Basic Aircraft & Multi-Engine Power Distribution Systems Flashcards
One of the most important systems on an aircraft is the power distribution system. The power distribution system is used to ______ from a multitude of sources to any device on the aircraft requiring power.
transfer power
All power sources are connected to a _____. A _____ is a simple copper bar capable of handling all of the power being transferred throughout the system. Between the power sources and the bus, there are protection and control devices.
bus bar
These protective devices include relays, current limiters, and switches. In the case of generators and alternators, _____ are used to disconnect the power supplies from the bus if a problem occurs that could result in damage or undesired effects on the bus.
These protective devices include relays, current limiters, and switches. In the case of generators and alternators, current limiters are used to disconnect the power supplies from the bus if a problem occurs that could result in damage or undesired effects on the bus.
For external power, a _____ is used to make sure that power is attached to the aircraft properly. If power isn’t connected properly, the relay won’t allow the external power to be connected to the bus.
relay
Relays also are used to keep power flowing in one direction. The _____prevents battery or external power from flowing towards the alternator when the alternator is idle.
Once the alternator is producing enough power, the _____ closes and connects the alternator to the main bus.
The Reverse Current Relay (RCR)
Once the alternator is producing enough power, the RCR closes and connects the alternator to the main bus.
Which of the following protective devices is used to disconnect faulty power generation units from the bus?
Current Limiters
Relays
Circuit Breakers
Current Limiters
Relays are used to prevent external power from being applied to the bus incorrectly and to protect the alternator from reverse current.
Circuit breakers protect the bus from faulty loads. Another device protects the bus from faulty generation devices.
All electrical and electronic devices connected to the main bus are considered loads. There are two types of loads:_____ and _____. _____ loads are those loads required to operate the aircraft safely. _______ loads are not required to keep the aircraft flying.
All electrical and electronic devices connected to the main bus are considered loads. There are two types of loads: essential and non-essential. Essential loads are those loads required to operate the aircraft safely. Non-essential loads are not required to keep the aircraft flying.
The _____ provides power to the loads via essential and non-essential buses. _____ buses can be independent or powered by the main. The buses are protected from individual equipment or circuit faults by circuit breakers.
The main bus provides power to the loads via essential and non-essential buses. Secondary buses can be independent or powered by the main bus. The buses are protected from individual equipment or circuit faults by circuit breakers.
Examples of a secondary bus are the _____ and ______. Secondary buses can contain essential and non-essential equipment just like the main bus. On the Avionics secondary bus, which is powered by the Main bus, the OPS/COM RECEIVER 2 and OPS/COM TRANSMITTER 2 would be considered non-essential during an emergency.
Examples of a secondary bus are the AVIONICS BUS and SEC. POWER BUS. Secondary buses can contain essential and non-essential equipment just like the main bus. On the Avionics secondary bus, which is powered by the Main bus, the OPS/COM RECEIVER 2 and OPS/COM TRANSMITTER 2 would be considered non-essential during an emergency.
The ______ is an independent, essential secondary bus for the FADEC B SYSTEM and ATTITUDE GYRO system. It provides emergency power directly from a ______ to these critical systems during a main bus failure. The FADEC system is essential for keeping the engine running, and the attitude gyro is an important flight instrument for maintaining straight and level flight.
The SEC. POWER BUS is an independent, essential secondary bus for the FADEC B SYSTEM and ATTITUDE GYRO system. It provides emergency power directly from a battery to these critical systems during a main bus failure. The FADEC system is essential for keeping the engine running, and the attitude gyro is an important flight instrument for maintaining straight and level flight.
The alternator in the power generation system must be capable of providing more power than the sum of the loads, as shown in this system. The alternator, rated at 300 amps, can handle the loads total of 253.5 amps. But what if the alternator fails in flight and the battery, rated at only 100 amps, must be used?
The power rating of the battery is not large enough to power all of the Liberty XL2 systems. In this case, the pilot should turn off any system that is not essential to flight to reduce the load to less than 100 amps. For example, the pilot of this aircraft turned off the items in red. Will the battery optimally meet the remaining load requirement?
What must the secondary power source (secondary battery) be rated to support the secondary power bus?
15 amps
25 amps
35 amps
35 amps
To determine the minimum rating of a power source, add up the circuit breaker values. The source amperage must be greater than the total bus amperage.
