Elektrik enerji sistemlerinde otomatik tekrar kapamaya bağlı olarak sistem kararlılığı
System stability in electrical power systems in relation to autoreclosing circuit breakers
- Tez No: 39794
- Danışmanlar: PROF.DR. NESRİN TARKAN
- Tez Türü: Yüksek Lisans
- Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
- Anahtar Kelimeler: Elektrik enerji sistemleri, Elektrik enerjisi, Otomatik sistemler, Şebeke kararlılığı, Electrical energy systems, Electrical energy, Automatic systems, Network stability
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
dP > ö d<5 which puts the power angle 5 on the positive slope of the power angle curve. The transient stability of a power system depends on the ability of the generators to adjust thier torque angles to compen sate for the sudden changes in the sys tem without losing their synchronism. The direct approach to transient stability involves solving the swing equation and study the corresponding 5, t curves. The equal-area method is an indirect approach but unfortunately appli cable to only the single-machine problem. On single- line transmission links, automatic rec lo şu re improves the security of supply by combating synch ronous instability following transitory faults. Interrup ting all three phases irrespective of the type of fault, although the simplest arrangment, has the disadvantage that subsequent reclosure must be rapid for any wortwhile improvement to be realised. Single-phase reclosing and opening is attractive because the reclosing time is less- critical than is required for 3 phase reclosure, and its application is based on much field evidence that supports the view that the majority of transitory faults involve only one phase and earth. The analysis of unsuccessful 3 phase reclosure on the double-cicuit system promotes a preference for pro viding eitheran early reclosure, designed to occur when the associated generator has reached a favourable rotor- angle deviation, or a late reclosure (greater than 5 sec), in which case the initial transients will have damped and the system will be more capable of coping with a second disturbance. The reclosing time attaching to the choice of an early reclosure should be calculable with some acur - acy, but little tolerance can be allowed on its value, and it will not be possible to cater for all conditions in the
Özet (Çeviri)
SUMMARY SYSTEM STABILITY İN ELEKTRICAL POWER SYSTEM İN RELATION TD AUTORECLOSING CIRCUIT BREAKERS in our country the consumption of the electrical energy increases proportionalled with the population increasing and the development of the industries. This leads to require the distribution of this energy to many location with transmission lines after it is produced in the big power plants and far away distance from the con¬ sumption place increasing of the production and the dis¬ tribution were caused to the important operating and contro'l problems. Öne of these probleme is associated witn the stability in the power systems. in this study, stability is examined för reactions of network to sudden changes, suçh as short circuit and switching of lines» ît was seen the best metod that was removing of the short circuit quickly obtain the trans¬ mission lines stability. The tendency of a power system ör a part of a power system to develop forces to maintain its equilibrium (to stay in synchronism ) is known as stability. Consider, f ör example, the simple system in which a synchronous mo¬ tor is connected to an infinite bus trough a transformer. Neglecting losses and representing the infinite bus by a costant voltage source, Em is excitation voltage and Xs is the synchronous reactance of the motor. By equation as follows» the (electrical) power transfer from the in¬ finite bus to the motor is E ı excitation voltage m,y X s synchorous reactance X_ s l ine and transformer reactance vii6 s the measure of the angle between the voltages ( the power angle) x = xs + XT ^ E. E. P =. Sin 5 = P.Sin<5 e ymax înitially» let the field current of the motor be adjusted so that the motor carries the machanical load Ps= Pl (shaft power) with unity pf at a power angle of 61. Then? since maximum power that can be supplied to the load is Prnax f ör 5 = 9ö~', theoretical l y, the shaft îoad can slowly be increased to this value. in practice, however, the changes are not gradual but sudden. Let consider us a step change of the shaft power from Pl to P2 with the excitation of the motor unchanged ( Em2 = Emi ). Then the new steady-state operation will be Pe = P2 at 52, However» since Pe = Pi and 5 = 5i at the instant of the load change, there is not enough power devoloped by the motor to the supply the required load. Instead, the required additionai power muşt come from the mecanical energy stored in the inertia of the rotating body of the motor.Consequentiy, the motor will start slowng down ( decelerating ). As the rotor slows» the power angle 5 increases, which in turn increases the electrical power is enough to supply the load, but the rotor cannot immediately stop decelerating. So it keeps on decelerating and as S becomes greater than 62, the electrical power becomes iarger than the load requires."