Ac Power Distribution System 6.10

AC POWER DISTRIBUTION SYSTEM 6.10

PRIMARY AC POWER • Primary AC Power: Engine driven generators – Depend on the type of aircraft arrangement and distribution APU generator External Power Unit Inverters- 115-200 V AC, 3-phase, 400 Hz Static inverter Rotary Inverter

TYPICAL ARRANGEMENT OF AC POWER DISTRIBUTION SYSTEM

Main AC and DC Distribution System •

The primary a.c. power source is 115 – 200 V, 3-phase 400hz is supplied i. Aircraft generator ii. Axiliary power unit APU iii. External power unit (EPU).

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The 4 power sources connected to the busbars

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i. Six 3-phase cct breakers, ii. 2 transfer relays which are energized and de-energized according to the switching selection made in the Generator Control Panel. The ammeters indicate the load current of both main generators.

• EXTERNAL POWER • When external power is connected to the aircraft and switched on, • The External Power Contactor closes • Both Bus Tie Breakers (BTB1 & BTB2 are energizes both the bus tie breakers and whole bussbar systems are connected • The transfer relays are energized to the “normal” position by the BTB’s.

• External Power Connected and “ON”

After aircraft starting • #1 Eng start Generator # 1 energises BTB 1 open to allow GCB #1 to close All system # 1 busbars are supplied from the generator # 1 • # 2 Bussbars are still supplied from external power. • # 2 engine started and its Generator switched on BTB 2 trips open, GCB 2 closes to connect the generator to the # 2 system bussbars, • This external power contactor also trips open.

• Consumer services connected to the ground service bus bar is operated from the external power, • this is achieved by putting ground power switch on the control panel in the “off” position, • This will switch on a separate ground service switch. • The switch energizes a ground service relay contact to change connection from generator bus # 1 to the external power busbar.

USING THE APU POWER •

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The APU generator is connected to all buss bar systems via its own threephase breaker, this, in turn, being energized by two generator switches (see control panel). Placing the number 1 switch to “on” closes the APU generator breaker and BTB 1, the number 2 switch placed to “on” the BTB 2 is closed. As in the case of connecting an external power supply, the transfer relays are energized to the “normal” position by the BTB’s. In the “normal” in-flight configuration all power distribution system is supply by each generator to bussbar via own breaker.

One Generator Failure • One or another generator, #1 fail • GCB 1 will open isolating the corresponding busbar. • A set of auxiliary contacts within the breaker permits the DC signal to flow from the Control Unit of Generator 2 via the bus transfer switch, to the “alternate” coil of transfer relay 1. • The contacts will change over so that power can be supplied to transfer bus 1 from generator 2 • which is still supplying its busbars in normal way. • A similar transfer of power takes place in the event of loss of power from generator 2. • This is call BUSS TRANSFER