荆州市TOOTEC阀门L-40DFS-65A L-40DFS-80A中山立讯电气有限公司直销韩国samwhadsp继电器。价格优惠。欢迎询价!
WKS-3212H04 3C 220V 12Amp. 4~32VDC
WKS-3225H04 3C 220V 25Amp.4~32VDC
WKS-3240H04 3C 220V 40Amp 4~32VDC
WKS-3250H04 3C 220V 50Amp 4~32VDC
WKS-3255H04 3C 220V 55Amp 4~32VDC
WKS-3270H04 3C 220V 70Amp 4~32VDC
WKS-3212HAC 3C 220V 12Amp 4~32VDC
WKS-3225HAC 3C 220V 25Amp 4~32VDC
WKS-3240HAC 3C 220V 40Amp 4~32VDC
WKS-3250HAC 3C 220V 50Amp 4~32VDC
WKS-3325H04 3C 440V 25Amp 4~32VDC
WKS-3340H04 3C 440V 40Amp 4~32VDC
WKS-3350H04 3C 440V 50Amp 4~32VDC
WKS-3355H04 3C 440V 55Amp 4~32VDC
WKS-3370H04 3C 440V 70Amp 4~32VDC
WKS-3325HAC 3C 440V 25Amp 85~240VAC
WKS-3340HAC 3C 440V 40Amp 85~240VAC
WKS-3350HAC 3C 440V 50Amp 85~240VAC
WKS-1212H04 2C 220V 12Amp 4~32VDC
WKS-1225H04 2C 220V 25Amp 4~32VDC
WKS-1240H04 2C 220V 40Amp 4~32VDC
WKS-1250H04 2C 220V 50Amp 4~32VDC
3)人的固有弱点:人具有遗忘、易出错、注意力不集中、情绪不稳定等固有弱点。设计良好的人机界面应尽可能减少用户操作使用时的记忆量,应力求避免可能发生的错误;4)用户的知识经验和受教育程度:使用计算机用户的受教育程度,决定了他对计算机系统的知识经验;5)用户对系统的期望和态度。[1]使用方法编辑明确监控任务要求,选择适合的HMI产品;在PC机上用画面组态软件编辑“工程文件”;测试并保存已编辑好的“工程文件”;PC机连接HMI硬件,下载“工程文件”到HMI中;连接HMI和工业控制器(如PLC、仪表等),实现人机交互。发展趋势编辑人机界面市场的发展现状是全球人机界面需求量的市场,但却不是全球人机界面产品销售额的市场。开关电源比线性电源要好。不过开关电源比较复杂,内部晶体管会频繁切换,若切换电流尚加以处理,可能会产生噪声及电磁干扰影响其他设备,而且若开关电源没有特别设计,其电源功率因数可能不高。主要用途编辑开关电源产品广泛应用于工业自动化控制、军工设备、科研设备、LED照明、工控设备、通讯设备、电力设备、仪器仪表、设备、半导体制冷制热、空气净化器,电子冰箱,液晶显示器,LED灯具,通讯设备,视听产品,安防监控,LED灯带,电脑机箱,数码产品和仪器类等领域。主要类型编辑现代开关电源有两种:一种是直流开关电源;另一种是交流开关电源。开关电源内部结构开关电源内部结构这里主要介绍的只是直流开关电源,其功能是将电能质量较差的原生态电源(粗电)。
WKS-1255H04 2C 220V 55Amp 4~32VDC
WKS-1270H04 2C 220V 70Amp 4~32VDC
WKS-1212HAC 2C 220V 12Amp 85~240VAC
WKS-1225HAC 2C 220V 25Amp 85~240VAC.
