Aircraft Operations Manual
EMB-110
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ELECTRICAL
GENERAL DESCRIPTION
The electrical system of the EMB-110 consists of a DC electrical Power System, AC
Electrical Power System, Lighting System, Warning and Alarm Systems.
The DC Electrical Power System provides information regarding DC power
generation and supply. Two engine-driven starter-generators supply the DC power
system during normal operation. During engine starting either the battery or an
external power source feeds the starter-generators to start the engines.
The AC power is supplied to the system by two static inverters: inverter N° 1 and
inverter N° 2. During normal operation the inverter N° 1 supplies AC power to the
system while inverter N° 2 works as stand-by for N° 1, which is automatically
engaged in the circuit should N° 1 inverter stop to operate. The Exterior lights consist
of navigation and anti-collision lights, landing and taxi lights, landing gear and wing
inspection lights. The Interior lights consist of panel lights, cockpit lights, utility lights,
passenger or cargo compartment flood lights, passenger reading, door and
emergency exit lights, baggage compartment and hydraulic compartment lights and
floor spar light.
Alarm System provides information regarding the multiple alarm systems, door ajar
warning, stall warning and passenger warning.
Miscellaneous Systems provides information regarding the windshield wipers.
CIRCUIT-BREAKERS
Except for the circuit breaker located in the electrical rack all other circuit-breakers
are for protection of the AC and DC electrical systems, and located on two circuit
breaker panels named: Right panel and Left panel being placed respectively on the
right and left sides of the cockpit. The circuit-breakers are of the “trip-free” type and
are distributed on the panels under general titles that refer to the system to which
they belong, also including the name of the specific ‘circuit in which they are
installed.
FUSES
The fuses that protect the electrical system indicators are installed on a panel located
on the aisle way wall of the electrical rack. These fuses can be tested visually, by
means of a yellow lamp existing on the assembly which you will go on when the test
wire is inserted in the holes of the fuse holder covers. Fuses F1, F2, F4 and F5 can
only be tested with at least one generator energized. Fuses F3 and F3 can only be
tested with electrical supply from the aircraft battery or external power source. Fuse
F15 cannot be tested.
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DC ELECTRICAL POWER SYSTEM
During normal operation, DC power is supplied by two engine-driven DC generators.
When generators are inoperative, DC power is supplied by the battery.
DC power is distributed throughout the aircraft by a system consisting of a 28 V DC
MAIN BUS BAR, 28 V DC EMERGENCY BUS BAR and the BATTERY BUS BAR.
An external power source may be used to feed the aircraft while on ground, and in
this case, the generator and the battery are prevented from feeding the bus bar. The
DC external power source should be connected to the receptacle situated on the left
front side of the fuselage.
Should one of the generators fail the other will supply enough power to meet the
aircraft requirements.
BATTERY SYSTEM AND EXTERNAL POWER SOURCE
The battery system and the external power source consist of a lead acid 24 V, 40
A/h, type battery: a “BATTERY MASTER” switch with two diodes; a current sensitive
contactor a protection relay for the external power source an external power
contactor and a receptacle for the DC external power source.
The battery master switch has three positions: “BATTERY”, “OFF” and
“EXTERNAL POWER” and its purpose is to connect either the battery or external
power source to the 28 V DC main bus bar. Two diodes prevent the current from
flowing through the switch in case of reversed polarity. When positioned to
“BATTERY” the battery of the aircraft is connected to the 28 V DC main bus bar by
the current sensitive contactor. If the battery charging current exceeds 350 A, the
current sensitive contactor will open the circuit, disconnecting the battery from the 28
V DC main bus bar.
Positioned to “EXTERNAL POWER” the switch energizes the external power
protection relay. This relay activates the external power contactor, connecting the
external power source to the 28 V DC main bus bar and opens the l circuits of the
generator reverse current relays. In either position “BATTERY” or “EXTERNAL
POWER” the voltammeter indicator located on the overhead panel will indicate that
the 28 V DC main bus bar is energized. With the switch positioned to “OFF”, neither
the battery nor the external power source will be connected to the 28 V DC main bus
bar.
