docCONDITIONS FAVOURING VOLTAGE COLLAPSE IN THE
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CONDITIONS FAVOURING VOLTAGE COLLAPSE IN THE
Conditions favouring voltage collapse in the operation of generator regulators – selected issues CONDITIONS FAVOURING VOLTAGE COLLAPSE IN THE OPERATION OF GENERATOR REGULATORS – SELECTED ISSUES Jacek Klucznik / Gdansk University of Technology Robert Małkowski / Gdansk University of Technology Piotr Szczeciński / Gdansk University of Technology Ryszard Zajczyk / Gdansk University of Technology 1. INTRODUCTION Generator regulator structures applied today and the presettings of main circuits of voltage regulators primarily affect voltage regulation rate and local stability. Signals from the regulation system, relating to the limitation of the synchronous generator field of action, play the key role in excitation control in hazardous from structure is equipped with: situations resulting low or high voltage. Every regulator apart from its inherent • underexcitation limiter, named also limiter of power factor angle [OKM] • excitation minimal current limiter of generator [OMPW] • induction limiter V/Hz [OI] • excitation current limiter of generator [OPW] • stator current limiter of generator [OPS] • overvoltage limiter [ONN]. A structural diagram of a multiparameter generator regulator for machine excitation diode in exciter and excitation rectifier) is presented Fig.1. Fig. 1. Structural diagram of multiparameter generator regulator for machine excitation systems [1] Abstrtact The paper focuses on selected issues relating to the operation of multiparameter generator regulators in voltage collapse. Results of studies are presented regarding the influence of the system stabiliser, a component of the generator regulator system so often neglected. Attention is brought to the advisability of automating the process of active power decreasing in increasing the capacity for reactive power generation. Furthermore, the paper indicates errors in the structure of the primary circuit for voltage regulation with the LV and HV gates intercepting signals in the system. systems (with AC 49 50 Jacek Klucznik; Robert Małkowski / Gdansk University of Technology ee e Piotr Szczeciński; Ryszard Zajczyk / Gdansk University of Technology eeeee ee e eeeee 2. IMPACT ANALYSIS OF PRESENT STRUCTURE, ACTING ALGORITHMS AND PRESETTING OF POWER SYSTEM STABILIZER (PSS) ON POTENTIAL VOLTAGE FAILURE AND RESULTANT COURSE OF EVENTS 2.1. Introduction electromechanical The excitation control system, increasing swinging damping, is called a system stabilizer, most often marked with the acronym PSS (Power System Stabilizer). The system, apart from limiters, constitutes an integral part of generator regulators used today. single We System stabilizers can be classified according to thenumber of input signals. can identify contain input and multi-input stabilizers. Stabilizer input signals or signal should information on the possible electromechanical swinging. Single-input stabilizers apply angular velocity of synchronous generator rotor, 1 active power generated or voltage frequency on generator terminals. Multi-input system stabilizers use two input signals. The most common systems used are those applying measuring generator shaft rpm or generator active power. The general structure of a single input system stabilizer is shown in Fig. 2, whereas a 2-input type system stabilizer is given in Fig. 3. Fig. 2. Structural diagram of 1-input system stabilizer Fig. 3. Structural diagram of 2-input system stabilizer of PSS2B type [4] structures: and A series of analysis was made for two NES used system stabilizers 1-input 2-input, to identify the relations between parameters of stabilizers and the system’s contribution to the loss of generator stability in terms of voltage collapse. Analysis of system stabilizers’ in conditions favouring the initiation of voltage collapse has operation demonstrated that stabilizer structure, amplification factor and values of input limits are of key significance. In some cases, operation of system stabilizers can be disadvantageous in terms of ensuring voltage stability. The problem can be explained by the fact that system stabilizers act in transient states when values of stabilizer input signals change. In synchronous generators equipped with a 1-input type system stabilizer, relying on measurement of active power, the functioning of system stabilizers is visible when the value of generated active power fluctuates. 