1
Q
When did The health and safety at work act 1874 become a law?
A
1st April 1990
2
Q
what does regulation 4 cover?
A
quality of system construction suitability, quality and maintance and use of systems
3
Q
what does regulation 5 cover?
A
to ensure that design specs are not exceeded in use
4
Q
what does regulation 8 cover?
A
requirements for earthing of equipment and circuits
5
Q
what does regulation 11 cover?
A
excess current protection in electrical circuits
6
Q
what does regulation 13 cover?
A
precaution for working on ‘Dead’ equipment
7
Q
what does regulation 14 cover?
A
when and when not to work in or near ‘live’ conductors
8
Q
what does regulation 15 cover?
A
requirements for adequate working space, access and lighting
9
Q
what is the definition of an electric shock?
A
the involuntary reaction of the human body caused by conducting an electrical current
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
11
Q
what are the main causes of accidents?
A
- pre-occupation
- ignorance or lack of skill
- over familiarity
- laziness
- fatigue
- physical hazards
- ‘horseplay’
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
13
Q
when work is carried out on ‘Dead’ equipment, how do you make sure is stays dead?
A
LOTO
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
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
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
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
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
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
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
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
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
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
24
Q
list the Advantages of brushless generators
A
- smaller in size
- less maintenance
- no rubbing parts
25
what is the disadvantage of a brushless generator?
slower in response than the conventional generator to load changes
26
What will happen in a open circuit diode condition?
- gen voltage output will fall and AVR will compensate
- resulting in extra strain on the remaining diodes
- gen should be offloaded within 30 mins
27
what will happen in a short circuit diode condition?
- 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
28
explain how cooling to generators is provided
- 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
29
in the vent of the air cooler of a gen failure, what can be done to keep it cool?
the vent flaps may be opened to allow free flow of compartment air across the gen
30
what daily checks are done on a generator?
- 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
31
what monthly checks are to be done on a generator?
- carry out VA and record readings
- condition monitor all bearings
- check for water in generator
- clean vent grills and emergency cooling flaps
32
explain the function of an AVR
- 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
33
what are the reason for the specific characteristics of the AVR response curve?
- reduces short circuit voltages
- prevents damage
- prevents damage to mechanical parts
34
what are the nine plug in units for an AVR set up? explain what they do.
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
35
explain the brushless generator start up sequence
-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
36
explain how voltage regulation happens while a generator is running
- 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
37
what dose the MK 1 protection unit provide protection for ?
- over voltage
- under voltage
- parallel gen fault
- open circuit rotating diode failure
- short circuit rotating diode failure
- low frequency or speed
38
what two conditions must ships generators still maintain terminal voltage within certain limits?
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
39
when would generator load trials be necessary?
- 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
40
what are the requirements needed to carry out load test?
- 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
41
What are the different types of tests in generator trails ?
- insulation resistance hot and cold
- heat run
- speed control
- voltage control
42
explain how insulation resistance hot and cold tests are done on generators
- 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
43
explain how heat run tests are done on generators
- temperature rise test
- full rated load, specified voltage and speed
- 6 hours or until temp has been constant for an hour
44
explain how speed control tests on generators
- assess response time of the governor
- transient test
- variation to 25% load changes
- steady state regulation
- variation 'No load' to 'Full load'
45
explain how voltage control tests are done on generators
- 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
what are the on-board requirements for generated voltage?
- 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
list the type 45 main electrical and propulsion system
- 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
what dose a type 45 HV switchboard supply?
460 volts
60 hz
3 phase
49
what is harmonic pollution?
- voltage distortion
- zero crossing noise
- unbalanced line currents
- overheating machinery
50
what is the purpose of HV harmonic filters?
- reduce heating effect caused by harmonic distortion
- provide a power factor correction
51
how are the the harmonic filters cooled?
- cooled by MIDEL fluid being pumped through the centre of the reactor
52
what is MEDEL ?
synthetic ester-based transformer fluid
53
what is the NERs earth fault rating?
10 amps
54
what is the emergency generator capable of supplying?
440 volts
3 phase
60 hz
55
how can an emergency generator be started manually?
battery- 2x12 volt batteries
hydraulically- kept de-pressurised and must be pressurised by a hand pump
56
what role of protection do the breakers play in the distribution system ?
- 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
what are the different types of switchboard breakers? explain their purpose
- 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
what are the four trips fitted to the breaker?
