Question

A separately excited DC generator supplies 150 A to a 145 V DC grid. The generator is running at 800 RPM. The armature resistance of the generator is 0.1 Ω. If the speed of the generator is increased to 1000 RPM, the current in amperes supplied by the generator to the DC grid is __________. (Give the answer up to one decimal place.)

Answer 1

I_L = 150 A

N₁ = 800 RPM, N₂ = 1000 RPM

R_a = 0.1 Ω

V_t = 145 V

I_a1 = 150 A

E_g1 = V_t + I_a1R_a

⇒ E_g1 = 145 + (150)(0.1) = 160 V

E_y ∝ N

\(\Rightarrow \frac{{{E_{g1}}}}{{{E_{g2}}}} = \frac{{{N_1}}}{{{N_2}}}\)

\(\Rightarrow \frac{{160}}{{{E_{g2}}}} = \frac{{800}}{{1000}} \Rightarrow {E_{g2}} = 200\;V\)

E_g2 = V_t + I_a2 R_a

⇒ 200 = 145 + I_a2(0.1)

⇒ I_a2 = 550 A