Aircraft Alternators and Generators

Aircraft Electrical Power

• Electrical power information for maintenance can be found in aircraft system manuals.
• Manuals include the Aircraft Maintenance Manual, Wiring Diagrams Manual, Illustrated Parts Catalogue, and vendor component manuals.
• Transport aircraft maintenance manuals follow Air Transport Association (ATA) Specification Reference chapters ATA 20 (Standard Practices) and ATA 24 (Electrical Power).

Electrical Power Distribution

• Large aircraft electrical systems supply both AC and DC power and include automatic/manual controls and protection.
• Standby AC or DC systems provide normal and emergency power.

AC Power Sources

• Typical aircraft AC power system includes these main sources:
• Left engine driven generator
• Right engine driven generator
• APU generator or starter-generator
• External power
• Also includes a standby power source.

Turbine Powered Aircraft

• Engine-driven generators are driven by a Constant Speed Drive (CSD) on turbine-powered aircraft like Boeing 727 and Fokker F28.
• Modern aircraft utilize Integrated Drive Generators (IDG), which combine the constant speed drive and generator.
• Generators supply AC 3-phase power at 115/200 volts, 400 Hz.
• AC power system design ensures that no two sources power the same load simultaneously.
• A static inverter provides single-phase 115 V AC to the AC standby power system.

DC Power Sources

• Normal DC power comes from Transformer Rectifier Units which convert 115 V AC to 28 V DC.
• Other possible DC power sources include:
• Aircraft main battery
• Main battery charger
• Auxiliary battery
• Auxiliary battery charger
• Batteries serve as a backup DC source which is controlled by a Standby Power Control Unit (SPCU).

Standby Power

• With normal power loss, the standby power system provides AC and DC power for essential systems to maintain safe flight for a limited duration (e.g., 60 minutes minimum).
• Batteries supply DC power while a static inverter generates AC power from battery power.
• The Standby Power Control Unit (SPCU) distributes both AC and DC standby power.

Electrical Power System Protection

• Automatic controls protect the electrical power system from source or load failures.
• Manual system control includes:
• Switches that energize or de-energize contactors (relays) to control electrical power.
• Instrumentation to monitor system status using lights and digital displays.

Electrical Bus Systems

• Generating source outputs connect to low resistance conductors called bus bars.
• Bus bars are made of copper or aluminum strips/cables, enabling supply and feed connections.
• Various bus bars are present in large aircraft, each serving a distinct function in power distribution and load sharing.
• Bus systems are categorized by priority:
• Hot Battery Bus
• Essential DC Bus
• AC Bus (main generator busses)
• AC Essential Bus
• AC Non-essential Bus

Hot Battery Bus

• The aircraft battery typically connects directly to the hot battery bus.
• The hot battery bus supplies power to critical loads like fire extinguishers and fuel/hydraulic fire shut-off valves.

Essential DC Bus

• Also termed the Battery Bus, it connects to the hot battery bus via a contactor

AC Bus

• The AC bus is supplied by main generators, e.g., AC bus 1 is fed from generator one.

Essential AC Busses

• Power essential lighting, flight control, communication, navigation, and high-priority electrical systems for safe emergency flight.

Non-Essential Bus

• Supplies galleys, non-essential lighting, and low-priority systems, which can be isolated during in-flight emergencies.
• These buses may also be called shed buses or isolation buses.

Load Shedding

• Non-essential systems are isolated during partial generator failure.
• This prevents overloading the operational generator, which would be incapable of supplying electrical power to all aircraft systems.

Basic DC Bus System

• Generators output is at a higher voltage than the output of the battery so generator charges the battery.
• The inverter provides the aircraft with AC voltage for some instruments.

Tied (Parallel) DC Bus Systems

• Older twin/multi-engine aircraft electrical systems parallel the outputs of the generators.
• Under normal conditions, the Bus Tie Breaker (BTB) is closed, and both generators supply both DC busses and share the load.
• Interconnected generator voltage regulators ensure equal load supply to the tied busses.
• Defects may cause the BTB to open and separate the busses.
• This prevents the defect from affecting the serviceable bus, and the generator supplying the affected bus disconnects and shuts down.

Split Bus System (DC or AC)

• The split bus system is common on contemporary aircraft.
• Each generator powers its own bus while operating normally, with the bus tie contactor open.
• The Bus Tie Contactor will close to connect the busses when only one generator is available.
• This is necessary in some cases:
• Generator malfunctions
• Generator is turned off
• Engine stalls
• After the start of one engine, but proceeding the start of a second

Basic Twin Engine AC Bus System

• Generators (alternators) supply individual buses.
• The AC bus powers the Transformer Rectifier Unit (TRU or T/R) for the aircraft's DC power and battery charging.
• The AC bus directly feeds the emergency AC bus.
• The static inverter starts and gives the Emergency AC from the battery if the AC supply fails.

