Synchronous Machines (hints: Write a technical report demonstrating Synchronous machine importance, construction; theory of operation, equivalent circuit)
Abstract
Synchronous Machine constitutes
of both synchronous motors and synchronous generators, both are very important
and have many applications in our life, synchronous machine consists of two
parts: stator and rotor (salient pole, cylindrical). theory of its operation depends on
Law of Electro-Magnetic Induction and Law
of Interaction. finally Equivalent
circuit of synchronous machine which is the same at salient pole or
cylindrical.
Table
of content
ABSTRACT ………………………………………………………………………………………….. 2
TABLE OF
CONTENT ………………………………………………………………………………. 2
LIST OF FEGURES ………………………………………………………………………………….. 3
LIST OF SYMBOLS
…………………………………………………………………………………. 3
INTRODUCTION AND RESEARCH
OBJECTEVS ……………………………………………….. 4
CONTENT
……………………………………………………………………………………………...
5
1.
Synchronous
machine importance ………………………………………………………………... 5
1.1.
Generators
……………………………………………………………………………………
5
1.2.
Motors
……………………………………………………………………………………….
6
2.
Synchronous
machine construction
……………………………………………………………….. 7
2.1.
Stator Construction ………………………………………………………………………….. 7
2.2.
Rotor
Construction
…………………………………………………………………………..
7
2.2.1. Salient-pole rotor ……………………………………………………………………….. 8
2.2.2. Cylindrical Rotor ……………………………………………………………………….. 9
3.
theory
of operation
………………………………………………………………………………….
9
3.1.
Law of
Electro-Magnetic Induction
………………………………………………………………..….…. 9
3.2.
Law of Interaction
……………………………………………………………………………………...
10
4.
Equivalent circuit
…………………………………………………………………………………..
10
REFRENSES ……………………………………………………………………………....…………… 11
LIST OF FIGURES
Figure 1.1 synchronous generator ………………………………………….. 5
Figure 1.2 synchronous motor ………………………………………………. 6
Figure 2.1 synchronous machine stator ……………………………………… 7
Figure 2.2.1 synchronous
machine (salient pole rotor) …………………………
8
Figure 2.2.2 synchronous
machine (cylindrical rotor) …………………………..
9
Figure 3.1 explain Law of Electro-Magnetic Induction ……………………………… 9
Figure
3.2 explain Law of Interaction
………………………………….……………. 10
Figure
4 Equivalent circuit
of the generator synchronous machine ……….. 10
LIST OF SYMBOLS
EF voltage
source
IF constant excitation current
Xa series-connected
Reactance
R resistance
Xl leakage
reactance
V The
machine terminal voltage
Zs the
synchronous impedance
Xs the synchronous reactance
Introduction and Research Objectives
A synchronous machine is an AC
rotating machine whose speed under steady state condition is proportional to
the frequency of the current in its armature. The magnetic field created by the
stator currents rotates at the synchronous speed, and that created by the field
current on the rotor is rotating at the synchronous speed also, and a steady
torque results. So, these machines are called synchronous machines because they
operate at constant speeds and constant frequencies under steady state
conditions. Synchronous machines are widely used as generators in the grid
power supply particularly for large power plants, such as turbine generators
and hydroelectric generators. Because the rotor speed is equal to the stator
magnetic field's synchronous speed, synchronous motors may be used in
circumstances where constant velocity drive is needed. Because the reactive
power produced by a synchronous machine can be changed by adjusting the
magnitude of rotor field current, unloaded synchronous machines are also
sometimes mounted for power factor correction or for reactive kVA flow control
in power systems. These devices, classified as synchronous condensers, can be
more economical than static capacitors in the large sizes.
Content
Synchronous Machine constitutes
of both synchronous motors as well as synchronous generators. The machine which
converts mechanical power into AC electrical power is called as Synchronous
Generator or Alternator. However, if the same machine can
be operated as a motor is known as Synchronous Motor.
1. Synchronous
machine importance:
1.1.
The electric current produced by a Synchronous Generator has a waveform
that is “synchronized” with the rotational speed of the generator.
Common applications:
(fig.1.1)
- Electrical
Power Generators — Speed is conveniently regulated and therefore frequency
regulated.
- Backup or
Backup Generators — Since modern standby generators emulate electrical
power provided by electrical utilities, they provide electrical power to
households, companies, industry and organizations in the event of an
interruption.
- Portable
generators — The most common type of portable generator generates a
comparable current to that of the utility. Based on the expected usage the
overall standard ranges from mediocre to outstanding. Portable generators
are operated by internal combustion engines and are designed to operate on
gaseous fuel such as propane, petrol or diesel.
- Automotive
Alternator — In the past, the battery was powered and the engine was
driven by a powerful DC generator. The silicon diode rectifier made
realistic use of a three-phase synchronous alternator.
- Wind
turbines — Certain home systems use a synchronous multi-phase generator to
generate AC current that is rectified to DC to charge batteries. The DC
current is usually inverted to 60 or 50 (North America or Europe) hertz AC
for use in the home.
1.2.
Motors:
Applications:
- Synchronous motors are used to
increase the power factor at generating stations and at substations
attached to the busbars. For this reason they are operated in over-excited
condition and without mechanical load on them. These devices supply the
reactive power to the grid when over enthusiastic, and help increase the
system's power factor
- They may be used for loads
needing constant speeds because of the higher performance relative to the
induction motors. Any of the traditional high speed synchronous engines
are drives such as fans, blowers, dc generators, line shafts, centrifugal
pumps , compressors, reciprocating pumps, rubber and paper mills
- Synchronous engines are used to
monitor friction at the end of the transmission lines
- Synchronous engines are used in
garment and paper industries to reach broad variety of speeds with
variable frequency control systems
2.
