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151/23/005 > P&D > Flashcards

P&D Flashcards

1
Q

When did The health and safety at work act 1874 become a law?

A

1st April 1990

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2
Q

what does regulation 4 cover?

A

quality of system construction suitability, quality and maintance and use of systems

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3
Q

what does regulation 5 cover?

A

to ensure that design specs are not exceeded in use

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4
Q

what does regulation 8 cover?

A

requirements for earthing of equipment and circuits

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5
Q

what does regulation 11 cover?

A

excess current protection in electrical circuits

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6
Q

what does regulation 13 cover?

A

precaution for working on ‘Dead’ equipment

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7
Q

what does regulation 14 cover?

A

when and when not to work in or near ‘live’ conductors

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8
Q

what does regulation 15 cover?

A

requirements for adequate working space, access and lighting

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9
Q

what is the definition of an electric shock?

A

the involuntary reaction of the human body caused by conducting an electrical current

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10
Q

what are the basic three causes of an electrical shock?

A
  • equipment failure- equipment casing becomes live and lethal
  • human failure- individual touches an exposed live terminal
  • combination of both- human failure causes equipment failure
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11
Q

what are the main causes of accidents?

A
  • pre-occupation
  • ignorance or lack of skill
  • over familiarity
  • laziness
  • fatigue
  • physical hazards
  • ‘horseplay’
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12
Q

what are the requirements for working on live equipment?

A
  • only to be done if Engineering officer is satisfied there is to alternative
  • personnel to be trained and briefed
  • a safety number is to be present, trained on shock procedures
  • avoid all direct contact with any circuit/component
  • ensure that no direct contact is made with any earthed metal
  • use insulated tools
  • take care with equipment to not short the circuit
  • wear ‘ Electrical workers gloves’
  • wear insulated shoes/stand on rubber mat
  • work on ‘live’ equipment not to go ahead is violent movement on ship
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13
Q

when work is carried out on ‘Dead’ equipment, how do you make sure is stays dead?

A

LOTO

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14
Q

what is the definition of high voltage?

A

where working voltage exceeds 1000 volts AC (RMS) or 1500 volts DC measured between 2 points

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15
Q

list all personnel involved when working with HV systems

A
  • Authorising Engineer- MEO
  • Authorised person- SR (WO2/CPO)
  • Authorised person in Control - (CPO)
  • Competent person
  • HV Aware
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16
Q

list all documentation involved when working on a HV System

A
  • Permit to work
  • Sanction foe test
  • limitation of access
  • switching schedule
  • isolation certificate
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17
Q

list some examples pf dangerous compartments on RN Ships

A

-paint store/inflame store
- aircraft hangers/ vehicle decks
- lox/gox plants
- certain workshops
- fuel stowage’s

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18
Q

what are the requirements for electrical installations in dangerous compartments?

A
  • cable runs, not to be run through compartment unless unavoidable. cables to closer than 5 feet to the deck
  • light fittings, must be flame proof
  • portable lighting, low voltage
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19
Q

what are the safety precautions for taking equipemnt in electrical compartments?

A
  • flameproof equipment is not to be opened up unless double pole switches are opened
  • no high voltage test equipment is to be taken into the test compartment
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20
Q

how does the ingress coding letters work?

A

first numeral - 0-6 indicate the level of protection of persons and resistances to soild objects
second numeral - 0-6 indicate the level of protection against the ingress of water

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21
Q

what are the performance requirements for voltage in a generator ?

A
  • rated voltage 450 volts
  • variations under balanced loads less than 1%
  • steady state voltage between 57hz and 63hz to be within 1% of 450 v
  • transient voltage variation, max 7.5% for 25% load going off and and 15% M load going on
    -time recovery to within 1% of the final voltage
  • harmonic content line voltage at no load 2% of nominal
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22
Q

what are the performance requirements for frequency in a generator?

A
  • nominal frequency 60 Hz
  • steady state frequency variation from no load load full to load
  • transient frequency variation 25% load chnages +or - 2.5% for mechanical governors, - or + 1.5.5 for ele
  • time recovary for transients within 1% for mechanical governos and 0.2% for electric governors is 2 secs
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23
Q

state and explain the formula for generator frequency output

A

f=np/60
f= frequency
p= no of pole pairs
n= prime mover speed

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24
Q

list the Advantages of brushless generators

A
  • smaller in size
  • less maintenance
  • no rubbing parts
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25
Q

what is the disadvantage of a brushless generator?