~ ~_ This excess power stpps the decleration and causes the rotor to'accelerate, which start to decrease 5. Depend- ing on the size and other particulars of the motor, the process continues för a while and tnen the system settles down at the second steady-state operating point. viiiHere, we shall asume that the system are critically damped, that is, the applications are such that the angle 5 moves from öne value to the next with no oscillations. Obviously, under this condiation =the staedy-state stabi- lity limit för the motor is Pmax for 6 = 90°. As with fault analyses, in stability analyses we shall neglect the cotribution to fault current made by induction motors during the subtransient period. Accord- ' ingly, the only power systero components left to analyze are synchronous machines. The steady-state stability limit of a synchronous. motor connected to a large power system ( infinite bus ) was found to be Pmax för 6 = 90 °. I f WB now replace the motor with a synchronous generator, then, with 5 positive the power delivered to the infinite bus is given with Em replaced by EB ( the generator's excitation voltage ). Mence, the steady-state stability limit of the generator connected to a large power system is also Pmax for 5=90 ? L. e t us summarize our findings. The steady-steate stability limite of synchronous generators and motors are given by E_. E.EM. E. G ıMı P =p =ore m a H xY A for 5 =90. in other words, synchronous generators and motors will have stable operations for gradual power changes for S < 90° This condition can also be expressed by saying that the steady-state operations are stabile for İMdP > ö d<5 which puts the power angle 5 on the positive slope of the power angle curve. The transient stability of a power system depends on the ability of the generators to adjust thier torque angles to compen sate for the sudden changes in the sys tem without losing their synchronism. The direct approach to transient stability involves solving the swing equation and study the corresponding 5, t curves. The equal-area method is an indirect approach but unfortunately appli cable to only the single-machine problem. On single- line transmission links, automatic rec lo şu re improves the security of supply by combating synch ronous instability following transitory faults. Interrup ting all three phases irrespective of the type of fault, although the simplest arrangment, has the disadvantage that subsequent reclosure must be rapid for any wortwhile improvement to be realised. Single-phase reclosing and opening is attractive because the reclosing time is less- critical than is required for 3 phase reclosure, and its application is based on much field evidence that supports the view that the majority of transitory faults involve only one phase and earth. The analysis of unsuccessful 3 phase reclosure on the double-cicuit system promotes a preference for pro viding eitheran early reclosure, designed to occur when the associated generator has reached a favourable rotor- angle deviation, or a late reclosure (greater than 5 sec), in which case the initial transients will have damped and the system will be more capable of coping with a second disturbance. The reclosing time attaching to the choice of an early reclosure should be calculable with some acur - acy, but little tolerance can be allowed on its value, and it will not be possible to cater for all conditions in thedesign. Consequently, adelayed 3 phase reclosure has ad vantages in multicircuit systems, though the total transi ent period is extended in the event of unsuccessful reclo sure, and ancillary equipment may be required to automati cally check whether condition are electrically favorable for resynchronisation. Successful 3 phase reclosure for the system consider ed improves the stability boundary only slightly over the boundary obtaining with no reclosure, and the effect has little dependence on the rec losing time. Reclosure on to a 3 phase fault lowers the stability boundary by about 15 V. when compared with no reclosure, and time period between unsuccessful reclosure and lockout assumes an Im portance that corresponds to that of the fault clearing time in the absence of reclosure. Successful single phase reclosure improves the double-line stability boundary by about 35 % compared with no reclosure. Unsuccessful single-phase reclosure lowers the stability boundary by about 8 %, but the boundary remains higher than that cor responding to a 3 phase fault at the same location but wi thou t rec 1 osure. >;a
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