ICEM98 OPTIMIZED DESIGN OF VARIABLE-SPEED DRIVES AND ELECTRICAL NETWORKS BASED ON NUMERICAL SIMULATION. J.-J.Simond, B.Kawkabani, A.Sapin, P.

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1 ICEM98 OPTIMIZED DESIGN OF VAIABLESPEED DIVES AND ELECTICAL NETWOKS BASED ON NUMEICAL SIMULATION J.J.Simond, B.Kawkabani, A.Sapin, P.Allenbach Swiss Federal Institte of Technology, Electrical Engineering Dept., CH1015 Lasanne tel: 4121 / , fax: 4121 / Switzerland Abstract: The present paper describes the modelling and the prediction of the steadystate or transient behavior of different modern variablespeed drives and electrical networks. The necessity of a performant nmerical simlation tool in order to garantee an optimized design is illstrated by examples based on existing large variablespeed drives and power plants. The following examples of application concern existing large variablespeed drives and power plants. These examples have been simlated with the simlation tool SIMSEN described in appendix. Example 1: 12 plse LCIfed synchronos Motor Keywords: variable speed drive, electrical network, converter, reglator, dynamic behavior. Smmary Dring the last few years the performances and therefore the complexity of the variablespeed drives as well as those of the modern power plants have considerably increased. Conseqently, an optimized design of these eqipments reqires sitable nmerical simlation tools in order to garantee the feasibility and the performances of sch eqipments in steadystate or transient operation. More precisely, it is no more sfficient to simlate separately the behavior of the different elements, even based on sophisticated models, it is necessary to simlate globally all the system in order to take into accont all the possible interactions which are often primordial for the system performances. Fig.1: ia1, ib1, ic1, ab1 12 plse LCIfed synchronos motor 21 MVA, 2x3.3 KV, Hz, 2p = 10 In a practical viewpoint a sitable simlation tool shold be able to consider all the elements sed in a complex system (machines, converters, load, spply, control and reglation eqipment, protection devices, filters,...) for any system topology. In this paper, the modelling of different existing large indstrial drives or electrical networks based on modern technologies are described, inclding the synchronos machine with 2x3 phase stator winding. It is shown how the se of performant simlation tools helps to reach an optimized design [1,2,3]. tem Examples of applications.

2 6 MVA, 11 KV, 50 Hz, 2p = 6 ia1, ib1, ic1, ab1 Fig.2: steadystate operation, tmec = 0.9, n = 1. ia1, ab1 n, tem, prot n, tem Fig.5: steadystate operation, n = 0.7, tmec= 0.89 ia1, ab1 Fig.3: Example 2: transient operation, modifications of the speed and torqe set vales Indction motor with a 6plsecascade n, tem Fig.4: Indction motor with a 6plse cascade Fig.6: transient operation, change of the speed set vale

3 Example 3: Indction motor with a 12 plse cascade Fig.7: indction motor with a 12plse cacade 6 MVA, 11 KV, 50 Hz, 2p = 6 ia1, ib1, ic1, ab1 n, tem n, tem, prot Fig.9: transient operation, change of the torqe set vale Example 4: Slipenergy recovery drive with indction machine and cycloconverter (dobly fed indction machine) Fig.8: steadystate operation, n = 0.7, tmec =0.89 ia1, ab1

4 Fig.10: Slipenergy recovery drive with indction machine and cycloconverter 230 MVA, KV, 50 Hz, 2p = 18 ab1, ab1eff (HV side of the transformer) In comparison with a conventional synchronos motorgenerator operating in a pmpstorage plant, a dobly fed indction machine offers the following important advantages[5]: Possibility of active power control in pmping mode in a specified pmp head range (contribtion to the network freqency control). n High efficiency and wide range operation in generating mode. Possibility of instantaneos power injection into the grid for eliminating power system flctations. Possibility of reactive power control at the interconnection point to the grid. Startingp into pmping mode withot any constraints for the machine and for the grid. Sch a large dobly fed indction machine mst be designed and optimized very careflly by taking into accont all the interactions between the different components of the system (indction machine, type of cycloconverter, control eqipment and strategy, pmptrbine, grid, operation reqirements). It is therefore indispensable to work with a sitable simlation tool, also in an economical point of view. Tem ia1, ab1 (indction machine) ia1, ab1 tem, prot Fig.12: transient operation, voltage dip 50 % dring 100 ms on the HV side of the transformer with a constant speed set vale Example 5: Shaft train torsional oscillations of large trbogenerators Fig.11 steadystate operation, n = 0.9, tmec = 0.7 The power plant shown in fig.13 consists of 4 grops, each inclding: a trbogenerator with its shaft train, a voltage reglation and a transformer. The 4 grops are connected to the grid throgh the same transmission line. One circit breaker is sed to prodce and to clear a three

