ELECTRICAL POWER CH 24
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TABLE OF CONTENTS ELECTRICAL SYSTEM - INTRODUCTION .......................................... 4 ELECTRICAL SYSTEM PANELS.......................................................... 6 ELECTRICAL LOAD DISTRIBUTION ................................................... 8 INTEGRATED DRIVE GENERATOR (IDG) ........................................ 10 IDG SERVICING.................................................................................. 12 IDG COOLING SYSTEM FOR GE ENGINE ....................................... 14 IDG AIR/OIL COOLING SYSTEM ....................................................... 16 IDG PRESSURE AND TEMPERATURE INDICATION..........................18 APU GENERATOR EXTERNAL DETAILS.......................................... 20 AC POWER SYSTEM ......................................................................... 22 GENERATOR CONTROL UNIT (GCU)............................................... 24 MAIN POWER BREAKERS................................................................. 26 GCU FAULT PROTECTION................................................................ 28 CURRENT SENSING .......................................................................... 30 BITE DISPLAYS .................................................................................. 32 LOAD SHEDDING ............................................................................... 34 BUS POWER CONTROL UNIT (BPCU) ............................................. 36 EXTERNAL POWER COMPONENTS ............................................... 38 EXTERNAL POWER QUALITY........................................................... 40 EXTERNAL POWER PROTECTION................................................... 42 GROUND SERVICE BUS CONTROL ................................................. 44 GROUND HANDLING SYSTEM ......................................................... 46 DC POWER GENERATION ................................................................ 48 TRANSFORMER RECTIFIER SYSTEM ............................................. 50 BATTERIES, CHARGING, AND TRU LOCATIONS............................ 52 MAIN BATTERY CHARGING SYSTEM .............................................. 54
STANDBY POWER SYSTEM.............................................................. 56 STATIC INVERTER ........................................................................ ..... 58 STANDBY POWER SYSTEM OPERATION..........................................60 HYDRAULIC MOTOR GENERATOR SYSTEM .................................. 62 HMG POWER DISTRIBUTION..............................................................64 HMG GENERATOR CONTROL UNIT................................................. 66 HYDRAULIC MOTOR GENERATOR CONTROL ............................... 68 HYDRAULIC MOTOR GENERATOR (HMG) OPERATION ................ 70 ELECTRICAL MAINTENANCE PAGE...................................................72
STUDENT NOTES:
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ELECTRICAL SYSTEM - INTRODUCTION AC Electrical Power AC electrical power for airplane ground operations is supplied from an external AC ground cart through the external power panel (P30) or from an Auxiliary Power Unit (APU) driven generator. For in-flight operations power is supplied from an Integrated Drive Generator (IDG) mounted on each engine or from the APU driven generator. The power sources are non-paralleling. Components associated with the AC system include: • • • •
3 Generator Control Units (GCU) 1 Bus Power Control Unit (BPCU) Power Panels (various) Equipment Racks
All these items are located in the main equipment center. DC Electrical Power Normal airplane DC power is produced by AC to DC conversion. Battery systems provide alternate DC and standby power. Components associated with the DC system include: • • • • • •
Main battery Battery charger Two Transformer Rectifier Units (TRU) Static inverter Power Panels (various) Equipment Racks
All these items are located in the main equipment center. The aft equipment center (E6) has components used with the APU DC system: • APU battery • Battery charger • Relay panel
Hydraulic Motor Generator (HMG) A Hydraulic Motor Generator (HMG) system operates as a non-time limited backup source in the event of loss of all main electrical power. The Generator provides power for the standby system, Captain’s flight instruments, and selected navigation, communication, lighting and anti-icing loads. The basic system hardware consists of the Hydraulic Motor Generator (HMG) and Generator Control Unit (GCU). System Control and Indication Manual or Automatic source selection is provided during ground and in-flight operations from the Electrical System Control Panel (P5) and Auxiliary Electrical System Control Panel (P61) located in the flight compartment. Electrical system monitoring is provided on the EICAS display units also located in the flight compartment. The electrical system incorporates automatic load transfer, automatic fault protection, and isolation.
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ELECTRICAL SYSTEM PANELS General Normal operation of the electrical power system is performed at the electrical system control panel and the auxiliary electrical system control panel. Both momentary and alternate action switchlights are used on the electrical panels. For all of these switches the normal position is IN or LATCHED. Switch position is indicated by the absence or presence of a mechanical legend in the switch face of all alternate action switchlights. All indicator lights are powered via the Master Dim and Test System. Electrical system control panel (P5) The momentary External Power Switch controls opening/closing of the External Power Contactor (EPC). A white AVAIL light indicates power is of proper quality. The white ON light indicates external power contactor position (closed). Generator Control Switchlights provide a control signal which closes the Generator Control Relay (GCR) and when proper power is available, and closes the Generator Circuit Breaker (GCB). The flow bar and ON legend indicate switch position. An amber OFF light illuminates whenever the associated GCB is open. The AC bus tie switchlights allow manual or automatic control of the Bus Tie Breaker (BTB). In the unlatched position the associated BTB will be opened, isolating the associated main AC bus from the AC tie bus. Operating the switch to the latched position, AUTO illuminated and ISLN extinguished, normally will enable automatic operation of the BTB. The AC BUS OFF lights illuminate when the associated Main AC Bus is deenergized. The Utility Bus Switchlights provide manual control of the power relays connecting utility and galley buses to the left and right main AC buses. The ON legend indicates switch position and is hidden when the switch is in the unlatched position. The amber OFF light illuminates if the associated Utility Bus Relay is open. The guarded momentary Generator Drive Disconnect Switches cause a mechanical disconnection between the IDG and the engine. The switch is spring loaded OUT. The amber DRIVE light in the switchlight indicates low IDG oil pressure or high IDG oil temperature.
The guarded Battery Switch controls connection of the battery bus to the left DC Bus or Hot Battery Bus. The ON legend indicates switch position and is not visible when the switch is unlatched. An amber OFF light illuminates when the battery switch is in the unlatched position during normal flight and ground operations and the Left DC Bus is powered. An amber DISCH light illuminates if the battery is discharging greater than 4 amps. Standby Power mode of operation is controlled by the Standby Power Selector Switch. The switch is rotary and has three positions: OFF, AUTO and BAT. An amber standby power bus OFF light will illuminate when the AC or DC Standby Bus is unpowered. Auxiliary Electrical System Control Panel (P61) The momentary Generator Field Manual Reset Switch will open or close the Generator Field Control Relay (GCR) if the Generator Control Switch (P5) is unlatched. A white FIELD OFF light illuminates when the Generator Control Relay (GCR) field is open.
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ELECTRICAL LOAD DISTRIBUTION General The electrical power load distribution system consists of both 115 and 28 volt AC and DC distribution buses. All power distribution is shown except galley buses. The sources of power for the distribution buses are the engine driven IDG, APU Generator, and External Power. Left And Right Main AC Buses The Main AC Buses supply all of the essential AC loads in the airplane. Each bus is divided into independent sections. An AC Tie Bus provides interconnection between the Main Buses under certain conditions. Left And Right Utility Buses The Utility Buses supply non-essential loads. The loads can be deenergized automatically for load shedding purposes. Ground Service Bus
Center Buses The Center Buses supply both AC and DC power to the center channel equipment of the autoland system. During category III autoland operation, the buses are supplied from sources isolated from the main buses. Transfer Bus The Left and Right Transfer Bus is considered part of the Main AC bus for most operations. The items on the Transfer Buses were moved from the Main Bus to allow the HMG (when operating) to power them independently. Flight Instrument Transfer Bus The flight instrument transfer buses supply power to selected captain and first officer flight instruments and allows automatic transfer to an alternate power source in case of primary source failure. Bus transfer between the primary and alternate power sources is controlled by the Instrument Bus Voltage Sensing Unit. 28 Volt AC Buses
The Ground Service Bus supplies both in-flight and ground loads that include Interior Lights, Battery Chargers and Cooling Fans. The Ground Service Extension Bus is sheddable in-flight to reduce electrical load during single engine operation.
