1302IEEE Transactions on Power Systems. Vol. 10. No. 3, August 1995 Standard Load Models for Power Flow and Dynamic Performance Simulation IEEE Task Force on Load Representation for Dynamic Performance* System Dynamic Performance Subcommittee Power System Engineering Committee Abstract - We recommend standard load models for power flow and dynamic simulation programs. The goal of this paper is to promote better load modeling and advanced load modeling, and to facilitate data exchange among users of various production-grade simulation programs. Flexibility of modeling is an important consideration. For transient stability, longer-term dynamics, and small-disturbance stability programs, we recommend the structure of multiple load types connected to a load bus. Load types are static including discharge lighting, induction motors, synchronous motors, and transformer saturation. For each load type, multiple models may be connected to the bus. For longer-term dynamics programs, a model for LTC transformers is also recommended. utilities, manufacturers, and consultants. The recommended models are implemented in large-scale, production-grade computer simulation programs used by utilities. There are over ten large-scale production-grade dynamic programs in use by utilities, and many more power flow programs. Individual utilities often use more than one program. Compatible models and data sets are essential. Keywords - load modeling, power flow program, transient stability, voltage stability, long term dynamics, induction motors 1.O A recent paper by the IEEE Task Force on Load Representation for Dynamic Performance [61 highlights the importance of load modeling in power system simulation studies. The paper describes different approaches and modeling practices used by electric utilities. In particular, the paper describes several alternative model structures. No recommendations, however, are made regarding standard models for industry use. Currently, there are no standard models for system loads. Emerging utility challenges related to voltage stability (also termed load stability) have placed increased emphasis on better load models, and on standard load models. Partly in response to voltage stability simulation needs, several transient stability and longer-term dynamics programs are now integrated. Introduction Nowadays, procedures are in place for exchange of power flow and dynamic simulation data among individual utilities, power pools, and reliability councils. These data exchange activities are greatly facilitated by IEEE committee work to standardize (or at least clearly define) models for generation and SVC equipment [1-51. The IEEE committee recommended models are developed by specialists from *W. W.Price, chairman. Contributors to paper were C, W.Taylor (writer/editor), W.W.Price, G. J. Rogers, K. Srinivasan, C. Concordia, M. K. Pal, K. C. Bess, P. Kundur, B. L. Agrawal, J. F. Luini, E. Vaahedi, and B. K. Johnson. 9L S M . 579-3 PWRS A paper recommended and approved . . b j t h e IEEE Power s y s i e i Engineering Committee of t h e IEEE Power Engineering Society for presentation a t t h e IEEE/PES 1991 Summer Meeting, San Francisco, CA, July 24 2 8 , 1994. Manuscript submitted December 20, 1993; made a v a i l a b l e f o r p r i n t i n g May 3, 1994. As power systems are designed and operated with less stability margin, the importance of good models and good data increases. Industry standard models facilitate the validation and certification of simulation software. Purpose of paper. This paper is a follow-up to the previous Task Force paper [SI, and recommends standard load models for power flow, transient stability, and longer-term dynamic simulation. The goal of this paper is two-fold: . 6 - to promote better load modeling, and advanced load modeling, - in widely used simulation programs; and to facilitate data exchange among users of various production-grade simulation programs. 0885-8950/95/$04.00 0 1994 IEEE This high voltage sensitivity may be due to distribution transformers operating in saturation. consider the following static model employed in several widely-used transient stability programs: P = v 2+ P . the models may be linearized by the smalldisturbance stability program.0 Models for Dynamic Programs Power Flow Program Models We recommend models that can be used in transient stability. 