A1-104 CIGRE 2012 Calculation of Electromagnetic Force on ...

)Eddy current in damping windingsFig.3 The magnetic field and eddy current in damping windingunder rated load operationBased on the numerical calculation <strong>of</strong> electromagnetic field and according to formula (2) to (4), theelectromagnetic force distribution acting on damping windings was shown in Fig.4 when the generator was in the state<strong>of</strong> rated load operation. Fig.4a) showed the electromagnetic force values <strong>of</strong> nine damping windings under the rated loadoperation. Fig.4 b) showed the electromagnetic force status <strong>of</strong> the No.1 damping winding as the time changed in acycle.<strong>Electromagnetic</strong> force(N)100500-50-100FrFt-1500 2 4 6 8 10Damping winding numbera) <strong>Electromagnetic</strong> force values <strong>of</strong> all damping windings<strong>Electromagnetic</strong> force(N)150100500-50-100 FrFt-1500 5 10 15 20Time(ms)b) The electromagnetic force <strong>of</strong> the No.1 damping windingas time changesFig.4 The electromagnetic force distribution acting on damping windings under rated running operationFrom Fig.4 a), it could be seen that along the rotor rotation direction the electromagnetic force <strong>of</strong> the first dampingwinding (1 # damping winding) was significantly greater than the rest <strong>of</strong> the damping windings. Meanwhile, thetangential magnetic force <strong>of</strong> the No.1 damping winding was greater than the radial electromagnetic force <strong>of</strong> that. FromFig.4 b), it indicated that the electromagnetic force <strong>of</strong> the No.1 damping winding which suffered the largest forcewould fluctuate in a time period, because <strong>of</strong> the harmonic current in damping winding.B. The Negative Sequence Operation ConditionThe hydro-generator which can withstand the most severe conditions <strong>of</strong> negative sequence is 12% negativesequence in China's regulation. So this paper mainly studied the 12% negative chronological asymmetric operating

conditions. Fig.5 showed the magnetic field distribution when the generator was under 12% negative sequenceoperation.a) T=40ms b) T=50msFig.5 The magnetic field distribution under asymmetrical operationFig.5 showed that in a cycle <strong>of</strong> the asymmetrical operation, the changes <strong>of</strong> the magnetic field distribution inmagnetic pole were very intense. The magnetic field near number 1 changed frequently and the amplitude was bigger.The magnetic field and eddy current in damping winding were shown in Fig.6. It could be seen from the figurethat the No. 1 damping winding had the highest magnetic flow density and others were low. The eddy current density inthe No.9 damping windings had the highest value.a)Magnetic field in damping windingsb)Eddy current in damping windingsFig.6 The magnetic field and eddy current in damping windingunder negative sequence operationFig.7 was the electromagnetic force distribution acting on damping windings. From Fig.7 a), it could be seen thatalong the rotor rotation direction the electromagnetic force <strong>of</strong> the last damping winding (9 # damping winding) wassignificantly greater than the rest <strong>of</strong> the damping windings. Meanwhile, the radial magnetic force <strong>of</strong> the No.9 dampingwinding was greater than the tangential electromagnetic force <strong>of</strong> the No.9 damping winding. From Fig.7b), it indicatedthat the electromagnetic force <strong>of</strong> the No.9 damping winding, which suffered the largest force, would fluctuate in a timeperiod, because <strong>of</strong> the harmonic current in damping winding.<strong>Electromagnetic</strong> force(N)10000-1000-2000FrFt-30000 2 4 6Damping winding number8 10a) <strong>Electromagnetic</strong> force values <strong>of</strong> all damping windings

<strong>Electromagnetic</strong> force(N)200010000-1000-2000FrFt-30000 5 10 15 20Time(ms)b) The electromagnetic force <strong>of</strong> No.9 damping winding as time changesFig.7 The electromagnetic force distribution acting on damping windings under negative sequence operationC. The Different Damper Winding Connection FeaturesHydro-generator rotor has damping system within the magnetic poles, and the damping system are composed <strong>of</strong>article damping, damping ring, damping ring joint piece and other parts. According to the joint form <strong>of</strong> damping ring,the damping system is divided into the damping system and half damping system. The connection modes <strong>of</strong> circuit intwo different kinds <strong>of</strong> damping ring connection forms are shown in Fig.8.a) The half damping systemb) The absolute damping systemFig.8 The connection modes <strong>of</strong> circuit in two different kinds <strong>of</strong> damping ring connection formsThe damping system is that the damping ring is fixed through the core tighten screw and the damping ringbetween adjacent poles is connected through the connecting link. This structure design makes the parallel dampingbars within the individual pole connect with other damping bars in other poles together. The half damping system is

