Electrical System

Gulfstream GVII

Eddie sez:



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Photo: GVII electrical system synoptics, Eddie's drawing
Click photo for a larger image

There is a lot of stuff here and more acronyms than any pilot should have to memorize. So I think you can get away with just reading the "How it Works . . ." section and then skip down to "Limitations and Abnormal Procedures . . .." If you want to get into the minutiae, the bulk of this page is dedicated to "The Components in Greater Detail . . ."

For a quick refresher or a good intro, be sure to see Ivan Luciani's notes: G500 Electrical System Notes.

There are also a few flash cards here: Quizlet.

Everything here is from the references shown below, with a few comments in an alternate color.

[PAS, p. 4-1] The electrical system is highly automated and requires very little crew input under normal conditions. AC power is used to create DC power which powers the majority of the aircraft’s subsystems. AC Power is normally supplied by an Integrated Drive Generator (IDG) located on each engine; however, AC Power can also be supplied by the APU Generator, Ram Air Turbine (RAT) Generator, or an External AC Power Cart for ground operations. DC Power is normally supplied by five (5) Transformer Rectifier Units (TRUs) which convert AC power to DC power. In addition to TRUs, DC Power is also available from aircraft batteries [Main Ship Batteries (2), Electrical Backup Hydraulic Actuator (EBHA) Battery, Uninterruptable Power Supply (UPS) Battery, and (2) Emergency Batteries (E-Batts)]. During ground operations, DC Power can be provided by an External DC Power Cart. AC and DC Electrical power distribution is controlled by two (2) Bus Power Control Units (BPCUs) and the Secondary Power Distribution System (SPDS). The SPDS distributes power to multiple aircraft systems. Protection is provided by traditional electro-mechanical circuit breakers and Solid State Power Controllers (SSPCs). SSPCs are part of the SPDS. SSPCs perform control (On and Off) and protection functions.

How it Works . . .

The Components in Greater Detail . . .

Other Notes

Limitations and Abnormal Procedures . . .

Last revision:

2020-03-07


How it Works . . .


Electrical Power Generation System (EPGS)



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Photo: GVII electrical power generation, Eddie's drawing
Click photo for a larger image

AC Power

[PAS, p. 4-2.] AC power is produced by:

  • Left and right engine Integrated Drive Generators (IDGs). An IDG normally powers only its respective Main AC Bus; however, any single generator (including APU), or the AC Power Cart, can provide power to both Main AC Buses via a Tie Bus.
  • An APU Generator is the primary source on the ground when engines are not operating.
  • An external AC power cart can provide an External AC Source which should provide 30 kVA, 115 VAC, 400 Hz, 3 Phase to powers all buses.

[PAS, p. 4-18.] AC power can be transferred between an IDG and other sources without interruption through the No Break Power Transfer (NBPT) Function.

[PAS, p. 4-7.] Alternate AC power is produced by:

[PAS, p. 4-3.] AC Power is first sent to two Power Distribution Boxes (PDBs), then is routed to:

[PAS, p. 4-4.] 60 Hz Converters convert 115 VAC, 3 Phase power to 115 VAC, 60 Hz, Single Phase (common electrical household power). So what's a "phase" anyway? See: Three Phase Electrical Power.

DC Power

[PAS, p. 4-5.] DC Power is produced by five Transformer Rectifier Units (TRUs) that convert 115 VAC power to 28 VDC power and are dedicated to powering their respective DC Buses. The Secondary Power Distribution System (SPDS) then receives DC power from the DC buses, except from the AUX DC bus which routes its power to the right PDB bypassing the SPDS.

  • The left main AC bus powers the left essential TRU, the left main TRU, and the AUX TRU.
  • The right main AC bus powers the right essential TRU, the right main TRU, and the AUX TRU if the left main AC bus is not powered.

These buses can also be powered by an External DC Source.

[PAS, p. 4-6.] A Ground Service Bus (GSB) uses various sources of DC power (usally the Right Main DC) to provide power for normal ground servicing.

[PAS, p. 4-9.] If a TRU failure occurs the AUX TRU sheds power to the AUX DC bus and you lose power to non-essential cabin equipment. The AUX TRU then powers one essential or main DC bus with the following priority: essential before main and left before right. This logic is accomplished by the BPCUs, repeating if additional TRUs fail.

