AC Generators Flashcards
How does a current transformer sense the amount of current in a wire?
Through electromagnetic induction
What are the required loads for a generator to supply to an aircraft?
Loads to a normally working system; essential loads after failed of and prime movers; essential loads after failure of any engine or multi-engine aircraft; essential loads for which AC source of power is required after any failure in one power supply system
How does an auto transformer work?
A tap contacts a single transformer coil at a point to output the exact required voltage.
What is the purpose of a bus bar?
A bus bar is used to distribute power over a set of contact points.
What are three circuit protection devices?
Circuit breakers, fuses, and current limiter
What are the three types of circuit breakers?
Thermal, magnetic, thermal-magnetic
What are the three types of fuses?
Normal, time delay, and very fast acting
What are the 2 types of switches?
Toggle and rotary
What are the requirements for aircraft wiring?
Design temperatures, flexibility, resistance, applied voltage, abrasion resistance, strength, insulation, weight, and current flow.
How many strands are in a small and large wire?
7 or 19 for small.
19 or more for large.
What is the difference between relays and solenoids?
Solenoids have a moveable core. Solenoids have heavy contacts that are capable of handling high amounts of current.
What are the classifications of relays?
Control relays, power relays (line contractors), revers current relays
What are Line contractors used for?
Controlling high voltages.
What are special about AC line contractors?
They have three leads, one for each phase.
How do reverse current relays work?
The generator powers a relay that, if not powered by the required voltage, opens, and prevents a current from flowing backwards to the generator.
What is a negative ground system?
The aircraft skin is a negative ground, providing a ground throughout the aircraft. This helps reduce the wires normally required for return grounds.
What is shed and non-shed?
Non-Shed: essential for safe aircraft operation
Shed: convenience, non-essential
What are some non-shed systems?
Essential lighting, flight control system, communication and nav radios, other high priority electrical systems.
What type of Voltage is used in an aircraft?
115VAC, phase 3, 400 Hz
How does a split bus system work?
Each bus can be powered by either generator, isolating the other in the event of failure, and automatically removes shed components
What are the types of external sources for AC?
Essex mobile and Hobart power cart, hangar deck and flight line hard-wired AC power
How many degrees is the sine wave of either phase from the other?
120*
What will a voltmeter read between 2 phases?
200 VAC
What will a voltmeter read between a phase and neutral?
115VAC
What is the name of the connection of the three phase leads?
Wye Connection
What are the components of a simple AC generator?
Pole pieces, armature loop, slip rings, and generator brush
What material are generator brushes made of?
High-grade carbon and graphite for the brush.
Copper for the pigtail
What is the name of the stationary and rotating components of a generator?
Stationary: Stator
Rotating: Rotor
What are the benefits of a brushless generator?
Low maintenance cost, high stability and consistency, better performance t high altitude, require much less iron and weigh less.
Describe the PMG process.
The rotor shaft spins a permanent magnet generating a single phase AC current to go to the GCU. The GCU rectifies the voltage to DC and powers an exciter field for a 3 phase generator. The three phase gen goes through a rectifier creating a stable DC exciter. That spins with the shaft creating a rotating field generating 3 phase AC
What are the three factors that directly affect generator output?
The speed the armature rotates, number of conductors, the strength of magnetic field (what is controlled by the GCU)
What are the functions of GCU protection?
Voltage regulation, reverse current protection, under/over frequency, phase differences, feeder fault (shorts)
When is APU power generation used?
Before engine start, during ground maintenance, and in-flight emergency when primary AC fails
What are the outputs of a rotary inverter with an input of 28 VDC?
115 VAC, single phase, 400 Hz
115 VAC, three phase, 400 Hz
200 VAC, three phase, 400 Hz
What are the types of inverters?
Rotary (PMG and inductor) and Static
What is a major safety concern for operating external power?
Never disconnect the external power connector with the aircraft systems running or the external source on.
The External Power Monitor will disconnect external power from the aircraft if it senses any of the following:
Under Voltage, over Voltage, under-frequency, over-frequency, improper phase sequence
