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1、基于电流变化率的短路检测保护技术研究Research of short circuit detection & protection technology based on current variance ratio庞元俊，吉增权 PANG Yuan-jun，JI Zeng-quan（平顶山工业职业技术学院，河南 平顶山 467001）(Pingdingshan Industrial College of Technology，Pingdingshan，467001，China)摘要：对基于电流变化率的短路检测技术进行了深入的研究，建立了基于电流变化率的短路检测保护技术理论。该技术与现有短路
2、检测技术相比，采用不同的技术思路和理论基础，是以重创新技术，解决了短路故障电流波形变化与其他故障电流波形变化的区分问题以及干扰电流波形突变与短路电流波形突变的识别问题，建立了数学模型，并在实际产品中检验了电流变化率短路检测保护技术的工作可靠性。Abstract：Researching on short circuit detection technology based on current variance ratio, we get a theory of short circuit detection & protecting based on current variance rati
3、o. New technology thought and theory basis were adopted, comparing with present theory on short circuit detection, the division problem of the variety fault current waveform between short circuit and others, and the problem of identifying break current waveform of short circuit from disturbance were
4、 solved. A mathematical model was made, and the reliability of real product based on this theory was validated.关键词：短路保护；检测技术；综合保护；故障诊断Key words：Short circuit protection, diction technology, integrated protection, fault diagnosis中图分类号：TP1 文献标示码：A 文章编号：前言国内外现有的短路检测保护技术，短路检测大致分为三种主要方式：一是基于检测短路电流大小的过流保护
5、技术，这种过流保护按照躲过电动机的最大启动电流的原则进行整定，在供电线路长时，线路末端短路时，短路电流很小，保护的灵敏度受到限制；二是基于相敏原理的短路保护技术，国内外研究较多，也比较成熟，虽然解决了保护灵敏度的问题，但此种技术只能保护三相短路，两相短路不动作；三是基于载频原理的短路保护技术，国内在煤矿煤电钻综合保护器中应用较多，此种保护对线路参数（电缆截面、长度和电源变压器等）要求严格，线路参数变化时易发生误动作，可靠性差。基于电流变化率的短路检测保护技术，是利用线路或用电设备发生短路时，线路电流发生突变的原理，采用单片机检测这一变化率，当电流变化率超过规定值时，单片机发出指令，切断供电电源
6、。此技术的特点是检测参数为线路电流变化率，检测参数与线路电流大小无关、与电压电流相位角无关、与供电线路参数无关，短路保护动作迅速，灵敏度高，工作性能稳定，安全可靠。1 拟解决的问题基于电流变化率的短路检测保护技术，必须解决两个关键性问题：一是区分短路故障电流波形变化与其他故障电流波形变化的差别。由于供电系统多呈感性负载，短路故障电流波形变化与其他故障电流波形变化的差别，使用常规方法在某些线路参数的情况下不易区分。二是干扰电流波形突变与短路电流波形突变的识别。由于本项目是利用短路电流波形突然变化进行故障识别，电流突变是识别的要素，在供电系统中常常存在着各种干扰，如电动机的启动、大型设备的起停、变
7、频调速、系统操作等，这些干扰很多情况下会影响检测点的电流波形，且干扰电流波形一般情况下也是呈突变形式，可能使检测产生错误识别。2 数学模型供电网络中，正常时线路电流：系统发生短路故障，电流由原来的负载电流增大为短路电流is，其值可由短路回路的微分方程确定：为一阶常系数非齐次微分方程，解为： 式中Um电源相电压的幅值；Im短路前负荷电流的幅值；负载的阻抗角；发生短路瞬间电源电压的初相角；ipe 短路电流周期分量； Ipe.m 短路电流周期分量幅值，即；iap 短路电流非周期分量； s 短路回路的阻抗角，即 ； Ts 短路回路的时间常数，即TsL/R 。短路电流的周期分量随时间按正弦规律变化：短路
8、电流的非周期分量随时间按指数规律衰减:i可以看出：短路电流由两部分组成，一是短路电流的周期分量，一是非周期分量，两者合成，短路电流将会产生一个冲击，这个冲击电流会产生阶跃突变，其波形的变化率将会很大。如图1所示。大 isiimIapipeiapu0Ipet暂态稳态图1 短路电流暂态过程波形Figure 1 Transient waveform of short circuit current设：供电系统变压器容量4kVA，电缆截面积6mm2，长度L=300m、控制额定电压127V，功率1.5kw煤电钻一台，功率因数cos=0.83，如图2所示。M660v127v煤电钻综合保护装置s36+163
9、00图2 系统接线图Figure 2 System wiring diagram系统正常运行的状态下负荷电流为：系统在末端短路时，系统阻抗最大，短路电流最小，保护应可靠的动作，设在t1时刻系统发生短路，短路电流：查：6mm2电缆R=1.45 忽略电感；最不利的情况下：系统时间常数Ta=0.05s，s=900，=00，t=0.01s，则短路电流的冲击值为：系统电流波形见图3，局部放大波形见图4。可以看出，短路电流的电流变化率远远大于其它电流的变化率。图3 短路电流波形Figure 3 Waveform of short circuitit0短路电流负荷电流t1t短路电流负荷电流tis短路电流图4
10、 短路电流波形（局部放大）Figure 4 Waveform of short circuit (partial enlarged)当时间t趋近于无穷小时，可以认为：即：实际系统中我们取t0.00001s，可认为：为使保护可靠，取系统末端短路电流 is=100A，t=0.00001s，代入电流表达式，算出各时间的电流值，以此为依据编写程序。当90o，即电流处于正半周的下降段短路时，正常的电流瞬时值减少，如此时短路，短路电流会突然大大增大，更有利于对电流变化率的检测与区别。电流波形见图5，局部放大图见图6。以上是电流的正半周短路的波形分析，电流的负半周可以采用全波整流的方式把负半周波形以横轴镜像
