Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Level 2 > trns 220 > Flashcards

trns 220 Flashcards

You may prefer our related Brainscape-certified flashcards:
Certified Sommelier Exam (CMS 2) flashcards
1
Q

What do transformers change values of? and whats the one thing it cant change?

A

-voltage
-current
-impedance
-CANT CHANGE FREQUENCY

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

All values of voltage,current and impedance in a transformer are ________________ to the turns ratio

A

proportional

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

The primary winding of a transformer is connected to the __________________. The secondary is connected to the __________

A

power source
load

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

A transformer that has a lower secindary voltage than primary voltage is called a _________

A

step down tranny

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

A transformer that has a higher secondary voltage than primary voltage is called a ___________ transformer

A

step up

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

An ______________ transformer has its primary and secondary windings electronically and mechanically seperated from eachother

A

isolation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is self induction

A

when a coil induces voltage into itself

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is mutual induction

A

when a coil induces voltage into another coil

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

isolation transformers help filter _______ and ____________ spikes between its primary and secondary side

A

voltage
current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

polarity dots are often added to schematic diagrams to indicate the _____________

A

tranny spolarity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What 2 ways can transformers be connected as

A

-additibe polarity
-subtractive polarioty

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what causes magnetomotive force

A

(mmf) created by moving electrical charges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

the amt of mmf produces by eacg turn of a coil is ________________ to the current it carries

A

proportional

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

The magnetizing force of a coil is equal to the _____________________

A

coil current in amps times the number of turns in a coil

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

The path through which the field passes is called a _____________

A

magnetic cct

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

______________ is the magnetic equivalent of mechanical friction or electrical resistance

A

reluctance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

equation for calculating current

A

emf divided by resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

equation for calculating flux

A

mmf divided by reluctance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

The term _____________ is used to decribe the material placed inside a coil to define the magnetic cct

A

core

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

An open coil has an _________ core

A

air

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What materials for an iron core provide lower reluctance cct than air an dmakes it possible to direct/focus the field along a certain path

A

-ferrite
-iron
-magnetic steel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

A continuous loop of ________________ material provides the strongest field

A

low reluctance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Openings in the core cct are called ___________

A

air gaps

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

the amount of emf is directly proportional to the ___________at which the magnetic flux is changing and the number of turns in each coil.

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

what does the polarity of the emf depend on

A

polarity of:
-field relative to orientation of the coil
-increasing or decreasing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what is a flux line called

A

maxwell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

in an electromagnetic coil what does a change in voltage do for current, flux and induced emf

A

-current changes
-flux changes
-induces an emf that opposes the change in current by oposing the change in supply voltage that caused it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

what does self inductance do

A

-oposes an increase or decrease in current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

what is the unit of inductance

A

Henery. based on the amount of emf induced into a coil for a specific rate of change in current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

what happens when theres a high voltage spike

A

can cause damage to insulation and voltage sensitive electronic components

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

what force is responsible for all magnetic fields

A

mmf, magnomotive force

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

what changes in a magnetic material when it becomes magnetized

A

-domains are aligned along the samw axis (clusters)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

how much mmf is generated by a coil with 100 turns when its carrying a 15 A current

A

1500mmf
(turns x amps)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

what property is the magnetic equivalient of electrical resistance

A

reluctance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

what effect does placing acurrent carying coil on a core made of magnetic material have on:
a) strengh of the field
b)shape of the field?

A

a) increases
b)more direct path.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

whats faradays law of electromagnetic induction

A

-any change in magnetic flux passing through a coil will induce a emf into the coil

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

when current in a coil stops rising and starts to fall what happens to the polarity of the cemf

A

reverses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Is the induced cemf higher when a DC coil is turned on or off

A

when on cemf cant exceed applied voltage when off its limited by the rate at which the field collapses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

differnece betweeen self inductance and mutal inductance

A

self- happens in a single cct or conductor
mutual- is about linking between 2 or more different ccts/conductors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

when a conductor is looped around the core of an operating transformer, a voltage appears across the ends of the conductor. Where does this voltage come from?

