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- 13 main distribution components- power relays (swicthing)
- circuit breakers (safety)
- current transformer (measuring) - 2Power relays2 types; Contactors and breakers
- they swicth 3 phase AC power to distribution system - 3AC power relays made up of- 3 high power main contacts (electromagnet)
- several aux contacts for; monitoring/indication, regualtion and protection - 4Contactors- electromagnet operating
device with an armeture and coil
- current through coil to induce magnetic field
- this moves the contacts and armeture in place. - 5Breakers- electromagnetic operating device with armeture and coil
- short pulse of current to close contacts
- a permenant magnet usually fixes this in place
- but a second pulse of current flows in opposite direction to weaken the magnetic field - 6adv of breakers over contactors- breaker coil can be smaller as no current is flowing to keep it in place. (less heat)
- breaker remains closed when no power available (due to permenant magnet) - 7Fuses and circuit breakers- both prevent overheat due to a short circuit
- short circuits create high current and heat
- so they prevent overheat by not allowing current to flow if heat is greater than the allownace of that wires cross section.
- so a CB or fuse is fitted where wires cross sections are reduced. - 8Fuses- used in high current devices
- easiest method to prevent over current
- has metal strip smaller x-section than what its protecting
- these metal strips melt when a component gets to hot to "short" the circuit.
- the fault has to be rectified and blown fuse replaced. (maybe spares on a/c) - 9advs of Circuit Breakers over fuses- reset quickly
- can be used as on/off switches
- can be used for fault detecting or deenergising components for maintenance activities. - 10CB locations- near what its protecting to keep wire length to a minimum
- only CB's protecting essential loads are within reach of pilot.
- protecting bus connections and large loads = in the electric bay (nose)
- protecting avionic systems = in the cockpit - 11CB's Funtion- prevent overheat by short circuit
- operate using thermosensitive devices
- uses a bi-metalic strip which is connected between two terminals on the CB
- when it heats the strip bends and triggers a release mechanism
- a knob pops out with a white band on it. this can be pushed back in via a spring mechanism - 12CB function cont.- current rating is labelled on the face of the knob
- rating = 0.5A to 125A
- time taken to release a CB depends on how much current was used and the type of strip (fast strip or slow strip) - 13CB release time cont.dependant on amount of current and type of strip.
eg. if current rating exceeds by double
- 9 seconds for fast type
- 30 seconds for slow type - 14CB reset- cant reset while strips bent
- needs a cool down period of approx 2 mins is needed.
- can only be reset once fault has been identified and rectified - 15Aircraft CB's- all trip free type
- this type trips an overloaded circuit even if knob is stuck in.
- some have coloured collars for ease of use and identification.
orange - for abnormal events
grey - for ground maintenance - 16Aircraft CB cont. (clips and tags)- red saftey clips; prevent being closed, when system isnt allowed to operate
- red safety tags; used during ground maint. tells people it shouldnt be closed due to current maintenance. - 17CB monitoring- green knobs for essential systems
- connected to a monitoring system
- info displayed on ECAM
- this details a caution message and the CB name and location. - 18Electronic CB- used for currents up to 15A
- called "solid state power controller"
- has a back up fuse in case of failure
- operated in cockpit by soft keys ( a password will be required)
- they have electronic safety tags set. - 19advs of electronic CB's- saves weight
- saves cockpit space
- trip values can be easily changed due to software change - 20Remote control CB's- fitted next to the consumer in equipment bays rather than in cabin or cockpit
- saves wire weight and space in cabin/cockpit - 21RCCB's operation- bi-metallic opens due to excessive current
- logic controller contact and aux contact to open
- indicator shows when tripped
- some have small controll CB installed in cockpit (opens when RCCB opens)
- RCCB can reset when control CB is reset - 22Programmable RCCB- These monitor current with built in current transformers or hall sensors.
- values sent to a computing device.
- contacts are opened if excessive current is measured. - 23Current transformerGCU needs to see output parametres from distributon so it can; control, protect and indicate.
current transformers measure current of AC current.
- CT's have a hole per phase (3 phases 3 holes) - 24CT construction- iron core around CT hole, core holds a coil of up to 1000 turns
- primary winding in the hole (measured)
- secondary winding outside the hole (1000 turns)
- current on secondary if current on primary.
- amount depends on the ratio of turns between the windings - 25Transformers equations.current in 2nd windings causes magnetic feild in opposite direction.
current1 x voltage1 = current2 x voltage2
or
current1/current2 = voltage1/voltage2 - 26CT cont.- Damaged if secondary windings are opened during normal operation(disconnected from GCU)
-this is because theres no magnetic field to oppose the primarys MF.
- must never be opened in a powered circuit. - 27Shunt Resistor- measures DC current
- fitted in line with current carrying line
- current flowing through shunt causes a small voltage drop that is measured
- Disadv; restricts main current flow - 28Hall Sensor- hall effect sensor used to overcome disadvantage of shunt
- measures magnetic field of a DC current
- crystal in the hall sensor supplied with a small stable current
- Main Dc field influences this crystal at 90 degrees.
- moving charges deflect to one side of the sensor
- sall voltage generated proportional to main DC current. - 29Integrated drive generator- where CSD (constant speed drive) and brushless generator are in the same housing
- oil is used by IDG to; lubricate, cool and during CSG operation.
- oil preffered over air as it has a better cooling effect. they can therefore be smaller and lighter. - 303 types of generators for cooling- Emergency Gen; use oil from hydraulic motors that are driving it.
- APU Gen; uses APU oil
- Variable Freq Gen; have their own oil circuit for cooling - 31Using air to cool generators- some use air if oil not practicable
- mainly older aircraft with separate constant speed drives and generators, and some APU generators have this.
- cooling air taken from engines or APU and is available while running the generators. - 32oil and air cooling.oil cooling gens have higher load current limit than air coolers.
some air cooled APU gens have lower load current limit while on the ground than during flight. - 33Generator Connections2 types; Conventional and terminal blocks
- 34Conventional connectors- used for low current connections such as exciter and PMG
- 35Terminal blocks- connects the generator feeder lines
- consists of 4 bolts , 1 for each phase and 1 for the neutral line.
- bolts all same size
- correct bolt needs to connect to correct phase;
A - T1
B - T2
C - T3
Neutral - N
colour coding may be used - 36Static inverters- consists of a transformer and a switch
- converts DC to AC
- no moving parts
- needed when AC power is needed but you only have DC
- some a/c use them during towing when only battery is available - 37Static inverter operation- Switch up - current flows through upper part of the primary winding of transformer
- Switch down - current flows through the lower part of the primary winding of transformer
This switching causes a change in direction and creates a magnetic field and induces an AC voltage - 38Static inverters on Aircraft2 types; Filter Network (placed in output circuit) and Solid state switches (controlled by a beats generator to control output)
- 39Constant Speed Drive (CDS)- if there was no CDS the generators would rotate dependant on throttle position and would not be constant. Aircraft require a constant 115v 400Hz to operate correctly.
- 40CDS cont.a typical generator with 2 pole pairs needs a constant 12000rpm to give 400Hz output. to maintain this;
at low speeds the CDS needs to increase = Overdrive
at high speeds the CDS needs to decrease = Underdrive
where input speed equals output speed = Straight drive - 41CDS further cont.- doesn't stay in straight drive very long due to it leading to an overheat if left in this state.
- usually achieves straight drive during acceleration or deceleration but doesn't stay there long.
- During cruise... Aircraft is in underdrive operation
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- Fichas sobre Sin título, creado por Aiden Grocock el 12/12/2017.
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- Aiden Grocock
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