[PAS, pp. 4-10 through .] DC Power Storage and Flow

Primary Power Distribution System (PPDS)

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Photo: AC and DC Bus Overview, PAS, p. 4-23
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[PAS, p. 4-14]

Secondary Power Distribution System (SPDS)

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Photo: G500 Electrical SPDS, PAS, p. 4-19
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[PAS, p. 4-19]

  • Distributes 115 VAC and 28 VDC to multiple aircraft systems
  • Controls “Hosted” portion of automated aircraft functions
  • Components include:
    • Electronic System Controllers (ESCs) (2). Perform system control functions (On and Off), controls some of auto functions of aircraft systems (like turning on IRUs when APU Gen comes online), send status messages to other aircraft systems via DCN, manage load shedding under abnormal conditions.
    • Modular Power Tiles (MBTs) (14): 400 Hz AC (3), 60 Hz AC (1), DC (10).
    • Solid State Power Controllers (SSPCs) located within MPTs acts as virtual circuit breakers. Will “Latch Open” for an electrical fault, eliminates weight of traditional circuit breakers, turns systems on and off when commanded by ESC.
  • Crew Interacts with SPDS via TSC #2, #3, #4, #5. Only 2 of 4 TSCs can access SPDS Menu at any given time. TSC #5 must be used to access SPDS when only ground service bus available.
  • SPDS Maintenance Test Switch located on System Monitor Test Panel is used to program SPDS into Standby or Maintenance Mode, grouping or collaring SSPCs, data loading. (Procedures found in Aircraft Maintenance Manual.)

The Components in Greater Detail . . .


60 Hz Converters

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Photo: G500 Electrical Normal Flow 60 Hz, PAS, p. 4-4
Click photo for a larger image

[PAS, p. 4-4] Two 60 Hz converters

  • Converts 115 VAC, 400 Hz, 3 Phase to 115 VAC, 60 Hz, Single Phase (Common Household Power). There are two, one in the Left Main AC and the other in the Right Main AC.
  • Located in tail compartment
  • Only one converter provides power at any given time, the other operates in standby and takes over automatically if active converter fails. The active converter switches on power up to exercise each.
  • Safety aspects: Outlet power inhibited unless a load is plugged in. Converter load sheds if cabin altitude ≥ 14,500’ to inhibit sparks with pax O2 masks deployed.
  • 60 Hz master switch is located on overhead panel, wired in series with cabin/galley master switch. When both switches are on/dark the 60 Hz converter receives power and TSC soft switches now available to allow control of each individual converter and cabin equipment.
  • Capabilities: Converters are limited to 30 Amps each. High draw items may limit ability to use every outlet at once. Cabin outlets rated 3 Amps. Galley, lavatory, baggage compartment outlets rated 15 Amps.

60Hz Ground Power Receptacle

[PAS, p. 4-6] Located in tail compartment. For cabin equipment only.

AC/DC Reset / Protection Latch

[PAS, p. 4-17] The BPCU protects and isolates the electrical system when a fault is detected by opening a contactor to lock out the affected bus, even if the fault was for a split second. Lockouts can be reset via the AC/DC reset switch if the fault no longer present. The BPCU will allow power to return to the bus, but it won’t allow good power to chase bad power or good power to a bad bus.

[PAS, pp. 4-34 to 35]

  • L/R AC Reset
  • Fault Sensed on AC Bus — AC legend illuminating indicates the BPCU’s having sensed a fault on an AC bus. When the BPCU’s sense a fault, they will automatically isolate the AC bus from the rest of the system and lock that bus out. Even when the fault is no longer sensed, the lockout will still keep the bus isolated. An illuminated legend could also indicate a logic fault within the BPCU, or a relay or component failure. One or both of the CAS messages shown at right will appear. If the BPCU’s no longer sense the fault and the RESET switchlight is pressed, the previously tripped relays will be allowed to close and the AC legend and CAS message(s) will extinguish.

  • L/R DC Reset
  • Fault Sensed on DC Bus — DC legend illuminating indicates the BPCU’s having sensed a fault on the DC bus. When the BPCUs sense a fault, they will automatically isolate the DC bus from the rest of the system and lock that bus out. Even when the fault is no longer sensed, the lockout will still keep the bus isolated. An illuminated legend could also indicate a logic fault within the BPCU, or a relay or component failure. One or both of the CAS messages shown at right will appear. If the BPCU’s no longer sense the fault and the RESET switchlight is pressed, the previously tripped relays will be allowed to close and the DC legend and CAS message(s) will extinguish.

  • L/R AC Reset
    L/R DC Reset
  • AC and DC legends illuminating indicates the BPCUs having sensed a fault on both AC & DC buses. When the BPCUs sense the fault, they will automatically isolate the faulted buses from the rest of the system and lock the buses out. Even when the fault is no longer sensed, the lockout will still keep the buses isolated. An illuminated legend could also indicate a logic fault within the BPCU, or a relay or component failure. Two or more of the CAS messages shown at right will appear. If the BPCUs no longer sense the fault and the RESET switchlight is pressed, the previously tripped relays will be allowed to close and the AC and DC legends and CAS messages will extinguish.

