P&D Flashcards
(96 cards)
1
Q
What date did the electricity at work regulations 1989 become law?
A
1st April 1990
2
Q
What does regulation 8 cover?
A
Requirements for earthing of equipment and components
3
Q
What does regulation 11 cover?
A
Excess current protection in electrical circuits
4
Q
What does regulation 13 cover?
A
Precautions for working on dead equipment
5
Q
State 4 references for electrical safety?
A
Electricity at work regulations 1989
Health and safety at work act 1974
BRd167 the safety, health and environmental manual
BR 2000(52) electrical power distribution and utilisation
6
Q
How do you comply with regulation 13?
A
LOTO
Permit to Work
7
Q
What does regulation 14 cover?
A
When and When not to work on or near ‘live’ conductors
8
Q
What is the definition of electric shock?
A
The involuntary action of the human body caused by conducting electrical current
9
Q
What are the causes of electrical shock?
A
Equipment failure
Human failure
Combination of both
10
Q
What are the causes of electrical accidents?
A
Pre-occupation
Lack of knowledge
Overfamiliarity
Laziness and fatigue
Physical hazards
Inappropriate behaviour
11
Q
What equipment is used to test for dead?
A
fluke 89
MIT 420
Fluke110
12
Q
What must be done prior to using test equipment?
A
Ensure equipment is approved for use at all main voltages
Checked against a known power supply
13
Q
What are the minimum precautions to be taken when working on live equipment? (6)
A
2nd trained man present- familiar with shock procedure
Use insulated tools
Adequate lighting
Wear insulated footwear
Stand on a rubber mat
Take care that tools/test equipment don’t cause a short circuit
14
Q
What are the minimum precautions to be taken when working on dead equipment?
A
Adhere to safety procedures and precautions
Isolate using LOTO
Check using test equipment between phases and each phase and earth to ensure its dead
Ensure capacitors have been discharged and shorting straps applied
Earthing arrangements are correctly connected
Use correct tool for the job
15
Q
What is the definition of high voltage?
A
Where the working voltage exceeds 1000V A.C or 1500V DC measured between any 2 conductors or between circuit conductor and earth
16
Q
Who are the HV key personnel?
A
Authorising engineer
Authorised person
Authorised person in control
Competent person
HV aware
17
Q
What is the documentation required for HV systems?
A
Permit to work
Sanction for test
Limitation of access
Switching schedule
Isolation certificate
18
Q
What is the definition of a dangerous compartment?
A
Any compartment that has a fire or explosion hazard
19
Q
List 4 examples of dangerous compartments
A
Aircraft hangers/ vehicle decks
Galley
Fuel stowage
Paint store
20
Q
What are the requirements for electrical installations in dangerous compartments?
A
Cable runs - 5 feet above deck
Light fittings - flameproof
Motors/ control gear- flameproof enclosure
Portable lighting- low voltage
21
Q
What is the maximum resistance between equipment and the ships hull of all fixed electrical equipment?
A
0.1Ω
22
Q
What voltage requirements need to be met by generators within the fleet?
A
Steady state condition
Line variation between phasesmust ot exceed 1% at all loads
At all loads and frequencies between 57-63Hz Voltage must be 450 ± 1%
Transient condition
Voltage variation for load on is 15% load off is 7.5%
Time of recovery to within 1% of final voltage is 1 second
23
Q
What frequency requirements need to be met by generators within the fleet?
A
Nominal frequency 60 Hz
Frequency variation from no load to full load 3.5-4%
transient frequency variation for 25% load changes , ± 2.5% for mechanical, ± 1.5% for electronic governors
Time of recovery to within 1% for mechanical and 0.2% for electronic is 2 secs
24
Q
What is the designed power factor for RN ships?
A
0.8 lagging which is due to the ships load being partly inductive
25
How does a brushless generator work?
Prime mover
HF generator
AVR
Exicter Stator
Rectifier assembly
Main generator
3 phase output
AVR
26
What is the sequence of rectification known as?
Poly-phase rectification
27
What are the 2 distinct faults conditions that can occur with the rotating rectifier assembly?
Open circuit diode condition
Short circuit diode condition
28
What is open circuit diode condition?
Generator output falls and is compensated by the AVR
Extra strain on remaining diodes- further breakdown
Generator offloaded within 30 minutes and fault investigated
29
What is short circuit diode condition?
