MESIN ELEKTRIK EBOOK

3.2.4 FORMULA EMF GENERATED AC GENERATOR(Apply)

Actually available voltage phase (rms) is
Ephase = 2 kf kd kp f ϕ Z
Ephase = 2.22 kd kp f ϕ Z

if the number of coil or turn per phase (T) is given,
Ephase = 2 kf kd kp f ϕ (2T)
Ephase = 4.44 kd kp f ϕ T

If you want to know the line of the voltage generator,

Eline = 3Ephase

3.2.5 SOLVE PROBLEMS AC GENERATOR(Apply)

Example 3_2

an alternator runs at 250 rpm and generates an emf at 50hz. There are
210 slots each containing 5 conductors. The winding is distribute and full
pitch. All the conductors of each phase are in series and flux per pole is
17.5mWb which is sinusoidal distributed. If the winding is star
connected, determine the value of induced emf line (Eline)

E  2 .22 k k f Z
phase dp

E  2 .22 k k f Z
phase dp

E  2 .22 (1)( 1)( 50 )( 17 .5  10  3 )( 210 )
phase

E  408 V #
phase

 The rms voltage line generates

Diketahui: E  3E
line phase

E 3E
line phase

E  3 ( 408 )
line  707 V #

E
line

3.2.6 LOSSES IN AC GENERATORS AC GENERATOR(Apply)

Figure 3.20: sources of potential motor efficiency losses that can be avoided with proper
maintenance

3.2.6 LOSSES IN AC GENERATORS AC GENERATOR(Apply)

Losses in AC machines can be grouped as:
• Resistive losses (I2R) in the stator circuit
• Resistive losses (I2R) in the rotor circuit
• Iron losses due to fundamental frequency ac flux in the

core. These are mostly in the stator core.

ii. Mechanical losses. These include friction in the bearings and a
term called windage. (wind (like the weather) -age) Windage is
due to air turbulence and shear as the rotor and stator move past
each other

iii. Stray losses. The other parts that aren't easily calculated. These
include harmonic losses in the core and current flow through the
core (rather than staying in the conductors where you would like
it to be)

3.2.6 LOSSES IN AC GENERATORS AC GENERATOR(Apply)

The load current flows through the armature in all AC generators.
Like any coil, the armature has some amount of resistance and
inductive reactance. The combination of these make up what is
known as the internal resistance, which causes a loss in an
AC generator. When the load current flows, a voltage drop is
developed across the internal resistance. This voltage drop
subtracts from the output voltage and, therefore, represents
generated voltage and power that is lost and not available to the
load.

The voltage drop in an AC generator can be found using
Equation:

Voltage drop = IaRa + IaXLa
Where
Ia = armature current
Ra = armature resistance
XLa = armature inductive reactance

3.2.6 LOSSES IN AC GENERATORS AC GENERATOR(Apply)

Core losses are allocated to the stator since this is where most of
the core losses usually occur and stray losses must be taken off
after the mechanical power is converted as it is not simple to
include them in the electrical model.

In some cases, to simplify matters stray, core and friction and
windage losses are grouped as "rotational losses" and all deducted
after calculating the power converted to the mechanical system.
These two loss calculation techniques are illustrated below.

3.2.7 GENERATOR VOLTAGE REGULATION AC GENERATOR(Apply)

Voltage regulation of Alternator
The voltage regulation of an Alternator is defined as the change
in terminal voltage from no-load to full-load condition expressed
as per-unit or percentage of terminal voltage at load condition;
the speed and excitation conditions remaining same.

Determination of Voltage Regulation
three methods which are used to determine the voltage
regulation of smooth cylindrical type Alternators
1. Synchronous impedance / emf method
2. Ampere-turn / mmf method
3. Zero power factor / Potier method

3.2.7 GENERATOR VOLTAGE REGULATION AC GENERATOR(Apply)

In a situation without a load connected to the generator, the
terminal voltage is equal to the voltage generated in the
generator, but when the load connected to the generator
terminal voltage value will change either increase or decrease
depending on the type of load applied.

