transformer final

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Any transformer flux that does not follow the core and escapes into the surrounding air is called ________

flux leakage

In three-phase transformer connections, the primary leads are labeled with the letter _____ and the secondary leads are labeled with the letter _____.

h,x

what type of core is often found on high voltage distribution transformers?

h-type

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

A wye-delta transformer has its _____ connected as a wye and its _____ connected as a delta.

primary; secondary

The transformer winding, which is the output winding, is called the __________ winding.

secondary

another name for the three phase wye connection is the_____ connection

star

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 the _____ connection.

wye

A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a ________ transformer.

isolation

Most transformers cares are not made from a solid piece of metal. Instead, they are assembled from many thin sheets of metal. This type of construction is called ________ _________.

laminated core

In a three-phase connection, the voltage measured between the lines is the _____ voltage.

line

The alternator must supply the _____ for each of the loads.

line current

In a three-phase circuit, the true power (watts) is found by _____.

multiplying apparent power by the power factor

A transformer supplying a house with 240/120 V has a secondary winding which is center tapped. The conductor connected to the center is called the ______ conductor.

neutral

In three-phase power systems, the delivered power _____.

never falls to zero

The main power distribution system of a large industrial plant is generally shown using a(n) _____ diagram.

one line

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

A transformer in which secondary voltage is less than the primary voltage is called a ________ _______ transformer.

step down

A transformer in which the secondary voltage is more than the primary voltage is called a ______ _______ transformer.

step up

If three-phase transformation is needed and a three-phase transformer of the proper size and turns ratio is not available, three single-phase transformers can be connected to form a _____.

three phase bank

A Tape wound core is assembled by

tightly winding 1 long continuous silicon steel tape into a spiral.

A tape wound core is also called a ________ core.

toroid

The magnetically operated device that can change values of voltages, current, and impedance without changing frequency is the ____________.

transformer

An Isolation transformer has the same input and output voltages. (T or F)

true

In a transformer, the turns of primary wire compounded to the turns of secondary wire is called the __________ ratio.

turns

An open delta connection is made using _____ single-phase transformers.

two

A delta connected set of windings has a phase voltage of 100 V. The line voltage is _____.

100 v

An alternator with a line voltage of 2400 V supplies delta-connected load. The line current supplied to the load is 40 A. Assuming the load is a balanced three- phase load, what is the impedance of each phase?

103.919 w

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

A three-phase load has a phase voltage of 240 V and a phase current of 18 A. What is the apparent power of this load?

12,960 VA

How many degrees out of phase with each other are the voltages of three-phase system?

120

Three-phase voltages are _____ out of phase with each other.

120

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-connected load has phase current of 25 A. How much current is flowing through the lines supplying the load?

25 A

An open delta transformer is assembled from two 150 kVA transformers. The output power of the open delta is _____.

259.8 kVA

a wye-connected load has voltage of 480 V applied to it. What the voltage dropped across each phase?

277.136

What is the apparent power of the circuit in Question 9?

VA = 166,272

If a three-phase load is a pure reactive load, then the power calculated has units of _____.

VARs

Line voltage and phase voltage are the same in the _____ connection.

delta

The transformer winding, which is the power input winding, is called the ________ winding.

primary

A delta-wye transformer has its _____ connected as a delta and its _____ connected as a wye.

primary; secondary

What are the two main types of three-phase connections

wye and delta

When connecting three transformers for three-phase use with a delta secondary, a voltage test should be done before closing the secondary. The correct voltage reading is

zero volts

In an open delta with single-phase loads, the high leg must be identified by _____.

both a and b

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 phase current?

1.6 amps

Often in calculations of values in three-phase systems, the square root of three occurs. The approximate value of this constant is _____.

1.732

The industrial use transformer that normally has 240 V or 480 V primary and a 120 V secondary is called a _________ transformer.

control

The three-phase connection in which three separate inductive loads have been connected together is the _____ connection.

delta

The transformer that converts high voltage from the power company down to 240/120 V for homes and businesses is called a _________ transformer.

distribution

In a transformer, even when there is no load connected, there will be some small current flow known as _______ current.

excitation

When single-phase loads are tied to a three-phase transformer, the phase currents of the transformer will be automatically balanced.

false

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%

A delta-connected set of windings has a phase current of 10 A. The line current is _____

17.32 a

In calculating power in a three-phase circuit, the phase values of voltage and current are multiplied by _____.

3

A transformer has a 240v primary and a 60v secondary. With a 5 ohm load connected, what is the primary current

3 A

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 secondary phase current?

3.2 a

A delta-wye transformer has a turns ratio of 9:1. The primary line voltage is 3600 V. What is the secondary line voltage?

692.8

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?

40 A

A delta-connected three-phase alternator is driving a wye-connected resistive load. The alternator output voltage is 480 V. The load resistors are 12 W each. What is the phase current in the alternator?

40 a

A Transformer has a 240v primary and a 120v secondary. With a 30ohm load connected, what is the primary volt-amps.

480

A delta connected set of windings has a phase voltage of 480 V. What is the value of the line voltage?

480 v

A wye-connected secondary has a phase voltage of 277.14 V. What is the line voltage?

480 v

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 current flow is in each load resistor?

5.54

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

51.96 A

A delta connection has a voltage of 560 V connected to it. How much voltage dropped across each phase?

560 v

A wye-connected alternator that has phase voltages of 277 V is feeding two loads. The first load is wye-connected inductors that have 40 W of XL. The second load is delta-connected capacitors that have XC of 60 W. How much is the alternator phase current?

6.93

A transformer has a 2:1 turns ration. 120v is applied to the primary. What is the secondary voltage?

60 v

In a balanced three-phase system, the conductors need be only about _____ the size of conductors for a single-phase, two-wire system of the same kilovolt-ampere (kVA) rating.

75%

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

An open delta transformer is assembled from two 50 kVA transformers. The output power of the open delta is _____.

86.6 kVA

In a three-phase connection, the voltage measured across a single winding is the _____ voltage

phase

In an open delta with a center-tapped transformer, label the two ends of the center-tapped transformer as L2 and L3 and label the high leg as L1. The current flow in the neutral (center tap) is equal to _____.

AN = A1 + (A2 - A3)

dielectric oil performs which of the following

all of the above

A transformer that has one winding, which is used for both the primary and secondary, is called a _______ __________.

autotransformer

The amount of current that flows into a transformer primary when voltage is first applied is called ________ current.

inrush

When calculating the power of a pure resistive load, the voltage and current are in phase with each other and the power factor is _____.

1

If the load in Question 7 is connected in wye, what would be the line voltage and line current supplying the load?

EL = 415.68 V


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