1914_機(jī)械廠變電所的電氣設(shè)計(jì)

1914_機(jī)械廠變電所的電氣設(shè)計(jì),機(jī)械廠,變電所,電氣設(shè)計(jì) 黃河科技學(xué)院畢業(yè)設(shè)計(jì) （ 外文翻譯 ） 第 1 頁 TRANSFORMER 1. INTRODUCTION The high-voltage transmission is requied in the case that electrical power is to be provided at considerable distance from a generating station. At some point this high voltage must be reduced, because it ultimately is must supplied to a load. The transformer makes it possible for various parts of a power system to operate at different voltage levels. In this paper we discuss the principles and applications of power transformer. 2. TOW - WINDING TRANSFORMERS A simplest transformer consists of two stationary coils coupled by a mutual magnetic flux. The coils are said to be mutually coupled because they link a common flux. In power applications, laminated steel core transformers (to which this paper is restricted) are used. Transformers are efficient because the rotational losses normally associated with rotating machine are absent, so relatively little power is lost when transforming power from one voltage level to another. Typical efficiencies are in the range 92 to 99%, the higher values applying to the larger power transformers. The current flowing in the coil connected to the ac source is called the primary winding or simply the primary. It sets up the flux f in the core, which varies periodically both in magnitude and direction. The flux links the second coil, called the secondary winding or simply secondary. The flux is changing; therefore, it induces a voltage in the secondary by electromagnetic induction in accordance with Lenz’s law. Thus the primary receives its power from the source while the secondary supplies this power to the load. This action is known as transformer action. 黃河科技學(xué)院畢業(yè)設(shè)計(jì) （ 外文翻譯 ） 第 2 頁 3. TRANSFORMER PRINCIPLES When a sinusoidal voltage Vp is applied to the primary with the secondary open-circuited, there will be no energy transfer. The impressed voltage causes a small current I? to flow in the primary winding. This no-load current has two functions: (1) it produces the magnetic flux in the core, which varies sinusoidally between zero and ± fm, where f m is the maximum value of the core flux; and (2) it provides a component to account for the hysteresis and eddy current losses in the core. There combined losses are normally referred to as the core losses. The no-load current I? is usually few percent of the rated full-load current of the transformer (about 2 to 5%). Since at no-load the primary winding acts as a large reactance due to the iron core, the no-load current will lag the primary voltage by nearly 90o. It is readily seen that the current component Im= I0sin? 0, called the magnetizing current, is 90o in phase behind the primary voltage VP. It is this component that sets up the flux in the core; f is therefore in phase with Im. The second component, Ie=I0sin? 0, is in phase with the primary voltage. It is the current component that supplies the core losses. The phasor sum of these two components represents the no-load current, or I0 = Im+ Ie It should be noted that the no-load current is distortes and nonsinusoidal. This is the result of the nonlinear behavior of the core material. If it is assumed that there are no other losses in the transformer, the induced voltage In the primary, Ep and that in the secondary, Es can be shown. Since the magnetic flux set up by the primary winding， there will be an induced EMF E in the secondary winding in accordance with Faraday’s law, namely, E=N?f/?t. This same flux also links the primary itself, inducing in it an EMF, Ep. As discussed earlier, the induced voltage must lag the flux by 90o, therefore, they are 180o out of phase with the applied voltage. Since no current flows in the secondary winding, Es=Vs. The no-load primary current I0 is small, a few percent of full-load current. Thus the voltage in the primary is small and Vp is nearly equal to Ep. The primary voltage and the resulting flux are sinusoidal; thus the induced quantities Ep and Es vary as a sine function. 