Abstract —This paper reports preliminary results of an attempt to ident ify cond ition s under which large induction motor s can positively impact the stability of a power system. This work also investigates the effect of using a dynamic model to represent the beha vior of large inducti on motors in power system transien t stabil ity studie s. The effect of induc tion motor on the transie nt stabil ity of power system is studie d using both a dynamic load model and a constant impedance load model and the results are compare d. The work ident ifies some of those conditio ns unde r which the presence of a large induction motor can have certain positive effect on the transient sta bi li ty of the system. It investigates the effect of some factors such as the proximity of the motor to the fault, and the type of induction motor load. The work als o highli ght s the impor tan ce of usi ng a dyn amic mode l to represent induction motor behavior in transient stability studies. Inde x Terms —indu ction motor, power system faults, power system stability, transient stability, dynamic model. I. INTRODUCTION t is generally known [1]–[6] that the presence of induction motors adverse ly aff ects the transient sta bil ity of power systems. Much research has been conducted on the effect offaults, int erru pti ons and vol tage sag s on ind uct ion mot or operation. Referen ce [1] inves tigate s moto r behavio r under source transfer and ride-through in the event of interruptions. It states that motor contr ol s tr ip the motor in 1 to 2 cycles wherea s motors can wit hst and voltag e drop s for 10 to 30 cycles because of its inerti a. Reference [2] shows the effects ofthe location of the fault, fault clearing time, type of fault, the system conf igur at ion and the inert ia of the motor on the behavior of an induct ion motor. Low inerti a loads rapidly decelerate and the supply is lost while high inertia loads can reaccelerate after fault is cleared. Reference [3] explores the prefault and postfault behavior of induc tion motors. Reference [4] investigates the effects of induction motor load variations on the system stability, and shows how the addition of load to a stable system reduces the syst em stability . Refere nces [5, 6] state the si gnif icance of using the corre ct load model representati on. Reference [5] st at es that the con st ant imped ance representat ion is not preferred because of its higher initial fault recovery voltage. Reference [6] explores the need for dyn ami c loa d mod eli ng and the drawbacks of usi ng the consta nt imped ance load model . Const ant imped ance model is an inadequate representation in cases involving large voltage This work was supported in part by Otter Tail Power Company, Fergus Falls, MN, and by the Electrical Utility Management Program, New Mexico State University. The author s are with the Kli psc h Sch ool of Ele ctri cal and Comput er Engineering, New Mexico State University, Las Cruces, NM, 88003 (e-mail: [email protected]). and frequency deviations and islanding situations. Thus it is evident that the effect of the induction motor beha vio r on the trans ient sta bil ity of a power syste m is an important aspect of stability studies. The work reported in this paper uses ride through via motor inertia of induction motors to investigate different situations in which the presence of an induct ion motor duri ng the fault hel ps the stabil ity of the system. Further, it is identified that the modeling of the load pl ays a cri ti cal rol e in the stabili ty st udies. This pap er implements the dynamic and constant impedance load models of an induction motor and their results are compared. Usually dynamic load model of induction motors is used for stability studies. For frequency dependent load, the slip is not consta nt so a dyn ami c mod el inc luding the mec hanica l dynamics, stator flux dynamics, rotor flux dynamics should be use d [6]. This pape r is divide d int o six sections. Sec tion II describes the transient behavior of an induc tion motor. Section III deal s wi th the mod elin g of the loa d. Sec tion IV demon- strates the result s for different fault locations, fault clearing times and ind uct ion motor load s. Sect ion V dis cusses the conclusions and further work to be done and section VI lists the references. Section VII is the appendix which tabulates the induction motor ratings, transmission line parameters and the system parameters. II. TRANSIENT BEHAVIOR OF AN INDUCTION MOTOR Induct ion motors are ubi qui tous in power systems and signi fican tly affect syst em stabil ity. Severe faults cause the voltage to drop to 50% or lower at the terminal s of the machine. Though the fault clearing process is very fast, and causes only momentary interruption in supply, it has drastic effects on the power system components. Seventy percent ofpower system loads comprise of induction motors [3]. So, it is imperative to understand how induction motors behave under transient fault conditions. During a fault, motor controls trip the motor in 2 to 3 cycles while the motors usually withstand the disturbance up to 20-30 cycles due to inertia. Since large induction motors have high inertia, it is sometimes beneficial to keep them online during faults. This is called ride through via motor inertia [2]. Stability of the system is investigated in this report using ride through via motor inertia of induction motors. Usu ally , the motor ma y decelerate for some time dur ing the fau lt clea ring time and then reac cel erat e to its normal speed. The postfault behavior of an induction motor is influenced by the factors below. 1. Dip in the system voltage and recovery The location of the fault and the type of fault determine the voltage waveform. The presence of the induction motor in Sirisha Tanneeru, Joydeep Mitra, Yashwant J. Patil, Satish J. Ranade Effect of Large Induction Motors on the Transient Stability of Power Systems I 223 978-1-4244-1726-1/07/$25.00 c 2007 IEEE
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