APU Generator

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Photo: G500 Electrical APU Connected, PAS, p. 4-29
Click photo for a larger image

[PAS, p. 4-2] AC power is produced by:

  • The APU generator is the primary source on the ground when engines are not operating. The APU has the same oil cooled generator as engines with same specs and powers all buses.

[PAS, p. 4-7] APU generator in flight:

  • In the event of an IDG or engine failure.
  • Capable of 100% load up to FL350.
  • Capable of 78.5% load above FL350 to FL450.

Bus Power Control Units (BPCUs)

[PAS, p. 4-17] BPCUs:

  • Identical and interchangeable microprocessors.
  • Left BPCU (located in LEER PDB).
  • Right BPCU (located in REER PDB).
  • Make all logical decisions for electrical distribution and protection.
  • Output critical findings to the CAS.
  • Close and open contactors and/or relays to efficiently supply power to buses, protect and isolate the electrical system when a fault is detected.
  • Provides protection, power and logic to AC/DC Reset / Protection Latch.
  • Monitors External AC and DC Power. Minimum main batteries ON to monitor. If quality power illuminates “AVAIL” light on the overhead EPCP. If not quality power, trips external power contactor to protect system. Gives External AC priority to connect over external DC. If External DC is powering aircraft when AC connected, cycle external power switch OFF then ON.
  • Controls the No Break Power Transfer (NBPT) function

Cockpit Controls

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Photo: G500 Electrical Cockpit Controls, PAS, p. 4-24
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Photo: G500 Electrical Power Control Panel, PAS, p. 4-25
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[PAS, pp. 4-26 to 4-37]

  • Left Generator Switchlight
    • IN (Normal Position). If the left engine is operating and the switchlight is pressed IN (normal position), the Left IDG will power the Left Main AC Bus, which in turn powers the Emergency AC Bus, and the L GEN “ON” legend will be illuminated.
    • IN (IDG Unpowered). When the switchlight is pressed IN and IDG is not powered by the engine, the OFF legend will illuminate and the ON legend will extinguish.
    • OUT. When the switchlight is pushed OUT, Left IDG power is isolated from the Left Main AC Bus. The OFF legend will also be illuminated in this configuration.
  • Right Generator Switchlight
    • IN (Normal Position). If the right engine is operating and the switchlight is pressed IN (normal position), the right IDG will power the right Main AC Bus and the “ON” legend will be illuminated.
    • IN (IDG Unpowered). When the switchlight is pressed IN and IDG is not powered by the engine, the OFF legend will illuminate and the ON legend will extinguish.
    • OUT. When the switchlight is pushed OUT, Right IDG power is isolated from the Right Main AC Bus. The OFF legend will also be illuminated in this configuration.
  • APU Generator Switchlight
    • When the switchlight is pressed IN (normal position), ON legend will illuminate (if the APU is running) and the APU generator will power the Left and Right Main AC Buses. If one engine is running (left engine, for example), the IDG will power the Left Main AC Bus and the APU generator will power the Right Main AC Bus. The opposite is true if the right engine only is running. If both engines are running, the IDG’s will power their respective Main AC Bus.
    • IN (APU Not Running). When the switchlight is pressed IN and APU is not running, the ON legend is extinguished. This is the normal in-flight condition because the APU is nearly always shut down in flight. The AC synoptic page will indicate an amber box surrounding the APU Generator in this condition
    • OUT. When the switchlight is pressed OUT, APU generator power will be unavailable to the Left and Right Main AC Buses and the ON legend will extinguish.
  • Ram Air Turbine Generator Guarded Switchlight
    • IN (Normal Position). When the plastic guarded switchlight is pressed IN (normal position), the amber OFF legend will extinguish and the RAT generator will power the Emergency AC Bus and the Left and Right Essential TRUs, provided the RAT is deployed
    • OUT. When the switchlight is pushed OUT, RAT generator power will be removed from the ability to power the Emergency AC Bus and the Left and Right Essential TRU’s. The amber OFF legend will also illuminate. This might be used in the event of a fault in the RAT system or if normal generator power is restored. It can also be used in the event the aircraft slows below minimum RAT operating speed of 200 knots to prevent power from possibly cycling on and off. In this case, once above 200 knots, the generator can be selected ON again (switchlight pressed IN).
  • External Power Switchlight
    • Valid AC or DC External Power Connected. Blue AVAIL legend will illuminate when AC or DC external power is plugged into the aircraft and the BPCU senses the power’s parameters are all correct for application into the aircraft. The AVAIL legend requires 24 VDC power to illuminate, so the Main Batteries would have to be selected ON. If both AC and DC external power are plugged into the aircraft, the right BPCU will prioritize the selection of AC external power.
    • IN (ON Illuminated). If the AVAIL legend is illuminated and the switchlight is pressed IN, the plugged in power source will be applied to the aircraft, the ON legend will illuminate and the AVAIL legend will extinguish.
    • IN (Both AC and DC External Power Connected). If both AC and DC external power are plugged into the aircraft and the switchlight in pushed IN, AC external power will be connected to the aircraft and the ON legend will illuminate. In this case, the AVAIL legend will stay illuminated to indicate that DC external power is plugged in and available for use.
  • AC/DC Reset Switchlight
    • Default State. Momentary contact switchlight that is normally not illuminated.
    • Fault Sensed on AC Bus. AC legend illuminating indicates the BPCU’s having sensed a fault on an AC bus. When the BPCU’s sense a fault, they will automatically isolate the AC bus from the rest of the system and lock that bus out. Even when the fault is no longer sensed, the lockout will still keep the bus isolated. An illuminated legend could also indicate a logic fault within the BPCU, or a relay or component failure. One or both of the CAS messages shown at right will appear. If the BPCU’s no longer sense the fault and the RESET switchlight is pressed, the previously tripped relays will be allowed to close and the AC legend and CAS message(s) will extinguish.
    • Fault Sensed on DC Bus. DC legend illuminating indicates the BPCU’s having sensed a fault on the DC bus. When the BPCUs sense a fault, they will automatically isolate the DC bus from the rest of the system and lock that bus out. Even when the fault is no longer sensed, the lockout will still keep the bus isolated. An illuminated legend could also indicate a logic fault within the BPCU, or a relay or component failure. One or both of the CAS messages shown at right will appear. If the BPCU’s no longer sense the fault and the RESET switchlight is pressed, the previously tripped relays will be allowed to close and the DC legend and CAS message(s) will extinguish.
    • Fault Sensed on Both AC and DC Buses. AC and DC legends illuminating indicates the BPCUs having sensed a fault on both AC and DC buses. When the BPCUs sense the fault, they will automatically isolate the faulted buses from the rest of the system and lock the buses out. Even when the fault is no longer sensed, the lockout will still keep the buses isolated. An illuminated legend could also indicate a logic fault within the BPCU, or a relay or component failure. Two or more of the CAS messages shown at right will appear. If the BPCUs no longer sense the fault and the RESET switchlight is pressed, the previously tripped relays will be allowed to close and the AC and DC legends and CAS messages will extinguish.
  • Left Bus Tie Switchlight
    • OUT (Normal Position). When the switchlight is pushed OUT (normal position), the AUTO legend will illuminate and allow BPCU logic to open and close the Bus Tie Relays as necessary to ensure buses remain powered in the event of an IDG failure.
    • IN. When the switchlight is pressed IN, ISLN L AC Isolation legend illuminates, BPCU logic is bypassed, and the Left Main AC Bus is isolated from the Right Main AC Bus.
  • Right Bus Tie Switchlight
    • OUT (Normal Position). When the switchlight is pushed OUT (normal position), the AUTO legend will illuminate and allow BPCU logic to open and close the Bus Tie Relays as necessary to ensure buses remain powered in the event of an IDG failure.
    • IN. When the switchlight is pressed IN, ISLN R AC Isolation legend illuminates, BPCU logic is bypassed, and the Right Main AC Bus is isolated from the Left Main AC Bus.

