AC Power Distribution Flashcards
The AC generators are connected to the what?
AC Busses
AC Generators (often called alternators) are used as the primary source of electrical power on what type of aircraft?
almost all transport category aircraft
Where DC is needed, what is used?
Rectifiers
For emergency situations some aircraft can utilize what?
APU or a Ram Air Turbine (RAT). Inverters can also be employed.
AC power can provide more what than a DC system?
power per weight of equipment
Most AC generators require what?
Constant Speed Drive (CSD) to maintain a constant frequency
The sole job of the CSD is to provide what?
constant 400Hz, regardless of throttle position.
Proper oil level is critical for what?
proper oil temperature
If a warning light comes on during flight, what should be done with the CSD?
disconnected immediately and inspected upon landing
Early generators were composed of what?
a generator unit and a CSD
The IDG contains both what?
the generator and the CSD in one unit
What generator is similar to the basic IDG?
The Variable Speed Constant Frequency (VSCF) generator
What happens to the RPM when dealing with the VSCF system?
The RPM of the drive and generator will change along with the engine.
How does the VSCF maintain a constant frequency?
Thru the use of solid state components
What does VSCF have located directly on the converter assembly?
BITE
The output of the typical AC generator is 115 AC. This is converted by what?
Transformer-Rectifier Units (TRU) where DC is needed
What is a TRU?
a step-down transformer and a full wave rectifier in one unit
What is the TRU’s output?
28vdc
What are two basic configurations used to distribute electrical power?
Split-buss system
Parallel system
The split-buss electrical system contains what?
the completely isolated power generating systems
When a generator fails, what happens to it?
the failed generator is isolated by the Generator Breaker (GB)
What is one advantage of the Split-buss system?
that each generator operates independently
Split-buss systems are more tolerant of what?
Frequency Variance
Parallel systems require what?
strict operating limits
What power distribution system has all AC generators connected to one distribution buss and maintains equal load sharing among all the generators?
Parallel
In a Parallel system, should a generator fail, what happens to the failed unit?
The failed unit is isolated from the bus by the GB and flight continues using the remaining two generators to supply power.
What are all generators synchronized and connected by?
The Tie Busses
The busses are often referred to as what?
Synchronizing tie busses
When closed, what does the Split System Breaker (SSB) do?
connects all generators together (paralleling the system)
On modern aircraft with a parallel or split-parallel buss system, what is essential?
a centralized means of controlling power distribution between individual load busses is essential
The power manipulation that happens between individual load busses must take place in a fraction of a second. To achieve this need, modern aircraft employ a what?
A solid State Buss Power Control Unit (BPCU)
What does the BPCU do?
Receives data from the Generator Control Units (GCU’s) and the various ties, busses, and breakers in the system.
They are essentially small computers for a specific purpose.
What are GCU’s used for?
GCU’s are used for each engine to monitor and regulate the generators output
If a GCU detects a malfunction it will inform what?
The BPCU
Which will then ensure the appropriate power distribution system configuration
What does the SSB control?
Controls power between all generators or parallels all the generators and is controlled by the BCU’s (BPCU’s)
The BPCU also receives what?
Input information from load controllers which sense real system current and provide control signals for the CSD or VSCF
If a system fault occurs, what does the BPCU do?
initiates the corrective action and records the fault in a non-volatile memory
What is a No-Break Power Transfer (NBPT)?
an incorporated system that can automatically change the AC power source without a momentary interruption of power
Synoptic pages cover what?
a variety of critical aircraft systems that are important for the pilot and also for the technician to help with troubleshooting
What do Synoptic pages provide?
they provide the viewer real time status data of the system and of the major components in the system