Tied (Parallel) AC Bus Systems

• Older aircraft typically use tied AC Bus systems which must synchronise before generators can be tied (paralleled).
• Synchronisation requirements are:
• Equal frequency
• In phase
• Correct phase rotation
• Equal output voltage
• Generators must connect lines in the same configuration for correct phase rotation.
• Otherwise, synchronisation cannot be achieved.

Aircraft AC/DC Power Distribution system

• This system has tied AC busses.
• The Split System Breaker (SSB) is typically closed when both generators are online.
• The SSB will open and divide / isolate the systems if any defect arises.
• The cause of this is the AC busses exceeding voltage limits, phase rotation sequence, or frequency.
• Setting the Generator Control Units (GCUs) correctly maintains output parameters.

Multiengine Split AC Bus System

• When external power ground operation connects with the engines not running all loads will be supplied by the external power through the external power relay and closed contacts of the BTB
• GCB's will be tripped with the changeover energized.

Aircraft engines start influence:

• When one aircraft engine is starting and the generator operations lie within system limits, its GCB will energise.
• The external power relay will cause an opening which removes external power.
• BTB stays closed and connects three-phase power from the three phase power into aircraft loads.

Double engine start influence

• When a second aircraft engine starts its generator within system limits, the GCB closes.
• As the power to the BTB's close coil gets redirected via the GCB's aux contacts to the BTB’s trip coil, the BTB gets tripped.

Generator bus distribution function:

• Generates power to AC non-essential loads & TRUs.

Essential AC loads function:

• The AC essential bus connects through a changeover to the No. 1 generator bus under normal conditions.

Generator failure/switch off influence

• If one generator stops (fails/turned off), its GCB trips.
• Power supplied via tripped GCB's auxiliary contacts to BTB's close coil closes BTB.
• When clossed, connects generator buses so the generator can power all system loads.

Emergency system details.

• Emergency and Essential busses are separated relating to redundancy after power failures.
• If both generators fail, GCBs trip. Battery power closes BTB; no power for non-essential laods. Changeover relay between No. 1 generator bus and essential AC bus de-energises and connects essential bus to static inverter.
• Essential AC loads become supplied by 115 VAC from the static inverter; non-essential AC loads isolated. Continued operation would see AC isolates the loads due to longer periods of battery operation. So a turned “OFF” circuit's turns off AC/DC loads, which ensure continued operation by DC power source.

Relays, Breakers and Contactors

• Electromagnets containing a fixed core and pivoting linkage are called relays.
• Relays are often for low-current switching
• The part of the relay affected closes the contact point called the armature, consisting in part of a bar acted upon by a magnetic field.
• In other words, The armature is attracted to the electromagnet, and the armature movement either opens or closes the contact points.
• It is often misunderstood the terminology of relays and solenoids, and some aircraft manufacturers swapped contactor, relay, or breaker with solenoid.

Bus Tie Breakers

• This is the three heavy duty contacts connects -3-phase power to generator bus bars.
• Where the aircraft AC loads sit.
• it will also contain - AUXILIARY - contacts connect various control/indication circuits within the distribution system.
• Power applied makes MAIN contacts to CLOSE/AUX contact changes. and the open circuits now is normally closed. Now breaker stays locked.
• Spring-tension will release power applied to trip - releases and the main contacts are opened by forces .
• The auxiliary switch contacts to close the current position.
• the parts can be swapped out.

Generator Circuit Breaker

• For instance: Figure 11 is similar to a Generator Circuit Breaker (GCB).

Main function of the GCB in a Split Bus.

• To connect the AC generator to its power bar if working.
• To ensure while the generator OUTPUT, connected to the Generator powers bar, the bus tie is tripped and ensuring AC loads POWER from ONLY power.
• Isolate/generator output, from aircrafts loads, in case a fault is identified from control.

Aircraft Battery Systems

• Nearly with no exceptions, aircraft use -ve ground, with A single Wire.
• The metallic areas make aircraft has -Negative POtential.

Grounding benefits.

• There is low risk of the development of Radio Frequency Interference (RFI) via a few wires
• The system and parts require single wire from +ve voltage, connecting into it Aircraft Struture

If composites are present instead

• To make up for conductive parts, there will be a 2-wire electrical system.

Positive terminal influence

• connects into the battery, what some manufactures
• Also contractors all work with single task.

Energizing coil functions

• After the coil energizing, the main power gets closed into completing circuit, over Electrical bus.

Freewheeling Diode.

• There is a coil installed in the solenoid so there is less spikes.
• There are voltage and current issues when the master switch is opened.
• Freewheeling helps allow the EMF for a colapse to go into the distribution.

Voltage and current flow

• AC generators (alternators) power the main source of electricity on all aircraft. Emergency situations have Auxiliary Power Units (APUs) or Ram Air Turbines (RATs).
• Higher power-to-weight ratio than DC systems, all AC generators need a constant-speed drive to keep consistent AC frequency.
• Constant-Speed Drive (CSD) is an automatic transmission that holds a consistent output rpm via variable input rpm.
• Little power use has AC use due to constant speeds. AC Alternators has high AC usage and is fixed by internal rectifiers by power.
• Classification follows ratings with voltage, amperage, and phase. This is typical for most aircraft.

