A/C, D/C, and Magnetism - Part 2
Three-phase voltages are _____ out of phase with each other.
120 degrees
A transformer has a 240 V primary and a 60 V secondary. With a 5 ohm load connected, what is the primary current?
3 A
The rotating part of a generator is called the _____.
Armature
A transformer has a 2:1 turns ratio. 120 V is applied to the primary. What is the secondary voltage?
60 V
A transformer has a 240 V primary and a 120 V secondary. With a 30 ohm 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 device that converts mechanical energy into DC electrical energy is a(n) _____.
Generator
In a transformer, the turns of primary wire compared to the turns of secondary wire is called the _____ ratio.
Turns
Shunt field windings are connected in parallel with the armature. They are wound with _____ turns of fairly _____ wire.
Many, small
The transformer winding, which is the power input winding, is called the _____ winding.
Primary
A transformer in which the secondary voltage is more than the primary voltage is called a(n) _____ transformer.
Step-up
In a three-phase circuit, the true power (watts) is found by _____.
multiplying apparent power by the power factor
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%
The _____ ride against the commutator segments and are used to connect the armature to the external circuit of the DC machine.
Brushes
The three-phase connection in which three separate inductive loads have been connected together is 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
_____ provide(s) the magnetic field necessary for the operation of the machine.
Pole pieces
Connection to the armature of an alternator is normally done by using _____.
Slipring
A transformer in which the secondary voltage is less than the primary voltage is called a(n) _____ transformer.
Step-down
Often in calculations of values in three-phase systems, the square root of three occurs. The approximate value of this constant is _____.
1.732
_____ operate on the same principle of electromagnetic induction as DC generators, but they have no commutator.
Alternators
The component of a DC generator that converts the armature AC into DC is the _____.
Commutator
A transformer in which the primary and secondary are physically separated and not connected by a conductor is called a(n) _____ transformer.
Isolation
The magnetically operated device that can change values of voltage, current, and impedance without changing frequency is the _____.
Transformer
Line current and phase current are the same in the _____ configuration.
Wye
A delta connected set of windings has a phase voltage of 100 V. The line voltage is _____.
100 V
A delta-connected set of windings has a phase current of 10 A. The line current is _____.
17.32 A
Line voltage and phase voltage are the same in the _____ connection.
Delta
In a transformer, even when there is no load connected, there will be some small current flow known as _____ current.
Excitation
Series field windings are connected in series with the armature. They are wound with _____ turns of fairly _____ wire.
Few, large
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 transformer winding, which is the output winding, is called the _____ winding.
Secondary
The series generator has only a series field, which is connected in _____ with the armature.
Series
An isolation transformer has the same input and output voltages.
True