A

slower in response than the conventional generator to load changes

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26
Q

What will happen in a open circuit diode condition?

A
  • gen voltage output will fall and AVR will compensate
  • resulting in extra strain on the remaining diodes
  • gen should be offloaded within 30 mins
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27
Q

what will happen in a short circuit diode condition?

A
  • will cause an overload of AC exciter resulting in further damage
  • gen voltage output will collapse due to loss of field current in exciter
  • supply breaker should open, under voltage protection
  • danger of over heating
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28
Q

explain how cooling to generators is provided

A
  • closed air circuit water cooler
  • achieved by a shaft mounted impeller, circulating internal air across the cooler tube stack and gen continuously
  • gen temp is maintained constant by adjustments of the cooling water flow rate
  • the cold air temp should be maintained 5 degrees above ambient
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29
Q

in the vent of the air cooler of a gen failure, what can be done to keep it cool?

A

the vent flaps may be opened to allow free flow of compartment air across the gen

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30
Q

what daily checks are done on a generator?

A
  • bearings and casing not overheating
  • gen air temp with in limits
  • no sign of leaking of air cooler
  • no undue noise or vibration
  • no apparent defects at permanent magnet generator drive belt
  • no diode failure warning light
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31
Q

what monthly checks are to be done on a generator?

A
  • carry out VA and record readings
  • condition monitor all bearings
  • check for water in generator
  • clean vent grills and emergency cooling flaps
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32
Q

explain the function of an AVR

A
  • maintain a constant voltage at the terminals of the ships main gen, to - or + 1% of nominal voltage
  • load range from 0-full when gradually applied to the gen
  • restore terminal voltage to within 1% of set voltage
  • voltage changes not exceed 15% when load increased, 7.5% when decreased
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33
Q

what are the reason for the specific characteristics of the AVR response curve?

A
  • reduces short circuit voltages
  • prevents damage
  • prevents damage to mechanical parts
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34
Q

what are the nine plug in units for an AVR set up? explain what they do.

A

MK168P low voltage power supply - provides stabilized and regulated +24 VDC and +15/-14 vDC for all low voltage applications within the AVR

MK28 CU Output control unit - provides the firing pulses for the MOSFETS

MK169P output power amplifier- the 4 MOSFETS array for excitation field current control

MK41 MU monitoring unit - to ensure all parameters are within tolerance

MK1 PN - protection unit- providing the system shut down facility should any fault condition arise

mk17 filter unit- improves HF 160 hz supply and incorporates the 168 low power unit for DC power rail supplies
mk1 EC excitation contactor- to connect the improved 160 Hz supply to the MOSFETS providing auto excitation control from the MK169P 24 VDC output
MK 1 UF interface unit - provides various voltages and frequency signals for several modules within the AVR
MK1 CN Compensation unit - compare the actual volts against the desired volts to produce an error output

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35
Q

explain the brushless generator start up sequence

A

-prime mover comes to speed
-rotating the shaft
- belt/shaftdriven PMG supplies 115v 1600hz to AVR
- Avr supplies variable DC supply to AC exciter
- AC EMF induced in Exciter rotor
- AC converted to DC by rotating rectifier and supplied to main gen rotor
- rotating mag field created around main gen rotor
- EMF induced in main gen stator
- sample fed to AVR to regulate the excitation voltgae

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36
Q

explain how voltage regulation happens while a generator is running

A
  • load applied to gen
  • terminal voltage drops
  • volt drop sensed at comparator
  • error signal increases
  • MOSFETS output increases
  • DC level output increases
  • AC EMF to rectifier increases
  • DC to main rotor windings increases
  • main rotor winding magnetic flux increases
  • induced EMF in the stator windings increases
  • terminal voltage rises
  • increased magnetic flux with in the generator gives rise to greater internal magnetic resistance which slows machine down
  • machine slows down governor will increase prime mover speed to maintain correct frequency
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37
Q

what dose the MK 1 protection unit provide protection for ?

A
  • over voltage
  • under voltage
  • parallel gen fault
  • open circuit rotating diode failure
  • short circuit rotating diode failure
  • low frequency or speed
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38
Q

what two conditions must ships generators still maintain terminal voltage within certain limits?

A

steady load - must be maintinaed within + or - 1% of nominal output
transient load - increase load - or + 15 % and decrease load + or - 7.5%, AVR must recover to within 1% in 1 sec

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39
Q

when would generator load trials be necessary?