The airplane is provided with 28 volt AC buses which supply various lights, instruments and other loads requiring 28 volt AC power. Each bus is supplied through a separate Auto-Transformer.
Ground Handling Bus
28 Volt DC Buses
The Ground Handling Buses are powered only on the ground from APU or External Power through the Ground Handling Relay. The Ground Handling Bus supplies loads such as cargo handling equipment and refueling that are used only during ground operations.
The Left and Right Main DC buses supply power to those loads requiring DC power. Each main DC bus is divided into two independent sections. A tie bus interconnects the Main Buses under certain conditions. The DC Standby Bus supplies power to certain essential airplane loads and will transfer sources in case of primary source load failure. The Battery Buses are powered from either a Battery Charger or Nickel-Cadmium Battery.
AC Standby Bus The AC Standby Bus supplies single phase power to essential flight loads and will automatically transfer power sources in case of primary source loss.
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INTEGRATED DRIVE GENERATOR (IDG) General The Sundstrand IDG housing is a two-piece magnesium casting with single bolted interface. The dry weight of the IDG is 117.7 lbs. Two electrical connectors interface with airplane wiring for control, protection and monitoring circuits. Connector A provides electrical connection for the Permanent Magnet Generator (PMG), charge pressure switch, and oil temperature bulbs. The input speed sensor, disconnect solenoid, internal Current Transformer (CT) assembly, and exciter field are connected through connector B. All wiring between the IDG components is located within the housing. The Main Generator Stator 3 phase output and neutral output leads are terminated at a 4 stud terminal block. The studs are 3/8" diameter stainless steel. The neutral output is grounded to the upper strut structure. A male spline on the IDG drive shaft provides the engine accessory gearbox connection. The shear section is designed to break with an input torque of 9000 +/-400 inch lbs. Disconnect Reset Ring The ring allows ground only restoration of engine accessory gearbox and IDG input spline mechanical connection by resetting a spring-loaded split-nut pawl. Engine rotation must be completely stopped in order to reconnect the IDG. Drain, Fill And Vent Ports Oil is drained from the IDG case by removal of the case drain plug. The pressure fill fitting connects to the pressure fill port for pressure filling of the IDG. The overflow drain connects to an internal standpipe, and is used during servicing. The case pressurization vent valve equalizes case and atmospheric pressures. Under normal operating conditions the case pressure is in the range of 5 to 10psi. Case Thermal Relief Valve The case thermal relief valve allows hot IDG oil to drain overboard through a drain mast or into the cowl during extreme over temperature condition by melting at 450F (232C).
Low Oil Level Indicator Note:
The prismatic light glass type indicator is not normally used.
Scavenge Filter And Delta Pressure Indicator A non-bypassing filter on the discharge side of the scavenge pumps, filters all oil flow from the IDG. The filtration rating is Beta 10-65. The scavenge filter contains a pop-up Delta Pressure Indicator (DPI). A red button pops out near the filter housing when the pressure drops across the filter reaches 60 psid. The DPI is locked out below 145F (63C) to prevent nuisance tripping. Governor Adjustment The governor adjustment allows adjustment of the IDG output frequency. One turn changes the frequency 3 to 3.5hz, counterclockwise to increase and clockwise to decrease. Only a one time adjustment after replacement is allowed.
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IDG SERVICING Oil Level Check CAUTION: IF IDG WAS DISCONNECTED DURING LAST ENGINE RUN, OR ENGINE HAS BEEN SHUTDOWN FOR OVER 90 MINUTES, FALSE OIL LEVEL READING WILL OCCUR. INCORRECT OIL QUANTITY IN IDG MAY DAMAGE IDG. An oil level check should follow any maintenance action that results in loss of oil. If the IDG to be checked has been disconnected or the engine has been shut down longer than 90 minutes, then run the engine until IDG outlet oil temperature reaches 80C or after 3 minute stabilization time. Check the oil level by servicing the IDG. IDG Oil Replenishment CAUTION: DO NOT INTERCHANGE THE PRESSURE FILL ELBOW COUPLING WITH THE OVERFLOW DRAIN COUPLING. THE IDG WILL BE DAMAGED DUE TO OVER-FILLING IF OIL IS PUMPED IN THROUGH THE OVERFLOW DRAIN. For pressure fill servicing a cart capable of pumping oil at 5 to 15 psi with a quick disconnect coupling on the fill hose and a drain hose is required. Remove the protective cover from the pressure fill valve and connect the pressure fill hose. Remove the protective cover from the overflow drain valve and connect the drain hose. CAUTION: WHEN REPLENISHING, DO NOT MIX TYPES OR BRANDS. Note:
Be prepared to catch a small amount of residual oil from the IDG standpipe.
Pump oil into the IDG under 5 to 15 psi pressure. Immediately remove the pressure fill hose from fill valve when oil flows from overflow drain. When oil from overflow slows to a pencil lead-thick stream (approaching a drip condition), or oil has drained for 60 seconds, remove drain hose and install protective cover
on the overflow drain valve. Install protective cover on the pressure fill valve. CAUTION: THE IDG OIL MUST BE DRAINED IF MAINTENANCE ACTION RESULTED IN AN OIL LOSS EXCEEDING APPROXIMATELY 1/2 PINT, OR IF REPLENISHMENT CANNOT BE PERFORMED WITHIN 3 HOURS OF ENGINE RUN TO 80OC MINIMUM IDG OUTLET OIL TEMPERATURE.
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IDG OIL COOLING FOR GE ENGINE Purpose The IDG Air/Oil Heat Exchanger cools the IDG oil when the Fuel/Oil Cooler has insufficient fuel flow. This is usually when the Engine is operating at a low power setting and Fuel Flow is low. Airflow through the heat exchanger is controlled by the IDG Air/Oil Heat Exchanger Valve.
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IDG COOLING SYSTEM General IDG oil is cooled by an external cooling system (one system for each IDG) with engine fuel flow used as the primary cooling source. Supplemental cooling is by air flow through the IDG air/oil heat exchanger. The cooling airflow is controlled by the generator control unit. Generator Control Unit When the engine is at idle power, the IDG inlet oil temperature is less than 127C (260F). The IDG cooling air shutoff valve solenoid is energized. The spring force on the actuator holds the valve open and fan air is supplied to the IDG air/oil heat exchanger. When the engine operates at more than minimum cruise power, 11th stage compressor bleed air forces the fan air shutoff valve closed. If the inlet oil temperature is more than 127C (260F), a generator control unit internal relay is energized. Power goes to K1031, L IDG air cooler valve and K468, L IDG valve failure relays. When K1031 is energized, the IDG cooling air shutoff valve solenoid is de-energized. This causes the valve to open. The generator control unit internal solid-state switch opens after the inlet oil temperature goes to less than 104C (220F). If both temperature bulbs fail, the GCU opens the cooling valve. If the IDG is not up to speed, the GCU keeps the valve closed, by the underspeed input, when the engine is running. The inlet oil temperature set point is selectable. An open input changes the inlet oil temperature valves to 113C (valve opens) and 79C (valve closes). Valve Position Indication If the shutoff valve does not open, K468 stays energized. A ground signal goes to EICAS. This makes the status and maintenance message, L IDG VALVE. The message is stored in non-volatile memory.
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IDG PRESSURE AND TEMPERATURE INDICATION General These indications alert the flight crew or maintenance personnel of a mechanical failure of the IDG: • IDG DRIVE light • EICAS message GEN DRIVE. Operation These indicators go to the DRIVE light logic circuit in the GCU: • IDG oil temperature • Oil pressure • PMG frequency. • The GCU turns on the drive light and sends a signal to EICAS to show the C level message GEN DRIVE when any of these conditions occur: • PMG frequency more than 440 HZ • Oil in and oil out sensors failed • Oil in and oil out temperature bulbs sense high oil temperature (oil in >176.6C and oil out >185C) • GCB trip caused by a frequency fault, reset, and trips again for a frequency fault within 2 seconds of the reset • Low oil pressure for longer than 1.8 seconds in any 10-second period. The maintenance message L(R) IDG OIL LEVEL shows when there is low oil pressure for longer than 0.15 seconds but less than 1.8 seconds in any 10second period.