WKS-1240HAC 2C 220V 40Amp 85~240VAC
WKS-1250HAC 2C 220V 50Amp 85~240VAC
WKS-1255HAC 2C 220V 55Amp 85~240VAC
WKS-1270HAC 2C 220V 70Amp 85~240VAC
WKS-1325H04 2C 440V 25Amp 4~32VDC
WKS-1340H04 2C 440V 40Amp 4~32VDC
WKS-1350H04 2C 440V 50Amp 4~32VDC
WKS-1355H04 2C 440V 55Amp 4~32VDC
WKS-1370H04 2C 440V 70Amp 4~32VDC
WKS-1325HAC 2C 440V 25Amp 85~240VAC
WKS-1340HAC 2C 440V 40Amp 85~240VAC
WKS-1350HAC 2C 440V 50Amp 85~240VACR
WKS-1355HAC 2C 440V 55Amp 85~240VAC
WKS-1370HAC 2C 440V 70Amp 85~240VAC
WKS-1212M04 2C 220VAC 4-32VDC
WKS-1225M04 2C 220VAC 4-32VDC
WKS-1240M04 2C 220VAC 4-32VDC
WKS-1250M04 2C 220VAC 4-32VDC
WKS-1212MAC 85-240VAC
WKS-1225MAC 85-240VAC
WKS-1240MAC 85-240VAC
WKS-1250MAC 85-240VAC
WKS-1325M04 2C 380&440VAC 4-32VDC
WKS-1340M04 2C 380&440VAC 4-32VDC
WKS-1350M04 2C 380&440VAC 4-32VDC
WKS-1325MAC 85-240VAC
WKS-1340MAC 85-240VAC
WKS-1350MAC 85-240VAC
WKS-3212M04 3C 220VAC 4-32VDC
WKS-3225M04 3C 220VAC 4-32VDC
WKS-3240M04 3C 220VAC 4-32VDC
WKS-3212MAC 85-240VAC
WKS-3225MAC 85-240VAC
WKS-3240MAC 85-240VAC
WKS-3325M04 3C 380 &440VAC 4-32VDC
WKS-3340M04 3C 380 &440VAC 4-32VDC
WKS-3325MAC 85-240VAC
WKS-3340MAC 85-240VAC
WKS-3212FRMP 3C 220VAC 12-24VDC
WKS-3225FRMP 3C 220VAC 12-24VDC
WKS-3240FRMP 3C 220VAC 12-24VDC
WKS-3212FRMN 12-24VDC
WKS-3225FRMN 12-24VDC
WKS-3240FRMN 12-24VDC
WKS-3325FRMP 3C 380 &440VAC 12-24VDC
WKS-3340FRMP 3C 380 &440VAC 12-24VDC
WKS-3325FRMN 12-24VDC
WKS-3340FRMN 12-24VDC
WKS-1212FRMP 2C 220VAC 12-24VDC
WKS-1225FRMP 2C 220VAC 12-24VD
WKS-1240FRMP 2C 220VAC 12-24VD
WKS-1212FRMN 12-24VDC
WKS-1225FRMN 12-24VDC
WKS-1240FRMN 12-24VDC
WKS-1203PBZN 1CH 220VAC 3Amp.LED 4~24VDC
WKS-1203PBZ 1CH 220VAC 3Amp
WKS-1202PB2Z 2CH 220VAC 2Amp
WKS-1210SQ 1C 220VAC.12A 4~32VDC
WKS-1212SQ 1C 220VAC.12A 4~32VDC
WKS-1220SQ 1C 220VAC.20A
WKS-1225SQ 1C 220VAC.25A
WKS-1240SQ 1C 220VAC.40A
WKS-1255SQ 1C 220VAC.55A
WKS-1270SQ 1C 220VAC.70A
WKS-1210SQAC 1C 220VAC.12A 85 ~240VAC
WKS-1212SQAC 1C 220VAC.12A 85 ~240VAC
WKS-1220SQAC 1C 220VAC.20A
WKS-1225SQAC 1C 220VAC.25A
WKS-1240SQAC 1C 220VAC.40A
WKS-1255SQAC 1C 220VAC.55A