2. In some cases. represent the aggregation of hundreds or thousands of individual component devices such as motors. Since. (These considerations also apply to dynamic simulation. Power flow programs should. the loads are voltage sensitive like transient stability program load models. For time frames of several minutes following a disturbance.) from companion power flow programs. LTc transformers. cables. and even relatively small synchronous or induction generators. desirable characteristics include correspondence to physical loads and flexibility. the model is not physically based. voltage sensitive loads.. be able to read load model data from dynamic program data files. or if the load is controlled to be constant power.s dynamic trajectory. For the area that is prone to voltage instability. Although constant (voltage insensitive) loads are usually assumed for base cases. For small-disturbance stability. Dynamic programs receive initial bus load ( P o+ j Q o ) and voltage magnitude (V. 3 . For the first. and small-disturbance stability programs. Except for detailed voltage stability analysis. 30-60 seconds following a disturbance (lhe or generator outage). representation of additional busses is required. constant power) model multiplied by a linearized frequency dependence term. AQ/AV is 4-7 per unitlper unit) C71. 1 Multiple loads on a bus concept Due to voltage stability challenges. With present-day and near future computer capabilities in mind. constant current. although off-nominal frequency effects could be represented. Therefore we recommend the load models be compatible with static models and data sets of companion dynamic simulation programs. Expanded representation of subtransmission networks may be Most dynamic programs allow multiple generators. In voltage stability studies. necessary.Af) P O VO This is the 'ZIP' (constant impedance. system frequency is assumed to be at rated value. As an example of a load model without physical correspondence.271. longer-term stability. multiple motor loads. and electrical appliances. however. reactive power compensation. For example. This.load tap changer transformers or distribution voltage regulators). Recommended models for dynamic simulation programs are presented below. the aggregated load model approximates the effects of subtransmission and distribution system lines. consideration should be given to including equivalents for subtransmissiod distribution feeder impedances and reactive power compensation [9. there is more reason than ever to increase model flexibility and fidelity. optionally. A similar equation is used for reactive power. the resistive portion of physical loads is not frequency dependent.e.0 The above model is also limited in its flexibility.) 3. In recommending load models. If the load is modeled at the high-side bus of bulk power delivery transformers. [PI(&) " 1 ficomme&tions. may require additional data preparation work: Characteristics of good load models. the bulk power delivery transformer reactance (typically about 10%) and the distribution transformer reactance (typically 2-3%) is neglected. for example. say. Generally. comprising several megawatts to tens of megawatts.g. Representation of the additional impedance is especially important if much of the load is motors. the aggregated load is usually the load as seen from bulk power delivery points. and a single static load model - I . what are loads' as represented in largescale computer simulations. It is difficult to model such a high (and nonlinear) voltage dependency over the voltage range of interest with the above model.. along with voltagdoad controls are represented (i. field tests often show the reactive portion of the load to be very voltage sensitive (e. Most power flow programs can model voltage sensitive loads as combinations of constant power and constant impedance loads.. lighting. power flows represent snapshots in time along the power system. loads are often considered constant power because of the action of LTC transformers and other load restoring equipment.1303 This paper is being coordinated with the work of the IEEE Power Systems Analytical Data Task Force. there is strong current interest in improved load models for power flow simulation.+ P 3 (l+L. In addition to load components. Better load models are required for relatively new problems such as voltage stability. voltage sensitive loads need to be modeled for snapshots in time shortly following a disturbance. distribution regulators. 3. we recommend the following model consisting of ZIP terms plus two voltage/f?equency dependent terms: P v = K (-) PhCPO pz v o 2+ K . As discussed in the introduction. Po and Qo are the initial model various types of loads. (Usually. Va2). The nominal load power is linearly reduced to zero starting at a specified threshold voltage (Val. The load powers are functions of bus voltage and frequency. the per unit voltage variation is much larger than the per unit frequency variation. loads are typically modeled as purely static (algebraic) functions of voltage and frequency. the powers meaning the load power at initial voltage and frequency dependent terms could be used to reprefrequency [231. P ' vo Kpz = 1. Po and Qo could be func.7 per unit. Data to be exchanged for each static model are listed in Table 1. only one static model is required per bus. Representation of loads by exponential models with exponent values less than 1. This feature