MAG Flashcards
Operating characteristics of the following DC generator?
(voltage - speed / Output - load applied)
Permanent magnet
Separately excited shunt
Shunt wound
Series wound
Compound
Permanent magnet - Voltage is directly proportional to speed / Output drops SLIGHTLY with a load applied
Separately excited shunt - Voltage is directly proportional to speed / Output drops SLIGHTLY with a load applied
Shunt wound - Voltage is NOT LINEAR to speed / Output drops MORE THAN permanent magnet with a load applied
Series wound - Voltage RISES RAPIDLY with load applied
Compound - FLAT voltage output
Aircraft applications for the following DC generator?
Permanent magnet
Separately excited shunt
Shunt wound
Series wound
Compound
Permanent magnet - Tacho generators
Separately excited shunt - None / Only in labs
Shunt wound - Light aircrafts
Series wound - None
Compound - Medium to heavy aircrafts
Operating characteristics of the following DC motors?
(Speed - load / Torque - load)
Permanent magnet
Shunt wound
Series wound
Split field series
Compound
Permanent magnet - Speed drops SLIGHTLY on load / Torque is directly proportional to the applied load
Shunt wound - Speed drops SLIGHTLY on load / Torque is APPROXIMATELY proportional to the applied load
(Approximately a cunt)
Series wound - Speed decreases and torque increases with load applied
Split field series - Speed decreases and torque increases with load applied
(Can reverse direction with switch)
Compound - Speed drops MORE THAN shunt and torque increases MORE THAN shunt
Aircraft applications for the following DC motor?
Permanent magnet
Shunt wound
Series wound
Split field series
Compound
Permanent magnet - None / Small machines only
Shunt wound - Electric fans, fuel boost pumps, motor generator units
Series wound - Starter motor, landing gear, fuel / hydraulic shut-off valves
Split field series - Actuators (flaps, trim tabs, landing gear)
Compound - Presses, shears, hydraulic pumps, reciprocating machines
4 main components of a single loop AC generator?
- Single conductive loop (rotor)
- Pair of slip rings
- Pair of brushes
- 2 x permanent magnets
4 main components of a single loop DC generator?
- Single conductive loop (rotor)
- Commutator
- Pair of brushes
- 2 x permanent magnets
What do the letters in the following equation stand for?
E = β L V Sinθ
E - Generator output voltage
β - Strength of magnetic field
L - Active length of conductor
V - Velocity / speed of cutting
Sinθ - Angle of cutting
What happens to the generator output when the rotor is spun in the opposite direction?
180 degrees out of phase
Describe the positioning of each finger as well as the applications for each of the following:
Flemming’s left hand rule (generators)
Flemming’s left hand rule -
Thumb - Direction conductor is traveling
Fingers - Current flow direction
What do the following components do?
Slip rings
Commutator
Brushes
Slip rings - Allows current to flow to the external circuit
Commutator - Allows current to flow to the external circuit / converts from AC to DC
Brushes - Used to transfer current from the slip rings or commutator to the external circuit
How can the DC ripple coming out of a DC generator be reduced?
Add more windings to smooth out the ripple
Difference between the stator and rotor?
Stator - STATIONARY part of the motor or generator
Rotor - ROTATING part of the motor or generator
Difference between a field and armature?
Field - Electromagnetic / current is applied to a ‘field coil’ to produce an electromagnetic field / can be part of a stator (motor) or rotor (generator)
Armature - Not a physical term like rotor or stator / Power producing component - where current comes out of
Components of a DC generator?
- End bell
- Brush assembly (Brush spring, brush, brush holder)
- Armature
- Frame
- Field coil (Field pole, field pole bolt)
- Commutator
Define self excited?
Does not rely on an external power source for field excitation
Define residual magnetism?
In self excited DC generators, the pole pieces are required to retain a small amount of magnetism so they can produce enough EMF to excite the armature upon start up
What can be done if we lose magnetism?
Flash the field
What would be the output of a generator in the following situations?
