transformers final exam review

magnetic flux

_____ _____ is any transformer flux that does not follow the core and escapes into the surrounding air

liquid - cooled

_____-_____ transformers are the most efficient type of cooled transformer

delta

______ construction is the most common on 3 phase transformer

inrush

______ current is the current that flows into a transformer primary when voltage is first applied

induction

______ is the result of the relationship between magnetism and electricity and creates an electrical potential through the relation motion of a conductor and a magnetic field

one line

a _____-_____ diagram is generally used to show the main power distribution system of a large industrial plant

67200 VA 560/14=40 560x40=22400 22400x3=67200

a delta connected three phase load is connected to a 560v line. the loads have an impedance of 14 ohms per phase what is the apparent power of the connection 22393 VA 116390 VA 38797 VA 67200 VA

17A

a delta connection has 30A of current flowing through each phase winding. how much current is flowing through each of the lines supplying power to the load

560v

a delta connection has a voltage of 560v connected to it. how much voltage is dropped across each phase

22,447 VA 240x18= 4320 4320x1.732=7482 7482x3=22,447

a three phase load has a phase voltage of 240v and a phase current of 18v. what is the apparent power of this load

29929 W 480/1.732=277 277x36=9972 9972x3=29929

a three phase wye connected load is connected to a 480v three phase line. the line current to the load is 36A. if this load is pure resistive what is the total amount of power being used in this circuit 51840 W 29929 W 7482W 12960W

induce a voltage into the other circuit

a transformer can magnetically transfer energy from one circuit to another and can ______

1:2

a transformer has 20A flowing in the primary winding and 10A flowing in the secondary winding. the turns ratio=_____

2.5A

a transformer has 240 primary and a 60 v secondary. with a 10 ohm load connected the primary current = ____

4:1

a transformer has 480v applied to the primary and 120v produced at the secondary. the turns ratio =______

60v

a transformer has a turns ratio of 4:1. 240v is applied to the primary the secondary voltage = _______

step down

a transformer in which the secondary voltage is less than the primary voltage is called a _____-_____

step up

a transformer in which the secondary voltage is more than the primary voltage is called a ____-_____

winding

a transformer is actually an inductor and the CEMF that is induced in the primary ______ the voltage that created it

auto transformer

a transformer that has one winding which is used for both the primary and secondary is called a _________

isolation

a transformer that is used solely to isolate the supply voltage from the secondary voltage and has a turns ratio of 1:1 is called a ________ transformer

25A

a wye connected load has phase current of 25A. how much current is flowing through the lines supplying the load 25A

277v

a wye connected load has voltage of 480v applied to it. what is the voltage drop across each phase

22393 VA 560/1.732=323 323/14=23 323x23=7429 7429x3=22287

a wye connected three phase load is connected to a 560 v line. the loads have an impedance of 14 ohms per phase. what is the apparent power of this connection 22393 VA 116390 VA 38797 VA 67200 VA

vault

all oil filled transformers over 35000 volts or 112.5 kva must be in a ______ if they are located indoors

installation

articles 450.8-450.13 of the NEC list the requirements for transformer ______

auto

boost and buck transformers are special types of ______ transformers that raise or lower supply voltages by small amounts

eddy

currents that flow into the core material of a transformer creating heat in the core are ______ currents

120

how many degrees out of phase are the voltages of a three phase system 60 90 120 180

120

how many degrees out of phase with each other are the voltages of a three phase system

core

in a transformer if we put a magnetic material such as iron or steel inside the coil we further concentrate the magnetic flux. the iron or steel is called the ____

voltage, turns

in a transformer the H winding should have a higher ______ than the X winding because the H winding will have more ______

CEMF

in a transformer the polarity of the induced voltage opposes the polarity of the voltage that created it. this opposition is known as ____

series

in a transformer with dual voltage primary ratings of 240 or 480 the dual windings must be connected in _______ for the higher voltage connection

parallel

in a transformer with dual voltage primary ratings of 240 or 480 the dual windings must be connected in _______ for the low voltage connection

cooling, insulation, light

name the three functions that dielectric oil performs for an oil cooled transformer

taps

single phase transformers are often constructed with one winding that has a number of different connection powers called _____

neutral

the NEC requires that the ______ point be grounded if this can be done so that no point on the system has potential of more than 150V to the ground conductor

wye-delta

the ____-____ connection is also common as a step down transformer connection

delta- wye

the ____-____ connection is also common as a step up transformer connection

15 A 25.98/1.732= 15

the delta alternator has a phase voltage of 480 and has a load that draws a current of 25.98 A on the lines. how much current is flowing in the phase windings 25.98 45 15 17.32

high, low

the most efficient way to distribute electrical power is the _____ voltage and ____ current

impedance

the total opposition to AC current in an AC circuit that includes resistance and reactance is known as ______

primary

the transformer winding to which the applied voltage is connected to is called the ____ winding

secondary

the transformer winding which is the output winding is called the ____ winding

inrush, sealed

the two types of current that control transformers must supply include _____ current and _______ current

strap, sheet

the two types of transformer conductors are _____ conductors and ______ conductors

480V

the windings of a three phase alternator are connected delta. the alternator is producing a line to line voltage of 480 V what is the voltage across the phase windings 480 120 277 831

flux losses

transformer flux that does not follow the core and escapes in the surrounding air is ____ ____

VA

transformer power is measured in _____

wye, delta

transformer windings are constructed of either ___ or ______

wye and delta

what are the two main types of three phase connections

current

when a large amount of AC must be measured a ____- transformer is used

step up

when the function of a transformer is to induce a secondary voltage that is higher than the supply voltage we call this transformer a _____ transformer

step down

when the function of a transformer is to induce a secondary voltage that is lower than the supply voltage we call this transformer a _____ transformer

excitation current

when there is no load connected in a transformer there will be some small current flow in the primary known as ____ ___

highest

when using an open delta with a center tapped transformer one wire is the high leg. the high leg is the one that has the highest voltage

- line current is higher than phase current by a factor of 1.732

which of the following is true for a delta connected three phase system - line current is higher than phase current by a factor of 1.732 - phase current is higher than line current by a factor of 1.732 - line current is less than phase current by a factor of 1.732 - line current and phase current are the same

- line voltage and phase voltage are the same

which of the following is true for a delta connected three phase system - line voltage is higher than phase voltage by a factor of 1.732 - phase voltage is higher than line voltage by a factor of 1.732 - line voltage is less than phase voltage by a factor of 1.732 - line voltage and phase voltage are the same

- line current and phase current are the same

which of the following is true for a wye connected three phase system - line current is higher than phase current by a factor of 1.732 - phase current is higher than line current by a factor of 1.732 - line current is less than phase current by a factor of 1.732 - line current and phase current are the same

- line voltage is higher than phase voltage by a factor of 1.732

which of the following is true for a wye connected three phase system - line voltage is higher than phase voltage by a factor of 1.732 - phase voltage is higher than line voltage by a factor of 1.732 - line voltage is less than phase voltage by a factor of 1.732 - line voltage and phase voltage are the same