could also be used to model some loads with electronic power supplies. A further feature of the recommended static model applies to the voltage/frequency dependent (fourth and fifth) terms in equations 1 and 3. with frequency sensitivity depending on the mechanical load characteristic. (It's better to represent the frequency dependence of the load directly rather than grossly approximating the effect as a generator damping term. -V +K.1304 to be connected to a bus. In longer. they may be termed the nominal load resentation of two types of motors. this models the extinction and re-ignition of discharge lighting. In order to standardize on a single static model.3-0.ware such as EPRI's LOADSYN program [13. Q=K QhcQo (-) qz 3 . static models for dynamic load components should be used cautiously. except for program logic that may convert static load to impedances at voltages below 0.) The active part of motor load is generally represented as voltage insensitive. tions of time.(Kpi+K. the freactive and reactive load powers from the power flow quency dependent terms could be used for static repbase case. both polynomial ('ZIP) and exponential models are used. . induction motor. P and Q are the consumed load pow. 2 Static model for dynamic simulation v 2+ K . For example. is the fraction of the bus load represented by the static model. Reference 6 describes several good candidate models. Recommendations. Tabfe 2 provilfzes data description. Each individual load type (static. see 93.0 (or by equivalent polynomial models) in a dynamic simulation is questionable [Ell. Nominal load power is ramped up for voltage recovery. Small synchronous or induction generators embedded in the load area may also be connected to the bus. As discussed below. Alternatively. In softers as a function of voltage and frequency. The model provides the flexibility to In the following equations. and transformer saturation) may have multiple representation. term dynamic simulations. +Kpl +K*) where P. the power is zero for voltage below a second threshold voltage (vbl. Discussion. Referring to $3..) V o where Qhc is the fraction of the bus load represented by the static model.10. These models are continuous over the entire voltage range. the model should be sufficiently flexible t o allow several forms of representation.the flexibility facilitates accurate aggregation of the estimated load composition. vb2). a bus load may consist of one or more static models.sent a motor and also fluorescent lighting. For instance. Note that K and K are computed rather than entered. synchronous motor. We recommend generalization of this capability to allow multiple loads of various types on a bus. Normally. -V +Kqc qVo (3) In large-scale transient stability simulations. and a synchronous motor. See Figure 1.321. As described in the Task Force paper [61. Each load type may have load shedding or disconnection logic. one or more induction motors. 141.99 power factor lagging. without rotor flux dynamics. say. The re-ignition delay is ignored. Motors that have difficulty reaccelerating following faults affect voltage recovery of important busses. 1. The sensitivity studies involve simulation * Although large motors dominate energy use. but not unity power factor at other voltages and frequencies. 3.7 per unit. Inertia effects are important in studies involving fiequency excursions. Undrill and Laskowski presented very strong arguments for representing major blocks of induction motor load by dynamic models including both inertial and rotor flux dynamics [U.1305 P Q 3. Between the two voltages. have shown that motors purchased individually (not part of an appliance) are typically oversized [lo]. Taylor showed that motor dynamics.161. peak load condtions could be dominated by smaller three-phase and single-phase air conditioning motors. and other sources [15. This determines the motor load factor defined as M W loadinghated MVA.7 per unit). Upon voltage recovery. Lack of dynamic motor models are suspected to be a major source of discrepancies between field measurements and large-scale simulation results.4 Dynamic induction motor models Fig. Use of typical motor data sets is better than using static models 1111. the nominal power is ramped to zero 115. mercury vapor. Although the extinction and re-ignition may have a hysteresis characteristic. dynamic motor models improve numerical performance of simulation programs. with reactive power compensation applied to match the initial conditions. and is consistent with the physical fact that near nominal load cannot be consumed at abnormally low voltage. most programs have provisions to convert all static load to constant impedance at very low voltage (0. Referring to Equations 3 and 4. Surveys in the US. . See reference 20. Below a certain voltage such as 0. all lamps are extinguished with power set to zero. For small motors.With today’s computer capabilities