黃河科技學(xué)院畢業(yè)設(shè)計(jì) （ 外文翻譯 ） 第 3 頁 The average value of the induced voltage given by Eavg = turns× changeinfluxinagiventimegiventime which is Faraday’s law applied to a finite time interval. It follows that Eavg = N 21/(2)mfj = 4fNf m which N is the number of turns on the winding. Form ac circuit theory, the effective or root-mean-square (rms) voltage for a sine wave is 1.11 times the average voltage; thus E = 4.44fNf m Since the same flux links with the primary and secondary windings, the voltage per turn in each winding is the same. Hence Ep = 4.44fN pf m and Es = 4.44fN sf m where Ep and Es are the number of turn on the primary and secondary windings, respectively. The ratio of primary to secondary induced voltage is called the transformation ratio. Denoting this ratio by a, it is seen that a = psEE = psNN Assume that the output power of a transformer equals its input power, not a bad sumption in practice considering the high efficiencies. What we really are saying is that we are dealing with an ideal transformer; that is, it has no losses. Thus Pm = Pout or VpIp × primary PF = VsIs × secondary PF where PF is the power factor. For the above-stated assumption it means that the power factor on primary and secondary sides are equal; therefore VpIp = VsIs from which is obtained 黃河科技學(xué)院畢業(yè)設(shè)計(jì) （ 外文翻譯 ） 第 4 頁 psVV = psII ≌ psEE ≌ a It shows that as an approximation the terminal voltage ratio equals the turns ratio. The primary and secondary current, on the other hand, are inversely related to the turns ratio. The turns ratio gives a measure of how much the secondary voltage is raised or lowered in relation to the primary voltage. To calculate the voltage regulation, we need more information. The ratio of the terminal voltage varies somewhat depending on the load and its power factor. In practice, the transformation ratio is obtained from the nameplate data, which list the primary and secondary voltage under full-load condition. When the secondary voltage Vs is reduced compared to the primary voltage, the transformation is said to be a step-down transformer: conversely, if this voltage is raised, it is called a step-up transformer. In a step-down transformer the transformation ratio a is greater than unity (a>1.0), while for a step-up transformer it is smaller than unity (a<1.0). In the event that a=1, the transformer secondary voltage equa ls the primary voltage. This is a special type of transformer used in instances where electrical isolation is required between the primary and secondary circuit while maintaining the same voltage level. Therefore, this transformer is generally knows as an isolation transformer. As is apparent, it is the magnetic flux in the core that forms the connecting link between primary and secondary circuit. In section 4 it is shown how the primary winding current adjusts itself to the secondary load current when the transformer supplies a load. Looking into the transformer terminals from the source, an impedance is seen which by definition equals Vp / Ip. From psVV = psII ≌ psEE ≌ a , we have Vp = aVs and Ip = Is/a.In terms of Vs and Is the ratio of Vp to Ip is ppVI = /ssaVIa = 2 ssaVI But Vs / Is is the load impedance ZL thus we can say that Zm (primary) = a2ZL This equation tells us that when an impedance is connected to the secondary side, it appears from the source as an impedance having a magnitude that is a2 times its actual value. We say 黃河科技學(xué)院畢業(yè)設(shè)計(jì) （ 外文翻譯 ） 第 5 頁 that the load impedance is reflected or referred to the primary. It is this property of transformers that is used in impedance-matching applications. 4. TRANSFORMERS UNDER LOAD The primary and secondary voltages shown have similar polarities, as indicated by the “dot-making” convention. The dots near the upper ends of the windings have the same meaning as in circuit theory; the marked terminals have the same polarity. Thus when a load is connected to the secondary, the instantaneous load current is in the direction shown. In other words, the polarity markings signify that when positive current enters both windings at the marked terminals, the MMFs of the two windings add. Since the secondary voltage depends on the core flux f 0, it must be clear that the flux should not change appreciably if Es is to remain essentially constant under normal loading conditions. With the load connected, a current Is will flow in the secondary circuit, because the induced EMF Es will act as a voltage source. The secondary current produces an MMF NsIs that creates a flux. This flux has such a direction that at any instant in time it opposes the main flux that created it in the first place. Of course, this is Lenz’s law in action. Thus the MMF represented by NsIs tends to reduce the core flux f 0. This means that the flux linking the primary winding reduces and consequently the primary induced voltage Ep, This reduction in induced voltage causes a greater difference between the impressed voltage and the counter induced EMF, thereby allowing more current to flow in the primary. The fact that primary current Ip increases means that the two conditions stated earlier are fulfilled: (1) the power input increases to match the power output, and (2) the primary MMF increases to offset the tendency of the