A ______ is provided to disconnect power from the bus. On some aircraft, this may only disconnect the battery; on others, both the battery and the generators will be disconnected. If the generators are not controlled by the ______, they will have individual switches to disconnect them.
master switch
Another important component of the power distribution system is the _____. This will indicate to a pilot how much power an alternator is producing. This is important when power is limited and loads need to be removed to compensate for a reduced output from the alternator.
ammeter
This importance of loads is known as________. When systems are designed, essential loads are placed on the bus system in places where faults are least likely to occur. This makes disconnecting non-essential loads much easier.
load hierarchy
The unit that controls the bus is called the______. There are many different control and monitoring units that feed into the bus power control unit. These units are constantly monitored to provide complete and uninterrupted power.
bus power control unit
On multi-engine, commercial, and military aircraft, the battery normally connects to a ______, not directly to the main bus. The ______ is then connected to the main bus and the emergency bus or essential bus.
battery bus
A ______ changes 24 - 28 VDC to 115 VAC to power essential AC systems such as flight instruments and avionics equipment.
static inverter
On many twin engine turboprops and jets, AC generators are used to provide power. A ______ is used to change the AC to DC for powering the DC bus circuits and equipment. In most cases, this DC voltage is 28 VDC. The output is connected to a DC bus.
transformer-rectifier
1 Generator Main Bus
To which electrical distribution bus is the battery connected on multi-engine, commercial, and military aircraft?
Non-Essential Bus
Battery Bus
Battery Bus
The battery may be connected directly to the #1 Generator Main Bus on single engine general aviation aircraft, but not on multi-engine, commercial, or military aircraft.
The battery would not be connected to the non-essential bus; it is an electrical system emergency backup component. Non-essential equipment includes those items not needed in an emergency.
What must a bus bar be capable of handling?
At least half of the power transferred through it
All of the power being transferred through it
At least twice the power being transferred through it
None of the above
All of the power being transferred through it
Which of the following types of information should you know about a load?
Power consumption rating
If it’s essential or non-essential
Its location on the bus
All of the above
All of the above
Almost all attachments made to a bus involve a _______.
diode
circuit breaker
relay
fuse
circuit breaker
Which loads are considered essential loads?
Devices needed to fly an aircraft safely
Loads that provide illumination
Loads that control cabin comfort
None of the above
Devices needed to fly an aircraft safely
Which of the following is NOT a protective device?
Bus bar
Relay
Circuit breaker
Diode
Bus bar
What device is used to convert DC to AC?
Bus control unit
Digital-to-analog converter
Direct alternating unit
Static inverter
Static inverter
On most commercial and military multi-engine aircraft, the DC system is used as______. It is also used on the ground to get AC power to the aircraft via the _____or an external power source.
On most commercial and military multi-engine aircraft, the DC system is used as a last resort emergency system. It is also used on the ground to get AC power to the aircraft via the APU or an external power source.
The battery, or in some cases batteries, are connected to the battery bus through a ____. The ______ is controlled from the battery switch in the cockpit. The battery switch is powered through a hot bus, which is directly connected to the battery.
The battery, or in some cases batteries, are connected to the battery bus through a battery relay. The relay is controlled from the battery switch in the cockpit. The battery switch is powered through a hot bus, which is directly connected to the battery.
During a full power generation emergency (when all engine generators, including the APU’s, were to fail) - as highly unlikely as that would be - the_____ would provide power to the essential DC systems. Critical AC systems would be powered by the ______ connected to the battery bus.
During a full power generation emergency (when all engine generators, including the APU’s, were to fail) - as highly unlikely as that would be - the battery bus would provide power to the essential DC systems. Critical AC systems would be powered by the static inverters connected to the battery bus.
During normal flight operation, the battery bus is powered by the______ through ______. The batteries are constantly being charged.
During normal flight operation, the battery bus is powered by the AC generators through transformer rectifiers. The batteries are constantly being charged.
Basic power distribution systems connect the engine power generation device to a _____. From there, the power is distributed to the aircraft systems through circuit breakers, relays, and specialized buses.
Basic power distribution systems connect the engine power generation device to a main bus. From there, the power is distributed to the aircraft systems through circuit breakers, relays, and specialized buses.
