EMB120 Electrical System

Question 1

How many Generators does the aircraft have?

Answer 1

5 total
2 main - 28vdc 400amp (600amp during start)
2 Aux - 28 vdc 150 amp
1 APU (Identical to Main start/gen)

Question 2

How many volts does the battery have?

Answer 2

24V

Question 3

How many volts does the generators have?

Answer 3

28V

Question 4

How long do the standby instruments last on the back up battery?

Answer 4

At least 30 min

Question 5

How many inverters does the aircraft have?

Answer 5

2 inverters, # one is always on and #2 is waiting for #1 to fail

Question 6

If you loose a generator can you power the system on the other main gen?

Answer 6

Yes, Both gens are connected to the central DC bus which acts as a bus tie

Question 7

What is the GCU?

Answer 7

Generator Control Unit

Question 8

What does the GCU do?

Answer 8

Controls all starting
Energizes and De-energize Ignition Circuits
Energizes return solenoid to empty drain collected tank
overspeed protection
De-energizes EPA return
Regulates output
over voltage protection
reverse current protection
generator field over exciting protection
Paralleling

Question 9

Where does all the starting function for the main engines and APU happen?

Answer 9

Central Bus

Question 10

What conditions have to happen for Emergency transfer made to happen?

Answer 10

1 gen has to be on

loss of power

Question 11

Can you start the APU or engines when in emergency transfer mode?

Answer 11

No, you have to take the system out of emergency transfer mode

Question 12

What is the EDC?

Answer 12

The Emergency DC, It contains all the essential equipment because it is always powered

Question 13

When does the Aux gens turn on?

Answer 13

70% Np

Question 14

If one EDC fails how can you tell which one is failed?

Answer 14

the Tq and T6 gauges

EDC 1 #1 engine
EDC 2 # 2 engine

Question 15

What generator is the EDC buses connected too normally?

Answer 15

Right Gen

Question 16

How many volts are the inverters?

Answer 16

250 volt inverters that convert 28VDC into 115VAC and 26VAC

Question 17

When does the generators convert from starters to generators?

Answer 17

50%Nh

Question 18

When can the APU gen provide electrical power to aircraft?

Answer 18

95% RPM

Question 19

When ground power is connected and the APU is running which has priority for supplying power?

Answer 19

Ground Power

Question 20

when the main gens are running and ground power is connected which has priority for supplying power?

Answer 20

Main Gens

Question 21

Is there any protection for overvoltage while on ground power?

Answer 21

Yes, an over voltage relay protects the central DC bus if external power exceeds 32VDC

Question 22

Is the battery connected to the hot batter bus?

Answer 22

Yes, During normal operations the power source powering the central DC bus powers the hot battery bus and charges the battery.

Question 23

If the aircraft looses 115VAC output will the system automatically swap inverters? If the aircraft looses 26VAC output?

Answer 23

loss of 115VAC auto switches inverters

loss of 26VAC requires manual selection of inverters

Question 24

How do you prevent a rest to Normal operation after Emergency transfer?

Answer 24

Emergency mode must be selected prior to turning off both gens.

Question 25

If Emergency transfer happens and APU is available can it be used to power system?

Answer 25

Yes, the system should be placed into normal mode prior to an air start of the APU

Question 26

What is on the hot battery bus?

Answer 26

Autotransfer
Clock/chronograph
Courtesy light
DC indication 1&2
Fire extinguishing, left & right
Forward entry door
Fuel shutoff valve, left & right 
Hydraulic shutoff valve, blue & green