;.;.5.2.5利用系數(shù)法確定計算負荷用利用系數(shù)法確定計算負荷時，不論計算范圍大小，都必須求出該計算范圍內(nèi)用電設(shè)備有效臺數(shù)及最大系數(shù)，而后算出結(jié)果。（1）用電設(shè)備組在最大負荷班內(nèi)的平均負荷：有功功率Pp=K1PN，kW（5-2-⑵無功功率Qp=Pptg①，kvar（5-2-13）式中PN——用電設(shè)備組的設(shè)備功率，kW；K1——用電設(shè)備組在最大負荷班內(nèi)的利用系數(shù)，見表5-2-6；tg3一一用電設(shè)備組的功率因數(shù)角的正切值，見表5-2-6。表5-2-6利用系數(shù)K1、cosP及tg3用電設(shè)備組名稱K1cos3tg3一般工作制小批生產(chǎn)用金屬切削機床（小型車、包U、插、銑、鉆床、砂輪機等）0.1~0.120.501.73一般工作制大批生產(chǎn)用金屬切削機床0.12~0.140.501.73重工作制金屬切削機床（沖床、自動車床、六角車床、粗磨、銑齒、大型車床、刨、銑、立車、鏜床）0.160.551.51小批生產(chǎn)金屬熱加工機床（鍛錘傳動裝置、鍛造機、拉絲機、清理轉(zhuǎn)磨筒、碾磨機等）0.170.601.33大批生產(chǎn)金屬熱加工機床0.200.651.17生產(chǎn)用通風機0.550.800.75衛(wèi)生用通風機0.500.800.75泵、空氣壓縮機、電動發(fā)電機組0.550.800.75移動式電動工具0.050.501.73不聯(lián)鎖的連續(xù)運輸機械（提升機、皮帶運輸機、螺旋運輸機等）0.350.750.88聯(lián)鎖的連續(xù)運輸機械0.500.750.88起重機及電動葫蘆（8=100%）0.15~0.200.501.73電阻爐、干燥箱、加熱設(shè)備0.55~0.650.950.33試驗室用小型電熱設(shè)備0.351.000.0010t以下電弧煉鋼爐0.650.800.75單頭直流弧焊機0.250.601.33多頭直流弧焊機0.500.701.02單頭弧焊變壓器0.250.352.67多頭弧焊變壓器0.300.352.67自動弧焊機0.300.501.73點焊機及縫焊機0.250.601.33對焊機及鉚釘加熱器0.250.701.02工頻感應(yīng)電爐0.750.352.67高頻感應(yīng)電爐（用電動發(fā)電機組）0.700.800.75高頻感應(yīng)電爐（用真空管振蕩器）0.650.651.17（2）平均利用系數(shù)為ZPK=——p1pZPN(5-2-14)式中ZPp——各用電設(shè)備組平均負荷的有功功率之和，kW；ZPN——各用電設(shè)備組的設(shè)備功率之和，kW。（3）用電設(shè)備的有效臺數(shù)幾yr是將不同設(shè)備功率和工作制的用電設(shè)備臺數(shù)換算為相同設(shè)備功率和工作制的有效值。故yxnyx(ZPN)二N—ZP21N(5-2-15)式中P1N——單個用電設(shè)備的設(shè)備功率，kW。1）當有效臺數(shù)為4臺及以上，且最大一臺設(shè)備功率PNmax與最小一臺設(shè)備功率Pvmin的比值m^3時，取1N,max1N,minn=n(5-2-16)yx在確定nW值時，可將組內(nèi)總功率不超過全組總設(shè)備功率5%的一些最小用電設(shè)備略去。yx2）當m〉3和K1p三0.2時，取ZPnyx0.5P1N,max(5-2-17)如按上式求得的“yr比實際臺數(shù)還多，則取%丫=n。yxyx3）當m〉3和K1p<0.2時，取，0.95（EPn）n=nn六N^^^^（P）2（ZP—P）2n1+Nn1nn一n11（5-2-18）n0.95n=yx^Xyxn（p'）2（1一p'）2n，1一n，（5-2-19）nPn——，,p=-n^~nZpN以上式中n——用電設(shè)備臺數(shù)；（5-2-20）n1——用電設(shè)備中，單臺設(shè)備功率不小于最大一臺設(shè)備功率一半的臺數(shù);n'——n1臺數(shù)的相對值；ZPn—-各用電設(shè)備組的設(shè)備功率之和，kW；Pn1——n1臺設(shè)備的總設(shè)備功率，kW；PPn1功率的相對值；n二一一有效臺數(shù)相對值，可根據(jù)相對值n'和P’,從表5-2-7查得。yx.f表5-2-7用電設(shè)備有效臺數(shù)相對值nvryx3設(shè)備所用的需用系數(shù)應(yīng)用范圍照明回路普通插座廚衛(wèi)插座空調(diào)0.90.90.950.5;.P'n，1.00.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.010.010.010.010.010.020.020.020.020.030.030.040.050.060.080.100.140.200.320.520.020.020.020.020.030.030.030.040.040.050.060.070.090.110.140.190.260.360.510.710.030.030.030.030.040.040.050.060.070.080.080.110.130.160.210.270.360.490.640.810.040.040.040.040.050.060.070.080.090.100.120.150.180.220.270.340.440.570.720.860.050.050.050.060.070.070.080.100.110.130.150.180.220.260.330.410.510.640.790.900.060.060.060.070