WKS-1270SQAC 1C 220VAC.70A
WKS-1320SQ 1C 440VAC.25A 4~32VDC
WKS-1325SQ
WKS-1340SQ 1C 440VAC.40A
WKS-1355SQ 1C 440VAC.55A
WKS-1370SQ 1C 440VAC.70A
WKS-1320SQAC 1C 440VAC.25A 85 ~240VAC
WKS-1325SQAC
WKS-1340SQAC 1C 440VAC.40A
WKS-1355SQAC 1C 440VAC.55A
WKS-1370SQAC 1C 440VAC.70ACR
WKS-0007PBZ 60VDC. 7A 4~24V
WKS-0203PBZ 200VDC. 3A
WKS-0007PBZL 60VDC. 7A(LED)
WKS-0203PBZL 200VDC. 3A(LED)
WKS-0030SQ 60VDC.30A 4~32vHS-10A
WKS-0050SQ 60VDC.50A HS-20A
WKS-0080SQ 60VDC.80A HS-40A
WKS-0140SQ 100VDC.40A HS-40A
WKS-0210SQ 200VDC.10A HS-10A
WKS-0220SQ 200VDC.20A HS-20A
WKS-0330SQ 300VDC.30A HS-20A
WKS-0530SQ 500VDC.30A HS-40A
WKS-0220MAB 200VDC 20A (2-SPDT, 1a1b) 12-24VDC
WKS-1220C2M04/AC 220VAC AC,DC
WKS-0030FRMP 60VDC 30A
WKS-0050FRMP 60VDC 50A DC60V
WKS-0225FRMP 200VDC 25A DC200V
WKS-0030FRMN 60VDC 30A DC60V
WKS-0050FRMN 60VDC 50A DC60V
WKS-0225FRMN 200VDC 25A DC200V
其周期决定于kf,振幅决定于ku,中曲线①,载波为双极性的等腰三角波,其周期决定于载波频率,振幅不变,与ku=1时正弦波的振幅值相等。调制波与载波的交点决定了逆变桥输出相电压的脉冲系列,此脉冲系列也是双极性的,但是,由相电压合成为线电压(uab=ua-ub;ubc=ub-uc;uca=uc-ua)时,所得到的线电压脉冲系列却是单极性的。(2)双极性调制的工作特点:逆变桥在工作时,同一桥臂的两个逆变器件总是按相电压脉冲系列的规律交替地导通和关断,毫不停息,而流过负载ZL的是按线电压规律变化的交变电流。实施SPWM的基本要求(1)必须实时地计算调制波(正弦波)和载波(三角波)的所有交点的时间坐标。因此电压互感器的容量很小,一般都只有几伏安、几十伏安,也不超过一千伏安。词条介绍了其基本结构、工作原理、主要类型、接线方式、注意事项、异常与处理、以及铁磁谐振等。中文名电压互感器外文名Potentialtransber简称PT作用变换线路上的电压解释带铁心的变压器组成主要由二次线圈、铁心和绝缘所属领域电力、能源涉及学科电学、电磁学目录1基本结构2工作原理3主要类型4铭牌标志5接线方式6注意事项7异常与处理?常见异常?处理方法8铁磁谐振?主要特点?消除办法基本结构编辑电压互感器的基本结构和变压器很相似,它也有两个绕组,一个叫一次绕组,一个叫二次绕组。两个绕组都装在或绕在铁心上。两个绕组之间以及绕组与铁心之间都有绝缘。
WKS-0030SQH HS-10A
WKS-0050SQH HS-20A
WKS-0080SQH HS-40A
WKS-0140SQH HS-40A
WKS-0210SQH HS-10A
WKS-0220SQH HS-20A
WKS-0330SQH HS-20A
WKS-0530SQH HS-40A
WKS-1210SQH HS-10A
WKS-1212SQH HS-10A
WKS-1220SQH HS-20A
WKS-1225SQH HS-20A
WKS-1240SQH HS-40A
WKS-1255SQH HS-300A
WKS-1270SQH HS-300A
WKS-1270SQF HS-300A/F
WKS-1210SQHAC HS-10A
WKS-1212SQHAC HS-10A
WKS-1220SQHAC HS-20A
WKS-1225SQHAC HS-20A
WKS-1240SQHAC HS-40A
WKS-1255SQHAC HS-300A
WKS-1270SQHAC HS-300A
WKS-1270SQFAC HS-300A/F
WKS-1320SQH HS-20A
WKS-1325SQH HS-20A
WKS-1340SQH HS-40A
WKS-1355SQH HS-300A