and numerical techniques. the time step must be small enough. Characteristic of discharge lighting or other discontinuous load as a function of voltage. may be sufficient 1211. is important in undervoltage load shedding program design [121. mostly integral horsepower threephase induction motors I101 . See Appendix A for fbrther discussion. On a global rather than individual bus basis. A dynamic program could automatically correct for unity power factor initial conditions by assuming the load is.161. This helps solution iterations to converge. Referring to the static model ($3. while uneconomical. Particularly for explicit integration methods. An exponential model is used above a certain voltage such as 0. but extinguish during low voltage. sodium vapor) are essentially static. An important input parameter is the machine load- Discharge lighting Discharge lighting may represent up to 20% of commercial load [61. Compared to a static constant power load. ing in per unit of motor MVArating. Table 1 provides data extracted from the LOADSYN reports. In the absence of specific data. Over a decade ago.2) and Figure 1. typical data sets for aggregated motors are available from the EPRI LOADSYN project 113. Because of significantly different characteristics. there is little reason to represent large motor equivalents with static models. This practice. Rotor flux transients affect damping of oscillations 1111. electricity consumption goes to power motors. Various types of discharge lighting (fluorescent.3 About 57% of the US. however. discharge lighting can be represented by the voltage/ frequency dependent terms using the load ramp down parameters. including rotor flux dynamics. there is obviously a problem if the load is unity power factor at initial voltage and frequency.3-0.8 per unit. improves system dynamic performance. a single-valued power voltage relation is normally used for modeling numerous individual lamps in transient stability programs. representation of inertia dynamics only. 0. An alternative to routine representation of motors is sensitivity studies for each new situation to be simulated. they will re-ignite after a short time delay. This can be avoided by separating the load and reactive power compensation. it may be desirable to model equivalents for both small and large motors 113-161. Figures 2 . and double-cage motors. In order to facilitate flexibility and compatibility of programs.of motor load for low voltage. Parameters are defined in Table 2 except for D. The most obvious need is for pumped storage plants. There is current research in modeling single-phase induction motors and variable speed drives in dynamic programs. high current) is involved 130. Differences between motor reactive power and bus initial reactive power (portions of Q. 4 . however. lasting a specified time. Table 1 lists mandatory and optional data exchange parameters. 2. Deep-bar induction motor steady-state equivalent circuit. and uses the same equivalent circuit data. Synchronous machine models are available in all programs. the same induction machine models and data sets should be used for induction generators. These models are outside the scope of this paper. automatically tracks changes in system frequency. TI. Table 3 provides typical data for use in large-scale simulations [13. Based on references 22 and 30-31. Single-cage induction motor steady-state equivalent circuit. we recommend the flexibility to represent both simpler models and more detailed models. especially if motor starting or stalling (i.4 show equivalent circuits for single-cage. The only requirement is the mechanical load torque model. The simpler model is an option to represent slip dynamics only. Ptfip. 3.141. Models representing three-phase motors with a single rotor circuit in each axis are generally appropriate for aggregated motors in large-scale simulations (third order model with slip and d. More detailed models may be required for representation of large industrial motors including power plant auxiliaries. For data exchange. The basic recommended model. and for representation of saturation of leakage inductances and magnetizing inductance. More detailed models are recommended for representation of double cage and deep-bar rotor types of motors.e. Double cage induction motor steady-state equivalent circuit. Recommendations. Fig. the recommended mechanical torque model is: Fig. Figure 5 shows a general purpose saturation model that is used with Figures 2-4 to represent magnetizing inductance saturation. q axis internal voltage or flux as state variables). Induction generators are often embedded in load areas. and for use in simulations where the frequency changes significantly. with rotor dynamics included. VI. Table 2 provides data description. this automatic tracking is lost. The motor's fraction of initial bus active load is an input parameter.