The main distinction of an AC bus is that it has a separate bus bar for each phase of the AC signal. To keep block diagrams simple, drawings typically use a ___ to represent the phase. A line with three ___ indicates 3-phase power, and a line with one ___indicates single-phase power. DC power will have no ______.
The main distinction of an AC bus is that it has a separate bus bar for each phase of the AC signal. To keep block diagrams simple, drawings typically use a slash to represent the phase. A line with three slashes indicates 3-phase power, and a line with one slash indicates single-phase power. DC power will have no slashes.
One type of multi-engine power distribution system is the ______system. This system is configured much like several independent basic generation systems. Each generating device powers its own distribution system. The various electrical systems are “split” between the independent buses.
One type of multi-engine power distribution system is the split-bus power distribution system. This system is configured much like several independent basic generation systems. Each generating device powers its own distribution system. The various electrical systems are “split” between the independent buses.
_____ are used in vehicles and aircraft to disable specific non-essential equipment at certain times of high current demand or reduced electrical power output. The relay automatically “sheds” the extra load during these times.
Shed relays are used in vehicles and aircraft to disable specific non-essential equipment at certain times of high current demand or reduced electrical power output. The relay automatically “sheds” the extra load during these times.
There are two classifications of power distribution buses: the non-shed bus, often called the essential bus, and the shed bus, often called the non-essential bus. Non-essential buses are connected to the main bus by_____.
There are two classifications of power distribution buses: the non-shed bus, often called the essential bus, and the shed bus, often called the non-essential bus. Non-essential buses are connected to the main bus by shed relays.
____ remove the non-essential bus from the main bus when a reduced power load is required.
Shed relays remove the non-essential bus from the main bus when a reduced power load is required.
On modern split-bus systems, a ______ connects the generator to the associated bus. The #1 GB connects the #1 generator to the #1 main bus, and the #2 GB connects the #2 generator to the #2 main bus.
On modern split-bus systems, a generator breaker (GB) connects the generator to the associated bus. The #1 GB connects the #1 generator to the #1 main bus, and the #2 GB connects the #2 generator to the #2 main bus.
The _____ is a heavy duty power relay used to control high voltages. It’s contacts are thick so the GB is capable of handling high levels of current. It has three separate contacts, one for each phase, and uses low voltage DC to control the high voltage AC from the generator.
The generator breaker is a heavy duty power relay used to control high voltages. The contacts of the generator breaker are thick so the GB is capable of handling high levels of current. The GB has three separate contacts, one for each phase, and uses low voltage DC to control the high voltage AC from the generator.
The generator breaker, controlled by the______, automatically disconnects the generator from its associated bus during engine shutdown or generator failure.
The generator breaker, controlled by the generator control unit (GCU) and/or the bus controller, automatically disconnects the generator from its associated bus during engine shutdown or generator failure.
The ______ are primarily used to connect main bus #1 and main bus #2 to external power or auxiliary power unit power. On some aircraft split-bus systems, the BTB is also used to connect the # 1 and # 2 buses together during a generator failure.
The bus tie breakers (BTB) are primarily used to connect main bus #1 and main bus #2 to external power or auxiliary power unit power. On some aircraft split-bus systems, the BTB is also used to connect the # 1 and # 2 buses together during a generator failure.
Bus tie breakers are controlled by a _____ or ____ in the ______.
Bus tie breakers are controlled by a bus controller or electrical panel switches in the cockpit.
What controls the generator breaker when an associated generator failure is imminent?
Switch on the cockpit
electrical panel
Transfer relay system
Generator control unit
Generator control unit
The cockpit switch can manually open the GB and disconnect the generator; however, human response would not be quick enough to avoid electrical system damage associated with a failing generator.
The _____is used in large multi-engine aircraft split-bus power distribution systems to reconnect essential loads to a power source in the event the bus’s associated generator fails. Aircraft with auxiliary power units (APUs) often use the this system.
The transfer relay is used in large multi-engine aircraft split-bus power distribution systems to reconnect essential loads to a power source in the event the bus’s associated generator fails. Aircraft with auxiliary power units (APUs) often use the transfer relay system.
Like the split-bus system, during normal operations, the parallel bus system ties each generator to a unique bus. However, in a parallel bus system, all the buses are connected together. To connect all of the buses together, the parallel bus system employs a ____, also called the synchronizing bus. The_____ is common to all generators so each generator must be at the same voltage, phase, and frequency at all times.
tie bus