WKS-1370SQH HS-300A
WKS-1370SQF HS-300A/F
WKS-1320SQHAC HS-20A
WKS-1325SQHAC HS-20A
WKS-1340SQHAC HS-40A
WKS-1355SQHAC HS-300A
WKS-1370SQHAC HS-300A
WKS-1370SQFAC HS-300A/F
WKS-1390SQH 1P 220/380/440VAC 90A 4~32VDC
WKS-13110SQH 1P 220/380/440VAC 110 4~32VDC
WKS-13130SQF 1P 220/380/440VAC 130 4~32VDC
WKS-3390HF04 Tb 3P 220/380/440VAC 90A 4~32VDC
WKS-33110HF04 Tb 3P 220/380/440VAC 110 4~32VDC
WKS-33130HF04 Tb 3P 220/380/440VAC 130 4~32VDC
WKS-3(2)90~110A 120*268*166 ??(W)??(L)??(H)
WKS-3(2)130A 120*288*166 ??(W)??(L)??(H))
WKS-3212HH04 HS-300A
WKS-3212HF04 HS-300A/F
WKS-3225HH04 HS-320A
WKS-3225HF04Tb HS-320A/FT
WKS-3240HH04 HS-330A
WKS-3240HF04Tb HS-320A/FT
WKS-3250HH04 HS-350A
WK-3250HF04Tb HS-330A/FT
WKS-3255HF04Tb HS-330A/FT
WKS-3270HF04Tb HS-350A/FT
WKS-3212HHAC HS-300A
WKS-3212HFAC HS-300A/F
WKS-3225HHAC HS-320A
WKS-3225HFACTb HS-320A/FT
WKS-3240HHAC HS-330A
WKS-3240HFACTb HS-320A/FT
WKS-3250HHAC HS-350A
WKS-3250HFACTb HS-330A/FT
WKS-3325HH04 HS-320A
WKS-3325HF04Tb HS-320A/FT
WKS-3340HH04 HS-330A
WKS-3340HF04Tb HS-320A/FT
WKS-3350HH04 HS-350A
WKS-3350HF04Tb HS-330A/FT
WKS-3355HF04Tb HS-330A/FT
WKS-3370HF04Tb HS-350A/FT
WKS-3325HHAC HS-320A
根据计算结果,有序地向逆变桥中各逆变器件发出“通”和“断”的动作指令。(2)调节频率时,一方面,调制波与载波的周期要同时改变(改变的规律本文不作介绍);另一方面,调制波的振幅要随频率而变,而载波的振幅则不变,所以,每次调节后,所胶点的时间坐标都必须重新计算。要满足上述要求,只有在计算机技术取得长足进步的20世纪80年代才有可能,同时,又由于大规模集成电路的飞速发展,迄今,已经有能够产生满足要求的SPWM波形的集成电路了。西门子420变频器PID调试:总结在变频器page5-13.14详细讲解在说明书page10-84.85..86.87.88.89.90.91.92.93.94重要几个参数为1.P0004改为22.page10-62.P2200改为1允许PID控制器投入3.P2257PID设定值的斜坡上升时间p2258PID设定值的斜坡下降时间P2261PID设定值的滤波时间常数P2264PID反馈信号P2265PID反馈滤波时间常数P2267PID反馈信号的上限值P2268PID反馈信号的下限值P2269PID反馈信号的增益P2270PID传感器的反馈型式P2280PID比例增益系数P2285PID积分时间P2291PID输出上限P2292PID输出下限P2293PID限幅值的斜坡上升/下降时间噪声与振动及其对策采用变频器调速。在这六种单管DC/DC转换器中,Buck和Boost式DC/DC转换器是基本的,Buck-Boost、Cuk、Zeta、SEPIC式DC/DC转换器是从中派生出来的。双管DC/DC转换器有双管串接的升压式(Buck-Boost)DC/DC转换器。四管DC/DC转换器常用的是全桥DC/DC转换器(Full-BridgeConverter)。隔离式DC/DC转换器在实现输出与输入电气隔离时,通常采用变压器来实现,由于变压器具有变压的功能,所以有利于扩大转换器的输出应用范围,也便于实现不同电压的多路输出,或相同电压的多种输出。在功率开关管的电压和电流定额相同时,转换器的输出功率通常与所用开关管的数量成正比。
WKS-3325HFACTb HS-320A/FT
