A 1000-kW generator has a 3500-lb rotor that is accelerated from rest to 3600 rpm in 10 seconds. Determine the torque required. Assume the rotor to be a solid cylinder 40 in. in diameter.
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First, we need to convert the rotational speed from revolutions per minute (rpm) to radians per second (rad/s) because the formula for torque requires the angular speed in rad/s.
1 revolution = 2π radians
1 minute = 60 seconds
So, 3600 rpm = 3600 * (2π / 60) = 377 rad/s
The moment of inertia (I) for a solid cylinder is given by the formula I = 0.5 * m * r^2, where m is the mass and r is the radius.
First, we need to convert the mass from pounds (lb) to kilograms (kg) because the formula for moment of inertia requires the mass in kg.
1 lb = 0.453592 kg
So, 3500 lb = 3500 * 0.453592 = 1587.57 kg
Next, we need to convert the diameter to radius and from inches to meters because the formula for moment of inertia requires the radius in meters.
1 inch = 0.0254 meters
So, 40 in. = 40 * 0.0254 = 1.016 m
The radius is half the diameter, so r = 1.016 / 2 = 0.508 m
Now we can calculate the moment of inertia:
I = 0.5 * 1587.57 kg * (0.508 m)^2 = 204.4 kg*m^2
The angular acceleration (α) can be calculated by dividing the change in angular speed by the time it takes for the change to occur.
α = (377 rad/s - 0 rad/s) / 10 s = 37.7 rad/s^2
Finally, we can calculate the torque (τ) using the formula τ = I * α:
τ = 204.4 kg*m^2 * 37.7 rad/s^2 = 7703.88 N*m
So, the torque required is approximately 7704 N*m.