Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

xxxAEIS > AC Systems > Flashcards

AC Systems Flashcards

1
Q

constant speed drive purpose

A

alternator will produce constant output frequency and voltage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is an IDG and what is its purpose

A

integrated drive generator

CSD and generator are mounted side by side to form 1 compact unit

prevents overheating & save space

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

difference between alternators and generators

A

alternators - field rotates

generators - armature rotates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

advantages of brushless generators

A

low maintenance cost - no slip rings or brushes

minimize chance of sparking of high current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

how to express emf VR, VY, VB in phasor form

A

VR = V < 0

VY = V < -120

VB = V < -240

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

impedance formula

A

Z = R + XL + XC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

formula for capacitance and inductance

A

XC = 1/ (j2pi * f * C)

XL = j2pi * f * L

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

I phase formula using Z

A

I phase = V phase / Z

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

balance star load, neutral wire how many amps?

A

0 A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

if is balance star load, what would be equal?

A

ZR = ZY = ZB

current will be similar

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

total apparent power formula

A

sqrt3 (V line * I line)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

total reactive power formula

A

sqrt 3 (V line * I line * sin theta)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

wattmeter formulas

A

W1 + W2 = sqrt 3 (VL * IL * cos theta)

W1 - W2 = VL * IL * sin theta

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

wattmeter formulas to find tan theta and cos theta (PF)

A

tan theta = sqrt 3 ( (W1 - W2)/(W1 + W2) )

power factor = cos theta = cos( arctan( sqrt3( (W1 - W2)/(W1 + W2) )))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is a motor

A

motor takes in electrical energy and converts it to mechanical energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

why are electric motors not 100% efficient?

A

electric energy is lost in the form of heat, from I^2R losses

17
Q

what equipment can be used to start synchronous motor?

A

pony motor starter

18
Q

are synchronous motors self starting

A

no, needs power supplied to rotor to start rotating

19
Q

how does induction motor works?

A

rotor flux interacts will rotating (main) flux, creating mechanical force that causes rotor to rotate in the same direction as magnetic field

20
Q

why does induction motors need to have slip? and what is slip

A

slip is the difference between magnetic field rotation and rotor’s rotating speed

if induction motor have slip = 0, there will be no flux cut as both field and rotor will be stationary wrt e/o

21
Q

advantages & disadvantages of single phase motor

A

adv:

1) small and cheap
2) no need 3 phase supply

disadv:

1) cannot self-start
2) creating a pulsating torque
3) less efficient

22
Q

how does resistance-split motor works?

A
  • starter winding’s current lags voltage by much less than 90deg
  • phase difference causes starter winding to be energised before main winding
  • centrifugal switch opens at 25% rated speed, disconnect starter winding
23
Q

how does capacitor-split motor work?

A
  • offsets inductance causes even greater phase shift between currents
  • used where good starting torque is important
  • centrifugal switch open at 25% rated speed
24
Q

how does shaded pole motor work?

A
  • increases inductance of copper ring’s shaded part
  • energies unshaded parts of poles first, creating magnetic fields in these areas
  • shaded magnetic field to lag behind unshaded magnetic field, creating rotational effect
25
Q

what is VVVF and its purpose

A

variable-voltage variable-frequency drive

control the speed and torque of ac motor

26
Q

parts of VVVF drive

A 
input power
bridge rectifier
filter
control circuit & inverter
pulse-width modulated (PWM) power
27
Q

what does a rectifier do

A

converts AC input to DC outputs

28
Q

what does a capacitor do in a rectifier?

A

during +ve half cycles: stores charge

during - ve half cycles: discharges

maintain constant output voltage across R

to reduce ripple, discharge time constant is increased

29
Q

silicon-controlled rectifier states of operation

A

1) forward blocking
2) reverse blocking
3) forward conducting

30
Q

auto transformer used for

A

circuits requiring only a small step-up or step-down of voltage

31
Q

an ac brushless generator is excited by the used of?

A

dc field exciter

32
Q

parts of a AC brushless generator

A

DC exciter
AC exciter
Rotating Rectifier assembly (rotor)
Main generator (AC output stator)

33
Q

why is alternator better than armature generator?

A 
rotating assembly (field winding) is lighter so easier to rotate
thicker conductors can be used to carry larger current and easier to cool down
34
Q

AC generator +ve and-ve sequence

A

+ve: RYB

-ve: RBY

xxxAEIS (9 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions