Chapter 17: Motor Stopping Methods

What benefits does a braking resistor have?

1. helps stop the motor faster 2. helps control motor torque during repeated on/off motor cycling.

What is another name for electric braking?

DC injection breaking

What type of motor is dynamic breaking more commonly used with?

DC motors

___ braking is a method of motor braking in which a motor is reconnected to act as a generator immediately after it is turned off.

Dynamic

What other breaking system is used with dynamic braking in applications that require the load to be held?

Electromechanical friction breaking

What is the oldest motor stopping method?

Friction Brakes

___ is the property of matter by which a mass persists in its state of rest or motion until acted upon by an external force.

Inertia

What are the conditions for the two methods used to connect the solenoid into the circuit?

The first method is used if the solenoid has a voltage rating equal to the motor voltage rating. The second method is used if the solenoid has a voltage rating equal to the voltage between L1 and the neutral.

What conditions are required for a motor to use the plugging stop method?

The motor has to be a reversible motor the motor has to be able to be reversed at full speed.

___ should always be used on electrical braking circuits.

Total interlocking

What is electric braking?

a DC voltage is applied to the stationary windings of a motor after the AC voltage is removed.

What is used to assist a motor drive in stopping a motor when you want the motor to stop fast (especially with high inertia loads)?

a braking resistor

Dynamic braking is normally applied to DC motors because there must be access to the ___ via the brushes to take advantage of the generator action.

armature

A motor cannot be used for plugging if it cannot be reversed ___.

at full speed

DC electric braking circuits, like most DC braking circuits, use a(n) ___ circuit to change the AC into DC.

bridge rectifier

The rotating motion of the motor is transmitted to the plugging switch contacts either by a _____________ or by a ____________.

centrifugal mechanism or by a magnetic induction arrangement.

How does dynamic breaking work?

connecting the motor in this way makes the motor act as a loaded generator that develops a retarding torque, which rapidly stops the motor.

Plugging is a method of motor braking in which the motor connections are reversed so that the motor develops a(n) ___ that acts as a braking force.

countertorque

What parameter is used to Stop a motor using a motor drive?

deceleration parameter

Electromechanical ___ brakes are often used along with dynamic braking in applications that require the load to be held.

friction

What is a danger to using the plugging method to stop the motor?

heat caused by high current

What are some disadvantages to dynamic breaking

it cannot bring a motor to a complete stop and it also cannot hold a load once it is stopped because there is no braking action

What are the advantages of friction brakes?

lower initial cost and simplified maintenance

Friction brakes normally consist of two friction surfaces (shoes or pads) that come in contact with a rotor (wheel) mounted on the ___.

motor shaft

A motor and load would start to run in the opposite direction without stopping if a ___ switch were not present when braking a motor using plugging.

plugging

When using electric braking in AC induction motors, the opposing magnetic fields are induced from the stator windings into the ___ windings by transformer action.

rotor

Friction brakes are normally controlled by a(n) ___, which activates the brake shoes

solenoid

What is the braking torque directly proportional to?

surface area and spring pressure.

What size of resistor should you use in dynamic breaking and why?

the smaller the resistance of the resistor, the greater the rate of energy dissipation and the faster the motor comes to rest.

What are the disadvantages of friction brakes?

they require more maintenance than other braking methods

What is the primary function of a plugging switch?

to prevent the reversal of the load once the countertorque action of plugging has brought the load to a standstill