General power system

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General power system
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objective

• Review general energy and power system
• Application of fundamental knowledge of principal
  machines , transformer and other power device to
  large electrical systems.
• To present general picture of typical electrical
  for High voltage generation , transformation and
  distribution
• Difference between shipboard and land based HV
  power generation

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RECAP

• Principle of electrical machines
• Power generation, transformation and distribution
  
• Electromagnetism
• Induction and transformer
• Losses
• Single and 3 phase circuit
• Active and reactive power
• Electric machine and power
• Ancillaries

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General Power Systems

• Majority of merchant ships have a 3-phase 3 wire,
  440 V insulated neutral earth power systems
• This power system falls in the category of LV and
  meets the power demands of medium capacity motors
  up to 200 kW
• When large loads are connected to the LV system
  the magnitude of current flow becomes too large
  resulting in overheating due to high iron and
  copper losses
• P VI Cos ?
• Copper loss I2 R kW
• Losses in Electrical Systems
• Copper Losses in electrical cables and machine
  windings
• Hysteresis Loss in magnetic cores
• Eddy current loss in conductors and cores
• All these losses are current dependent and rise
  to very high levels in LV machines for large
  power ratings

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Introduction to Machinery Principles
An electric machine
is a device that can convert either mechanical
energy to electric energy or vice versa.
A generator
converts mechanical energy to electrical energy.
A motor
converts electrical energy to mechanical energy.
Almost all practical motors and generators
convert energy from one form to another through
the action of a magnetic field.
Another closely related device is the transformer.
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Introduction to Machinery Principles . . . . .
A transformer
is a device that converts ac electrical energy
at one voltage level to ac electrical energy at
another voltage level, but with the same
frequency.
In general, transformers operate on the same
principles as generators and motors, and are
usually studied together with generators and
motors.
These 3 types of devices are inevitable in modern
daily life.
Motors find applications in several home
appliances.
In the work place, motors provide the
motive power for almost all tools.
Generators are essential to supply the
power used by all these motors.
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INTRODUCTION
The electromagnetic system is a necessary element
of all rotating and static electric machinery and
electromechanical devices.
The role of electromagnetic system is to
establish and control electromagnetic fields for
carrying out conversion of energy, and transfer.
Practically all motors and generators, depend
upon the magnetic field as the coupling medium
allowing interchange of energy in either
direction between electrical and mechanical
systems.
A transformer though not an electromechanical
conversion device, provides a means of
transferring electrical energy between two
electrical ports via the medium of a magnetic
field.
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MAGNETIC FIELD . . . .
2. A time-changing magnetic field induces a
voltage in a coil of wire if it passes through
that coil. This is the basis of transformer
action.
3. A current-carrying wire in the presence of a
magnetic field has a force induced on it. This
is the basis of motor action.
4. A moving wire in the presence of a magnetic
field has a voltage induced in it. This is the
basis of the generator action.
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THREE PHASE CIRCUITS
Introduction
Three-phase systems differ from single-phase
systems in that they use a set of three voltages
instead of one.
In general, a three-phase system is merely a
combination of three single phase systems of
which the three voltages differ in phase by 120
electrical degrees from each other in a
particular sequence.
There are two basic three-phase connections, the
wye (star) and the delta connections.
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Analysis of three-phase balanced circuits . . . .
Wye connection Delta connection
Voltage magnitudes
Current magnitudes
ABC phase sequence VAB leads VA by 30? IA lags IAB by 30?
ACB phase sequence VAB lags VA by 30? IA leads IAB by 30?
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Active power and reactive power calculations
The total average power absorbed by a three phase
balanced load delivered by a three-phase
generator, is equal to the sum of the powers in
each phase. The voltage and current in each phase
are equal.
PT P1 P2 P3
PT P1 P2