A
  • if prime mover, AVR, exciter, generator rotor or start has been changed, had major repairs or had a huge over haul
  • after modification to switchboard wiring
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40
Q

what are the requirements needed to carry out load test?

A
  • a load barge or dockside load test facility
  • a high speed pen recorder, laptop computer or new data acquisition recorder
  • the generator isolated from the distribution system
  • trails from D346
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41
Q

What are the different types of tests in generator trails ?

A
  • insulation resistance hot and cold
  • heat run
  • speed control
  • voltage control
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42
Q

explain how insulation resistance hot and cold tests are done on generators

A
  • min insulation value of 1 Megaohms for stator, field coils of exciter and armature
  • 0.1 megaohms is acceptable for rotor gen windings.
  • readings to be taken when generator is still hot on completion of trial
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43
Q

explain how heat run tests are done on generators

A
  • temperature rise test
  • full rated load, specified voltage and speed
  • 6 hours or until temp has been constant for an hour
44
Q

explain how speed control tests on generators

A
  • assess response time of the governor
  • transient test
    • variation to 25% load changes
  • steady state regulation
    • variation ‘No load’ to ‘Full load’
45
Q

explain how voltage control tests are done on generators

A
  • asses the response time of the voltage regulator to changes in load
  • transient state
    • 0 50 and 94 % of normal full load at correct power factor, with additional load called M LOAD. 50 % of FLC is applied
  • steady state
    • load steady 100 75 and 25 % of NFL and at zero load
46
Q

what are the on-board requirements for generated voltage?

A
  • to supply power when and where required
  • the system must be flexible
  • must be able to provide alternative supplies to vital equipment
  • must have a spare capacity
  • must minimise the effects of action damage by maximising the dispersal of important services
  • the generator and associated switchboard must be close together
  • the system can be controlled from one central point or separated into individual switchboard operations
47
Q

list the type 45 main electrical and propulsion system

A
  • 2xWR21 gas turbines rated at 21.8MW, each connected to 21 MW alternator
  • 2x Wartsilla diesel engines each 2MW, with an alternator each
  • 2x Alstom VDM 25000 Plused width modulated converters, 3 channels 5 phases
  • 2 x 15 phase advanced induction motors, 20 MW
  • 2x 2MW ship service transformers
  • 2x HV Harmonic filters (passive)
  • 2x LV harmonic filter (active)
  • 2x HV switchboards
  • 2x LV switch boards
  • 4x Neutral Earthing Resistors
  • 6x Dynamitic braking resistors
48
Q

what dose a type 45 HV switchboard supply?

A

460 volts
60 hz
3 phase

49
Q

what is harmonic pollution?

A
  • voltage distortion
  • zero crossing noise
  • unbalanced line currents
  • overheating machinery
50
Q

what is the purpose of HV harmonic filters?

A
  • reduce heating effect caused by harmonic distortion
  • provide a power factor correction
51
Q

how are the the harmonic filters cooled?

A
  • cooled by MIDEL fluid being pumped through the centre of the reactor
52
Q

what is MEDEL ?

A

synthetic ester-based transformer fluid

53
Q

what is the NERs earth fault rating?

A

10 amps

54
Q

what is the emergency generator capable of supplying?

A

440 volts
3 phase
60 hz

55
Q

how can an emergency generator be started manually?

A

battery- 2x12 volt batteries
hydraulically- kept de-pressurised and must be pressurised by a hand pump

56
Q

what role of protection do the breakers play in the distribution system ?

A
  • over current protection
  • under voltage protection
  • reverse current protection
  • fault discrimination
  • open and close the circuit safely
  • clear the maximum short circuit fault current safely
57
Q

what are the different types of switchboard breakers? explain their purpose

A
  • supply breakers - connects/disconnects the generator output to the switchboard
  • interconnector breakers- links FWD and AFT switchboards together
  • bus bar linking breakers- links switchboard sections together at the bus bars
  • feeder breakers - provides power to EDC/EPC
  • shore supply breakers - connects the SS/SA connection box, on the upper deck to the switchboard bus-bars
58
Q

what are the four trips fitted to the breaker?

A
  • under voltage
  • over current
  • anti-shock
  • position interlock
59
Q

what are the three different trip levels for a overcurrent unit?

A

L- long-time delay
S- short time delay
I - instantaneous

60
Q

what are the two methods of control supply for SACE Ottomax breaker operation?