- under voltage
- over current
- anti-shock
- position interlock
59
what are the three different trip levels for a overcurrent unit?
L- long-time delay
S- short time delay
I - instantaneous
60
what are the two methods of control supply for SACE Ottomax breaker operation?
- manual-
- automatic
61
explain how to manually operate the SACE ottomax breaker.
- 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
explain how the SACE ottomax breaker automatically operates
- 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
what are the two sizes that MCCB come in?
100 amps
250 amps
64
what are the five safety devices fitted to MCCBs?
- thermal-magnetic trip unit
- manual trip
- electro- magnetic trip
- current limiting fuses
- residual current devices
65
explain how a thermal magnetic strip works
senses the heat resulting from an overload condition and the high current resulting from a short circuit
66
explain how a manual trip works
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
when do electro magnetic trips work best?
for a short circuit
68
what is an Residual current device RCD?
they balance current
they operate when residual current is between 50% and 100%
69
explain how a RCD works
- 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
what are the different types of change over switches ?
- hand change-over switch
- automatic change-over switch
- remote operated change-over switch
- fast acting change over switch
71
why are there a limited amount of change over switches on board?
- overloading supply
- weight
- cost
72
what precautions need to be taking when operating hand change over switches?
- 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
give examples of equipment/services that are supplied by an HCOS
- fire pumps
- portable pump
- ventilation system
74
state how ACOS breakers work
- 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
what equipment is supplied by an ACOS?
- MDF pumps
- steering motors
- chilled water pumps
- weapon systems
76
what equipment do FACOS supply?
- radar electronic support measures
- two internal communications network nodes
- combat management systems
- principal anti-ait missile systems
77
what are the typical routines checks carried out on an ACOS?
- 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
on a type 23 there are two thyristor converters, one for each motor. what are the two DC loads that convert?
- 750 v DC at 2250 amps for the armature circuit
- 270 v DC at 42.5 amps for the field circuit
79
Harmonic currents can penetrate the power supply what issues dose this cause?
- voltage distortion
- zero crossing noise
- unbalanced line currents
- overheating of machinery
80
what are the reasons for using electrical propulsion?
- 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
what is the definition of a converted supply ?
a converted supply is a supply derived from the main 450v, 60Hz, 3 phase supply, which requires a change in frequency/voltage
82
give some examples of typical converted supplies and equipment
- 24V DC TRU/ batteries/RTRs
- 50 V DC TRU/batteries/ RTRs
- 115v 400HZ - SFCs
- 200 V 200Hz - Aircraft supplies
83
what conditions will the SFC trip, for fault protection
- 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
what safety precautions should be incorporated into the design and usage of any compartment being used to maintain/service batteries ?
- 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
how is corrosion prevented on the ships hull?
- correctly applied paint
- efficient cathodic protection system
86
how does corrosion occur?
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
what is rust?
the formation of ferric hydroxide
FE(OH)3
88
what is the zone of cathodic protection?
- 750mV - -850 mV
89
when cathodic protection is over charged what is there risk of?
risk of alkali attack
blistering of paint
90
when cathodic protection is under charged what is there risk of?
intense corrosion
freely corroding
91
what is checked daily when monitoring the cathodic system?
output voltage
ships speed
each reference electrode potential
92
how are monthly cathodic systemchecks done?
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
what equipment does the emergency generator supply on a type 23?
- 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
state four references to aid compliance with electricity at work regulations
- 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
with relation to regulation 11, who’s job is it to check on protective devices?
ships staff
96
state 5 PPE precautions that are required when working the batteries
- PVC Gauntlets
- PVC apron, white
- rubber boots
- goggles
- overalls with sleeves rolled down
97
what equation would you use to find a fuse size?
NFL/1.66
98
what are the two main types of fire? give a a brief description of each
Fast burning- flaming soon after ignition
slow burning - initial phase may not flame but likely to be very smokey
99
name 4 fire detection heads
- optical
- ionisation
- heat
- infra-red
100
describe the operation of a DOL starter, using the circuit diagram
- 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
when measuring main V up to 750 volts which two items of GPTME are used?
- fluke 89 and MTI 420
- to be checked against a known source before and after use
102
what 3 modes dose an emergency DG have?
- automatic
- manual
-test
103
explain the operation of an SFC
- 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
Draw the basic governor motor
105
draw the brushless generator
106
draw the AVR response curve
107
draw the SFC block diagram
151/23/005
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