Brainscape's Knowledge GenomeTM

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


See full index

Power System Studies > MOTOR ACCELERATION STUDY > Flashcards

MOTOR ACCELERATION STUDY Flashcards

1
Q

TORQUE FORMULA

A

TORQUE=(VOLTAGE)^2

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

WHAT IS SLIP?

A

DIFFERENCE BETWEEN ROTATING MAGNETIC FIELD SPEED AND ROTOR MAGNETIC FIELD SPEED

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

WHY MAGNETIZING CURRENT OF MOTOR IS GREATER THAN MAGNETIZING CURRENT OF TRAFO?

A

BECAUSE PERMEABILITY OF MOTOR IS LESS WHILE PERMEABILITY OF TRAFO IS HIGH

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

WHICH HAS HIGHER PERMEABILTY ,TRAFO OR MOTOR?

A

TRAFO

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

WHICH NEEDS HIGHER MAGNETIZING CURRENT MOTOR OR TRAFO?WHY

A

MOTOR BECAUSE PERMEABILTY OF MOTOR IS LESS

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

LOAD TORQUE CHARECTERISTICS SHOULD BE HIGER OR LESS THAN MOTOR LOAD CHARACTERISTIC

A

LESS THAN MOTOR LOAD CHARECTERISTIC

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

MOTOR WONT START IF

A

MECHANICAL TORQUE IS GREATER THAN ELECTRICAL TORQUE

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

MOTOR ACCELERATES AND START IF

A

ELECTRICAL TORQUE IS GREATER THAN MECHANICAL TORQUE

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

MOTOR MAY STALL IF

A

ELECTRICAL TORQUE EQUAL TO MECHANICAL TORQUE

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

WHAT ARE THE THINGS ARE PROVIDED BY STATIC MOTOR STARTING STUDY

A

1) MOTOR’S STARTING CURRENT
2) VOLTAGE AT MOTOR TERMINAL DURING STARTING
3) STARTING POWER FACTOR OF MOTOR

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

IF MOTOR STARTS IN STATIC MOTOR STARTING STUDIES

A

IT WILL DEFINITELY START INDYNAMIC MOTOR STARTING STUDIES

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

FORMULA FOR MOTOR EFFICIENCY?

A

EFFICIENCY= OUTPUT POWER(MECHANICAL)/INPUT

POWER(ELECTICAL)

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

EFFICIENCY OF MOTOR IS DETERMINED BY

A

2 TYPES OF LOSSES

1) FIXED LOSSES-INDEPENDENT OF LOAD
2) VARIABLE LOSSES-DEPENDENT ON LOAD

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

FACTORS BEHIND FIXED LOSSES

A

1) LOSSES DUE TO CORE MAGNETIZATION(HYSTERISIS AND EDDY CURRENT LOSSES)\
2) FRICTION LOSSES
3) WINDAGE LOSSES

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

FACTORS BEHIND VARIABLE LOSSES

A

1) STATOR i^2R LOSS(DEPENDS ON MOTOR LOAD AND MAGNETIZING CURRENT)
2) ROTOR i^2R LOSS(DEPENDS ON MOTOR LOAD)
3) STRAY LOSSES( IS AND IEC STANDARDS TAKES FIXED VALUE AS 0.5% OF INPUT FOR THIS LOSS)

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

ELECTRICAL POWER (P) FORMULA?

A

P=SQR ROOT OF 3 VI* COS (PI) AND P= APPARENT POWER * COS(PI)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

APPARENT POWER FORMULA?

A

APPARENT POWER =SQR ROOT OF 3VOLTAGELINE CURRENT(IL) OR POWER TRIANGLE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

(KVA AMPS) i FORMULA?

A

I= RATED MECHANICAL POWER / EFFICIENCY*PF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

WHAT IS SERVICE FACTOR?

A

;;NEED A PROPER EXPLANATION

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

SLIP FORMULA?

A

SYNCHRONOUS SPEED-(MINUS) ROTOR SPEED/SYCHRONOUS SPEED

SLIP=(Ns - ROTOR SPEED)/Ns

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

IF MOTOR LOADING INCREASES WHAT HAPPENS TO LOSSES AND EFFICIENCY?