Open circuit field winding
Open circuit armature
Loss of residual magnetism
Open circuit field winding - Lower than the rated output
Open circuit armature - If there is only one winding, the output would be zero / If there was more than one winding, the output would be lower than the rated output but not zero
Loss of residual magnetism - Field would fail to build up / start
What causes armature reaction?
Displacement of the neutral plane
What happens if we get armature reaction?
Reactive sparking
3 ways to correct armature reaction?
- Brush positioning
- Compensation windings
- Interpoles
Describe back EMF in DC motors?
- Creates the total speed limitations of the motor
- As the motor is starting to build up speed, the back EMF is small
- As the motor gets faster and faster, the back EMF increases proportionally
- Once the motor stops, the back EMF is zero
- Affects the efficiency of the motor
Fill in the missing words:
In a compound generator or motor the series winding has _______ turns of _______ wire
Few turns of heavy gauge wire
Fill in the missing words:
In a compound generator or motor the shunt winding has _______ turns of _______ wire
Many turns of fine wire
Advantages of a starter generator system?
Starter motor and generator in one
- Ideal for small gas turbine aircrafts where weight is a major consideration
(Diagram with the start button)
Applications for a linear actuator?
Linear actuator - Goes in a straight line
- Flight controls (trim system)
- Primary flight controls
- Secondary flight controls
- Auto pilot
- Undercarriage
- Cargo doors
- APU ducting
- Cargo ramp on (fixed wing and rotary wing transport aircrafts)
- Cooling air ducts
- Cargo locking
- Seat positioning
Applications for a rotary actuator?
- Flight controls (trim system)
- Fuel control
- Hydraulic controls
- Bleed air control
- Heating and cooling control
- Radar
- Satcom
- Water flow control
Components of a DC linear actuator?
- Lead screw
- DC motor
- Ball mechanism!!!!!!!!!!!!!!
- Gear train
What prevents an actuator from exceeding its limits?
Limit switches
What provides positional feedback for a rotary actuator?
- Potentiometer
- Hall effect (magnets)
- Digital encoder type devices
Components of a rotary actuator?
- Worm screw
- worm gear
- potentiometer!!!!!!
Potentially a wormy worm
3 main sections in a brushless generator?
- PMG (Permanent magnement)
- Exciter
- Main generator
Output voltage and frequency of an AC brushless generator?
Output voltage - 115v
Frequency - 400Hz
6 functions of a GCU?
GCU - Generator control unit
- Voltage regulation
- Frequency protection
- Voltage protection
- Phase sequence
- Differential current protection
- Warning system
Maximum and minimum voltage that a GCU will allow?
100V - 130V
Maximum and minimum Frequency that a GCU will allow?
365Hz - 430Hz
How does a GCU regulate output voltage
- A sample of the 3 phase AC voltage levels from main genrator is sent to the GCU, if the output voltage is higher or lower that 115V GCU will add or reduce voltage to the excitor to make the main output 115V again
- Remember a brushless AC geerator is made of 3 parts, permanent magnet generator, exciter and main generator
Advantages of the following:
IDG
Variable speed constant frequency generator
Variable frequency generator
IDG (Integrated drive generator) - Ideal for fault finding / AC brushless generator combine with a CSD
Variable speed constant frequency generator - Voltage and frequency control imbedded into the generator
Variable frequency generator - No longer requires a CSD
Maximum and minimum limits for frequency in a variable frequency generator?
360Hz - 800Hz
Describe the construction of a single phase induction motor:
Rotor
Stator
Rotor - No traditional copper wire / Steel laminations with aluminium or copper bars embedded
Stator - Laminated iron core with copper windings
Describe the construction of a 3 phase induction motor:
Rotor
Stator
Also known as a ‘Polyphase motor’
Rotor - Laminated iron core / Heavy copper bars laid into slots
Stator - Sheet metal punching with slots on the inner surface
Punched steel - both cannot be steel
What is a main issues with a single phase induction motor?
- Constantly changing polarity
- No starting torque is produced
- Rotor will begin the oscillate back and forth between the poles
3 starting systems for a single phase AC induction motor?
- Split phase
- Capacitor start
- Shaded poles
Applications for the following single phase AC induction motor starting systems?