A
  • manual-
  • automatic
61
Q

explain how to manually operate the SACE ottomax breaker.

A
  • depress the spring charging handle downward approximately 11 times. once fully charged there will be no resistance to the lever pumping. white flag will now be yellow
  • press ‘I’ button to close breaker
  • action of the breaker closing will charge open springs
  • once the breaker has closed safety devices monitor parameters and trip the breaker when required
62
Q

explain how the SACE ottomax breaker automatically operates

A
  • spring charge is accomplished by a 220v AC single phase motor
  • the motor takes 20 seconds to charge the springs
  • the white flag turns yellow
  • the breaker can now be closed from the local position or remotely
  • closing of the breaker will charge the open springs
  • safety devices will monitor the parameters and trip the breakers as required
63
Q

what are the two sizes that MCCB come in?

A

100 amps
250 amps

64
Q

what are the five safety devices fitted to MCCBs?

A
  • thermal-magnetic trip unit
  • manual trip
  • electro- magnetic trip
  • current limiting fuses
  • residual current devices
65
Q

explain how a thermal magnetic strip works

A

senses the heat resulting from an overload condition and the high current resulting from a short circuit

66
Q

explain how a manual trip works

A

by pressing the PUSH TO TRIP the tripper bar rotates up and to the right this allows the tripper bar to unlock releasing the mechanism

67
Q

when do electro magnetic trips work best?

A

for a short circuit

68
Q

what is an Residual current device RCD?

A

they balance current
they operate when residual current is between 50% and 100%

69
Q

explain how a RCD works

A
  • incoming supply passes through an iron core
  • this acts as a primary winding of a current transformer
  • a secondary winding around the toroid is connected to the trip
  • normal circumstances the phase and current are equal and opposite so no flux therefore no current flows
  • insulation fault occurs and current flows to earth, currents are no longer balanced.
  • flux will be induced therefore current flows to the secondary winding, activating the trip
70
Q

what are the different types of change over switches ?

A
  • hand change-over switch
  • automatic change-over switch
  • remote operated change-over switch
  • fast acting change over switch
71
Q

why are there a limited amount of change over switches on board?

A
  • overloading supply
  • weight
  • cost
72
Q

what precautions need to be taking when operating hand change over switches?

A
  • only operate in an emergency
  • never operate on load
  • ensure remote start is inhabited/not operated during the changeover
  • ensure motor is stopped before operation
73
Q

give examples of equipment/services that are supplied by an HCOS

A
  • fire pumps
  • portable pump
  • ventilation system
74
Q

state how ACOS breakers work

A
  • supply must not be paralleled
  • both N and A supplies are in tolerance, N selected automatically
  • when N falls far enough below its normal value A is Auto selected
  • there is a delay before this occurs to prevent the switch operating on voltage transients
  • when N is restored to normal, it is selected auto
  • there must be a delay between disconnection of one supply and reconnection of the load to another.
75
Q

what equipment is supplied by an ACOS?

A
  • MDF pumps
  • steering motors
  • chilled water pumps
  • weapon systems
76
Q

what equipment do FACOS supply?

A
  • radar electronic support measures
  • two internal communications network nodes
  • combat management systems
  • principal anti-ait missile systems
77
Q

what are the typical routines checks carried out on an ACOS?

A
  • insulation resistance checks
  • earth bonding inspection and testing
  • internal cleaning
  • tightness of connections
  • inspections of relays and contactors
  • timing and functional checks
  • tightness of all connections
  • check contactors and relays
  • drop off and pick up limit test
78
Q

on a type 23 there are two thyristor converters, one for each motor. what are the two DC loads that convert?

A
  • 750 v DC at 2250 amps for the armature circuit
  • 270 v DC at 42.5 amps for the field circuit
79
Q

Harmonic currents can penetrate the power supply what issues dose this cause?

A
  • voltage distortion
  • zero crossing noise
  • unbalanced line currents
  • overheating of machinery
80
Q

what are the reasons for using electrical propulsion?

A
  • economy and environment
  • flexibility of layout
  • load diversity between ships service load and propulsion
  • ease of control and reduced manning
  • low noise and vibration
81
Q

what is the definition of a converted supply ?

