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Electrical Machines Flashcards

1
Q

What are the FOUR of the items checked during running generator daily rounds?

A

Bearing Temperature
Generator air temperature
Mk 1 PN Protection Unit
Anti-Condensation Heaters off

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2
Q

What is cooling of the AC Generator provided by?

A

A closed Circuit water cooler

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3
Q

What speed does a brushless generator shaft rotate at?

A

1200rpm

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4
Q

What fault is apparent when the AVR compensates by increasing Excitation?

A

Open Circuit

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5
Q

What fault is apparent when the generator output voltage collapses due to lack of excitation?

A

Short circuit

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6
Q

What is the function of the AVR

A

To maintain the terminal voltage of the generator to an accuracy of ± 1 % of the nominal voltage for all loads from zero to full load.

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7
Q

What is the Ships main distribution supply?

A

450v, 60Hz, 3 phase

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8
Q

How is the generator output frequency controlled?

A

By controlling the speed of the Prime Mover

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9
Q

How is the Generator cooled if the SW cooler fails?

A

By opening the emergency cooling flaps at either end of the cooler.
Allows cool air from the compartment to be circulated around the generator.

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10
Q

What is the definition of an electric shock?

A

The involuntary action of the human body caused by conducting an electric current

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11
Q

What is the definition of HV for AC and DC?

A

Where the working voltage exceeds 1000 volts AC (RMS) or 1500 volts DC measured between any two points in a circuit

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12
Q

What are the basic causes of electrical shock?

A

Equipment failure, human failure, a combination of both.

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13
Q

State FOUR of the onboard references to aid compliance with the Electricity at Work Regulations 1989.

A

Memorandum of Guidance on the Electricity at Work Regulations 1989

JSP 430 – MOD Ship Safety Management Handbook

BR2000(20) – Safety Considerations and Precautions

BRd 167 – The Safety, Health and Environment Manual (SHE Manual)

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14
Q

State the main causes of accidents

A

Pre-occupation, ignorance or lack of skill, over-familiarity, laziness and fatigue, physical hazards, ‘horseplay’

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15
Q

What is the maximum resistance between equipment framework and the ships hull for all fixed electrical equipment

A

0.1 Ohm

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16
Q

What date did the Electricity at Work Regulations become law?

A

1st April 1990

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17
Q

Regulation 13 of The Electricity at Work Regulations 1989 deals with working on dead equipment. What procedure is used in the RN to prevent dead equipment becoming live during maintenance?

A

LOTO (Lockout/ Tagout)

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18
Q

Who is the Authorising Engineer?

A

The [Authorising Engineer (AE)] is normally the MEO.

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19
Q

Who is the Authorised Person?

A

The [Authorised Person (AP)] is an Officer or Senior rate that is adequately trained and possesses sufficient knowledge, approved and endorsed by the AE.

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20
Q

What FOUR compartments are classed as typical Dangerous Compartments?

A

Lox/Gox Plant

Inflammable Store

Vehicle Deck

Aircraft Hanger

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21
Q

What are the correct FOUR minimum precautions that are to be taken when work has to be carried out on live equipment.

A

Use insulated tools

Work on live equipment should only be carried out if the responsible Engineering Officer is satisfied that there is no alternative

Avoid all direct contact with any circuit and/or component, which may be electrically energised

Wear ‘Electrical Worker Gloves’ as specified in JSP 437. These should be visually inspected prior to use.

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22
Q

When measuring mains voltages up to 750V DC and 650V AC, which two items of GPTME are acceptable for use and what is the procedure prior to the measurement and after?

A

Fluke 89 and MIT 420. The approved tester must be checked against a known good power supply both before use and after use

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23
Q

What are the 5 HV safe systems of work documents?

A
  1. Limitation of Access
  2. Permit to Work
  3. Switching Schedule
  4. Isolation Certificate
  5. Sanction for Test
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24
Q

Regulation 11 of The Electricity at Work Regulations 1989 deals with protective devices. Whose responsibility is it to check these devices?

