【正文】 rom the primary system, which also supplies the distribution transformers providing secondary voltages over singlephase threewire circuits for residential and mercial customers at 120 V/240 。一次系統(tǒng)也給經(jīng)過(guò)單相三線電路為居民用電和商業(yè)用戶提供120V/240V二次電壓的配電變壓器供電。 illustrated in , the aggregated load represented at a transmission substation(bus A)usually includes, in addition to the connected load devices, the effects of substation stepdown transformers…，在輸電變電站（母線A）所給出的集合負(fù)荷，除了所連接的負(fù)荷設(shè)備以外，通常還包括變電站降壓變壓器的影響……。, loads are devices those consume electric energy or electric power consumed by customers mainly in distribution ，負(fù)荷是主要在配電網(wǎng)中消耗電能的設(shè)備或者由用戶消耗的功率。 loads absorb electric energy from the power system and converts it into energy of other forms, which may be heat energy to heat water or to melt irons, or mechanical energy to drive a machine, ，并將其轉(zhuǎn)換為其他形式的能量，可能是燒水或溶化鋼鐵的熱能，或者是驅(qū)動(dòng)機(jī)器的機(jī)械能等。 kind of loads, especially those consume energy calculated by standard coals more over 10 thousands of tons per year, has a name of high energy consuming ，尤其是那些年耗能萬(wàn)噸標(biāo)準(zhǔn)煤以上的負(fù)荷，被稱為高耗能負(fù)荷。 synchronous machine as an AC generator driven by aturbine is the device which converts mechanical energy to electrical energy, in powers ranging up to ，同步電機(jī)是將機(jī)械能轉(zhuǎn)化為電能的設(shè)備，其功率范圍高達(dá)1500MW。 plants can cause low dissolved oxygen levels in the water, a problem that is harmful to riverbank ——（這是）一個(gè)對(duì)岸邊生存環(huán)境有害的問(wèn)題。 instance, in the United States, water power accounts for less than 20% of the total and that percentage will drop because most of the available sources of water power have been ，在美國(guó)，水電在全部電力中所占的比例不到20%，并且，因?yàn)榇蠖鄶?shù)可用的水電資源已被開(kāi)發(fā)，該百分?jǐn)?shù)還會(huì)下降。 stations have ratings between 200 MW and 1500 MW so as to attain the high efficiency and economy of a large ，以實(shí)現(xiàn)大站的高效經(jīng)濟(jì)（運(yùn)行）。 stations are usually located near a river or lake because large quantities of cooling water are needed to condense the steam as it exhausts from the ，這是因?yàn)樾枰罅康睦鋮s水在蒸汽從汽輪機(jī)排出時(shí)將其冷凝。 plants fueled by uranium account for a continually increasing share of the load, but their construction is slow and uncertain because of the difficulty of raising capital to meet the sharply rising cost of construction, constantly increasing safety requirements which cause redesign, public opposition to the operation of the plants, and delays in through a circuit, the current will lose part of it ，要損耗掉一部分能量。（現(xiàn)在分詞短語(yǔ)作狀語(yǔ)）Doing experiment is of great help to 。（動(dòng)名詞作主語(yǔ)）By changing the resistance，we can change the ，我們就能改變電流。（動(dòng)名詞作介賓）Mechanization is using machines instead of hand 。（動(dòng)名詞作表語(yǔ)）When an electric current flow through a wire it meets some ，它會(huì)遇到某種阻力。（狀語(yǔ)從句）Before one studies a system, it is necessary to define and discuss some important ，必須定義并討論一些重要的術(shù)語(yǔ)。（狀語(yǔ)從句）It is possible that we use a puter to solve these plicated 。（表語(yǔ)從句）You should determine which of the following functions is 。（賓語(yǔ)從句）The fact is that radio waves travel as fast as light 。（表語(yǔ)從句）The places where small puters can be used appear 。（定語(yǔ)從句）The instrument that we often use is very good in 。（定語(yǔ)從句）The places where small puters can be used appear 。（定語(yǔ)從句）The instrument that we often use is very good in 。（定語(yǔ)從句）Now we can determine where the slope is 。（賓語(yǔ)從句）This is how a puter 。（賓語(yǔ)從句）Electrons always move toward where the potential is 。（介賓從句）The fact that everything around us is matter is known to 。（同位語(yǔ)從句）Section 2 Exercise 3Section 3 Exercise3 必須強(qiáng)調(diào)的是線性電阻器是一個(gè)理想的電路元件；它是物理元件的數(shù)學(xué)模型。我們可以很容易地買到或制造電阻器，但很快我們發(fā)現(xiàn)這種物理元件只有當(dāng)電流、電壓或者功率處于特定范圍時(shí)其電壓——電流之比才是恒定的，并且這個(gè)比值也取決于溫度以及其它環(huán)境因素。我們通常應(yīng)當(dāng)把線性電阻器僅僅稱為電阻器。只有當(dāng)需要強(qiáng)調(diào)元件性質(zhì)的時(shí)候才使用更長(zhǎng)的形式稱呼它。而對(duì)于任何非線性電阻器我們應(yīng)當(dāng)始終這么稱呼它，非線性電阻器不應(yīng)當(dāng)必然地被視為不需要的元件。Section 4 Exercise 3 如果一個(gè)電路有兩個(gè)或多個(gè)獨(dú)立源，求出具體變量值（電流或電壓）的一種方法是使用節(jié)點(diǎn)分析法或網(wǎng)孔分析法。另一種方法是求出每個(gè)獨(dú)立源對(duì)變量的作用然后把它們進(jìn)行疊加。而這種方法被稱為疊加法。疊加法原理表明線性電路某個(gè)元件兩端的電壓（或流過(guò)元件的電流）等于每個(gè)獨(dú)立源單獨(dú)作用時(shí)該元件兩端的電壓（或流過(guò)元件的電流）的代數(shù)和。Section 5 Exercise 3 相電壓與相電流之比等于電路的阻抗，符號(hào)為字母Z，阻抗是一個(gè)具有量綱為歐姆的復(fù)數(shù)量。阻抗不是一個(gè)相量，因此不能通過(guò)把它乘以并取其實(shí)部把它轉(zhuǎn)換成時(shí)域形式。但是，我們把電感器看作是通過(guò)其電感量L表現(xiàn)為時(shí)域形式而通過(guò)其阻抗表現(xiàn)為頻域形式，電容在時(shí)域里為電容量C而在頻域里為，阻抗是某種程度上的頻域變量而非時(shí)域變量。Section 6 Exercise 3