Q7-9. All generators, regardless of the size or
The three-phase ac generator is most commonly
connected in what is called a FOUR-WIRE WYE. In
whether they are ac or dc, work on the
this system the common connection for the phases,
principle of magnetic induction?
called NEUTRAL, is connected to ground. There is also
1. True
a THREE-WIRE WYE, accomplished by connecting
2. False
one of the phases to ground, usually the B phase. If this
Q7-10. What is the one major difference between an
system is used, care must be taken to ensure that all
three-phase equipment have the same phase grounded.
ac generator and a dc generator?
Another method of connecting the phases is called
1. The ac generator has brushes and the dc
DELTA. In this system, a common connection of two of
generator does not
the phases is grounded. Figure 7-33 shows the
2. The ac generator has several brushes and
grounding of the three-phase systems.
the dc generator has only one brush
3. The ac generator has slip rings and the
In the dc systems, the negative (-) side of the circuit
dc generator has a commutator
is usually connected to ground (determined by the way
4. The ac generator has a rotating field and
the power supply is connected).
the dc generator has a stationary field
Any wire that completes the circuit to the ground
Q7-11. A generator that supplies its own field
network for an equipment is designated with the letter
excitation is referred to as what type of
N. Any wire so designated may come in contact with
ground at any point without causing malfunction of the
generator?
equipment.
1.
An ac generator
2.
A dc generator
A grounded circuit has advantages since it reduces
3.
A self-contained generator
overall weight by using fewer conductors. This results
4.
A self-excited generator
in a reduction in cost and space requirements. Other
advantages are that troubleshooting is simplified to
Q7-12. Which of the following parts of the generator
some extent and the impedance of the ground return
does the regulator control to control the
path is lower than that of a wire conductor. The
generator output?
grounded system also has disadvantages. Short circuits
1.
The armature voltage
result when a bare spot on any ungrounded conductor
2.
The field excitation
touches ground.
3.
The stator voltage
4.
The winding voltage
UNGROUNDED SYSTEMS
Q7-13. The two types of ac generators are
The term ungrounded system means that the circuit
rotating-field and rotating-armature?
is in no way connected to ground. All conductors are
run from the power source to the loads. Circuits of this
1. True
2. False
type are often referred to as being above ground. The
ungrounded system has a number of advantages. It
Q7-14. The ac generator voltage regulation is
prevents one circuit from feeding into another. No
obtained by controlling the output of which of
malfunction of equipment occurs should one
the following components?
conductor become accidentally grounded. The circuits
1.
The exciter
are completely insulated from each other. The system
2.
The regulator
has the disadvantage of adding more weight because it
3.
The stator
requires more conductors than the grounded system.
4.
The rotor
This results in added cost and space requirements.
Q7-15. What is the ac phase-to-phase voltage of a
Q7-8. Which of the following is NOT a method of
increasing the output of a generator?
support equipment power generator?
1.
Increase the strength of the magnetic field
1.
115 Vac
2.
Increase the speed of the conductor
2.
120 Vac
3.
Increase the number of brushes
3.
208 Vac
4.
Increase the length of the conductor
4.
220 Vac
7-30
