EMB-120 Electrical Flashcards Preview

Embraer Brasilia EMB-120 > EMB-120 Electrical > Flashcards

Flashcards in EMB-120 Electrical Deck (69):

Describe the Electrical System:

Voltage / Battery:

28 Volt DC System.

24 Volt / 43 Amp lead-acid battery.


What power sources can power the electrical system in normal mode?

2 Main Generators.

APU Generator.




What is the primary source of power?

Two 28 Volt / 400 amp engine-driven starter / generators.


When does the starter-generator become a generator?

50% Nh


What power sources can power the electrical system in electrical emergency mode?


Aux Gens.


How do you get into electrical emergency mode?

Manually with switch.

Automatically, via auto transfer when:
1) Power select switch on “BATT”
2) Both Main Gens off
3) At least one Main Gen switch on


What happens in electrical emergency mode?

Load shedding- DC Bus 1, 2, 3 and Central Bus.

Emergency Buses powered by Aux Gens or Battery.

Battery being charged by Aux Gens (or not at all).


In electrical emergency mode, with battery power, what remains on?

Hot Battery Bus.

Emergency Bus 1 & 2.

Radio Master Emergency DC1.


Which power source(s) to the Central Bus are not able to charge the main battery?



What power sources are directly connected to the Central Bus?

1) APU
2) Main battery
3) External power (GPU)


What are the Hot Battery Bus items?

1) Door
2) Courtesy Lights
3) Auto transfer
4) DC indicator
5) Fire extinguishers
6) Fuel SOV
7) Hydraulic SOV


How long will the battery supply the essential loads without generators?

30 Minutes.


What happens to the backup battery in electrical emergency mode?

Totally disconnected from DC system.


When do you get a battery temperature warning?

70 degrees.


What are the max amps for the Main Gens?

Up to 27,000’ or ISA + 27˚c = 400 amps.

Above 27,000’ or > ISA + 27˚c = 380 amps.


What are the max amps for the Aux Gens?

Up to 18,000’ = 150 amps.

Above 18,000’ = 140 amps.


What avionics are available after total (all 5) generator failure?

Items powered by Master Radio DC Bus
1) VHF Comm 1
2) ADF 1
3) XPDR 1


What powers Master Radio DC Bus 1?

Emergency DC Bus 1.


How do you start the APU in electrical emergency mode?

1) Reduce Load
2) Turn both Main Gen switches OFF
3) Fire test


What are the functions of the backup battery?

1. Normally, it provides a stable power source for that equipment controlled by RCCBs.

2. In EMERGENCY mode (Auto or Manual Transfer), the BACK-UP BATTERY is totally disconnected from the DC system, thereby preserving its charge for when it is really needed.

3. When emergency bus voltage drops to 19V, i.e. all generators have failed and the main battery is depleted, a transfer relay connects the STANDBY ATTITUDE INDICATOR to the the BACK-UP BATTERY, which, if fully charged, will supply power for 5 hours.

4. The Back-Up battery also supplies power to the FMS data.


What is the normal in-flight position of the backup battery?



What happens to the backup battery when the electrical system transfers into electrical emergency mode?

No longer charges.

Powers standby horizon if Emergency DC Bus 1 drops below 19 volts.


How do you know if Emergency DC Bus 1 has dropped to less than 19 volts?

White backup battery light ON.


Describe the AC System -115 VAC & 26 VAC:

Which is normally used?
What if one fails?

Inverter 1 normally used, powered by DC Bus 2.

Inverter 2 is backup, powered by Emergency DC Bus 1.

If 115 VAC side of Inverter #1 fails, Inverter #2 automatically picks up everything (w/ radio master switch on).

If 26 VAC side of Inverter #1 fails, you must turn OFF Inverter # 1 for # 2 to pick it up.


What power source do you need to make a 115v transfer?

Radio master power.


If there is an ELEC light on the MAP and both 26 VAC BUS OFF lights illuminated on the panel, what’s the problem and how do you handle it?

#1 Inverter 26V side failed and did not transfer to #2.

26 volt AC Buses are de-energized- QRH directs you to turn off # 1 to make transfer to #2.


How many volts is the electrical system?



What is the normal battery voltage?



What are the minimum battery volts for an APU start?



Describe the backup battery:

24 volt, 5 amp


What powers the MAP?

Emergency DC Bus 1 & 2.


What buses are needed to start the engines?

1) Central bus

2) Respective DC Bus (to close starter relays)


What buses are required to start the APU?

1) Central Bus

2) DC Bus 2 (to close starter relay)


What charges the battery in electrical emergency mode?

Emergency DC Bus 2 via the Aux Gens.


When does the battery power Emergency DC Bus 1 and 2?

In electrical emergency mode when Aux Gens are below 24 volts.


What charges the battery in normal mode?

Central DC Bus.


What powers the emergency buses in normal mode?

DC Bus 2.


What powers the Emergency Bus in electrical emergency mode?

1) Aux gens

2) Battery


What powers the fire protection?

Hot Battery Bus.


What powers the fire detection?

Emergency DC Bus.


What type of buses are the Central DC and Aux DC Buses?

Feeder or Relay.


