Electrical Power

Electrical Power S64F Model Helicopter 11-

Basic Electrical Familiarization • AC System • Part Location • AC / DC power distribution • AC power normal operation • Transfer AC power • DC power distribution 11-

Key Components • Autotransformers • Ground inverter • Generators • Generator switches • Current transformers • Current limiters • Under Frequency switch (WOW switch) • Supervisory and voltage regulator (Sup Panel) 11-

Parts Locations 11-

Parts Location 11-

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. 11-

20 KVA Generators #2 #1 11-

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. 11-

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. 11-

Supervisory and Voltage Regulator Panel (SUP Panel) 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. 11-

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. 11-

AC Distribution AC External Power #1 Generator #1 External Power PrimaryBus Relay SupervisoryPanel and Regulator #1 MonitoredBus Relay Current Transformers External PowerMonitored Bus Relay #1 Primary Bus Relay #1 Primary Bus #1 Monitored Bus To #2 Primary Bus Relay For TRANSFER #1 Inverter Transfer Relay Normal Power Sensing and Control Voltage External Power Transfer Power #1 Inverter Bus 11-

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. 11-

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. 11-

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. 11-

AC Transfer #2 Generator Failure #1 Generator #2 Generator #1 ExternalPower PrimaryBus Relay #2 ExternalPower PrimaryBus Relay #1 Primary BusRelay #2 Primary BusRelay AC Current Limiters #1 Monitor BusRelay #2Monitor BusRelay #1 Monitored Bus #2 Monitored Bus #2 Primary Bus #1 Primary Bus 11-

Inverter AC System • Inverter Components • Inverter power relay • Inverter transfer relay • Inverter control relays • Switch on Master Panel • When the generator power is on-line, the inverter bus loads are transferred to the primary busses. Ground Inverter 11-

Ground Inverter If both generators fail a 250VA ground inverter supplies emergency AC power to the inverter bus loads. INV Trans Relay INV INV Trans Relay D C B U S INV Power Relay INV Control Relay Inverterb AC Bus INV Control Relay #1 Primary AC Bus INV Switch On Master PNL #2 Primary AC Bus 11-

Ground Inverter • 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. 11-

Inverter Control Dual Generator Failure #1 Primary AC Bus #2 Primary AC Bus #1 InverterTransfer Relay #2 InverterTransfer Relay #2 Inverter Bus #1 Inverter Bus Inverter #2 Autotransformer 26VAC #1 Autotransformer 26VAC Primary DC Bus 11-

External Power • An AC external power receptacle and associated circuitry permit use of an auxiliary power unit for ground power application. 11-

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. 11-

DC Distribution #1 Primary AC Bus #2 Primary AC Bus #1 Transformer/ Rectifier #2 Transformer/ Rectifier #1 ReverseCurrent Cut-Out Relay #2 ReverseCurrent Cut-Out Relay Primary DC Bus Aircraft Battery Battery Relay Monitored DC Bus Relay Monitored DC Bus 11-

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. 11-

24 volt Battery Located on the left side of the Aircraft 11-

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. 11-

Electrical Power