Electricity 2 Final

The power input of winding of a transformer is called the

primary winding

the rotating part of an alternator is called the

rotor

When a squirrel-cage motor is first started, the value of the current draw is

several times the running current

In a wye connected system, the line voltage is higher than the phase voltage by a factor of

square root of three

Another name for a three phase wye connection is the

star connection

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

step down transformer

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

step up transformer

a wye delta transformer has a turns ratio of 2:1, it has a secondary line voltage of 480v, secondary has 50ohms, what is the secondary phase current

3.2 amps

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

excitation

In a transformer, the turns of primary wire compared to the turns of secondary wire is called the

turns ratio

A transformer has a 240v primary and a 120v secondary, with a 30 ohms load, what is the primary volt amps

480

A wye delta transformer has a primary line voltage of 7200v and a secondary line voltage of 480v, what is the turns ratio

8.66:1

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

flux leakage

in order to increase the efficiency of the cooling, some alternators operate in a

hydrogen atmosphere

the alternator must supply_____for each of the loads

line current

a transformer supplying a house with 240/120v has a secondary which is center tapped, the conductor in the center is called the

neutral conductor

power is carried to the outside circuit of a revolving armature type alternator vie brushes riding against the

slip rings

In a three phase motor, the speed of rotation of the magnetic field is called the

synchronous speed

an open delta connection is made using____single phase transformers

two

for most squirrel cage induction motors the typical percent slip is about

two to five

The three phase connection in which one of the windings are connected together is called a

wye connection

most transformer cores are made of thin sheets of metal, this is called

laminated

In a three phase circuit, the true power is found by

multiplying apparent power by the power factor

what is one factor that controls the output frequency of an alternator

number of stator poles and rotor speed

the test equipment needed to test the rotation direction of the new motor is a

phase rotation meter

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

phase voltage

three lines supply power to a three phase motor, if one of these lines should open, the motor will be connected to single phase power, this is condition is known as

single phasing

Line current and phase current are the same in the _____ configuration.

wye

A tape wound core is also called a

toroid core

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

three

if three phase transformation is needed and a three phase transformer of the proper size is not available, three single phase transformer can be connected in a

three phase bank

A wye delta transformer has a primary voltage of 7200v and a secondary voltage of 360v, what is the turns ratio

11.55:1

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

120 degrees

A wye connected alternator that has phase voltages of 277 V is feeding two loads, the frst is wye connected with 40 ohms Xl, the second is delta connected with 60 ohms Xc, what is phase current

14.93 amps

The horsepower rating of three phase motors and the kilovolt amphere rating of three phase transformers are _____ greater than single phase motors

150 percent

A synchronous motor is an induction motor

false

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

false

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

isolation transformer

the revolving armature type alternator is capable of___power output and is, therefore____often used than revolving fields

less, less

In a three phase connection, what is the voltage measured between lines

line voltage

An isolation transformer has the same input and output voltages.

True

_____alternators have a fan attached to one end of the shaft

air cooled

alternators of small kva rating are generally

air cooled

to reverse the direction of rotation of a three phase motor, reverse

any two leads

A transformer that has one winding, which is used for both primary and secondary is called an

autotransformer

in an open delta with single phase loads, the high leg must be identified by

both a and b

a delta delta transformer has a primary voltage of 7200v and a secondary voltage of 360 what is the turns ratio

20:1

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

3 amps

a squirrel cage rotor induction motor has a synchronous speed of 3600 rpm and a rotor speed of 3450 rpm what is the percent slip

4.17 percent

a wye delta transformer has a turns ratio of 2:1, it has a secondary line voltage of 480v, secondary load of 50 ohms, what is the current flow

5.54 amps

a three phase alternator containing six poles is turning at 1000 rpm, what is the output frequency

50 hz

A delta wye transformer has a turns ratio of 9:1, the primary line voltage is 3600v, what is the secondary