that when the damping ring is fixed in each pole, it will not connect with other damping rings in adjacent poles. Thisstructure design makes the damping bars in a pole only mutual parallel itself.The rated operation and negative sequence operation researched above mainly researched on the half dampingsystem. When the generator adopted the absolute damping system in negative sequence operation, the calculationresults were as follows. The magnetic field and eddy current in damping winding <strong>of</strong> the absolute damping system wereshown in Fig.9.a)Magnetic field in damping windingsb)Eddy current in damping windingsFig.9 The magnetic field and eddy current in damping winding <strong>of</strong> the absolute damping systemIt could be seen from Fig.9 that the No.1 damping winding had the highest magnetic flow density and the otherswere less. The eddy current density in the No.1 damping winding was bigger than the others. Fig.10 showed theelectromagnetic force distribution acting on damping windings.From Fig.10 a), it could be seen that along the rotor rotation direction the electromagnetic force <strong>of</strong> the first dampingwinding (1 # damping winding) was significantly greater than the rest <strong>of</strong> the damping windings. Meanwhile, thetangential magnetic force <strong>of</strong> the No.1 damping winding was greater than the radial electromagnetic force <strong>of</strong> the No.1damping winding. From Fig.10 b), it indicated that the electromagnetic force <strong>of</strong> the No.1 damping winding whichsuffered the largest force would fluctuate in a time period, because <strong>of</strong> the harmonic current in damping winding. Theradial electromagnetic force and the tangential electromagnetic force played respective role at different time.2000<strong>Electromagnetic</strong> force(N)0-2000-4000FrFt-60000 2 4 6 8 10Damping winding numbera) The electromagnetic force <strong>of</strong> the No.1 damping winding<strong>Electromagnetic</strong> force(N)Fr0.5Ft0-0.5-10 5 10Time(ms)15 201 x <strong>104</strong>b) The electromagnetic force <strong>of</strong> the No.1 damping winding as time changes

Fig.10 The electromagnetic force distribution acting on damping windings under negative sequence operation <strong>of</strong>absolute damping systemIV. CONCLUSIONSThe mathematic model <strong>of</strong> electromagnetic force calculation <strong>of</strong> damping system is established in this paper, whichcombined large hydro-generator with Lorentz force method. Taking the 1000MW large hydro-generator as an example,the electromagnetic force distribution under rated operation and negative sequence operation condition wererespectively analyzed. The conclusions obtained were as follows:1) Along the rotation direction <strong>of</strong> the rotor, the electromagnetic force <strong>of</strong> the first damping winding (1 # dampingwinding) was significantly greater than the rest <strong>of</strong> the damping windings in rated operation and the radialelectromagnetic force was greater than the tangential electromagnetic force.2) Along the rotation direction <strong>of</strong> the rotor, the electromagnetic force <strong>of</strong> the last damping winding (9 # dampingwinding) was significantly greater than the rest <strong>of</strong> the damping windings under negative sequence operation.Meanwhile, the tangential magnetic force <strong>of</strong> the No.9 damping winding was greater than the radial electromagneticforce <strong>of</strong> the No.9 damping winding.3) When the absolute damping system was adopted, the electromagnetic force <strong>of</strong> the first damping winding (1 #damping winding) was significantly greater than the rest <strong>of</strong> the damping windings along the rotation direction <strong>of</strong> therotor. Meanwhile, the radial magnetic force <strong>of</strong> the No.1 damping winding was greater than the tangentialelectromagnetic force <strong>of</strong> the No.1 damping winding.4) Under the negative sequence operation <strong>of</strong> the generator, the radial electromagnetic force played more importantrole than the tangential magnetic force. Under the rated load operation, this otherness was inconspicuous.REFERENCES[1] Li Shufang. Yao Ruoping, and Gao Yougang. “A new method to determine the 3-D field andtransposition way <strong>of</strong> large generator[C],” Power Engineering Society 1999 Winter Meeting, Vol.2 , No.1,pp.9-12, 1999.[2] Johann Hal demand. “Transposition in stator bars <strong>of</strong> large turbogenerators[J],” IEEE Transactionson onenergy conversion, Vol.119, No.3, pp.553-560, 2004.[3] Nabeta S.I, Foggia A , Coulomb J-L , and Reyen,G . “A non-linear time-stepped finite-elementsimulation <strong>of</strong> a symmetricl short-circuit in a synchronous machine[J],” IEEE Trans on Magnetics,Vol.31, No.3, pp.2040-2043, 1995.[4] Sturgess J P,Zhu M,and Macdonald D Cl.“Finite-element simulation<strong>of</strong> a generator on load duringand after a three-phase fault[J],” IEEE Trans on EC,Vol.7, No.4, pp.787-793, 1992.[5] Sun Yuguang, Wang Xiangheng, Gui Lin, and Wang Weijian. “Transient calculation <strong>of</strong> stator’s internalfaults in synchronous generator using FEM coupled with multi-loop method[J],” Proceedings <strong>of</strong> theCSEE, Vol.24, No.1, pp.136-141, 2004. (in Chinese)[6] He Chenbing, Gu Yujiong, and Xing Cheng. “Coupled flexural and torsional vibrations analysis <strong>of</strong>turbine generator shaft systems caused by short circuit fault[J],” Proceedings <strong>of</strong> the CSEE,Vol.30, No.32,pp.84-90, 2010. (in Chinese)[7] Men Liang , Luo Yingli , and Liu Xia<strong>of</strong>ang , Yang Jinfu,Chi Yongbin . “A case study <strong>of</strong>electromagnetic force distribution on rotor core surface <strong>of</strong> turbo generator[J],” Proceedings <strong>of</strong> theCSEE,Vol.25, No.1, pp.81-86, 2005 .(in Chinese)[8] Li Zhiqiang,Luo Yingli,and Meng Liang.“The calculation <strong>of</strong> local magnetic force in turbogeneratorwith FEM based virtual work principle[J],” Proceedings <strong>of</strong> the CSEE, Vol.27, No.15, pp.47-52, 2006. (in Chinese)