8. Electrical Power
S64F Model Helicopter
Rev. Sept. 18, 2007
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9. 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
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10. Key Components Generators Generator switches Autotransformers
Current transformers
Current limiters
Under Frequency switch (WOW switch)
Supervisory and voltage regulator (Sup Panel)
Autotransformers
Ground inverter
Rev. Sept. 18, 2007
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11. Parts Locations
Rev. Sept. 18, 2007
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12. Parts Location
Rev. Sept. 18, 2007
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13. 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
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14. 20 KVA Generators #2 #1
Rev. Sept. 18, 2007
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15. 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
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16. 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
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17. Supervisory and Voltage Regulator Panel (SUP Panel)
Rev. Sept. 18, 2007
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18. 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
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19. 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
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20. AC Distribution Normal Power Sensing and Control Voltage
AC External Power
#1 Generator
#1 External Power Primary Bus Relay
Supervisory Panel and Regulator
#1 Monitored Bus Relay
Current Transformers
External Power Monitored Bus Relay
#1 Primary Bus Relay
#1 Primary Bus
#1 Monitored Bus
To #2 Primary Bus
Relay For
TRANSFER
Normal Power
#1 Inverter Transfer Relay
Sensing and Control Voltage
External Power
Transfer Power
#1 Inverter Bus
Rev. Sept. 18, 2007
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21. 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
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22. 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
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23. 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
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24. AC Transfer #2 Generator Failure #1 Generator #2 Generator
#1 External Power Primary Bus Relay
#2 External Power Primary Bus Relay
#1 Primary Bus Relay
#2 Primary Bus Relay AC
Current
Limiters
#1 Monitor Bus Relay
#2Monitor Bus Relay
#1 Monitored Bus
#2 Monitored Bus
#2 Primary Bus
#1 Primary Bus
Rev. Sept. 18, 2007
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25. 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
Rev. Sept. 18, 2007
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26. 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
Inverterb AC Bus
INV
Control
Relay
INV
Control
Relay
#1 Primary AC Bus
INV
Switch On
Master PNL
#2 Primary AC Bus
Rev. Sept. 18, 2007
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27. 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.
Rev. Sept. 18, 2007
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28. Dual Generator Failure #1 Inverter Transfer Relay
Inverter Control
Dual Generator Failure
#1 Primary AC Bus
#2 Primary AC Bus
#1 Inverter Transfer Relay
#2 Inverter Transfer
Relay
#2 Inverter Bus
#1 Inverter Bus
Inverter #2
Autotransformer
26VAC #1
Autotransformer
26VAC
Primary DC Bus
Rev. Sept. 18, 2007
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29. 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
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30. 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
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31. DC Distribution #1 Primary AC Bus #2 Primary AC Bus #1 Transformer/ #2
Rectifier #2
Transformer/
Rectifier
#1 Reverse Current
Cut-Out
Relay
#2 Reverse Current
Cut-Out
Relay
Primary DC Bus
Aircraft
Battery
Battery
Relay
Monitored
DC Bus
Relay
Monitored DC Bus
Rev. Sept. 18, 2007
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32. 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
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33. Located on the left side of the Aircraft
24 volt Battery
Located on the left side of the Aircraft
Rev. Sept. 18, 2007
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34. 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.
Rev. Sept. 18, 2007
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