Delmar9/10
In calculating apparent power (VA) in a three-phase circuit, the phase values of voltage and current are multiplied by _____. three four five six
3
The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a(n) _____ transformer. auto distribution isolation control
control
In a 60-Hz AC circuit, how many times does the voltage change polarity? 30 60 90 120
60
A delta connected set of windings has a phase voltage of 480 V. What is the line voltage? 277.14 V 480 V 831.36 V 1440 V
480 V
In three-phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter X; H H; X L; X X; L
H; X
When resistors of Load 1 are connected in a delta, the line current is the same as the phase current. True False
F
In a double-delta connection, the two delta windings are connected in reverse so that they have an angular difference of 180° with respect to each other. True False
T
Ripple is pulsations of voltage. True False
T
The transformer that converts a high voltage from the power company down to 240/120 V for homes and businesses is called a(n) _____ transformer. auto distribution control household
distribution
What should the ohmmeter indicate when testing checks for shorted windings between the primary and secondary? opens grounds shorts infinity
infinity
Most transformer cores are assembled from many thin sheets of metal. This type of construction is called _____. laminated toroid H core
laminated
In three-phase power systems, the delivered power _____. falls to zero three times per cycle falls to zero once per cycle never falls to zero falls to zero at least three times per cycle
never falls to zero
When calculating the power of a pure resistive load, the voltage and current are in phase with each other and the power factor is _____. one two three four
one
The main power distribution system of a large industrial plant is generally shown using a(n) _____ diagram one-line wiring three-line pictorial
one-line
The power input winding of a transformer is called the _____ winding. primary secondary tertiary tapped
primary
What is used to indicate a direction of additive and subtractive polarity on a schematic? dots asterisks arrows squiggly lines
squiggly lines
A transformer in which the secondary voltage is less than the primary voltage is called a(n) _____ transformer. step-up isolation step-down auto
step-down
A tape-wound core is also called a(n) _____ core toroid solid H E
toroid
When a transformer is shown on a schematic diagram, what is the common practice to indicate polarity of the transformer windings? using dots using asterisk using arrows using the letter X
using dots
Line current and phase current are the same in the _____ configuration. delta wye
wye
The three-phase connection in which one end of each of the windings are connected together is called a(n) _____ connection. delta wye open delta open wye
wye
The output winding of a transformer is called the _____ winding. primary secondary tertiary tapped
secondary
Which connection is mainly used to establish a neutral point for the grounding of fault currents? Scott connection zig-zag connection T-connection
zig-zag connection
What induces a voltage in the secondary for a transformer? primary current secondary current polarity current
primary current
A wye-delta transformer has its _____ connected as a wye and its _____ connected as a delta. secondary; primary primary; secondary
primary; secondary
Load 2 is formed from three inductors in a delta with an inductive reactance of 10 ohms each. What is the phase current? 56 A 96.992 A 40.416 A 53.888 A
56 A
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio? 8.66:1 9: 66 10:15 15:1
8.66:1
When testing a transformer, what will reveal problems of insulation breakdown that an ohmmeter will not? galvometer wattmeter MEGGER ammeter
MEGGER
Which nameplate requires the name of manufacturer and related kilovolt-ampere? NEC® 440.33 NEC® 430.24 NEC® 450.11 NEC® 440.3
NEC® 450.11
A buck connection is defined as connecting transformer windings as an autotransformer and testing for additive or subtractive polarity. True False
T
The nameplate lists the current rating of the windings. True False
T
The polarity of transformer windings can be determined by connecting them as an autotransformer and testing for additive or subtractive polarity. True False
T
Three-phase transformers are sometimes connected in such a manner as to provide more than three phases. T F
T
Transformer impedance is determined by the physical construction of the transformer. T F
T
When Load 2 is made up of inductors, the reactive power can be calculated using the line values of voltage and current supplied to the load. True False
T