A

Ship’s staff

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25
What are the 7 requirements of a distribution system?
To supply power when and where required The system must be flexible Must be able to provide alternative supplies to vital equipment Must have spare capacity Must minimise the effects of action damage by maximising the dispersal of important services The generators and associated switchboard must be close together The system can be controlled from one central point or separated into individual switchboard operations
26
What are FOUR of the principal components of the Type 45 electrical and propulsion system
2 × WR21 advanced cycle gas turbines, rated at 21.8 MW, each connected to a 4160 V 21 MW alternator, collectively known as the gas turbine alternators (GTAs) 2 × Wärtsilä diesel engines, each connected to a 4160 V 2 MW alternator, collectively known as the diesel generators (DGs) 2 x Alstom VDM 25000 Pulse Width Modulated Converters each consisting of 3 channels and 5 phases per channel 4 × Neutral Earthing Resistors (NERs)
27
What are the problems caused by harmonic pollution?
Voltage distortion Zero crossing noise Unbalanced line currents Overheating of machinery
28
Why are HV Harmonic Filters fitted on a type 45?
To REDUCE HEATING EFFECTS in the alternators caused by harmonic distortion emanating from the propulsion converters & to provide POWER FACTOR CORRECTION.
29
What are the Harmonic filter reactor conductors cooled by?
MIDEL 7131 biodegradable synthetic ester‑based transformer fluid pumped through the centre of the reactor and a MIDEL/water heat exchanger
30
What is the purpose of the harmonic filter reactor conductors?
To remove waste heat. MIDEL 7131 fluid is an effective coolant, is fire safe, performs well across a broad range of temperatures, and has excellent electrical insulating properties.
31
What is the purpose of an NER (Neutral Earthing Resistor)?
To limit the earth fault current to an acceptable level, approximately 10 A for a solid earth fault.
32
What is the output rating of the emergency diesel generator on a Type 45?
450 V 60 Hz 3 ph 250 kW
33
The Emergency Diesel Generator (EDG) has 3 modes of operation. What are they?
Automatic, Manual, Test
34
The Emergency Diesel Generator (EDG) can be started in 2 ways. What are they?
Battery or Hydraulically
35
What is the function of a Supply Breaker?
Connects/disconnects the generator output to the switchboard
36
What is the function of an Interconnecting Breaker?
Links two switchboards, not within the same section, together
37
What is the function of a Busbar Linking Breaker?
Links 2 Switchboards, within the same section, together
38
What is the function of a Feeder Breaker?
Provides power to the EDCs/EDPs
39
What is the function of a SS/SA Breaker?
Connects the box on the upper deck to the switchboard
40
There are 4 trips (or devices which affect the operation of trip mechanism) fitted to a breaker. What are they?
Under-voltage, over-current, anti-shock, position interlock
41
Regarding breakers, even though each breaker in a distribution system may have a different ‘role’ to perform, they will all have the same protection facilities. What are the 6 protection facilities that apply?
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
42
Moulded Case Circuit Breakers (MCCBs) come in two basic frame sizes/continuous current capacities. What are they?
100A and 250A
43
How many times should you depress the charging handle on a breaker?
11 times
44
Which button will close the breaker?
I button
45
Which button will open the breaker?
O button
46
What equipment/ services are supplied by an ACOS?
MDFL pumps steering motors chilled water pumps weapons systems
47
What equipment/ services are supplied by a HCOS?
Fire pumps portable pump sockets ventilation system
48
Regarding change-over switches, which type do the following precautions apply? · Only operate when ordered in an emergency · Never operate on load · Ensure remote start facility is inhibited/not operated during the changeover sequence · Motor is stopped before operation · If motor cannot be sighted, pause for 10 seconds to allow rotating field to dissipate
HCOS
49
Regarding ACOS, one of the requirements of their design is that ‘the two sources of supply must not be paralleled through the switch under any circumstances’. What is the reason for this?
It is likely that the distribution system will be is ISLAND MODE. Attempting to parallel the two together at the ACOS, if it were possible, would cause a significant SHORT-CURCUIT.
50
Why is the number of Automatic change-over switches (ACOS) limited onboard?
If one generator failed, the automatic throw-over load onto the other generator(s) could cause large voltage transients or even OVERLOADING of the alternative supply. Weight and cost.
51
What are the monthly procedures for monitoring the cathodic system and how do we carry them out?
Monthly - Using the PORTABLE REFERENCE ELECTRODE, lower 8FT below waterline & RECORD POTENTIAL DIFFERENCE between the electrode and the ships hull. At laid down points around the ships hull. The ship must be STATIONARY whilst readings are taken.
52
What are the DAILY procedures for monitoring the cathodic system and how do we carry them out?
Record the TOTAL ANODE CURRENT and each INDIVIDUAL ANODE CURRENT. Also record each REFERENCE ELECTRODE POTENTIAL including that of the monitoring electrode.
53
Describe how an AC induction motor works.
The 440V 3 phase supply to the windings of the stator produce a rotating magnetic field with the two poles. (A 3 phase two pole induction motor).
54
What are the equations for speed control and the fuse size required for a AC induction Motor?
F= (N x P) / 60 (NFL x 8) / 1.66
55
When running emergency cables, what steps/ precautions must be taken?
