DC Systems Flashcards
what are generators
electromagnetic devices that converts mechanical energy into electrical energy by electromagnetic induction
what maintains the aircraft battery at its fully charged condition?
dc generator
purpose of reverse current cut out relay
prevent battery current from flowing into generators (may burn armature)
sequence of start up power
engine starts generator > voltage regulator > RCR
2 components in a dc generator, and which is stationary
stator (stationary)
rotor (turns)
components in a stator and its purpose
magnetic frame (yoke) - provides path for the flux produced
poles - provides low reluctance path for the magnetic flux
field coils - produces magnetic flux
brushes & bearings - collects current from the commutator and delivers to external load circuit
components in a rotor and its purpose
armature core - provides low reluctance path for the magnetic flux
armature windings - to generate emf if the machine is generator/ to allow current to flow and develop force if machine is motor
commutator - rectify ac current into dc current
4 types of dc generator
series, shunt, compound, separately-excited
methods of winding armature & its applications
wave winding - low current, high volt
lap winding - high current, low volt
how does a carbon-pile voltage regulator work
as volt increase, carbon-pile decompresses, resistance increases, shunt field current drops, generator voltage drops
how does reverse-current-cut-out relay works
it will disconnect the generator from the battery when V gen < V batt
purpose of current limiter
protect generator from excessive loads (prevent overheating)
generator control unit components and its order of placement
from generator:
1) voltage regulator
2) current limiter
3) reverse current cutout relay
requirements and considerations in designing electrical power distribution system
1) power-consuming equipment must not be deprived of power in the event of power failure unless total power demand exceeds available supply
2) faults on the distribution system should have minimum effect on systems
3) power-consuming equipment faults must not endanger supply of power to other equipments
advantages and disadvantages when generators are connected in parallel
adv:
no break in supplies if a generator fails
share loads equally to improve life expectancy
disadv:
additional circuits are required to ensure both machines share equal loads
3 services of the busbar
1) vital/critical services - required during emergency (fire extinguisher, etc)
2) essential services - required to ensure safe flight in emergency situation (autopilot)
3) non-essential services - can be isolated in an in-flight emergency (IFE)
difference between ac motor and dc motor
ac motors has no commutator (brushes & slip rings)
speed of ac motor is determined by frequency (dc has no frequency)
dc generator vs dc motor
dc motor converts electrical energy into mechanical energy
series wound motor characteristics
high starting torque
never run without a load
can be started on full load
shunt wound motor characteristics
constant speed
torque is proportional to armature current
must be started on light or no load
compound wound motor characteristics
good starting torque and stability in speed
provides benefits of series and shunt wound
which dc motor can be started on a full load?
series wound motor
which dc motor can be started on light or no load?
shunt wound motor
what is a starter generator
single component starter and generator