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APU GENERATOR EXTERNAL DETAILS Purpose The APU Generator provides 115 volt AC power either inflight as a back-up source or during ground operation. Location The unit is mounted to the auxiliary power unit accessory gearbox. Physical Description/Features The electromagnetic components of the Auxiliary Generator are the same as those used in the IDG and are interchangeable except that the APU Generator is contained in its own magnesium cast housing and has a different input spline and mounting flange. The generator weighs 61.9 pounds (27.63 kg) dry weight. Keyhole slots allow mounting of the generator to the Auxiliary Power Unit (APU) accessory gearbox. An aluminum seal plate is installed between the generator Mounting Flange and Gearbox Drive Pad. The Mounting Flange incorporates three locating pins to position the generator on the APU flange. Elastomer compound inserts are installed in the seal plate OIL-IN and OIL-OUT ports. The Input Shaft incorporates a shear section that shears at 4700 +/- 300 in-lbs. The APU generator is spray oil cooled and lubricated using APU engine oil. Pressurization, scavenging, and filtering of the oil is provided by the Auxiliary Power Unit. Generator case pressure, 5 psig above ambient, is introduced from the APU gearbox through a rotating screw passageway in the input shaft. APU Generator Oil is filtered by a 20/40 micron filter. The delta pressure (popout) indicator activates at 20psid. A mechanical lockout prevents activation when oil temperature is below 115F (46C). When the filter Delta Pressure (DP) reaches 35 psid and oil temperature above 46C (115F) an APU Auto Shutdown is initiated by the Differential Pressure Switch. A terminal block with four stainless steel studs provides the feeder connections. A single electrical connector provides all other electrical connections.
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AC POWER SYSTEM Power Sources There are two Integrated Drive Generators (IDG) mounted to and driven by the Engine Accessory Gearboxes. The Auxiliary Generator is mounted to and driven by the APU. External power is supplied through the External Power Receptacle, P30, located on the lower right side of the fuselage just aft of the Nose Gear. All sources produce 90kva, 115/200 volt AC, 3 phase, 400hz power. Generator Control Unit (GCU) The three GCU's, Left IDG, Right IDG, and APU are mounted in the Main Electrical Equipment Center on the E1 and 2 Racks. Each GCU provides Generator Field excitation, voltage regulation and controls the associated Generator Circuit Breaker (GCB) and Bus Tie Breaker (BTB). All protection functions for the generating channel are contained in the GCU. A receiver and transmitter sends system status information over the serial data link. Bus Power Control Unit (BPCU) One BPCU controls the External Power Contactor (EPC), the Ground Handling and Ground Service Relays, provides external power monitoring, and protection functions. The BPCU also controls electrical system load shedding of Utility and Galley buses, BITE, and fault isolation controls for the electrical system. The BPCU receives and transmits system status information over the serial data link.
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GENERATOR CONTROL UNIT (GCU) General
In addition, the GCU contains Built-In-Test-Equipment (BITE) circuitry to aid in on-aircraft fault isolation.
The Generator Control Unit (GCU) used in the electrical system provides;
Communication between the GCU and the BPCU is initiated by the BPCU.
• • • • •
generator excitation voltage regulation manual and automatic control indication protective functions for each generating channel
The same control units are used for the IDGS and the APU generator. The GCU maintains direct control of the GCR, GCB, and BTB closing and tripping in response to Point Of Regulation (POR) power, quality, source availability, automatic protective functions, and manual commands. Physical Characteristics Each unit is packaged in an ARINC 600 3 MCU case and weighs 7.5 lbs. The GCU's are rack mounted in the main equipment center on ARINC 600 trays in the E1 and E2 equipment racks, held in with an extractor front hold down assembly. Forced air cooling is provided through the racks. The power required to operate internal GCU circuits and external GCB and BTB contactors is derived from the IDG Permanent Magnet Generator (PMG) source with back-up from the airplane 28 volt DC system. Two circuit breakers are provided on the GCU to protect external circuits. Input/output All input signals are run through input conditioning circuits to provide; • • • •
signal shaping peak holding averaging discrete signal levels for sensed inputs
Output conditioning circuits provide digital-to-analog conversion and discrete signal levels.
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MAIN POWER BREAKERS General The Generator Circuit Breakers (GCB), Bus Tie Breakers (BTB), and the Auxiliary Power Breaker (APB), are all identical and interchangeable, each weighing 3.75 lbs. Physical size of the units is 4.7" high x 6.1" long x 4.1" wide. All units are mounted in the main equipment center. The left generator power panel P31 contains the left channel GCB and BTB. The P32 right generator power panel contains right channel GCB and BTB. The APB is mounted in the P34 APU/External Power Panel. Main Contacts The main contacts allow an electrical power source to be connected to the Main Load Bus or AC Tie Bus. The feeder circuit wiring to the main contacts is completed using 3/8" diameter nut stud main terminals. The Main Contacts are three pole, single throw, magnetic latching type, rated at 275 amperes, 115/200 volt AC, 400hz. Auxiliary Contacts A single electrical connector is provided for auxiliary contacts and control coil power. Seven normally open, seven normally closed single pole, single throw contacts are rated at 1 ampere at 240 volt AC and 7.5 amperes at 28 volt DC. The breaker actuator is held open by a core spring. The self de-energizing close coil supplies actuator closing force. A permanent magnet provides closed contact holding force. The self de-energizing trip coil overcomes the permanent magnet holding force.
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GCU FAULT PROTECTION General The Generator Control Unit (GCU) protective functions monitor system parameters including current, voltage, and frequency. They protect the main generating channel in the event of system faults and protect equipment connected to the system from out-of-limits electrical power quality. The limits and time delays of the various protective functions are such as to selectively isolate any fault with a minimum reduction of generating capacity and a minimum interruption of power to the airplane load buses. A reset must be initiated if any fault produces a signal which trips both the GCR and GCB. The reset is accomplished by unlatching and re-latching the Generator Control Switch. The GCR is closed and GCB will be enabled for automatic operation. A reset can also be generated by removing and applying power to the corresponding Generator Control Unit. Inputs The GCU senses three phase power from the Permanent Magnet Generator for frequency protection functions. The Point Of Regulation (POR) feedback provides three phase AC input for under/over- voltage protection functions. Generator internal current transformers provide current sensing for open phase and shorted rotated diode protection. Protective Functions Over-voltage protection determines if the highest phase of the three-phase voltages has exceeded limits at the Point Of Regulation. Under-voltage protection senses the average of the three-phase peak sensed voltages at the Point Of Regulation. The shorted Permanent Magnet Generator protection prevents GCU damage in the event of a short to ground on any PMG phase. For this type of fault, a large AC component in the three-phase half-wave rectified PMG input to the voltage regulator would be detected. Over-frequency and under-frequency protection information is sensed from the Permanent Magnet Generator frequency.
A shorted diode in the Generator Rotating Rectifier assembly is detected by sensing the average exciter field current and the average three-phase main generator current. Under most operating conditions, this method of detecting a shorted diode will also sense two open diodes and provide a GCR trip. The shorted diode protection is locked out by under-speed to prevent nuisance trips. In addition, shorted rotating diode protection is locked out during single IDG operation. After automatic load reduction a single Generator with one or two open diodes will be capable of carrying the remaining load without causing a protective trip. A four pole Magnetic Pick-up Unit (MPU) located on the IDG input shaft senses the IDG input speed and provides an output signal proportional to input speed to the GCU under-speed protection.
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CURRENT SENSING General A single-type of Current Transformer Assembly (CTA) is used in various locations of the electrical power system. They operate in conjunction with the IDG's, auxiliary generator, GCU's, and BPCU to provide the required primary current sensing. Function The CTA's provide load current sensing to the GCU's. They are used in open phase, load monitoring, overload protection circuits, and in conjunction with similar current transformers integral to the IDG and auxiliary generator. The BPCU uses CTA current sensing for Tie Bus Differential Protection (DP), external power overload, and external power load monitoring circuits. Mechanical and electrical construction The CT assembly comprises three (3) toroidal current transformer sections in a single package. They are rated at 250 amperes primary current, and have a primary to secondary current ratio of 1000:1. Each transformer consists of 1000 turns of number 28 wire wound on a toroidal core. The CT's are capable of operating over a frequency range from 350 to 440hz.
