Electronics L3 Final

What is the meaning of “3 Phase (Φ) AC

3 Alternating Current Sinusoidal sign Waves with the

The speed of an AC motor is largely dependent upon two factors:

• Frequency of the incoming AC power

• Number of poles

What converts fixed voltage/frequency into adjustable voltage/frequency

• Drive controller

Main type of AC Drive

• typical three phase squirrel cage motors

six-step voltage source inverter is know as ____

Variable Voltage Inverter

four main sections of a VVI

• Converter

• Intermediate Circuit

• Inverter

• Control Circuit

What switches AC to pulsating DC

• Converter

Converter- For higher power applications, what is used?

Three-phase rectifier

Converters - Two types of three-phase rectifiers?

Controlled rectifier

Uncontrolled rectifier

What are the two types of rectifiers

• Uncontrolled

• Controlled

Intermediate Circuit Transforms the pulsating DC to a _____ DC waveform

Smooth

Intermediate Circuit Output is called the _________

DC Bus Line

Inductive Filter • LC Filter • Chopper are what

Three types of circuits typically used:

The function of the inverter is to _____ the DC bus line voltage back to a simulated AC voltage

Invert

An inverter consists of ___ electronic switching devices used to approximate a three-phase AC source for the motor

Six

(T/F) The VVI Drive inverter controls nothing but frequency.

True

________ _______ Receives the operating commands from the control panel and sets the system variables

Control Circuit

Control Circuit Generates the command pulses which turn the semiconductors ___ and ___

off and on

What Produces outputs for the control panel to display various operating conditions

Control Circuit

Control Circuit Performs an orderly shutdown procedure in the event of an ______ ______

abnormal condition

Control Circuit Operation

The speed control (________) feeds an input signal into the control circuit input terminal

rheostat

Control Circuit Operation

This control signal is delivered, (Before or after) conditioning, to a shift register

After

If the ________ of the drive voltage is changed without changing the motor voltage, the current, and therefore the torque, of the motor will _______

• frequency

• change

Voltage/Hz Ratio

To increase the torque of a motor you must _____ the frequency

Lower

the motor may overheat from excessive current if the Frequency is too (High or Low)

Low

____ _____ ____ Ratio is used to maintain constant current and torque under varying frequency conditions

voltage-to-frequency ratio

Drive Functions

provides soft start or ramping =

Acceleration

Drive Functions

rapid stopping of the motor

Deceleration

Drive Functions

alters the start/stop curve of the motor

S-Curve

What type of motor controller that drives an electric motor by varying the frequency and voltage supplied to the electric motor.

VFD- Variable Frequency Drive

What are the 4 other names for a VFD

• variable speed drive

• adjustable speed drive,

• adjustable frequency drive,

• AC drive

In a VFD the Frequency is directly related to the motors _______

• Speed (RPM)

when using a VFD, to increase the speed of a motor you must____ ___ _____

• Increase the Frequency

Why is a VFD good if the load does not require the full power of the motor

The VFD can adjust the speed of the motor to meet the requirements of the load

What is the first stage of a VFD

• Converter

How many Diodes are in the Converter of a VFD

• 6 (Full wave)

The Converter (6 Diodes) allows the Current to flow in what direction (both or one)

• One Direction

We can get rid of the AC ripple on the DC bus

• by adding a capacitor

capacitor absorbs the ac ripple and delivers a ______ dc voltage

smooth

The AC ripple on the DC bus is typically less than ____ Volts

• 3

The actual voltage will depend on the voltage level of the _____ feeding the drive

• AC line

When we close one of the bottom switches in the converter, that phase is connected to the negative dc bus and becomes ________. (Positive or Negative)

• negative

True or false

we can make any phase on the motor become positive or negative at will and can thus generate any frequency that we want.

True

we can make any phase be _____. _____ or _____

• Positive

• Negative

• Zero

the waveform of a VFD is _______ wave form

• Rectangular

VFD’s do not produce a _______output

• sinusoidal

This ________ waveform would not be a good choice for a general purpose distribution system, but is perfectly adequate for a motor

• rectangular

How do we reduce the motor frequency to 30 Hz

simply switch the inverter output transistors more slowly

if we reduce the frequency to 30Hz, what must we do?

• we must also reduce the voltage to 240V in order to maintain the V/Hz ratio

What is PWM

• Pulse Width Modulation

IGBT

Transistor

How are we going to reduce the voltage if the only voltage we have is 650VDC?

Use a PWM (Pulse Wave Modulation)

Why Should I Use A VFD?

Reduce Energy Consumption and Energy Costs

VFDs allow you to _____ the speed of the motor-driven equipment to the load requirement.