A
  • changing fiels passing through the coil
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

in a transformer cct what electrical quanity is a measure of field strength?

A

-induced voltage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

what is a tap in a transformer

A

-connection made at somepoint in the winding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

whats the primary in a transformer

A

-input side of the transfromer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

whats the secondary in a transformer

A

-output side of the transformer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

how can you calculate the volts/turns of a transformer winding?

A

V/T= total voltage across windings divided by the number of turns

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

how can you calculate the ampere-turns of a transformer winding?

A

A/T= winding current x # of turns

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

an ampere-turn is a unit of _____________–

A

magnomotive force (mmf)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

what are the most common construction arrangements in a transformer

A

-shell
-core

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

whats a shell-type transformer

A

-primary and secondary windings are wound into a form in alternating layers, results in a single loop which is then enclosed by the iron core

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

What is a core-type transformer

A
  • core iron is a single loop and the windings encircle the core legs.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

what material can transformer coils be made from

A

-copper
-aluminum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

in large shell type transformers how are the windings aranged

A

-in concentric layers or pancake coils

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

in small transformers how are the windings arranged

A

-duct sticks are inserted berween the layers to create gaps through the coils for more effective cooling

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

what is vaccum pressure impregnation used for

A

improve varnish protection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

what are taps used for

A

so turns ratio can be adjusted to compensate for a supply voltage that is slightly avove or below the rated voltage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

Taps with a higher voltage rating then the nominal are called ____________ taps

A

above normal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Taps rated for less than the nominal are called ____________- taps

A

below normal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

What happens to other taps when one is energized

A

-when one is all are

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

where are the taps on small dry type transformers

A

individual leads for the main and tap connections

60
Q

where are the taps on larger dry type transformers

A
  • seperate tap connections accessible right on the winding assembly.
61
Q

when are shielded transformers used

A

when neccesary to provide total isolation

62
Q

what precautions must be taken with lead-type transformer taps?

A
  • make the right connection
    -dont connect a supply from one tap to another
    -make sure they are isolated because they are live
63
Q

what precautions must be used when the taps are short tabs mounted directly on the winding assembly?

A
  • when any tap is energized they all are
    -winding insulation is brittle
    -easily damaged
    -careful when tightening lugs
    -support stud with second wrench
64
Q

What special hazard exists with transformers tapped for multiple standard voltages?

A
  • when one is energized they all are to hookup the right voltafe to the right tab
65
Q

what precautions must be taken with tap switches?

A
  • denergize the transformer before switching off bc it can create an arc blast capsulating magnetic form
66
Q

what is the purpose of the typical on-line tap changer?

A
  • regulate voltage without denergizing
67
Q

how are dual windings usually installed

A
  • in series with a centre tap
68
Q

transformers that are not liquid filled are _______

A

dry types

69
Q

an ____________ type transformer has no enclosure

A

open

70
Q

largre dry type transformers are usually _________ type

A

core

71
Q

most highvoltage distribution transformers are filled with a ________________

A

dielectric (insulating) liquid
light mineral oil
acts like a coolant

72
Q

what improves heat transfer

A

fins
tubes

73
Q

what is used to allow the connecting conductors to pass through the container wall without causing an electrical short or an oil leak

A

bushings on top and smaller low voltage bushings on the side

74
Q

when oil filled transformers are mounted indoors what requirement do they have to meet

A

they are a fire hazard abd must be inside a fireproof vault

75
Q

do liquid or dry types have a longer service life

A

-liquid able to handle temperary overloads better

76
Q

where are open type transformers normally found

A

-equipment enclosures
-smaller appliances

77
Q

most small dry type transformers have a _________– coil and core construction

A

shell

78
Q

Extra low voltage control transformers can be mounted directly into a knockout on an electrical box. What are the high and low voltage connections made to transformers of this type?

A

Exposed leads or terminals
extra-low voltage can be on outside of the box

79
Q

Why is it unsafe to mount a transformer on or near conbustable material?