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BITE DISPLAYS Maintenance BITE General BITE diagnoses failures in the GCU and BPCU circuitry and associated LRUs which include:
This performs a limited end-to-end check of GCUs and BPCU. The BPCU contains a 24-character alphanumeric light emitting diode (LED) display. BIT switch
• • • • • • • •
IDG's APU Generator GCUs BPCU GCBs BTBs APB EPC
The GCU's and BPCU each contain BITE circuitry and nonvolatile memories for the associated generating channel. GCUs communicate system faults and status to the BPCU through the serial data link. BITE for both the GCU and BPCU can be divided into two functional areas: • operational bite • maintenance bite Operational BITE Made up by event driven functions such as protection trips or commands to operate breakers and status monitors which check the BPCU or GCU for known regions of correct operation. For protection trips operational BITE identifies what trip has occurred and attempts to isolate what Line Replaceable Unit (LRU) causes the trip. If an LRU can not be identified, a message which points to an area of the system will aid in determining what caused the trip. For the breaker commands operational BITE looks for a cause and effect relationship. The status monitors look at the circuits within the GCUs and BPCU to insure operation within a known band, if the operation falls outside the band an isolation procedure is started to identify the problem.
The BIT switch retrieves the fault messages stored in NVM that are the result of protection trips. The fault message identifies what protection trip occurred, it then identifies the failed LRU or circuit. If there is no fault data stored for a flight, the message OK will be displayed. BITE displays external power system faults followed by LEFT, RIGHT and APU power system faults. BITE system will pause momentarily between display of each fault. Fault data for previous flight cycles can be retrieved by pushing the BIT switch within a certain time period after the END OF DATA message. Previous flight data can be retrieved for up to seven (7) flight cycles. RESET Switch (guarded) Inhibits interrogation of stored memory by erasing all BITE NVM. PERIODIC TEST Switch (guarded) The PERIODIC TEST switch initiates the MAINTENANCE BITE test of the GCUs and the BPCU. The results are stored in NVM. Contents of the NVM are displayed for that flight after test completion. The NVM contents are the maintenance test results, fault isolation data, messages generated by breaker commands, and messages that are the result of the operational status routines. Note:
The PERIODIC TEST is intended for use at scheduled maintenance checks.
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LOAD SHEDDING Purpose The primary purpose of AC load shedding is to protect an electrical power source (generator or external power) from an existing overload or from an anticipated overload. An overload is anticipated, for example, when a source is lost during operations that would normally use two sources. Another purpose of load shedding is to maximize the pneumatic output of the APU for engine starting when the APU is also being used to supply electrical power to the airplane. Load shedding is accomplished automatically using relays, power breaker and switch position and load shed logic in the BPCU. Electrical power is selectively removed from non-essential loads, such as those powered from the utility buses and galleys. Load Shedding Controlled by the Bus Power Control Unit (BPCU) Certain load sheds are completely controlled by load shed logic in the BPCU. If a generator is lost in the air mode, the BPCU automatically trips Utility Bus Relays (UBR's) and Electrical Load Control Units (ELCU's) to remove non-essential utility bus and galley loads. The purpose of this load shed is to prevent an overload of the remaining generator. In the ground mode, loss of a generator does not automatically cause a load shed. In this mode, one source operation is normal. Another example of load shedding controlled completely by the BPCU is a generator overload not caused by the operation of electric hydraulic pumps. The BPCU automatically removes power to non-essential loads powered by the overloaded source by tripping the appropriate Utility Breakers (UBR’s) and Electrical Load Control Units (ELCU’s). Load Shedding Controlled by Relays Some load shedding is automatically controlled by relays, using switch and breaker positions (APB and GCBs). An example is the engine start load shed. If the APU is being used for both electrical power and pneumatics, an engine start automatically causes load shedding of any utility bus and galley loads powered by the APU generator.
Another example of load shedding controlled by relays, and using switch and breaker positions, is the fuel jettison load shed. If the fuel jettison switch is ON, and only one source is available, then the closed position of both BTB's and load shed relays are used to remove power to additional (other than utility bus and galley loads) non-essential loads. If an Engine is shut down in the air mode, and the Right Utility Bus Relay is open, a Load Shed Relay is energized to remove power from the Ground Service Extension Bus. This is another example of a load shed controlled by relays and, in this case, engine speed cards. Load Shedding Controlled by Relays and the Bus Power Control Unit (BPCU) There is a load shed which is controlled by both the BPCU and relays. On the ground with the APU or external power supplying electrical power to the airplane, if any electric hydraulic pump (other than the right pump) is operating and the source becomes overloaded, then galley loads are automatically shed. This is accomplished using relays and pump switches to sense pump operation. In addition, the BPCU, senses the overload condition. Load Shed Reset In most cases, a load shed is reset automatically when the condition causing the load shed goes away. The exception is a load shed caused by a source overload. This requires a manual reset and is usually accomplished by cycling Utility Bus Switches corresponding to the shed utility bus and galley loads. There are six different ways load shedding can occur.
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BUS POWER CONTROL UNIT (BPCU) Purpose The Bus Power Control Unit (BPCU) controls electrical system external power monitoring and protection, load shedding, tie bus differential protection, autoland power transfer and BITE. Location The BPCU is located in the Main Equipment Center (MEC), rack mounted on the E2-4 shelf. Physical Description/Features The BPCU is packaged in an ARINC 600 3MCU enclosure and weighs 7.7 pounds. The BPCU is held in the tray with an extractor front hold down assembly. Forced air cooling is provided through the rack. The air enters BPCU through a matrix of small openings in the base and is baffled by the chassis before exiting through holes in cover. A BITE display panel and controls are located on the box front panel. Power The power required to operate internal BPCU circuits, external contactors and relays is derived from external power, Airplane Battery Bus and the Right Main DC Bus. Front panel circuit breakers (CB1, CB2 and CB3) are used to isolate power to external circuits. Operation The BPCU contains all of circuitry necessary for: • • • • • •
External Power Monitoring/Protection Load Shedding of the Utility And Galley Buses Tie Bus Differential Protection Control of the External Power Contactor Control of the Ground Handling Relay Control of the Ground Service Relays
In addition, Built-in Test Equipment (BITE) circuitry is included to aid on-aircraft fault isolation for external power. The BPCU utilizes a microprocessor system for control, protection, and BITE functions. The basic software timing cycle is 5 msec which gives sufficient time to perform the longest operating path. The approximate division of time for flight or ground operations is protection (1 msec), control (1 msec), and BITE (3 msec). The information required by the microprocessor comes from peak sensing circuits that sense external power voltage, current, frequency, and phase. Additional inputs are external power and Ground Service Switch inputs, External Power Contactor Auxiliary Contacts, Generator Control Unit (GCU) BITE information. The switch, auxiliary contact, and voltage/current peaks are brought into the microprocessor system through input conditioning circuits. The microprocessor system in turn supplies both digital and analog outputs through output conditioning circuits. A non-volatile memory in the BPCU is used to store external power system passive BITE and fault data. The non-volatile memory is an Electrically Alterable Read Only Memory (EAROM). Digital data communication links between the BPCU and the three generator control units are provided within the BPCU. System status, control, and BITE information is exchanged on these serial data links.
