This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON POWER SYSTEMS 1 Dynamic Modeling of Power Systems Experiencing Faults in Transmission/Distribution Networks Sajeeb Saha, Member, IEEE, and Mohammad Aldeen, Senior Member, IEEE Abstract—In this paper we address some shortcomings in ex- isting nonlinear dynamic models of power system experiencing symmetrical and unsymmetrical faults in their transmission/dis- tribution networks. The shortcomings relate to: 1) approximations relating to stator dynamics, internal voltage of the positive se- quence network and the dynamics of the negative and zero sequence networks, and 2) existing models are time -variant, which may not be suitable for system studies such as stability and fault detection studies that require time invariant model. The approximations outlined in 1) adversely affect the mod- eling accuracy, especially that of the system response during the period immediately after the occurrence of faults. We present in this paper a full fault-dependent time-invariant dynamical model of power systems experiencing symmetrical and unsym- metrical faults in their transmission/distribution networks and verify it through simulation studies mimicking real life scenarios. IEEE 30 bus power system is considered as the study case. The simulation results are compared to Matlab’s “SimPower” and PSCAD/EMTDC software packages. Index Terms—Dynamic modeling, stator dynamics, symmetrical components, synchronous generator, unsymmetrical faults. NOMENCLATURE Quantities (voltage , current , flux ) in rotating frame. Field winding quantities. Damper winding quantities. “ ” sequence quantities. (positive), 2 (negative), 0 (zero). Per unit resistance of stator winding. Per unit resistance of field winding. Per unit resistance of damper windings. Quantities in rotating frame. Quantities in (real and imaginary) co-ordinate. Load angle and speed deviation, respectively. Mechanical power input to the synchronous machine. Mechanical torque. Electric torque. Manuscript received January 06, 2014; revised May 07, 2014, July 10, 2014, and September 14, 2014; accepted October 26, 2014. This work was supported by the Australian Research Council through discovery project DP140102180. Paper no. TPWRS-00022-2014. The authors are with the Future Grid Research Laboratory, Melbourne School of Engineering, The University of Melbourne, VIC 3010, Australia (e-mail: sajeebs@unimelb.edu.au; aldeen@unimelb.edu.au). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TPWRS.2014.2365809 Load bus quantities. Generator bus quantities. , , , Single line to ground, double line to ground, line to line, and three phase fault, respectively. I. INTRODUCTION I T is common that when fault-dependent models of power systems are derived, the stator transients of the synchronous machine are ignored for simplicity [1]–[5]. As a result, the dy- namics of the synchronous machine is not fully captured, es- pecially during the transient periods. In order to overcome this problem, a decaying DC “offset” current is introduced at the in- stant of fault in [6], [7]. It is obvious that DC offset approaches require the time constant to be computed from Thevenin equiv- alent circuit of the faulted power system, which is a difficult if not impossible task to achieve for even modest size systems. This fact is confirmed by the authors’ [6] own statement that “the computation of the DC offset is not straightforward”. Electromagnetic transient (EMT) type synchronous machine models which include complete dynamics of the synchronous machine usually represent stator and rotor flux- voltage dy- namics by a set of differential equations in dq0 co-ordinate. This representation is commonly known as dqo EMT model [8]. There are two other EMT type synchronous machine models available in the literature. They are commonly known as phase domain (PD) model [9] and voltage behind reactance (VBR) model [10]. PD and VBR models represent synchronous machine stator dynamics in abc-coordinate and rotor dynamics in dq co-ordinate. It is shown in [11] and [12] that all three types of EMT type models are equivalent. Although the dq0 model offers best computational speed, it requires a smaller time step to maintain the precision and numerical accuracy of PD and VBR models, especially during transient operating conditions. In terms of time variance, PD and VBR models (being derived in the abc-coordinate) are time-variant under any operating condition due to time-variant nature of the self and mutual inductance [1] of the stator circuit. The dq0 model, on the other hand, becomes time variant under unbalanced operating conditions as stator and rotor quantities (flux, voltage and current) exhibit second harmonics components during such condition, as described in detail in Section II. In order to utilize the properties of each of the three models above, the dq0 model is combined with each of the other two models to produce PD-dqo [13] and VBR-dqo [14] models with improved computational efficiency. However, the two combined models still are time variant as outlined above. 0885-8950 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.