Fokker 50-Electrical System

GENERAL

Fleet differences

Within the fleet three different supplementary electrical power suppliers can be found, the following table is showing the differences:

Type I Type II Type III AC external power AC external power AC external power DC external power NO DC external power NO DC external power APU APU NO APU

Description

The aircraft electrical system comprises 115 V/400 Hz three phases AC power and 28 V DC power and can be controlled from the ELECTRIC panel and the APU panel. Failures will be detected and the relevant alerts presented.

AC power

AC power can be supplied by two engine driven generators, an APU driven generator, or an AC external power source. During normal operation GEN 1 and GEN 2 supply AC bus 1 and AC bus 2 respectively. The AC EMER bus 1 is also energized. If a generator becomes inoperative, AC power transfer is automatic. The output from one engine driven generator is sufficient to meet the aircraft electrical power requirements. AC power from the APU generator is available on the ground only.

DC power

DC power is supplied by two Transformer Rectifier Units (TRU), two batteries or an external DC power source. TRU 1 and TRU 2 supply DC bus 1 and DC bus 2 respectively. The DC EMER buses are also energized. The output from one TRU is sufficient to meet all aircraft DC power requirements. DC power supply includes two battery chargers. They are powered from AC bus 1 and AC bus 2 respectively.

The batteries supply power to: DC EMER bus 1 and DC EMER bus 2. AC EMER bus 1 via a static inverter. AC ground service bus via a ground service inverter.

The batteries can supply power for at least 30 minutes.

Fokker 50 - Electrical System

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Functional diagrams

Functional diagrams - Type I


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Functional diagrams - Type II


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Functional diagrams - Type III


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AC POWER

Generation

Normal AC generation

There are four sources of AC power; two engine driven generators, an APU generator, and AC external power.

Engine driven generators

The engine driven generator is mounted in the same assembly as the Constant Speed Drive (CSD). This assembly is called an Integrated Drive Generator (IDG). The function of the CSD is to ensure that the generator rotational speed is constant, thus resulting in a constant frequency of 400 Hz.

When for any reason the temperature of the oil inside the CSD starts to rise to a point where seizure might occur, a thermal disconnect separates the CSD from the engine. Rotation ceases and the IDG is protected against serious damage. In this case it is not possible to re-engage the CSD.

The IDG output is controlled by a Generator Control Unit (GCU). When voltage and frequency are within predetermined limits the GCU automatically connects the generator to the aircraft electrical system. The GCU will automatically disconnect the generator from the aircraft electrical system if a failure is detected.

APU driven generator (Type I and II) The APU driven generator provides auxiliary AC power and can be used on the ground only. The generator output is controlled by a GCU. When the voltage and frequency of the generator are within limits, the AVAIL light, at the APU GENERATOR pushbutton illuminates. When this pushbutton is depressed from AVAIL to ON, the entire electrical system is energized. The generator is not equipped with a CSD since the APU runs at a constant speed.

When AC power is supplied by one engine generator and the APU generator is available, the engine generator will supply its respective AC bus while the APU generator will supply the other AC bus. When AC power is supplied by both engine generators and the APU generator is available the engine driven generators have priority.

AC external power (All) A receptacle on the right-hand side of the front fuselage is used to connect AC external power to the aircraft. A Ground Power Control Unit (GPCU) is provided to protect the aircraft electrical system against damage. When AC external power is plugged in and meets minimum quality standards, the AVAIL light, at the EXTERNAL POWER pushbutton illuminates and the AC ground service bus is energized automatically. When this pushbutton is depressed from AVAIL to ON, the entire electrical system is energized and the EXT PWR FED light at the connector is ON. .


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When AC power is supplied by one engine generator and the AC external power is available, the engine generator will supply its respective AC bus while the AC external power will supply the other AC bus. When AC power is supplied by both engine generators and AC external power is available the engine driven generators have priority.

For type I and II When the APU generator and AC external power are available, the APU generator power has priority.

Distribution

The AC electrical system incorporates: AC bus 1 and AC bus 2. AC EMER bus 1 AC ground service bus.

AC bus 1 and AC bus 2

AC bus 1 and AC bus 2 are normally supplied by the respective generator. If either of the generators becomes inoperative, both AC bus 1 and AC bus 2 are automatically supplied by the operative generator. An AUTO AC X-FEED push button is provided to cancel this automatic crossfeed if required.

NOTE: AC galley power is automatically shed during all single-generator operation.

AC EMER bus 1

AC EMER bus 1 is normally connected to AC bus 1. If both AC buses become de-energized, the batteries are connected automatically to a static inverter and the output of the inverter is fed to AC EMER bus 1, to provide essential AC power.

AC ground service bus

The AC ground service bus is energized both on the ground and in flight when AC power is available. Without AC power available on the ground, the AC ground service bus can be energized by the batteries via a ground service inverter. A ground service TRU provides power to the DC ground handling bus.


