Intro To Motors

Question 1

Counter torque produced by dynamometer or peony brake is product of two mechanical quantities

Answer 1

Force
Radius

Question 2

Mechanical power is product of two mech quantities

Answer 2

Torque
Number of turns (speed)

Question 3

Losses in a motor
Electrical and mechanical?

Answer 3

Elec-iron losses and copper
Mech-friction and windage

Question 4

Wound rotor motor (WRM)

Answer 4

Terminates in slip rings
•carbon brushes , adjustable resistance
•increase motor start torque , decrease start current

Question 5

Squirrel cage motor
Most common

Answer 5

Rotor bars ( slanted to prevent mag locking)
•bars r permanently shorted by end rings
•can’t add external resistance

Question 6

IEC name for Rotor speed

Answer 6

Rotational frequency

Question 7

Stator core of induction ion motor has thin silicon steel laminations for what purpose?

Answer 7

Reduce electrical power loss

Question 8

The end rings of squirrel cage rotor do ?

Answer 8

Path for rotor currents to flow

Question 9

Electrical frequency is low at no load speed. This produces?

Answer 9

Low electrical losses
Hysterisis and copper

Question 10

Fractional horsepower frames

Answer 10

42,48,56

Question 11

Alphanumeric code 215T frame

Answer 11

Mounting arrangements
Mounting hole placement
Frame dimension

Question 12

Nema standards nameplate

Answer 12

Voltage not exceed 10%
Frequency 5%
Combined 10%

Question 13

Mech load is lower= current lower

Answer 13

More current=less voltage

Question 14

Insulation class

Answer 14

Class h - high temp
Class A- rare
Class B and F -common

Question 15

Nema starting code

Answer 15

A - low starting current
V- high starting current
H-6.8-7.09 kva per horsepower

Question 16

Service factor

Answer 16

1.15 or greater = 125% fla
1.15 or less = 115% fla

Question 17

Slip percent of sync

Answer 17

2-5% sync speed

Question 18

Rotor frequency formula
Rotor reactance formula

Answer 18

F= s x f(br)
X= s x X(br)

Question 19

Wound rotor motor

Answer 19

Best starting torque , low current and full load eff
• con cost alot