1 This is the most commonly applied solution in generation units operating in NES [National Electrical System] Vg [-] Vg [-] Conditions favouring collapse in the operation of generator regulators – voltage selected issues 51 Variations of generator active power can be generated by the following two factors: – in the • external such as short-circuits or violent voltage instability power system, occur • internal – related with the turbine regulation system, when variations of turbine mechanical power in result of activated primary or secondary regulation or with malfunctions related with boiler operation. If during external disturbances system stabilizers function correctly, increasing the damping of from electromechanical swinging, we can observe phenomena, resulting turbine power instability, that may contribute to voltage collapse. dPg 2 < 0 , When the decreases output signal of the stabilizer is positive U generation > 0 the stab dt increased excitation voltage and in effect generatorvoltage. Such a situation does not generate a resulting in dPg risk for loss of voltage stability. The situation can become worse with increasing turbine power, when dt > 0 < 0. The and stabilizer signal has a negative value U stabilizer added to the voltage error of primary signal stab circuit regulator results indipping both excitation voltage as well as generator voltage. 2.2. Exemplary results of simulation studies e An example of the operation referred to above is presented in Fig. 4a. The simulatione was performed in a one-machine system for 235MVA turbo-set, equipped with a machine excitation system. The amplification factor e of the system stabilizer varied, taking 50%, 100% and 200% of the base value, corresponding to the markings in Fig. 4a. (k = 0.5, k = 1 and k = 2). In an extremely adverse situation, the system stabilizer can generate a signal, resulting from stabilizer , VSmax, at the level of – 0.05÷0.09. Therefore, in the worst case the stabilizer can cause a drop in limits V Smin generator voltage of about 0.05, which coinciding with dipping generator voltage can pose the risk of voltage collapse. To counteract the above, the system stabilizer limiter should be set unsymmetrical VS max > VS min to stabilizer the the limit excessive fall of generator voltage. Another option for restricting output signal involves reduction of the stabilizer amplification factor, but this leads to decreased operational efficiency of the system stabilizer. b) a) k = 2 k = 1 k = 0.5 k = 1 k = 0.5 k=2 1.001 1.005 1 1 0.995 0.999 0.99 0.998 0.985 0.997 0.98 0.996 0.975 0.995 0 10 20 30 0 10 t [s] 20 30 t [s] PSS na Rys.wartości 4. Wpływ wartości współczynnika wzmocnienia PSS na przebieg napięcia Rys. 4. Wpływ współczynnika wzmocnienia przebieg napięcia generatora przy skokowej zmianie generatora mocy zadanej turbozespołu; zadanej jednowejściowy, b) a) stabilizator jednowejściowy, b) stabilizator dwuwejściowy przy skokowej zmianie mocy turbozespołu; a) stabilizator stabilizator dwuwejściowy Two-input stabilizers, basing on measurement of generator active power and its stator rpm, are free of the resulting from power instability3. defect involving generation of a na non-grounded signal U > 0wyjściowego Wady, polegającej generowaniu input niezerowego V pssturbine > 0 przy pss sygnału Inzmianach effect, no voltage error appears with turbine power changes. curves dwuwej ściowe,The bazuj ące napresented pomiarze in Fig. 4b show mocy turbiny, pozbawione są stabilizatory 3 system stabilizer. In effect, there that turbine power variations lead to a very small output signal from the mocy czynnej generatora i prędkości obrotowej wirnika generatora . Dzięki temu nie powoduj power is in practice no voltage dipping on generator with increasing of the generating unit, thus ą one