When the “BATTERY VOLTAGE” button is pressed the left voltammeter indicates
battery voltage. Voltage from the external power source can be checked on the right
voltammeter by pressing the “MAIN BUS BAR VOLTAGE” button.
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DC POWER GENERATOR SYSTEM
The DC generator system consists of DC generator, a reverse current relay (RCR), a
generator control unit (GCU), two line protection relays, auxiliary relays, a voltammeter and switch, for each engine.
The starter-generator of each engine works initially as a starter motor when engine
reaches 45% RPM (Ng), it starts to work as a generator independently or combined
with the other generator.
Each generator is capable of continuously supplying 200 A at 28 V DC and is
provided with reverse current over voltage (set at 32 V DC) and current (limited to
250 A) protections. Whenever any of the generators is disabled a light will go on, on
the annunciator panel. With both generators connected to the bus bar, the generator
control units balance power distribution. Two magnetic indicators show when
generators are connected to the bus bar and voltammeters show the voltage and
current in each generator.
Immediately upon completion of the starting cycle, the generator control unit (GCU)
uses the generator residual magnetization to feed its field and rapidly increase its
voltage.
When reaching 27.5 V DC, the voltage regulator circuit starts to control the field
current so as to maintain a steady voltage. Then the voltammeter will indicate the
generator voltage.
Should the generator voltage be higher than that of the main bus bar when the
generator switch is turned on, then the reverse current relay (RCR) will connect the
generators to the bus bar. The magnetic indicator will show the generators ON
condition, and the voltammeter will indicate the voltage and current supplied by the
generator. As the drain on generator current increases, the voltage regulator will
increase the field current so as to keep a constant voltage. If this drain on generator
current exceeds 275 ± 25 A, the generator control unit (GCU) current limiting circuit
will act over the voltage regulator and reduce the generator voltage, to keep the
current at 275 ± 25 A, and not damage the generator.
If by a system failure voltage should exceed 32 ± 0.5 V, the generator control unit
(GCU) over voltage circuit will dc-energize the generator, tripping its field circuit, stop
reverse current relay (RCR) feeding, and the generator will be disconnected from the
bus bar.
If system failure should cause a generator voltage drop, the reverse current relay
(RCR) contacts will open as soon as current flowing from the bus bar to the
generator exceeds 15 A.
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In case of any of the failures described above, the generator warning lights on the
annunciator panel will go on the voltammeter will indicate zero voltage and current.
Setting the generator switch to RESET position, will reset the GCU is and the
generator is connected to the bus bar. If the failure still persists, the anti-cycling relay
will prevent the GCU from being reset and thus the RCR from cycling ON and OFF.
To reset again it is necessary to move the switch to ON or OFF position and move it
back to RESET.
When the two generators are connected to the bus bar both GCUs are
interconnected and the parallel control circuits control the voltage, so as to equally
distribute the load between the generators (2). If in this condition one of the systems
should fail only the faulty generator will be disabled the same occurring in case of
over voltage since the other generator will be working on low field current which will
inhibit the functioning of its over voltage circuit.
DC ELECTRICAL SYSTEM POWER SUPPLY DISTRIBUTION
The 28 V DC main bus bar in the electric rack can be supplied by the generators by
the internal battery or by the DC external power source.
Normal feeding is accomplished by the generators. The main bus bar feeds the main
bus bar of the circuit breaker panels and the emergency bus bar through the
normally closed contacts of the emergency bus bar relay and a 50 A current limiter
when the EMERGENCY BUS BAR switch is positioned to NORMAL.
In case of failure of both generators, the emergency bus bar switch should be
positioned to EMERGENCY. This will de-energize the battery relay, disconnecting
the battery from the main bus bar and, at the same time, connecting the battery to
the emergency bus bar, power supply being limited to only this bus bar. All circuits
supplied by the main bus bar will then be de-energized. The battery bus bar is
located on the right circuit breaker panel and is supplied directly by the battery
through a 50 A current limiter.