Match

What are the other methods of AC electric motor control

• There are none

Electric motor systems are responsible for more than ___ of the power consumption in industry today.

65%

Optimizing __________ by installing or upgrading to ___ can reduce energy consumption in your facility by as much as ____%

• motor control systems

• VFDs

• 70%

VFD On conveyors and belts you eliminate _____

jerks on start-up.

To make equipment will last longer and have less downtime due to maintenance you should install a _____

VFD

When you start a load with a VFD you will not subject the motor or driven load to the ____ _____

instant shock”

VFDS allow the motor to start ______

Slow and smoothly

If you use a VFD you can …..

A) Drive a sports car

B) Date the Prom queen

C) All of the above

All of the above

The half-wave rectifier is constructed by inserting a diode in s______ with a load

Series

When voltage becomes negative at the anode, the diode turns _____

off

Although the voltage is pulsating or turning on and off, it never _____ direction.

Reverses

Three-phase rectifiers can be divided into two types:

half-wave and the bridge

DC machines can be either

-DC generators

-DC motors

What convert mechanical energy into electrical energy

DC generators

What converts the electrical energy into mechanical energy

DC motor

Different Types of DC Motors

• Series

• Shunt

• Compound

How is a DC shunt Motor connected

Parallel

What are the 6 main parts of a DC Motor

• Yoke

• Field Winding

• Poles

• Armature

• Commutator

• Brushes

DC Series Motor is connected in

• Series

if the field current is the same as the Armature current, what type of motor is it

• Series

Is the resistance of a series field winding Smaller or larger compared to that of the armature resistance

• smaller

What are the types of Compound Motors

• Long Shunt Compound

• Short Shunt Compound

How is a Long Shunt motor connected

long shunt dc motor, shunt field winding is connected across the series combination of the armature and series field winding

How is a Short Shunt motor connected

armature and field windings are connected in parallel with each other and this combination is connected in series with the series filed winding.

How are the Series and Shunt winding connected in a cumulative compound motor?

• series and a shunt winding, are connected in the same direction to add together

How are the Series and Shunt winding connected in a differential compound motor?

• the shunt winding is connected in parallel with the armature, while the series winding is connected in series with the armature

Shunt Motor Applications

What type of motor has constant speed control?

Shunt Motor

Which device converts mechanical energy into DC electrical energy? 
a. an alternator 
b generator

c. a motor 
d. an inverter 

a generator

2. The rotating part of a generator is called the _____. 
a. stator 
b. field 
c. armature 
d. exciter 

armature

3. What is the component of a DC generator that converts the armature AC into DC? 
a. commutator 
b. alternator 
c. converter 
d. field 

commutator 

4. Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. 
Which type of winding provides low voltage and high current? 
a. frogleg-wound 
b. lap-wound 
c. wave-wound 
d. brush-wound

lap-wound

5. Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. 
Which type of winding provides high voltage and low current? 
a. frogleg-wound 
b. lap-wound 
c. wave-wound 
d. brush-wound 

wave-wound 

6. Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. 
Which type of winding provides moderate voltage and moderate current? 
a. frogleg-wound 
b. lap-wound 
c. wave-wound 
d. brush-wound 

frogleg-wound 

The _____ ride against the commutator segments and are used to connect the armature to the external circuit of the DC 
machine. 
a. field windings 
b. pole pieces 
c. armature windings 
d. brushes 

brushes 

What provide(s) the magnetic field necessary for the operation of a DC machine? 
a. brushes 
b. pole pieces 
c. the armature 
d. the case 

pole pieces

Series field windings are connected in series with the armature. They are wound with _____ turns of fairly _____ wire. 
a. many; large 
b. many; small 
c. few; large 
d. few; small 

few; large 

Shunt field windings are connected in parallel with the armature. They are wound with _____ turns of fairly _____ 
wire. 
a. many; large 
b. few; large 
c. many; small 
d. few; small 

many; small 

11. The series generator has only a series field, which is connected _____ with the armature. 
a. in series 
b. in parallel 
c. cumulatively 
d. differentially

a. in series 

Shunt generators contain only a shunt field winding connected _____ with the armature. 
a. in series 
b. in parallel 
c. cumulatively 
d. differentially 

in parallel

The output voltage of a generator is usually controlled by the amount of _____. 
a. field excitation current 
b. input voltage 
c. input torque 
d. armature excitation current 

field excitation current 

14. A generator containing both series and shunt fields is called a _____ generator. 
a. self-excited 
b. separately excited 
c. complex 
d. compound

compound

15 The relationship of the strengths of the two fields in a generator determines the amount of _____.

a. complexing

b. compounding

c. exciting

d. differential setting

compounding