Electrical Backup Hydraulic Actuator (EBHA) Battery

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Photo: G500 Electrical EBHA, PAS, p. 4-12
Click photo for a larger image

[PAS, p. 4-12] Electrical Backup Hydraulic Actuator (EBHA) Battery

  • 25 Volts, 53 amp/hr, Ni-Cad
  • Located in tail compartment
  • Backup power source for EBHA DC bus when emergency AC bus is unpowered. Powers Motor Control Electronics (MCEs), providing backup hydraulic and electrical power to Primary flight control surfaces and outboard spoiler panels. Lasts approximately 30 Minutes.
  • When emergency AC Bus is powered, it keeps EBHA battery charged. AC power converted to DC power via an external EBHA battery charger / TR located in tail compartment. It is powered EBHA DC Bus to maintain state of charge of EBHA battery (regardless of EBHA battery switch position).
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Photo: G500 Electrical Aft PDB, EBHA PDB, PAS, p. 4-16
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[PAS, p. 4-16] The EBHA PDB is in the tail compartment and contains the EBHA Bus.

[PAS, p. 4-16] EBHA Switchlights

  • IN (Normal Position). When AC power is being produced and the plastic guarded switchlight is pressed IN (normal position), the amber OFF and ON legends are extinguished and the EBHA contactor is closed, allowing power to the EBHA Bus.
  • IN (No AC Power). If the switchlight is pressed IN, the ON legend will illuminate, informing the crew that the EBHA Bus is being powered by the EBHA battery. Additionally, a light in the upper right corner of the Security/Ground Service Panel would also illuminate for this condition. The EBHA ON legend will also illuminate, informing the crew that the EBHA Bus is being powered by the EBHA battery if switch is left pressed IN and the ships batteries are selected OFF with all other power OFF
  • OUT. When the switchlight is pushed OUT, the amber OFF legend will illuminate and power is removed from the EBHA Bus.

