Electric Machines Speed-Torque Characteristics

Questions and Answers

In which type of load is the load torque proportional to the square of the speed?

Fans and rotary pumps

What type of speed-torque characteristics are exhibited by certain types of lathes, boring machines, and steel mill coilers?

Hyperbolic speed-torque characteristics

For separately excited DC generators connected to a constant resistance load, what are the speed torque characteristics?

Linear rising characteristics

What does the speed/torque characteristic equation T = To + (TR - TO) / (nr)^(x) help determine?

The relationship between motor speed and load torque Signup and view all the answers

In the context of the speed/torque characteristics, what does it mean if x = 0 in the equation T = To + (TR - TO) / (nr)^(x)?

The load torque remains constant regardless of speed Signup and view all the answers

What does the exponential factor 'x' in the speed/torque characteristic equation represent?

The change in the resisting torque with change in speed Signup and view all the answers

What happens to the armature during dynamic braking of a compound motor?

It is disconnected from the supply and connected across the braking resistor Signup and view all the answers

How does the magnetizing force of the series field winding vary in the counter current braking of a compound motor?

It varies linearly with armature current Signup and view all the answers

What happens to the speed torque characteristics during regenerative braking of a compound motor?

It forms a straight line Signup and view all the answers

Why is the series field winding of a compound motor connected like a shunt motor during regenerative braking?

To avoid demagnetization of the motor Signup and view all the answers

Study Notes

Load Torque Characteristics

Load torque is proportional to the square of the speed in a quadratic load.

Speed-Torque Characteristics

Certain types of lathes, boring machines, and steel mill coilers exhibit a quadratic speed-torque characteristic.

Separately Excited DC Generators

Separately excited DC generators connected to a constant resistance load have a linear speed-torque characteristic.

Speed-Torque Characteristic Equation

The equation T = To + (TR - TO) / (nr)^(x) helps determine the speed-torque characteristic of a motor.
If x = 0 in the equation, it means the speed-torque characteristic is linear.
The exponential factor 'x' in the speed-torque characteristic equation represents the type of load.

Compound Motor Braking

During dynamic braking of a compound motor, the armature acts as a generator.
During counter-current braking of a compound motor, the magnetizing force of the series field winding varies inversely with the speed.
During regenerative braking of a compound motor, the speed-torque characteristic becomes linear.
The series field winding of a compound motor is connected like a shunt motor during regenerative braking to achieve a linear speed-torque characteristic.