Split phase
Capacitor start
Shaded poles
Split phase - Most common
Capacitor start - Small blower motors in equipment cooling and ECS
Shaded poles -Light duty fridge circulation and air cons / environmental conditioning
Applications for a 3 phase squirrel cage induction motor?
(Squirrel cage induction motor)
- Hydraulic pumps
- Galley and lavatory pumps
- Flap power drive units
- Horizontal stabiliser trim actuators
How do you reverse the direction of a 3 phase induction motor?
Reverse any 2 supply connections to the stator winding
Construction of a single phase synchronous motor?
- Induction motor
- Rotor with a strong magnetic field
Applications for a single phase synchronous motor?
- Clocks
- Timers
- Recording systems
- Tachometer system
What is the construction of a polyphase synchronous motor rotor?
Rotor - Wire wound
Salient pole for low speed
Cylindrical pole for high sped
Applications for a 3 phase synchronous motor?
- Constant speed power application (15w-75Kw)
- Electrically driven hydraulic pumps
What is the difference between synchronous speed and actual speed called?
Slip
Describe the following electrical connection methods:
Plugs and receptacles
Terminal lugs
Plugs and receptacles - Variety of sizes, pin configurations and wire gauges, convenient way to connect and disconnect
Terminal lugs - Used where a plug or socket is not suitable or appropriate
Steps of de-powering an aircraft?
- Shut down engine and/or auxiliary power unit
- Shut down ground power and remove ground-power receptacle
- Raise appropriate power restriction in CARS
Steps of de-powering a specific system?
- Trip relevant circuit
- Tag relevant braker
- Raise applicable entry into AMD
8 electrical system safety considerations?
- High voltage
- Working at heights
- Heavy objects
- Rotating parts
- Liquid / chemical spills
- Concurrent maintenance
- Battery safety
- Jewellery / hair
Publication for aircraft maintenance on a operational level?
Relevant - 2 / relevant aircraft pubs and manuals
3 main components of the Main generator in an AC brushless generator
- Output stator winding
- Rotating Field winding
- Rotating Rectifier
Stater generator characteristics?
- Start the engine of aircraft
- Used to recharge battery and to supply DC bus
When is Flemming’s left hand rule used?
Generators
Describe the attachment methods:
Flange mounted devices
Popular on aircrafts, located on accessory case, auxiliary gearbox and reduction gearbox as well as starter motor, AC/DC generators
Like wheels on a car - partially threaded studs
Describe the following attachment methods:
Direct mounted hardware
Types of fastenings can include: bolts, nuts, lock washers, self locking nuts, plate number and screws
Describe the following attachment methods:
Quick attach detach ring
Adapter that is bolted into the drive unit and a rotating ring / requires special maintenance
Circle clamps
Describe the following attachment methods:
Rack mounted
Quick release trays are common among avionic devices
Describe the following attachment methods:
Vibration isolation
Shock mounts fitted under the tray, device or rack / ideal for sensitive aircraft electrical hardware
Describe the following attachment methods:
Aircraft battery mounting
Fixed on the aircraft frame / Type of tray in dictated by the type of battery, size and location
What is the make up of the rotary in a generator (AC or DC)
- Windings
- Commutator (DC) / Split ring (AC)
- Armature
- Shaft
Make up of the stator in a generator (AC or DC)
ANYTHING THAT IS STATIONARY!!!!
- Frame / end bell
- Field assembly (Pole, coil, bolt)
- Brush assembly (Brush, holder, spring)
The button has been pressed - Starter generator or motor?
Starter motor
The button has been released - Starter generator or motor?
Starter generator
Describe differential current protection?
- Used to detect imbalances in each phase of the generator
- Current in should equal current out / DCP transformer is used to detect this
What is special about the variable frequency generator?
- No longer requires the CSD
- Weight saving advantage
What connects the brushes to the external circuit?
Pig tails
Fill in the blanks:
Squirrel cage induction motor exhibits ______ speed characteristics and _______ starting torque.
Constant
Low
How is frequency determined?
- Speed of spinning
- Number of poles