Thus a voltage regulation circuit held for the purpose of
stabilizing the terminal voltage of the variable as a result of the
applied load or also referred to as a result of load power factor.
Load power factor influencing the voltage drop is due to the
following factors namely:

i. The stator coil resistance
ii. Stator coil impedance and
iii. Due to the armature reaction

3.2.7 GENERATOR VOLTAGE REGULATION AC GENERATOR(Apply)

Ac generator voltage regulation is usually expressed as a
percentage and defined as follows;
“Regulation is the difference between no-load terminal voltage
of the generator terminal voltage to full load per with full load
terminal voltage”

% regulation = (Vnl−Vfl) = Eg−Vt
Vfl Vt

Vnl= Eg= No-load terminal voltage (the voltage is generated in
the generator, Eg)

Vfl = Vt= Terminal voltage when full load (when load is applied
on the generator).

3.2.7 GENERATOR VOLTAGE REGULATION AC GENERATOR(Apply)

The frequency of the generated voltage is dependent on the

number of field poles and the speed at which the generator is

operated, as indicated in Equation:

N= 60f [RPM]

if the rotor contains a multiple number of poles (2, 4, 6, etc) then
2
wrotor = 2πf (rad/sec)

Np = 120 RPM

Where:

f = frequency (Hz)

P = total number of poles

N = rotor speed (rpm)

120 = conversion from minutes to seconds and from poles to pole

pairs

Synchronous speed versus poles for a 60Hz machine:

P (poles) 2 4 6 8 10

N (RPM) 3600 1800 1200 900 720

3.2.8 DESCRIBE THE VOLTAGE REGULATION AC GENERATOR(Apply)

Alternator on load
As the load on alternator is varied, its terminal voltage is also found
to vary as in dc generator. This variation in terminal voltage V is due

to the following reasons:-

i. Voltage drop due to armature resistance Ra
ii. Voltage drop due to armature leakage reactance XL
iii. Voltage drop due to armature reaction XL

Load change, the terminal voltage also change
• Armature resistance(Er)=IRa v/phase=phase of Ia
• Armature reactance(Ex1)=Ix1 Xa v/phase, the phase lead 900 of

Ia
• Armature reaction(Ear)=Ixa- consider 3 cases, when load is

i. power factor unity

ii. power factor zero lagging

iii. power factor zero leading

3.2.9 synchronous impedance method TOPIC 3: A.U GENERATOR

Terminal voltage increases or decreases depend on the load usage
• Power factor for load is 1 @lagging the terminal voltage is

decreases
• Power factor for load is leading the terminal voltage is increases

3.2.11 parallel ac generator TOPIC 3: A.U GENERATOR

During paralleling operations,
• voltages of the two generators that are to be

paralleled are indicated through the use of

voltmeters.
• Frequency matching is accomplished through the

use of output frequency meters.
• Phase matching is accomplished through the use

of a synchroscope,

a device that senses the two frequencies and

gives an indication of phase differences and a

relative comparison of frequency differences.

3.2.11 parallel ac generator TOPIC 3: A.U GENERATOR

3 conditions must be met prior to paralleling/synchronizing) AC generators

1. Their terminal voltages must be equal.
If the voltages of the two AC generators are not equal, one of the AC
generators could be picked up as a reactive load to the other AC
generator. This causes high currents to be exchanged between the two
machines, possibly causing generator or distribution system damage.

2. Their frequencies must be equal.
A mismatch in frequencies of the two AC generators will cause the
generator with the lower frequency to be picked up as a load on the other
generator (a condition referred to as "motoring"). This can cause
an overload in the generators and the distribution system.

3. Their output voltages must be in phase.
A mismatch in the phases will cause large opposing voltages to be
developed. The worst case mismatch would be 180° out of phase,
resulting in an opposing voltage between the two generators of twice the
output voltage. This high voltage can cause damage to the generators
and distribution system due to high currents

3.2.11 parallel ac generator TOPIC 3: A.U GENERATOR

• Paralleling AC Generators Most electrical power grids and
distribution systems have more than one AC generator

operating at one time.
• Normally, two or more generators are operated in parallel in

order to increase the available power.

3.1 Construction & principles TOPIC 3 A.U GENERATOR

3.1 Construction & principles TOPIC 3 A.U GENERATOR

3.1 Construction & principles TOPIC 3 A.U GENERATOR

3.1 Construction & principles TOPIC 3 A.U GENERATOR