WKS-3340HHAC HS-330A
WKS-3340HFACTb HS-320A/FT
WKS-3350HHAC HS-350A
WKS-3350HFACTb HS-330A/FT
WKS-1212HH04 HS-300A
WKS-1225HH04 HS-300A
WKS-1240HH04 HS-320A
WKS-1250HH04 HS-330A
WKS-1255HH04 HS-330A
WKS-1270HH04 HS-350A
WKS-1270HF04Tb HS-330A/FT
WKS-1212HHAC HS-300A
WKS-1240HHAC HS-320A
WKS-1250HHAC HS-330A
WKS-1255HHAC HS-330A
WKS-1270HHAC HS-350A
WKS-1340HHAC
WKS-1350HHAC
WKS-1370HHAC
WKS-3212HHAC
WKS-3225HHAC
WKS-3240HHAC
WKS-3250HHAC
WKS-3325HHAC
WKS-3340HHAC
WKS-3350HHAC
WKS-1270HFACTb HS-330A/FT
WKS-1325HH04 HS-300A
WKS-1340HH04 HS-320A
WKS-1350HH04 HS-330A
WKS-1355HH04 HS-330A
WKS-1370HH04 HS-350A
WKS-1370HF04Tb HS-330A/FT
WKS-1325HHAC HS-300A
WKS-1340HHAC HS-320A
WKS-1350HHAC HS-330A
WKS-1355HHAC HS-330A
WKS-1370HHAC HS-350A
WKS-1370HFACTb HS-330A/FT
(T.P.R)
WKS-1212SQTM 220VAC 12Amp 0-500KΩ
WKs-1225SQTM 220VAC 25Amp 0-500KΩ
WKS-1240SQTM 220VAC 40Amp 0-500KΩ
WKs-1325SQTM 20VAC 25Amp 0-500KΩ
WKS-1340SQTM 220VAC 40Amp 0-500KΩ
(T.P.R )
WKS-1212SQTMH HS-10A 0-500KΩ
WKS-1225SQTMH HS-20A 0-500KΩ
WKS-1240SQTMH HS-40A 0-500KΩ
WKS-1325SQTMH HS-20A 0-500KΩ
WKS-1340SQTMH HS-40A 0-500KΩ
电源
WK-15AF 15 1 90 ~260 VAC
WK-15AB
WK-15BX
WK-15CX
WK15-3B
WK15-3C
WK-30AF
WK-30AB
WKS-30BX
WKS-30CX
WKS-303BX
WKS-30-3X
WK-50AF 50 1 90 ~ 130/180 ~ 260VAC
WK-50AB 2
WK-50BD
WK50-3X 96*153*43(W*L*H)
WK-75AF
WK-75AB
WK-75BD
WK-60BX
WK-60CX
WK-100AF
WKS-90AB
WKS-100CX
WKS-100AM
WK-100DM
WK-150AF
WK-150CX
WK-130MR
在圆盘上产生一转矩。在20%~40%的动作电流整定值下,圆盘开始旋转。此时由于扇齿与蜗杆没有咬合,故继电器不动作。当线圈中的电流增大至整定电流时,电磁力矩大于弹簧的反作用力矩框架转动,使扇齿与蜗杆咬合,扇齿上升。此时继电器的动铁在扇齿顶杆的推动下,使导磁铁右边气隙减少,左边气隙增大,因而动铁被导磁铁吸合,使继电器触点动作。当继电器线圈中的电流为整定值时,感应元件的动作时限与电流的平方成反比。随着电流的增加,导磁体饱和,动作时限逐渐趋于定值。当线圈中的电流大到某一电流倍数时,电磁元件瞬时动作,因而继电器的动作时限具有有限反延时的特性。继电器具有若干抽头,用以调整感应元件与电磁元件的动作电流。另外用倍流螺钉改变动铁与电磁铁之间的气隙来调整电磁元件动作电流。方向是从T2流向Tl。从图中可以看到,触发电流越大,转折电压就越低,这种情形和普通可控硅的触发导通规律是一致的,当加到主电极上的电压使Tl对T2的极性为正时,叫做反向电压,并用符号U12表示。当这个电压达到转折电压值时,图3(b)右边的可控硅便触发导通,这时的电流为I12,其方向是从T1到T2。这时双向可控硅的特性曲线,如图4中第三象限所示。四种触发方式由于在双向可控硅的主电极上,无论加以正向电压或是反向电压,也不管触发信号是正向还是反向,它都能被触发导通,因此它有以下四种触发方式:(1)当主电极T2对Tl所加的电压为正向电压,控制极G对电极Tl所加的也是正向触发信号(图5a)。双向可控硅触发导通后。
