week 2 (chapter 2)

Question 1

changing any two of the three phases in a three phase motor will effect it how?

Answer 1

direction of rotation

Question 2

what are three advantages of three phase over single phase systems?

Answer 2

1. 73% more power for 50% conductor increase
2. less pulsating force
3. smaller and less expensive equipment

Question 3

what is the degree of separation for the coils of a three phase motor?

Answer 3

120 deg

Question 4

there is a ________ _______ between any two phases at any time throughout the cycle of a three phase sine wave.

Answer 4

potential difference

Question 5

in a three phase sine wave, one phase is at ______ and the other two are?

Answer 5

zero/providing power

Question 6

in actual practice, within a three phase generator the ____ are stationary and the ________ ____ is rotating?

Answer 6

coils/magnetic field

Question 7

what two configurations can three phase generators be connected in?

Answer 7

delta and wye

Question 8

what is the square root of 3? why does it matter?

Answer 8

1.732/used to calculate voltage difference between phases and the neutral

Question 9

in a _____ system, coil and phase current are the same.

Answer 9

WYE

Question 10

in a _______ system, system voltage is the same as phase voltage.

Answer 10

DELTA

Question 11

in a delta system, phase current is higher than coil current by how much?

Answer 11

a value multiplied by 1.732

Question 12

on historical _____ systems, it was thought a lineman could barehand a phase safely with no electrocution risk.

Answer 12

DELTA

Question 13

which system is the one of choice for today’s utilities?

Answer 13

WYE

Question 14

WYE systems can serve a given load with less or more current than a DELTA system?

Answer 14

less

Question 15

where do DELTA systems exist today?

Answer 15

isolated areas

Question 16

what two systems can look alike but are not the same?

Answer 16

DELTA and three wire WYE (no neutral)

Question 17

to verify a system is in fact DELTA or three wire WYE, you must check the?

Answer 17

secondary connections of the substation transformer bank.

Question 18

four wire WYE is more reliable in regards to?

Answer 18

fault protection

Question 19

voltage of each phase is dependent on the?

Answer 19

degree of rotation

Question 20

in order for generators to be connected via the grid, they ALL must have?

Answer 20

exactly the same angle of rotation

Question 21

if all generators on a transmission system are not in unison, their _____ will be different.

Answer 21

voltages

Question 22

the direction a motor spins depends on _____________________ and __________________?

Answer 22

direction the generator that powers it spins

how the electricians hooked up the motor

Question 23

ABCABCABCABC is a representation of what?

Answer 23

phase sequence

Question 24

if a source supplies ABC phase sequence to a motor that requires right hand rotation, but the phases are connected BCA, will the motor still turn to the right?

Answer 24

yes

Question 25

what are all the possible connections of ABC phase sequence that would result in clockwise rotation?

Answer 25

ABC....BCA......CAB

Question 26

if BCA results in right hand rotation of a motor, then what would CBA result in?

Answer 26

reverse rotation

Question 27

if a change in phase sequence occurs at a point on the power line, where is the rotation effected?

Answer 27

downline from the sequence (farther from source)

Question 28

what can be done to prevent a rotation problem when removing and re-installing jumpers?

Answer 28

draw the connections on the job print

Question 29

phase sequence has to be _______ before the worksite can be left

Answer 29

proven

Question 30

to prove a corner is reconstructed properly, many companies require the line be phased where?

Answer 30

at the open switch

Question 31

high voltage meter used for proving phase sequence?

Answer 31

phasing meter

Question 32

if voltage is read across two corresponding conductors of an open point, what has happened?

Answer 32

phase sequence has been changed.

Question 33

if you read voltage across an open point of a single phase you SHOULD get a reading of?

Answer 33

0 volts

Question 34

three phase induction motors have both a ___ and ____.

Answer 34

rotor/stator

Question 35

in an induction motor, as the magnetic field peaks between the stator poles, _____ is induced in the rods of the rotor

Answer 35

current

Question 36

to get peak voltage from RMS, use?

Answer 36

RMS x 1.414 = peak

Question 37

to get RMS voltage from peak use?

Answer 37

peak x .707 = RMS

Question 38

"WYE is current the same", is a trick to remember?

Answer 38

that current stays the same in a WYE circuit