Question

Q1 [35] DC shunt motor has the following parameters: 10,1 kW, 150 V, 805 rpm, R=0.212, R=200 2. When the motor is not loaded it draws 10 A from the voltage source of 150 V. a) [10]Calculate the efficiency at full load, rotating at 805 rpm. b) [10] Calculate the torque when there is no load on the rotor. c) [15] If total torque on the rotor is 91 Nm, calculate the control resistance of the armature to set the speed to 80 rad/s.

Answer 1

Ra The be T Ta If Razo Ra=0.21 20012 At no load motor gives rotational loss. Given Pout = 10.1 kW = 10100 Watt = 0.211 RA = 200.2 can equivalent Circuit for DC motor drawn as 1500 Rf Eb Load I=10 A 150 Ia = - If Protational Eb la at no -0.75 A L 200 = 10-0.75 =.9.25 A E = V - IaRa = 150 – 9.25 x 0.21 148.0575 V 148.0575 x 9.25 = 1369.53 watt Now, at full load let to current is drawn by armature Now, CScanned with CamScanner Pdeveloped = Pout + Protational

5 Eь та = 10100 + 1369.53 148.0575 Tas = 11469.53 11469.53 Ian 148.0575 Tal = 77.47 A het I, current is drawn from the supply at full load. " I = Part If I = 77.47+ 0.75 옥 = 78.22 A .: Input power = Pinput = V I = 150 x 78.22 = 11733 watt X100% -X100 % = ... Poutput %= Pinput 10100 11733 86.08. M At no load Eb = 148.0575 V Power developed at No load, = Ep I a Where Ia = 9.25A Paeveloped 148.0575 X 9.25 6. - CScanned with CamScanner

T 2IN = 1369.53 > > 60 1359.53X 60 T = 2 T X 805 C T = I al is 16.13 Nm c) At no load. T = 16.13 Nom = 9.25 A het T2 = 91 Nm and Iaz to T Ta o la AS remain Constant T, Tas T, Iaz 16:13 9.25 91 Tar 9.25 X 91 16.13 52.19 A CScanned with CamScanner - Taz 3 » > Taz

ป% Inara 80 rad/s - ก 1s = xo m V 2TU Co at Ebi = 148.0575 Ni = .805 rpm Now Eb2= 150 52.19 ra N₂ = 21 rad I revolution > I rad revolution. 20 min Go N SU X 80x60 rpm 20 0 > N, N = 763.94 pm Now Eb a N as flux is constant N Eb2 148.0575 805 150-52.19 8a 763.94 150-52.19 ra= 148.0575 x 763.94 805 = 140.51 52-19 ra= 9.49 0.18 ra= 52.19 CScanne wiesistance of armature is to set at 0.182 Ebl = 150-52:19 PM 9.49