Electronic System Controllers (ESCs)

[PAS, p. 4-19] There are two Electronic System Controllers (ESCs) which are the "brains of the SPDS" and perform system control functions (on and off) and control some of the auto functions of aircraft systems.

Emergency Battery Packs (EBPs)

There are six major batteries of which three are nicads (2 main ship batteries and 1 for the EBHA) and three lead acids (2 EBPs and 1 UPS).

We are told that we need to open the Main Entrance Door using the emergency door panel switch to test the Fwd EBP. But the "Arm" switch has FWD and AFT capsules so doesn't it do this? Then we are told that opening the MED requires a greater amperage since a high-draw solenoid is needed to lift the door before it is allowed to fall and this is what this test is for. I'm not so sure, but this is what we are told.

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Photo: G500 Electrical Emergency Batteries, PAS, p. 4-10
Click photo for a larger image

[PAS, p. 4-10]

  • 24 Volts, 10.5 amp/hr, lead acid with internal charger
  • Forward E-Batt located in LEER
  • Aft E-Batt located in FWD BEER
  • 3 modes of operation
    • Charge (1.5 Hours to Fully Charge), L Main AC Bus → Fwd E-Batt, R Main AC Bus → Aft E-Batt.
    • TR Mode: 24 Volts, 14 amp/hr for emergency power when power to an Ess DC Bus lost and E-Batt still receiving AC power.
    • Discharge (last resort DC power and TR mode unavailable). Provides approx 45 Mins of power for: Emergency lighting, Standby Flight Displays (SFDs), IRUs, VHF 1 Radio, Touch Screen Controllers (TSCs #2 and #3), Opening main entrance door (FWD E-Batt Only).
  • Armed E-Batts activate when L or R Ess DC Bus < 20 Volts, anytime a break power transfer occurs.
  • CAS Messages when activated: Fwd Emer Battery On, and Aft Emer Battery On.
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Photo: G500 Electrical Emergency Power Selected Off, PAS, p. 4-38
Click photo for a larger image

[PAS, p. 4-38] Emergency Power Selected Off. If ESS DC Bus > 20V DC. Emergency Power System is Shut OFF. FWD and AFT Switch Legends Light Up Amber, indicates FWD and AFT Emer Power NOT ARMED and FWD and AFT Emer Power is OFF

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Photo: G500 Electrical Emergency Power Selected Armed, PAS, p. 4-38
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[PAS, p. 4-38] Emergency Power Selected ARMED. If ESS DC Bus > 20V, arms FWD and AFT E-Batts, allows Auto Switching to Emer Power When ESS DC < 20V. FWD and AFT Switch Legends Extinguish, indicates FWD and AFT Emer Power ARMED, FWD and AFT Emer Power NOT OFF.

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Photo: G500 Electrical Emergency Power Selected On, PAS, p. 4-39
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[PAS, p. 4-39] Emergency Power Selected ON. Can be activated 2 Ways: ON Switch Depressed or ARMED Switch Depressed and L or R ESS DC < 20V (Even Momentarily). When Activated, FWD and AFT Switch Legends Light Up Amber in ON Switch (indicates FWD and AFT E-Batts Powering L and R Emer DC Buses and Emer Lighting). CAS Messages: Aft Emer Battery On and Fwd Emer Battery On.

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Photo: G500 Electrical Cockpit Display with Emergency Power Only, PAS, p. 4-39
Click photo for a larger image

[PAS, p. 4-39] Emergency Power Indications (Airplane Power-Up). Verify Following are Powered: Emergency Lighting, Standby Flight Displays (2), TSC #2 and #3, (Backup Engine/Radio Display, but Engine Data will be Blank)

External AC Source

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Photo: G500 Electrical External AC Connected, PAS, p. 4-32
Click photo for a larger image

[PAS, p. 4-2] AC power is produced by:

  • External AC power cart — 30 kVA, 115 VAC, 400 Hz, 3 Phase, powers all buses.

External Battery Switch

[PAS, p. 4-59] The external battery switch:

  • Turns on both main batteries
  • It therefore powers both essentials

  • Turns on the anti-collision beacon

External DC Source

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Photo: G500 Electrical External DC Connected, PAS, p. 4-33
Click photo for a larger image

[PAS, p. 4-8] The external DC power cart powers: Left Essential DC Bus, Right Essential DC Bus, Left Main DC Bus, Right Main DC Bus (which powers the Ground Service Bus), and the Aux DC Bus.