11、处理后，按同样方法处理即可。it0短路电流负荷电流图5 90o短路时电流波形Figure 5 Waveform when90o short circuittt负荷电流短路电流is图6 90o短路时电流波形（局部放大）Figure 6 Waveform when90o short circuit (partial enlarged)根据以上数学模型，用单片机技术检测电流，计算出故障状态下短路电流的变化率，以此数据为依据开发单片机程序，设计单片机电路，单片机输出通过接口电路控制执行元件，达到快速开断故障的目的。3 干扰电流突变与短路电流突变的识别干扰电流突变与短路电流突变的识别，采用软滤波和硬滤波
12、两种方法解决。软滤波：就是根据干扰信号的特点一般是无规律的短时几个窄脉冲的特点，如图7所示，设计单片机滤波程序，在0.1ms内连续检测1020次电流变化率，将干扰电流突变排除，当检测到的多次变化率都超过正常值时，认为是发生了短路故障，发出执行信号。通过试验，选择了在0.1ms内连续检测10次电流变化率的最佳连续检测次数方案。短路电流负荷电流短路电流干扰信号图7 软件滤波波形示意图Figure 7 Waveform of filtering by softwareN个t硬件滤波：就是在供电主回路设置阻容滤波电路，滤除干扰杂波。CBARX1-3RX4-6CX1-3图7 阻容滤波电路Figure 8
13、 Circuit of resistor-condenser filter滤波电路如图7所示。4 创新点本项目建立了基于电流变化率的短路检测保护技术。该技术与现有短路检测技术相比，采用不同的技术思路和理论基础，是以重创新技术。5 技术应用利用本技术，可根据被保护设备及线路的实际情况，开发出不同的电气保护产品。为了验证电流变化率短路检测保护技术在实际应用中的可靠性，项目组结合煤矿电气设备的特点，开发了ZBZ4.0/660（380）Z型煤电钻综合保护装置，利用开发的新型煤电钻综合保护装置，检验了电流变化率短路检测保护技术在电气设备现场的工作可靠性。参考文献：1 王久和.井下短路电流快速检测的研究J
14、.华北科技学院学报,2002(1):16-17.2 王怀群.低压供电系统微机综合保护J.煤矿设计，2001(6):15-16.3 王宾，祝龙记.基于凌阳16位单片机的矿用电机相敏保护的实现J.煤矿机械，2005(8)：115-117.4 郭强, 张玉献.相敏和远端短路保护装置在井下的应用J.安徽科技,2004(11).5 郗忠梅,等.智能型相敏保护在煤矿中的应用J.山东农业大学学报(自然科学版), 2004(1).6 成凌飞，邹有明.新型快速断电煤电钻综合保护装置J.煤矿机械，2004(6)：81-83.7 王文清.煤电钻综合保护装置中短路快速取样技术的探讨J.煤炭科学技术,1997(2):1
15、5-18.8 权耀庭.无触点电钻综合保护装置的开发应用J.煤炭科学技术,1998(6):30-32.9 成凌飞，邹有明.基于单片机的煤电钻漏电保护设计J.煤矿机械，2005(9)：16-18.基金项目：河南省2007年重点科技攻关计划项目，编号：072102240021第一作者简介：庞元俊（1951 ），男，河南通许人，毕业于中国矿业大学自动化专业，研究方向：供配电技术，电力电子技术。联系方式：平顶山市水库路3号，平顶山工业职业技术学院科研处，Email:jizq686 电话：0375-2067290 13937557609Editors note: Judson Jones is a met
16、eorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear t
17、he faint beeps of the worlds first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the s
18、huttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxiou
19、s for the next one: a space capsule hanging from a crane in the New Mexico desert.Its like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there
20、Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line we would be go for launch.I feel
21、 this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never
22、reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it
23、was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and capcom (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappoint
24、ing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule
25、attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and
26、into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, Fearless Felix will unclip. He will roll back the door.Then, I would assume, he w
27、ill slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, hell be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will
28、 be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this
29、will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes its not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 fe
30、et (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it wont. Baumgartner still will free fall at a speed tha
31、t would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way Id miss this.
