Electrical system

Question 1

If a CB trips, how many reset attempts are allowed?

Answer 1

1 reset attempt is allowed

Question 2

How many types of Electrical Power Supply for we have?

Answer 2

28V DC (MAIN ELECTRICAL POWER)
2x 28VDC 400A Starter/Generators
2x 24VDC 43Ah Ni-Cad Batteries
1x 28VDC External Power Supply

Question 3

EMERGENCY POWER SUPPLY

Answer 3

1x 24VDC 5Ah Battery comprised of
rechargeable D cells

Question 4

115V/26VAC

Answer 4

2x single phase 400Hz Inverters

Question 5

115/200 VAC ‘Wild’

Answer 5

2 x 3 phase 115VAC Generator 460 – 600Hz

     (for Ice protection and galley mug ONLY)

Question 6

2 x 24VDC 43Ah Ni-Cad BATTERIES

Answer 6

installed outside the pressure hull
fitted with thermal protection sensors
1 hour discharge rate (refer E17)

Question 7

No Batt start

Answer 7

57 - 71 degrees
No CWP light

Question 8

Hot Batt

Answer 8

Above 71 degrees

Question 9

should the Generator temperature reach 150ºc

Answer 9

GEN OV TEMP light on the overhead panel will illuminate, along with a CWP

the Generator is NOT Automatically taken off line

Question 10

External power

Answer 10

EXTERNAL POWER ALWAYS HAS PRIORITY OVER THE BATTERY AND THE GENERATOR RELAYS

Question 11

1 x 24VDC 5Ah BATTERY
(EMERGENCY POWER SUPPLY)
Location and how does it work?

Answer 11

• located in the Avionics Rack
• 1 hour duration of power
• has its own integral heater (temp kept
  between 27ºC and 55ºC)
• when the L BAT Bus is powered, the
  EMERGENCY BATTERY is charged from this bus
• requires a Battery Switch to be ON to
  power Emergency Bus
• supplies power to the Emergency Bus,
  when the L Bat Bus voltage drops below
  24 VDC (provided a Battery Switch is ON)

An EMER POWER light on the overhead panel will illuminate if:

• Emergency Battery voltage drops below 24 VDC
• Emergency Bus not powered
• Emergency Battery is not being charged

Question 12

INVERTER light will illuminate if

Answer 12

the selected 115 VAC inverter fails, or the switch is set to OFF

the Inverters are protected against:
over/under voltage
over/under frequency
over temperature

Question 13

2 x 115/200 VAC ‘WILD’ GENERATORS

Answer 13

driven from the Propeller Gear Boxes
for Ice protection ONLY

Question 14

GENERATOR CONTROL UNITS:

Answer 14

provide both control and protection for the
starter/generator, in both start and generate modes

Start Mode:
energises the start relay
disables GCU control functions
starter cut out at 55% Ng

at 55% Ng, the starter “CUTS OUT” and the
STARTER /GENERATOR becomes a GENERATOR

Question 15

GCU will de energize a generator relay

Answer 15

• over voltage (>40VDC)
• short circuit
• reverse currents
• Fire Handle pulled

Question 16

BUS TIE RELAY

Answer 16

IN ORDER TO ENERGIZE THE BUS TIE RELAY:

• THE LEFT BATTERY SWITCH MUST AT SOME TIME HAVE BEEN TURNED ON

when the Bus Tie Relay is energized, it connects the L GEN BUS to the R GEN BUS (it ties the 2 sides together)

This allows:
- External Power to energize ALL buses
when it is switched on

• to enable ONE Generator to energize
  ALL buses (exception: Utility Bus)
• to connect the 2 Batteries
• the Bus Tie Relay is protected against short circuiting, by a Bus Tie Overcurrent Relay
• If the current from 1 Gen Bus to another exceeds 800A, the Bus Tie Relay is de-energized
• it can be reset via cb K1
• During a start, the amperage across the Bus TieRelay can be as much as 1600A
  so the Bus Tie Overcurrent Relay is inhibited during an engine start

Question 17

BUSES THAT ARE ENERGIZED WITH BATTERIES ONLY

Answer 17

• L/R HOT BATTERY BUSES
• L/R BATTERY BUSES
• L/R GENERATOR BUSES
• L/R ESSENTIAL BUSES
• EMERGENCY BUS

(Essential Avionics Switch ‘ON’ also)
- ESSENTIAL AVIONICS BUS
- EMERGENCY AVIONICS BUS

Question 18

When starting the engine on battery power

Answer 18

L/R ESS busses are taken offline

Question 19

When starting the engine with ground power

Answer 19

L/R ESS bus are taken offline
L/R ESS main smart bus are online

Question 20

After start Electrical sequence

Answer 20

• Both generators are running
• Left engine powers L and Right powers R
• Generators are the source of power and keep the battery charged
• ## The Bus tie is NOT connected

Question 21

When will the EMER PWR overhead panel light illuminate?

Answer 21

Emergency Bus is not powered, or
Emergency Battery Voltage drops below
24 VDC

Question 22

At what temperature will the BAT HOT light
illuminate, and will the Battery Relay be
deenergized (open)?

Answer 22

71ºc, yes

Question 23

How are the Batteries cooled?

Answer 23

fan on the ground, ram air when airborne

Question 24

What is indicated by illumination of L/R MAIN BUS light?

Answer 24

associated bus is not powered

Question 25

Both Batteries ON, External Power ON, why are the L/R BAT lights illuminated?

Answer 25

external power has priority over the
batteries, and the L/R battery relays have
been deenergized (open)

Question 26

To read External Power, must the EXT PWR switchbe ON?

Answer 26

no

Question 27

Is the Bus Tie relay protected against overcurrent?

Answer 27

yes, by the 800A overcurrent relay
(reset by K1)