Mod 3-4-5 Flashcards
(27 cards)
What are some characteristics of a series wound motor?
- Field windings are wound in series
- Increase in current strengthens the field of both the field and armature
- Gives high start torque
- However, speed changes with varying load
What are some characteristics of a shunt wound motor?
- Field windings are wound in parallel
- Field current and output speed is fairly constant regardless of changes in the load
- However, does not have a high starting torque
What are characteristics of a compound wound motor?
- Best of both worlds of series and shunt
- High starting torque speed, fairly constant output in varying load conditions.
Difference between intermittent and continuous duty?
Intermittent = Can only be operated for brief periods of time before needing to cool down Continuous = Can operate at rated power for long periods
How can motor direction be reversed?
Either with a SPDT switch and a split winding OR a DPDT switch to reverse the current within either the field windings or the armature
How can motor speed be changed?
Increasing / decreasing the amount of current to the field windings
What is torque?
Tendency of a force to produce rotation - Developed by the reacting field of a conductor through another magnetic field
List the 4 main parts of a motor
- Armature assembly
- Field assembly
- Brush assembly
- End frames
What is counter EMF?
Counter EMF = The reverse current that fights back against the current flowing through the armature
How do we calculate the Net EMF?
Applied EMF - Counter EMF = Net EMF
What is motor braking?
When the motor needs to be stopped at precise points - Used for landing gear, flaps, autopilots, etc.
What does a motor clutch do?
Disengages the motor from the load (gearbox) if necessary - Uses spring pressure
Difference between generator and motor?
- Generator turns the rotor in a field to produce current
- Motor applies current to a rotor in a field to make it turn
Difference between generator armature and alternator armature?
Generator = armature moves in stationary field Alternator = Moving field around a stationary armature
3 main parts of an alternator?
Stationary armature, rotating field, rectifier bridge circuit
Main advantage of having an alternator over a generator?
Eliminates the need for a commutator and brushes. They are potential contact issue points. Alternators can supply current to the aircraft directly
How many phases on a typical aircraft alternator?
3
How does an alternator produce DC output?
By rectifying the AC input with 6 diodes
Why does an alternator not need a reverse current relay?
The diodes resist any current flow to the armature
What 2 means of control are required for an alternator?
Voltage regulator or a current limiter
Whats the purpose of the zener diode in a solid state voltage regulator
It acts as a voltage reference or as a relief valve that opens at a given pressure. When conducting, the control transistor shuts off the power transistor
Advantage of using transistorized voltage regulator?
No moving parts, no contacts, less wear and tear
3 differences between aircraft and automotive alternators?
Through bolts are made of stronger steel
Includes signal interference protection
Rotor has shorter shaft and smaller thread
Whats an ACU and what does it do?
Alternator Control Unit - Regulates alternator output voltage and turns off the charging system if over voltage exists
