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ME 151/23/005 > P and D > Flashcards

P and D Flashcards

1
Q

What are the steady state voltage performance requirements

A

Variation between the three line voltages under all balanced loads are less than 1%

Steady state voltage at all loads and frequency’s between 57hz and 63hz to be within 1% of 450v

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2
Q

What are the transient voltage performance requirements

A

Variation maximum of 7.5% for 25% load going off and 15% of load going on

Time of recovery to within 1% of the final voltage (1 second for AVR MK 100)

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3
Q

What is the designed power factor and why

A

0.8 lagging due to the ships load being mostly inductive

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4
Q

What are the advantages of the brushless generator

A

Smaller in size
Less maintenance
No rubbing parts

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5
Q

What is the disadvantage of the brushless generator

A

Slower in response than a conventional generator to load changes

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6
Q

What is used on the rectifier assembly to early detection of defects

A

Diode failure indicator unit / rectifier failed device

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7
Q

What are the two distinct fault conditions that can occur on the rotating rectifier assembly

A

Open circuit diode condition

Short circuit diode condition

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8
Q

On the rotating rectifier assembly explain what happens after open circuit diode condition fault indicates

A

Generator output voltage drops and will be compensated by the AVR
This will result in extra strain leading to further breakdown
The generator should be off loaded within 30 minutes and fault investigated

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9
Q

On the rotating rectifier assembly explain what happens after short circuit diode condition fault indicates

A

This will cause an overload of the AC exciter resulting in further damage to diodes
Generator output voltage will collapse
Supply breaker should open on under voltage to protect distribution system
Due to high current there is risk of overheating

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10
Q

What are the daily checks for the brushless generator

A

Bearings and casing not overheating
Generator air temp within limits
No signs of cooler leaking
No undue noise or vibration
No defects at the PMG drive belt
No diode warning
Mk 1 protection unit
Anti condensation heaters off when gen is running
PMG belt tension and condition

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11
Q

What are the monthly checks of the brushless generator

A

Carry out VA and record readings
Condition monitor all bearings
Check for water in generator
Clean ventilation grills and cooling flaps

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12
Q

What is the role of the AVR

A

Must maintain constant voltage at the terminals of the ships main generator to an accuracy of +/-1%

Under rapidly changing load conditions it must restore terminal voltage to within 1% within 1 second

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13
Q

Page 2.16 MK121

A
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14
Q

Generators must be tested to maintain the required standard, what are the 4 changes that require tests

A

If the following are changed / modified
Prime mover / govenor
AVR
Generator rotor / stator

Or after a major modification to switchboard wiring

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15
Q

What are the requirements of carrying out generator tests

A

Large dock / load test facility
A high speed pen recorder
Generator isolated from distribution system
Trials form D346 (F)

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16
Q

Fingerprint tests page 2.22

A
17
Q

Generated voltage on board must meet 7 basic retirements

A

Supply power when and where needed
System to be flexible
Provide alternate supplies to vital equipment
Have spare capacity
Minimise effects of action damage by spreading dispersal of main services
Generators and switchboards to be close
System can be controlled from one central point

18
Q

What are the 5 reasons for electric propulsion

A

Economical and environmentally friendly
Flexibility of layout
Load diversity between ship service and propulsion
Ease of control and reduced manning
Low noise and vibration characteristics

19
Q

What are the main parts of a type 45 electrical and propulsion system

A

2 x GT 21.8MW
2 x DG 2MW
4 x NER
2 x SSTX
2 x HVHF
2 x LVHF
2 x HVSB
2 x LVSB
6 x DBR
PMS
EPCAMS
2 x PMs

20
Q

Switching of the IGBT generates harmonic current which can cause what problems

A

Voltage distortion
Zero crossing noise
Unbalanced line currents
Overheating of machinery

21
Q

What is the purpose of the HVHFs

A

Reduce heating effects on the alternators
Provide a form of power factor correction

22
Q

What is the purpose of NERs

A

Should a prime mover have a short fault to ships the NER will reduce current to an acceptable level of 10A

23
Q

How many island modes can a type 45 go to

A

1, 2, 3 and 4

24
Q

What protection do breakers provide onboard

A

Over current protection
Under current protection
Reverse current protection
Provide fault discrimination
Open and close circuit safely
Clear the max short current fault safely

25
Q

Name and describe the 5 types of main switchboard breakers

A

Supply breaker - connects / disconnects the generator to switchboard
Interconnector breaker - links forward and aft switchboards
Bus bar - links switchboard sections together
Feeder breaker - provides power to EDCs/EDPs
Shore supply - redundancy

26
Q

What are the 4 types of trip on sace Ottomax breakers

A

Under current
Over current
Anti shock
Position interlock

27
Q

What are the 3 trip levels of the sace ottomax over current trip

A

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

28
Q

Page 4.9 manual and automatic operation

A
29
Q

What are the four types of change over switches

A

Hand change over
Automatic change over
Remote operated change
Fast acting change

30
Q

What should be considered when choosing change over switches

A

Weight, cost and throw over

31
Q

What precautions should be made when operating hand change over switches

A

Only operate when ordered in emergencies
Never operate on load
Ensure remote start facility is inhibited in change over sequence

32
Q

Automatic change over switches page 5.4

A
33
Q

What are examples of equipment that use fast acting change over switches

A

Radar electronic support measures
Two internal communications network nodes
Combat management systems
Anti air middle systems

34
Q

What equipment does a type 23 electrical propulsion system use

A

Two 750V DC, separately excited motors
- used for propulsion- integrated into the ships propeller system

35
Q

How is a type 23 propulsion motor cooled

A

The motor is cooled by and “open system”
Machinery space air is drawn in through a filter by two forced vent fans mounted on top of the motor

36
Q

What type of converters are used on a 23 and what are their values

A

Two thyristor converters - one for each motor - each supplies two DC loads

750V DC at 2250 amps for amature current
270V DC at 42.5 amps for field current

37
Q

What equipment is used for power generation on a type 45

A

2 x GT 21.8 MW
2 x DG 2MW
2 x Alston VDM
2 x 15 phase induction motors
2 x HV harmonic filters

38
Q

What is the principle of catholic protection

A

The ships hull is kept at a negative potential
Measured by a silver electrode with pre set voltage of 0.8V

39
Q

What are the effects of over and under current protection on the cathodic system

A

Over protection - causes paint blistering around the andodes and hydrogen embrittlement
Under protection - does not prevent corrosion

ME 151/23/005 (1 decks)

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