It means that the efficiency is maximum at a load when the copper-loss (variable loss) equals the core-loss (constant loss). Thus for maximum efficiency Copper loss(Variable loss) = Core loss(constant loss) Core loss = 450 Watt = Copper loss Cooper loss = 450 Watt
The speed of the synchronous motor is given as Ns = 120f/P Therefore by changing the number of poles and frequency, we can change the speed of the synchronous motor.
EXAMIANS