Tumilty, R. and Bright, C.G. and Burt, G.M. and Anaya-Lara, Olimpo and McDonald, J.R. (2007) Applying series braking resistors to improve the stability of low inertia synchronous generators. In: CIRED 2007, 2007-05 (original) (raw)
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Today, installation of small generators has been increased because of their considerable benefits in distribution systems in distributed generation. One of the most important problems for transient stability is the effects of the faults of system. Small scale generators have low constant inertia and protection relays have slow performance in distribution systems. Therefore transient instability is a probable phenomenon for the systems with these generators. In this paper, dynamic response of generator has been studied in different fault conditions and then by introducing the concept of " critical fault clearing time ", the sensitivity of this time to the fault type and also fault location parameters have been studied. Then a new protection scheme has been proposed to prevent of transient instability for small scale generator. This protection scheme uses a new evolutionary algorithm based on the active power of generator and critical fault clearing time. The proposed relay ...
Improving Transient Stability Using Combined Generator Tripping and Braking Resistor Approach
In this paper, improving in transient stability is sought through adevelopment of combined approach. Since, in power systems, the maximum use of existing capacities along with the increased powers transferred through the transition lines make transient stability studies even more important. When the fault occurs, the kinetic energy of system is increased and if the system kinetic energy exceeds a certain amount, system instability will meet. Generator tripping is also one of the most effective methods of improving stability in case of severe faults. In this method, we trip a number of units of a certain unit to stabilize the system. In fact, siftingparticular set ofgenerators, it will decrease the kinetic energy of the system so that stability can be achieved. In generator tripping, for such reasons, the system has to maintain stability where lest number of units can be possibly blown out. Due to its thermal limitations, fixed place of resistor bank and possibility of back swing, however the braking resistor is less efficient than generator tripping. Inour proposed combined method, system stability against severe turbulence is tackledwith minimum tripping of generator units.At this proposal, the intensity of faultwill be valuably lessen by applying braking resistor, and then, for the purpose of improving transient stability, the kinetic energy is reduced by removingcertain unit at the right time.The approach has been tested on 9-bus with 3-generator system to demonstrate promising effects.
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This paper shows the influence of grid frequency oscillations on synchronous machines coupled to masses with large moments of inertia and solves the maximum permissible value of a moment of inertia on the shaft of a synchronous machine in respect to the oscillation of grid frequency. Grid frequency variation causes a load angle to swing on the synchronous machines connected to the grid. This effect is particularly significant in microgrids. This article does not consider the effects of other components of the system, such as the effects of frequency, voltage, and power regulators.
Transient Stability of Asynchronous Generator on Distribution Network
– Dispersed generation (DG) brings together wide range of technologies for electricity production. Most frequently used electric machines for electricity production at each technology that belongs to DG group are: synchronous generators, asynchronous generators (AG) and power converters. This paper deals with transient stability of AG. Typical model of distribution network (DN) is developed with AG connected to it. The modelling and simulation are performd with NEPLAN and MATLAB/SIMULINK/Simpowersystems toolbox software packages. AG with squirrel cage is used. Several short circuits are simulated in order to investigate dynamic behaviour of AG. Following parameters are analyzed: rotor speed, active and reactive power, and currents of AG. Critical clearing time is calculated for keeping stable operation of AG. Several useful and practical conclusions are obtained.
Enhancement of a Power System Transient Stability Using Static Synchronous Series Compensator SSSC
DOAJ (DOAJ: Directory of Open Access Journals), 2013
Transient stability investigations consist of studying the rotor oscillations of generators (electro-mechanic oscillations, 0.1-2 Hz) after the occurrence of a fault of large amplitude, e.g. short circuit. The goal is t o indicate if the generators are capable to stay synchronous after a fault has occurred. The fault duration is one of the most important factors t o be determined. In fact, the shorter the fault, the more the maintaining of synchronisation can be guaranteed. Now in case of a fault, a fault current limiter has an extremely fast current transition in comparison t o electro-mechanic time constants. This implies a quasi-instantaneous elimination of the fault through a limitation of the current and consequently a better ability to maintain the synchronisation of the system. We recall that in a classic system, the elimination of a fault, by opening a circuit breaker, is carried out in two or three cycles in the best case. We have here studied a simple, radial electric network configuration with a machine and an infinite network. The study covers simulations of a fault that can occur in a network and the consequences of the recovery time of t h e fault current limiter.
