ACTA TECHNICA CORVINIENSIS - Bulletin of Engineering

ACTA TECHNICA CORVINIENSIS – BULLETIN of ENGINEERINGthe unexcited model generator to the networkunder the various initial rotor slips were carriedout without the account and in view ofchanging the rotor speed at transient .Theinvariable rotor speed was simulated by way ofsetting the great value of the inertia constant [9].As follows from comparison of the resultsobtained for the given slip values, equal to 0 ;0.01 ; 0.03 ; 0.05 and 0.1 put., the changes in thetime-dependence of the generalized statorcurrent vector and electromagnetic torquepractically does not differ from the analogouscalculations made on the basis of the Parc-Gorev equations. In these cases the difference inthe maximum values of the similar operatingvariables being compared did not exceed 10.4%.The typical changes in the transients differ not atall. So, when making use of the static frequencyresponsecharacteristics, one can infer that theelectromagnetic processes may be identifiedwith a sufficiently high degree of accuracy.The analysis of the transients calculated withtaking into consideration the rotor speedchanges, following the connection of the modelgenerator, points to some differences in thetime-dependent variables. By way of example, inthe Figure 2 are shown the results of calculatingthe transients at connection the unexcitedmodel machine to the network with the fieldwinding short-circuited.The calculations carried out in compliance withthe system of Parc-Gorev equations (see dottedline) reflect the features connected with changesin the current, I s ,and electromagnetic torque,T , with the rotor speed changes. The timedependence of the slip in the case underconsideration has the oscillatory character.Mathematical simulation based on the staticcharacteristics (see solid line) brings about themonotonous changes in the rotor slip under thetransient process. Meanwhile, the resultant timeof approaching the rotor speed to thesynchronous one, being estimated at the instanta rotor slip for the second time passes throughzero, practically agrees with the time beingdetermined from the solid line obtained atsimulating the transients by means of themethod proposed. As may be seen from theFigure 2.Distinguishing features of the variables beingconsidered are in close agreement; theirmaximum values appearing at the initial stage ofthe transient process correlate well with the datagot without regard for speed changes of therotor. In the Figure 3 are given the curvesreflecting the changes in the variables at theshort-circuit on the terminals of the inductionmotor ДАЗО-1914-10/12А type.Figure 2 Connection to the network of the unexcitedmodel turbo generatorThe quantities of the motor equivalent circuitssynthesized in accordance with [4,10] havingthree parallel branches and the magnetizing one,separated in the manner as is shown in theFigure 1, are as follows (in per unit on machinebase) :RXδ+ Xγ= 2.19 ; X = 0.271 ; X2X3= 0 .717 ;R0 .6241== 0 .0055;R3 12=1.1790 .1139The comparative analysis of the results obtainedby calculating the generalized stator currentvector, Isand electromagnetic torque, T ,calculated by various methods points to theirclose agreement because of the maximumvalues of the mentioned variables differ less than7,8%.The analysis of the electromechanical transientsat starting the non-loaded motor also indicatesto the satisfactory coinciding of the resultsobtained by using the mentioned calculationtechniques. In particular, the starting timedetermined by the technique proposed differsfrom the same parameter obtained through theuse of the Parc Gorev equations less than 9, 2%.2010/Fascicule 2/April­June /Tome III 71