When are the Aux Gens connected to the electrical system?

Powered when Np > 70%


On taxi, with Power Levers in ground idle and Condition Levers in min, the 2 AUX GEN OFF BUS lights are illuminated. How do you handle the problem?

No problem, Np would be below 70% in this situation.


What is the procedure for a tripped circuit breaker?

On ground- contact maintenance.

In flight- QRH or, if no procedure, at captains discretion (1 time only).


“EMER BUS OFF” light- How do you check which emergency bus is off?

Check T6 and Torque gauges (left = Emer DC1, right = Emer DC2)


“BUS 1 OFF” light- What does it mean?

No power to bus.


“GEN OFF BUS” light- What does it mean?

Main Gen contactor is open, disconnected from the bus.


Explain the emergency lights:

Has its own source of power.

Will last 17 minutes, take 22 hours to recharge.


What lights work in electrical emergency mode?

1) Left landing light
2) Emergency lights
3) 3 out of 6 fluorescent lights on the panel
4) Two spotlights in the cockpit
5) No Smoking and Seat Belt sign


What sources of power are able to power the EMB-120 electrical system in Electrical Emergency Mode?

• Battery
• Aux Gens


How can we identify which source is powering the electrical system in the Emergency Mode?

Transfer Fail Light:

Light on – Battery (Aux Gens failed to transfer power from DC Bus 3 to Emer DC Bus 1 & 2)

Light off – Aux Gens


What three conditions are required for an auto transfer to Electrical Emergency Mode?

• Power select to battery
• Both main generators offline
• At least one main generator switch is ON


Which bus(es) are shed in the Electrical Emergency Mode?

• DC Bus 1,2 & 3
• Central Bus


What 3 avionics items are available after total (all 5) generator failure?

• VHF Comm 1
• ADF 1
• XPDR 1
(Items powered by Master Radio Emer DC Bus 1)


What happens to the back-up battery when the electrical system transfers to the Emergency mode?

1) No longer charges

2) Powers standby attitude indicator if Emer DC Bus 1 drops below 19 volts.


Which power sources connect directly to the Central Bus?

• Main Battery


Which power source in the Electrical Emergency Mode is required to charge the Battery?

Aux Gens.


The aircraft entered the Electrical Emergency Mode automatically and you wish to start the APU.

1. What must you do to start the APU?

2. What bus must be powered to close the APU Start Contactor?

Get below FL200 and reduce speed to 135-200 KIAS.

Reduce Load, turn off both main gen switches, and perform a fire test.

• DC Bus 2


Cruising at FL 260 and ISA +10, the maximum continuous main generator amperage is limited to what?


(> 27,000 ft or ISA +27 = 380A)


During an auto transfer to Emergency Mode with the TRANSFER FAIL light extinguished, what is the power source to the Emergency busses?

Aux Gens.


During taxi with the engines stabilized at Ground Idle (Nh 62% & Np 50%) which buses will the Aux generators power?

None, Aux Gens become powered at Np > 70%


What buses are required to start the APU?

DC bus 2 and Central bus.


What are remote control circuit breakers?

The primary circuit breaker for some of the heavy draw (over 40 amps) equipment such as electric hydraulic pumps have the primary circuit breaker located outside the cockpit. This avoids long runs of heavy wire to and from the cockpit. These RCCBs are connected by a small wire to a related circuit breaker on the cockpit. The cockpit CB acts as a slave to the RCCB master.

All cockpit CBs rated at 1/2 amp are connected to RCCBs. All 1/2 amp cockpit CBs for a particular bus system are connected to the respective relay bus.

Additionally, RCCBs require uninterrupted power and stable voltage to operate. Therefore, in addition to the normal power source, they are connected to the Back-up Battery Power system to provided continued operation during voltage fluctuations.


If the Back-up Battery is turned ON with no other
power on the bus system what happens?

If the Back-up Battery is turned ON with no other
power on the bus system, the aural warning system will be heard announcing a series of malfunctions.


GENERATOR CONTROL UNITS for all 5 generators provide:

a. Voltage regulation to 29 volts.
b. Paralleling between two or more generators within 10%.
c. Field weakening control during start
d. Reverse current protection
e. Overspeed protection if shaft shears during start
f. Auto cancellation of the start cycle.
g. Overvoltage protection at 32 VDC.
h. Fault protection.
i. Auto excitation of field.
j. Overcurrent protection starting at 680 amps for 20 sec. curving down to
1050 amp for 2 sec. Then opens respective Bus Tie contactor and removes
the battery from the Central Bus. If problem persists, opens generator relay.


During a failure of 115V side of inverter 1,
successful transfer would be indicated by:

Illumination of Inverter 1 “Inop” light (top left yellow light)


EMERGENCY MODE w/o AUX GEN would look like what on the AC Power panel? (Inverters)

Illumination of Inverter 1 “Inop” and “115V Bus Off” and “26V Bus Off” lights. (three left yellow lights)


A failure of the 26VAC side of the #1
inverter would be indicated by:

Illumination of 26V Essential and EMER bus lights. (two bottom yellow)


What light stays out during the FFOD auto transfer test?

Emerg Bus OFF light.