secondary MMF to reduce the flux. In general, it will be found that the transformer reacts almost instantaneously to keep the resultant core flux essentially constant. Moreover, the core flux f 0 drops very slightly between no load and full load (about 1 to 3%), a necessary condition if Ep is to fall sufficiently to allow an increase in Ip. On the primary side, Ip’ is the current that flows in the primary to balance the demagnetizing effect of Is. Its MMF NpIp’ sets up a flux linking the primary only. Since the 黃河科技學(xué)院畢業(yè)設(shè)計(jì) （ 外文翻譯 ） 第 6 頁 core flux f 0 remains constant. I0 must be the same current that energizes the transformer at no load. The primary current Ip is therefore the sum of the current Ip’ and I0. Because the no-load current is relatively small, it is correct to assume that the primary ampere-turns equal the secondary ampere-turns, since it is under this condition that the core flux is essentially constant. Thus we will assume that I0 is negligible, as it is only a small component of the full-load current. When a current flows in the secondary winding, the resulting MMF (NsIs) creates a separate flux, apart from the flux f 0 produced by I0, which links the secondary winding only. This flux does no link with the primary winding and is therefore not a mutual flux. In addition, the load current that flows through the primary winding creates a flux that links with the primary winding only; it is called the primary leakage flux. The secondary- leakage flux gives rise to an induced voltage that is not counter balanced by an equivalent induced voltage in the primary. Similarly, the voltage induced in the primary is not counterbalanced in the secondary winding. Consequently, these two induced voltages behave like voltage drops, generally called leakage reactance voltage drops. Furthermore, each winding has some resistance, which produces a resistive voltage drop. When taken into account, these additional voltage drops would complete the equivalent circuit diagram of a practical transformer. Note that the magnetizing branch is shown in this circuit, which for our purposes will be disregarded. This follows our earlier assumption that the no-load current is assumed negligible in our calculations. This is further justified that it is rarely necessary to predict transformer performance to such accuracies. Since the voltage drops are all directly proportional to the load current, it means that at no-load conditions there will be no voltage drops in either winding. 黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 I 頁機(jī)械廠變電所的電氣設(shè)計(jì)摘要本文介紹了機(jī)械廠變電所的電氣設(shè)計(jì)。文中對變電所所址的選擇、主接線的選擇、高壓設(shè)備的選擇、負(fù)荷計(jì)算、短路電流計(jì)算、各種繼電保護(hù)選擇及防雷系統(tǒng)皆有說明。特別對主接線的選擇,變壓器的選擇與短路電流的計(jì)算作了詳細(xì)的說明和分析。其中還對變電所的主接線，高低壓側(cè)的一些保護(hù)裝置等通過 CAD 制圖直觀的展現(xiàn)出來。通過查找大量相關(guān)資料并到工廠實(shí)習(xí)，本次設(shè)計(jì)的內(nèi)容更加接近實(shí)際。設(shè)計(jì)中進(jìn)行了防雷和接地的設(shè)計(jì)。這樣可以使變電所有效的避免雷擊，保證變電站的安全；可以有效的保護(hù)用電設(shè)備，防止過電流的危害；可以保證該變電站具有穩(wěn)定的輸出電壓。本次設(shè)計(jì)采用兩臺主變壓器。一次接線采用單母線，二次接線采用單母線分段制。這種接線方案不僅保證了供電的可靠性，而且靈活方便，適應(yīng)負(fù)荷的發(fā)展。同時(shí)經(jīng)濟(jì)性也較好，減少了投資和有色金屬的消耗量。關(guān)鍵詞：變電所，設(shè)計(jì)，選擇，安全黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 II 頁The Electrical Design of The Mechanical Plant SubstationAuthor:Shi weiTutor:Mu Guo HuaAbstractThis article describes the electrical design of the mechanical plant substation. The choice of the substation site, the choice of the main wiring , high voltage equipment selection, load calculations, short circuit current calculations, various relay’s selection and lightning protection systems are instructed. In particular, this paper gave a detailed description and analysis to the choice of the main wiring , the choice of the transformer and short circuit current calculations. The main connection of the substation, the protection device of high voltage and low voltage side are unfolded through the CAD drawing.Searching a lot of relevant information and visiting many factories, the design contents is closer to reality. This paper designs lightning protection and grounding. This allows the substation to avoid lightning and to ensure the safety of the substation. It can protects the power equipment and prevents the hazards of the overcurrent. And it ensures that the substation has a stable output voltage. The design uses two main transformers. The prinary side using a single bus. The secondaly side using a segmented single busbar. This wiring scheme ensures the reliability of electricity supply, it’s flexible and convenient ,and it adapt to the development of load. At the same time,it makes the economy is better, reduces the consumption of investment and non-ferrous