ATR SYS ELEC

Question 1

Where is the DC generator mounted on the engine?

Answer 1

It is mounted on the accessory gear box (AGB) and driven by the HP compressor spool.

Question 2

When is the starter generator used?

Answer 2

Starting before propellor rotation, starting with propellor rotation, starting inflight, and providing normal 28VDC.

Question 3

What is the voltage characteristics of the DC generator?

Answer 3

61.5% NH is generator mode. It supplies 28V DC (27 - 31 Volts, nominal setting is 30V). Rated output power 12 kW (400A).

Question 4

How many emergency sources are there?

Answer 4

Three sources may be used for emergency battery supply, main and emergency battery, and the TRU.

Question 5

What is the voltage and capacities of the batteries?

Answer 5

For the main battery (engine starts) the voltage is 24 Volts, NiCa and has a capacity of 43 Ah.
For the emergency battery (power transients when engine start) the voltage is 24 Volts, NiCa and has a capacity of 15 Ah.

Some contacts and the batteries are monitored by the MFC’s. The MFC controls the charging of the batteries in a way to prevent thermal runaway.

Question 6

Describe the start and generation logic?

Answer 6

A, The START CONTACTOR connects to BATTERY START CONTACTOR (BSC) or EXTERNAL POWER CONTACTOR.

Once NH reaches a point of self sustaining at 45% the starter will disengage and the light will extinguish. Once at 61.5 NH and providing the EXT PWR PB is deselected then each DC BUS is automatically fed through a GENERATOR CONTACTOR (GC).

This starting process is controlled through the GENERATOR CONTROL UNIT (GCU).

A BUS TIE CONTACTOR is provided to connect the busses in the event of a GEN failure or if powered by EXT PWR.

A BUS POWER CONTROL UNIT (BPCU) is the controlling unit for the BTC, BSC, EXT PWR, DC SVCE BUS contactors, and load shedding.

Question 7

How many buses are there?

Answer 7

11

Question 8

Describe the buses and their uses?

Answer 8

DC BUS 1 SUPPLIES the HOT EMER BAT BUS + DC EMER BUS + DC SBY BUS + UTLY BUS 1 + INV 1 + DC SVCE BUS

DC BUS 2 SUPPLIES the HOT MAIN BAT BUS + DC ESS BUS + UTILITY BUS 2 + INV 2

UTLTY BUS 1 + 2 supply non essential loads.

DC SVCE BUS supplies power to servicing operations. Is controlled by the CC at the rear of the A/C, when supplied by DC BUS 1 the BAT SW must be selected ON. With EXT PWR only the CC has control, this can be achieved through the PB.

GND HDLG BUS supplies power on GND for servicing operations, even with the BAT switch OFF.

Question 9

What are the conditions to supply the GND handling bus?

Answer 9

It is supplied only on the GND in three different ways;

1, BAT OFF or ON with the EXT PWR not available it is serviced by the HOT MAIN BUS for ground servicing when, the refueling panel is open, the cargo door control panel is open, and the passenger door is open. It is disconnected when airborne.

2, BAT OFF or ON EXT PWR avaliable but not ON, it is supplied directly from the external power.

3, BAT ON with EXT PWR ON or with one GEN on line, it is supplied by the DC SVCE BUS.

Question 10

What happens to the busses with one GEN failure?

Answer 10

The BTC is closed and the remaining GEN supplies all the busses.

Question 11

What does a battery charge PB fault light indicate?

Answer 11

BAT CHG PB, ON controls the operation of the associated battery charge contactor, it will open if there is thermal runaway, undervoltage, with the start sequence both the BCC are open until the rotary selector leaves start crank. Discharging.
FAULT illuminates and the CCAS is activated if an overheat is detected by the MFC, or a failure of the charge contactor.

Question 12

Some gauges are lost with certain buss failures, outline the significant ones?

Answer 12

Emergency bus = TQ, essential bus = next three gauges below, standby bus = hydraulic gauges.

Question 13

What does a red light note the due panel indicate?

Answer 13

Fuel panel red light will illuminate when draining from the battery.

Question 14

What happens with a dual GEN failure with first and second over rides?