( A + B + D ) (7) Motor starter ac contactors or undervoltage protec- Synchronous motors sometimes need to be represented.) unused by other load types) are resolved by adding shunt reactive power compensation.301. Except for mechanical loaaprime mover data. Fig.5 Dynamic synchronous motor models C = 1. . tion may trip motors at low voltage. In the simple model with only inertial (slip) dynamics.. the motor terminal bus frequency should be used to compute slip to modify the steadystate equivalent circuit. deep-bar. Reference 11 and 22 provide equations for modeling induction motors. The corresponding initial reactive power load is computed during model initialization. 3.313. We recommend provision to trip a percentage. and Dr which are saturation coefficients that are computed internally from saturation current 122.1306 with and without dynamic motor models. Underfrequency or undervoltage load shedding models are required for some dynamic and quasidynamic simulations. Recommendations. 2 = %lo% Transformer saturation Distribution transformers. The simplest assumption is to . load restoration by LTC transformers and distribution voltage regulators may need to be modeled. Td. and 2-4 volts bandwidth based on 120 volts. The recommended load torque model is the same as the induction motor load torque model given by Equations 6 and 7. Fig. intentional time delay.The transformer exciting current as a function of voltage is represented by a piecewise linear characteristic. Additional buses may be required compared to traditional representation.8 Q. Table 1 lists data exchange parameters and Table 2 provides data description. i t may be desirable to have compatible transformer saturation models in both stability and power flow programs. Figure 6 shows a typical situation involving a bulk power delivery LTC transformer. This model is also used to represent induction motor magnetizing inductance saturation (83. Tdl. Saturation function for induction motors and transformers. Typical North American data is +lo% voltage tap limits.. . Figure 7 shows the recommended model. 5/8% voltage tap steps (+16 steps). Figure 5 shows the recommended model. To more correctly represent reactive power demand as seen from the bulk power network. and thereby voltage sensitive load. involving both pure time delays and deadbands. the fraction of initial active and reactive bus load are input parameters. If desired. 3. Modeling for longer-term voltage stability analysis usually requires expanded representation of subtransmission. High voltage bus Distribution equivalent. 6. between tap steps is typically 5-10 seconds. however.1307 Recommendations. which may be considered part of the load.7 Models for load shedding Load tap changing transformers This is actually a network rather than a load model. Accurate evaluation of potentially damaging temporary overvoltages. Tap changing regulates load-side voltage. Loads with voltage controlled by tap changers require LTC transformer representation in the power flow case. between tap steps can be modeled. Table 1lists data exchange parameters and Table 2 provides data description. This has implications for small-disturbance analysis. Reference 23 provides additional information. XE 10% limits I Ldad Recommendations. Provision is made for line drop compensation. 3. Note that the model is discontinuous. LTC transformer and distribution equivalent for voltage stability simulation. reactive power may change as the third to seventh power of voltage. Transformer saturation will limit fundamental frequency temporary overvoltages. The mechanism delay. including European practices (a limitation of the recommended model is that inverse-time relay control of tap changing is not included). Similar to synchronous generators.. For small changes. and equivalents for distribution 1231. T . of 30-120 seconds. require evaluation by electromagnetic transients programs. - *= 2 VI--G - Slope of region 1 Slope of region 2 Slope of region 1 Slope ofregion 3 b 1 Excitation current Fig. normally operate with significant magnetizing induction saturation. 3.4).6 For longer-term dynamics. North American practice is to start tap changing after an initial time delay. 5. Many field tests show large voltage sensitivity of reactive power load following voltage changes. Tapping then continues until the voltage is within a bandwidth. 1308 h h h VI A i i i A 8 Qa. I .$3 '8 0 II 6 e 3 rl at O d d I II 9 -A--- ' r l I II . 251. highly insulated homes. Industry activity to define standard relay models for dynamic programs would be valuable. second integrating) relay may be used. motor load.These models approximate both active and reactive power dynamics of aggregated loads. .GI. .Gq I Rc. The low voltage period may start after tap changer controls reach boost limits. rather than tripping load directly [121. 3. constant energy loads cause loss of load diversity. we do not recommend specific models and data exchange parameters. 