Generator Control Units (GCUs)

The purpose of GCUs is to provide quality power by protecting and monitoring their associated generators.

[PAS, p. 4-17]

  • Produce quality power by controlling generator’s output and fault protection. When voltage, frequency or amperage out of parameter, opens contactor to take gen offline and transmits data to BPCU (except RAT GCU).
  • Engine and APU GCUs are identical and interchangeable, operate independently of each other, and are located in the LEER and REER.
  • RAT GCU is not identical to engine and APU, but similar in function.
  • GCUs reset by cycling applicable gen switch OFF then ON, re-initializes software. If failure condition still detected, GCU will again fail-safe

Ground Service Bus (GSB)

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Photo: G500 Electrical Various DC Panels, PAS, p. 4-6
Click photo for a larger image

[PAS, p. 4-6] Ground Service Bus (GSB)

  • Normal Power Source is Right Main DC Bus
  • Provides DC power to perform minimal aircraft ground servicing: Lights, External Water Level Indicator, Engine Oiler, Hydraulic Replenisher, Left and Right Fueling Shutoff Valves, Left and Right Fuel Quantities, Cabin Gnd Svc, Water System, TSC 5, TPMS.

[PAS, p. 4-6] On ground with Right Main DC initially unpowered

  • GSB Power Activated by any of 4 GSB Switches Located: Tail Compartment Ground Service Panel, Security/Ground Service Panel (Left Fwd Fuselage), Refuel Panel (Right Fuselage), System Monitor Test Panel (Cockpit Fwd of REER).
  • For push button switches → Press and hold min 3 secs to activate.
  • Beacon will illuminate with a GSB switch ON.
  • Powered By: External DC if connected, Right Main Battery (if External DC not connected).
  • 1 of 4 doors must be open to power GSB from Rt Batt or Ext DC: Main Door, Tail Compartment Door, Security/Ground Service Panel Door, Refuel Panel Door

Integrated Drive Generators (IDGs)

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Photo: AC Power, L/R Generators, PAS, p. 4-2.
Click photo for a larger image

[PAS, p. 4-2] Left and right engine generators (IDG’s)

  • Mounted on accessory gearbox of each engine.
  • Oil cooled generator produces 40 kVA, 115 VAC, 400 Hz, 3 Phase.
  • A Constant Speed Drive (CSD) maintains constant generator speed despite variable engine speeds to produce a constant generator power output.

Main Ship Batteries (MSBs)

There are six major batteries of which three are nicads (2 main ship batteries and 1 for the EBHA) and three lead acids (2 EBPs and 1 UPS).

It is said that when you are down to your MSBs, you have ten minutes left, assuming two APU start attempts.

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Photo: G500 Electrical Main Batteries, PAS, p. 4-11
Click photo for a larger image

[PAS, p. 4-11]

  • 25 Volts, 53 amp/hr Ni-CAD (22 Volts minimum)
  • External battery chargers / TRs (2)
  • Located in tail compartment
  • 3 Modes:
    • Charge. When L / R Main AC Bus power available. Transforms 115 VAC to DC up to 32 Volts regardless of main battery switch ON or OFF, approx 90 mins to recharge battery. If battery voltage < 22V refer to Mx manual.
    • Transformer Rectifier (TR). Supplies 40 amps of DC Power when battery(s) required for APU start, aux pump operation, or when an Essential TRU fails and power needed by an Essential DC Bus. Main battery switches must be ON.
    • Discharge. When Main AC Power not available to power: APU start (Left Batt only), AUX hydraulic pump operation (L and R Batt), Left Ess DC Bus (L and R Batt), Right Ess DC Bus (L and R Batt), Ground Service Bus (Right Batt Only) when not powered by normal source of power. Will provide a minimum of 10 mins of power after 2 APU start attempts.
  • Remove for cold soak conditions (-20°C)
  • Disconnect if aircraft shutdown ≥ 5 Days

[PAS, p. 4-40] Main Battery Switches

  • OFF: switch in OUT position, legend dark.
  • ON: switch is pushed In, battery available for use according to system logic. Switch legend Amber ON for APU start, AUX pump operation, or if ESS DC buses have no other source of power.
  • OUT: switch in OUT position, legend Amber ON if an external battery switch is selected ON.
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Photo: G500 Electrical Cockpit Display with Main Battery Power Only, PAS, p. 4-43
Click photo for a larger image

[PAS, p. 4-43] With main battery power only, you will have the following cockpit displays: OHPTS 1 and 2, Both SFDs, DUs 1 and 4, landing gear lights, and all TSCs.

