1. Electrical Theory I - The Basics
Let there be light….

2. Introduction Basic Terminology Ohm’s Law
Kirchhoff’s Laws & Applications
Basic Circuit Analysis
Transformers & Rectifiers

3. How is Electricity Produced?
Friction: “static electricity” from rubbing (walking across a carpet)
Pressure: piezoelectricity from squeezing crystals together (quartz watch)
Heat: voltage produced at junction of dissimilar metals (thermocouple)
Light: voltage produced from light striking photocell (solar power)
Chemical: voltage produced from chemical reaction (wet or dry cell battery)
Magnetism: voltage produced using electromotive induction (AC or DC generator).

4. Basic Terminology Electromotive Force (E or V)
Force which causes electrons to move from one location to another
Known as emf, potential difference, or voltage
Unit is volt (V)
Source:
Generator
Battery
Like pump that moves water through “pressure”

5. Basic Terminology Current (I)
Flow of electric charges - electrons (or holes) - through a conductor or circuit per increment of time
Unit is ampere (number of charged particles passing a point each second)
1 amp = 1 coulomb/sec = 6x1018 electrons/sec
Like rate of flow of water through a pipe

6. Basic Terminology Resistance (R) Conductor
An electrical circuit’s opposition to the flow of current through it
Measured in ohms (W)
Conductor
All materials will conduct electricity, but at varying resistances
Good conductors have little resistance (ie: silver, copper, aluminum, iron)

7. Basic Terminology Insulator Power (P)
Substances which offer high resistance to current flow (ie: wood, rubber, plastics)
Circuits made of wires covered with insulator
Power (P)
Rate at which work is performed
Measured in watts (W)

8. Ohm’s Law & Applications
Law: current of a circuit is directly proportional to the applied voltage and inversely proportional to circuit resistance
I a V, I a 1/R V =IR
Power
P = VI P = (IR)I = I2R

9. Kirchhoff’s Laws Kirchhoff’s Current Law (KCL)
A node is any junction in a circuit where two or more elements meet
Currents into a node sum to zero OR
Current entering a junction is equivalent to the current leaving a junction

10. Kirchhoff’s Laws Kirchhoff’s Voltage Law (KVL)
A loop is any path in a circuit that current can take so that it meets back up to where it starts
Voltages around a CLOSED loop sum to zero

11. Applications Resistors in Series Resistors in Parallel
RT = R1 + R2 + R
Resistors in Parallel
1/RT = 1/R1 + 1/R2 + 1/R
Examples: should be able to find total current flow in circuit, current flow through each resistor, voltages, power dissipated, etc.

12. Questions?

13. Electrical Theory II – The Applications
Harnessing the Power…

14. Power Generation Chemical Cells Magnetism Electrodes Electrolyte
Conductor
Wet/Dry Batteries
Magnetism

15. Electromagnetic Induction
Faraday (1831):
Showed that an emf is induced in a conductor if a magnet passes by a conductor
When pole of magnet entered coil, current flowed in one direction
When direction of magnet reversed, current flowed in opposite direction

16. Electromagnetic Induction
Magnitude of induced current can be increased by:
Increasing strength of magnetic field
Increasing speed of relative motion
Positioning of field & conductor to increase number of magnetic lines of flux cut
Magnetic field usually produced by electromagnet

17. Electromagnet Soft iron core wound with coils of wire
When current present (excitation current), core becomes magnetized
Field strength determined by number of turns and magnitude of current:
B a NIDC

18. Electromagnetic Induction
Results in:
Generator action: generator converts mechanical to electrical energy
Motor action: motor converts electrical to mechanical energy

19. Generator Action For emf/current (electricity):
Magnetic Field
Conductor
Relative Motion b/t the two
Voltage produced: “induced emf/voltage”
Current produced: “induced current”
Left-hand rule for generator action

20. Motor Action For motor action (torque/motion):
Magnetic Field
Conductor
Current flow in conductor
Torque produced: “induced torque”
Right-hand rule for motor action

21. Standard Terminology
Stator: stationary housing of the generator or motor
Rotor: rotating shaft inside the stator
Field windings: conductors used to produce electromagnetic field
Armature windings: conductors in which output voltage is produced (or input is provided)

23. Basic Terminology Direct Current (DC) Alternating Current (AC)
Current flow is unidirectional and of constant magnitude (battery)
Alternating Current (AC)
Magnitude & direction of current flow periodically change
Each sequence called a cycle
Frequency is cycles per second (Hz)

24. AC Generators Most electrical power used is AC made by AC generators
Basic principle: rotating magnetic field “cutting through” a conductor
Regardless of size, all AC generators work on same principle
Two types:
Revolving armature (NOT used)
Revolving field (Used in SSTG’s, GTGS, DG)

25. AC Generators Two types: Revolving armature (NOT used)
Revolving field (Used in SSTG’s, GTGS, DG)

26. AC Generators Armature windings on stator Field windings on rotor
DC current provided for field via slip rings and brushes (vice commutator rings)
Rotor turned by prime mover creates rotating magnetic field
Armature windings on stator
As field rotates, AC current produced in armature
Since stationary contacts, no arc-over

27. AC Generators Determining speed of AC machine:
f = P(RPM)/ RPM = 120f/P
Must maintain constant 60Hz output use speed governor to maintain constant RPM (independent of loading)
Must also regulate voltage output
Since constant RPM, must control field excitation (DC current) to control output voltage

28. Three Phase (3f) AC Power
Phases: number of sets of armature windings on stator
3f has three sets of armature windings
Voltage induced is 120o out of phase for each
Output: 3 sinusoidal voltages and currents
Allows more power to be delivered with a smaller design generator

29. Three Phase (3f) AC Power

30. AC Motors Use AC current as input to produce work
Many different types depending on number of phases of AC input & construction
Ex: induction motor
Input AC current on stator produces rotating field
Current produced in conductors on rotor produces torque

31. DC Generators
Basic Principle: rotate a conductor within a magnetic field to induce an EMF
Field windings located on stator & receive current from outside source

32. DC Generators Armature windings on rotor
Commutator rings used to mechanically reverse the armature coil connection to the external circuit
EMF developed across the brushes becomes a DC voltage/current (pulsating and unidirectional)

33. DC Motors Essentially the same in construction as DC generator
Based on principle that current carrying conductor placed at a right angle to a magnetic field tends to move in a direction perpendicular to magnetic lines of flux
Only need to change relative voltage to go between generator motor

34. AC vs DC power Many different voltages required on board ship
Easier to transform AC power for each application

35. Electrical Devices Transformer
Device w/o moving parts that transfers energy from one circuit to another by electromagnetic induction
Consists of ferromagnetic core & sets of windings
Step-up: Vin Vout
Step-down: Vin Vout
Only works with AC

36. Electrical Devices Rectifier Converts AC DC
Designed to have small resistance to current flow in one direction & large resistance in opposite direction
Typically called a diode or rectifier

37. Questions?