Section 3 (Jasons notes)

For constant-horsepower loads, what is the relationship between horsepower and speed?

Horsepower is constant at any speed.

What is accomplished by using drives for a motor?

Increased run and cost efficiency

For constant torque loads, horsepower is directly proportional to the motors ___________.

Speed

What 3 things must be considered when selecting a drive for a certain application?

Speed, torque, and horsepower (Load characteristics of the application)

An example of application of constant-horsepower loads is a machine called a ________.

lathe

In a __________ __________ ____________, a variable resistor is used to increase voltage and current in either the field winding to affect the motor's speed. If voltage and current are increased in the field winding the motor's speed will ___________.

DC shunt motor Decrease

What is the most effective and efficient method of stopping an AC motor and is used to stop high speed, high inertia loads?

Dc injection braking

Variable-torque loads can be used for what 3 applications?

Fans, pumps, and blowers

_____________ use dynamic braking to lift heavy loads that are difficult to stop.

Forklifts

Variable-torque loads require lower torque at _____1_____speeds and high torque at ____2_____ speeds.

1) low 2)high

To use a motor as a brake, a drive will insert resistance to the stator field which is known as _____1_____. Once deenergized, the motor is immediately rewired to run as a _____2_____.

1)dynamic braking 2)generator

To change the speed of an AC motor either the ________1_________ or the _____________2____________ must be changed

1)frequency 2)number of poles (number is set by manufacturer)

Drives allow motors to change speed, direction, and torque . In this capacity, a drive can allow a motor to function as a _______1_______ or a ___2___.

1)generator 2)brake

Constant-horsepower loads require high torque at ____1____ speed and low torque at ____2____ speed.

1)low 2)high

For Variable-torque loads, horsepower increases proportionally with ____1_____ and _____2______.

1)torque 2)speed

To change the speed of a DC shunt motor which method is more expensive. Which method loses torque?

Adding a rheostat to the armature of a motor is more expensive. (And electrically inefficient) Adding resistance to the field windings loses torque

__________ are the best representation of constant-torque loads

Conveyers

Most motors have a _________ ______ connected directly to the motor that rotates at rotor speed cooling the stator as the motor runs and dissipates heat.

Cooling fan

To adjust the speed of a _______ __________ ____________ resistance must be inserted to the field or armature windings.

DC Shunt motor

______________ applies DC voltage to the stator of an AC motor after AC has been removed from the motor. (To stop the motor)

DC injection braking

To change the speed of an AC motor, _________ are used to change the frequency of the source voltage.

VFDs

While changing the speed of an AC motor, the ratio of what two things must be maintained?

Voltage and frequency

Dynamic breaking (can/cannot) completely stop a motor

cannot

Because a load cannot be completely stopped or held by dynamic braking, _______________ ____________ ____________are used in coordination with this drive setting .

electromagnetic friction brakes