CRJ 200 Electrical System Sample Questions

• What is the voltage of the AC and DC system?

  The voltage is 115-volt AC and 28-volt DC electrical power.

• What are the sources of AC electrical power for the aircraft?

  The primary sources of AC electrical power are two engine driven integrated drive generators (IDGs). The APU has an AC generator mounted on it. An air driven generator (ADG) can provide AC power if there is a total loss of AC power. On the forward right side of the fuselage there is a receptacle for AC ground power.

• What provides power if there is a total loss of AC electrical power in flight?

  From the right side of the forward fuselage an air driven generator (ADG) is deployed to provide AC power.

• What are the sources of DC electrical power?

  1. Five transformer rectifier units (TRUs). 2. Two nickel cadmium (nicad) batteries. 3. 28-volt external power.

• What is the kilo volt-amperes (KVA) rating of the integrated drive generators (IDG)?

  The IDG rating is 30 KVA up to 35,000 feet, then 25 KVA to 41,000 feet.

• What type of power do the IDG's supply?

  The IDG's supply 115-volt AC, 400-hertz 3-phase electrical power.

• Does the IDG RPM vary with engine RPM?

  No, the generator must turn at a constant RPM to produce a steady 400-Hz. The constant speed drive (CSD) unit accomplishes this task.

• How does the CSD accomplish a constant RPM?

  The CSD is a hydro-mechanical unit and uses an integral oil system to drive the generator at a constant RPM. The CSD is driven by the engine accessory gearbox, which turns at a variable speed based on engine speed.

• How is the internal oil of the CSD cooled?

  The oil in the CSD is cooled by an air/oil heat exchanger. The air used to cool the oil is from the N1 fan.

• What does the "FAULT" light in the IDG switch light indicate?

  This light will illuminate when the IDG oil overheats or oil pressure drops below limits. This FAULT light will also illuminate an IDG caution message on the EICAS.

• What are the ways that the IDG can disconnect from the engine gearbox?

  By pressing the associated IDG DISC switch. When CSD internal temperature raises to a certain temperature the IDG will disconnect. An over torque condition of the CSD will cause the shearing of the IDG drive shaft.

• What monitors the generator system?

  Each generator has a generator control unit (GCU) that controls and monitors the related generator system. The GCU provides protection and voltage regulation for the associated generator.

• What part of the electrical system does the ADG power?

  The ADG powers the essential buses in flight, but only when all other AC generators are not providing AC power. The ADG powers the AC ESS Bus, which powers the ESS TRU 1. The ESS TRU 1 powers the DC ESS Bus and the BATT Bus.

• What will the ADG power when it deploys with all other AC power inoperative in flight?

  The ADG bus powers the AC ESS BUS and the ACMP 3B hydraulic pump. The AC ESS BUS then powers the ESS TRU 1, DC ESS BUS, and the BATT BUS.

• When will automatic deployment of the ADG in flight occur?

  When all three generators are not providing AC power and AC BUS 1 and 2 are not powered.

• What powers the DC UTIL BUS 1 or 2 when the associated TRU that normally powers the bus fails?

  When the TRU that is associated with the DC UTIL BUS fails, that DC UTIL BUS will be load shed to reduce DC electrical loading. The DC tie contractors accomplish the load shedding.

• What is the purpose of the DC TIE Contactors?

  There are two purposes that the tie contactors provide at the same time. First, when there is a TRU failure, the DC tie associated with that TRU is closed to provide the affected bus with other power. Second, at the same time the DC tie will interrupt power to other buses to prevent overloading of the TRUs.

• What happens to the DC TIE if there is a failure of TRU 1?

  The SERV TRU would provide power with TIE 1 closing and UTIL BUS 1 being shed to prevent overloading of the TRUs. If the SERV TRU were not available, both DC tie 1 and 2 would close allowing TRU 2 to power BUS 1. This allows two sources of backup power to DC BUS 1 and 2, the SERV BUS and TRU 1 to backup DC BUS 2 and TRU 2 to backup DC BUS 1.