5 phase falt on the HV side of the transformers in two different cases. MS1 T1 L1 S1 U1 ME1 D1 MS2 T2 Time [s] U2 tkt, tkt1 ME2 MS3 T3 U3 ME3 MS4 T4 Fig.13: U4 ME4 Shaft train torsional oscillations of large trbogenerators Fig.15: Electromagnetic torqe of the generator MS1 ( tem : 1gen., tem1 : 4 gen.) Mechanical torqe between GEN and LP3 ( tkt : 1 gen., tkt1 : 4 gen.) Time [s] [p.] Fd Fq i [p.] S GEN LP3 LP2 LP1 HP Example 6: Sbsynchronos resonance Fig.14: Noload characteristics and shaft redction. In the first case only the generator 1 is in operation, in the second case all generators are in operation bt neqally charged. In both cases the generator 1 has the same conditions of operation. As expected, the plots on the fig. 15 show the same behavior of the generator 1 in both cases till the falt clearing time and another one after this time. Fig. 16 shows an example of the torsional interaction phenomenon [4]. A generator operating on fll load feeds two lines. The ncompensated line S2 carries approximately 1% of the total power. At time s this line is disconnected, this small change leads to an interaction effect dring which the torqe in the shaft section GEN LP3 begins to plsate with an increasing amplitde. At time 3.8 s the disconnected line is reconnected and the torsional oscillations begin immediately to decrease, bt with another time constant. tem, tem1

6 U1 MS1 ME1 T1 L1 S1 D1 L2 S2 [1]A.Sapin, J.J.Simond: SIMSEN: A Modlar Software Package for the Analysis of Power Networks and Variable Speed Drives, EPE Lasanne [2]J.M.Merino, A.Lopez: ABB Varspeed generator boosts efficiency and operating flexibility of hydropower plant. ABB eview 3/1996, S 2 GEN 3 LP3 4 LP2 5 LP1 6 HP [3]W.L.Brggisser: The largest rotating converters for interconnecting the railway power spply with the pblic electricity system in Kerzers and Seebach, Switzerland, BBC eview (11) Fig.16: tem Sbsynchronos resonance de to a torsional interaction [4]I.M.Canay: A novel approach to the torsional interaction and electrical damping of the synchronos machine. Part I: Theory, IEEE, Vol. PAS101, No 10, October [5]D.Schafer, J.J.Simond: Adjstable Speed Asynchronos Machine in Hydro Power Plants and its Advantages for the Electric Grid Stability. CIGE, Paris, session Appendix : SIMSEN a new modlar software package for the nmerical simlation of power networks and variable speed drives. tkt Fig.17 Conclsions Sbsynchronos resonance de to the interaction effect tem : electromagnetic torqe tkt : mechanical torqe GEN LP3 Based on different examples of practical applications it has been shown how a performant simlation tool can be sefl for an optimal technical, feasible and economical design of a complex variable speed drive or of an electrical network. Sch a tool permits the comparison between different possible technical soltions and the verification of the reqired performances of the eqipment. eferences: The above described variable speed drives have been simlated with a new software package developed at the Federal Institte of Technology in CHLasanne. The main featres of this simlation tool rnning on PC are the following: SIMSEN is based on a modlar strctre which enables the nmerical simlation of the behavior in transient or steady state conditions of power networks or variable speed drives with an arbitrary topology. The ser bilds its network directly on the screen by choosing and linking adeqately the sitable nits shown in table 1 in order to create the desired topology. Each nit represents a specific element in the network, it incldes a set of differential eqations based on the nit modelling. An original algorithm generates atomatically the main set of differential eqations for all the system taking into accont all the possible interactions between the different nits. A transient mode of operation may inclde several sccessive pertrbations. For applications withot nits having semicondctors the initial conditions are obtained with a loadflow program. The nmerical integration works with a variable step size, it is therefore possible to detect exactly all the events in time as the onoff switching of a semi condctor or of a circit breaker. The open strctre of SIMSEN allows newly developed nits to be easily implemented. An existing nit can also be modified withot difficlties. It is ths possible to widen the applications field frthermore in the ftre.

7 The only restriction on the size of the power network to simlate is prescribed by the available memory of the microcompter. The dynamic administration of the memory makes possible the simlation of large networks (p to 1000 state variables). Table 1: nonexhastive list of SIMSEN nits.