A

LOSSES INCREASES AND EFFICIENCY DECREASES

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

FAULT CURRENT FORMULA?(LRA)

A

LRA =FLA/%Z WHEREAS %Z = X’’

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

X’’=%Z AND X’’ FORMULA

A

X’’= (FLA/LRC) * (100 IF NECCESARRY)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

(LRC FAULT CURRENT’S KVA) FORMULA?

A

LRC’S APPAERNT POWER =1.732VLRC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

1 HP IS EQUAL TO

A

1 HP=0.746 TIMES OF KW(MECHANICAL OUTPUT)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

HOW WILL YOU CONVERT MECHANICAL OUTPUT POWER 34 KW OF MOTOR INTO HP HORSE POWER?

A

HP=34(KW)/0.746

since 1 HP = 0.746 TIMES OF KW(MECHANICAL OUTPUT)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

TORQUE FORMULA ?

A

T = (9.55* MECHANICAL RATING )/RATED SPEED OF ROTOR

UNIT CAN BE IN N-M OR KN-M

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

MAXIMUM BREAK DOWN TORQUE IS SAME AS

A

PULL OUT TORQUE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

AT MOTOR STARTING CONDITION MOTOR ACT AS WHAT TYPE OF LOAD?

A

CONSTANT IMPEDANCE LOAD

NOTE: (VOLTAGE DECREASES STARTING CURRENT DECREASES)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

WHEN WE NEED STARTER FOR MOTOR?

A

IF MOTOR BUS VOLTAGE IS NOT WITHIN LIMITS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

WORST CASE SCENERIO FOR MOTOR STARTING STUDIES

A

CONSIDER BASE LOAD AT TIME OF MOTOR STARTING

CONNECTED TRAFO MUST BE FULLY LOADED UNDER THIS CONDITION

32
Q

PERFORM MOTOR STARTING STUDIES FOR (WORST CASE SCENERIO)

A

1) FOR HIGHEST RATED MOTOR SINCE HIGH FLA RESULTS IN HIGH LRC WHICH CAUSES MAXIMUM VOLTAGE DIP(THIS CONDITION AFFECTS OTHER RUNNING LOADS COZ OF VOLTAGE DIP AT COMMON BUS CONNECTED TO LOAD)
2) SMALL MOTOR WITH LONGEST CABLE LENGTH(IT WILL NOT AFFECT OTHER RUNNING LOADS SINCE COMMON BUS VOLTAGE REMAINS UNAFFECTED BUT IT WILL AFFECT SMALL MOTOR ITSELF COZ OF VOLTAGE DIP AT MOTOR TERMINAL)

33
Q

What motor is this which

1) Draws high starting current
2) low rotor resistance
3) has low starting torque
4) rotor heating is low at start
5) Leakage reactance is low

A

Single cage induction motor

34
Q

What motor is this which

1) Draws low starting current
2) high rotor resistance
3) has high starting torque
4) rotor heating is high at start
5) Leakage reactance is high

A

Double cage induction motor

35
Q

what are the purpose of motor starting studies?

A

1) to know voltage dip
2) to know starting current
3) helps us to provide input for protection
4) to know current drawn by motor

36
Q

what is static motor study?

A

it is nothing but load flow study at motor starting, before motor starting, after motor starting.
it is performed when motor data is not available

37
Q

what are the inputs required for static motor stating study?

A

1) grid short circuit current
2) motor parameters(kw, kva,v)
3) normal load flow parameters

38
Q

what are the inputs required for dynamic motor stating study?

A

1) motor model
2) motor type
3) what kind of load
3) inertia of the system
4) resistance and reactance of motor
5) load characteristics of motor

39
Q

why inertia of system is so important?

A

because it determines the acceleration time of motor

40
Q

what happens if inertia is higher?

A

motor will take long time to start

41
Q

what happens if motor takes long time to start?

A

larger the current(starting current) is needed to start a motor.it causes temp rise which cause to exceed thermal limit of motor, thermal damage, insulation damage.

42
Q

what is a breakdown torque?

A

maximum torque a motor able to produce

43
Q

what is an advantage of double cage induction motor?

A

1) it provides high starting torque and low starting current during starting
2) it provides good operating efficiency and speed regulation during running condition

44
Q

what is the criteria for motor starting study?

