1、翻译部分SOME OF OUR EFFORTS ON THE IMPROVEMENT OF MINING SAFETY AND THE RELIABILITIES OF MINING MACHINERIESAbstract: To improve the safety of coal mine and the reliabilities of mining machineries is the main aspect of present scientific research. This paper introduces some of efforts and achievements in
2、 this field. They are: (1) The selective earth leakage protection of 6 KV underground power supply system with insulated neutral ; (2) The detection of mine methane and power supply tripping device ; (3) The protection against the hazard of underground static electric charge ; (4) The research of re
3、liability of the shearer motor ; (5) The test and improvements of the reliabilities of mining machineries.INTRODUCTION In the last 50 or 60 years the coal mining industries all over the world made great advances in mechanization and safety. Our country had also large improvements in these fields, bu
4、t large amounts of works have to be done. Recently the problem of reliabilities of mining machineries drew much attentions of many countries and was considered as the main direction of mining research . For more than a decade , in the same time of improving the degree of mechanization of our coal mi
5、nes, we worked also on mine safety and reliabilities of mining machineries and got some achievements. Let me make some simple introduction on them.THE SELECTIVE EARTH LEAKAGE PROTECTION OF 6 KV UNDERGROUND POWER SUPPLY SYSTEM WITH INSULATED NEUTRAL According to clause No, 393 of “Safety Regulation o
6、f Coal Mine” which was published in 1980 by Ministry of Coal Industry and is valid now, the underground power supply system of our coal mine is a system with insulated neutral. On clause No.407 of the same regulation it rules also that “selective earth leakage protection should be installed on the h
7、igh tension feeder of underground substation” and “For the feeder to supply mobile substation, this kind of protection must be installed.” We have developed such earth leakage protection. It is easy to understand the meaning of this regulation especially that of the last clause. Since the growing of
8、 underground mechanization, the power of electrical apparatus become larger and larger; the machines produce coal more and more in the same time; and the workers will have much more chance to contact the apparatus which is in earth leaking condition. For the safety of workers, finding the fault in t
9、he time shortening the time of stoppage to avoid the severe effects on coal production, this regulation must be strictly obeyed. The phase comparison between the zero sequence current and voltage signals is used to get the earth leakage signal with selectivity. When earth leakage occurs in 6KV power
10、 supply system with insulated neutral, zero sequence C.T. and P.T. will all give out signals, but the phase relation of these two signals is different between the fault feeder and other feeders. Utilizing this difference we can cut of f the fault quickly with selectivity. In this way not only lager
11、area power cut off can be avoided, longer time to find out which feeder is the fault one is not needed, but also the time of personal contact to live wire can limited within a safe time interval by cut off power quickly and let the energy through human body right below. Type BLD-2 earth leakage prot
12、ection device our prototype. It is a double function play of earth leakage protection and insulation and earth continuity monitoring of shielded power cable. The basic of earth leakage protection is to make comparison between zero sequence C.T. signal pulse through voltage transformation, signal dis
13、crimination and zero sequence P.T. When the pulse signal is with the rectangle signal , the relay will be energized, gives out alarm and trips off the power supply of this feeder. The C.T. signal must be discriminated in order to sieve out these transient pulses of the network which can make the rel
14、ay work in mistake. The purpose of phase shift treatment of P.T. signal is to compensate the phase angle of the P.T. This protective device had been tried many times with artificial earth of 6KV power supply network both on the surface and underground . All tests prove this devices reliability in pr
15、otection. Its sensitivity and time response are all satisfactory in compare with its design parameters. This type and its simplified type BLD-3 had been put into bulk production and vastly adopted in coal mines. In order to improve their characteristics new models of this device were developed. Thei
16、r corresponding types are BLD-4 and BLD-5. Its current voltage and power supply circuits are made of sophisticated I.C. Is simplifies the circuitries and gets higher reliability, but its working principle is entirely the same as stated before. The block diagram of its earth leakage protection part is as follows:The technical data of this device are：1. Sensitivity of zero sequence current: I 150 ma2. Time response t 100 m.s