Overload of the exciter stator
Further damage to the diodes
Generator output voltage collapse due to loss of exciter field current
Supply breaker opens to protect distribution system
Danger of overheating
30
What rounds are carried out on a generator daily?
bearings and casing not overheated
generator air temperature within the prescribed limits
no signs of leaking of the air cooler from tun dish outlet or cooler stack
no undue noise or vibration
no apparent defects at the permanent magnet generator drive belt
no diode failure warning at the diode failure detector unit
31
What rounds are carried out on a generator monthly?
VA and record in log
Condition monitor all bearings
Check for water in generator, remove if present
Clean ventilation grills and emergency cooling flaps
32
What requirements are required to carry out load trails?
Conditions of a steady load --> generator voltage must be maintained within ± 1% of nominal output
Conditions of transient load --> the maximum voltage variation must be within V 15% with load increase and ± 7.5% with load decreases the AVR should recover within 1% in 1 sec
33
What is a transient load?
15% with load increase
7.5% with load decrease
34
List 5 AVR Units and briefly explain
Mk 17 filter unit --> improves the HF 160Hz supply and incorporates the MK 168 low power unit for the DC Power rail supplies
Mk 1 EC Excitation contactor --> connect the improves 160 Hz to the MOSFETS
Mk 1 PN Protection unit --> providing the system shut down facility should any fault condition arise
Mk 1 UF Interface unit --> provides various voltages and frequency signals for several modules within the AVR
Mk 1 CN Compensation unit --> compare the actual volts against the desired volts to produce an error output
35
What is the operation of a generator?
The Mk 121 AVR is designed to regulate the field and hence the output of a standard 2 stage brushless generator
Power supplied from a 77V 160Hz PMG
PMG output is improved by the Mk17 FU
Output from the MK17 FU is passed via the Mk1 EC to the Mk 1 UF, rectified and used to drive the MOSFETS in the power amplifier
Mk CN compares the generator output with a reference voltage to produce an error signal
Error signal is passed to the Mk 28 CU which processes the error signal to control the current flow through the MOSFETS
A voltage proportional to the exciter field is fed back to modify the error signal- Transient feedback
Mk1 PN monitors generator output voltage, exciter field voltage, PMG Frequency and ripple content for the rotating rectifier. Anything out of tolerance will result in de-energising the excitation contactor coil and illumination of the fault LED indicator
36
What are the requirements for carrying out load trails?
Trails form D346 (F)
Load barge/ dockside load test facilities
high speed pen recorder, laptop computer, acquisition recorder
Generator isolated from the distribution system
37
List 5 reasons for electric propulsion
Economical and environmentally friendly
Flexibility of layout
Load diversity between ships service load and propulsion
Ease of control and reduced manning
Low noise and vibration characteristics
38
List 6 things the power system on a T 45 consists of
2x HV harmonic filters
2x LV harmonic filters
2x HV switchboards
2x LV switchboards
4x neutral earthing resistors
2x 2MW ship service transformers
39
What is the purpose of the neutral earthing resistor (NER)?
HV systems are earthed at the star point if an earth fault occurs on one phase unacceptable levels of fault current will flow and cause damage to the system equipment with the possibility of arching and fire damage. NER limits the earth fault current to an acceptable level
40
Why is each alternator connected to earth through its own NER?
To limit individual alternator fault currents to approximately 10 A for a solid earth fault
41
What is a emergency generator capable of providing?
440V 3 phase 60Hz 250 KW of electrical power
42
What are the 3 modes which the Emergency diesel generator can be operated?
Automatic
Manual
Test
43
How can the emergency generator be started manually?
Hydraulically
Battery
44
What does the emergency switchboard supply and how?
Supplies vital and essential equipment via MCCBs
45
How many MCCBs are fitted in the emergency switchboard and what are they?
5 Spare
Supply to no3 AC compressor
Normal supply to STBD steering motor
Alternative supply to PORT steering motor
Emergency DC cable connection
10 supplies to emergency distribution boxes ES1,ES3-ES11 all via hand change over switches
46
What is the output/PF/Frequency of the generators rated 600V?
1.3MW
0.684 lagging
61.2 Hz
47
What is the output/PF/Frequency of the MG sets rated 450V?
1.1 MW
0.8 lagging
60 Hz
48
Name and explain 5 different types of breakers
Supply breaker --> connects/disconnects the generator output to the switchboard, largest capacity breaker in the system
Inter-connecter breaker --> links forward and aft switchboards together via interconnecting cables
Bus-bar linking breaker --> links switchboard sections together at the busbar
Feeder breaker --> provides power to EDCs/EDPs
Shore supply breaker --> connects the SS connection box to the switchboard busbars
49
What ships equipment can be supplied in an emergency onboard?