powstawania uchybu napięciaterminals przy zmianach mocy turbiny. Przedstawione na eliminating the great defect of 1-input stabilizers basing on the measurement of generator active power. rysunku 4b przebiegi wskazują, Ŝe zmiany mocy turbiny powodują powstawanie bardzo niewielkiego sygnału wyjś ciowego stabilizatora systemowego. Dzi ęki temu przy zwiększaniu 2 The amplification factor is negative, causing inversion of input signal phase by 180º. mocy jednostki wytwórczych praktycznie nie dochodzi do obniŜania napięcia na zaciskach 3 Today NES applies voltage frequency measurement of generator in place of the rpm measurement, however this does not alter the principle of generatora, co było główną wad stabilizatora jednowej ściowego bazującego na pomiarze ą stabilizer operation mocy czynnej generatora. Jacek Klucznik; Robert Małkowski / Gdansk University of Technology Piotr Szczeciński; Ryszard Zajczyk / Gdansk University of Technology 52 2.3. Conclusions The conducted analysis pointed to the following conclusions: • Single-input system stabilizers, with measurement of active power, can lead to dipping generator voltage in result of turbine power instability. The voltage decrease depends on stabilizers presettings – amplification factor and limiters of input signal. We can assume, on the basis of selected stabilizer presettings used in NES that maximum voltage decrease in the effect of stabilizer operation can achieve 5%. This value, in case of extremely unfavourable voltage values, can put stability at risk. The problem can be solved by locking decreasing block power in case of dipping voltage, what is also advantageous from the point of view of 4 . Dobór nastaw nowopowstających i modernizowanych blokach tego typu układów stator current limiter. Another solution is the usage of 2-input stabilizers, where problems with takich voltage error stabilizatorów musi4 odbywać sięnever indywidualnie dla kaŜdego z bloków z uwzględnieniem in turbine power instability practically occur. 4 nowopowstających i modernizowanych blokach tego typu układów . Dobór nastaw takich .stabilizers Dobór nastaw takich nizowanych•blokach tego typu układów stabilizatorów musi odbywać się indywidualnie dla this kaŜdego zmoŜna bloków z uwzględnieniem No ich impact of two-input on potential voltage failure is observed. Thus, of installation specyfiki, sposobu powiązania z systemem elektroenergetycznym itp. Nietype w ich specyfiki, sposobu powiązania z systemem elektroenergetycznym itp. Nie moŜna w 4 ać się indywidualnie dla każdego z bloków z uwzględnieniem . Presettings selection of stabilizers should be done is proposed on all newly and modernized sposób ogólny podaćbuilt zalecanych nastaw,blocks zaleŜą one od efektów, które ma powodować sposób ogólny podać zalecanych nastaw, zaleŜą one od efektów, które ma powodować iązania z systemem elektroenergetycznym itp. Nieinto można w stabilizator individually for each block taking consideration its specifics, connection to the power system, etc. w odniesieniu do danego generatora (kołysania własne) stabilizator w odniesieniu do danego elektroenergetycznego generatora (kołysania (kołysania własne) i systemu i systemu obszarowe i międzyobszarowe). anych nastaw, zależą one recommendations od efektów, które should ma powodować Presetting not be generalised as the presettings depend on the stabilizer’s effects elektroenergetycznego (kołysania obszarowe i międzyobszarowe). u do danego on generatora (kołysania własne) i power systemu the generator (own swinging) and system (area and inter-area swinging). 3. Zasady odciąŜania turbin w celu zwiększenia generacji mocy biernej ysania obszarowe i międzyobszarowe). 3.1 Wstęp Wartość mocy biernej generowanej przez generator synchroniczny, jest nierozerwalnie 3. Zasady odciąŜania turbin w celu zwiększenia generacji mocy biernej związana z wartościąREACTIVE napięcia generatora. Ograniczeniem generowanej przez generator 3. PRINCIPLES OF TURBINES UNLOADING TO INCREASE POWER GENERATION w celu zwiększenia generacji mocy biernej synchroniczny mocy biernej jest wartość dopuszczalna prądu stojana i prądu wzbudzenia. 