A
  • generate heat
    -during fauls or faliures can get hot enough to start a fire
80
Q

how do you acess the connections for a typical mid-size dry type transformer

A

removable panels

81
Q

why are oil filled transformers rarly used indoors

A

-fire hazard
-need a fire vault

82
Q

what benifets does transformer oil provide?

A

-longer service life
-better at handling temperaty overloads

83
Q

what is the purpose of a berm around a large high-voltage transformer

A

-contains the oil if the tank leaks

84
Q

in transformer windings the lower the resistance the __________ turns

A

less

85
Q

What does the letter H and X indicate on transformer windings

A

h- high voltage winding. more resistance smaller wire, less current
x- low voltage winding, less resistance, bigger wire more current

86
Q

Whats the standard location for H1 in transformers with fixed terminals or bushings Drawings use a ___________ view

A

-on the right when facing high voltage side
-top view

87
Q

What does H2 indicate

A

tap with the lowest voltage rating, H3 is the next

88
Q

X1 has __________ instantaneous polarity as H1

A

the same

89
Q

if H1 and X1 are at the same end, the transformer has a _____________ connection. if they are at opposite ends the transformer is said to have a _________ connection

A

-subtractive
-additive

90
Q

the connection arangement ___________ affect the actual terminal polarity

A

does not

91
Q

AC voltages and currents have a __________ polarity relative to one and another

A

instantaneous

92
Q

what is instantaneous polarity

A
  • polarity of voltages or the firection of the currents has to be compared at the same instant in time
93
Q

X1 terminal must have the same instantanous polarity as ___________

A

H1

94
Q

transformers are listed by _______ with the primary voltage first

A

voltage

95
Q

At the instant current entres H1 supply from the supply, it exits _______ of the load

A

x1

96
Q

On a transformer with dual secondary windings, which terminal has the same instantaneous polarity as X1?

A

X3

97
Q

where should you look for information before connecting any equipment?

A

nameplate

98
Q

would the instantaneous polraity of the X1 terminal vhange if a transformer were converted from additive to subtractive connection arrangement?

A

no

99
Q

larger single-phase transformers are usually core types with 2 seperate windings assemblies, each containing _______ of the primary and _____ of the secondary winding

A

half
half

100
Q

The start and finish of high voltage windings are identified as:

A

H1 H2

101
Q

CEC requires the secondary winding to be ___________

A

grounded, for 3 wire systems its always applied to the centre connection

102
Q

Why does changing taps change the output voltage?

A

different amount of turns

103
Q

If the high voltage winding has 4 taps, marked H2,H3,H4 and H5, the connection with the lowest voltage ratings will be H1 to __________

A

H2

104
Q

A transformer is rated 600:120/240V. How should the secondary windings be connected to supply a 120V load?

A

in parallel

105
Q

What is the purpose of turns ratio compenstation?

A

-without, output voltage would be low
-with, the full load is close to nameplate rating

106
Q

What effect will turn ratio compensation have if a step-down transformer is connected for a step-up operation?

A
  • work backwards
107
Q

A transformer has dual 120V secondary windings, and the X1 and X2 markers have accidentally been interchanged. What effect does this have when the windings are connected:
a)in series
b)in parallel

A

a) would get 0 volts, volts would cancel eachother out. Would read 120 for 120 but read 0 for 240V
b)it would create a short in the cct, would trip out from the high current

108
Q

A 480:120/240V transformer is used to supply a 2 wire 120V cct. What would be wrong with using only one of the windings, instead of both winfings in parallel?

A

coukd overload secondary transformer

109
Q

What is one advantage and one disadvantage to using a 3 wire 120/240V cct instead of 120V cct to supply a group of 120V loads

A

A- less current
D- more wires

110
Q

A 600:120/240V transformer is used to supply a 2 wire 240V cct. What differences would it make if the seondary ground were applied to X4 instead of X2-X3?