metals.Key word: Transformer substation, design, choice, safety黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 III 頁目錄1 緒論 ....................................................................................................................11.1 課題背景 .................................................................................................11.2 我國電力工業(yè)概述 ..................................................................................11.2.1 我國目前電力工業(yè)的發(fā)展方針 ...................................................11.2.2 變電所的分類 ...............................................................................22 負(fù)荷計(jì)算和無功功率補(bǔ)償 ................................................................................42.1 負(fù)荷計(jì)算的目的、意義及原則 .............................................................42.2 負(fù)荷計(jì)算方法 .........................................................................................42.3 全廠負(fù)荷計(jì)算 .........................................................................................52.4 無功功率補(bǔ)償 .........................................................................................93 變電所位置和形式的選擇 ..............................................................................113.1 變電所所址的選擇 ................................................................................113.2 變電所形式的選擇 ...............................................................................113.3 變電所位置和形式的確定 ...................................................................124 變壓器的選擇 ..................................................................................................144.1 主變壓器臺數(shù)的確定 ...........................................................................144.2 主變壓器容量的確定 ...........................................................................145 電氣主接線的設(shè)計(jì) ..........................................................................................155.1 電氣主接線的概述 ...............................................................................155.2 電氣主接線的設(shè)計(jì)原則和要求 .........................................................155.2.1 電氣主接線的設(shè)計(jì)原則 ..........................................................155.2.2 電氣主接線設(shè)計(jì)的基本要求 ....................................................165.3 電氣主接線方案的比較 .....................................................................176 短路電流計(jì)算 ..................................................................................................196.1 確定基準(zhǔn)值 ...........................................................................................196.2 計(jì)算短路電路中各主要元件的電抗標(biāo)幺值 .......................................19黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 IV 頁6.3 計(jì)算 k-1 點(diǎn)的短路電路總電抗標(biāo)幺值及三相短路電流和短路容量206.4 計(jì)算 k-2 點(diǎn)的短路電路總電抗標(biāo)幺值及三相短路電流和短路容量207 導(dǎo)線的選擇和校驗(yàn) ..........................................................................................227.1 選擇原則 ................................................................................................227.2 選擇架空線截面 ....................................................................................227.3 高壓側(cè)電纜的選擇 ...............................................................................237.4 低壓側(cè)各車間的進(jìn)線的選擇和校驗(yàn) ...................................................237.5 高壓側(cè)選斷路器 ....................................................................................247.6 高壓側(cè)隔離開關(guān) ....................................................................................247.7 電流互感器 ...........................................................................................258 高壓側(cè)繼電保護(hù)選擇及整定 ..........................................................................278.1 變壓器的繼電保護(hù) ................................................................................278.2 變壓器的瓦斯保護(hù) ................................................................................289 防雷設(shè)計(jì) ..........................................................................................................309.1 架空線路的防雷措施 ...........................................................................309.2 變電所的防雷措施 ...............................................................................3010 接地 ................................................................................................................3210.1 接地與接地裝置 ..................................................................................3210.2 確定此配電所公共接地裝置的垂直接地鋼管和連接扁鋼 .............32結(jié)論 ......................................................................................................................34致謝 ......................................................................................................................35參考文獻(xiàn) ..............................................................................................................36黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 1 頁1 緒論1.1 課題背景目前，我國的城市電力網(wǎng)和農(nóng)村電力網(wǎng)正進(jìn)行大規(guī)模的改造，與此相應(yīng)， 工廠變電所也必須進(jìn)行更新?lián)Q代，我國電力網(wǎng)的現(xiàn)實(shí)情況是常規(guī)變電所依然存在，小型變電所、微機(jī)監(jiān)測變電所、綜合自動(dòng)化變電所相繼出現(xiàn)，并取得了迅猛的發(fā)展。