A 220 V DC machine supplies 20 A at 200 V as a generator.

A 220 V DC machine supplies 20 A at 200 V as a generator. The armature resistance is 0.2 ohm. If the machine is now operated as a motor at same terminal voltage and current but with the flux increased by 10%, then ratio of motor speed to generator speed is

For Generator, E = V + I_a R_a
= 200 + 20 × 0.2 = 204 V
For Motor, V = E – I_a R_a
E = 200 – 20 × 0.2 = 196 V

∴	E₁	=	N₁	×	φ₁
	E₂		N₂		φ₂

⇒	204	=	N₁	×	1
	196		N₂		11

and	N₂	=	196	= 0.87
	N₁		204 × 1.1