692.8v

what type of core is often found in high voltage distribution transformers

H type

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

VARs

the frequency of the current in a squirrel cage rotor___as the rotor approaches synchronous speed

decreases

In a three phase power system, the delivered power

never falls to zero

an altenator has 8 poles per phase turning at 900 rpm, what is the output frequency

60 hz

A transformer has a 2:1 turns ratio, 120V is applied to the primary, what is the secondary voltage

60 volts

a tape wound core is assembled by

winding a long continuous tape into a sprial

an alternator containing eight poles per phase is turning at 1500 rpm, what is the output frequency

100 hz

A delta connected set of windings has a phase current of 10A, what is the line current

17.32A

what function is performed by dielectric oil

all of the above

an alternator that has a separate small alternator mounted on the shaft is equipped with a

brushless exciter

by increasing or decreasing the strength of the magnetic field of the rotor, the_____is controlled

output voltage

A delta connected set of windings has a phase voltage of 100V, what is the line voltage

100 volts

In three phase transformer connections, the primary leads are labeled with the letter__ and the secondary with__

H, X

what machines operate on the same principle of electromagnetic induction as DC generators, but they have no commutator

alternators

The industrial use transformer that normally has 240/480v primary and 120 secondary is called a

control transformer

A three phase connection in which separate inductive loads are connected is a

delta connection

the amount of current that flows into a transformer primary when voltage is first applied is called

inrush current

A wye connected secondary has a phase voltage of 277.14v, what is the line voltage

480v

the squirrel cage rotor is constructed of____and end____embedded in steel laminations

bars, rings

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

The main power distribution system of a large industrial plant is generally shown using a

one line diagram

some motors are constructed so that they will operate on either of two voltages. When they are connected to operate on the higher of the two voltages, the windings are connected in

series

the squirrel cage rotor letters indicate the shape of rotor bars, different types of bars have a large effect on the____of a motor

starting torque

the non rotating part of a revolving field type alternator is called the

stator

In a balanced three phase system, the conductors need to be only ______the size of conductors for a single phase

75 percent

A delta connected three phase alternator is driving a wye connected load, output voltage is 480 volts, load resistors are 12 ohms each, what is the phase current

40 amps

a wye delta transformer has a secondary phase voltage pf 480v, with a 12 ohm load in each leg, what is the current in each load leg

40 amps

A delta connected set of windings has a phase voltage of 480V, what is the line voltge

480 volts

the transformer that converts a high voltage from the power company down to homes and businesses is called a

distribution transformer

the direct current that is an input to the alternators rotors is the

excitation current

an open delta transformer is assembled from two 150kva transformers. the output power of the open delta is

259.8kva

using_____is one method of preventing induced voltage from becoming excessive

field discharge resistor

when connecting three transformers for three phase using delta secondary, a voltage test should be done before closing the secondary, the correct voltage reading is

zero volts

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

delta

the torque of a squirrel cage induction motor will me max when the phase angle between the stator and rotor fields is

0 degrees

a wye delta transformer has a turns ratio of 2:1, it has a secondary line voltage of 480v, secondary has 50ohms, what is the primary line current

1.6 amps

a wye delta transformer has a turns ratio of 2:1, it has a secondary line voltage of 480v, secondary has 50ohms, what is the primary phase current

1.6 amps

an open delta transformer is assembled from two 50kva transformers. the output power of the open delta is

86.6 kva

what is a magnetically operated device that can change values of voltage, current and impedance without changing frequency

a transformer

the higher power output alternators use a revolving

field

when using an open delta with a center tapped transformer, one wire is the high leg, which has the

highest voltage

for installations that will have both three phase and single phase loads on a transformer, the utility company often provides an

open delta with one transformer center tapped

If one alternator does not produce sufficient power to supply a load, another alternator can be connected to the circuit. The second alternator is connected in _____.

parallel

the direction of magnetic field rotation is known as

phase rotation

a delta wye transformer has its____connected as a delta and its_____connected as a wye

primary, secondary

a wye delta transformer has its_____connected as a wye and its_____connected as a delta

primary, secondary

a______is used to measure the difference in voltge and frequency between two alternators

synchronoscope