Rev. Sept. 18, 2007 11-1

Electrical Power

S64F Model Helicopter

Rev. Sept. 18, 2007 11-2

Basic Electrical Familiarization AC System

Part Location AC / DC power distribution AC power normal operation Transfer AC power DC power distribution

Rev. Sept. 18, 2007 11-3

GeneratorsGenerator switchesCurrent transformersCurrent limitersUnder Frequency switch

(WOW switch)Supervisory and voltage

regulator (Sup Panel)

AutotransformersGround inverter

Key Components

Rev. Sept. 18, 2007 11-4

Parts Locations

Rev. Sept. 18, 2007 11-5

Parts Location

Rev. Sept. 18, 2007 11-6

AC System

The AC system is 115 volts, three phase, 400 cycle, neutral ground, supplied by two 20KVA brushless generators designated as No. 1 and No. 2.

Both generators are driven by the accessory section of the main transmission at a rotation speed of 8000 rpm which can be driven by the engines or by the auxiliary power plant (APU) during ground operations.

Rev. Sept. 18, 2007 11-7

20 KVA Generators

#2

#1

Rev. Sept. 18, 2007 11-8

Definitions Normal operation: associated primary loads and

monitored bus loads are assumed by each generator. Primary loads are those that are essential for normal

flight and for mission accomplishment. Monitored Bus loads are those that are not essential for

normal flight or for mission accomplishment.

Rev. Sept. 18, 2007 11-9

AC Power Normal Operation

Three Phase, unregulated AC voltage from the permanent magnet, brushless generator is fed to the No. 1 supervisory and voltage regulator panel.

The Supervisory panel monitors the output from the generators and protects against overvoltage, undervoltage, underfrequency, and feeder fault conditions which might arise.

The unregulated AC voltage is rectified and

filtered, supplying control and operating voltages within the panel and DC voltage for external use.

Rev. Sept. 18, 2007 11-10

Supervisory and Voltage Regulator Panel (SUP Panel)

Rev. Sept. 18, 2007 11-11

AC Power Normal Operation When the No. 1 generator control switch is placed ON, the

panel supplies generator excitation current for main generator AC voltage build-up and DC voltage to energize the No. 1 primary and monitored AC bus relays.

With excitation current available, rated generator AC voltage is available at the contacts on the No. 1 primary and monitored bus relays.

AC is also provided to the Autotransformer to provide a 26vac output for instrumentation.

Rev. Sept. 18, 2007 11-12

AC Power Normal Operation With both relays energized, normal three phase AC power is

delivered directly to the No. 1 primary AC bus and through de-energized external power relay to the monitored AC bus for distribution.

The No. 1 inverter bus obtains AC power directly from the respective primary AC buses through the de-energized No. 1 inverter transfer relay.

Rev. Sept. 18, 2007 11-13

AC Distribution#1 Generator

SupervisoryPanel and Regulator

#1 External Power Primary

Bus Relay

#1 MonitoredBus Relay

#1 Monitored Bus#1 Primary Bus

#1 Primary Bus Relay

External PowerMonitored Bus Relay

#1 Inverter Bus

#1 Inverter Transfer Relay

Current Transformers

AC External Power

To #2 Primary BusRelay For

TRANSFERNormal PowerSensing and Control VoltageExternal PowerTransfer Power

Rev. Sept. 18, 2007 11-14

Transfer AC Power The following description assumes that the No. 2 generator

has failed and only the No. 1 generator is supplying AC power.

With the failure of the No. 1 generator, DC control voltage from the No. 2 supervisory and

regulator panel is removed from the No. 2 primary AC bus solenoid and No. 2 monitored AC bus solenoid, de-energizing the relays.

Rev. Sept. 18, 2007 11-15

Transfer AC Power The de-energized relays remove both No. 2 primary and No. 2

monitored AC bus loads from the No. 2 generator. With the No. 2 primary AC bus relay de-energized, DC voltage

from the No. 2 sup panel is fed to the caution-advisory panel No. 1 GENERATOR caution capsule.

DC control voltage is supplied from the No. 1 sup panel to the No. 1 monitored AC bus relay. This opens the monitor bus relay removing the #1 monitor bus and transferring power through the current limiters, through the de-energized #2 external power relay, to the #2 primary bus relay.

