Introduction 3 Phase Motors

Front 1

Calculate the counter torque produced by a prony-brake producing a force of 3 N on a scale that is 2 m from the centre of the prony-brake drum

Back 1

3

Front 2

Speed regulation of a SCIM is most related to the percentage of:

Back 2

Rotational frequency change from no load to full load speeds

Front 3

Rotational frequency is measured in revolutions per minute

Back 3

True

Front 4

Calculate the percent efficiency of a 10hp motor that has total losses of 1017 watts at full load

Back 4

88%

Front 5

The stators rotating magnetic field of a squirrel cage induction motor rotates:

Back 5

At a continuous and uniform speed

Front 6

The formula to determine the mechanical power of a rotating machine is:

Back 6

P= n*T

9.55

Front 7

A difference between a WRIM and a SCIM is:

Back 7

A WRIM has insulated rotor conductors and a SCIM has uninsulated rotor conductors

Front 8

What type of motor enclosure allows outside air to cool the rotor directly

Back 8

DP

Front 9

The following information is taken from the nameplate of a motor

Volts: 208 - 230/460 V

FLC: 2.4 - 2.2/1.1 A

What is expected FLC at nominal voltage of 208v

Back 9

2.4 A

Front 10

When not used with a variable frequency drive, squirrel cage induction motors:

Back 10

Are to be constant speed motors

Front 11

Information that can be derived from an induction motors nameplate but that is not explicitly stated on the nameplate is the:

Back 11

Number of poles

Front 12

The rotor of a SCIM will turn if all rotor conductors are open circuit

Back 12

False

Front 13

When using Fleming’s left hand rule for generators:

Back 13

Forefinger = flux, Thumb = motion, Centre finger = current

Front 14

Service factor indicates the degree to which a motor can be loaded above the stamped horsepower or kilowatt power output under specific conditions

Back 14

True

Front 15

Rotor conductors in a squirrel cage induction motors are left uninsulated because:

Back 15

Rotor voltages are small and the resistance of the varnished laminations are high

Front 16

Two advantages of a wound rotor motor compared to the SCIM are

(higher/lower) starting torque and

(Higher/lower) starting current

Back 16

Higher

Lower

Front 17

Calculate the output of an induction motor producing a torque 55.73 Nm at a speed of 1,150 r/min.

The output power in horsepower is Hp.

Back 17

9

Front 18

A 4 pole, 50 Hz, SCIM has a no load speed of 1498r/min and a full load speed of 1452r/min what is the percent speed regulation?

Back 18

3.168%

Front 19

T is ________

Measured in ________

Back 19

Torque

Newton meters (Nm)

Front 20

F is __________

Measured in _______

Back 20

Force

Newtons (N)

Front 21

R is _________

Measured in _________

Back 21

Radius

Meters (m)

Front 22

P is _______

Measured in ________

Back 22

Mechanical power

Watts (w)

Front 23

n is _______

Measured in _________

Back 23

Rotational speed

r/min

Front 24

1 hp = _______w

Back 24

746

Front 25

1 hp =_________Kw

Back 25

.75

Front 26

Pf is (Inversely/proportion) to slip

Back 26

Inversely

Pf goes up as slip goes down

Front 27

Prony brake and dynamometer measure:

Back 27

A motors torque

Front 28

Losses in a induction motor are ______ and ________

Back 28

Electrical and mechanical

Front 29

Electrical losses are:

Back 29

Iron losses and copper losses

Front 30

Mechanical losses are:

Back 30

Friction and windage

Front 31

Induction motor is made of 3 main parts

Back 31

The frame

The stator

The rotor

Front 32

Frame consists of

Back 32

End brackets, bearings in the end brackets and the jb

Front 33

Stator produces a

Back 33

Rotating magnetic field

Front 34

The stator core provides

Back 34

A high permeability path for magnetism

Front 35

Pitch is:

Back 35

Span from one side of a coil to the other

Front 36

The stator windings of a 3 phase induction motor are connected to a 3 phase source to produce a rotating magnetic field. This rotating magnetic field has a_____________________

Back 36

Constant magnitude and rotated at a constant speed called synchronous speed

Front 37

For a current to be induced there must be a difference between:

Back 37

Rotor speed and synchronous speed of a stators magnetic field. This difference is called slip speed

Front 38

End rings provide current to flow from

Back 38

1 rotor bar to another

Front 39

Insulation class is the temperature tolerance of the motor windings

They have a designation of:

Back 39

H- withstand highest temperature,

A- rarely used on modern motors

B and F- are common

Front 40

Duty is:

Back 40

Amount of time that a motor can run without a cooling period

The duty affects the size of conductors and insulation of conductors

Front 41

Rotor designs are

Back 41

Design A- normal starting torque, high starting current, handle brief periods of overload

Design B- most common, normal starting torque, low starting current

Design C- high starting torque, low starting current, starting heavy loads,

Design D- high starting torque, low starting current, high inertia starts, poor speed regulation

Front 42

Slip speed is typically _____ to _____% of synchronous speed

Back 42

2-8%

Front 43

Magnetomotive force is:

Back 43

Movement of electric charges that creates magnetic flux

Front 44

Induction motor uses transformer action to:

Back 44

Transfer energy from stator to rotor

Front 45

Induction motor as transformer the secondary current is controlled by the_________

Back 45

Slip speed

Front 46

Nameplate includes the:

Back 46

Manufacturer, catalog #, specifications, serial # of motor

Front 47

Nameplate helps select:

Back 47

The overcurrent device type and size,

The starter type and size,

The overload device or setting,

Wiring means and conductor type and troubleshoot the motor

Front 48

Frame two categories:

Back 48

Fractional horsepower and integral horsepower

Front 49

The current displayed on the nameplate is what the motor can draw under___________ conditions

Back 49

Full load

Front 50

Regarding variations, the NEMA standard states:

Back 50

Voltage variations may not exceed 10%

Frequency variations may not exceed 5%

The combined variation may not exceed 10%