DONE BY MY COLLEAGUES IN COLLEGE BSEE-5

2.  DIRECT CURRENT (DC) GENERATOR
 ALTERNATING CURRENT (AC)
GENERATOR
☺

5.  TWO-WIRE GENERATOR- have only two line
terminals, one known as the positive
terminal and the other as the negative
terminal.
 THREE-WIRE GENERATOR- a direct-current
generator with both slip rings and a
commutator used for supplying current to a
direct-current three-wire system whose
neutral wire is connected to the center
point of a high-reactance winding
connected across the slip rings and whose
two main conductors are connected to the
commutator brushes

7.  MOTOR-GENERATOR SET-A motor generator set is a
device used for the conversion of electrical energy,
typically in the form of frequency or voltage, into
another form of energy.
A motor-generator (an M-G set or
a dynamotor for dynamo-motor) is a device for
converting electrical power to another form. Motor-
generator sets are used to convert frequency, voltage,
or phase of power. They may also be used to isolate
electrical loads from the electrical power supply line.
In the context of electric power generation and
large fixed electrical power systems, a motor-
generator consists of an electric motor mechanically
coupled to an electric generator (or alternator).

10.  ROTARY CONVERTER-A rotary
converter is a type of electrical
machine which acts as a
mechanical rectifier or inverter. It was
used to convert AC to DC or DC to
AC power before the advent of
chemical or solid state power
rectification. They were commonly
used to provide DC power for
commercial, industrial and railway
electrification from an AC power
source.

12.  MERCURY-ARC RECTIFIER- A mercury-arc valve or mercury-
vapor rectifier or (UK) mercury-arc rectifier is a type of
electrical rectifier used for converting high-voltage or high-
current alternating current(AC) into direct current (DC). It is a
type of hot cathode gas discharge tube but is unusual in that
the cathode, instead of being solid, is made from liquid
mercury and is therefore self-restoring. As a result, mercury-
arc valves were much more rugged, long-lasting and
capable of carrying much higher currents than most other
types of gas discharge tube.
Mercury-arc rectifiers were used to provide power for
industrial motors, electric railways, streetcars, and electric
locomotives, as well as for radio transmitters and for high-
voltage direct current power transmission. They were the
primary method of rectification before the advent
of semiconductor rectifiers such as diodes, thyristors and gate
turn-off thyristors(GTOs).

15. Method of Excitation:
› Self-excited
SERIES
SHUNT
COMPOUND
1. SHORT SHUNT AND LONG SHUNT
2. FLAT COMPOUNDED,
OVERCOMPOUNDED AND
DIFFERENTIALLY COMPOUNDED

17.  Long shunt - the
series field coils are
connected in
series with the
armature coils
while the shunt
field coils are
connected across
the series
combination.

18.  Short Shunt - the
series field coils
are connected
in series with the
load while the
shunt field coils
are connected
across armature
coils

19.  Flat-compound – if the series field amp-turns
are such as to produce the same voltage
at rated load as at no-load.
 Over-compound – if the series field amp-
turns are such that the rated-load voltage is
greater than the no load voltage.
 Differentially compound-has an external
characteristic similar to that of a shunt
generator but with large demagnetization
armature reaction. Hence, it is widely used
in arc welding where larger voltage drop is
desirable with increase in current.

21.  Number of Poles
› Bipolar- two poles, one north and one
south
› Multipolar- must always be equal to a
multiple of two because it was found
necessary to use more than 2 poles;
hence, today all DC generators have at
least 4 poles.
› Homopolar- designed w/ the armature
conductors revolving in a unidirectional
field, thusthe emfs generated in them do
not alternate during the revolution of the
armature;hence, no commutator is
needed.

22.  Types of Armature Winding
› Multiple or Lap
- contains as many parallel paths as the
generator has many poles.
-requires as many brush studs as the
generator has many poles.
› Series, two circuit or wave
- contains only two parallel paths
irrespective of the number of main poles.
- requires only two brush studs irrespective
of the number of main poles.

23.  Combination of Multiple and Series-
also known as “frog-leg winding”
-consists essentially of a standard
multiple winding and a standard series
winding placed together in the same
armature slots and connected to the
same commutator.

24.  Method of Prime-Mover Drive
› Engine Type- has its armature mounted
on a continuation of the engine
crankshaft.
› Direct connected to steam turbine- often
used as spare exciters in steam power
plants.
› Geared to steam turbines
› Water Turbines- found in hydraulic power
plants where spare exciter units are
direct- connected to water wheels.

