Electrical Power System

Question 1

What configuration is the electrical system?

Answer 1

The electrical system is a DC split bus configuration.

Question 2

How do the left and right electrical buses operate during normal conditions?

Answer 2

The left and right electrical buses are isolated from each other during normal conditions.

Question 3

How are the left side buses powered during normal conditions?

Answer 3

The left engine generator and the left battery power the left side buses.

Question 4

How are the right sided buses powered under normal conditions?

Answer 4

The right generator and the right battery power the right side buses.

Question 5

What happens to the two systems under abnormal flight conditions?

Answer 5

Under abnormal flight conditions, the two systems (sides) may be tide together through a bus tie relay controlled from the cockpit.

Question 6

Why are the two sides tied together under abnormal flight conditions?

Answer 6

They are tided together to ensure electrical supply to critical flight systems.

Question 7

Electrical power comes from four sources. Name them?

Answer 7

1. Left engine-driven starter-generator.
2. Right engine-driven starter-generator.
3. APU (starter-generator)
4. EPU

Question 8

Split Bus Safety and protective features (8)

Answer 8

1. Only one generator is connected to a single bus system at any time.
2. EPU overvoltage/undervoltage protection.
3. Two separate distribution systems supply power.
4. A malfunctioning power source cannot prevent the remaining power sources from furnishing power.
5. Individual or collective disconnection of electrical power sources is available in flight.
6. When either ENG FIRE PUSH button is pressed, the respective generator is deactivated.
7. Generator overvoltage protection is provided at 35 +/- 0.5 volts.
8. All circuit breakers are push to reset type and cannot be reset if a fault is present in the circuit.

Question 9

Which EMER BUS does the EPU connected to?

Answer 9

To the right EMER BUS.

Question 10

Which EMER BUS does the APU connect to?

Answer 10

The APU connects to the left EMER BUS.

Question 11

Describe the electrical EICAS display.

Answer 11

The electrical area is divided into two columns representing the left and right electrical bus systems.

During normal operation, the digital displays will be colored green.

In an abnormal condition the digits will turn to an inverse video amber or inverse video red.

Invalid data is presented as Amber dashes.

Question 12

What does a - sign infront of the battery amp number indicate?

Answer 12

The battery is being discharged.

Question 13

What happens when the battery button is indicating ON?

Answer 13

In the ON position the battery relay closes and connects the battery bus to the emergency bus.

Question 14

What happens when the EXT PWR button is annunciated AVAIL and the button is pressed.

Answer 14

If the button is pressed, then the external contractor closes and the ON annunciation displays.

External power is then supplied to the right emergency bus for distribution to the electrical system.

Question 15

What happens when the L/R AVN buttons are annunciated ON.

Answer 15

The L/R AVN: Buttons distribute power from the main DC buses to the avionics buses through the avionics relays.

Question 16

The left and right interior relays are simultaneously opened and closed with a two-position INTERIOR button.

Describe the NORM annunciation?

Answer 16

NORM - Closes the interior relays and supplies power to both interior buses and the cabin J-box circuit breakers. All cabin equipment is powered except cabin emergency lighting.

Question 17

The left and right interior relays are simultaneously opened and closed with a two-position INTERIOR button.

Describe what happens when the OFF is illuminated.

Answer 17

OFF- Opens the interior relays and de powers the cabin equipment.

Cabin emergency lighting, PAX Safety, and cabin entry lights are unaffected by the INTERIOR button.

Question 18

L/R ELEC/NORM/EMER: The button positions are either NORM or EMER.

When it is on NORM, how is the bus powered?

Answer 18

NORM - The generator is powering their buses and charging the battery. The relays have the ability to automatically open or close as commanded by start logic.

Question 19

The left and right electric relays are simultaneously opened and closed with a two-position L/R ELEC/NORM/EMER button.

When it is on EMER, what is the position of the relay?

Answer 19

EMER- The relay is open. Manually opening the electric relay illuminates the DC EMER BUS CAS message.

Question 20

When the EICAS button is ON, how is its bus powered?

Answer 20

When the button ON, emergency bus power is supplied to the EICAS bus.

Question 21

When the STBY POWER switch is ON, which bus supplies the power?

Answer 21

ON- Powers the standby bus through the left main electrical bus, or, through the right main electrical bus if the left is not available.

Question 22

Standby power is available for?

Answer 22

180 mins.

Question 23

Power from the emergency bus is available for?

Answer 23

60 mins.

Question 24

If the DC EMER BUS Land/or R is displayed and the amps show a >30 amps discharge, which bus has a fault?

Answer 24

Fault on the emergency bus.

Question 25

If the DC EMER BUS Land/or R is displayed and the amps show a < or =30 amps discharge, which bus has a fault?

Answer 25

Fault on main bus.