隨著改革的不斷深化，經(jīng)濟(jì)的迅速發(fā)展。各電力部門對變電所設(shè)計(jì)水平的要求將越來越高。現(xiàn)在所設(shè)計(jì)的常規(guī)變電所最突出的問題是設(shè)備落后，結(jié)構(gòu)不合理，占地多，投資大，損耗高，效率低，尤其是在一次開關(guān)和二次設(shè)備造型問題上，與國際先進(jìn)水平還有一定差距，從發(fā)展的觀點(diǎn)來看，將越來越不適應(yīng)我國城市和農(nóng)村發(fā)展的要求。因此,本設(shè)計(jì)根據(jù)本廠所能取得的電源及本廠用電的實(shí)際情況，并適當(dāng)考慮到工廠生產(chǎn)的發(fā)展，按照安全可靠，技術(shù)先進(jìn)，經(jīng)濟(jì)合理的要求進(jìn)行設(shè)計(jì)。變電所擔(dān)負(fù)著從電力系統(tǒng)受電，經(jīng)過變壓然后配電的任務(wù)。車間變電所主要用于負(fù)荷大而集中、設(shè)備布置比較穩(wěn)定的大型生廠房內(nèi)。車間變電所一般位于車間的負(fù)荷中心，可以降低電能損耗和有色金屬的消耗量，并能減少輸電線路上的電壓損耗可以保證供電的質(zhì)量。因此，對這種車間變電所的設(shè)計(jì)技術(shù)經(jīng)濟(jì)指標(biāo)要求比較高。車間變電所是工廠供電系統(tǒng)的樞紐，在工廠里占有特殊重要的地位，因而設(shè)計(jì)一個(gè)合理的變電所對于整個(gè)工廠供電的可靠、經(jīng)濟(jì)運(yùn)行至關(guān)重要。本設(shè)計(jì)是從工程的角度出發(fā)，按照變電所設(shè)計(jì)的基本要求，綜合地考慮各個(gè)方面的要素，對供電系統(tǒng)進(jìn)行了合理的布局，在滿足各項(xiàng)技術(shù)要求的前提下，兼顧運(yùn)行方便、維護(hù)簡單，盡可能地節(jié)省投資 [6]。1.2 我國電力工業(yè)概述1.2.1 我國目前電力工業(yè)的發(fā)展方針1、在發(fā)展能源工業(yè)的基本方針指導(dǎo)下發(fā)展電力工業(yè)。2、電力工業(yè)發(fā)展速度必須與國民經(jīng)濟(jì)發(fā)展速度相適應(yīng)。3、發(fā)揮水電優(yōu)勢，加快水電建設(shè)。黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 2 頁4、建設(shè)大型礦口電廠，搞好煤、電、運(yùn)平衡。5、在煤，水能源缺乏地區(qū)，有重點(diǎn)有步驟地建設(shè)核電廠。6、政企分開，省為實(shí)體，聯(lián)合電網(wǎng)，統(tǒng)一調(diào)度，集資辦電。7、因地制宜，多能互補(bǔ)，綜合利用，講求利益。8、節(jié)約能源，降低消耗。9、重視環(huán)境保護(hù)，積極防止對環(huán)境的污染。變電所是聯(lián)系發(fā)電廠和用戶的中間環(huán)節(jié)，起著變換和分配電能的作用。1.2.2 變電所的分類1、樞紐變電所：位于電力系統(tǒng)的樞紐點(diǎn)，連接電力系統(tǒng)高壓和中壓的幾個(gè)部分，匯集多個(gè)電源，電壓為 330～500kV 的變電所，稱為樞紐變電所。全所停電后，將引起系統(tǒng)解列，甚至出現(xiàn)癱瘓。2、中間變電所： 起系統(tǒng)交換功率的作用，或使長距離輸電線路分段，一般匯集2～3 個(gè)電源，電壓為 220～330kV，同時(shí)又降壓供當(dāng)?shù)赜秒姡@樣的變電所起中間環(huán)節(jié)的作用，所以叫中間變電所。全所停電后，將引起區(qū)域電網(wǎng)解列。3、地區(qū)變電所：高壓側(cè)一般為 110～220kV，向地區(qū)用戶供電為主的變電所，這是一個(gè)地區(qū)或城市的主要變電所。全所停電后，僅使該地區(qū)中供電。4、終端變電所：在輸電線路的終端，接近負(fù)荷點(diǎn)，高壓側(cè)電壓一般為 6-35kV，經(jīng)降壓后直接向用戶供電的變電所，即為終端變電所。全所停電后，只是用戶受到損失 [2]。在電力系統(tǒng)中，除應(yīng)采取各項(xiàng)積極措施或減少發(fā)生故障的可能性以外，故障一旦發(fā)生，必須迅速而有選擇性地切除故障元件，這是保證電力系統(tǒng)安全運(yùn)行的最有效方法之一。切除故障的時(shí)間常常要求小到十分之幾甚至百分之幾秒，實(shí)踐證明只有裝設(shè)在每個(gè)電氣元件上的保護(hù)裝置才有可能滿足這個(gè)要求。這種保護(hù)裝置直到目前為止，大多是由單個(gè)繼電器或繼電器與其附屬設(shè)備的組合構(gòu)成的，故稱為繼電保護(hù)裝置。在電子式靜態(tài)保護(hù)裝置和數(shù)字式保護(hù)裝置出現(xiàn)以后，雖然繼電器以被電子元件或計(jì)算機(jī)所代替，但仍沿用此名稱。在電業(yè)部門常用繼電保護(hù)一詞泛指繼電保護(hù)技術(shù)或由各種繼電保護(hù)裝置組成的繼電保護(hù)系統(tǒng)。繼電保護(hù)裝置一詞，則指各種具體的裝置。我國電力工業(yè)自動(dòng)化水平正在逐年提高，20 MW 及以上大型機(jī)組以采用計(jì)算機(jī)監(jiān)黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 3 頁控系統(tǒng)，許多變電所以裝設(shè)微機(jī)綜合自動(dòng)化系統(tǒng)，有些已實(shí)現(xiàn)無人值班，電力系統(tǒng)已實(shí)現(xiàn)調(diào)度自動(dòng)化。迄今，我國電力工業(yè)已進(jìn)入了大機(jī)組，大電廠，大電力系統(tǒng)，高電壓和高自動(dòng)化的新階段。國家方針、政策、技術(shù)規(guī)范和標(biāo)準(zhǔn)是根據(jù)國家實(shí)際情況、結(jié)合電力工業(yè)的技術(shù)特點(diǎn)而制定的準(zhǔn)則，是把科學(xué)、技術(shù)總結(jié)成條理化，也是長期生產(chǎn)實(shí)踐的結(jié)晶，在進(jìn)行論證分析階段，更應(yīng)辯證的統(tǒng)一供電可靠性與經(jīng)濟(jì)性的關(guān)系，方能達(dá)到先進(jìn)性與可行性。黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 4 頁2 負(fù)荷計(jì)算和無功功率補(bǔ)償2.1 負(fù)荷計(jì)算的目的、意義及原則供電系統(tǒng)要能安全可靠地正常運(yùn)行，其中各個(gè)元件（包括電力變壓器、開關(guān)設(shè)備及導(dǎo)線、電纜等）都必須選擇得當(dāng)，除了滿足工作電壓和頻率的要求外，最重要的就是要滿足負(fù)荷電流的要求。因次，有必要對供電系統(tǒng)中各個(gè)環(huán)節(jié)的電力負(fù)荷進(jìn)行統(tǒng)計(jì)計(jì)算。計(jì)算負(fù)荷是供電設(shè)計(jì)計(jì)算的基本依據(jù)。計(jì)算負(fù)荷確定的是否正確合理，直接影響到電器和導(dǎo)線電纜的選擇是否經(jīng)濟(jì)合理。如果計(jì)算負(fù)荷確定的過大，將使電器和導(dǎo)線電纜選的過大，造成投資和有色金屬的浪費(fèi)。如果計(jì)算負(fù)荷確定的過小，又將使電器和導(dǎo)線電纜處于過負(fù)荷下運(yùn)行，增加電能損耗，產(chǎn)生過熱，導(dǎo)致絕緣過早老化甚至燃燒引起火災(zāi)，同樣會造成更大損失。由此可見，正確確定計(jì)算負(fù)荷意義重大。平均負(fù)荷為一段時(shí)間內(nèi)用電設(shè)備所消耗的電能與該段時(shí)間之比。常選用最大負(fù)荷班（即有代表性的一晝夜內(nèi)電能消耗量最多的一個(gè)班）的平均負(fù)荷，有時(shí)也計(jì)算年平均負(fù)荷。平均負(fù)荷用來計(jì)算最大負(fù)荷和電能消耗量。計(jì)算負(fù)荷又稱需要負(fù)荷或最大負(fù)荷。計(jì)算負(fù)荷是一個(gè)假想的持續(xù)性的負(fù)荷，其熱效應(yīng)與同一時(shí)間內(nèi)實(shí)際變動(dòng)負(fù)荷所產(chǎn)生的最大熱效應(yīng)相等。在配電設(shè)計(jì)中，通常采用30 分鐘的最大平均負(fù)荷作為按發(fā)熱條件選擇電器或?qū)w的依據(jù)。尖峰電流指單臺或多臺用電設(shè)備持續(xù) 1 秒左右的最大負(fù)荷電流。一般取啟動(dòng)電流上午周期分量作為計(jì)算電壓損失、電壓波動(dòng)和電壓下降以及選擇電器和保護(hù)元件等的依據(jù)。在校驗(yàn)瞬動(dòng)元件時(shí)，還應(yīng)考慮啟動(dòng)電流的非周期分量。2.2 負(fù)荷計(jì)算方法目前負(fù)荷計(jì)算常用需要系數(shù)法、二項(xiàng)式法、和利用系數(shù)法,前二種方法在國內(nèi)設(shè)計(jì)單位的使用最為普遍。此外還有一些尚未推廣的方法如單位產(chǎn)品耗電法、單位面積功率法、變值系數(shù)法和 ABC 法等. 常采用需用系數(shù)法計(jì)算用電設(shè)備組的負(fù)荷時(shí)，應(yīng)將性質(zhì)相同的用電設(shè)備劃作一組，并根據(jù)該組用電設(shè)備的類別，查出相應(yīng)的需用系數(shù) ，xK黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 5 頁然后按照上述公式求出該組用電設(shè)備的計(jì)算負(fù)荷。