Wear rubber gloves Run cables from the service back to the supply. Lash cables overhead where possible. Use through bulkhead terminals, permanent risers, deck tubes. Do not pass cables through doors and hatches, especially those which are watertight. Keep the cable off the deck and out of the water. It should be carried to its place of use and not dragged. Fixed equipment being supplied via emergency cables should have a danger notice posted. Check all connections are tight, cables correctly secured and cable bights clear of obstruction Where portable equipment is being used, ensure that the earth connections are correctly made. Carry out final check of the emergency run, before connecting to a live source. If cables are being run to a live though bulkhead terminal, do not connect to this point until the remainder of the run is complete and checked.
56
State the siren in Manual Control Pre-Requisites.
24V DC supply energises RL1/1 which closes RL1.1 115V supplied energises RL4/1 which closes RL4.1 RL4/1 Energising closes RL4.1 and illuminates lamps.
57
Modern construction of warships incorporates a ‘thin hull’. It is vitally important that corrosion is prevented, otherwise major structural damage will quickly occur. There are three methods of protection, which are normally used together. These are?
A correctly applied paint scheme impressed current cathodic protection (ICCP) sacrificial anodes
58
What is the ‘zone of cathodic protection’ for steel when measured with respect to a silver/silver chloride (Ag/AgCl) reference electrode?
-750 mV to -850 mV
59
What are the results of an over-protected steel hull?
Risk of alkali attack blistering of paint danger of hydrogen embrittlement
60
What are the results of an under-protected steel hull?
Freely corroding/intense corrosion
61
What 5 things must be recorded in the ICCP system daily readings?
Individual anode currents Total anode currents Output volts Ship’s speed Reference electrode voltage
62
Fast burning fires are categorised by what symptoms?
A flaming phase very soon after ignition
63
A slow burning fire can be categorised by?
An initial phase which may not flame at all but is likely to be very smoky.
64
Which type of detector head operates by sensing light from smoke particulates?
Optical
65
What occasions will require a fingerprint Trial to be carried out?
Following a Generator load trial for base line datum reference. As required when the performance of the prime mover, generator or AVR is suspect.
66
What are the design parameters of the Emergency Diesel Generator on a Type 45
450v AC 250 KW 60Hz 3 Phase
67
List the Services Supplies from the Type 45 Emergency Switchboard
No 3 Air Compressor Normal Supply to the Stbd Steering Motor Alt Supply to Port Steering Motor One Emergency DC Cable Connection 10 supplies to Emergency Distribution Boxes
68
Name the Five Common ACB's and their function
Supply breaker Bus Bar Linking Breaker Inter-connector Breaker Feeder Breaker Shore Supply/Ship Alongside Breaker
69
Each type 23 Propulsion converter regulator has TWO electrical supplies, state the values of the supplies and which circuits they apply to.
Armature circuit 750v DC @ 2250 Amps Field Circuit 270V DC @ 42.5 Amps
70
State the FOUR reasons for choosing electrical propulsion
Economical and environmental Flexibility of Layout Low noise and vibration characteristics Ease of control and reduced manning
71
Using the siren circuit diagram, State the prerequisites required for siren operation
24vDC 115v 60Hz 1 phase and RL 4 to be energised
72
List Five personal precautions required when working with batteries
PVC Gauntlets PVC Apron White Clean Rubber Goggles Rubber Boots Overalls with sleeves rolled down
73
List the protection facilities built into the Mk 15 SFC and their trigger points
Over voltage protection 126.5 V (10% over) Power Module over temp 120°C Current limiter when current exceeds 10.2 Amps (130%)
74
Name FOUR detector heads associated with the T890 Fire detection system
Optical lonisation Heat Infa Red
75
State the services supplied by the emergency generator on a T23
Two of the five fire pumps GT power turbine cool down pup Smoke clearance fans Emergency Lighting Sickbay Services Portable fuse Panels
76
With Regards to EWR act 1989, how do we comply with the following:- Regulation 13
Tag out, LOTO, PTW, UMMS
77
What rounds are carried out on a generator MONTHLY?
Carry out VA and record readings in LOG Condition monitor all bearings Check for water present in generator Clean vent grills and emergency cooling flaps
78
Describe and draw the operation of a Brush-less Generator.
Prime mover rotates the generator shaft @ 1200 RPM. PMG is belt or shaft driven. The PMG supplies AC exciter via avr. The avr in turn supplies DC signal to the exciter stator, the magnetic field set up in the exciter stator induces EMF into the exciter rotor producing an AC. This AC is passed to. the rotor of the main generator via cables fed through the rotor shaft creating a rotating magnetic field. This magnetic field cuts across the 3 stator windings inducing an EMF into them. This 450v 3phase 60HZ is then passed to the switchboard. A sample is taken to the AVR compared with a reference, which in turn increases or decreases the field current to the AC exciter.
79
What are the 4 control and communication switchboard functions?
Control the operation of the converted supply Control the distribution of converted supplies to the services requiring them Control the charge/ discharge arrangements of the ships main LP battery Provide testing and monitoring facilities for supplies controlled from the switchboard
80
Stages of a block diagram of an SFC
Transformer ———> Rectifier ———> Smoothing circuit ———> Inverter ———> Filter
81
Examples of the typical converted supplies?
24V DC: TRUs/Batteries/RTRs 50V DC - TRUs/Batteries/RTRs 115V 400Hz - SFCs 200V 200Hz- Aircraft supplies.

Machine Principles (2 decks)

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