3. and because data exchange between different programs is unlikely to be needed in the near future. In most cases. Automatic load restoration following recovery of frequency or voltage is also applied by some utilities. To limit the scope and length of this report. Because of limited experience with these models. industrial heating.23. Sometimes it may be desirable to trip specific components (static load. Depending on the time constant.9 Dynamic constant energy load models and generic dynamic load models For simulation of wintertime voltage stability situations.loads are assumed to be unity power factor and only cant time delay [121. In some installations.281. load restoration dynamics by induction motors. Other loads such as water heating. Bus nameds) and kV identification not included. An inverse time delay (volt.Vi. Therefore thermostatic control usually need not be modeled.V2. In highly detailed studies. For example. older homes. several constant energy Circuit breaker operating times are usually 5-15 cycles.x c-. . This may be important in preventing overfrequency as a result of overshedding [291.273. and other constant energy loads (water heating. facility to ramp or otherwise change the load as a function of time is . and cooking are either automatically or manually controlled to deliver constant energy.Ttn a. underfrequency or undervoltage relays trip lines with tapped load. E. cooking. Models are provided in several existing programs. time constant) models have been proposed to model Several steps of underfrequency load shedding may aggregated constant energy loads 117. but have operating times of 6-9 cycles. First order (single time delay. Recently.). Individual loads stay on longer. For low voltage.10 Load changes as a function of time Recommendations. Thermostatically-controlled air conditioner loads are essentially constant power load (load restoration by induction motor action). mented in a longer-term dynamics program [221. More comneed to be represented at a single bulk power deliv. or constant energy mechanisms can be approximated. T --. load models with different time constants could be used at a bus.18. Time constants may be as short Most underfrequency relays have no intentional as several minutes [17. load tap changers. I 9 I I I trip each part of the load according to its proportion of the total load.26.active power dynamics are modeled. etc. DB. industrial heating) could be represented with W e r e n t time constants.25. response of a large number of individual loads. several generic first-order dynamic models have been proposed for longer-term voltage stability simulation [18. thermostatically-controlled conductance (heating) load is important. The Undervoltage relays normally trip load after signifi.1309 Table 1: Load Model Types and Data Exchange Parameters I I Synchronous motor Discharge lighting Transformer saturation LTC transformer See text See static model 10. we do not recommend standard models in this paper.plex physically-based models have been impleery bus. we are interested in the composite For longer-term dynamics. a m Tal . Motor rated voltage. may be different than power flow bus rated voltage. KD1 1 npv2 p Induction motor Frequency sensitivity (term 1). I Motor and motor load inertia in MW-s/MVA. a. Voltage sensitivity exponent (term 2).3. reactive load data is similar-see equations 1-4.1310 Table 2: Dynamic Data Description Fraction of total active or reactive nominal (initial) load. Per unit of active load that is voltage and frequency sensitive (term 1 ) .or 5. Frequency sensitivity (term 2). Per unit voltage at which load is set to zero (Figure 1 ) . Per unit of active load that is voltage and frequency sensitive (term 2). Per unit of active load that is constant current. Only data for active load is described. Dynamic order of model: 1. Per unit of active load that is constant. Tap range and tap step size is assumed to available from the companion power flow program data. Per unit voltage at which load starts to be ramped to zero (Figure 1). MVA and Pfmct determines motor load factor. Motor rated MVA. . b. 091 I 2. R. 0 .33.064 I 0. A = 1.As a fraction of Qo.1.This data is now available in a textbook C271.018. Kpz = 0.qz = -0. va1= 0. commercial. 20% fluorescent lighting.8. = 0. and 50% small industrial motors with load factor of 0. All static model.5.059 I 0.1516is computed internally (capacitive shunt compensation to resolve the mismatch between the load component power factors and the forecasted reactive power).10. Kql=0. = 0.672 (additional input data). 0 .X . Kqz = 0. 2 (small induction motor) The power factor of heating is 1 . X.0. Kpz is computed to be 0.). The load changes may be different for different load classes (residential. the data is: Pfrac = Qfrac = 1 .344MVAr). Kql= 0.0. npv2= 0. the shunt compensation is KPI.6. = 3. H = 0.0. v b l = 0. clothes dryer. = 0.18.npn= 1 .0.1311 Table 3: Typical Induction Motor Data [13.5. active power.5. morning load pickup may be critical in voltage stability analysis.0. X . required.6. v b l = 0. 