ELECTRICAL_GND POWER and BUS SWITCH PANEL

Question 1

GND POWER AVAILABLE Light

What does this light mean? (1sp)

Answer 1

[1sp - ground power is connected, and the quality is good]

Illuminated (Blue):

• ground power connected and is of good quality
• stays on until you remove external power source

Question 2

GND PWR Switch

- 3 position -

Answer 2

Notes.

• 3 position switch spring loaded to neutral

OFF:

• disconnects ground power from AC xfer busses

ON:

• if momentarily moved to ON and ground power IS available
  
  • removes previously connected power from AC xfer busses
  • connects gnd power to AC xfer busses if power quality is correct

NEUTRAL: spring-loaded position

Question 3

TRANSFER BUS OFF Light

What does this light mean? (1sp)

Answer 3

[1sp - means the respective transfer bus is not powered]

Illuminated (Amber):

• transfer bus is not powered
• illuminates the MC and ELEC cautions

Question 4

SOURCE OFF Light

1sp - what does the source off light mean?

Answer 4

[1sp - means we have to manually select a source (we have 3 sources to choose from (eng, apu or gnd)]

Illuminated (Amber):

• no source has been manually selected to power the related transfer bus OR
• the manually selected source has been disconnected
• can also be said - a transfer bus is not energized by the source you last selected

LEFT SOURCE OFF light: (related to the following)

• IDG 1 (GEN 1 switch)
• APU (LEFT APU Gen switch)
• External power (Gnd power switch)

RIGHT SOURCE OFF Light:

• IDG 2 (GEN 2 switch)
• APU (RIGHT APU Gen switch)
• External power (Gnd power switch)

* if a source has been selected to power the OPPOSITE Transfer bus, BOTH transfer busses are powered.

** Source off does NOT mean the transfer bus is unpowered

Question 5

GEN OFF BUS Light

What does the GEN OFF BUS Light Indicate? (1sp)

Answer 5

[1sp - Indicates the generator breaker is open. Which means Gen is not powering the bus - this light does NOT indicate the quality of power]

Illuminated (Blue):

• IDG is not supplying power to the related transfer bus

Question 6

GENERATOR Switches

Answer 6

Notes.

• 3 positions switch (spring loaded to neutral)

OFF: Disconnects IDG from related AC transfer bus (opens generator CB)

ON: Connects IDG to related AC transfer bus (disconnects previous power source and closes generator CB)

* Pulling the FIRE HANDLE or DISCONNECTING THE IDG will also OPEN the CB (i.e ‘OFF’)

Question 7

BUS TRANSFER Switch

How does the bus transfer switch work in the AUTO position? (1sp)

What happens if we move the switch to the OFF position? (1sp)

Answer 7

[1sp - in case you lose the generator, as long as you have the bus transfer switch in auto, through the BTB other generator will power the respective transfer bus

(b) - when you go to OFF you open the TR 3 disconnect relay and you lose the bus transfer protection, the BTBs will remain open so you will not have the transfer protection

BTBs are relays which is a circuit that will close when electrically energized]

OFF:

• isolates AC transfer bus 1 from AC transfer bus 2 (if one IDG is supplying power to BOTH busses)
• DC CROSS TIE RELAY opens to isolate DC bus 1 from DC bus 2

AUTO: (Guarded)

• BTBs operate automatically to maintain power to the AC transfer busses from ANY operating Generator or external power
  
  • DC CROSS TIE RELAY automatically provides normal OR isolated operation as required.
  • TR3 transfer relay energizes which will allow TR 3 to get power from Transfer bus 1 if Transfer 2 looses power

Question 8

APU GEN OFF BUS Light

What does this light mean? (1sp)

Answer 8

[1sp - it means that the APU is running and its available but its not powering the bus - APU power is available, and the quality is good]

Illuminated (blue) - APU is running (95%) but it is NOT powering any busses

Question 9

APU Generator Switches

Answer 9

Notes.

• 3 position spring loaded to neutral
• there are 2 switches - one for each BTB

OFF:

• with the APU powering BOTH transfer busses -
  
  • if you move ONE switch to OFF - related [SOURCE OFF] illuminates but APU still powers transfer busses
  • if you moved BOTH to OFF - disconnects the APU GEN from tie bus and removes APU power from transfer busses
• with APU powering ONE transfer bus and IDG powering the other -
  
  • moving the related APU GEN switch OFF DISCONNECTS the APU from the tie bus AND transfer busses - which then allows the IDG to power both AC transfer busses.

ON:

• with neither AC transfer bus powered by IDG
  
  • moving a SINGLE APU Gen switch to ON connects both transfer busses to APU
  • disconnects external power (if connected)
  • opposite [SOURCE OFF] illuminated (until the other switch moved to ON)
• BOTH transfer busses powered by IDG -
  
  • moving a SINGLE APU Gen switch ON powers the related transfer bus from the APU Gen
  • the other AC transfer bus continues to recieve power from the IDG