【正文】 圖 3所示。 )()()( 111112211111 ???? ??? thththL ZEZVZZV [1] )()()( 122112112122 ???? ??? thththL ZEZVZZV [2] 1111111 )()( Eththth IZVZE ?? ?? [3] 2122122 )()( Eththth IZVZE ?? ?? [4] 由 戴維南定理得來自第一和第二母線的電流 1EI 和 2EI 。發(fā)電機負載母線的電流被用來估計戴維南等效的輸電方向。該方法的主要缺點是在戴維南定理的估算 , 它在不同時刻獲得兩個測量值。 為了克服上述缺點的多個方法已經在文獻上提到 ,比如分叉理論 [3],能量法[4]、本征值法 [5],多個負載流解法 [6]等。決定最大允許負載 ,在電壓穩(wěn)定極限內 ,在電力系統(tǒng)運行和規(guī)劃研究中已成為一個非常 重要的問題。 寬松的 政策 迫使發(fā)電企業(yè)要更好地利用電力系統(tǒng)中的輸電。本文描述了一 個測量相鄰系統(tǒng)母線并考慮到的負荷預期變化的擴展的 VIP技術。輸電系統(tǒng)中電能的傳輸依賴于輸電線路的拓撲結構 ,發(fā)電和負載 ,以及無功電源的出處。 where subscript z denotes the we have: L o a dth evL o a dZ Z ZZV S M ?? [12] The above equation assumes that both load impedances ( 1Z , 2Z ) are decreasing at a steady rate, so the power delivered to bus 1 will increase according to Equation (7). However once it reaches the point of collapse power starts to decrease again. Now assume that both loads are functions of time. The maximum critical loading point is then given by Equation(13): 011 ?? dtdsS Critical [13] Expressing voltage stability margin due to load apparent power as ( SVSM ), we have: C rit ic a l L o a dC rit ic a lS S SSV S M ?? [14] Note that both ZVSM and SVSM are normalized quantities and their values decrease as the load increases. At the voltage collapse point, both the margins reduce to zero and the corresponding load is considered as the maximum permissible loading. Fig. 5. VIP algorithm . Voltage Stability Margins and the Maximum Permissible Loading System reaches the maximum load point when the condition: thevload ZZ ? is satisfied (Figure5).Therefore the voltage stability boundary can be defined by a circle 6 with a radius of the Th233。venin?s parameters are constant at the time of estimation. ????????????????????????????????????????12211111121212112112112111121 *thththththLthLZEZEZZZZZZZZVV [6] Where, 111 ?? LZy 11212 ??Zy and 122 ?? LZy The system equivalent seen from bus is shown in Figure 3. Figure 4(a) shows the relationship between load admittances ( 1y and 2y ) and voltage at bus . Power delivered to bus is ( 1S ) and it is a function of ( 1LZ , 2LZ ). 1211 * LyVS ? [7] Equation 7 is plotted in figure 4 (b) as a ?landscape? and the maximum loading point depends on where the system trajectory ?goes over the hill?. Fig. 1. 3Bus system connections Fig. 2. 1Bus model Fig. 3. System equivalent as seen by the proposed VIP relay on bus 1 (2bus model) 4 (a)Voltage Profile (b) Power Profile Fig. 4. Voltage and power profiles for bus 1 . OnLine Tracking of Th233。venin?s equivalent, which is obtained from two measurements at different times. For a more exact estimation, one requires two different load measurements. This paper proposes an algorithm to improve the robustness of the VIP algorithm by including additional measurements from surrounding load buses and also taking into consideration local load changes at neighboring buses. 2. Proposed Methodology The VIP algorithm proposed in this paper uses voltage and current measurements on the load buses and assumes that the impedance of interconnecting lines ( 12Z , 13Z ) are known, as shown in (Figure 1). The current flowing from the generator bus to the load bus is used to estimate Th233。 1 原文 : A SPECIAL PROTECTION SCHEME FOR VOLTAGE STABILITY PREVENTION Tara Alzahawi Student Member, IEEE Mohindar S. Sachdev Life Fellow, IEEE G. Ramakrishna