3.1 Wstęp Definicja ograniczeń opisanych zaleŜnościami (1) i (2) pozwala na wyznaczenie obszaru 3.1. Introduction dopuszczalnej pracy na płaszczyźnie P-Q, co pokazano na rys. 5. Wartość mocy biernejingenerowanej generator synchroniczny, nierozerwalnie Reactive power, generated synchronous przez generators, is inseparably relatedjest to the generator voltage. + Q ≤ S = (V × I ) enerowanej przez generatorz synchroniczny, jest nierozerwalnie związana wartością napięcia generatora.P Ograniczeniem generowanej przez generator (1) 2 g 2 g 2 g 2 The admissible value of stator and excitation currents is limited by the generated reactive power from the syna generatora. Ograniczeniem generowanej generator synchroniczny biernejprzez jest wartość dopuszczalna stojana prądu wzbudzenia. chronous generator.mocy The definition of limits delineated by and (2)iidentifies the area of permit the × V (1) V relations V prądu ≤ P + Q + est wartość ted dopuszczalna prądu stojana i prądu wzbudzenia. xpozwala (2) operation on plane P-Q,opisanych which is presented in Fig. 5. x Definicja ograniczeń zaleŜnościami (1) i na wyznaczenie obszaru (2) h zależnościami (1) i (2) pozwala na wyznaczenie obszaru dopuszczalnej pracy na płaszczyźnie P-Q, co pokazano na rys. 5. yźnie P-Q, co pokazano na rys. 5. 2 2 g P + Q ≤ S = (Vg × I gM ) 2 g 2 g 2 Vg2 Vg × V fM ≤ P + Qg + x x d d 2 g 2 g gM g d fM 2 d 2 2 g 2 g g (1) (1) 2 (2) (2) Rys. 5. Obszar stanów dopuszczalnych pracy generatora synchronicznego przy napięciu Fig. 5. The area of admissible synchronous generator operation states at rated voltage (continuous lines) and at voltage less than rated (intermittent znamionowym (linie ciągłe) i przy napięciu mniejszym do znamionowego (linie przerywane). limit (1)(current) – granicalimit wynikająca z dopuszczalnej obciąŜalności prądowej stojana, by (2)stability – granica lines). (1) – admissible stator ampacity limit , (2) – admissible voltage of excitation, (3) – natural balance (conditioned wynikająca z dopuszczalnego napięcia (prądu) wzbudzenia, (3) – granica równowagi requirement). To simplify the figure only limits resulting from admissible current of machine rotor and stator are presented. naturalnej (wynikająca z warunku zachowania stabilności). Dla uproszczenia na rysunku When the value of generated reactive power Postulat is too high, i.e. exceeds the generator permitted operation ten jest zgodny z zapisami w IRiESP [6] area, the generator regulator changes operational priorities, from voltage regulationto operation with quasi fixed value of stator or rotor current. In such circumstances systems called rotor current limiters or stator current limiters reduce the generator excitation voltage reducing the excitation current (rotor current) and generator voltage reducing the generator stator current according to Formula (1). Enhancing the generating possibilities of reactive power range is important particularly in case of low generator voltage. In result of low voltage, stator current increases as well as the generated active power Pg1. Reduction of reactive power is necessary to prevent overheating of stator windings. This is illustrated in Fig. 5, where the generated reactive power must be lowered from Qg1 to Qg2 following lower generator voltage from Vg1 to Vg2 to keep the generator in the acceptable range. The problem grows if a permanent reactive power deficiency occurs. synchronicznego przy napięciu ch stanów pracy generatora Another current limitation method is to decrease active power generation. The decreasing of active rzy napięciu mniejszym dostator znamionowego (linie przerywane). opuszczalnej obciążalności prądowej stojana, (2) stanów – granicapracy generatora synchronicznego przy napięciu Rys. 5. Obszar dopuszczalnych napięcia (prądu) wzbudzenia, (3) – granica równowagi 4 This proposal complies with IRiESP (Instrukcja ruchu i eksploatacji sieci przesyłowej) notations [Electrical Power Transmission Network znamionowym (linie ciągłe) i przy napięciu mniejszym do znamionowego (linie przerywane). Running and Operating Instructions] [6]. unku zachowania stabilności). Dla uproszczenia na rysunku w IRiESP [6] 4 (1) – granica wynikająca z dopuszczalnej obciąŜalności