The generator control units (GCU) are installed on the back part of the electrical rack
one for each generator. Their purpose is to control the starter-generator during either
the starting cycle or during the DC current generating cycle. Each generator control
unit (GCU) consists of: a field weakening circuit, a speed sensor circuit, a voltage
regulator circuit, a current limiter circuit, a parallel circuit and an over voltage circuit,
tripping relays and an anti-cycling relay.
During starting cycle, the generator control unit (GCU) initially applies the total
voltage from the bus bar onto the starter-generator field. As the armature current
decreases due to the effect of the electromotive force at high speed, the GCU field
weakening circuit decreases the current to the starter-generator field, so as to
maintain the armature current, and thus the torque. When engine speed reaches 45
± 5% RPM (Ng), the speed sensor circuit will end the starting cycle and the startergenerator will begin to operate as a DC generator.
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During DC power generation, the voltage regulator circuit of the generator control
until (GCU) maintains generator voltage at 27.5 ± 1 V DC in all operating conditions.
The current limiter circuit limits the generator current to 250 ± 20 A. The parallel
circuit evenly distributes the power from both generators, when both are operating.
The over voltage circuit will trip the generator control unit (GCU) and de-energize the
generator if voltage exceeds 32 ± 1 V DC. In case of a short-circuit in the line, the
generator control unit (GCU) tripping relays will trip, opening the generator control
unit (GCU) field circuit and the reverse current relay (RCR), causing in addition, the
generator warning light to go on.
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THE AC ELECTRICAL SYSTEM
DESCRIPTION
The AC electrical system consists of two static inverters, two inverter power relays
two 115 V AC sensor relays, one 26 V AC sensor relay, one transfer relay, two
control switches. Depending on the aircraft model, either 600 or 250 VA static
inverters are installed and supplied from the main bus bar, to generate 115 V AC/400
Hz and 26 V AC/400 Hz alternate voltages. During normal operation, the 115 V AC
and 26 V AC bus bars are supplied by inverter n° 1.
When inverter n° 1 is turned off or has failed, inverter n° 2 will supply the bus bars.
Failures in either the 115 V AC or the 26 V AC supplies are indicated on the multiple
alarm panel.
Should inverter n° 1 be off or have failed, the sensing relay will be de-energized and
the transfer relay will be energized and will connect inverter n° 2 to the bus bar.
The 26 V AC sensing relay applies a warning signal when one of the inverters is on,
its 115 V AC sensing relay is energized and the 26 V AC bus bar voltage is out of
limits (18 to 32 V AC).
During normal operation, both “INVERTERS” switches) are positioned to “ON”. The
switches actuate the power relays, which in turn, connect the DC power to the
inverters and the 115 V AC and 26 V AC output to the transfer relay. At the same
time, the switches will energize the inverter warning light on the annunciator panel,
while the 115 V AC sensing relays are not energized. If the inverters are normal, the
sensing relay will be energized and the warning connection will be disengaged.
The transfer relay normally connects inverter n° 1 output to the bus bar.
INVERTERS N° 1 AND N° 2
Both inverters are installed in the bottom of the electrical rack. They are fed by the 28
V DC main bus bar and supply 115 V AC outputs. The 26 V AC output is limited
to150 VA and the 115 V AC output to 100 VA on 250 VA static inverters on aircraft
models equipped with 600 VA static inverters, the 26 V AC output is limited to 125
VA and the 115 V AC output to 475 VA. The inverter will accept an overload of 150%
for five minutes, and will not be damaged by an output short-circuit.
All inverter switches are installed on the overhead panel.
When the switches are positioned to “ON”, the magnetic indicators will align with the
AC bus bar. If one of the inverters or only the 26 V AC output should fail, the
corresponding warning light will go on, on the annunciator panel and the master
caution light will blink.
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LIGHTING SYSTEM
EXTERIOR LIGHTS
The aircraft exterior light switches, installed on the overhead panel comprise off:
Navigation Lights
Two tip lights (red and green) and the tail light (white).
Anti-collision Lights
Two red rotating beacons, each incorporating two highintensity lights, one installed on the tail fin top and the other
on the center of the fuselage bottom.