A

a converted supply is a supply derived from the main 450v, 60Hz, 3 phase supply, which requires a change in frequency/voltage

82
Q

give some examples of typical converted supplies and equipment

A
  • 24V DC TRU/ batteries/RTRs
  • 50 V DC TRU/batteries/ RTRs
  • 115v 400HZ - SFCs
  • 200 V 200Hz - Aircraft supplies
83
Q

what conditions will the SFC trip, for fault protection

A
  • output voltage exceeds 126.5V ( 10% over- voltage)
  • the power module temperature exceeds 120 degrees
  • the SFC also incorporates a current limiting device which comes into operation when the load current exceeds 10.2 amps (130%)
84
Q

what safety precautions should be incorporated into the design and usage of any compartment being used to maintain/service batteries ?

A
  • adequate ventilation
  • rubberised paint only to be used
  • neutralising agents available
  • eyewash bottles available and in date
  • safety notices to be available and displayed
    -safety equipment to be available
  • notice board for charging times on and off
  • running fresh water
  • lead lined sinks
85
Q

how is corrosion prevented on the ships hull?

A
  • correctly applied paint
  • efficient cathodic protection system
86
Q

how does corrosion occur?

A

two dissimilar metals are immersed in seawater and connected together, a current will flow through the water from the more reactive metal to the less reactive.

87
Q

what is rust?

A

the formation of ferric hydroxide
FE(OH)3

88
Q

what is the zone of cathodic protection?

A
  • 750mV - -850 mV
89
Q

when cathodic protection is over charged what is there risk of?

A

risk of alkali attack
blistering of paint

90
Q

when cathodic protection is under charged what is there risk of?

A

intense corrosion
freely corroding

91
Q

what is checked daily when monitoring the cathodic system?

A

output voltage
ships speed
each reference electrode potential

92
Q

how are monthly cathodic systemchecks done?

A

carried out when ship is stationary, not along side another ship or stopped at sea

hull potential readings are taken using the portable reference electrode lowered to 8 foot below the waterline and held close to the hull

93
Q

what equipment does the emergency generator supply on a type 23?

A
  • 2 of 5 fire pumps
  • gas turbine power turbine cool down pump
  • emergency lighting
  • all sickbay services
  • 5 smoke clearance fans
  • portable pump sockets
  • steering gear via an emergency connection box
94
Q

state four references to aid compliance with electricity at work regulations

A
  • the electricity at work regulations 1989
  • JSP 430 - MOD ship safety management handbook
  • BR 2000/20 - safety considerations and precautions
  • BR 167 - SHE manual
95
Q

with relation to regulation 11, who’s job is it to check on protective devices?

A

ships staff

96
Q

state 5 PPE precautions that are required when working the batteries

A
  • PVC Gauntlets
  • PVC apron, white
  • rubber boots
  • goggles
  • overalls with sleeves rolled down
97
Q

what equation would you use to find a fuse size?

A

NFL/1.66

98
Q

what are the two main types of fire? give a a brief description of each

A

Fast burning- flaming soon after ignition
slow burning - initial phase may not flame but likely to be very smokey

99
Q

name 4 fire detection heads

A
  • optical
  • ionisation
  • heat
  • infra-red
100
Q

describe the operation of a DOL starter, using the circuit diagram

A
  • 440 v enters at L1, L2, L3
  • passes through the isolation switch, CON 1.1, 1.2,1.3, and OL1 to reach terminals A,B,C
  • 440v is tapped off from L1, L2 via FS 1 and 2
  • 440v is converted to 115V by T1
  • 115v travels through FS8, OL1, removable links, stop switch, local start switch, CON1/4 and FS6 back to T1
  • Closing CON 1.1,1.2,1.3 supplying 440v to terminals A,B,C
  • CSR provides the hold path for CON 1 when local start is released
  • stopping the motor is achieved by operating the stop switch
101
Q

when measuring main V up to 750 volts which two items of GPTME are used?

A
  • fluke 89 and MTI 420
  • to be checked against a known source before and after use
102
Q

what 3 modes dose an emergency DG have?

A
  • automatic
  • manual
    -test
103
Q

explain the operation of an SFC

A
  • frequency changes from 60hz supply to 400 hz to control steering gear, stabilisers and aircraft serving
  • the transformer takes the 440 volt 60hz input and transforms this to DC voltage
  • the smoothing circuit, consisting of capacitors and inductors, produces a smoother
  • the inverter changers DC to AC
  • the filter cleans the wave form and produces a sine wave
104
Q

Draw the basic governor motor

A
105
Q

draw the brushless generator

A
106
Q

draw the AVR response curve

A
107
Q

draw the SFC block diagram

A

151/23/005 (13 decks)

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