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EXTERNAL POWER COMPONENTS Ground Power Current Transformer (CT) The Current Transformer Assembly (CT) senses external power current flow. It is located in the P34 APU/ External Power Panel and weighs 1.2 lbs. Power feeders pass through the primary windings with a single electrical connector for secondary output. There is a primary to secondary current ratio of 1000:1. External Power Contactor (EPC) The External Power Contactor (EPC) is an electrically held 3 phase contactor that controls use of external ground power. The unit is mounted in the P34 APU/External Power Panel and weighs 3.5 lbs. Nut stud feeder connections are provided for 115 volt AC. A single electrical connector is provided for auxiliary contact/coil circuits. The EPC is a solenoid operated, 3 pole, normally open type contactor. A pull-in coil operates with 15 to 29.5 volts DC, while the holding coil operating voltage is 10 to 29.5 volts DC. Ground Power Transformer Rectifier Unit (TRU) The Ground Power TRU is a solid state device that converts 115 volts AC to 28 volts DC power. The unit is mounted in the P34 APU/External Power Panel and weighs 5 lbs. Input and output connections are made to a terminal strip. Input power is 115 volts AC, 3 phase, 380 - 440hz and output power is 28 volts DC at 20 amperes. Ground Handling Relay The Ground Handling Relay is used to transfer the ground handling bus power source. The relay is a 3 PDT center-off type. The coils are energized by 28 volts DC. The relay is mounted in the P34 APU/External Power Panel. Ground Service Select Relay The Ground Service Select Relay selects the ground service bus ground power source. The relay is 3 PDT type. The coil is energized by a 28 volt DC signal phase power. The relay is mounted in the P34 APU/External Power Panel.
Ground Service Transfer Relay The Ground Service Transfer Relay transfers Ground Service Bus power sources. The relay is a 3 DPT type. The coil is energized by a 28 volt DC signal. The relay is mounted in the P33 panel.
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EXTERNAL POWER QUALITY External Power Available The following is a summary of the conditions involved in producing an external power available signal, AVAIL light on. External ground cart 3 phase, 115/200 volt AC power is applied through pins A, B, C, and N. In the Bus Power Control Unit (BPCU) the overvoltage cutout detector will energize an overvoltage cutout relay if the highest phase voltage exceeds 150 volts rms. Energizing the overvoltage cutout relay prevents components on the internal 28 volt DC bus from being damaged by voltage in excess of 43 volts DC. If no back-up DC is available the BPCU will remain unpowered until the highest phase voltage drops below 150 volts rms. Normal BPCU powering (AC or DC applied to the BPCU) will cause a power-up reset signal. The power-up reset input is the start signal for the micro-processor to begin executing instructions contained in the Read Only Memory (ROM). The external power plug completes the external power interlock circuit through pins E and F. Before the external power contactor is allowed to close, external power quality is sensed by the BPCU. The BPCU checks the external power for Over/Under Voltage (OV, UV), Over/Under Frequency (OF, UF) and phase sequencing. The highest phase voltage is sensed for OV and a 3 phase average is determined for UV. Single phase frequency sensing is used for UF and OF. Two phases are sensed to determine phase sequence. Indications Poor power quality inhibits external power contactor closure. For good quality power the external power AVAIL (P5 panel), AC CONNECTED and NOT IN USE (P30 panel) lights are illuminated. Maintenance Tip If the Interlock Fuses between pins E and F are blown, external power cannot be applied to the airplane. Also, there will be no AVAIL light on in the Flight Deck or External Power Panel. These fuses are located in the MEC on the P34 Panel.
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EXTERNAL POWER PROTECTION General
OV protection determines if the highest phase of the three phase voltages at the EPC terminals has exceeded limits. UV protection senses the average of the three phase voltages at the EPC terminals.
The BPCU protection functions monitor external power parameters including current, voltage, frequency, and tie bus differential current. These monitored functions, along with lockout signals from the GCU's, work to prevent or limit damage to the generating system, loads and the external power sources from out-of-limits power quality or fault conditions.
External power OV cutout protection operates to open an internal BPCU relay located between the external power input and BPCU power supplies when an OV condition exists.
Inputs The BPCU receives three phase AC power through circuit breaker C320 EXT PWR BPCU to perform voltage, frequency, and phase sequence protective functions. Current transformer assemblies T112 L BUS TIE DPCT, T113 R BUS TIE DPCT, T115 APU TIE BUS DPCT, and T116 EXT PWR TIE BUS DPCT monitor current flow information for tie bus differential fault protection sensing. The T122 GND PWR CURRENT XFMR supplies current flow data for detecting open phase, overcurrent, and overload faults. Protective Functions The phase sequence protection prevents EPC closure if the voltage phase sequence at the receptacle side of the EPC is not A-B-C. Phase A and B voltages are sensed. Tie bus differential protection isolates any short circuit fault on the external power feeder or tie bus with a minimum interruption of power. The tie bus differential protection trip times are carefully coordinated with the differential protection time delays in the generating channel. Overfrequency (OF) and Underfrequency (UF) protection information is sensed on phase A at the External Power (EP) receptacle side of EPC. Overcurrent (OC) protection operates in conjunction with a current transformer located on the EP receptacle side of the EPC. The BPCU monitors external power overload current via the ground power current transformer. In the event of an external power source overload the appropriate Electrical Load Control Units (ELCU) and Utility Bus Relays (UBR) are shed in sequence and after the time delays shown in load shedding section.
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GROUND SERVICE SYSTEM General The Ground Service Bus (GSB) is used for both ground and flight operation. There are three possible power sources for the GSB: • Right Main AC Bus • External power • APU Components The components associated with the GSB are the BPCU in the MEC, Ground service switch on Main Deck Door Panel, and one Ground Service Transfer Relay (GSTR). When energized the relay provides a path for APU or external power to power the GSB. When de-energized the relay allows Right main AC bus to power the GSB. One Ground Service Select Relay (GSSR) when de-energized external power is selected or when energized APU power is selected. Right Main AC Bus Power With the Right Main AC bus powered, the GSTR is de-energized allowing the Right Main AC bus to power the GSB. External Power For external power to power the ground service bus the BPCU checks for the following conditions; • Ground Service Switch pressed if external power available with no faults • Right main bus is not powered. To determine this, the BPCU receives discretes from auxiliary contacts in the GCB and BTBs • Transfer relay not energized When the above conditions are met the BPCU sets a latch that energizes the GSTR and turns on the light in the ground service switch. This latch is reset and the GSTR relay de-energized when; • An external power fault occurs • Right main bus is powered
• Cycling the GS switch on the ground • Loss of external power • Power up of the BPCU APU Power For APU to power the ground service bus the BPCU checks that the following conditions are true: • Ground service switch pressed or • APU power available in air mode (no power on the Right Main Bus) This logic allows the APU to power the ground service bus in flight if the right main bus is locked out. When the above conditions are met the BPCU sets a latch that energizes the GSTR and turns on the light in the ground service switch. This latch is reset and the GSTR de-energized when: • • • •
Right Main Bus is powered Cycling the GS switch on the ground Loss of APU available Power up of the BPCU
To apply APU power to the GSB the Ground Service Select Relay (GSSR) must also be energized. To accomplish this the BPCU checks for external power not being available. APU Power APU available comes to the BPCU over a digital bus from the APU GCU. It indicates that the voltage is correct and APU speed is greater than 95%. When these conditions are met the BPCU energizes the GSTR allowing the APU generator to power the GSB. With the GSSR and GSTR energized (APU powering the GSB) a new external power available signal is locked out and APU power is maintained on the GSB.
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GROUND HANDLING SYSTEM General The Ground Handling Bus (GHB) is used for ground operations and can only be powered on the ground. The bus is powered by either external power or the APU generator. External power has priority if both are available. The BPCU controls the application of power to the GHB. External Ground Handling Power The BPCU energizes the GHR to the external power position when any of the following are true: • EXT PWR is available without faults • APU power avail, in air and Right Main Bus not powered This insures that when the APU is powering the ground service bus in the air that the ground handling bus can not be powered. The external power fault protection latch is reset to zero on initial BPCU power up when no faults are present. With no faults and external power available the BPCU energizes the Ground Handling Relay to select external power to power the Ground Handling Bus. If the fault protection module detects any one of the following the fault latch is set and external power is removed from the Ground Handling Bus: • • • • • •
Open Phase (sensed by CT) Over current (sensed by CT) Differential fault (sensed by CT) Internal failure of BPCU Over/Under frequency Over/Under voltage
A reset can be accomplished by: • Cycling the GS switch on the ground • Resetting the External Power Plug • Power up of the BPCU
APU Ground Handling Power APU generator available and on ground are received by the BPCU over a digital data link from the APU GCU. The AVAIL signal indicates no faults, Generator Control Relay (GCR) closed and APU speed greater than 95%. When external power is not available, APU generator power is available and on the ground, the BPCU energizes the Ground Handling Relay to select APU power.
