A DC shunt generator (20 kW, 200 V, 1800 RPM) has Ra= .1 ohm, Rfw= 150 ohm. Assu

Question

A DC shunt generator (20 kW, 200 V, 1800 RPM) has Ra= .1 ohm, Rfw= 150 ohm. Assume that Ea = Vt at no load. Data for magnetization curve at 1800 RPM are below.

If 0 0.125 0.25 0.5 0.625 0.75 0.875 1 1.25
Ea 5 33.5 67 134 160 175 190 200 214

If 1.5
Ea 223


The machine is operated at If = 1.0 A. The terminal voltage of the DC machine is 220 V and the developed torque is 100 Nm. Determine the speed of the machine when it operates as a machine and as a generator

Explanation / Answer

We know that T=0.159Ia(øPZ/A) given torque =100Nm =>100=0.159Ia(øPZ/A) =>(øPZ/A)=100/(0.159Ia) and we also know E=(øZN/60)(P/A) when operating at If=1amp we have E=200 =>200=(N/60)(100/0.159Ia) the rated current is given by Ia=20000/200=100amps =>200=(N/60)(100/15.9) =>N=1908rpm is the same speed for machine and generator..

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