WKS-140MR
WKS-102CT 106*199*50(W*L*H)
WKS-128M
WKS-150MR
WK-903M
WK-903MX
WK-200AF
WK-200CX
WK-160MR
WK-200MR
WK-250A~F 100*200*90
WK-300A~F
WK-400A~F
WKS-500A~F
WKS-600A~F
WKS-750A~F
WKS-1000A~F
WKS-1200A~F
WKS-1500A~F
WKS-1210SQ
WKS-1220SQ, WKS-1225SQ
WKS-1320SQ, WKS-1325SQ
WKS-1240SQ, WKS-1340SQ
WKS-1255SQ, WKS-1270SQ
WKS-1355SQ, WKS-1370SQ
WKS-3212H, WKS-1212H
WK-1225H, WKS-1325H
HS-300A/F DC24V60*60mm WKS-1270SQ, WKS-1370SQ
WKS-3212H HS-320A WKS-3225H , WKS-3325H
WKS-1240H,
WKS-1340H HS-320A/FT Bolt DC24V,AC22080*80mm
WKS-3225H , WKS-3240H
WKS-3325H , WKS-3240H
WKS-1250H , WKS-1350H
WKS-3240H , WKS-3340H
WKS-1250H , WKS-1255H
WKS-1350H , WKS-1355H
HS-330A/FT DC24V,AC22080*80mm
WK-3250H , WK-3255H04
WKS-3350H , WKS-3355H04
WKS-1270H , WKS-1370H
WK-3250H , WKS-3350H
WKS-1270H , WKS-1370H
WK-3270H04, WK-3370H04
WKS-BKT
DSP-VPFR22/44/69
DSP-VIP-PL
DSP-VIP-PM
DSP-VIP-CM
DSP-VIP-CL
DSP-VIP-RTM
DSP-VIP-5EM/5TM/5CM
DSP-VIP-5EL/5TL/5CL
DSP-COM,CCM(485),CTM(4-20mA)
DSP-COL,CCL(485),CTL(4-20mA)
DSP06-3ESSG
DSP06-3ESS(30,60,120)
DSP-10SP, 20SP, 30SP
DSP-SP 01
DSP-30ES
DSP-06ES, (06, 10, 30, 50)
DSP-06ES2, 30-ES2, 60-ES2, 120-ES2
DSP06-SS (30, 60, 120)
DSP-SS 120
DSP-326L DSP-346L DSP-336L DSP-143R DSP-146L DSP-136L DSP-126L DSP-123R DSP-133R
DSP-DGFR DSP-VIP-4EL05Z7-DC DSP-SDTR DSP-UVR110 DSP-UVR220 DSP-UVR380 DSP-OVR380
DSP-OVR220 DSP06-UCR, (30, 60) DSP-WL252R-S DSP-GR 600
DSP-E2CV DSP-NGR44 DSP-NGR22 DSP-APS-BMH DSP-APS-BRH
而负载电机的频率高于变频器的输出频率,负载电机处于发电状态,机械能转化为电能,并被变频器直流侧的平波电容吸收,当这种能量足够大时,就会产生所谓的“泵升现象”,变频器直流侧的电压会超过直流母线的电压而跳闸,对于这种故障,一是将减速时间参数设置长些或增大制动电阻或增加制动单元;二是将变频器的停止方式设置为自由停车。5)电机发热,变频器显示过载对于已经投入运行的变频器如果出现这种故障,就必须检查负载的状况;对于新安装的变频器如果出现这种故障,很可能是V/F曲线设置不当或电机参数设置有问题,如一台新装变频器,其驱动的是一台变频电机,电机额定参数为220V/50Hz,而变频器出厂时设置为380V/50Hz。用于测量仪表的电流互感器宜装在发电机中性点侧。接线方式电流互感器的接线方式按其所接负载的运行要求确定。常用的接线方式为单相、三相星形和不完全星形三种,分别如图4a、图4b和图4c。电流互感器接线方式电流互感器接线方式额定变比和误差:电流互感器的额定变比KN指电流互感器的额定电流比。即:KN=I1N/I2N电流互感器原边电流在一定范围内变动时,一般规定为10~120%I1N,副边电流应按比例变化,而且原、副边电压(或电流)应该同相位。但由于互感器存在内阻抗、励磁电流和损耗等因素而使比值及相位出现误差,分别称为比差和角差。比差为经折算后的二次电流与一次电流量值大小之差对后者之比,即fI为电流互感器的比差。