2.3 全廠負(fù)荷計(jì)算本設(shè)計(jì)采用需要系數(shù)法確定。機(jī)械廠負(fù)荷原始資料如表 2.1 所示。主要計(jì)算公式有： 有功功率： P30 = Pe·Kd無功功率： Q30 = P30·tanφ視在功率： S30 = P30/cosφ計(jì)算電流： I30 = S30/（ ） [2]NU3表 2.1 機(jī)械廠負(fù)荷資料廠房產(chǎn)編號廠房名稱 容量Pe /kW需要系數(shù) Kd 功率因數(shù)cosφ1 焊接車間 200 0.35 0.602 沙庫 120 0.70 0.603 鍛造車間 320 0.35 0.554 電鍍車間 220 0.50 0.805 金工車間 950 0.20 0.656 機(jī)修車間 180 0.20 0.207 污水處理 14 0.60 0.608 熱處理車間 190 0.60 0.609 食堂,鍋爐房 30 0.60 0.6010 倉庫 15 0.30 0.3011 料場 40 0.30 0.3012 辦公區(qū) 20 0.80 0.801、焊接車間Pe=200 kW，K d=0.35，cosφ=0.60，tanφ=4/3有功計(jì)算負(fù)荷： P30(1)= Pe×Kd=70 kW無功計(jì)算負(fù)荷：Q 30(1) = P30（1） tanφ=70 kW×（4/3）=93.33 kvar視在計(jì)算負(fù)荷：S 30(1)= P30/cosφ= 116.664 kVA黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 6 頁計(jì)算電流：I 30(1)= S30/（ ）=117.26 ANU32、沙庫Pe=120 kW，K d=0.70，cosφ=0.60，tanφ=4/3有功計(jì)算負(fù)荷： P30(2)= Pe×Kd=84 kW無功計(jì)算負(fù)荷：Q 30(2) = P30（1） tanφ=84 kW×（4/3）=112 kvar視在計(jì)算負(fù)荷：S 30(2)= P30/cosφ= 140 kVA計(jì)算電流：I 30(2)= S30/（ ）=212.17 ANU33、鍛造車間Pe=320 kW，K d=0.35，cosφ=0.55，tanφ=1.52有功計(jì)算負(fù)荷： P30(3)= Pe×Kd=112 kW無功計(jì)算負(fù)荷：Q 30(3) = P30（1） tanφ=112 kW×1.52=170.2 kvar視在計(jì)算負(fù)荷：S 30(3)= P30/cosφ= 203.78 kVA計(jì)算電流：I 30(3)= S30/（ ）=309.62 ANU34、電鍍車間Pe=220 kW，K d=0.50，cosφ=0.80，tanφ=3/4有功計(jì)算負(fù)荷： P30(4)= Pe×Kd=110 kW無功計(jì)算負(fù)荷：Q 30(4) = P30（1） tanφ=110 kW×（3/4）=82.5 kvar視在計(jì)算負(fù)荷：S 30(4)= P30/cosφ= 137.5 kVA計(jì)算電流：I 30(4)= S30/（ ）=208.92 ANU35、金工車間Pe=950 kW，K d=0.20，cosφ=0.65，tanφ=1.17有功計(jì)算負(fù)荷： P30(5)= Pe×Kd=190 kW無功計(jì)算負(fù)荷：Q 30(5) = P30（1） tanφ=190 kW×1.17=222.3 kvar視在計(jì)算負(fù)荷：S 30(5)= P30/cosφ= 292.43 kVA計(jì)算電流：I 30(5)= S30/（ ）=444.31 ANU36、機(jī)修車間黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 7 頁P(yáng)e=180 kW，K d=0.20，cosφ=0.65，tanφ=1.17有功計(jì)算負(fù)荷： P30(6)= Pe×Kd=36 kW無功計(jì)算負(fù)荷： Q30(6) = P30（1） tanφ=36 kW×1.17=42.12 kvar視在計(jì)算負(fù)荷： S30(6)= P30/cosφ= 55.4 kVA計(jì)算電流：I 30(6)= S30/（ ）=84.17 ANU37、污水處理Pe=14 kW，K d=0.60，cosφ=0.80，tanφ=3/4有功計(jì)算負(fù)荷： P30(7)= Pe×Kd=8.4 kW無功計(jì)算負(fù)荷：Q 30(7)= P30（1） tanφ=8.4 kW×（3/4）=6.3 kvar視在計(jì)算負(fù)荷：S 30(7)= P30/cosφ= 10.5 kVA計(jì)算電流：I 30(7)= S30/（ ）=15.95 ANU38、熱處理車間Pe=190 kW，K d=0.60，cosφ=0.60，tanφ=4/3有功計(jì)算負(fù)荷： P30(8)= Pe×Kd=114 kW無功計(jì)算負(fù)荷：Q 30(8) = P30（1） tanφ=114 kW×（4/3）=152 kvar視在計(jì)算負(fù)荷：S 30(8)= P30/cosφ= 190 kVA計(jì)算電流：I 30(8)= S30/（ ）=288.68 ANU39、食堂,鍋爐房Pe=30 kW，K d=0.60，cosφ=0.60，tanφ=4/3有功計(jì)算負(fù)荷： P30(9)= Pe×Kd=18 kW無功計(jì)算負(fù)荷：Q 30(9) = P30（1） tanφ=18 kW×（4/3）=24 kvar視在計(jì)算負(fù)荷：S 30(9)= P30/cosφ= 30 kVA計(jì)算電流：I 30(9)= S30/（ ）=45.58 ANU310、倉庫Pe=15 kW，K d=0.30，cosφ=0.85，tanφ=0.62有功計(jì)算負(fù)荷： P30(10)= Pe×Kd=4.5 kW無功計(jì)算負(fù)荷： Q30(10) = P30（1） tanφ=4.5 kW×0.62=2.79 kvar黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 8 頁視在計(jì)算負(fù)荷： S30(10)= P30/cosφ=5.2947 kVA計(jì)算電流：I 30(10)= S30/（ ）=8.04 ANU311、料場Pe=40 kW，K d=0.30，cosφ=0.60，tanφ=4/3有功計(jì)算負(fù)荷： P30(11)= Pe×Kd=70 kW無功計(jì)算負(fù)荷：Q 30(11) = P30（1） tanφ=40 kW×（4/3）=16 kvar視在計(jì)算負(fù)荷：S 30(11)= P30/cosφ= 20 kVA計(jì)算電流：I 30(11)= S30/（ ）=30.39 ANU312、辦公區(qū)Pe=20 kW，K d=0.80，cosφ=0.80，tanφ=3/4有功計(jì)算負(fù)荷： P30(12)= Pe×Kd=16 kW無功計(jì)算負(fù)荷：Q 30(12) = P30（1） tanφ=16 kW×（3/4）=12 kvar視在計(jì)算負(fù)荷：S 30(12)= P30/cosφ= 20 kVA計(jì)算電流：I 30(12)= S30/（ ）=30.39 ANU3因此總的計(jì)算負(fù)荷為（取 K∑p =0.95，K ∑q =0.97）P30=0.95× (P30(1) +……+P30(12))=736.16 kWQ30=0.97×（Q 30(1) +……+Q30(12)）=935.58 kvarS30= P30/cosφ=1190.48 kVAI30= S30/（ ）=1808.8 ANU3負(fù)荷計(jì)算基本完成，詳細(xì)數(shù)據(jù)見表 2.2。黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 9 頁表 2.2 機(jī)械廠的電力負(fù)荷計(jì)算表計(jì) 算 負(fù) 荷廠房編號廠房名稱 容量Pe /kW需要系數(shù)Kdcosφtanφ P30 /kW Q30 /kvarS30 /kV·AI30 /A1 焊接車間 200 0.35 0.60 4/3 70 93.33 116.664 177.262 沙庫 120 0.70 0.60 4/3 84 112 140 212.713 鍛造車間 320 0.35 0.55 1.52 112 170.24 203.78 309.624 電鍍車間 220 0.50 0.80 3/4 110 82.5 137.5 208.925 金工車間 950 0.20 0.65 1.17 190 222.3 292.43 444.316 機(jī)修車間 180 0.20 0.65 1.17 36 42.12 55.4 84.177 污水處理 14 0.60 0.80 3/4 8.4 6.3 10.5 15.958 熱處理車間 190 0.60 0.60 4/3 114 152 190 288.689 食堂，鍋爐房30 0.60 0.60 4/3 18 24 30 45.5810 倉庫 15 0.30 0.85 0.62 4.5 2.79 5.2947 8.0411 料場 40 0.30 0.60 4/3 12 16 20 30.3912 辦公區(qū) 20 0.80 0.80 3/4 16 12 20 30.39總計(jì) 取 K∑p =0.95，K ∑q =0.97 736.16 935.58 1190.48 1808.82.4 無功功率補(bǔ)償工廠中由于有大量的感應(yīng)電動(dòng)機(jī)，電焊機(jī)，電弧爐及氣體放電燈等感性的負(fù)載，從而使功率因數(shù)降低。在充分發(fā)揮了設(shè)備潛力，改善設(shè)備運(yùn)行性能，提高其自然功率因數(shù)的情況下，尚達(dá)不到規(guī)定的工廠功率因數(shù)時(shí)，則需增設(shè)無功功率補(bǔ)償裝置。無功功率補(bǔ)償計(jì)算如下：補(bǔ)償前：變壓器側(cè)的視在計(jì)算負(fù)荷為：S30= P30/cosφ=1190.48 kVA根據(jù)主變壓器容量的選擇條件：S NT≥S 30 ，因此沒有進(jìn)行功率補(bǔ)償時(shí)，主變壓器的容量應(yīng)該選擇 1250 kVA。