electrical theory and distribution Flashcards
Current (I)
flow of electric charge, measured in amperes or amps
Voltage (V)
a difference in electric potential. measured in volts
resistance (R)
an electrical circuit’s opposition to the flow of current. measured in ohms
conductor
little resistance to current (silver, copper, iron, etc.)
insulator
high resistance to current (wood,paper, plastic, etc.)
Ohm’s Law
current in a circuit is directly proportional to the applied voltage, and inversely proportional to the circuit resistance V=IxR
Faraday’s Law of Induction
3 requirements to produce current: magnetic field, conductor, motion between the conductor and magnetic field. when a permanent magnet is moved relative to a conductor (or vise versa) an electric current is produced
Direct current (DC)
current flows in one direction and is of constant magnitude. Produced by: battery, DC generator, AC to Dc conversion, solar panel. Measured in Volts
Alternating Current (AC)
Cycles, direction and magnitude of current in an AC circuit will periodically change. Measured in Volts and frequency (Hz). Frequency is the number of cycles per second. Function of time, sine wave
Alternating current generator
Conductor loop rotates in magnetic field. slip rings rotate with the conductor loop. Stationary brushes ride against the slip ring. voltage generated across brushes
AC vs DC
AC POWER: easier to generate, uses less complex equipment, voltages can be raised w/ a transformer, cannot be stored in a battery.
DC POWER: can be stored in battery, cannot raise or lower voltages w/ a transformer
Ship electrical power distribution
Generators, switchboards, load centers, distribution panels, circuit breakers, fuses, loads
Electrical generators
Convert mechanical energy into electrical enegery. powered by steam turbines, gas turbines, diesel engines, electric motors
switchboards
contains controls for the production, regulation, and distribution of electricity. distribute electricity to shipboard equipment. house bus-work, circuit breakers and fuses. Receive electricity from generators
Excessive electric current
Causes: reduced component lifespan, component failure, electrical fire.
Protection devices: circuit breakers, fuses
Circuit breakers
opens at various set points (currents) protects generators & equipment. Operated Manually (locally) or Electrically (remotely) changes the electrical plant configuration. Isolates equipment and are reusable
Fuses
encased this metal wire, high current (heat) melts the fuse. Causes an open circuit. Protects the circuit/equipment from excessive current. Single use. replace “blown” fuses
Vital Equipment
Required for safe operation of a ship. Multiple power sources. Power source shifts to continue operation during casualy. (firefighting pumps, stering gear, weapon systems)
Non-vital equipment
Not required for safe operation of a ship. Ex: laundry equipment, galley. Not preferentially powered during casualty. conserves power for vital equipment
Personal Protective Equipment (PPE)
Rubber gloves, face shield, rubber matting, remove all conductive clothing (belt,watch, necklace…)
Electrical fires
secure power, battled with CO2. don’t use water stream: electrocution hazard, prevents further damage
.001 amps = 1 milliamp
tingles sensation
.01 amps = 10 milliamps
severe shock, uncontrolled muscle spasms
.1 amps = 100 milliamps
DEATH
DANGER TAG
operation will cause injury, death or equipment damage. Equipment shall NOT be operated
CAUTION TAG
Used as a precautionary measure. provides temporary special instructions for equip. Ahere to specific instructions
Electronic equipment maintenance
De-energized AND mark with DANGER TAG. Energized equipment REQUIRES CO authorization and safety observer
Writing a tag
Requires 3 people. 1st person: identifies scope of work, writes tags to isolate work boundaries. 2nd person: Verifies the scope of work, ensures the tag adequately isolates the work boundaries. 3rd person: Officer to verify and approve hanging
Hanging a tag
1st person: Places valve/breaker in correct position, hangs tag. 2nd person: independently verifies, valve/breaker in correct position, tag is on correct equipment. Officer authorizes work
