- Understand of basic electrical theory by definition, DC and AC.
- Understand How to use Ohm and Kirchoff law to apply on simple network.
- Understand of how electric current is merged
- Understand of generator part basic and the function.
- Understand of generator classification
- Understand of how the electric appliance below work :
- Current (I): flow of electricity per time unit, in Ampere or A unit.
- Electromotive Force (emf) (E): potential difference "electric pressure" that is force electric current, measure in "volts" (V)
- Resistance (R): electrical network that is against of electric current, measure in "ohms" (W)
- Conductor: material that have little resistant of electric current, such silver, copper, iron, etc.
- Insulator: material has high resistant to electric current such as wood, paper, plastic, etc.
Direct Current (DC)
Electric current having same big and same direction
Ohm law : Electric current is directly proportional to potential difference and inversely proportional to the network resistance.
V = I . R
P = I2 . R = V . I
1. Sum of all potential difference in close network is zero.
In Series Network: Rc = R1 + R2 + R3 + ...
On closed circuit is installed 3 resistances in serial order, each of this resistance 5 ohm, What is the Resistance total on that circuit?
Rc = R1 + R2 + R3 = 5 + 5 + 5 = 15 ohm
In Parallel Network: 1/Rp = 1/R1 + 1/R2 + 1/R3 + ...
On closed circuit is installed 3 resistances in parallel order, each of this resistance 5 ohm, What is the Resistance total on that circuit?
1/Rp = 1/R1 + 1/R2 + 1/R3 = 1/5 + 1/5 + 1/5 = 3/5
Rp = 5/3 = 1 2/3 ohm = 1.667 ohm
2. The sum of all electric current in = sum of all electric current out
Alternating Current (AC)
- Electric Current will change the big and its direction for the same interval.
- Current have time function and always vary as sinus function.
- Faraday founded that emf being inducted to the conductor if the magnet passing conductor, so that the moving between magnet and conductor will cut band flux of magnetic.
- Direction of emf induction depend on the direction magnetic moving between magnet and conductor.
- Current big inducted depend on the magnet flux, magnet speed when passing conductor and the number of flux magnet that is cut.
3 ways should be attention on produce potential difference
- Magnetic field
- Relative movement
Emf (Electromotive Force) inducted direction
Permanent magnet always too weak for any application
Parts of Generator:
- Prime mover: mechanic force that move rotor, such as turbine gas, diesel engine, etc.
- Armature windings: conductor in which is the potential out inducted
- Field windings: conductor used for resulting magnetic field (need DC current)
- Stator: static generator housing
- Rotor: rotate inside stator, moved by prime mover (steam turbine, gas turbine, internal combustion engine, etc.)
- Sliding contacts (slip-rings and brushes): Used for electric transfer in magnetic field or armature to and from rotor.
Simple AC Generator
There are two kind of AC Generator
- Rotor is armature that is rotate inside of static electromagnetic field.
- Seldom to use because power out should be transfer through slip-ring and brush
- DC electric is supplied by motor cause the magnetic field rotate inside stator.
- More simple because supply current need by field smaller than current out from armature.
Relationship of generator speed and frequency.
N x P = 120 x f
"Nuclear Power is 120 times as Fun"
Three Phase Electric Power
- Using 3 armature circumference to yield three different output.
- Armature circumstance physically separated 120o each others, so every phase separated of 120o.
- Power resulted by generator higher by certain weight and dimension.
- Continuously giving energy to electric appliance even broken of one phase.
- Number of phases: most shipboard electrical power is 3 phase
- Frequency: most shipboard electrical power is60 Hz, some electronic equipment operate at 400 Hz or higher
- Voltage: usually 450 V, smaller appliances use 120 V
- Power rating: measured in kW, most shipboard generators are 2,000 - 3,000 kW