這時(shí)變電所低壓側(cè)的功率因數(shù)為：黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 10 頁cosφ=736.155/1190.48=0.62補(bǔ)償后：由于電力系統(tǒng)的發(fā)展，變電所高壓側(cè)的功率因數(shù)已經(jīng)不滿足于僅僅大于 0.9，在此要求其高壓側(cè)的功率因數(shù)大于 0.95，則取 cosφ’=0.98要使低壓側(cè)功率因數(shù)由 0.62 提高到 0.98，低壓側(cè)需要裝設(shè)的并聯(lián)電容器容量為：QC=736.16×（tanarccos0.62－ tanarccos0.98）=782.112 kvarS30’=751.98 kVA因此，主變壓器容量可改選為 800 kVA，比補(bǔ)償前容量減少 450 kVA。變壓器的功率損耗為：△P T≈0.015× 751.98 kVA=11.28 kW△Q T≈0.06×751.98 kVA=45.12 kvar變電所高壓側(cè)的計(jì)算負(fù)荷為：P30’=736.16+11.28=747.44 kWQ30’=（935.58—782.112）+45.118=198.5886 kvarS30’= P30/cosφ=773.37 kVAI30’= S30/（ ）=1175.05 ANU3補(bǔ)償后，功率因數(shù)為：cosφ’=747.44/773.37=0.966＞0.95因此這一功率因數(shù)滿足（0.95）要求，并且由此可知，采用無功功率補(bǔ)償來提高功率因數(shù)，能使工廠取得可觀的經(jīng)濟(jì)效果。黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 11 頁3 變電所位置和形式的選擇3.1 變電所所址的選擇變電所位置的選擇，應(yīng)根據(jù)下列要求經(jīng)技術(shù)、經(jīng)濟(jì)比較確定：1、接近負(fù)荷中心；2、進(jìn)出線方便；3、接近電源側(cè)；4、設(shè)備運(yùn)輸方便；5、不應(yīng)設(shè)在有劇烈振動(dòng)或高溫的場所；6、不宜設(shè)在多塵或有腐蝕性氣體的場所，當(dāng)無法遠(yuǎn)離時(shí)，不應(yīng)設(shè)在污染源盛行風(fēng)向的下風(fēng)側(cè)；7、不應(yīng)設(shè)在廁所、浴室或其他經(jīng)常積水場所的正下方，且不宜與上述場所相貼鄰；8、不應(yīng)設(shè)在有爆炸危險(xiǎn)環(huán)境的正上方或正下方，且不宜設(shè)在有火災(zāi)危險(xiǎn)環(huán)境的正上方或正下方，當(dāng)與有爆炸或火災(zāi)危險(xiǎn)環(huán)境的建筑物毗連時(shí)，應(yīng)符合現(xiàn)行國家標(biāo)準(zhǔn)《爆炸和火災(zāi)危險(xiǎn)環(huán)境電力裝置設(shè)計(jì)規(guī)范》的規(guī)定；9、不應(yīng)設(shè)在地勢低洼和可能積水的場所 [2]。3.2 變電所形式的選擇變電所的型式應(yīng)根據(jù)用電負(fù)荷的狀況和周圍環(huán)境情況確定，并應(yīng)符合下列規(guī)定：1、負(fù)荷較大的車間和站房，宜設(shè)附設(shè)變電所或半露天變電所；2、負(fù)荷較大的多跨廠房，負(fù)荷中心在廠房的中部且環(huán)境許可時(shí)，宜設(shè)車間內(nèi)變電所或組臺式成套變電站；3、高層或大型民用建筑內(nèi)，宜設(shè)室內(nèi)變電所或組合式成套變電站；4、負(fù)荷小而分散的工業(yè)企業(yè)和大中城市的居民區(qū)，宜設(shè)獨(dú)立變電所，有條件時(shí)也可設(shè)附設(shè)變電所或戶外箱式變電站；黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 12 頁5、環(huán)境允許的中小城鎮(zhèn)居民區(qū)和工廠的生活區(qū)，當(dāng)變壓器容量在 315KVA 及以下時(shí)，宜設(shè)桿上式或高臺式變電所。變電所的形式有：1、車間附設(shè)變電所；2、車間內(nèi)變電所；3、露天（或半露天）變電所；4、獨(dú)立變電所；5、桿上變電臺；6、地下變電所；7、樓上變電所；8、成套變電所；9、移動(dòng)式變電所 [2]。3.3 變電所位置和形式的確定我們的工廠是 10kv 以下，變電所的位置應(yīng)盡量接近工廠的負(fù)荷中心，工廠的負(fù)荷中心按負(fù)荷功率矩法來確定。在工廠的平面圖（圖 3.1）下側(cè)和左側(cè)，分別作一條直角坐標(biāo)的 x 軸和 y 軸，然后測出各車間和宿舍區(qū)負(fù)荷點(diǎn)的坐標(biāo)位置， (4)(5)(6)(7)(10)(9)(8)(1)(2)(3)圖 3.1 黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 13 頁機(jī)械廠平面圖p1、p2、p3……p10 分別代表廠房 1、2、3……10 號的功率，設(shè)定 p1、p2……p10 并設(shè)定 p11 為生活區(qū)的中心負(fù)荷，如圖（3.2）所示。而工廠的負(fù)荷中心的力矩方程，可得負(fù)荷中心的坐標(biāo)：把各車間的坐標(biāo)帶入（3-1） （3-2），得到 x=5.38，y=5.38.由計(jì)算結(jié)果可知，工廠的負(fù)荷中心在 6 號廠房的西北角（如圖 3.2）。考慮到周圍環(huán)境和進(jìn)出線方便，決定在 6 號廠房的西側(cè)僅靠廠房建造工廠變電所，器型為附設(shè)式。圖 3.2 變電所位置黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 14 頁4 變壓器的選擇4.1 主變壓器臺數(shù)的確定為保證供電的可靠性，避免一臺主變故障或檢修時(shí)影響供電，變電所一般裝設(shè)兩臺主變壓器，但一般不超過兩臺變壓器。當(dāng)只有一個(gè)電源或變電所的一級負(fù)荷另有備用電源保證供電時(shí)，可裝設(shè)一臺主變壓器。對于大型超高壓樞紐變電所，裝設(shè)兩臺大型變壓器，當(dāng)一臺發(fā)生故障時(shí)，要切斷大量負(fù)荷是很困難的，因此，對大型樞紐變電所，根具工程具體情況，應(yīng)安裝 臺24:主變壓器。這種裝設(shè)方法可以提高變電所的供電可靠性，變壓器的單臺容量以及安裝的總?cè)萘拷钥捎兴?jié)約，且可根據(jù)負(fù)荷的實(shí)際增長的進(jìn)程，分別逐臺裝設(shè)變壓器，而不致積壓資金。當(dāng)變電所裝設(shè)兩臺以及以上的主變時(shí)，每臺容量的選擇應(yīng)按照其中任一臺停運(yùn)時(shí)，其余變壓器容量至少能保證所供的一級負(fù)荷或?yàn)樽冸娝控?fù)荷的 60%～75% 。通常一次變電所采用 75%，二次變電所采用 60%。本設(shè)計(jì)采用兩臺變壓器。4.2 主變壓器容量的確定正常情況下兩臺變壓器都參加工作，這時(shí)，每臺變壓器均承受 50%最大負(fù)荷，這種備用及能滿足正常工作時(shí)經(jīng)濟(jì)運(yùn)行的要求，又能在故障情況下承擔(dān)全部負(fù)荷，是比較合理的備用方式。每臺變壓器的容量 SNT 應(yīng)滿足：1、任一臺變壓器單獨(dú)運(yùn)行時(shí)，宜滿足總計(jì)算負(fù)荷 S30 的大約 60%~70%的需要，即：SNT=（ 0.6~0.7）S 302、任一臺變壓器單獨(dú)運(yùn)行時(shí)，宜滿足全部一、二級負(fù)荷的需要，即：SNT≥S 30（Ⅰ+Ⅱ） [2]所以 SNT=（0.6~0.7）×800kVA=（480~560）kVA且 SNT≥S 30（Ⅰ+Ⅱ） =371.28kVA根據(jù)數(shù)據(jù)選 SCB8-500/10 型變壓器。黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 15 頁5 電氣主接線的設(shè)計(jì)5.1 電氣主接線的概述變電所主接線(一次接線) 表示變電所接受、變換和分配電能的路徑。它由各種電力設(shè)備( 隔離開關(guān)、避雷器、斷路器、互感器、變壓器等)及其連接線組成。通常用單線圖表示。主接線是否合理,對變電所設(shè)備選擇和布置,運(yùn)行的靈活性、安全性、可靠性和經(jīng)濟(jì)性,以及繼電保護(hù)和控制方式都有密切關(guān)系.它是供電設(shè)計(jì)中的重要環(huán)節(jié)。 在圖上所有電器均以新的國家標(biāo)準(zhǔn)圖形符號表示，按它們的正常狀態(tài)畫出。所謂正常狀態(tài)，就是電器所處的電路中既無電壓，也無外力作用的狀態(tài)。對于圖中的斷路器和隔離開關(guān)，是畫出它們的斷開位置。在圖上高壓設(shè)備均以標(biāo)準(zhǔn)圖形符號代表，一般在主接線路圖上只標(biāo)出設(shè)備的圖形符號，在主接線的施工圖上，除畫出代表設(shè)備的圖形符號外，還應(yīng)在圖形符號旁邊寫明設(shè)備的型號與規(guī)范。從主接線圖上我們可了解變電所設(shè)備的電壓、電流的流向、設(shè)備的型號和數(shù)量、變電所的規(guī)模及設(shè)備間的連接方式等，因此，主接線圖是變電所的最主要的圖紙之一。5.2 電氣主接線的設(shè)計(jì)原則和要求5.2.1 電氣主接線的設(shè)計(jì)原則 1、考慮變電所在電力系統(tǒng)的地位和作用變電所在電力系統(tǒng)的地位和作用是決定主接線的主要因素。變電所不管是樞紐變電所、地區(qū)變電所、終端變電所、企業(yè)變電所還是分支變電所，由于它們在電力系統(tǒng)中的地位和作用不同，對主接線的可靠性、靈活性、經(jīng)濟(jì)性的要求也不同。2、考慮近期和遠(yuǎn)期的發(fā)展規(guī)模變電所主接線設(shè)計(jì)應(yīng)根據(jù)五到十年電力系統(tǒng)發(fā)展規(guī)劃進(jìn)行。應(yīng)根據(jù)負(fù)荷的大小及分布負(fù)荷增長速度和潮流分布，并分析各種可能的運(yùn)行方式，來確定主接線的形式以及所連接電源數(shù)和出線回?cái)?shù)。