Synchronous machine construction:
An alternator is
made up of two parts: the stator, and the rotor. The stator is the machine's
stationary component, and the rotor is the machine's rotary component. The
stator carries the winding of the armature in which the voltage is produced,
and its output is taken. The machine's rotor generates the principal flux.
2.1.
Stator
Construction:
2.2.
Rotor
Construction:
The rotor
construction is of two types:
2.2.1.
Salient-pole
rotor:
·
Important implies 'projecting.' A
salient-pole is made up of poles which are extended out of the rotor core
sheet. These are placed on four or five poles for the rotors.
·
The rotor is prone to shift in magnetic
forces, which is why it is constructed in steel laminations to reduce the loss
of eddy current. Identical dimensional poles are mounted to the necessary
length by piling laminations and then riveting together. After each pole body
is mounted along the field coil, these poles are connected to a steel spider
keyed to the shaft with a dove-tail joint. At a rapid shift in load conditions,
salient-pole rotors have faces to tamp out the rotor oscillations. A
non-uniform air distance goes for a synchronous salient-pole unit.
·
The air distance below the centers of the
pole is small and it is full between the poles. The pole faces are so formed
that the duration of the radical air gap decreases from the middle of the pole
to the tips of the pole, such that the air gap's flux distribution is
sinusoidal. This will help produce sinusoidal e.m.f to the computer.
·
· The salient-pole generators have a greater number of poles and lower level of service.
(Fig.2.2.1)
·
Salient-pole alternators are called
hydro-alternators or hydro-generators and are powered by water turbines.
2.2.2.
Cylindrical
Rotor:
·
The rotor-cylinder machines are also
classified as non-salient pole rotor motors. The rotor construct is such that
it forms a smooth ring. It has no actual points, as in the building of the
salient-pole. Such rotors are constructed of high-grade
Nickel-Chrome-Molybdenum alloy robust forgings.
·
Holes are placed at frequent intervals and
parallel to the shaft at about two thirds of the rotor circumference.
·
In those slots the d.c field windings are
related. The winding is kind of spread. The unslotted rotor part shapes two
sides of the shaft. These devices have a long axial duration and a broad
diameter.
·
· Cylindrical-rotor engines drive steam or gas turbines. The synchronous rotor-cylinder generators are called turbo-alternators or turbo-generators.
( Fig.2.2.2)
3.
theory of
operation:
A synchronous machine
is just an electromechanical transducer which converts mechanical energy into
electrical energy or vice versa. The fundamental phenomenon or law which makes
these conversions possible are known as the Law of
Electromagnetic Induction and Law
of interaction.
3.1.
Law of Electro-Magnetic Induction:
This law is often
called the First Law of Electromagnetic Induction of Faraday. This law relates
to emf output, i.e. emf is produced in a conductor any time it cuts through the
magnetic field as shown (fig.3.1)
3.2.
Law of Interaction:
This
rule applies to force or torque output, i.e., if a current carrying conductor
is put in the magnetic field by the interaction of the magnetic field generated
by the current carrying conductor and the main field, force is exerted on the
generating torque conductor. The number reveals (Fig.3.2)
4.
Equivalent circuit:
If a synchronous machine has a cylindrical or salient-pole
rotor, the operation is the same when producing power and is better illustrated
in terms of the representation seen in (Figure.4) The synchronous machine's
corresponding circuit includes an EF voltage source that is constant for a
constant IF excitation current and a series-connected Xa reaction. The machine terminal voltage V is obtained from Er by
recognizing hat the stator phase windings have a small resistance RL and a
leakage reactance Xl (about I0 per cent of Xa) resulting from flux produced by
the stator but not crossing the air gap. The reactances XL and Xa are usually
considered together as the synchronous reactance Xs,
(Fig.4)
The machine phasor
equation is: EF =V + I × Zs
where
Zs is the synchronous impedance,
Zs=R+j(Xl+Xa), or Zs =R+jXs Where Xs is the synchronous reactance:
Xs=Xa+Xl
References
[1]. D.
Fodorean, A. Djerdir, I. Viorel and A. Miraoui, "A Double Excited
Synchronous Machine for Direct Drive Application—Design and Prototype
Tests," in IEEE Transactions on Energy Conversion, vol. 22, no. 3, pp.
656-665, Sept. 2007
[2]. R. Mikkonen,
L. Soderlund and J. -. Eriksson, "The design and construction of a 1500 W
HTS superconducting synchronous machine," in IEEE Transactions on
Magnetics, vol. 32, no. 4, pp. 2377-2380, July 1996
[4]. H. Tsai, A. Keyhani, J. Demcko and
R. G. Farmer, "On-line synchronous machine parameter estimation from small
disturbance operating data," in IEEE Transactions on Energy Conversion,
vol. 10, no. 1, pp. 25-36, March 1995.
[5]. R.
F. Schiferl and C. M. Ong, "Six Phase Synchronous Machine with AC and DC
Stator Connections, Part I: Equivalent Circuit Representation and Steady-State
Analysis," in IEEE Transactions on Power Apparatus and Systems, vol.
PAS-102, no. 8, pp. 2685-2693, Aug. 1983
[6]. M.
L. Bash and S. Pekarek, "Analysis and Validation of a Population-Based
Design of a Wound-Rotor Synchronous Machine," in IEEE Transactions on
Energy Conversion, vol. 27, no. 3, pp. 603-614, Sept. 2012.
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