5 HPSW pump
5 smoke clearance fans
Portable damage control pump sockets
Sick bay and operating theatre services
Emergency lighting
Steering gear via emergency connection box
Flexible emergency cabling system via an ESB
Gas turbine power turbine cooling down pump
50
What protection does each breaker in the system provide?
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
51
Describe the manual preparation and operation of a breaker?
Depress the spring charging handle downward approx 11 times. When fully charged there will be no resistance to the lever pumping action the original white flag will be replaced with a yellow one
pressing the I button will close the breaker
The action of the breaker contacts closing will charge the opening springs
Once the breaker has closed the safety devices will monitor their parameters and trip the breakers as required
Pressing the O button will open the breaker
52
Describe the automatic preparation and operation of a breaker?
Spring charging is accomplished by a 22V AC single phase motor
Once power is applied on either side of the ACB, the motor will run as long as LMS is closed
The motor takes approx 20 secs to charge the springs
White flag will be replaced by a yellow indicator flag
the breaker can now be closed from local or remote position
53
What maintenance routines should be undertaken on the SACE Ottomax breaker?
Operate breakers left open for 6 months
Inspect earth bonding
Measure earth bonding
visually inspect, clean, lubricate, and functionally check positional interlock
measure insulation resistance
ACB inspection, cleaning and contact setting
Survey and clean cubicle
Overhaul ACBs
54
What are the types of defects on the SACE Ottomax breaker?
Blown fuses- replace
Discrepancy switches defective - replace
Limit switches defective - replace or adjust
Mechanical jamming - free breaker/locate defect
55
What are the 2 basic frame sizes of MCCBs?
100A and 250A continuous current capacity.
56
What are the 5 safety devices normally fitted to MCCBs?
Thermal-magnetic trip unit
Manual trip
Electro-magnetic trip
Current limiting fuses
Residual current devices
57
What are the loads of the two thyristor convertors on a T23?
750V DC at 2250A for armature circuit
270DC at 42.5 for field circuit
58
What are the 3 position on the switch on the local control panel (LCP)?
Local
Revisionary 1 (local)
Revisionary 2 (manual)
59
What problems can switching of the IGBTs cause?
Voltage distortion
Zero crossing noise
Unbalanced line currents
Overheating of machinery
60
List examples of services supplied by an emergency power supply
Steering gear
Weapons systems
bridge supplies
sensors
main machinery auxiliaries
fire pumps
61
In the event of an apparent power supply failure what action should be taken in the local vicinity?
check power supply has actually failed (not blown a fuse etc)
Use an alternative switch using the change over switch and report to HQ1
Where there is no alternative supply report loss to the switchboard
No cables are to be connected to any equipment or supplies without permission of DCO(L)
62
What does the emergency generator hardwired to supply power to?
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
63
What safety precautions should be taken when providing emergency power supplies?
Wear rubber gloves
Run cables from service to supply
Lash all cables overhead where possible
Use through bulkhead connectors, permanent risers, deck tubes
Keep cables off the deck and out of water
A danger notice should be posted at all live points
Check connections are tight, secure and clear of obstructions
Ensure earth connections are correctly made on all portable equipment
Carry out a final check of the emergency run before connecting to a live source
If cables are being run to a live through-bulkhead connector don't connect until remainder of the run is complete and checked
64
What are the 6 principle tasks of the I/C of electrical repair team when closing up for action?
Organise teams
Delegate authority
Prioritise tasks
Set up communications
Test all equipment
Train team members
65
How do we prevent corrosion?
Full protection relies on:
A correctly applied paint scheme
An efficient cathodic protection system (sacrificial and impressed current)
66
Describe the basic operation of a ships cathodic protection system?
To prevent corrosion the ships hull must be maintained at a negative potential when measured with a silver reference electrode (-0.75-0.85V)
Cathodic protection systems use the potential measured by the silver electrode compared with a pre-set voltage (-0.8V)
These two voltages when compared across an amplifier input will produce a signal output which is used to control a thyristor bridge and hence control current to the hull anodes
The value of -0.8V is critical
Over or under voltage will produce damaging effects on the ships hull
67
What is recorded on the cathodic protection system daily?
