EE301 Lesson 35 Shipboard Power Systems
EE301 Lesson 35 Shipboard Power Systems
EE301 Lesson 35 Shipboard Power Systems
1
Learning Objectives
• Explain the rating of a Ships Service Diesel Generator (SSDG).
• Draw and explain the simplified diagram of a warship’s 450-
VAC/120-VAC distribution system.
• Discuss the concept of vital and non-vital busses and the loads
typically powered by each.
• Explain the purpose of shore power and how it is paralleled with
ship’s power.
• Define a bus, bus-tie breaker, split-plant operation, and parallel
plant operation.
2
Bus (Switchboard)
• A Bus is a conductor that connects multiple circuits or loads to
a common voltage supply.
• Large Loads and Power Distribution panels are connected
to a bus via a Breaker.
• A bus is physically heavy gauge wire or a metal bar.
• You can think of it as a VERY LARGE circuit breaker box.
3
Bus
4
Busses…
• Busses are categorized as VITAL or NON VITAL.
• Typically located in a SWITCHBOARD, which is a watertight
enclosure.
• Usually numbered 1S, 2S, 1B, 2B, 1E, 2E.
• Odd numbers are Starboard busses.
• S=Ship Service (450 VAC, 60 HZ).
• B=Battery Bus (High Voltage DC).
• E=Emergency Bus.
5
Power Distribution Panel
6
Vital Loads
• Vital loads are electrical loads deemed critical to safe
operation of the vessel:
• Bilge pump.
• Hydraulic steering pumps.
• 1MC system.
• Reactor Coolant Pumps.
• Lighting (required to be able to successfully combat any
casualty).
• For maximum reliability, vital loads
should be capable of being powered
by different sources – termed redundancy.
7
Non-Vital Loads
• Non-Vital loads are not critical to safe operation of
the vessel:
• Galley power.
• Hot water heater.
• Fans and ventilation.
• Because reliability isn’t critical, non-vital loads are
typically powered by a single source.
8
Typical Bus Arrangement
Alt.
Shore Power 2S
#1 (Stbd) SSDG 1S
9
Circuit Breakers
10
Circuit Breakers
11
Motor Operated Breaker
Adjustable Over
Current and Time
Delay Settings
12
Typical Bus Arrangement
Supply Bkr Feeder Vital Power Panel
Bkr
#2 (Port) SSDG Norm.
Alt.
Individual
Bus Tie Bkr
load
Shore Power 2S
Load Bkr
Non Vital Power
Panel
#1 (Stbd) SSDG 1S
13
Split Plant (Full Power Lineup)
Vital Power Panel
Alt.
#1 (Stbd) SSDG 1S
14
Split Plant Operations
15
Cross-Connected (Parallel)
Plant Operations
Port & Stbd SSDGs operating, Bus Tie Bkrs Shut
Vital Power Panel
Alt.
Shore Power 2S
17
Half-Power (Single SSDG)
Plant Operations
Stbd SSDG operating, Bus Tie Bkrs Shut
Vital Power Panel
Alt.
Shore Power 2S
Alt.
Shore Power 2S
#1 (Stbd) SSDG 1S
19
Shore Power Lineup
20
Designed for Reliability
• Electric Plant is designed to be reliable.
• A faulted piece of equipment will not bring down the
entire distribution system.
• Fault: A piece of equipment is shorted:
• Short circuit causes generator to see near zero
resistance; generator must supply near infinite
current.
• Too much current is an overload; with no
protective action (breaker opening, fuse blowing)
excessive heat and fires can result.
21
Designed for Redundancy
• Failure of any single component does not cripple the
ship.
• Failure of a single supply will not cause a complete loss
of power.
22
Designed for Redundancy
23
Ships Service Power
24
Shipboard AC Overview
• Majority of the loads are AC powered.
• 60 Hz .
450 VAC.
− Produced by generators.
− Required by large machines: pumps, air conditioners.
• 120 VAC.
− Stepped down by transformers.
− Required by lighting and most electronic equipment.
− Many 120 VAC loads are single phase.
25
120 VAC Power Distribution
26
Requirements prior to Parallel AC
Power Source
• When two different sources or loaded busses need
to be connected, we must Parallel them.
• This means Frequency and Phase Angle must be
matched before shutting a breaker.
• Shutting a breaker with a large phase difference:
• Arcing and sparking = fire =>BAD
• Equipment could be reverse powered (running equipment
could be overloaded).
27
Requirements prior to Paralleling
1. Voltage matched.
2. Phase sequence matched.
3. Incoming Frequency slightly greater than running
(so incoming machine will take load).
4. In phase.
28
Requirements prior to Paralleling
• A Synchroscope is used to compare the frequency difference
between the two sources.
29
Navy Ungrounded Systems
30
Grounded System:
Personal Safety
• The person is touching cabinet when one of the electrical phases shorts to it.
• The current from the fault flows directly back through the grounding strap to the
neutral line on the generator WITHOUT passing through person’s body.
SSDG Load
SSDG
Load
32
Navy Ungrounded Systems
• EQUIPMENT RELIABILITY is the issue!
• If a piece of equipment shorts to the hull, that piece of
equipment usually will continue to operate.
• Since the hull is not grounded to the neutral of the generator,
only a very small current flows.
• Small current = no fire!
• Small current = circuit breakers don’t trip, equipment
continues to run!
• Electrical plant operator checks for grounded equipment once
per hour. If a ground is discovered, equipment is sequentially
switched around until the grounded equipment is found.
• If two different pieces of equipment on different phases are
shorted, circuit breakers trip and/or a fire occurs!
33
QUESTIONS?
34