5 . npvl= 1.83(Q = Ptan4 = 1.7. assume a load delivery point consists of 30% heating (space heating. Type 2 Type 3:Water pump. : Large industrial motor.9 (Q = Ptang = 0.the power factor of fluorescent lighting is 0. the standard load model data is as follows.4.0.n fl = 1.R .969 MVAr).2. cooking.31. Data is suitable for large-scale simulations where motors do not stall Type 1: Small industrial motor. This is a desired feature of longer-term dynamics programs [231. There are also many other sources of data.ngv2= 0 . X.7 (fluorescent lighting) Kp2 = 0. Type 5:Weighted aggregate of residential motors. Data for the dynamic (motor) portion of the load is: Pfrac = 0.3. Implementation details and data exchange are outside the scope of this paper. Using equation 5. The total load is forecasted to be Po + j Q o = 1O+j2 MW.4845 and Kq2= 0. = Xr = 0.nqfl= -2. Shunt compensation is internally added to resolve mismatch with the forecasted reactive power. MVA = 8. nqfl= -2. K p i = Kpc = Kp2 =K q i = Kqc= Kqz= 0 As an example.nqvl= 3.nqn= 1 . 0 K p i = Kpc= Kqi = Kqc = 0 Kpl= 0.2 10 10 I 0. B = 0 The initial motor reactive power is computed based on the terminal voltage. Type 4: Power plant auxiliary. Static and dynamic model.8.8. Using the LOADSYN data values. It may also be desirable to change load on a zone or area basis. 9 . etc.npvl= 1 . and the power factor of the small induction motor is 0.Order = 3.7duorescent lighting) Computed internally.8. water heater. nqvl = 3. = 0.0 Val= 0. Type 6 :Weighted aggregate of residential and industrial motors.0.031. Based on equations 1-5.2. Example Based on Load Composition Typical data values were summarized as part of the EPRI LOADSYN computer program development [131. npfl= 1. For example.8 a. This can be done by changing the Po and Qo of individual busses or load types. and equivalent circuit parameters. Type 7 :Weighted aggregate of motors dominated by air conditioning. Data for the static portion of the load is: Pfrac = Qfrac = 0. industrial).969. I . In some cases.14Ia 7 I 0.34 - I 0. the data may be the aggregate response of load components as determined by system measurements. 4.071 I 0.23 I 0. 167-179.S . H. Volume 2 is a load modeling reference manual. Los Angeles. Programs. ”T)ynamic Models for Fossil Fired Steam Units in Power System Studies.pp. 4. 12. 1. k Wey Fo. “Load Representation for Dynamic Performance Studies. 7.3. Vol. and W. Segerqvist. No.Greenberg. IEEE Standard 1110-1991.K.” CZGRk. Section 6. 24. Static models are suitable for power flow simulations. S. 16. 3. Thylor. Miller. ”Modeling and Analysis of Under-Load Tap Changing Transformer Control Systems. I. K. 1986. IEEE Dunsactions on Power Systems. pp. 9. EPRI Final Report EL-5003. S . 26. K . 75.5-1992. IEEEPES 1978 Summer Meeting.July 1984. G.” IEEE %ns- .” IEEE lFansactions on Power Systems. 5. 2. 2. W.* International Workshop on Bulk Power System Voltage Phenomena: Voltage Stability and Security.(Four volumes. Schmus. W. and B. “T’emporary Load-Voltage Characteristics for Voltage Stability StudienField and Laboratory Measurements. Kundur. 6. IEEE Committee Report. Modelling of Voltage Collapse Including Dynamic Phenomena.Calovic. 753761. Karlsson. “Voltage Control in a Large Industrialized Load Area Supplied by Remote Generation. “Concepts of Undervoltage Load Shedding for Voltage Stability. “Load Modelling and Dynamics. “Model Selection and Data Assembly for Power System Simulation.IEEE Recommended Practice for Excitation System Models for Power System Stability Studies. “Modeling of Power System Components at Severe Disturbances.No. 1173-1181. Energy-EfficientMotor Systems: A Handbook on Technology. Vol.” paper A 78 559-7. B. 2.4-7August 1991. Mansour. Vol.”Dynamic Simulation of Voltage Collapse Processes in EHV Power Systems. 11. January 1989. paper 38-205. Alves. McGraw-Hill. 7 . May 1992. Maryland. CIGRE Task Force 38-02-05. ZEEE Guide fir Synchronous Generator Modeling Practices in Stability Analyses. D.No. Price. W. W. Kurita.September 1982.Proceedings of CIGRE. Williams. C. Shepard. Stenborg. M.April 1982. 8 . January 1987. NO. 3 .pp. 10961103. 2.” IEEE Dansactions on Power Systems. and for dynamic simulations at locations where results are not sensitive to load modeling. F. M.Price.” paper A 78 558-9.” IEEE fiansactions on Power Apparatus and Systems. 8.pp.” I E E W E S paper 93 WM 185-9PWRS. Hill.” CIGR& paper 38-204.pp. Karlsson.” paper 93 WM 173-5PWRS.Walve. 403-410. “Modelling and Identification of NonLinear Dynamic Loads in Power Systems. Vol. No. D. 1993. “Voltage Stability Analysis Using Generic Dynamic Load Models.K.” Proceedings: Bulk Power System Voltage Phenomena-Voltage Stability and Security. Vol. Ahmed-Zaid. Vol. D. 7 . General Electric Company. American Council for an Energy-Efficient Economy. and Policy Opportunities.Lindbn. 