Delmar section 9/10
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.
150%
Which of these formulas is used to calculate three-phase watts of a three-phase power circuit?
D
In a 60-Hz AC circuit, how many times does the voltage change polarity?
60
The double-wye connection must have two secondary windings that produce equal voltage.
true
oad 2 is formed from three inductors in a delta with an inductive reactance of 10 ohms each. What is the phase current?
56A
A delta connected set of windings has a phase voltage of 480 V. What is the line voltage?
480V
In this image, is there a transformer secondary with a center-tapped winding?
No
The current of the secondary induces a ___________ in the secondary windings that is in opposition to the countervoltage induced in the primary.
counter voltage
The diametrical connection is not preferred because it requires one low-voltage winding on each transformer.
false
The nameplate lists the current rating of the windings.
false
When a load is connected to the primary, current begins to flow.
false
When resistors of Load 1 are connected in a delta, the line current is the same as the phase current.
false
What should the ohmmeter indicate when testing checks for shorted windings between the primary and secondary?
infinity
When testing a transformer, what will reveal problems of insulation breakdown that an ohmmeter will not?
meggar
In an open delta with single-phase loads, the high leg must be identified by _____.
none of the above
The main power distribution system of a large industrial plant is generally shown using a(n) _____ diagram.
one-line
The power input winding of a transformer is called the _____ winding.
primary
The output winding of a transformer is called the _____ winding.
secondary
A transformer in which the secondary voltage is less than the primary voltage is called a(n) _____ transformer.
step-down
In calculating apparent power (VA) in a three-phase circuit, the phase values of voltage and current are multiplied by _____.
three
A buck connection is defined as connecting transformer windings as an autotransformer and testing for additive or subtractive polarity.
true
An isolation transformer has the same input and output voltages.
true
If Load 1 is pure resistive, true power can be calculated using the line and phase current values.
true
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
Power input must equal power output, which enables the current rating for a winding to be determined.
true
The circuit power factor is the ratio of apparent power and true power.
true
The polarity of transformer windings can be determined by connecting them as an autotransformer and testing for additive or subtractive polarity.
true
Three-phase transformers are sometimes connected in such a manner as to provide more than three phases.
true
Transformer impedance is determined by the physical construction of the transformer.
true
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
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.
true
When the secondary side of the transformer bank is a delta connection, either a wye or a delta primary could be used.
true
this picture represents the line current to Load 1 (resistive). Il(load 1)
true
When a transformer is shown on a schematic diagram, what is the common practice to indicate polarity of the transformer windings?
using dots
When single-phase loads are tied to a three-phase transformer, the phase currents of the transformer will be automatically balanced.
false
What would be calculated by using the above formula? I=VA/E
full-load current rating of the secondary winding
What does this picture represent? Ep(load)
phase voltage of the load
A wye-delta transformer has its _____ connected as a wye and its _____ connected as a delta.
primary; secondary
A transformer in which the secondary voltage is more than the primary voltage is called a(n) _____ transformer.
step-up
A 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?
1.6A
Which nameplate requires the name of manufacturer and related kilovolt-ampere?
NEC® 450.11
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
In three-phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter _____.
H; X
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.
open delta with one transformer center tapped
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
Ripple is pulsations of voltage.
true
A tape-wound core is also called a(n) _____ core.
toroid
If the transformer bank has been properly sized for the maximum connected load, no one phase will become overloaded.
true
What connection is used primarily for grounding purposes?
zig-zag connection
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
11.55:1
In three-phase power systems, the delivered power _____.
never falls to zero
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?
40.416 A
Which of these formulas is used to calculate apparent power of a three-phase power circuit?
A
Which of these formulas is used to calculate circuit power factor?
A
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
Line current and phase current are the same in the _____ configuration.
Wye
The three-phase connection in which one end of each of the windings are connected together is called a(n) _____ connection.
Wye
Most transformer cores are assembled from many thin sheets of metal. This type of construction is called _____.
laminated
If a three-phase load is a pure reactive load, then the power calculated has units of _____.
VARs
A delta connected set of windings has a phase voltage of 100 V. What is the line voltage?
100v
A delta-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
20:1
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?
40A
The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a(n) _____ transformer.
Control
In which connection are the secondary windings of each transformer providing the phases of a two-phase system?
Scott connection
What is used to convert three-phase power into two-phase power using two single-phase transformers?
Scott connection
Which type of load is this image depicting?
Wye
What is used to indicate a direction of additive and subtractive polarity on a schematic?
arrows
A transformer that has one winding, that is used for both the primary and secondary is called a(n) _____.
autotransformer
Line voltage and phase voltage are the same in the _____ connection.
delta
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.
distribution
What induces a voltage in the secondary for a transformer?
primary current
If the phase windings of the alternator are connected in a wye, the phase current is the same as the line current.
true
An open delta connection is made using _____ single-phase transformers.
two
Which connection is mainly used to establish a neutral point for the grounding of fault currents?
zig-zag connection