.080.090.100.120.130.150.180.210.260.310.380.470.580.700.830.920.080.080.080.090.110.120.130.150.170.200.240.280.330.400.480.570.680.790.890.940.100.090.100.120.130.150.170.190.220.250.290.340.400.470.560.660.760.850.920.950.150.140.160.170.200.230.250.280.320.370.420.480.560.670.720.800.880.930.950.200.190.210.230.260.290.330.370.420.470.540.640.690.760.830.890.930.950.250.240.260.290.320.360.410.450.510.570.640.710.780.850.900.930.950.300.290.320.350.390.430.480.530.600.660.730.800.860.900.940.950.350.330.370.410.450.500.560.620.680.740.810.860.910.940.950.400.380.420.470.520.570.630.690.750.810.860.910.930.950.450.430.470.520.580.640.700.760.810.870.910.930.950.500.480.530.580.640.700.760.820.870.910.940.550.550.520.570.630.690.750.820.870.910.940.950.600.570.630.690.750.810.870.910.940.950.650.620.680.740.810.860.910.940.950.700.660.730.800.860.900.940.950.750.710.780.850.900.930.950.800.760.830.890.940.950.850.800.880.930.950.900.850.920.951.000.95;.;.;.(4)計算負荷及計算電流：有功功率尸=KSp,kw(5-2-21)jsmp無功功率。=KSQ,kvar(5-2-22)jsmp視在功率S.,=P2+Q2,kVA(5-2-23)jsjsjsS計算電流I.,=4：，A(5-2-24)js3UN式中UN——額定電壓，kV;Km——最大系數(shù)1,根據(jù)有效臺數(shù)幾和平均利用系數(shù)K,,從表5-2-8查得。myx1p表5-2-8最大系數(shù)KmK1pnyx0.10.150.20.30.40.50.60.70.80.943.433.112.642.141.871.651.461.291.141.0553.232.872.422.001.761.571.411.261.121.0463.042.642.241.881.661.511.371.231.101.0472.882.482.101.081.581.451.331.211.091.0482.722.311.991.721.521.401.301.201.081.0492.562.201.901.651.471.371.281.181.081.03102.422.101.841.601.431.341.261.161.071.03122.241.961.751.521.361.281.231.151.071.03142.101.851.671.451.321.251.201.131.071.03161.991.771.611.411.281.231.181.121.071.03181.911.701.551.371.261.211.161.111.061.03201.841.651.501.341.241.201.151.111.061.03251.711.551.401.281.211.171.141.101.061.03301.621.461.341.241.191.161.131.101.051.03351.561.411.301.211.171.151.121.091.051.02401.501.371.271.191.151.131.121.091.051.02451.451.331.251.171.141.121.111.081.041.02501.401.301.231.161.141.111.101.081.041.02601.321.251.191.141.121.111.091.071.031.02701.271.221.171.121.101.101.091.061.031.02801.251.201.151.111.101.101.081.061.031.02901.231.181.131.101.091.091.081.051.021.021表5-2-8的Km數(shù)據(jù)是按0.5h最大負荷計算的。計算以中小截面導線為基準，其發(fā)熱時間常數(shù)t為10min,負荷的熱效應(yīng)達到穩(wěn)態(tài)的持續(xù)時間t,按指數(shù)曲線約為3t,即0.5h。對于變電所低壓母線或低壓干線來說，TN20min,tN1h。當t>0.5h,最大系數(shù)按下式換算

1001.211.171.121.101.081.081.071.051.021.021201.191.161.121.091.071.071.071.051.051.021601.161.131.101.081.051.051.051.041.021.022001.151.121.091.071.051.051.051.041.011.012401