30 Questions
What is the purpose of a Bus Tie Breaker (BTB) in a split bus system?
To couple the power from one bus to another
In a basic twin-engine split AC bus system, what component provides the DC requirements of the aircraft?
Transformer Rectifier Unit (TRU)
What would happen if the AC supply fails in a twin-engine split AC bus system?
The static inverter would start and provide emergency AC from the battery
What is the main function of the inverter in an aircraft electrical system?
To provide AC voltage to the aircraft
How is a tied bus configuration different from a split bus configuration in an aircraft system?
In a tied bus configuration, the power from one bus is coupled to another in case of a failure
What is the purpose of an emergency AC bus in an aircraft's electrical system?
To receive power from the static inverter in emergencies
What is the purpose of using white petroleum jelly on quick-release battery terminals?
To prevent corrosion on the contacts
Why should connectors without inbuilt locking devices be lockwired closed with 26 AWG copper wire?
To prevent unscrewing during flight
What is the purpose of securely mounting aircraft batteries?
To protect against loose movement or detachment
Why should all types of securing nuts for batteries be lockwired?
For security purposes
What should be ensured before installing any battery in an aircraft?
It is the correct type as per the aircraft maintenance manual
What type of connectors should have lugs built into the cover for hold down bolts?
Large metal batteries
What is a disadvantage of a rotary inverter compared to static inverters?
Lack of frequency control
Why is the control box on top of the inverter not supposed to be disassembled in the field?
To avoid electrical hazards
What happens when a load is activated in a rotary inverter?
The inverter starts operation
Why do rotary inverters generally require more scheduled maintenance than static inverters?
Because they have more moving parts
What is a key advantage of a static inverter over a rotary inverter?
Less required maintenance
What type of current does the unit shown produce?
Single-phase alternating current
What is the main function of a Generator Circuit Breaker (GCB) in a split bus system?
To connect the AC generator's output to its respective bus
What is the purpose of auxiliary contacts in the interlocking circuitry of contactors and breakers?
To prevent the connection of unsynchronised power sources in parallel
In what scenario would the bus tie breaker be tripped according to the text?
When a fault is detected by the generator control unit
What is the purpose of isolating the generator's output from the aircraft's loads?
To ensure power continuity in case of generator failure
How does interlocking circuitry prevent unsynchronised power sources from being connected in parallel?
By using both normally closed and normally open contacts in auxiliary contacts
What happens to all other generator breakers when ground-power is connected as per the text?
They trip and disconnect their generators
What is the purpose of the inverse time delay in the system described?
To prevent nuisance tripping under transient conditions
What happens when switch S1 is made in the system?
Interrupts the generator excitation field circuit
What is the purpose of differential fault protection in the system described?
To protect against generator feeder cable shorting to the airframe
How are toroidal current transformers used in the system?
To sense generator feeder fault
What does a difference between the outputs at the generator and load bus indicate?
Ground (short) or leakage in the feeder lines
Why is differential fault protection typically the only protection available for generator feeder cables?
To protect against shorting to the airframe
Study Notes
DC Generation Bus System
- It prevents overloading of the active generator, which would be incapable of supplying electrical power to all aircraft systems.
Single-Generator System
- In a simple single-generator system, the battery is charged from the bus when the generator is outputting at a higher voltage.
- An inverter provides the aircraft with AC voltage.
Twin-Engine Split DC Bus System
- Each generator powers its own individual bus.
- If one generator fails, the failed generator is isolated from its bus, and the power on the other bus is coupled to that bus by a Bus Tie Breaker (BTB).
Twin-Engine Split AC Bus System
- AC generators (alternators) supply their individual buses.
- The AC bus feeds the Transformer Rectifier Unit (TRU or T/R), which provides the DC requirements of the aircraft and charges the battery.
- Emergency AC bus is fed directly from the AC bus.
- If the AC supply fails, the static inverter starts and provides emergency AC from the battery.
Battery Connections and Installation
- Battery connections require a positive locking device to prevent unscrewing during flight.
- Quick-release type battery connections are lubricated with white petroleum jelly to prevent corrosion.
- Batteries need to be securely mounted in the aircraft, whether in their own isolated compartment or shared space, and firmly bolted into a mounting cradle.
Maintenance and Safety
- Before installing any battery, ensure it is the correct type, and refer to the aircraft maintenance manual.
- The frequency is 400 Hz for all phases.
- Maintenance of rotary inverters is outlined in the manufacturer's maintenance or service manual.
Rotary Inverters
- They have automatic load demand and shut down when the load is removed.
- Disadvantages include lack of frequency control, low surge capability, and lower efficiency.
- They require more scheduled maintenance than static inverters due to mechanical aspects (brushes and commutator).
Static Inverters
- They serve the same function as rotary inverters but have no moving parts and less maintenance problems.
- An example of a static inverter uses an input voltage of 18 to 30-V DC and produces an output of 115 V, single-phase AC with a frequency of 400 Hz.
Generator Circuit Breaker (GCB) and Bus Tie Breaker (BTB)
- The same contactor can be used as a GCB or BTC, but each performs different functions within the electrical circuit.
- GCB functions include connecting the AC generator's output to its respective bus, ensuring power from only one source, and isolating the generator's output if a fault is detected.
Auxiliary Contacts and Interlocking Circuitry
- Auxiliary contacts are used to prevent unsynchronized power sources from being connected in parallel.
- Interlocking circuitry prevents ground-power connection to any generator.
Fault Protection
- Differential fault protection is used to protect against generator feeder cable shorts to the airframe.
- Toroidal current transformers sense generator feeder faults.
Test your knowledge on aircraft electrical connectors, including the importance of positive locking devices and lockwiring techniques to prevent unscrewing during flight. Learn about quick-release battery connections and the use of white petroleum jelly for corrosion prevention.
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