3、考慮用電負(fù)荷的重要性分級和出線回?cái)?shù)多少對主接線的影響黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 16 頁對一級用電負(fù)荷，必須有兩個(gè)獨(dú)立電源供電，且當(dāng)一個(gè)電源失去后，應(yīng)保證全部一級用電負(fù)荷不間斷供電；對二級用電負(fù)荷，一般要有兩個(gè)電源供電，且當(dāng)一個(gè)電源失去后，能保證大部分二級用電負(fù)荷供電，三級用電負(fù)荷一般只需一個(gè)電源供電。4、考慮主變臺數(shù)對主接線的影響變電所主變的容量和臺數(shù)，對變電所主接線的選擇將會產(chǎn)生直接的影響。通常對大型變電所，由于其傳輸容量大，對供電可靠性要求高，因此，其對主接線的可靠性、靈活性的要求也高。而容量小的變電所，其傳輸容量小，對主接線的可靠性、靈活性的要求低。5、考慮備用容量的有無和大小對主接線的影響發(fā)、送、變的備用容量是為了保證可靠的供電，適應(yīng)負(fù)荷突增、設(shè)備檢修、故障停運(yùn)情況下的應(yīng)急要求。電氣主接線的設(shè)計(jì)要根據(jù)備用容量的有無而有所不同，例如，當(dāng)斷路器或母線檢修時(shí)，是否允許線路、變壓器停運(yùn)；當(dāng)線路故障時(shí)否允切除線路、變壓器的數(shù)量等，都直接影響主接線的形式。5.2.2 電氣主接線設(shè)計(jì)的基本要求變電所的電氣主接線應(yīng)根據(jù)該變電所在電力系統(tǒng)中的地位，變電所的規(guī)劃容量、負(fù)荷性質(zhì)、線路、變壓器連接總數(shù)、設(shè)備特點(diǎn)等條件確定。并應(yīng)綜合考慮供電可靠、運(yùn)行靈活、操作檢修方便、投資節(jié)約和便于過渡或擴(kuò)建等要求。1、可靠實(shí)用所為可靠性是指主接線能可靠的工作，以保證對用戶不間斷的供電。衡量可靠性的客觀標(biāo)準(zhǔn)是運(yùn)行實(shí)踐。經(jīng)過長期運(yùn)行實(shí)踐的考驗(yàn)，對以往所采用的主接線經(jīng)過優(yōu)選，現(xiàn)今采用主接線的類型并不多。主接線的可靠性是它的各組成元件，包括一、二次部分在運(yùn)行中可靠性的綜合。因此，不僅要考慮一次設(shè)備對供電可靠性的影響，還要考慮繼電保護(hù)二次設(shè)備的故障對供電可靠性的影響。同時(shí)，可靠性不是絕對的，而是相對的。一種主接線對某些變電所是可靠的，而對另一些變電所可能是不可靠的。2、運(yùn)行靈活主接線運(yùn)行方式靈活，利用最少的切換操作，達(dá)到不同的供電方式。根據(jù)用電負(fù)荷大小，應(yīng)作到靈活的投入和切除變壓器。檢修時(shí)，可以方便的停運(yùn)變壓器、斷路器、母線等電氣設(shè)備，不影響工廠重要負(fù)荷的用電。黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 17 頁3、簡單經(jīng)濟(jì)在滿足供電可靠性的前提下，盡量選用簡單的接線。接線簡單，既節(jié)省斷路器、隔離開關(guān)、電流和電壓互感器、避雷器等一次設(shè)備，使節(jié)點(diǎn)少、事故和檢修機(jī)率少；又要考慮單位的經(jīng)濟(jì)能力。經(jīng)濟(jì)合理地選用主變壓器型號、容量、數(shù)量，減少二次降壓用電，達(dá)到減少電能損失之目的。4、操作方便主接線操作簡便與否，視主接線各回路是否按一條回路配置一臺斷路器的原則，符合這一原則，不僅操作簡便、二次接線簡單、擴(kuò)建也方便，而且一條回路發(fā)生故障時(shí)不影響非故障回路供電。5、便于發(fā)展設(shè)計(jì)主接線時(shí)，要為布置配電裝置提供條件，盡量減少占地面積。但是還應(yīng)考慮工廠企業(yè)的發(fā)展，有的用戶第一期工程往往只上一臺變壓器，經(jīng) 3~5 年后，需建設(shè)第二臺主變壓器，變電所布局、基建一般都是根據(jù)主接線的規(guī)模確定的。因此，選擇主接線方案時(shí)，應(yīng)留有發(fā)展余地。擴(kuò)建時(shí)可以很容易地從初期接線過度到最終接線。5.3 電氣主接線方案的比較變電所的接線應(yīng)從安全、可靠、靈活、經(jīng)濟(jì)出發(fā)。本次設(shè)計(jì)的機(jī)械廠 10KV 降壓變電所，地位較為重要，應(yīng)盡量保證供電的可靠性。從經(jīng)濟(jì)性來考慮主接線不宜復(fù)雜。1、只裝有一臺主變壓器的總降變電所主接線通常采用一次側(cè)無母線、二次側(cè)為單母線的主接線。一次側(cè)采用斷路器為主開關(guān)。其特點(diǎn)是簡單經(jīng)濟(jì)，但供電可靠性不高，只適用于三級負(fù)荷。2、一次側(cè)為內(nèi)橋式接線的總降變電所主接線這種主接線的運(yùn)行靈活性較好，供電可靠性較高，適用于一、二級負(fù)荷。這種內(nèi)橋式接線多用于電源線路較長而主變壓器不須經(jīng)常切換的總降壓變電所。3、一次側(cè)為外橋式接線的總降變電所主接線這種主接線也適用于一、二級負(fù)荷。這種外橋式接線多用于電源線路不長而主變壓器需經(jīng)常切換以適應(yīng)經(jīng)濟(jì)運(yùn)行的總降壓變電所。黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 18 頁4、一、二次側(cè)均采用單母線分段的總降壓變電所主接線這種主接線兼有上述內(nèi)橋式和外橋式兩種接線的運(yùn)行靈活性的優(yōu)點(diǎn)，但所用高壓開關(guān)設(shè)備較多，投資較大?？晒┮?、二級負(fù)荷，適用于一、二次側(cè)進(jìn)出線較多的情況。5、一、二次側(cè)均采用雙母線的總降壓變電所主接線采用雙母線接線較之采用單母線接線，供電可靠性和運(yùn)行靈活性大大提高，但開關(guān)設(shè)備也大大提高，從而大大增加了初投資，所以雙母線接線在企業(yè)中少用，主要用于電力系統(tǒng)中。綜合上述的主接線方案的比較,一次側(cè)選用線路—變壓器組接線方式,即采用兩臺變壓器分列運(yùn)行,二次側(cè)采用單母分段接線方式。黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 19 頁6 短路電流計(jì)算此機(jī)械廠短路計(jì)算電路如圖 6.1 所示。圖 6.1 機(jī)械廠短路計(jì)算電路6.1 確定基準(zhǔn)值取 Sd=100MVA，U c1=10.5 kV，U c2=0.4 kV而 I d1=Sd/( Uc1) =5.50 kA3I d2= Sd/( Uc2) =144 kA6.2 計(jì)算短路電路中各主要元件的電抗標(biāo)幺值 1、電力系統(tǒng)電抗標(biāo)幺值取 Soc=750MVA ，因此：X1*=（100MVA）/（750MVA）=0.13332、架空線路電抗標(biāo)幺值由《工廠供電》表 3—1 查得 X0=0.35（Ω/km） ，因此X2*=0.35（ Ω/km）×1kM×[（100MVA ）/（10.5 kV ）]= 0.31753、電力變壓器電抗標(biāo)幺值黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 20 頁查《工廠供電》附錄表 5 得 Uk%=5，因此X3*=（5×100MVA）/（100×800 kVA）=6.25繪制短路等效電路圖如圖 6.2 所示。圖 6.2 變電所短路等效電路圖6.3 計(jì)算 k-1 點(diǎn)的短路電路總電抗標(biāo)幺值及三相短路電流和短路容量1、總電抗標(biāo)幺值X∑(k-1) *= X1* +X2*=0.45082、三相短路電流周期分量有效值I k-1(3)= I d1/ X∑(k-1) *=12.2 kA3、其他三相短路電流I＂ (3)=I∞ (3) = I k-1(3) =12.2 kAish(3)=2.55 I＂ (3) =2.55×12.2=31.11 kAIsh(3)=1.51 I＂ (3) =1.51×12.2=18.422 kA4、三相短路容量Sk-1(3)=Sd/X∑k-1 *=221.83 MV·A6.4 計(jì)算 k-2 點(diǎn)的短路電路總電抗標(biāo)幺值及三相短路電流和短路容量黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 21 頁1、總電抗標(biāo)幺值X∑(k-2) *= X1* +X2*+X3* //X4*=3.57582、三相短路電流周期分量有效值I k-2(3)= I d2/ X∑(k-2) *=40.27kA3、其他三相短路電流I＂ (3)=I∞ (3) = I k-2(3) =40.27 kAish(3)=2.55 I＂ (3) =1.84×40.27=74.10 kAIsh(3)=1.51 I＂ (3) =1.09×40.27=43.89 kA4、三相短路容量Sk-2(3)=Sd/X∑ k-2*=100/3.5758=27.97 MVA短路計(jì)算基本完成，具體數(shù)據(jù)見表 6.1。表 6.1 械廠短路計(jì)算表三 相 短 路 電 流/ kA 三相短路容量/ MVA短路計(jì)算點(diǎn)I k(3) I＂ (3) I∞ (3) ish(3) Ish(3) Sk(3)k-1 12.2 12.2 12.2 31.11 18.422 221.83k-2 40.27 40.27 40.27 74.10 43.89 27.97黃河科技學(xué)院畢業(yè)設(shè)計(jì)說明書 第 22 頁7 導(dǎo)線的選擇和校驗(yàn)7.1 選擇原則1、導(dǎo)線的材質(zhì)組成有鋁，鋁合金，銅和鋼，按結(jié)構(gòu)又可分為單股，多股膠線和復(fù)合材料，多股膠線，在選擇導(dǎo)線時(shí)，首先要考慮在最大負(fù)荷的情況下，保證導(dǎo)線始終通過允許電流而導(dǎo)線不過熱；第二要保證在風(fēng)冰等外載荷情況下不致發(fā)生斷線事故，第三要滿足保護(hù)條件，以保證所安裝的保護(hù)開關(guān)或熔斷器能對導(dǎo)線起到保護(hù)作用，另外還要滿足電壓損失條件，在滿足上述條件后可按下面方法選擇導(dǎo)體截面。2、導(dǎo)線機(jī)械強(qiáng)度：選出的導(dǎo)線應(yīng)有最小截面的限制，一般情況主干線鋁芯不小于35mm2　，銅芯不小于 25mm2；支線鋁芯不小于 25mm2，銅芯不小于 16 mm2。3、導(dǎo)線截面：還應(yīng)用最大允許載流量來校核.如果負(fù)荷電流超過了允許載流量，則應(yīng)增大截面?？砂淬~線不大于 7A/