No Break Power Transfer (NBPT) Function

AC

[PAS, p. 4-18] No Break Power Transfer (NBPT) Function

  • Controlled by Left and Right BPCU
  • Prevents instability of electrically powered devices
  • Ensures AC power transfer without interruption of power. An IDG must be involved and the transfer cannot be due to a fault or failure.
  • BPCU Signals the GCU of the IDG to adjust frequency and/or phase output to match other source of AC power being applied to the electrical system. (Makes sources congruent prior to switching source.)
  • Can occur on ground or in flight

Power Distribution Boxes / Buses (PDBs)

The FSI Maintenance Manuals calls these Power Distribution Boxes while the pilot manual, Production Aircraft Systems, calls them Power Distribution Buses. The AFM? Box it is. Box or bus, a PDB is a common location where big power cables are split into smaller cables through circuit breakers.

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Photo: G500 Electrical Left, Right PDBs, PAS, p. 4-15
Click photo for a larger image

[PAS, p. 4-15] The Power Distribution Buses (PDBs)

  • A PDB provides protection through traditional electro-magnetic circuit breakers.
  • The Left PDB is in the LEER and sends power to the Left Essential, Left Main, and Control buses.
  • The Right PDB is in the REER and sends power to the Right Essential, Right Main, External DC, Aux DC, Control, and Ground Service Bus (GSB) Control buses.

Aft PDB

[PAS, p. 4-16] The Aft PDB is in the tail compartment and includes six CBs for battery buses and GSB control.

EBHA PDB

[PAS, p. 4-15] The EBHA PDB is in the tail compartment and contains the EBHA bus.

RAM Air Turbine (RAT) Generator

The Ram Air Turbine provides power to your most important DC buses by powering the most important AC buses: the L ESS AC, R ESS AC, and Emer AC buses. Through that, you get power to the L ESS DC, R ESS DC, EBHA DC, and UPS DC bus.

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Photo: G500 Electrical RAT, PAS, p. 4-7
Click photo for a larger image

[PAS, p. 4-7]

  • 15 KVA, 115 VAC, 400 Hz, 3 Phase
  • No Time Limit
  • Powers: Left Essential TRU, Right Essential TRU, Emergency AC Bus (EBHA Charger, UPS Charger, Horizontal Stab CH 1, L and R Side windshield heat).
  • Used When all generators (engine and APU) have failed or during electrical failures involving Emergency AC Bus, Left ESS DC Bus, or Right ESS DC Bus.
  • Dedicated GCU with switch located on cockpit overhead EPCP.
  • Manually Deploy: Rotate handle on floor aft of center pedestal.
  • Requirements: Deploy Mach ≤ .925, Maintain > 200 kts.
  • Can’t stow inflight; stows on ground with hand pump.

You may have noticed that under RAT-only power that your side windows will be heated but your front windshields will not. We asked the question and were told that it is because the front windshields draw more current and would put the RAT load over the limit.

Solid State Power Controllers (SSPC)

For more about "virtual" circuit breakers, see: Circuit Breakers.

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Photo: G500 Electrical Secondary Power Distribution System, PAS, p. 4-52
Click photo for a larger image

[PAS, p. 4-52]

  • Accessed from TSC 2 through 5
  • Distributes power to various aircraft loads (including engines)
  • Electronic System Controllers (ESC) (2) Selectable left or right (Selected is controlling, other in standby)
  • Provides summary of all SSPC’s: Tripped, Failed, Pulled, Collared
  • Search SSPC by ID / ATA #
  • Search SSPC by system
  • Navigate to cabin power page
  • Access backup system switches
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Photo: G500 Electrical Secondary Power Distribution System, PAS, p. 4-53
Click photo for a larger image

[PAS, p. 4-53]

  • Electronic or solid state circuit breakers
  • Accessible at any time; but on GSB power → Only TSC 5 has access
  • Search by System, ID / ATA #
  • View by status: tripped, failed, pulled, collared
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Photo: G500 Electrical Secondary Power Distribution System, PAS, p. 4-54
Click photo for a larger image

[PAS, p. 4-54] SSPCs provide detailed info for every load: Rating → Max amp, Bus → Power source, Status → Of circuit, Switch state, Current, Bus Voltage.

Transformer Rectifier Units (TRUs)

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Photo: G500 Electrical TRUs, PAS, p. 4-5
Click photo for a larger image

[PAS, p. 4-5] Five Transformer Rectifier Units (TRUs) Convert 115 VAC Power to 28 VDC Power and are dedicated to power their respective DC Bus. The Secondary Power Distribution System (SPDS) then receives DC Power from the DC Buses, except from the AUX DC Bus which routes its power to the Right PDB bypassing the SPDS.