A

-shock hazard
-would be 240 instead of 120

111
Q

why are instrument transformers a better solution

A

-safer
-easier to apply bc it can they isolate the instruments from the power cct voltages and currents

112
Q

when are potential transformers used

A

-when voltages are too high
-reasons for isolation

113
Q

where is the voltmeter conneted

A

-directly across the output terminals of the PT
-the actual power cct voltage is the meter reading times the PT voltage ratio

114
Q

when are current transformers used

A

–when the current is too high, the voltage is too high, or there is some other reason to avoid connecting an ammeter or other current monitoring instrument directly into the power cct.
-connected across the output of a ct is directly propotional to thecurrent across the output of the a ct is directly proportional to the current through the power cct conductior

115
Q

why are instrument transformers not used in DC systems?

A

-dont work on dc
-not changing magnetic fields

116
Q

Typical PTs have secondary windings rated at what voltages?

A

120V

117
Q

typical CTs have secondary windings rated at what cuurent?

A

5A

118
Q

A PT transformer is normally connected to the power cct through a set of _____________________

A

-protective fuses

119
Q

the primary of the CT is always connected in _______________- with the load

A

series

120
Q

The secondary windings of a CT must be connected to a _____________- load such as an armature or shorted with a jumper

A

low impedance

121
Q

Voltage induced into a CT winding is ______________________ to be high enough to be dangerous and may cause insulation failure that destroys the CT.

A

less likely

122
Q

Bushing CTs dont have have primary terminals but what do they have instead

A

-polarity mark on one side that is normally turned to the face the supply

123
Q

The primary of a strap type CT is protected by the _________________________

A

power cct fuses

124
Q

The secondary windings of a CT is grounded where

A

at one end

125
Q

How much voltage does a ungrounded terminal have

A

almost no voltage to ground

126
Q

Why is one terminal of a PT or CT connected to ground?

A

-prevent voltage- ground from rising due to capacitance couplings, refrence it to ground

127
Q

What is likely to happen if the ground is removed from the secondary of an instrument transformer?

A

-high voltages

128
Q

What are the letter and number markings at the polarity marked terminals of a typical PT?

A

H1, X1 and sometimes a dot

129
Q

Sould the H1 terminal of a PT be connected to the power cct or the instruments?

A

-power cct

130
Q

When the current flows into the polarity marked terminal of a PT or CT, will it flow into, or out, the polarity secondary terminal?

A

out of X1

131
Q

when its safe to open the short-circuting device provided in the secondary cct of a CT?

A

when its enrgized

132
Q

What meter would be used to measure tge output of a PT, and how should it be connected?

A
  • voltmeter in paralell
133
Q

What meter would be used to measure the output of a CT, and how should it be connected

A

amp meter in series

134
Q

what is a capacitive coupling?

A

-if not grounded voltages can add together

135
Q

volts/turn= _________________

A

volts/turn

136
Q

The ____________ of a transformer is connected of supply voltage

A

primary

137
Q

The ___________ of a transformer is connected to the load

A

secondary

138
Q

The primary voltage of a step up transformer will be ________ than the secondary voltage

A

lower

139
Q

The primary voltage terminals of a step down transformer will be _________ than the secondary voltage

A

higher

140
Q

The higher voltage terminals of a transformers always marked with the letter ___________

A

H

141
Q

The lower voltage terminals are marked with the letter _________

A

X

142
Q

The primary terminals of a step up transformer would be marked with the letter ___________

A

X

143
Q

What is the relationship between H1 and X1

A

they have the same intaneous polarity

144
Q

Whats the code rules for impedance and short ccts

A

Section 14

145
Q

What to parallel transformers need

A

-identical voltage and frequency ratings
-impedance ratings within +-7.5%
-combines KVA that is equal or greater than the requirements of the load

146
Q

If one transformer gas a lower impedance what happens to the other

A

-output voltage will stay higher as the load demand is increased
-transformer with the lowest impedance will tend to take a larger share of its total load

Level 2 (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions