Three Phase

Question 1

To reverse the rotation direction of the magnetic field

Answer 1

Just reverse any two leads of a three phase motor

Question 2

A four pole three phase motor has how many coils

Answer 2

12

Question 3

The torque on the rotor depends on how fast the rotor drifts…

Answer 3

Backwards through the rotating magnetic field

Question 4

The speed at which the magnetic field rotates is called the

Answer 4

Synchronous speed of the motor

Question 5

On starting, the slip of the motor is at …

Answer 5

100%

Question 6

In general the power factor of an induction motor increases with the load until the maximum power factor is reached at

Answer 6

Full load

Question 7

Maximum torque is always developed when the phase angle is at

Answer 7

45 degrees

Question 8

The rotor of a squirrel cage induction motor has four basic parts…

Answer 8

Core, conductors, end rings, shaft

Question 9

Low starting torque is a result of the low resistance and high…

Answer 9

Reactance of the rotor

Question 10

The wound rotor motor is always started with blank blank in the rotor circuit

Answer 10

Maximum resistance

Question 11

The life of a motor is determined largely by the

Answer 11

Life of its insulation

Question 12

A synchronous motor requires two sources of electric power…

Answer 12

One ac and one D.C.

Question 13

When the D.C. Power is applied to the rotor, a set of what is produced

Answer 13

North and south poles

Question 14

With a low D.C. Field current the ac current in the armature blanks the applied ac potential difference

Answer 14

Lags

Question 15

Slipping a pole causes a blank of current in the D.C. Line during the blank period

Answer 15

Surge, slipping

Question 16

Increasing the D.C. Current in the rotor winding increases the phase angle in the

Answer 16

Lagging direction thus reducing the power factor

Question 17

A motor with a single winding can be connected for either…

Answer 17

Four pole or eight pole operation

Question 18

Variable torque motors do what

Answer 18

Designed to give an increase in torque with an increase in speed

Question 19

In a constant horsepower motor the torque…

Answer 19

Doubles when the speed is cut in half so the power delivered by the motor remains unchanged

Question 20

A two parallel Y connection requires a blank potential difference than a series Y connection

Answer 20

Lower

Question 21

Avoid using too much solvent because it can

Answer 21

Flow into places too difficult to remove, and if left too long could damage insulation

Question 22

The standard temp for measuring insulation resistance is

Answer 22

40 degrees C, 104 degrees F

Question 23

The first symptom of an open rotor circuit is a lack of

Answer 23

Torque, the speed decreases and the motor makes a growling noise

Question 24

Angular loads are a combination of

Answer 24

Radial and thrust loads

Question 25

For the average service conditions bearings may be safely operated at temperatures up to...

Answer 25

95 degrees C, 200 degrees F

Question 26

The capacity of the power supply limits the size of a blank that may be started across the line

Answer 26

Motor

Question 27

At full load a motor will develop its rated power, draw its rated current, and run with its rated power factor, but with that there will be a

Answer 27

Rise in the motors internal temperature

Question 28

The max torque a motor can deliver is usually

Answer 28

150 to 225% of the rated full load torque | Ex. Rated at 2HP full load can make 3 to 4.5 HP

Question 29

Connecting an inductor in series with the motor windings is another method of

Answer 29

Reducing the starting current

Question 30

The inductor adds inductive reactance to the circuit which is the basis for the name

Answer 30

Reactor starter

Question 31

To ensure that a three phase motor control equipment is in good operating condition you should

Answer 31

Maintain a regular and systematic plan of inspections

Question 32

When the starter contacts drop out when the potential difference across the line falls too low, is called...

Answer 32

Low voltage release

Question 33

During plugging the current in an induction motor is higher than the locked rotor current. Blank blank is about three times the loss during normal starting

Answer 33

Power loss

Question 34

What provides both backspin protection and surge protection when the motor stops

Answer 34

Off delay relay

Question 35

What provides surge protection when the motor starts

Answer 35

On delay relay

Question 36

The blank provide a reduced potential difference across the motor windings for starting

Answer 36

Autotransformers

Question 37

Which method of starting produces the smoothest starting conditions of any of the methods of starting

Answer 37

Reactance starting

Question 38

When a large number of steps is required to start what must be used

Answer 38

Resistance starting

Question 39

What kind of winding can be a part of either the rotor or the stator in the alternator

Answer 39

Supply winding

Question 40

The armature of an alternator always has the blank number of poles as the blank winding

Answer 40

Same, field

Question 41

The current an alternator can conduct without overheating is determined by the size of the

Answer 41

Conductors in the winding

Question 42

If the load is inductive the current blanks the voltage

Answer 42

Lags

Question 43

If the armature of an alternator has four poles, how many poles does the field winding have

Answer 43

Four

Question 44

Interlocks can be used in motor starting circuits so the motors can be started in a sertain sequence, the largest motor is started...

Answer 44

First

Question 45

Power failure relays act if the potential difference across any phase drops below blank or less of the rated value

Answer 45

70%

Question 46

Whenever an auxiliary generator starts it should run until when

Answer 46

All parts reach their normal operating temperature

Question 47

When only one cranking period is provided it duration should be how long

Answer 47

At least 15 seconds

Question 48

If more than one cranking period is provided each period should last how long

Answer 48

At least 7 seconds

Question 49

When making a schedule for inspecting generators match the schedule to the maintenance schedule for the

Answer 49

Prime mover

Question 50

The potential difference at which the electric systems of the utility company and the plant are connected

Answer 50

Service voltage

Question 51

The major benefits of system grounding are

Answer 51

Longer insulation life, improvement in protective relaying, extra protection

Question 52

A relay that operates faster as the current increases is said to have...

Answer 52

Inverse time characteristics

Question 53

In a cascade system of large air gap circuit breakers the number of cascades steps should not exceed...

Answer 53

Two

Question 54

In general three phase motors will give satisfactory service when operated at blank or more of their rated potential difference

Answer 54

90%