Proceedings of The 3rd World Sustainability Forum, 2013
This paper is a sequel to a study by the authors of electric power systems comprising the generator circuit-breakers (GCBs) at power plant generator terminals. A sustainable assessment of the current interruption requirements of a GCB addresses the main stresses on the generator circuit breaker, revealing that the GCB current interruption requirements are significantly higher than for the distribution network circuit breakers. Hence, generator circuit-breakers are subject to unique demanding conditions caused by specific stresses, namely: high asymmetrical fault currents resulting from high d.c. components of the fault current; greater electrical, thermal and mechanical stresses when interrupting longer arcing time faults; and important dielectric stress after the electric arc extinction caused by the transient recovery voltage (TRV). This paper extends other studies of the authors on the energetic and exergetic transformation chain at the interruption current OPEN ACCESS 2 transient process in an electric power system that comprises the generator circuit-breaker, as well as the transient recovery voltage which appears after the interruption of a short-circuit fed by the synchronous generator or by the main step-up transformer. For achieving the TRV equivalent configuration the authors applied the method of operational symmetrical components (o.s.c.), and utilized the operational impedances of the synchronous generator and of the main transformer, depending on the fault location. Modeling the transient recovery voltage of circuits emphasizes aspects with direct implications on commutation equipment. Thus, the o.s.c. method can be applied at the poles of any breaker, for any eliminated fault type, if the network configuration and elements are known. The TRV, which appears after the interruption of a short-circuit fed by the generator, may be considered like an oscillation, where the oscillation factor and the rising rate (RR) of the TRV are established by the electrical machine parameters: resistance, inductance and capacitance. Consequently, modeling of concentrated equivalent parameters of the synchronous generator at perturbations caused by current interruption transient processes is achieved in this study through an approach based on sustainability concepts. These findings allow for simulations of the transient recovery voltage and comparisons with experimental results.
2012 IEEE Power and Energy Society General Meeting, 2012
This paper focuses on analyzing the impact of the excitation control mode of synchronous generators when operating connected to power distribution systems, through the study of a system derived from a real distribution feeder from a Brazilian utility. The number of connections of distributed generation has increased over the last years, bringing new technical issues when planning and operating a distribution system. In Brazil, the major part of the distributed resources applications is composed by synchronous generators directly connected to the distribution system. The objective of this paper is to contribute to the stability analysis of these systems, as there is still no consensus among the electric energy companies about the best control mode of synchronous generators in the context of distributed generation.
International Journal of Renewable Energy Research, 2014
A comparison among series connected auxiliary devices, such as Superconducting Fault Current Limiter (SFCL), Dynamic Voltage Restorer (DVR), Thyristor Switched Series Capacitor (TCSC), and Series Dynamic Braking Resistor (SDBR), is performed in terms of fault ride through capability improvement, harmonics suppression, controller complexity, and cost of a fixed speed wind generator system. The tested system consists of one synchronous generator and one squirrel cage induction machine based wind generator, which feed an infinite bus through a double circuit transmission line. Simulation results show that all the devices perform well during symmetrical faults, however, in spite of its controller complexity, the DVR has the best performance among all devices in terms of voltage and speed control of wind generators. The SFCL is the costliest among all devices, however, it is the most efficient in reducing the fluctuations of active power and stator current of the wind generators. The SDBR is the cheapest, and shows a better enhancement in damping active power and limiting fault current as compared to the DVR and TCSC. Despite the ability of TCSC to compensate the reactive power for power quality improvement, it is less desirable to achieve a better performance under transient conditions.
2013
This paper is a sequel study by the authors on the electric connection circuits comprising the generator circuit-breakers (GCBs) at generator terminals, which was undertaken since GCBs offer many advantages related to the sustainability of an electric power station. This paper extends other studies of the authors which have examined the exergetic transformation chain at the interruption current transient process in an electric power system that comprises the generator circuit-breaker, as well as the transient recovery voltage (TRV) which appears after the interruption of a short-circuit fed by the synchronous generator. For achieving the TRV equivalent configuration the authors applied the method of operational symmetrical components, and utilized the operational impedances of synchronous generator and/or of main transformer, depending on the fault location. Since the TRV which appears after the interruption of a short-circuit fed by the generator may be considered like an oscillati...