Question

A three-phase, 50-Hz, 4-pole, 575-V (line-line, rms) induction motor drive has a full-load (rated) speed of 1450 rpm. The rated torque is 50 Nm. Keeping the air gap flux-density peak constant at its rated value, (a) plot the torque-speed characteristics (the linear portion) for the following values of the frequency: 50 Hz, 40 Hz, 30 Hz and 20 Hz. (b) This motor is supplying a load whose torque demand increases linearly with speed such that it equals the rated motor torque at the rated motor speed. Calculate the speeds of operation at 50 Hz, 40 Hz, 30 Hz and 20 Hz.

Answer 1

Solution Given - 3-phase, P=4,5043 575 v kine-line). Rated speed NR = 1450 Rated, torqur = 50 Nam. full Load Ns = 120XF INS = 120f Ng = 12 of Р Р Ns = 12of Р = 120 x 50 4 Ns = 1500 som = 120X40 4 Ng = = 1200 som = 120x30 4 Ns = goo rom = 120X20 4 Ns Goorpm NR (Rated speed) Nm torque 1 1450 INS (synchronous Spud) 600 900 1200 1500 Speed No for dineas condition S, 15oo-goo S, 1500-1200 15oo S3 =1000-600 Woo 11 оо = 0.04 cole -0.06. 0.6 02 As frequency dicuases slip Increasy

b) Tx suz f. sue T,=50=Trated. 2 . TI sit T2 Safi Ni Na fi 2 1500 x 50 1 2 N2 No=1800 (1-02) -1470 N₂ 2 = 25XrX15 1200 rpm 2 at 40 Hz Ne = 2553 7sars 1677 opin. 30 Hg = 1500x5=1936.5 3 spm 2 150oXS = 2371 2 spm 2 2003 Na