  • The Left Main AC Bus powers the:
    • Left Ess TRU, which powers the Left Ess DC bus, which powers the SPDS and Left Emergency DC bus.
    • Left Main TRU, which powers the Left Main DC bus, which powers the SPDS.
    • Aux TRU, which powers the AUX DC Bus.
  • The Right Main AC Bus powers the:
    • Right Ess TRU, which powers the Right Ess DC Bus, which powers the SPDS and Right Emergency DC bus.
    • Right Main TRU, which power the Right Main DC bus, which powers the SPDS and Ground Service Bus.
    • AUX TRU if the Left Main AC Bus isn't powered.

[PAS, p. 4-9] If a TRU failure occurs:

  • AUX TRU sheds power to the AUX DC bus and you will lose power to non-essential cabin equipment.
  • AUX TRU then powers one of the buses connected to a failed TRU under the priority essential before main, and left before right.
  • The priority logic is carried out by the BPCUs and is repeated for additional TRU failures.

Uninterruptable Power Supply (UPS) Battery

There are six major batteries of which three are nicads (2 main ship batteries and 1 for the EBHA) and three lead acids (2 EBPs and 1 UPS).

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Photo: G500 Electrical UPS, PAS, p. 4-13
Click photo for a larger image

[PAS, p. 4-13] Uninterruptable Power Supply (UPS) Battery

  • 24 Volts, 10.5 amp/hr, Lead Acid
  • Located in REER
  • Backup power source for UPS DC bus when emergency AC bus is unpowered. Components powered: 2 of 4 FCC Channels (1A and 2B), Backup Flight Control Unit (BFCU), 1 of 2 power sources for all REUs. Lasts Approximately 30 Minutes.
  • When emergency AC Bus is powered, it keeps UPS battery charged. AC Power converted to DC power via the UPS battery’s charger / TR.
  • Gulfstream Recommends Performing an Immediate Landing when Operating on Main, UPS and EBHA Batteries Only.

[PAS, p. 4-45] UPS Switchlights

  • IN (Normal Position). When AC power is being produced and the plastic guarded switchlight is pressed IN (normal position), the amber OFF and ON legends are extinguished and the UPS contactor is closed, allowing power to the UPS Bus.
  • IN (No AC Power). If the switchlight is pressed IN, the ON legend will illuminate, informing the crew that the UPS Bus is being powered by the UPS battery. Additionally, a light in the upper right corner of the Security/Ground Service Panel would also illuminate for this condition.
  • OUT. When the switchlight is pushed OUT, the amber OFF legend will illuminate and power is removed from the UPS Bus.

Other Notes


Prolonging Battery Life

[The Gulfstream Journal, January 2020, p. 6]

  • The battery service life and electrolyte consumption of Ni-Cad Batteries will vary depending on the duty cycle, average ambient temperature, and charge method utilized. The Gulfstream large cabin family of aircraft implements Ni-Cad Batteries in the Left/Right Main Ship Battery (MSB) positions. G650/G650ER and G500/G600 also have an Electrical Backup Hydraulic Actuator (EBHA) Battery.
  • Gulfstream suggests the following recommendations to prolong the life of these batteries:
  • Duty Cycle. Battery life is negatively-impacted with higher utilization. While both Left/Right MSBs are used to support aircraft power on and Aux Hydraulic Pump operation, the Left MSB is used to assist an APU Start. As a consequence, the higher duty cycle experienced by the Left MSB will result in lower service life compared with the other Right MSB. The EBHA Battery will mostly remain as a backup power source with a much lower duty cycle compared with the MSBs. Gulfstream Recommendation: an effective way to compensate for the difference in duty cycle between the Left and Right MSB is by doing a scheduled rotation that will swap both MSB at a given interval. That practice will contribute to balance and maximize the life between both MSBs. Another important recommendation to reduce the duty cycle on MSBs is minimizing the time spent on batteries only and avoiding running the Aux Hydraulic pump for extended durations.
  • Average Ambient Temperature. Intrinsic to the Ni-Cad technology is the fact that battery life will reduce with the increase of average ambient temperature. A rule is that battery life is reduced in half (TBC) for every 10C° increase in average ambient temperature. Gulfstream Recommendation: operators may want to consider removing the battery from the aircraft and keep those in ambient room conditions in case of prolonged parking in hot weather conditions.
  • Charge Method. All Gulfstream large-cabin aircraft utilize a dedicated Battery Charger to charge each battery individually, and this is considered by battery manufactures the best method to ensure a longer battery life in the field when compared with float charge.

Limitations and Abnormal Procedures


Limitations

[AFM, §01-24-10]

  • Deployment of the RAT is prohibited when normal AC power is available except during emergency conditions and as directed by abnormal or emergency procedure checklists.

  • Minimum airspeed for effective RAT operation is 200 KCAS.

See Also:

Gulfstream GVII-G500 Airplane Flight Manual, Revision 3, July 16, 2019

Gulfstream GVII-G500 Production Aircraft Systems, Revision 3, July 15, 2019

The Gulfstream Journal, January 10, 2020