prądowej stojana, (2) – granica wynikająca z dopuszczalnego napięcia (prądu) wzbudzenia, (3) – granica równowagi naturalnej (wynikająca z warunku zachowania stabilności). Dla uproszczenia na rysunku 5 Conditions favouring voltage collapse in the operation of generator regulators – selected issues 53 power generation from Pg1 to Pg2 increases potential reactive power generation in each case. Reactive power generation can decrease to Qg3, i.e. by ∆Qg. In case of reactive power generation deficit, possible reactive power generation growth is a desirable feature. To recapitulate, by decreasing active power we can increase the generated reactive power, within admissible stator current limits, without decreasing generator voltage. The solution was mentioned in a paper on voltage collapse of 26-th June 2006 [2], however, the problem was not extensively discussed. 3.2. Examples of simulation study results Today, generator unloading as a preventive measure against generator overloading in case of voltage collapse risk is described in emergency procedures. The only drawback of such unloading is its manual character at dispatcher’s command. Results of simulation studies for automatic generator unloading are presented below. Dipping voltage and appearance of reactive power swinging in result of limiters reaction of power angle and stator current5 triggered the procedure of generator unloading. The first stage of unloading was activated directly following disclosure of “inter-forcing” of limiters (acting OPS, OKM and reactive power swinging). The following two stages are activated after a specified interval, provided the conditions for stage 1 are met. Unloading power in the following stages was 5% Pgn. Professional literature refers to various conditions required to initiate the process of automatic unloading. These involve either voltage level or delay or reactive power close to zero at activated power angle limiter. Constant values of delay and voltage presettings can be a defect in the first case, while in the second case the defect may involve negligence of dynamic alteration of activation limit for OKM depending on voltage and no reversal of OPS sign). The proposed solution does not feature the level (OKM activation at QogrOKM > 0, defect. Results of simulator study examples for a case of dynamic Qogr = f(Vg), Fig.7, and constant limit value OKM, (Fig. 6.) confirm the above. Fig. 6. Effects of generator unloading operation, taking into account the sign of reactive power in OPS. Regulator structure – correction: a) generator c) power, voltage, b) excitation current, generator current, d) generator reactive power, e) generator active f) signals form individual limiters. OGR – overall signal. Problems resulting from inter-forcing of limiters are elaborated in [5]. 5 54 Jacek Klucznik; Robert Małkowski / Gdansk University of Technology Piotr Szczeciński; Ryszard Zajczyk / Gdansk University of Technology Not all structures of power angle limiters (OKM) take into account the influence of generator voltage. However, voltage value on generator bus-bars has a significant impact on the value of the stability limit (falling voltage results in limit displacement to point of inductive power, see: Fig. 5, curves 3). The power angle limiter should change the limitation position depending on voltage value. Results obtained for the case shown in Fig. 6 are presented below, however, in this case the impact of changing limitation level, initiated by alternating voltage on generator terminals is taken into account. Fig. 7. Effects of generator unloading taking into account the sign of reactive power in OPS. Regulator structure – corrective accounting for dynamic active power, variation of QogrOKM = f(Vg): a) generator voltage, b) excitation current, c) generator current, d) generator reactive power, e) generator f) signals from individual limiters. OGR – overall signal. 