When single-phase loads are tied to a three-phase transformer, the phase currents of the transformer will be automatically balanced. True False
False
If Load 3 is pure capacitive, the current and voltage are 90 degrees out of phase with each other and the power factor is zero. True False
T
If the phase windings of the alternator are connected in a wye, the phase current is the same as the line current. True False
T
What does EpLoad represent phase current of the load phase voltage of the alternator phase voltage of the load line voltage of the load
phase voltage of the load
A transformer in which the secondary voltage is more than the primary voltage is called a(n) _____ transformer. step-down step-up isolation auto
step-up
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio? 1:20 2:1 10:11.55 11.55:1
11.55:1
Power input must equal power output, which enables the current rating for a winding to be determined True False
T
wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. What is the primary line current? 1.6 A 1.924 A 2.77 A 3.2 A
1.6 A
A wye-delta transformer has a secondary phase voltage of 480 V. A delta-connected resistive load has a resistance of 12 Ω in each leg. What is the current in each load leg? 30.33 A 40 A 53.1 A 69.28 A
40 A
If a three-phase load is a pure reactive load, then the power calculated has units of _____. VA W VARs
VARs
A delta connected set of windings has a phase voltage of 100 V. What is the line voltage? 57.7 V 100 V 173.2 V 300 V
100 V
A delta-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio? 11.55:1 15:11.55 20:1 51:20
20:1
In which connection are the secondary windings of each transformer providing the phases of a two-phase system? Scott connection zig-zag connection T-connection
Scott connection
What is used to convert three-phase power into two-phase power using two single-phase transformers? Scott connection zig-zag connection T-connection
Scott connection
IL (Load1) represents resistive load 1 TRUE FALSE
True
A transformer that has one winding, that is used for both the primary and secondary is called a(n) _____. distribution transformer step-up transformer autotransformer control transformer
autotransformer
Line voltage and phase voltage are the same in the _____ connection. delta wye
delta
For installations that will have both three-phase and single phase loads on a three-phase transformer, the utility company often provides a(n) _____ three-phase transformer. three-wire delta three-wire wye open delta with one transformer center tapped
open delta with one transformer center tapped
The diametrical connection is not preferred because it requires one low-voltage winding on each transformer. T F
F
When a load is connected to the primary, current begins to flow. T F
F
The current of the secondary induces a ___________ in the secondary windings that is in opposition to the countervoltage induced in the primary. true power induced voltage applied voltage countervoltage
countervoltage
The circuit power factor is the ratio of apparent power and true power. True False
T
The double-wye connection must have two secondary windings that produce equal voltage. True False
T
When the secondary side of the transformer bank is a delta connection, either a wye or a delta primary could be used. T F
T
When the primary of a transformer is connected to power but there is no load connected to the secondary, current is limited by the inductive reactance of the primary. T F
T
Load 3 is formed from three capacitors with a capacitive reactance of 8, connected in a wye and the phase voltage is less than the line voltage by a factor of 1.732. What is the phase current? 56 A 96.992 A 40.416 A 53.888 A
40.416 A
In an open delta with single-phase loads, the high leg must be identified by _____. using orange wire tagging None of the above All of the above
None of the above
The horsepower rating of three-phase motors and the kilovolt-ampere rating of three-phase transformers are about _____ greater than for single-phase motors or transformers with a similar frame size. 75% 100% 150% 200%
150%
An isolation transformer has the same input and output voltages. True False
T
If Load 1 is pure resistive, true power can be calculated using the line and phase current values. True False
T
If the transformer bank has been properly sized for the maximum connected load, no one phase will become overloaded. T F
T
I=VA maximum current of the secondary maximum current of the primary transformer power full-load current rating of the secondary winding
full-load current rating of the secondary winding
An open delta connection is made using _____ single-phase transformers. one two three four
two
What connection is used primarily for grounding purposes? Scott connection zig-zag connection T-connection
zig-zag connection
