Supply & Distribution Flashcards
What three basic things are needed to generate power?
Prime mover
AC Generator
Switchboard
What does EDC stand for?
Electrical distribution center.
Explain a generic main supply system.
Usually minimum of 4 generators with a supply breaker in its own switchboard section with its own bus-bars, linked by a busbar linking breaker. Two switchboards (fwd/aft or port-stbd) are linked by interconnecting breakers. Each switchboard has its own set of bus bars. Bus bars supply power to the EDC via feeder breakers. EDC's are situated around the ship and contain switches known as MCCB's. MCCB's feed power to the ships services.
What does MCCB stand for?
Moulded case circuit breakers.
What 5 main breakers are fitted to a ship main distribution system and their uses?
Supply breaker - connects generator to bus bars
Shore supply breaker - allows isolation between ship from another ship or shore supply
Bus bar linking breaker - allows isolation of busbars from each other
Inter-connector breaker - allows isolation between switchboards
Feeder breaker - connects aparatus and switchboard
What are the 7 main components of the power distribution system?
Generator Supply, busbar linking and interconnecting breakers Switchboard Feeder breaker EDC Fuse panels
What does the power book show?
Distribution of all 450 V services
Drawings of generator and switchboard circuit layout
Drawings of the distribution circuits
What does the low power & lighting book contain?
Distribution of all 115 V services
Specifically concerned with lighting system
What does the portable apparatus drawing book contain?
Distribution of all 115/230 V services
Specifically concerned with power supplies to 115/230 V sockets
What main reference books are there?
The power book
Low power and lighting book
Portable apparatus book
Where are the books normally kept?
A central place ie main switchboard or electrical workshop
What is the main supply?
450 v, 60 hz, 3 phase
Where is the main supply fed to?
The EDC
Where is the main supply distributed to?
The ships services
What is the main supply transformed to?
115 v, 60 hz, 3 phase
What do breakers and fuses protect?
The power supply.
What is the first breaker to trip?
The MCCB
What is the last breaker to trip?
The supply breaker
Which fuse will blow first?
The one nearest to the fault.
What ratio does 440 V discrimination use?
3:1
What ratio does 115 V discrimination use?
2:1
Where is power and distribution controlled from?
Primary control position PCP
Secondary control position SCP
There is the PCP?
In the ship’s control center (SCC)
What does PCP show?
Plan of whole electrical distribution system up to the EDC
State of all breakers and generators
What does the PCP control?
All main breakers
All generator voltages
All generator frequencies
Anti-condensation heaters in switchboard
Where is the SCP?
In the machinery sections.
What does the SCP show?
Plan of electrical distribution system fed from the section
State of all breakers and generators controlled by the section
What does the SCP control?
All breakers controlled by section switchboard
All generator voltages controlled by section switchboard
All generator frequencies controlled by section switchboard
Anti-condensation heaters in switchboard
What meters are attached to switchboards?
Voltmeter Frequency meter Watt meter Ammeter Syncroscope Earth fault indicator
What does a discrepancy switch do?
Shows if there is a discrepancy between the breaker and the switchboard and allows the breakers to be controlled. If the light is on, there is a discrepancy.
What four controls do switchboards have?
Start/stop switch
Selector switch
Control switch
Discrepancy switch
What six indicator lights do switchboards have?
Control available/ not available Generator running Fire detected Over temperature Breaker tripped Earth fault
What are the 9 steps required for connecting to shore supply?
Send signal to port Raise permit to work Rack out breakers Prove box dead Obtain castel key Test shore supply cables Bring on and secure cables Connect cables Inform dockyard
Where must the ship be earthed when connected to shore supply?
To the jetty
The the ship alongside
At two points not less than half the ships length apart
Gangways are earthed
What checks are done after shore power is switched on but before connecting to ship?
Voltage and frequency
Stability of supply
Proper connection of cables
If power cables are connected correctly, what will the phase sequence indicator show?
The light on the right will be bright, the light on the left will be dim.
What will happen if phases are incorrectly connected?
Motors and pumps will run backwards and damage equipment.
What must be done before shore supply cables can be connected to shore supply box?
The cables must be checked for dead.
What are three categories of change over switches?
Automatic ACOS
Remote operated ROCOS
Hand HCOS
Which two supplies are all essential equipment provided with?
Normal
Alternative
Where is a remote operated change over switch located?
Ships control center SCC
What are the three types of hand change over switches?
Normal/alternative
Normal/emergency
Normal/alternative/emergency
What position is a HCOS kept in and when will a HCOS position never be changed?
Kept in normal position
Never changed while equipment is running
If the normal supply fails, what will an ACOS do?
Automatically switch to the alternative supply
Which two ways are earth faults indicated?
Indicator light on PCP and SCP switchboards
Audible alarm
How are earth faults tested in a 450 V ac system?
Automatically
How and where are earth faults tested on a 115 V ac system?
Done at the first fuse panel after the transformer.
Usually by using insulation resistance test using MIT 420.
Why is the 115 V system not tested for earth faults the same way as the 450 V system?
Because there is an air gap between the primary and secondary coils of the transformer, so there is no physical connection between the two.
How do you test for earth faults on a control and communications switchboard?
Push the two buttons simultaneously to test the lights, push each button individually to test the positive and negative side of the DC supply.
What voltage emergency supply does the C&C switchboard supply?
24 v DC
How is an earth fault indicated on a electrical distribution panel EDP?
An earth fault indication light will illuminate if there is an earth fault in any circuit powered by the EDC.
What equipment must be earth bonded?
All equipment generating or operating at greater than 35 v AC or 50 v DC must be earth bonded.
What are the two classifications of portable electrical equipment?
Class 1
Class 2
What voltage and fuse rating limited to for portable equipment?
115 v AC
20 Amps
What does a postcode identify?
Where power is coming from
Where power is going to
How many EDCs are there in a generic distribution system?
4
What is the reference book and what is it used for?
Documents and is used in conjunction with the power book and lists all fittings, the number fitted, component symbols and pattern numbers.
What is the name for the collection of reference books?
Engineers as fitted books.