3.3. Conclusions from simulation studies The following conclusions are drawn from the simulation study results: • Generator unloading by alteration of generator active power presetting value increases the generator volt age stability margin in case of voltage collapse. Automation of the process is desirable. The criterion referred to in the paper can be applied for this purpose– individually or jointly with other criteria. • Active power limiters should be above all installed in blocks, which are most susceptible to voltage collapse. • Active power decreasing for generating blocks is pointless, if the limitation of reactive power generation is not caused by generator regulator systems, but by ARNE system. Therefore, correct presettings of reactive power limiters in ARNE systems should be reviewed. • Dynamic alternating of reactive power limit Q = f(Vg) in OKM is necessary. into account the generaogr Taking tor ‘s actual voltage level facilitates effective protection of the generator against stability loss (compare Fig. 6 and Fig. 7) 4 Wpływ lokalizacji bramek wybierających sygnał w głównym torze układu Conditions favouring voltage collapse in the operation of generator regulators – regulacji napięcia na przebieg awarii napięciowej selected issues e e e 4.1 Wstęp eeee 55 4. IMPACT SIGNAL SELECTION GATES POSITIONING IN THE PRIMARY VOLTAGE W OF układach analogowych i cyfrowych w głównym torze regulacji stosuje CIRCUIT się z reguły REGULATION SYSTEMjako ONwzmacniacza VOLTAGE FAILURE SEQUENCE strukturę regulatora, ze sprzężeniem korekcyjnym, rys. 1. Jedną z różnic w spotykanych w KSE układach analogowych i cyfrowych jest sposób 4.1. Introduction wprowadzania sygnałów z ograniczników do toru głównego regulacji. As a rule, regulator structure is applied as a correction coupling amplifier (Fig.W1), układach in digital and analogue analogowych sygnały ograniczników wprowadzane są do węzłów sumacyjnych przed lub za systems in the primary regulation circuit. wzmacniaczem z członem korekcyjnym. W stosowanych obecnie cyfrowych układach One of the differences between digital and analogue systems in NES is the method of signal input from liwzbudzenia stosuje się wprowadzenie ograniczników poprzez bramki przejmujące miters to the primary regulation circuit. In sygnałów analogue systems limiters signals feed the summing junction before sygnały LV i HV. Wprowadzenie przez jeden z ograniczników do bramki LV wartości or after the correction coupling amplifier unit. Contemporary digital excitation systems feed the limiter signals mniejszej od sygnału z głównego toru regulacji jest jednoznaczne z przejęciem regulacji through gates accepting LVand HV signals. The access a signal below the primary regulation circuit to LV of wzbudzenia przez sygnał z ogranicznika. Wprowadzenie do bramkiHV sygnałów większych gate through one of limiters is synonymous with the signal from the limiter intercepting excitation regulation. od sygnału z toru głównego regulacji, powoduje przejęcie regulacji wzbudzenia przez sygnały Input of signals to HV gate over the primary regulation circuit signals results in signals from those limiters z tych ograniczników. Przy niepobudzonych ogranicznikach sygnał z ograniczników takingover control. In the case of inactivated limiters, their signalinput to LV gate is 10V, and on HV excitation wchodzący na bramki LV wynosi 10V, a na bramkę HV odpowiednio 0V. gate 0V, respectively. Przykładową strukturę stosowanych regulatorów przedstawiono na rys. 8. Stosowane An example of regulator structure is presented in Fig. 8. The applied solutions of limiters’ signal input to rozwiązania z wprowadzaniem sygnałów z ograniczników do węzłów sumacyjnych przed lub summing junctions before or after the correction amplifier unit, can be met in technologically older excitation zawzmacniaczem korekcyjnym, można spotkać w starszych technologicznie z członem systems. układach wzbudzenia. diagram regulation systems. Fig. 8.Rys. Block of primary circuit for voltage applied by domestic and foreign producersof automatic voltage 8. Schemat blokowy toru regulation głównego regulacji napięcia stosowany u krajowych i zagranicznych producentów układów automatycznej regulacji napięcia. The presently applied digital systems of generators’ regulation, in which regulation algorithms take into consideration gates intercepting signals, do not require additional system locking