A

As per std we should perform motor starting study if

1) motor kva rating(HP) exceeds 30% of base kva rating of supply trafo
2) motor kva rating(HP) exceeds 10% to 15% of generator kva rating

45
Q

what is the other name for static motor study?

A

voltage drop snap shot study

46
Q

what are the output given by dynamic motor starting study?

A

1) accelaration time
2) accelaration torque
3) voltage
4) load torque
5) motor torque
6) speed of motor
7) slip of motor
8) current
9) frequency
10) regulator response
12) exciter operation
13) governor action

47
Q

if there is high voltage drop at pcc what happens to short circuit current?

A

short circuit current decrease

48
Q

motor starting study should be performed at which s.c. current?

A

in both max and min s.c.current

49
Q

what is a weak system?

A

it has high source impedance , low s.c. current, high voltage drop

50
Q

what is a stong system?

A

it has low source impedance , high s.c. current, low voltage drop

51
Q

if voltage drop beyond required limit during motor starting study what is remedy?

A

starters

52
Q

FLA FORMULA

A

KW/1.732VPF*efficiency

kw= mechanical output

53
Q

Torque formula

A

9550*kw/rotor speed

54
Q

what other methods you can use to decrease voltage drop

A

1) increasing cable size(only in lv not mv)
2) adjusting transformer impedance(but effect will be minimum)
3) adjusting OLTC level

55
Q

what is W*R^2?

A

inertia
w- weight of motor
R- radius
H-inertia constant

56
Q

what is the relationship between speed and slip

A

speed is inversely proportional to slip

57
Q

what is acceleration torque?

A

difference between motor torque and load torque

58
Q

motor should be chosen based on what?

A

load inertia

59
Q

how will reduce acceleration time of motor?

A

by giving lower inertia of

60
Q

if load is 30kw how we should model motor?

A

we should oversize the motor to make it run at 80% of its full load

61
Q

what will you do if you don’t have R and X parameters for dynamic motor starting study?

A

perform dynamic motor starting study by going for characteristic modelling by obtaining data for torque-slip characteristic data(by knowing torque, PF, current and slip)

62
Q

what are types of motor connected loads?

A

1) constant torque
2) constant horse power
3) variable torque

63
Q

what is constant torque load and eg?

A

it has same torque at all speeds. but horse power varies with speed

about 90% of all application except pump

eg: conveyors, hoisting load, surface winding machines ,positive displacement pumps, piston, screw compressor

64
Q

what is constant horsepower load and eg?

A

it has high torque at lower speed and low torque at higher speed
eg: lathes, milling machine, drill press and center winders

65
Q

what is variable torque load and eg?

A

torque varies to the square of speed and horse power requirements increase as the cube of speed.

eg: centrifugal pump, turbine pump, centrifugal blowers, fans, and centrifugal compressors

66
Q

objective of motor starting study?

A

1) to check whether motor starts or not during load condition
2) TO find whether there is disturbance to other loads which are connected, because of voltage dip during starting

67
Q

why sometimes motor cannot start?

A

1while starting motor takes huge starting current which results in voltage drop in network due to transformer impedance and cable impedance. since Torque=V^2.while starting if voltage drop increase then electrical torque is decreased and if electric torque is less than mechanical torque required by motor then motor wont able to accelerate with connected load( Te

68
Q

from where you will get load model parameters?

A

from mechanical team

69
Q

what is the output of motor starting study?

A

1) voltage dip during motor starting
2) motor starting current
3) motor starting power factor

70
Q

advantages of slip ring motor?

A

1 )external resistance circuit so speed control is possible

2) starting torque is high
3) less starting current and PF

71
Q

disadvantages of slip ring motor?

A

1) copper loss is high
2) efficiency is low
3) requires much maintainence

72
Q

application of slip ring motor?

A

in high torque applications

73
Q

advantages of squirrel cage motor?

A

1) construction is simple
2) efficiency is high
3) less maintainence

74
Q

disadvantages of squirrel cage motor?

A

1) starting torque is low
2) high starting current and pf
3) no external resistance

75
Q

Application of squirrel cage motor?

A

in low torque application

Power System Studies (10 decks)

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