week 2 (chapter 2) Flashcards

1
Q

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

A

direction of rotation

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2
Q

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

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

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

A

120 deg

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4
Q

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

A

potential difference

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5
Q

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

A

zero/providing power

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6
Q

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

A

coils/magnetic field

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7
Q

what two configurations can three phase generators be connected in?

A

delta and wye

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8
Q

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

A

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

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9
Q

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

A

WYE

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10
Q

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

A

DELTA

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11
Q

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

A

a value multiplied by 1.732

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12
Q

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

A

DELTA

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13
Q

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

A

WYE

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14
Q

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

A

less

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15
Q

where do DELTA systems exist today?

A

isolated areas

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16
Q

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

A

DELTA and three wire WYE (no neutral)

17
Q

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

A

secondary connections of the substation transformer bank.

18
Q

four wire WYE is more reliable in regards to?

A

fault protection

19
Q

voltage of each phase is dependent on the?

A

degree of rotation

20
Q

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

A

exactly the same angle of rotation

21
Q

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

A

voltages

22
Q

the direction a motor spins depends on _____________________ and __________________?

A

direction the generator that powers it spins

how the electricians hooked up the motor

23
Q

ABCABCABCABC is a representation of what?

A

phase sequence

24
Q

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?

A

yes

25
Q

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

A

ABC….BCA……CAB

26
Q

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

A

reverse rotation

27
Q

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

A

downline from the sequence (farther from source)

28
Q

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

A

draw the connections on the job print

29
Q

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

A

proven

30
Q

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

A

at the open switch

31
Q

high voltage meter used for proving phase sequence?

A

phasing meter

32
Q

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

A

phase sequence has been changed.

33
Q

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

A

0 volts

34
Q

three phase induction motors have both a ___ and ____.

A

rotor/stator

35
Q

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

A

current

36
Q

to get peak voltage from RMS, use?

A

RMS x 1.414 = peak

37
Q

to get RMS voltage from peak use?

A

peak x .707 = RMS

38
Q

“WYE is current the same”, is a trick to remember?

A

that current stays the same in a WYE circuit