Lecture Aircraft power systems

Lecture Aircraft power systems

21PJE – Palubní přístroje - LS 2012/2013

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Digital avionics is more sensitive on supply voltage variations and high-frequency noise than analog alternatives. Requirements for electric power are specified by: MIL-STD-704 RTCA DO-160

MIL-STD-704 says what the user can expect to see in term of normal conditions, over and under voltage and frequency drift. It describes the electrical power quality for military aircraft and how the equipment is required to operate. RTCA DO-160: Environmental Conditions and Test Procedures for Airborne Equipment presents comparable information to MIL-STD-704 but for civil aircrafts.

MIL-STD-704 The steady state AC power characteristics for standard military 115 V, 400 Hz Voltage (108 – 118) V rms Frequency (393 – 407) Hz Maximum DC component ±0.1 V Phase unbalance 3V Phase difference (116 – 124) deg 21PJE – Palubní přístroje - LS 2012/2013

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MIL-STD-704 115V, 400 Hz power system under various conditions


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MIL-STD-704 115V, 400 Hz frequency allowance under various conditions


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MIL-STD-704 28V DC power system under various conditions


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MIL-STD-704 270 V DC power system under various conditions


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RTCA DO160 it does not levy power quality requirements, but rather describes series of input conditions, testing conditions, and the behavior. It establishes 4 classes of equipment: Type A – equipment is intended for usage on aircraft that use primarily AC power and any DC power is derived from transformer/rectifier units. Floating a battery on a DC bus is optimal. Type B - equipment is intended for usage on aircraft where DC power is supplied by engine-driven alternator/rectifiers or generators, and there is a battery of substantial capacity floating on the bus at all times. Type E – equipment is power by only AC power. Type Z – equipment may be used on all other types of systems covered by the document.


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Comparison of aircraft electrical power: MIL-STD-704 x RTCA DO-160


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Electrical systems

 Alternators  Produces sufficient amount of electrical current at slower RPM by producing AC current that is converted to DC  More constant at different ranges of engine speeds  Lighter weight  Less costly to maintain  Less prone to overloading

 Generators  Do not produce enough electrical current at low engine RPM to operate entire electrical system.  Electrical needs often rely on battery, which is quickly depleted

Requirements: higher reliability, working under difficult climatic conditions, lighter per power horse


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Electrical systems

Alternator

Small aircrafts Alternator

Engine

DC generator Battery


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Electrical systems

Alternator

Small transport aircrafts Alternator

DC generator Engine

Battery

AC generator


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Electrical systems Engine

CSD

AC generator Rectifier

Large transport aircrafts

Battery

Engine

Frequency alternator

AC generator

Rectifier

Large transport aircrafts

Battery


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Battery

Min. diff. relay

Appliances

DC gen.

Exc. winding

Carbon regulator

DC generator with a carbon regulator and shunt excitation

Overvoltage relay

Carbon regulator


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Contactless alternator Rotor

Stator Switch off

Terminal amplifier

Power exciter

Regulation Basic exciter

CSD 21PJE – Palubní přístroje - LS 2012/2013

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Power bus

Single phase stationary alternator

Output voltage Square gen. 400 Hz

Voltage regulation

Power amplifier

Transformer + Filtering

Output current


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Output observer

Output

Simplified diagram of a stationary alternator DC 28V to AC 115 V, 400 Hz


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Twelve phase aircraft rectifier

Filter

Filter


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Basic arrangement of a CSD unit


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Simplified diagram of an electrical system for a large transport twinjet


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Palubní síť soudobého vojenského letadla


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Palubní síť soudobého dopravního letadla


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ELEKTRICKÉ ZDROJE NĚKTERÝCH LETADEL TYP LETADLA

HLAVNÍ ZDROJ

POMOCNÝ ZDROJ

ZÁLOŽNÍ ZDROJ

L39 28 V 9 kW NÁPOROVÁ TURBINA 9 kW SS 28V 6kW L410 L59 28 V 9 kW 28 V 6 kW ATR72 28V 12kW 115V 20 kVA 3x115V 35kW 28 V 5,6 kW L159A 28 V 15kW 28 V 5,6 kW 4 měniče 3x115V 1,7kVA L159B CHALLANGER 3x115V 30kVA 3x115V 15kVA BOEING 737

3x115V 40kVA

3x115V 40kVA

AIRBUS A310

3x115V 90kVA

3x115V 90kVA

28V 15kW, 3x115V 5kVA

AIRBUS A320

3x115V 90kVA

3x115V 90kVA

28V 15kW, 3x115V 5kVA

SOKOL

28V 7,5kW ,3x115V 40kVA,

BELL 412

28V 5,6 kW

BO105

28V 5,6 kW


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Generator feeder lines based on B737


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Electrical/electronics compartments


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Flight deck control panels P1 – captain’s flight instrument panel P2 – center engine instrument panel P3 – first officer’s flight instr. panel P5 – overhead control panel P7 – glare shield panel containing annunciator lights for each pilot

P8 – fire protection system control panel P9 – weather radar display indicator and radio communication system selector controls


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Overhead control panel


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P6 and P18 panel


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Lecture Aircraft power systems

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