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Functional diagram

Functional diagram - Type I and Type II


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Functional diagram - Type III


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Controls and indicators

Controls and indicators Type I


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Controls and indicators Type II


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Controls and indicators Type III


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Controls and indicators Type I en Type II


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Alerts

GENERATOR + AUTO X-FEED FAULT

2

CAUTION

BUS FAULT

LOSS OFF BOTH GENERATORS

3

AURAL MWL/MCL CAP LOCAL CONDITION(S) / LEVEL

WARNING

AC SUPPLY

BAT PWR ONLY

BUS FAULT

AUTO AC X-FEED

FAULT

FFAULT

GENERATOR

GENERATOR FAULT

2

CAUTION

FAULT

GENERATOR


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AUTO AC X-FEED FAULT

2

AURAL MWL/MCL CAP LOCALCONDITION(S) / LEVEL

CAUTION

FAULT

AUTO AC X-FEED

BUS FAULT

2

CAUTION

BUS FAULT


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DC POWER

Generation

Normal DC generation

Normal DC power is supplied by two TRUs, which are connected to the AC buses.

Transformer rectifier unit Each TRU receives AC power and provides DC power to the respective DC bus and DC EMER bus. The TRU is automatically disconnected in case of overheat or reverse current.

Battery power Battery power is provided by two batteries connected in parallel. Each battery has a battery charger that receives power from the respective AC bus. Each battery charger monitors the condition of the respective battery and regulates the charging current to avoid battery overheat. In case of a battery overheat the L/R BAT OVHT light on the CAP illuminates. A BATTERIES switch is provided to connect the batteries to the DC system and should be ON during all normal operating conditions. If the batteries are the only available source of power, the BAT PWR ONLY light illuminates. During battery power only operation, selected DC electrical loads are automatically shed to provide a minimum of 30 minutes battery power supply.

DC External power (Type I) A receptacle on the RH side of the front fuselage is used to connect DC external power to the aircraft. When DC external power is plugged in and if it meets minimum quality standards the AVAIL light illuminates. When DC power external power is connected to aircraft systems several services are not available. See system operation as well. AC power has priority over DC external power.

Distribution

The DC electrical system incorporates: DC bus 1 and DC bus 2. DC EMER bus 1 and DC EMER bus 2. DC ground handling bus.

DC bus 1 and DC bus 2 DC bus 1 and DC bus 2 are normally supplied by TRU 1 and TRU 2 respectively. If either of the DC buses becomes de-energized, both DC buses could be powered by one TRU if the DC X-FEED is manually switched ON. Both buses are interconnected automatically during engine start.


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DC EMER bus 1 and DC EMER bus 2 DC EMER bus 1 and DC EMER bus 2 are normally supplied by TRU 1 and TRU 2 respectively. If either of the TRUs becomes de-energized, both EMER DC busses will be powered automatically by the operative TRU. If both TRUs become de-energized, both EMER DC busses are automatically connected to the batteries, to provide essential DC power for at least 30 minutes.

DC ground handling bus Power is automatically available to the DC ground handling bus from the batteries or the AC external power source. The DC ground handling bus supplies the following services: Passenger door operation Hydraulic fluid quantity checks Refueling

There are no lights or pushbuttons in the flight deck directly related to the ground handling buses.


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Functional diagram

Functional diagram - Type I


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Functional diagram - Type II and Type III


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Controls and indicators

Controls and indicators - Type I


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Controls and indicators - Type II and Type III


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Alerts

BATTERY OVERHEAT

3

AURAL MWL/MCL CAP LOCAL CONDITION(S) / LEVEL

WARNING

L BAT OVHT

R BAT OVHT

BUS FAULT

2

CAUTION

BUS FAULT

TRU FAULT

2

CAUTION FAULT

TRU

CHARGER

FAULT

BUS FAULT

BATTERY CHARGER FAULT

2

CAUTION

FAULT

CHARGER

OR


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CIRCUIT BREAKERS


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SYSTEM OPERATION

System data

DISPLAY SELECTOR LH ELECTRIC DISPLAY RH ELECTRIC DISPLAY BUS 1 BUS 2 26 - 31 26 - 31

111 - 119 111 - 119

BUS VOLT DC/EMER DC AC EMER AC 111 - 119 -

VOLT FREQ EXT PWR VOLT-FREQ 110 - 120 385 - 415 GEN GEN 1 GEN 2 LOAD (%)

CONTINUOUS 100 100 5 MIN 113 113 5 SEC 150 150 VOLT 111 - 119 111-119 FREQ 395 - 405 395 405 BAT BAT 1 BAT 2 LOAD (A) +40 / -40 +40 / -40 VOLT 23 - 32 23 - 32 TRU TRU 1 TRU 2 LOAD (%)

CONTINUOUS 100 100 2 MIN 133 133 5 SEC 300 300 VOLT 26 - 31 26 - 31

Type I When on DC external power amongst other systems the following services are not available: AHRS Cooling. Avionics rack cooling. Instrument cooling. Recirculation fans. Window heating. Hydraulic system electrical pump. Water quantity indication.

Due to lack of avionics cooling the use of DC external power must be restricted to a few minutes when the outside air temperature is 25 degrees or above.


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Fokker 50-Electrical System