Embraer E-Jet Electrical System

The electrical system of the Embraer E190 and E190-E2 produces 115 V three-phase AC and DC for the whole aircraft. In normal operation the engines' integrated drive generators (IDG) supply the AC buses, transformer rectifier units (TRU) turn AC into DC, and a hierarchy of essential buses keeps the equipment needed to fly powered after failures. The APU generator and ground power stand in for the IDGs, the batteries back up the DC network, and a ram air turbine (RAT) generator takes over when no AC bus is powered.

The two generations differ in important details. The E190-E2's IDGs are rated at 50 kVA against 40 kVA on the first-generation E190, and the E2 has neither the AC standby bus nor the static inverter that the E1 uses for engine ignition. This article describes the E190 and the E190-E2 and says which one each figure belongs to; the other models are introduced in E-Jet family and flight deck. General principles are covered in electrical power distribution, AC generators, CSD and IDG and aircraft batteries.

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Power sources

The first-generation E190 adds a static inverter, which turns battery DC into AC for the AC standby bus, and a separate fly-by-wire backup battery described below.

AC generation

On the first-generation E190 each IDG is a 40 kVA, 115 V three-phase generator with a hydro-mechanical constant speed drive, controlled by its own generator control unit (GCU). The E190-E2's IDGs are rated at 50 kVA, so its 40 kVA APU generator is smaller than either of them.

On the E190-E2, each AC bus is normally fed by the IDG on its own side. When an IDG is lost, the bus takes the replacement source in a fixed order: the APU generator, then the AC GPU (on the ground only), then the opposite IDG. With the APU generator running in flight, an IDG 1 failure therefore puts AC bus 1 on the APU generator. The RAT plays no part, since it deploys only when no AC bus is powered at all.

On the ground the E190-E2's APU generator also comes before the AC GPU: selecting the APU generator on switches the GPU offline. Source changes on the E190-E2 use the no break power transfer (NBPT): where possible the outgoing and incoming sources are connected in parallel for a few milliseconds, so the transfer happens without a break in power, but they are never left in parallel. After engine start on the first-generation E190, the crew wait 30 s once N2 has stabilised before shutting down the APU or disconnecting the GPU.

On the E190-E2 an IDG can be disconnected but not reconnected in flight. The crew hold the IDG knob in DISC for at least 1 s but less than 3 s, and a disconnected IDG can be reset only on the ground by maintenance. The IDG also disconnects itself if its shaft fails or its temperature becomes excessive.

DC system and batteries

On the E190-E2, three TRUs rated at 300 A each are the normal source of DC, and the batteries are the secondary source. The DC side comprises DC bus 1 and DC bus 2, the DC essential (DC ESS) buses, the hot battery (HOT BATT) buses, the DC ground service bus and the APU START bus.

Battery temperature limits the APU start (see E-Jet engines and APU). With BATT 2 below -20 °C, or with the batteries unavailable, the APU is started from a DC GPU instead, and the cold weather limitations give the same -20 °C minimum battery temperature for the E1 and the E2. At the hot end, an E190-E2 battery at 70 °C or more for 2 s is shown in red with an OVERTEMP warning; the trigger is temperature, not voltage. The E2's electrical synoptic page also shows battery current, which the first-generation page did not.

The first-generation E190 has two further items. The AC standby (AC STBY) bus and its static inverter exist for engine ignition; the E190-E2, whose ignition is powered from DC, has neither. And a separate fly-by-wire backup battery, a lead-acid unit charged from DC ESS bus 3, keeps the elevators and rudder controllable for 15 min when neither normal nor emergency power is available. It has no switches and no EICAS messages, and it cannot power any other bus.

Bus distribution

The buses form a hierarchy. On the E190-E2, AC bus 1 and AC bus 2 are each fed by their own IDG, and IDG 2 normally powers the AC essential (AC ESS) bus. The essential buses, AC ESS and the DC ESS buses, are the ones kept powered after the main sources are lost: in an electrical emergency the E190-E2's emergency sources feed only the "inner circle", the essential buses and the HOT BATT buses, and AC buses 1 and 2 and DC buses 1 and 2 are left unpowered.

Where a load sits shows how long it survives. Some examples from the fuel, hydraulic and flight control systems:

On the ground, the E190-E2's ground service (GND SVC) function powers selected loads from the GPU alone. With the AC GPU available but its power switched off in the cockpit, it supplies only the AC and DC GND SVC buses, which carry items such as the AC outlets, galley jug heaters, sidewall lights and cargo loading lights. The GPU CONNECTED caution appears if an AC or DC GPU is connected and the parking brake is released.

The E190-E2 has three kinds of circuit breaker. The secondary power distribution assemblies (SPDA) use electronic breakers that the crew can reset, a trip giving the REMOTE CB TRIP advisory. The thermal remote breakers in the ICCs can be reset only on the ground by maintenance, and the two cockpit circuit breaker panels hold thermal, non-remote breakers. The SPDA load-shedding list contains the galleys and the right windshield heating (see E-Jet ice and rain protection).

At power-up, the electrical built-in test takes about 2 min on the E190-E2 against 3 min on the first generation, and the aircraft must not be moved while it runs.

Emergency power and the RAT

On the E190-E2 the ram air turbine (RAT) deploys automatically when no AC bus is powered, and the ELEC EMERGENCY warning appears. The emergency sources then feed only the inner circle. Losing both IDGs does not trigger it while the APU generator is powering the AC buses.

On the E190-E2, hydraulic system 3, which supplies flight controls, is part of the emergency load: in an electrical emergency its electric pump ACMP 3A is powered from the AC ESS bus. From the start of RAT deployment until that pump is running again, the system 3 accumulator supplies the flight controls, and an unloader valve and a flow limiter valve keep the pump from overloading the RAT (see E-Jet hydraulic system). The design differs from the A320, whose RAT pressurises the blue hydraulic system, which then drives the emergency generator.

On the first-generation E190, the sequence depends on airspeed:

• Before the RAT generator is online, the batteries supply the DC ESS buses directly and the AC STBY bus through the inverter.
• At or above 130 kt, the RAT generator powers the AC ESS bus, the AC STBY bus and DC ESS buses 1, 2 and 3.
• Below 130 kt, the RAT supplies only the AC ESS bus, and the batteries take over the DC ESS buses and the AC STBY bus. As the speed falls further, load is shed, and in the end the AC ESS bus is lost too.

Other systems run at reduced capability. On the first-generation E190 the slats and flaps move at half rate and only channel 2 of the horizontal stabiliser actuator control electronics (HS-ACE) is enabled, with manual and autopilot pitch trim at half rate (see E-Jet flight controls). On the E190-E2, DU 1 and DU 4, the PFD positions, remain available.

Abnormal procedures

The ELEC EMERGENCY procedure in the QRH prepares a flaps 3 landing, with a higher approach speed and no autoland, on the first-generation E190 and on the E190-E2.

When several electrical messages appear together on the E190-E2, they are dealt with in a set order: warnings first, then AC cautions, DC cautions, DAU, MAU and avionics cautions, SPDA advisories, and finally any other cautions.

On the E190-E2 the other common cases follow from the protections above. An IDG lost in flight is replaced by the next source in the priority order, without crew action; an IDG overheat at 168 ± 5 °C needs the crew to disconnect it; and after a REMOTE CB TRIP advisory the crew may reset the SPDA breaker, whereas a tripped ICC breaker waits for maintenance on the ground. For comparison, see the 737 electrical system.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.