sympathetic,sns数据是什么意思?
硬件、软件、服务及网站应用,加上四字构成的词组更符合中国人的构词习惯,因此人们习惯上用社交 *** 来代指SNS(包括Social Network Service的三层含义),用社交软件代指Social Network Software,用社交网站代指Social Network Site。SNS专指旨在帮助人们建立社会性 *** 的互联网应用服务。 医学领域:Sympathetic Nervous System变压器励磁涌流有哪些特点?
励磁涌流的危害性
1.1引发变压器的继电保护装置误动,使变压器的投运频频失败;
1.2变压器出线短路故障切除时所产生的电压突增,诱发变压器保护误动,使变压器各侧负荷全部停电;
1.3a电站一台变压器空载接入电源产生的励磁涌流,诱发邻近其他b电站、c电站等正在运行的变压器产生“和应涌流”(sympatheticinrush)而误跳闸,造成大面积停电;
1.4数值很大的励磁涌流会导致变压器及断路器因电动力过大受损;
1.5诱发操作过电压,损坏电气设备;
1.6励磁涌流中的直流分量导致电流互感器磁路被过度磁化而大幅降低测量精度和继电保护装置的正确动作率;
1.7励磁涌流中的大量谐波对电网电能质量造成严重的污染。
1.8造成电网电压骤升或骤降,影响其他电气设备正常工作。
帮我写一编关于成长的英语演讲稿?
Learn How to Say No
We've all been taught that we should help people. It is the right thing to do and will make us popular with others. It may even win us favors in return. However, we must be realistic. We can't say yes to every request. If we did, we would fail or go crazy for sure. Sometimes we simply don't have the time to help. In this case, we must know how to say no politely.
When we need to say no, here is one method we can try. First, we should tell the truth. If we really can't do something, we should just say so. Second, we should remember to refuse requests politely. We must communicate clearly, but must also be sincere and sympathetic. A true friend will understand. Finally, we must not feel guilty about saying no. Sometimes refusing others is the right thing to do. It can save ourselves, and them, a lot of trouble. In short, we cannot please everyone all the time. Refusing favors is a part of life.
励磁涌流的计算?
励磁涌流(inrush current)的发生,很明显是受励磁电压的影响。即只要系统电压一有变动,励磁电压受到影响,就会产生励磁涌流。在不同的情况下将产生如下所述的初始(initial inrush)、电压复原(recovery inrush)及共振(sympathetic inrush 共感)等不同程度的励磁涌流。其瞬时尖峰值及持续时间,将视下列各因素的综合情况而定,可能会高达变压器额定电流的8~30倍。
计算
变压器是根据电磁感应原理制成的一种静止电器,用于把低电压变成高电压或把高电压变成低电压,
u1=umcos(wt+α)=i1R1+N1dφ/dt (1)
u1:一次电压,
um:一次电压的峰值,
α:合闸瞬间的电压初相角,
R1:变压器一次绕组的电阻,
N1:变压器一次绕组的匝数,
φ:变压器一次侧磁通。
由于i1R1相对比较小,在分析瞬态过程初始阶段可以忽略不计,所以
发电机组功率特性取决于什么的特性?
取决于激磁电流的特性。励磁涌流(inrush current)的发生,很明显是受励磁电压的影响。即只要系统电压一有变动,励磁电压受到影响,就会产生励磁涌流。
在不同的情况下将产生如下所述的初始(initial inrush)、电压复原(recovery inrush)及共振(sympathetic inrush 共感)等不同程度的励磁涌流。
其瞬时尖峰值及持续时间,将视下列各因素的综合情况而定,可能会高达变压器额定电流的8~30倍,而且发电机组功率特性也取决于激磁电流的特性。