signal easy to handle; low-pass filtering removes high frequency signal and pattern Wave voltage, etc., enable the relay to effectively detect the physical quantity of each site. Measuring part. It detects the physical quantity related to the protected object after being processed by the on-site signal input circuit, and compares it with the given set value or the automatically generated criterion, and gives “yes†or “no†according to the comparison result. That is, a set of logic signals or level signals of 0 "or 1 nature, it is judged whether the protection is activated or not. The logical judgment part. It is based on the size, nature, logic state, output order and other information of each output of the measurement part, combined and calculated according to a certain logical relationship, and finally determines whether the circuit breaker should trip or signal, and pass the relevant command to the execution part. . Commonly used logic generally has functions such as "and", "or", "non-delay", and "memory". Execution section. It is based on the exit signal sent by the logic judgment part, completes the final task of the protection device, and is mainly responsible for the isolation, connection, level conversion, power drive of the outlet trip, and the return of the field device status information of the protection device and the field device, In order to make the relay protection device work reliably: the electrical equipment and the power equipment trip when the fault occurs, the signal is issued during the abnormal operation, and the ideal state does not operate normally. 3 Conclusion The protection of coal mine underground electrical equipment and power supply system is of great significance to the safe production of coal mines. With the development of power systems and the increasing requirements for safe operation of coal mines, in addition to enhancing stability, reliability and rapid response, data communication will become more important in future protection devices. 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