25.  Type of Service
› General Power and Lighting- are generally
wound for 125 and 250 volts. The voltage
regulation should not be more than 2%.
› Railway-have compound-wound fields and
are designed for 550 or 600 volts for city
railway service, 1200 volts for interurban
service, and 3000 volts for trunk-line
electrification.
› Electrolytic Works- usually low-voltage
machines of large current capacity. Often
separately excited from a source higher
voltage.

28. › Electric Furnace Work- shunt or
differentially compound excitation is
desirable, since such generators will not
maintain large current on short circuit.
› Boosters- are DC generators connected
in series with the line to raise or lower the
voltage. They are generally low voltage
machines of large current capacity and
are usually driven at constant speed by
shunt motors. They may be shunt, series,
or compound-wound.

30. › Exciters- generally designed for 125
to 250 volts normal. They may be
either shunt or compound-wound.
› Balancer- consists of two similar DC
machines directly coupled to each
other and connected in series
across the outer conductors of a 3-
wire system of distribution. Can be
either shunt or compound wound.

32.  Special Feature of Construction
› Noncommutating-pole Machines
› Commutating-pole Machines
› Compensating Wound Machines-
are essential on rolling-mill motors
and generators subjected to
sudden changes of load, as, for
example, in railway service.
› Diverter-pole Machines

34.  Compound wound direct-current
generator with the series winding of the
diverter pole opposing the flux
generated by the shunt wound main
pole; provides a close voltage
regulation.

35.  Similar to the conventional DC Generator.

36. By voltage regulation of a generator is
meant the change in its terminal voltage
with the change in load current when it is
running at a constant speed. If the change
in voltage between no-load and full load is
small, then the generator is said to have
good regulation but if the change in
voltage is large, then it has poor regulation.
The voltage regulation of a d.c. generator is
the change in voltage when the load is
reduced from rated value to zero,
expressed as percentage of the rated load
voltage.

37.  Stray Losses
› Mechanical
 Windage
 Bearing Friction
 Brush Friction
 Hysteresis Loss
 Eddy- current Loss
 Iron

38. Copper Losses
› Shunt-Field Copper Loss
› Series-Field Copper Loss
› Armature Copper Loss
› Commutating-Field Copper Loss
Load Losses

39. - A machine that converts mechanical
power into alternating-current electric
power.

41.  Synchronous AC Generator-used
because they offer precise control of
voltage, frequency, VARs and WATTs. This
control is achieved through the use of
voltage
regulators and governors. A synchronous
machine consists of a stationary
armature winding (stator) with many
wires connected in series or parallel to
obtain the desired terminal voltage.

42.  INDUCTION GENERATOR-The induction
generator is nothing more than an
induction motor driven above its
synchronous speed by an amount not
exceeding the full load slip the unit
would have as a motor.
 PHASE CONVERTER-A phase converter is
a device that produces three-phase
electrical power from a single-phase
source, thus allowing the operation of
three-phase equipment at a site that
only has single-phase electrical service.

43.  FREQUENCY-CHANGER SET--A frequency
changer or frequency converter is
an electronic device that converts
alternating current (AC) of
one frequency to alternating current of
another frequency. The device may also
change the voltage, but if it does, that is
incidental to its principal purpose.

44.  Frequency
› 60 cycles per second
› 25 cycles per second-railway service.
 Number of Phases
 Single phase
 Two Phase
 Three Phase
 Wye connected
 Delta connected

45.  More capacity can be obtained
out of a given armature than
when wound single or two phase.
 It is more economical to transmit
power over a 3-wire 3-phase
circuit than over a 4-wire 2-phase
circuit.

46.  Relative Motion
› Revolving Armature Type
› Revolving Field Type
 Type of Prime Mover
› Engine-Type Alternators
› Steam Turbine Type
› Water-wheel Type Alternators
› Vertical
› Horizontal

47.  The armature end windings can be more
satisfactorily braced in the case of a
stationary armature.
 With the terminal voltages obtained from
present-day alternators, it is entirely out
of the question to use rubbing contacts
to collect the current from the armature.
 Cheaper construction

48.  Designed for
operation w/
reciprocating
steam engines
and internal
combustion
engines, which
may be either
gas or oil engines.

49.  Units are driven
by water
turbines, which
may be of the
impulse,
reaction, or
propeller type.

51.  Such generators are designed for
operation with steam turbines.
 In the early development of such units
vertical mounting was considered
feasible, but it was soon realized that
the horizontal method of mounting
was superior in many details.

53.  Armature Yoke
 Armature Core-forms the part of the
magnetic circuit in the stator.
 Armature-Coil Supports-use to withstand the
large stresses produced under load, short-
circuit conditions.
 Rotor
 Field Windings- generally composed of
strap copper laid flatwise in the rotor slots.
This bring pressure to centrifugal force on
the flat side of the copper; hence there is
no possibility of the insulation between turns
becoming chafed or cut.