1991. “Hydraulic Turbine and Turbine Control Models for System Dynamic Studies. Nozari. 4 .1993. McGrawHill. P. Okubo. CIGRG Task Force 38-02-10. 7. M.” Electra.” by N. J. “’kansient Stability Sensitivity to Detailed Load Models: a Parametric Study.1312 combined with the Kqz term. 9. and H. IEEE Standard P421. W. W. May 1990. Vol. Laskowski. S. No. “A Multi-Faceted Approach to Power System Voltage Stability Analysis. “Nonlinear Dynamic Load Models with Recovery for Voltage Stability Studies. Power System Voltage Stability. K. D.IEEEPES 1993 winter meeting. Power System Stability and Control. 0. 1909-1915. 124-142. Table 1 summarizes the data to be exchanged for the several types of models and Table 2 provides data description. “I‘ransmission Voltage Recovery Delayed by Stalled Air-conditioner Compressors. No.” IEEEPES paper 93 W M 171-9PWRS. Hill. Undrill and T. 1994.May 1993. 472-482. N.November 1987. 1992. J. F.W. Clark and T. Klaus-Martin G d .IEEEPES Summer Meeting. 480488. Price.0 Summary We recommend standard load models for power flow and dynamic simulation programs. R.” paper 38-18. 2 1 .1992. Kankam. Xu and Y. IEEE Committee Report. M.. Dawson. W.May 1991. J. pp.pp.1978. M.. C. 7.) 1 4 . 22. F.” IEEE h n s a c t w n s on Power Systems. Deep Creek Lake. 13. de Almeida. IEEE Committee Report. Yorino et al. T.No.” IEEE Zkansactions on Power Systems. 6 . 17. 600-611. 1992.pp. D. 27. 6. B.” ZEEE hnsactions on Power Systems. Laskowski.” ZEEE Dansactions on Power Apparatus and Systems. 1991.C. “FirstOrder Induction Machine Models Near Voltage Collapse.mapper. C. H. and W. 25.Nadel. R. Load Modeling f i r Power Flow and Dansient Stability Computer Studies. 15. Katz. 2 3 . and D. 33334341. July 1621. With more complex load mixtures. W. a computer program such as LOADSYN can be used for aggregation and for computing data for the models. W e b . 2 0 . and D. 2. We recommend induction motor models for use at locations where results are sensitive to load modeling. ZEEE h n s a c t w n s on Power Delivery. PAS-101.A. pp. Pal. PAS-103.pp.February 1992. Laskowski. A. 28. M. and D.0 Referencedselected Bibliography 1. CIGRE Brochure No. “Static Var Compensator Models for Power Flow and Dynamic Performance Simulation. Washington. describes LOADSYN computer program. discussion of “An Investigation of Voltage Instability Problem. 2. Vol. We also recommend models for longer-term dynamic simulations. 5. IEEE Committee Report.No. 7 . pp. Vol. C. F. 19. EPRI EL-6183. 1 0 .Clark. “Aggregation of Induction Motors for Transient Stability Load Modeling. Taylor. T. August 1992. D. 18. “Northwest Power Pool Transient Stability and Load Shedding Controls for Generation-Load Imbalances. W. 8 . i The base values used in developing model parameters from field tests could have different meanings. July 1981. pp. G.A Wirgau.Mitsche. In the computer world. C. W. the instrumentation and the methods used for obtaining parameters should be clearly described.1978.Price.pp. pp. 1. Nassief. . Then computing per unit reactive power. Rogers and D. E. L.” Archiv fur Ekkhtechnik. “Load Modeling for Power Flow and Transient Stability Computer Studies.J. “An Induction Motor Model with Deep-Bar Effect and Leakage Inductance Saturation. 29. however.” IEEE lhnsactions on Energy Conversion. A El-Kady. PAS-100. Vol.No. and R. becomes erratic. 193-201. and M.Taylor. Vol. Q/Qo. 180-187. 3 .pp. 3486-3495.1313 actions on Power Systems. No. J. J. V. we recommend this convention in equations 1and 3.) In providing data from field tests. or use of Po as the base for reactive power. Cresap.W. February 1993.” IEEE lhnsactions on Power Systems.February 1988. 622-628. Most commonly. 30. Benaragama. the base values are from a solved power flow.No. however. 60. 32. Appendix A: Base Values for Load Data Equations 1and 3 contain base values for active and reactive power. recommend either use of So (apparent power) as the base for both active and reactive power. “Induction Machine Modelling for Electromagnetic Transient Program. 4 . Vol. 31. Vol. A particular problem occurs if the initial measured reactive power is very small. Shirmohammadi.December 1987. F. S . Murdoch. EC. Rogers and D. base power could be transformer or load MVA rating.”IEEE Dansactions on Power Apparatus and Systems. This avoids difficulties when reactive power is small or zero. and voltage.2 . Vaahedi. G. For instance. 1. R. S6me experts. Because prevailing practice and nearly all data sets are based on use of Po in computing per unit active power and Qo in computing per unit reactive power. (The meaning of exponents nqvl and n m in Equation 3 if obtained by tests is AQ/AV per unitlper unit. Vol. A. K. the base values are the initial values of active and reactive power.
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