Generator Voltage Regulation

• Efficient Operation follows voltage depending system is following load requirements. Amongst various things , field strength control that will be used.

Field Current.

• Its installed on the field coil.
• Then resistance increase by field, then the current slows over field this will then be decreased this magnetic fields which reduce armature outputs.
• As the field, reduce via rheostat , currents increase - with increased armature output and bigger Voltage too output
• In contrast weakness.
• An Increase strength follows force that follows armature, plus additional increase over-come to additional armiture.

Voltage Regulators

• As output/input is consistent, voltage regulates field and load conditions. The voltage maintains consistent output voltage automatically. DC Generators/alternators has 28v, which is very easy to regulate. Also 115 AC and 200AC via 3 ( 0 ).

Rheostat use

• It makes electric addition over voltage change with varrience.
• If output increases, the pull exeedds contancts, reasserting, resistance helps, it causes lowereage and voltage output.
• Contact voltage output decreases. It causes Short then it rises. This maintains voltage without changing load. This helps smoothen the operation by Dampners to prevents the contact which cause eliminates sparking
• At the same time it increases correct output as voltage.

3-Unit Regulator

• It provides limiters by adjusting voltage regulator.
• To have certain aircraft that require the unit. They will then limit, shorted - reverse, that have multiple or the other

Regulator

• It provides 3, reverse cuts offs, voltage limits, and reverse. And also it allows operation if reverse is lower to battery output.

Current limiters

• It lowers loads, from max-min. The regulator overloads as increased load to the demands. - to protect the device or machine.

Reverse current cut-out relay

• The combination gives relays in one combination.
• It means when current flows. The direction is always energized via voltage sensing. The flow goes into gen to batt due - windings/ same winding flow. These are voltage turns of fine wire:

RCCR winding detail

• Voltage or "SHUNT" means turns from fine wire.
• Current or series wind with wire with heavy heavy

RCCR details

• if gen is better / outputs better volts; starts output with voltage with higher than the the volts .
• Volts can increase the batt. Which is at point where " C3", get close via battery that starts, which has more power and creates more power. From a better L5 magnetic pull with high increases to C3 contacts
• The Generator power will fall due lower voltage through ANY reason (shuts down/fails).
• Will direct volts will reverse / will run over . L4 the volts and battery will over come voltage with gen.
• Will decrease from contacts (3)

Diode

• As current flow, armature goes through the generator when battery output is higher. This turns as motorized

Carbon-Pile Voltage Regulator

• Vibrating - cant use with the Generator

Heavy Generators

• It needs heavy regulation, like carbon

Carbon-Pile Regulators

• Alternates disk within the tubes/ends, and also carbon in the disk

One ending notes.

• Many parts exist - against. A number of radial arranged in various springs help keep the disks together. When compressed lowers disk but resistance decrease - placed in position where output can rise for safe power.

Voltage Regulators parts

• Consistence exist with resistance over and over , with electromagnet. The carbon does connect from series field + resistance, what then shunt acrss outputs. The series of the -the voltage will give a voltage over

Parallel connect.

• Parallell connet is consistent for safe out puts, one is a output and the other must follow and vice versa.
• Voltage will need to set up greater load in the in outputs.
• To help that an equalizing or other parallels cause evenly distribution amongst

AC Equalizing circuit.

• All must combine shunt of each generator to provide each other.
• Output goes across shunt in value/current.

Solid State Voltage Regulators

• The Grounded Regulator- adjusts ground in-wire
• The types of regulators that use this. In-the ground via-power cord , for power in 3 .

Surge

• Transistors has taken over all forms for power on-boards
• The voltage here has regulator, is the main aspect of the operation.
• The indicator will help.

How transistor regulates:

• Resistence lowers voltage and diode stop and power increases . Process continues

• For when power is consistent then diode will make the field , with transistors and it stop by damage.

Brushless alternator control basics

• Separate generators 3 inside as seen from above.
• The three have -permanent PMG , generator and main one. And from new the brushless alternators

Permanent. - The rotator helps the windings - G CU the alternating current from EXCITED-Field that has windage, helps get rotating direct helps into field, with induces, direct from generator, main field.

Voltage Regulators parts

• Then power comes from it.
• GCU checks to the voltage if more is used more amps will come output more.

Constant speed drive systems facts and benefits

• Neccasry and needed, to stay constant especially in power system
• So if the generators work, must be stable, its constant

Its complete- by control output-speed to input which hydraulic maintains constacnt rpm for drive the to maintain hz also.

• Quick attach/detach: - csd/generator it separate An in-end for assembly its the similar-oil. Each also gets detach

Explore the principles, operation, and maintenance of electrical generators and alternators in aircraft. Learn about DC alternators, AC generators, Constant-Speed Drives (CSD), and the impact of load on voltage output. Discover the importance of proper electrical systems in modern aircraft.