limiters, as in the case of Obecnie stosowane cyfrowe układy regulacji generatorów, których algorytmy regulacji older, power angle and stator current analogue systems for generator regulation. The priority of the control uwzględniają stosowanie bramek przejmujących sygnał, nie wymagają dodatkowych układów signal in digital systems is defined by the position of the gate intercepting control signals. According to Fig. 8, blokujących ograniczniki, jak to jest w ogranicznikach kąta mocy i ogranicznikach prądu the stojana signal is w fedstarszych, from the power angle limiter to theregulacji HV gate secondary to the LV gate. In effect, analogowych układach generatorów. Nadrzędność sygnałuthe signal from the sterowania power anglewlimiter (OKM) is secondary output from the limiter of excitation current (OPW) and układach cyfrowych jesttodefiniowana kolejnością rozmieszczenia bramek signals (OPS). kąta sygnały sterujące. Zgodnie z rys. 8 sygnał z ogranicznika mocy jest fromprzejmujących the limiter of stator current wprowadzany do bramki HV, podrzędnej względem bramki LV. Powoduje to, że sygnał z kąta mocy (OKM) 4.2.ogranicznika Results of simulation studiesjest podrzędny względem sygnałów z ogranicznika prądu wzbudzenia (OPW) i z ogranicznika prądu stojana (OPS). Figures 9, 11, 13 and 15 show the curves of active and reactive power, generator current and voltage, excitation voltage and current and signals from individual limiters in the case of dipping voltage in the power supply system to 370 kV in the structure shown in Fig. 8. Dipping voltage in electric power systems with proper4.2 Wyniki badań ly operating limiters insymulacyjnych the structure, shown in Fig. 8, reduce the voltage of synchronous generator excitation and may, inNasome result loss of generator synchronism. Dipping voltage in power activate rys. cases, 9, 11, 13 i 15inprzedstawiono przebiegi mocy czynnej i mocy biernej, prądusystems i the napięcia excitation generatora, current limiter and later limiter and limiter, (Fig. 15). Repeated napięcia i stator prądu current wzbudzenia orazexcitation sygnały current z poszczególnych activation of excitation current limiter results in de-excitation of the synchronous generator and its falling out 9 of step. As presented in Fig. 15, the operation of the stator current limiter, in terms of reactive power consumption and power angle limiter, do not influence the generator regulator system in result of signals flowing from both limiters to the secondary gate. Incorrect positioning of signal intercepting gates intercept the signal in the primary regulation circuit, the high signal input from the power angle limiter to the HV gate cannot take over control. Operation of the minimum current excitation limiter in this case is too slow, because excitation current reaches the maximum value when excitation voltage falls to zero, Fig. 13. Minimum current excitation limiter traces the value of the excitation current but that limiter is activated too late, practically after falling out of step. Structure alteration of the primary regulation circuit, which involves a change in sequence of gates intercepting signals of LV to HV limiters, results in the power angle limiter taking over control of the signal. The signal from the power angle limiter and stator current limiter in terms of reactive current consumption will be, 56 Jacek Klucznik; Robert Małkowski / Gdansk University of Technology Piotr Szczeciński; Ryszard Zajczyk / Gdansk University of Technology in this case, primary signals. Figures 10, 12 and 14, 16 present active and reactive power curves, generator current and voltage, excitation voltage and current and also signals from individual limiters in the case of dipping voltage electric power system to 370 kV,for generator regulator system with altered structure of main in circuit, shown in Fig. 17 . Fig. 9. Curves of active and reactive power at slow electric power voltage reduction below 370 kV Fig. 10. Curves of active and reactive power at slow electric power voltage reduction below 370 kV. Change in LV HV gate sequence Fig. 11. Curves of voltage and current of synchronous generator at slow