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DC POWER GENERATION Purpose The DC power system is provided on the 767 airplane to supply loads requiring DC power. System Description The main DC system is a 2-wire system using the airframe structure as the ground return circuit. Two main distribution buses, located in the P6 panel, supply essential and non-essential loads. Transformer Rectifier Units (TRU), energized by the main AC buses, separately power each Main DC bus. The battery/battery charger systems consist of a 24 volt vented nickel-cadmium battery and a separate dedicated battery charger to recharge and maintain the battery at its full state of charge. A standby power system is provided to supply 28 volt DC and single phase 115 volt AC power to essential instrument, communication, and navigation equipment in the event of complete loss of primary AC power. The standby system also serves as an independent source for the autoland system center channel. General Component Locations The TRU's, Main Battery/Battery Charger system, and Static Inverter are located in the Main Equipment Center, E 3 rack. A second separate Battery/ Battery Charger system is located in the aft equipment center, E6. General Subsystem Features The TRU's normally operate isolated to supply there respective load buses. In addition, under normal system operation, the Battery Bus, DC Standby Bus, and the Center DC Bus are supplied from the left 28 volt DC Bus. A DC Tie Bus and automatic operating DC Tie Control Unit allows a single TRU to supply both Main DC Buses. Battery charging is constant current and temperature compensated to prevent thermal runaway. A temperature sensing device and a thermal switch, both
integral to the battery, provide temperature sensing and overtemperature protection signals for charger control and deactivation. The second Battery/ Battery Charger system is dedicated to supply DC power to start the Auxiliary Power Unit (APU). The static inverter converts DC power to single phase AC power for the AC Standby Bus. Two switches located on the P5 panel control the standby system. The Battery Switch controls Inverter DC input power and the STANDBY POWER rotary switch controls Auto/Manual standby modes. The DC system status information is displayed on EICAS and control panel CAUTION lights.
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TRANSFORMER RECTIFIER SYSTEM Transformer Rectifier (TRU) The TRUs are non-regulated AC to DC converters. They convert 115/200 ac, three-phase, 400 Hz power to 28v DC power for main DC systems. Each TRU requires a 115 volt AC input from either the left or right main AC bus. The TRU circuitry employs a wye primary winding and two parallel wye-delta secondary connections, with full-wave rectification of the output through a silicon diode bridge network. The pulsating DC from the rectifier is smoothed by the output LC filter to reduce ripple. The input LC filter provides EMI suppression. The three-phase input wiring to each TRU is protected by a 3 phase thermal circuit breaker. The DC output feeder is adequately sized to carry DC fault currents up to a level that causes the 3 phase input thermal circuit breaker to trip. A calibrated shunt provides the EICAS computers with signals indicating output current flow. DC Tie Bus and DC Tie Control Unit During normal operation, the two unregulated main TRUs are operated isolated, and each supplies its associated main DC bus. The DC tie bus interconnects the main DC buses through the DC Tie Contactor. This allows DC system operation should either TRU fail. The DC Tie Control Unit (DCTCU) senses the voltage of the left and right main DC buses. When the output of either bus falls to 20 +/-1 volt DC, or lower, for 11.5 +/-1.5 seconds, the solid state switch in the DCTCU latches in the conducting state. This provides a ground to the K108 DC Tie Relay. The DCTCU unlatches when the control power, Battery Bus, to the DCTCU is removed for 600 milliseconds or both voltage sense inputs fall to or below 20 +/ -1 volt dc for 11.5 +/-1.5 seconds. The closure of the DC Bus Tie Relay is inhibited if either left or right Bus Tie Switch is not in AUTO. When K108 is energized a status and maintenance message T-R UNIT is displayed on EICAS. This normally indicates a TRU failure.
Autoland If either the captain's or first officer's Flight Instrument Transfer Bus switches to its alternate power source during autoland, then a ground signal is applied from either instrument bus voltage sensing unit (M1217 or M1079) through K123 center bus isolation relay to energize K108. Note:
Normally auto DC power back-up is isolated during an autoland situation.
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BATTERIES, CHARGING AND TRU LOCATIONS Battery and Charger Locations The Main Battery is located left of the E3 rack and the Main Battery Charger is located on the E3-3 shelf in the main equipment center. The APU battery and charger are located in the E6 rack in the aft equipment center.
Location A Main Battery Shunt is connected on the ground side of the Main Battery. An APU battery shunt is connected on the ground side of the APU Battery Charger. The Main Battery Current Monitor is mounted in the Main Equipment Center.
Battery
Physical Description/Features
The Main Battery is a 40 amp-hour, 20 cell, nickel-cadmium battery rated at a nominal 24 volts DC. The electrolyte is a solution of potassium hydroxide and water. The Cells are assembled in an uncoated stainless steel container with a cover. An Internal Thermal Switch provides overtemperature protection. A Thermistor, thermal sensor, provides the battery charger with battery internal temperature information. The battery is cooled by natural convection. The Main and APU batteries are identical, interchangeable and each weighs 96 lbs.
The Shunts are calibrated resistance elements rated at 150 amp/50 MV. The Main Battery Current flow is sensed by routing the ground side of the Battery Feeder through a hole in the Battery Current Monitor.
Battery Charger The Battery Charger uses nominal 115 volt AC, 3 phase, 400hz power as an input. The Battery Charger has three distinct modes of operation. The charge mode (constant current region) will supply 38 +/-2amps at 20 to 36 volts DC. The Charge Mode, constant voltage region, will supply 0 to 38 +/-2amps at 27.75 volts DC and the TR mode, main charger only, will supply 0 to 64 +/1amps at 27.75 volts DC. The Battery Charger is packaged in a 6 MCU case and weighs 21 lbs. A 12 pin male connector is used for AC input power, control, and sensing. The DC power output connection is a 5/16" negative terminal and a 3/8" positive terminal. The case has convection orifices and both sides are externally finned heat sinks. Both forced air and convection cooling is available. The APU and Main Battery chargers are identical and interchangeable, even though their operation differs. BATTERY SHUNTS AND CURRENT MONITOR The DC Current Shunts input a voltage to EICAS proportional to sensed current flow. The Battery Current Monitor senses current flow into and out of the Battery.
Operation The Battery Current Monitor is energized by the Battery Bus during normal flight operation. During autoland operation the Battery Current Monitor is de-energized. When the Main Battery is discharging greater than 6 amperes a ground signal is provided to illuminate the discharge DISCH light. The signal also activates the MAIN BAT DISCH advisory level EICAS message. Dispatch Deviation • APU Battery or Charger may be INOP or removed providing the APU is not needed. Transformer Rectifier (TRU) The Left and Right Transformer Rectifier Units are on the E3 rack. They weigh 23 pounds.
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MAIN BATTERY CHARGING SYSTEM AC Input The Battery Charger operates with 105 to 122 volts AC, 400hz, 3 phase input voltage. The Ground Service Bus powers the Battery Charger via K115, the Main Battery Charger Relay. The AC input to the charger is removed when k115 is energized. K115 will be energized if either the STBY PWR Switch is positioned to BAT or when the Battery Thermal Switch closes. Battery Charger Charge Mode When the Battery Switch is unlatched, the Main Battery Relay, K104, will be deenergized. This will disconnect the Battery Bus from the Hot Battery Bus. It will also signal the Battery Charger to initiate a constant current battery charge cycle. The constant current charge is limited to 38 amps. The battery charger output voltage rises to about 31 volts DC, the battery temperature compensated voltage limit, continues rising until proportionate overcharge is completed, then drops to 27.75 volts DC. The battery charger then enters the constant voltage portion of the charger mode (still current limited). Battery Charger Transformer-Rectifier (T-R) Mode When the Battery Switch is latched in, relay K104 will be energized. This will connect the Battery Bus to the Hot Battery Bus. The battery charger will be signaled to initiate a charging cycle in the T-R mode. In this mode the output is 27.75 volts DC, constant voltage, at up to 64 amps. This mode of charging maintains battery charge without unnecessary electrolyte loss and is applicable to the main charger installation only. Battery Current Monitor The Battery Current Monitor consists of two Current Sensors which sense the battery discharge and battery charge currents from the Main Battery Cable. With battery discharge greater than 6 +/-1amp, the unit will provide an unlatched ground signal to the EICAS computers and an advisory message MAIN BAT DISCH will be displayed. The DISCH light on the P5 panel will also illuminate.