Individual anode current
Total anode current
Output voltage
Reference electrode voltage
Ships speed
68
Describe the procedure for carrying out monthly cathodic readings?
Carried out as convenient
When the ship is stationary
Use portable reference electrode
Lowered 8 feet below water line
Kept close to ships hull
Record difference between electrode and ships hull
At pre-determined points on the ships hull
69
What happens if we under protect the ships hull?
Corrosion
70
What happens if we over protect the ships hull?
Risk of alkali attack
Blistering of paint
Danger of hydrogen embrittlement
71
What are the 4 types of change over switches used on board?
Hand change over switch
Automatic change over switch
Remote operated change over switch
Fast acting change over switch
72
Why is there a limit to the number of automatic change over switches?
Cost
Weight
Throw-over
73
What equipment is supplied by a HCOS?
Fire pumps
Portable pump sockets
Ventilation system
74
What are the requirements of a standard ACOS?
Two sources of supply must not be paralleled through the switch under any circumstances
When both N and A Supplies are within tolerance N should be selected automatically
When N falls far enough below its nominal value A is automatically selected
There is a suitable delay before this occurs to prevent the switch operating on voltage transients
When N is restored to its nominal value it is selected automatically
There must be a delay between disconnection of one supply and reconnection of the load to another. this allows the rotating field in any motor to die away
75
Give 4 examples of equipment supplied by an ACOS
MDFL pumps
Steering motors
Chilled water pumps
Weapons system
76
What equipment is supplied by a FACOS?
Radar electronic support measures
2 internal communications network nodes
Combat management systems
Principle anti-air missile systems
77
What is a typical maintenance routine 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
Check contactors and relays
Drop off and pick up limit tests
78
What precaution must be observed when operating a hand change-over switch?
Only operated in an emergency
Never operate on load
Ensure remote start is not inhibited
79
What is the definition of a converted supply?
A supply that is derived from the main 450V, 60Hz, 3 phase supply which requires a change in frequency and/ or voltage (except 115V 60Hz 1 phases lighting supplies)
80
List the personal protection to be worn when working with batteries
PVC apron
PVC gauntlets
Rubber knee boots
Rubber goggles
Full face visor
81
List safety precautions when servicing 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 when charging
Safety equipment available
Notice boards for charging times on and off
Running fresh water
Lead lined sinks
82
List the static frequency changer fault protection
The output voltage exceeds 126.5V (10% overvoltage)
Power module exceeds 120°C
SFC incorporates a current limiting device which comes into operation when the load current exceeds 10.2 amps (130%)
83
Fire falls into two main categories what are they and what are their characteristics?
Fast burning --> flaming phase very soon after ignition
Slow burning --> initial phase may not flame but likely very smoky
84
Name the 4 types of detection heads?
Optical
Ionisation
Heat
Infra-red
85
What are the advantages of an AC induction motor?
Smaller in size to a DC motor
Simple construction
Easy to maintain
No electrical connection between stator and rotor
86
What are the disadvantages of an AC induction motor?
High starting current
High fuse rating
Dedicated starters or variable speed drivers are required for speed control
87
What problems does harmonic pollution cause?
Heat
Lower efficiency
88
What are harmonic filters fitted to reduce?
Harmonic frequency
89
Harmonic filters are cooled by what and what is its purpose?
MIDEL fluid being pump through the centre of the reactor to cool the system
90
Describe how an AC induction motor works?
440V 3 phase supply is applied to the stator windings
This produces a rotating magnetic field, which is set up in the windings
The field sweeps past conductors at synchronous speed
EMFs are induced in the conductors of the rotor which causes a field to be set up and interact with the stator rotating field
Interaction of the fields cause a torque to be applied to the rotor which is free to turn, which will move in the direction of the rotating field
As the rotor picks up speed, the rotating field cuts the conductors less and the induced EMFs and currents decrease resulting in the rotor running at a speed slightly less than sychronous
91
Siren in manual control and pre-requisits?
92
What controls the timing for the siren in automatic?
93
How is the cooling of a generator achieved?
Closed air circuit water cooler fitted over the stator frame
94
How is cooling of the generator achieved in an emergency?
Emergency ventilation flaps open and allow air flow across the generator
95
96
What are the pre-requisites for the siren?
24V DC and 115V 60Hz 1 phase
24V DC at SKT A 4 and 6 RL1 is energised and relay contact RL1.1 closed
115V 60Hz 1 phase is available for SKT A 9 RL4 is energised and relay contact RL 4.1 closed