Answer 14

After a dual DC GEN loss, the UNDV is triggered when the DC SBY BUS <19.5 Volts. Then by pushing the OVRD the DC and AC SBY BUS are transfered from the HOT MAIN BUS right side, to the HOT EMER BAT BUS left side. First is 20 min, Second is 10 min.

Question 15

What is the device used to provide DC power under emergency supply?

Answer 15

TRU, which is fed of ACW 2, this is why the green hydraulic pump needs to be switched off with a double generator failure.

AC INV are 26 and 115, probably a good idea to use it!!!!

Question 16

What type of inverters are there and where are they located?

Answer 16

The source of constant frequency (400 Hz) AC power consists of two static inverters (INV). The inverters are rack mounted and cooled by forced air with provisions for natural convection cooling. They are 115 V and 26 V, at 400 Hz. The minimum supply voltage for inverter 1 is 18 V, this is why the UNDV light illuminates at 19.5V adding 1.5V protection above the minimum.

Question 17

What happens in the event of a inverter failure?

Answer 17

In event of inverter failure or input power loss the associated AC BUS is isolated from affected inverter and, provided the BTC pb is not in ISOL position. The AC BUS 1 and 2 are automatically tied together.

In event of INV 1 failure or input power loss, AC STBY BUS is automatically supplied from INV 2.

Question 18

What does the BTC PB control?

Answer 18

BTC PB controls the BTC, under normal conditions it is controlled by the BPCU. When the ISOL white light is illuminated then the obvious !!!

BTC PB also controls the AC BTR which when closed connects both AC BUSES. Under normal conditions the BPCU controls the BTC and a separate logic controls the AC BTR it is normally open. Although if there is a INV failure the AC BTR will automatically close the INV FAULT light will illuminate but the AC BUS OFF light remains extinguished, respectively.

Question 19

Where are the ACW generators mounted and how are they controlled?

Answer 19

They are mounted on the propellor reduction gear boxes. Each is controlled by its own generator control unit (GCU).

Question 20

What is purpose each GCU?

Answer 20

A, They each provide protection against;
over voltage,
power and fault current limiting,
bus tie lock out,
under voltage,
differential protection,
under frequency,
open phase,
over frequency,
voltage regulation.

Question 21

What does the BPCU do?

Answer 21

The BPCU once again provides the function of control and protection of the EXT PWR, BUS TIES and SVCE BUS.

Question 22

What is the purpose of the TRU?

Answer 22

The TRU allows the ACW 2 GEN and BUS to partially power the DC system if needed.

Question 23

When is ACW power available?

Answer 23

When the propeller brake is off and unfeathered and NP is a minimum of 66%. Nominal operating is 70.8%.

Question 24

How many buses are there, and what are they?

Answer 24

3

ACW BUS 1 and 2, are normally supplied by their respective generators.
Note; The BTC will automatically supply both busses through BTC 1 and 2 in the event of a ACW GEN/GCU failure.
Also if EXT PWR is connected and checked as being acceptable by the BPCU then it will automatically have priority over the GEN’s.

ACW SVCE BUS can be supplied by EXT PWR or ACW BUS 1. It is supplied by ACW GEN 1 through the GXC. If EXT PWR is “available” then it is supplied through the EXC. It is always shed with one GEN of line so therefore it is shed with one online!!!!!

Question 25

What does a ACW GEN FAULT LIGHT indicate?

Answer 25

ACW GEN FAULT illuminates with CCAS if the GCU has tripped. An auto reset will occur if caused by NP overspeed for less than 3 seconds. Either way the BTC will close and the remaining GEN will supply both.

Question 26

What does a ACW BUSS OFF light indicate?

Answer 26

ACW BUSS OFF illuminates with CCAS when the associated bus is not supplies.BTC PB in the normal position BTC 1 and 2 are controlled by the BPCU. With external power connected or single GEN failure BTC 1 and 2 are automatically closed.

Question 27

What does the EXT PWR take preference over?

Answer 27

In the case of EXT PWR being available and considered as being acceptable by the BPCU, providing the PB is selected ON then it will take priority over all of the GEN’s.