The Main Battery Shunt provides DC current inputs to the EICAS computers for ELEC/HYD maintenance page displays. It is a calibrated magnate alloy resistance element rated at 150 amp/50 mv. Charge Cycle Initiation Conditions The battery charger will initiate a new charge cycle when one of the following occurs: • AC input power is applied or interrupted and then reapplied • Sensed battery voltage drops below 23 volts DC • The charger is switched from the T-R mode to the charge mode Charger Shut-Down Conditions The battery charger will shut-down under the following conditions: • Input voltage is under 94 volts AC or over 134 volts AC • The battery sense and control cable is not connected (battery interlock) • The battery power connector is disconnected when the charger is energized • Or the battery temperature exceeds 155F (68C), or an internally caused overcurrent condition occurs When a battery interlock or battery overtemperature shut-down occurs an open signal is provided to the EICAS computers and a status and maintenance message MAIN BAT CHGR will be displayed.
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STANDBY POWER SYSTEM General The standby power system operates when the normal electrical power sources do not supply power to the left and right transfer buses. Standby power goes to these buses: • • • •
DC standby bus Battery bus Hot battery bus AC standby bus.
Standby power comes from the hydraulic motor generator or the main battery. Standby power comes from the main battery and the APU battery. Main Battery The main battery supplies 28v dc power to the standby system if the left AC bus does not. To supply power to the standby system, the main battery supplies power to the hot battery bus. The hot battery bus supplies power to the battery bus. The battery bus supplies power to the static inverter, so that the AC standby bus has power. Operation The standby power switch on the P61 overhead maintenance panel has three positions: • OFF • AUTO • BAT
The standby power switch lets you do these functions only on the ground: • De-energize the AC standby bus (OFF position) • Arm the standby system for automatic operation (AUTO position) • Energize the standby buses when AC power is not available (BAT position, when the battery switch is in the ON position) Start a self-check of the DC/standby system (BAT position, when AC power is available).
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STATIC INVERTER General The Static Inverter converts nominal 28 volt DC power to nominal 115 volt, 400hz, single phase AC power. The Inverter supplies selected equipment during normal ground operations, and powers flight critical AC loads during a loss of all other AC power. Physical Characteristics The Static Inverter is located in the Main Equipment Center on E3-2 shelf. The inverter is packaged in a 6 MCU enclosure and weighs 22.5 lbs. Normally the inverter is forced air cooled. During automatic standby operation the unit is cooled by natural convection. All electrical connections are made on the front of the unit. The DC input power connections consist of stud terminals on a terminal block and the AC output power connections are through a 4-pin connector. Electrical characteristics The static inverter is rated at 1000 va (1 kva) for an input voltage range of 18 to 29.5 volts DC. The output is 115 +/-5 volts AC at 400 +/-0.1hz for the entire load range. The inverter will supply 100% of the rated load for 30 minutes and 150% of the rated load for 5 minutes when forced air cooled. The Inverter is capable of supplying full rated load for 30 minutes with natural convection cooling only.
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STANDBY POWER SYSTEM OPERATION Functional Description Normal operation occurs when the STBY POWER Switch on the P5 Overhead panel is in the AUTO position. Standby Bus Power comes from the Main AC and DC buses. The Main Battery Transfer Relay is energized. The Standby Power Relays are de-energized switching power to the Standby Buses. The Bus Off Relays energize, breaking the ground connection to the Standby Bus OFF light and EICAS computers. The Static Inverter receives input power, but supplies no load. If the Left Main AC Bus loses power or an autoland signal is received, the Main Battery Transfer Relay de-energizes. The Main Battery Relay energizes, connecting the Hot Battery Bus to the Standby Bus, through the Standby Power Relay. The AC Standby Transfer Relay is de-energized, connecting the Static Inverter to the AC Standby Bus. If only the Left Main DC Bus loses power, the Main Battery Transfer Relay deenergizes. The Main Battery Relay closes supplying the DC Standby Bus from the Hot Battery Bus. The AC Standby Bus is powered as normal. Turning the STBY POWER Switch to BAT position causes the system to operate as would occur if the Left Main AC Bus lost power. Turning the STBY POWER Switch to OFF position removes power from the Standby Bus. The amber OFF light on P5 overhead comes on. The EICAS computers display a STANDBY BUS OFF message. The Standby Buses will be off if the BAT Switch on the P5 overhead is OFF and the Main Buses lose power. The Standby Buses will also be off if the BAT switch is OFF and an autoland signal is received. The Standby Bus OFF light and STANDBY BUS OFF message will be on under two conditions: • Either standby bus is unpowered • Either the Main Battery Transfer Relay or AC Standby Transfer Relay fails to switch when the STBY POWER switch is in BAT position Standby Power When all Main AC and DC Buses are powered, and the STBY PWR Switch is in AUTO, and the BAT switch is ON, K105 and K113 UNDER VOLTAGE SENSE
relays are energized. The AC Standby Bus is powered from the L 115 volt AC Bus. K106 MAIN BAT XFR Relay energizes and the K104 MAIN BAT Relay is de-energized. The Static Inverter is powered from the L 28 volt DC Bus, but has no load. With loss of power to the L 115 volt AC bus and to the L AC Transfer Bus, HMG not operating, the AC Standby Power Relay, K105 relaxes and the Static Inverter supplies the 115 volt AC Standby Bus. With no power on the L 28 volt DC Bus the Undervoltage Sense Relay, K113 and the Main Battery Transfer Relay, K106, are de-energized. The Main Battery Relay, K104 is energized and the Battery supplies the Static Inverter and the DC Standby Bus. The DISCH light illuminates and MAIN BAT DISCH EICAS advisory message is displayed. BAT Switch OFF When the BAT switch is OFF, released to out position, and the Left Main DC Bus is energized, powering the MASTER DIM & TEST system, the amber OFF light in the Battery Switch is illuminated and the BATTERY OFF EICAS advisory message is displayed. CAT III Autoland Power During autoland the AC and DC Center Bus power sources are transferred when K123 CTR BUS ISOL Relay is energized. The energizing of K123 causes K105 and K106 to relax. The Static Inverter supplies the 115 volt AC Standby Bus while the DC Standby Bus is powered from the Hot Battery Bus. Static Inverter Failure If the Static Inverter output voltage is less than 106 volt AC or greater than 124VAC with the Battery Switch latched ON, then EICAS displays the latched status and maintenance message STBY INVERTER.
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HYDRAULIC MOTOR GENERATOR SYSTEM General
Release of the switch shuts down the HMG system. Loads are transferred back to normal sources and EICAS messages HYD GEN ON and HYD GEN VAL are removed from display.
The Hydraulic Motor Generator System provides a non-time limited backup source after loss of all generator electrical power.
Hydraulic Motor Generator
System Description
The following loads can get power from the Hydraulic Motor Generator:
The Hydraulic Motor Generator (HMG) is located in the left wheel well. The Generator is driven by a Hydraulic Motor supplied from the Center Hydraulic System. An Air-Driven Hydraulic Pump (ADP), supplied by left or right engine bleed air, can pressurize the Center Hydraulic System. A Motor Driven Hydraulic Shutoff Valve provides ON/OFF control for the HMG. Automatic activation of the HMG System occurs with loss of power to both Main AC Buses. A Flow Limiter regulates hydraulic flow to the Trailing Edge Flaps and Leading Edge Slats during HMG operation. Control and protection functions are performed by the Generator Control Unit located in the P65 panel. A momentary test switch on the P61 panel, is provided for system checkout. The HMG System operational status and electrical parameters are monitored by EICAS.