Rev. Sept. 18, 2007 11-16

Transfer AC Power The No. 1 generator then supplies both primary AC buses,

and both monitored AC buses are dropped. When either primary AC bus relay is de-energized, such as

the No. 2 relay in this example, the monitored DC bus control relay is de-energized .

This in turn de-energized the DC monitored bus relays, and the DC monitored bus is dropped from the DC circuit.

Rev. Sept. 18, 2007 11-17

AC Transfer

#1 Primary BusRelay

#2 Generator

#1 Monitor BusRelay #2Monitor Bus

Relay

#1 ExternalPower Primary

Bus Relay

#1 Generator

#2 ExternalPower Primary

Bus Relay

#2 Primary BusRelay

#1 Primary Bus

#1 Monitored Bus

#2 Primary Bus

#2 Monitored Bus

#2 Generator Failure

ACCurrentLimiters

Rev. Sept. 18, 2007 11-18

Inverter AC System

When the generator power is on-line, the inverter bus loads are transferred to the primary busses.

Ground Inverter

Inverter ComponentsInverter power relayInverter transfer relayInverter control relays Switch on Master Panel

Rev. Sept. 18, 2007 11-19

Ground InverterIf both generators fail a 250VA ground inverter supplies emergency AC power to the inverter bus loads.

#1 Primary AC Bus

#2 Primary AC Bus

INVControlRelay

INVTransRelayINV

INVControlRelay

INVTransRelayINV

PowerRelay

DC

BUS

INV Switch On

Master PNL

Inverterb AC Bus

Rev. Sept. 18, 2007 11-20

The inverter control relays, sense the absence of AC power on the AC primary buses and provide a path to energize the No. 1 and No. 2 inverter transfer relays.

The inverter transfer relays, in turn connect the No. 1 and No. 2 inverter buses to the inverter output and energize the power relay, which supplies 28VDC to the inverter which delivers rated AC voltage to the inverter bus through the closed contacts of the inverter transfer relay.

Should the generator begin supplying AC power to the primary bus, the inverter control relays would energize, de-energizing the inverter transfer relays and inverter power relay, shutting down the inverter.

Ground Inverter

Rev. Sept. 18, 2007 11-21

Inverter Control#1 Primary AC Bus #2 Primary AC Bus

#2 Inverter Bus#1 Inverter Bus

Primary DC Bus

Inverter

#1 InverterTransfer

Relay

#2 InverterTransfer

Relay

Dual Generator Failure

#1Autotransformer

26VAC

#2Autotransformer

26VAC

Rev. Sept. 18, 2007 11-22

External Power

An AC external power receptacle and associated circuitry permit use of an auxiliary power unit for ground power application.

Rev. Sept. 18, 2007 11-23

DC Power Distribution Primary DC loads are loads that are considered to be loads

essential for maintaining normal flight and for mission accomplishment. Monitored DC loads are non-essential. But for our purposes all DC loads are considered essential.

DC power is supplied by two 28 volt, 200 amp. Converts (transformer-rectifiers) designated as No. 1 and No. 2. System operation is automatic; control switches on master switch panel and monitor warning lights on the caution-advisory panel are provided.

Rev. Sept. 18, 2007 11-24

DC Distribution#1 Primary AC Bus

#1 Transformer/

Rectifier#1 ReverseCurrent Cut-Out

Relay

#2 Primary AC Bus

#2 Transformer/

Rectifier#2 ReverseCurrent Cut-Out

Relay

Primary DC Bus

Monitored DC BusRelay

Monitored DC Bus

BatteryRelay

AircraftBattery

Rev. Sept. 18, 2007 11-25

DC Power Distribution Normally, primary DC loads are assumed by both T/R’s. If one T/R fails , the associated reverse current cutout relay

will remove the failed T/R from the primary DC loads. The remaining operating T/R will assume the primary DC loads, and the monitored DC loads will be dropped.

A sealed lead-acid battery provides 24 VDC power when no other source is available.

Rev. Sept. 18, 2007 11-26

24 volt Battery

Located on the left side of the Aircraft

Rev. Sept. 18, 2007 11-27

DC Power Distribution A DC external power receptacle and associated circuitry

permit use of an auxiliary power unit for ground power application. Battery and external power switches are located on the Master switch panel.