【正文】 l EquipmentMetal conduit and cases which enclose electrical conductors must be the ungrounded(hot)conductor es in contact with a metal enclosure which is not grounded, a voltage will be present between the enclosure and the presents a potential ic in contact with the enclosure and ground will plete a noncurrentcarrying metal parts of electrical installations should be tightly bonded together and connected to a grounding electrical continuity should be ensured through all metal current caused by accidental grounds will be conducted through the enclosures, the grounding conductor, and the grounding electrode to the the current is false enough, it mill cause the overcurrent device to Ground Fault ProtectionA groundfault protector(GFP)is a device which senses ground faults and opens the circuit when the currant to ground reaches a predetermined groundfault circuit interrupter(GFCI)is a device which opens the circuit when very small currents flow to is no way to determine in advance the impedance of an accidental circuits are protected by 15 A(ampere)or larger overcurrent the impedance of a ground fault is low enough, such devices will open the about currents of less than 15 A? It has been proven that currents as small as 50 mA through the heart, lungs, or brain can be equipment exposed to moisture or vibration may develop highimpedance between a conductor and the frame of equipment may cause a fire, yet the current may be less than 1 current caused by dirt and /or moisture may take place between the conductor and the tools are frequently not properly the only path to ground is through the body of the groundfault circuit interrupter was developed to provide protection against groundfault currents of lessthan 15 GFCI is designed to operate on twowire circuits in which one of the two wires is standard circuit voltages are 120 V and 277 time it takes operate depends upon the value of the groundfault currents of 20 mA or less may flow for up to 5 s before the circuit is current of 20 mA will cause the GECI to operate in less than time/current element provides a sufficient margin of safety without nuisance GFCI operates on the principle that an equal amount of current is flowing though the two a ground fault occurs, same of the currant flowing through the ungrounded(hot)wire does not flow through the grounded wire。電荷是構(gòu)成物質(zhì)的原子微粒的電氣屬性，它是以庫侖為單位來度量的。We consider the flow of electric 。主機使我們在需要可靠性、數(shù)據(jù)安全性以及集中處理的情況下提供了可選擇的計算機。超級計算機上所完成的一個使人留下深刻印象的仿真是對數(shù)以千計的塵埃微粒的運動進行追蹤，這些塵埃微粒就象被一場龍卷風(fēng)所拋擲一樣。一臺個人計算機、服務(wù)站或者向服務(wù)器申請數(shù)據(jù)的軟件被稱為客戶，例如在網(wǎng)絡(luò)上，一個服務(wù)器可能會用一個網(wǎng)頁來回應(yīng)客戶的要求。內(nèi)存一片空白時，計算機電源是關(guān)閉的，因此配置信息不能被儲存在那里。CMOS是公正的車票。當您更改您的計算機系統(tǒng)，通過增加內(nèi)存，例如，在CMOS數(shù)據(jù)必須更新配置。為了防止不同大小的電壓無限制地增多，工業(yè)上使用標準標準化電壓等級。With the development of the AC/DC隨著直交轉(zhuǎn)換設(shè)備的不斷發(fā)展，高壓直流輸電系統(tǒng)（HVDC）在特殊場合變得更有吸引力，更加經(jīng)濟。電力系統(tǒng)中任何一個環(huán)節(jié)中的故障都有可能導(dǎo)致用戶供電的中斷。一般把這些一個系統(tǒng)必須處理的要求叫做性能指標。第三個部分與參數(shù)變化引起的系統(tǒng)誤差相聯(lián)系。Peak Overshoot尖峰超越量This is measured when the response has maximum is an indication of the largest error between input and output during the transient the system considered we observed that the peak overshoot increased as the damping ratio concept of peak overshoot is not limited to only secondorder is often used for higherorder systems that have adominant pair of plex poles are those located nearest the imaginary most welldesigned systems ,peak overshoots are lower than 30%.這個是在響應(yīng)有最大值的時候測量得到的。它還經(jīng)常用在有一對顯性的復(fù)數(shù)極點的高階系統(tǒng)。它定義了響應(yīng)從穩(wěn)定部分誤差的10%上升到90%需要的時間。Settling Time穩(wěn)定時間The settling time is defined as the time necessary for the response to increase to and stay within a specified range of its final of five percent is often stated as the tolerable number of oscillations necessary to reach this condition is also a useful 。高階系統(tǒng)可以有多個阻尼比，而由主導(dǎo)極點做對應(yīng)的阻尼是最重要的。System specifications are also given in terms of the error constants as well as the system error constants are used to relate the system gain and time constants to the system error of a unity feedback measure directly the minimum ideal steady state error of a system for a step ,ramp and parabola 。s daily lives and industrial production is closely related to the extraordinarily rapid development of relatively more mature industry has bee an important ponent of the widely used in industry, agriculture, national defense and other fields, in the national economy is playing an increasingly important more, Electrical Engineering and Automation is very hard to graduate should obtain much knowledge and as natural science foundations include more sturdy mathematics, physics, etc, better Humanity, social science basic for sum foreign language for integration the essential technological basic theory knowledge of the originally professional field, mainly include circuit, electric magnetic field theory, electronic technology, information place in system Paying attention to, control theory, puter software andhardware basic so theory and electrical network theory is a professional electrical engineering and automation of the base, power electronics technology, puter technology is its main technical means, but also includes a system analysis, system design, system development and system management and decisionmaking are some characteristics of the profession, that is, bining the strength of power, electrical and electronic technology, software and hardware bined with a crossdisciplinary nature, electricity, electronics, control, puter integrated multidisciplinary, so that graduates with strong adaptation 魏學(xué)軍25號