Fire Warning RAT Control Equipment Cooling Hyd. Pump Control Master Warning ADIRU Standby Power Control Spoilers Capt./FO Instruments Flight/Cabin Interphone VOR C/L MMR Standby Engine Ind. Engine Start & Ignition EFIS Symbol Gen. Captains/FO FMCS Captain’s VSI Auto Pressurization L Radio Altimeter Man. Pressurization Fuel Crossfeed Outflow Valve Fuel Shutoff Capt. & Aux Pitot Heat Capt. Panel Flood Lights AOA Probe Heat Wing Anti-ice Eng Tt2 Probe Heat Bleed Valves Cargo Heat Control Rudder Trim HF Communications Probe Heat Indication Flap Position Ind. Eng EEC Discretes Capt. Altimeter Aisle Stand Flood Light Ovhd Pnl/Aisle Stand Lights
Operational Checkout A momentary toggle switch (EQUIP COOL/HYD GEN) on the P61 right side panel initiates system checkout. A complete checkout is accomplished with main buses energized, EICAS operating, pneumatic power available to operate Air Driven Pump and the C1 and C2 AC Electrically Driven Hydraulic Pumps (ACMP) activated. When toggled to the HYD GEN position, the test switch opens the sensing leads to the L and R AC bus off sensing relays to simulate bus loss, and provides a signal to start-up the HMG system. The test switch also deactivates the main battery charger during the test. After the HMG is started and the Captain's Instrument Transfer Bus Relay transfers, a HYD GEN ON (C,S) is displayed on EICAS. If the hydraulic shutoff valve is not fully closed, a HYD GEN VAL (C,S) message appears after a 5 second time delay. The EICAS ELEC/HYD maintenance page displays the AC and DC output voltage and the AC frequency during the checkout test.
Stall Warning Standby Instruments Clocks YSM RDMI Defueling Valves APU Start EADICapt/FO EHSI L DME Atl Gear Extend Gear Indication Antiskid Thrust Reverser VHF Communications Packs Control
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HMG POWER DISTRIBUTION General Operation AC bus transfer relays connect the left and right AC transfer buses and the captain flight instrument transfer bus to the hydraulic motor generator AC output. Two 115/28v ac single-phase auto transformers supply 28v ac loads from he left and right AC transfer buses. A DC contactor connects the hydraulic motor generator DC output to the hot battery bus.
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HMG GENERATOR CONTROL UNIT Purpose The Generator Control Unit (GCU) provides both main generator voltage regulation and control sensing for system operation. Location The GCU is located inside the P65 Hydraulic Generator Power panel. This panel is installed forward of the EICAS E8 rack on the left lower sidewall of the MEC. Physical Description/Features The GCU is a convection-cooled, solid-state unit attached to back of the P65 panel. A single electrical connector allows interface with the Hydraulic Motor Generator. The test connector is used for shop checkout. Power GCU operational power is derived from the HMG Permanent Magnet Generator. Operation The primary operational functions of the unit are: • • • • •
Voltage Regulation Control Field Excitation Undervoltage Underfrequency Protection Application, removal and lockout of the power ready signal to External Bus Transfer Relays • An electrical speed control signal to the Electrohydraulic Servo Valve in response to deviations in generator output frequency
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HYDRAULIC MOTOR GENERATOR CONTROL Control/Operation Sequence With the Left and Right 115 volt AC Buses powered, K858 and K859, L or R AC Bus Off Relays energized, and after a 0.5 second time delay, the K860 HYD GEN Control Relay close coil is energized. The loss of voltage to both Main AC Buses inflight for at least 0.5 seconds energizes the open coil of K860. A Permanent Magnet holds the relay in open position, until the close coil is energized, to prevent power loss on touchdown. Energizing the Open Coil of K860 completes the power ready circuit to external bus transfer relays. K873 Generator Reset Relay sends a reset signal to the Generator Control Unit, K865 HYD GEN ADP CMD Relay applies ground to K684 ADP On Demand Relay to turn on the Air Driven Pump. The V147 HYD MTR GEN Shutoff Valve opens, supplying hydraulic pressure to the HMG. When the shutoff valve is not fully closed, EICAS displays HYD GEN VAL (S,M) message (after 5 second time delay). The constant speed variable displacement motor is controlled electronically by the remotely located GCU, utilizing the generator frequency signal for feedback. When first energized hydraulically the motor is at maximum displacement due to a stroking piston spring. The Electrohydraulic Servo Valve is slightly biased in the maximum displacement direction to prevent destroking before the GCU is energized. As the motor accelerates, the Permanent Magnet Generator (PMG) provides GCU operational power. The PMG frequency is also used as a feedback signal to the GCU speed control module. The frequency feedback signal is compared to a reference frequency and any error is transmitted to the electrohydraulic servo valve to modulate displacement. Electrohydraulic Servo Valve primary components are: • • • •
Torque Motor Jet Pipe Slide Valve Feedback Spring (not shown)
A change in generator load causes a speed change. The speed control module supplies servo power and completes the circuit to either increase or decrease speed coil. Motor displacement increases or decreases causing an increase of decrease in motor speed. When the slide valve feedback spring torque equals the Torque Motor torque, the jet pipe returns to center position stopping flow to the Slide Valve.
The Electrohydraulic Servo Valve maintains Main Generator output frequency at 400 ±2hz under steady-state conditions. In the event of feedback signal or Electrohydraulic Servo Valve failure, a Mechanical Overspeed Governor maintains the frequency at 430 ±10hz.
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HYDRAULIC MOTOR GENERATOR OPERATION General Bus Operation With HMG Operation The Permanent Magnet Generator (PMG) power enters the GCU and is three phase full-wave rectified to produce 28 volt DC power. The power is used by the GCU voltage regulator and sensing circuits. The average of the point of regulation AC voltage is monitored by the voltage regulator for supplying exciter generator field excitation. When Hydraulic Motor Generator (HMG) output voltage and frequency reach the power ready limits of 100 volts AC and 380hz, and K873 Gen. Reset Relay is relaxed, enabling signals are applied to gate 1. The Generator Power Ready Relay closes and DC power is applied to K861and K862. Ground signal removal from the sensing level shift circuit enables the undervoltage and underfrequency trip levels at 104.5 ±1.5 volts AC, (three phase average), and 385 ±5hz. The fault signal path from gate 2 to gate 3 is inhibited. When energized the K861 HYD GEN Power Relay connects the DC Generator output to the Hot Battery Bus and disables K873 GEN RESET relay, energizing the K862. Also, both EICAS Computers receive a DC voltage input, K862 energized, that activates the HYD GEN ON (S,M) message (NVM in air). An undervoltage or underfrequency fault condition that lasts longer than 9 ±1 seconds trips the Generator Power Ready Relay, de-energizing the bus transfer relays. The Generator still receives excitation current. A ground applied to the sensing level shift circuit enables power ready sensing. K873 applies a reset signal automatically for 1.5 seconds after the trip occurs. If the fault condition has not cleared, the generator power ready relay is inhibited from closing by a fault signal from gate 2 through relay contacts to gate 3. If the fault condition has cleared, the 1.5 second reset signal removes lockout and after K873 relaxes the Voltage Regulator is enabled. The Generator Power Ready Relay closes after power ready limits are reached. Bus Transfer Relays close automatically to re-energize loads. If power to both Main AC Buses is recovered, the HMG shuts down and deenergizes the Bus Transfer Relays.
AC Bus Transfer Relays connect the Left and Right AC Transfer buses and the Captain's Flight Instrument Transfer Bus to the HMG AC output. Two 115/28 volt AC single phase Auto Transformers supply 28 volt AC loads from the Left and Right AC Transfer Buses. A DC contactor connects the HMG DC output to the Hot Battery Bus.
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ELECTRICAL MAINTENANCE PAGE EICAS DC Displays The DC current shunts send a voltage to EICAS proportional to sensed current flow. The DC bus voltage inputs to EICAS are from the appropriate DC bus. The left EICAS computer monitors the APU battery bus. The right EICAS computer monitors the hydraulic motor generator DC output. When the standby power switch is selected to the battery position, EICAS shows main and APU battery voltages in DC-V positions. The current and voltage indications show on the EICAS ELEC/HYD maintenance page in digital readouts. The DC voltage range is from 0 to 40 volts. The DC current range is 0 to +/- 150 amperes.
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