electric power voltage reduction below 370 kV Fig. 12. Curves of voltage and current of synchronous generator at slow electric power voltage reduction below 370 kV. Change in LV HV gate sequence Fig. 13. Curves of excitation voltage and current of synchronous generator at slow electric power voltage reduction below 370 kV Fig. of control signals in voltage regulator at slow electric 14.Curves power voltage reduction below 370 kV. Change in LV HV gate sequence Fig. 15. Curves of control signals in voltage regulator at slow electric power voltage reduction below 370 kV Fig. 16. Curves of excitation voltage and synchronous generator current at slow electric power voltage reduction below 370 kV. Change in LV HV gate sequence The change of gate sequence provides protection of the synchronous generator against falling out of step. According to Fig. 16, the excitation current limiter is the first to react to voltage dipping, and is followed the by the stator current limiter, and the superior signal of power angle limiter takes control and becomes over superior control signal. Change of gate positions allows for compliance with design assumptions of analogue excitation systems. Conditions favouring voltage collapse in the operation of generator regulators – selected issues RA – regulacja automatyczna Ograniczniki: UNast Ug - Σ + KA 1+sTA 1+sTB 1+sTC 1+sTD OKM [V] OPW [V] RR – regulacja ręczna IfNast Ifg - Σ + 57 Nastawy: OKM [V] 0-10 [V] OPW [V] 0-10 [V], I2t [A2s] OPS [V] 0-10 [V], I2t [A2s] OPS [V] KIA 1+sTIA 1+sTIB RA LV GATE RR RA – regulacja automatyczna RR – regulacja ręczna HV GATE Ust Fig. 17. Correct sequence of gates selecting the signal in the primary voltage regulation circuit 4.3. Conclusions In new, contemporary digital generator regulation systems, the sequence of gates selecting signals in the primary regulator circuit conform to the standard [4]. According to the standard and in the some digital generator regulation systems, the sequence of gates selecting signals follows the pattern in Fig. 7 (HV gate; LV gate). Gates thus positioned select the signal from limiters of stator and rotor currents as the superior si a structure is gnal. The signal of the power angle limiter entering the first gate selects the higher signal. Such inadmissible and in states of low voltage reduces the exciting voltage of the synchronous generator by current limiters, signals of which feed the second gate, selecting the lower signal value. In such a structure of primary voltage regulation circuit, the last element of the circuit is superior in the regulation system; which does not conform to the precursors’ assumptions for analogue systems. 5. SUMMARY An extensive analysis of generator regulator operations indicates the hazards relating to seemingly known structures of synchronous generators regulation systems. In conditions of dipping voltage, a malfunctioning generator regulator can cause a voltage collapse or augmented consequences. Elimination of risks described in the article will significantly improve electric power system operational safety. LITERATURE 1. Zajczyk R., Modele matematyczne systemu elektroenergetycznego do badania elektromechanicznych stanów nieustalonych i procesów regulacyjnych, Wydawnictwo Politechniki Gdańskiej, Gdańsk 2003. 2. Madajewski K., Sobczak B., Trębski R., Praca ograniczników w układach regulacji generatorów synchronicznych w warunkach niskich napięć w systemie elektroenergetycznym, materiały konferencyjne APE ’07, Gdańsk 2007. 3. Kundur P., Power system stability and control, McGraw-Hill 1994. 4. IEEE Std 421.5 – 2005 IEEE Recommended Practice for Excitation System Models for Power System Stability Studies. 5. Analiza stanu obecnego i opracowanie zmian w układach regulacji napięcia i mocy biernej w elektrowniach, stacjach sieci przesyłowej i w sieciach rozdzielczych w celu zmniejszenia ryzyka powstania awarii napięciowych w systemie elektroenergetycznym. Etap II, praca badawczo-rozwojowa wykonana dla PSE-Operator SA. 6. IRiESP – Warunki korzystania, prowadzenia ruchu, eksploatacji i planowania rozwoju sieci v. 1.2. Tekst jednolity obowiązujący od dnia: 5 listopada 2007 roku.