Strobe Lights
Three identical strobe lights are installed next to each
navigation light. They are used for the same purpose as the
red anti-collision lights; however, they produce a high
intensity blue flash which is visible at a great distance.
Landing Light
Two 450 Watt landing lights are installed in the wing leading
edge.
Taxi Light
A 450 Watt light is installed on the nose landing gear.
Inspection Lights
To illuminate the nacelles, wing leading edges and landing
gear. Some aircraft have inspection lights to illuminate the
horizontal empennage leading edge.
The NAC/LANDING GEAR switch permits energizing the inspection lights which
illuminate the nacelles, the wing leading edges (one on each side of the fuselage),
the main landing gear (one in each nacelle) and the horizontal empennage leading
edge (when installed). It has two positions: ON and OFF.
The NAV, ANTICOLLISION, LANDING and TAXI switches control navigation,
Anti-collision and strobes lights, landing and taxi lights, respectively. The NAV,
LANDING and TAXI switches have two positions: ON and OFF.
The ANTICOLLISION switch has two positions and is used to control the anticollision rotating beacon lights.
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On aircraft equipped with strobe lights this switch has three positions:
OFF, ROTATING and ON. The first position turns off the system, the second controls
the two red anti-collision lights and the third operates the three strobe lights without
turning off the rotating beacons.
CAUTION
• Turn off strobe lights when taxiing in vicinity of other aircraft or during flight through
cloud, fog or haze.
• Anti-collision light should not be operating in actual IFR conditions, especially at
night, since reflected light can produce special disorientation to the pilot.
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INTERIOR LIGHTING
PASS CABIN Switch
Controls cabin general lighting. The switch has three
positions: OFF, PARTIAL and FULL ON.
COCKPIT
Controls energization of a light at the cockpit entrance
permitting to illuminate the cockpit and the electrical rack.
Switch
PANELS
Switch
and ‘PANELS LIGHT



When moved ON permits energizing all the panel lighting
system, which comprises of:
Instrument lights, Overhead and circuit breaker panels.
Trim tab indicator lights.
The PANEL LIGHTS knob sets the brightness control rheostat of instrument
lights, with a sense indicating arrow “DIM” or “BRIGHT”.
In some airplanes, four separate knobs control the light intensity of the
following portions of the panel: pilots, copilots, central panel and overhead and
circuit breaker panels.
In some airplanes when “PANELS” switch is turned ON the “STEERING”.
“BETA” and “GO AROUND” lights decrease the intensity automatically.
Utility Lights
They are installed on the ceiling, above each piloting station. The utility lights
incorporate a switch and an intensity control rheostat, in addition to a red filter
selector. They can be used for focusing a spot in the cabin or, when detached from
their holder, as a portable flash light.
FASTEN SEAT BELTS and NO SMOKING Switches.
The two switches control the illumination of the corresponding placards in the
passenger cabin, to make them visible when the warning is necessary.
Emergency lighting
Adjacent to the engine instruments is a three-position switch that controls the
emergency lighting. On the central position, the system is turned OFF. On the
ON/TEST position (ON position, for airplanes post-mod SB. 110-34-071 or S/N
110.451 and on), the emergency exit lights are illuminated. On the ARM position, the
emergency exit lights will be automatically turned ON in the event of main bus bar
failure.
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On airplanes pre-mod S.D. 110-34-071 this switch controls the emergency exit lights
and the emergency supply to the pilot’s attitude indicator .
Passenger Reading Lights, each passenger has at his disposal an individual
steerable light with switch. The system is fed whenever the main bus bar is
energized.
Door Lights, they are controlled by parallel systems, between the lock micro switches
and the switches next to the doors. Their energization does not depend on the
battery master switch position. The switches have three positions: “OFF” (light is
off) “AUTO” (light turns on when the door is opened) and “ON” (light remains on, if
the main bus bar is energized).
Baggage Compartment Light
The baggage compartment lighting is controlled by an “ON- OFF” switch, installed
next to the lamp.
Hydraulic Compartment Light
The two lights in the hydraulic compartment are controlled by an “ON-OFF” switch
inside the compartment.
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