Boeing 757 Electrics __ Battery_Standby Power System

Hot Battery Bus.

Battery Bus.

Standby DC Bus.

Standby AC Bus.

Electrics - Battery & Standby Power System

Amendment: Description amended to include single battery installations.

The Battery/Standby Power System can supply DC and AC power to selected flight instruments,

communications and navigation systems, and other critical systems, if there are main AC and DC

electrical power system failures.

The Battery/Standby Power System comprises the following Buses:

If all generator power is lost, these are the only buses that can be powered by the batteries.

See: Battery Schematic

See: Bus Equipment List

BATTERIES

Battery Installations

Each battery has a charger powered from the Ground Service Bus.

HOT BATTERY BUS

The hot battery bus provides power to items that must be continuously powered, such as the Clock's

time reference.

Prior to establishing electrical power, the Main Battery powers the Hot Battery Bus. After

establishing electrical power, the Main Battery charger powers the Hot Battery Bus.

BATTERY BUS

Prior to establishing electrical power, [and] when the Battery Switch is ON , the Main Battery powers

the Battery Bus.

The Main Battery also powers the Battery Bus if the the Standby Power Selector Switch is in the

BAT position.

After establishing electrical power, the Left DC system powers the Battery Bus, and the main battery

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provides a backup source of power.

The Battery DISCH light illuminates when the main battery is discharging. If EICAS is powered,

the advisory message MAIN BAT DISCH also displays.

The MAIN BAT DISCH light illuminates when the Main Battery is discharging. If EICAS

is powered, the advisory message MAIN BAT DISCH also displays.

The Battery OFF light illuminates and the EICAS advisory message BATTERY OFF displays if the

battery switch is OFF after electrical power is established.

STANDBY DC BUS

The Standby DC Bus can be powered by several sources.

Prior to establishing electrical power, when the battery switch is

ON and the standby power selector is in AUTO , the main battery powers the standby DC bus.

The Battery DISCH light illuminates when the main battery is discharging.

After establishing electrical power, the left DC system powers the standby DC bus and the main

battery provides a backup source of power.

When the standby power selector is in BAT , the main battery powers the standby DC bus.

Prior to establishing electrical power, when the Battery Switch is ON and the

Standby Power Selector is in AUTO , the Main Battery and the APU Battery are

paralleled to power the Standby DC bus. The MAIN BAT DISCH light and the APU BAT DISCH

light illuminate when the main battery and APU battery are discharging.

After establishing electrical power, the Left DC system powers the Standby DC bus and the Main

Battery and APU Battery provide a backup source of power.

When the Standby Power Selector is in BAT , the main battery and the APU battery are paralleled

to power the Standby DC Bus.

The Standby Bus OFF light illuminates and the EICAS advisory message STANDBY BUS OFF

displays if the Standby DC bus is unpowered.

STANDBY AC BUS

The Standby AC bus can be powered by several sources.

Prior to establishing electrical power, when the battery switch is

ON and the standby power selector is in AUTO , the main battery powers the standby inverter

which provides AC power to the standby AC bus.

After establishing electrical power, the left AC system powers the standby AC bus and the main

battery and standby inverter provide a backup source of power.

When the standby power selector is in BAT , the main battery and standby inverter power the

standby AC bus.

Prior to establishing electrical power, when the Battery Switch is ON and the Standby Power

Selector is in AUTO , the Main Battery and the APU Battery parallel to power the Standby Inverter

which provides AC power to the Standby AC bus.

After establishing electrical power, the Left AC system powers the Standby AC Bus and the Main

Battery, APU Battery and Standby Inverter provide a backup source of power.

When the standby power selector is in BAT , the Main Battery, APU Battery and Standby Inverter

power the Standby AC Bus.

The Standby Bus OFF light illuminates and the EICAS advisory message STANDBY BUS OFF

displays if the Standby AC Bus is unpowered.


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STANDBY POWER SELECTOR

OFF

In the OFF position, the selector cuts off all sources of power to the Standby DC and Standby

AC Buses.

BOEING In flight, loss of Standby DC power is sensed as a double engine failure and unlocks

the RAT. If the Standby Power Selector is placed OFF (in flight) on the 757, full RAT deployment

could be expected due to the spring extension mechanism.

AUTO

The Standby Power Selector affects the power going to the Standby DC and Standby AC buses.

With the selector in the AUTO position, left main DC and AC power have priority in supplying

the two Standby Buses.

When the Battery Switch is ON , the AUTO position also permits the main battery, APU battery

and battery chargers to act as backup power sources for the two buses.

BAT

Selecting the BAT position cuts off main AC and DC power to the standby system. The only

power remaining for the standby system is battery power. In this case even the battery chargers

are disconnected from the Ground Service Bus.

With the Battery Switch ON , the battery supplies Standby DC and Standby AC through the

Static Inverter.


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AFM Flight beyond 30 minutes (90 minutes if 2 batteries installed) will result in complete loss

of electrical power.

© Biggles Software 2002-2010


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Boeing 757 Electrics __ Battery_Standby Power System

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