I.SHIP POWER STATIONS AND NETWORKS
LECTURE 2
Ship Electric Power Stations and Their Classification
Lecture plan:
1. General information on ships’ electric power stations
2. General information on ships’ generators
Literature:
1. H.A. Mehdiyev, Z.Ə. Həsənov, T.H. Şabanov. Avtomatlaşdırılmış gəmi
elektrik intiqalları. Bakı, «Nurlan», 2005. – 358 səh
2. H.A Mehdiyev «Gəmilərin elektrik avadanlığı» Bakı, «Ti- Media», 2008 – 398
səh.
Test questions:
1. How ship electric power stations are classified by their functions?
2. Rated voltages used for ship electric power installations.
3. The main parameters of synchronous generators.
4. Rated voltage of ships’ lighting network.
Ship electric power stations (SES) produce electrical energy, control it
quantitively and qualitively and also distribute the produced electrical energy to
ship consumers.
The electric power stations used in modern ships are autonomous power
installations equipped by all the necessary devices, apparatus and other
facilities. In general ship electric power stations consist of synchronous
generators driven by engines, and main switchboard (MS).
The frequencies of 50 Hz and 60 Hz are usually nominated for ship electric
power stations. Sometimes, especially at necessity to optimize (minimize)
dimensions of ship electrical installations, the rated frequency of 400 Hz is used.
The following rated voltages are used in ship electrical installations:
- 12 V and 24 V – for non-stationar electric lamps, some secondary circuits
such as signalisation and control ones and their elements and also starter
launching;
- 42 V – for non-stationar electric instruments (accepted by Russian Maritime
Register);
- 220 V and 380 V – for electric equipment permanently connected to the ship
network.
Use of higher electric voltages leads to decreasing of cable networks’ weight.
The total length of all the ship electric cables reaches a hundred kilometers
(100 km). Increasing of higher nominal voltages leads to decreasing of cable
conductors’ cross-section. So, for high power electrical installations there
have been used high rated voltages, such as 3300 V, 6600 V, 12000 V and
15000V. In normal cases the rated voltage of 400 Volts at 50 Hz frequency
and 450 Volts at 60 Hz frequency are used. The voltage of lighting network is
220 Volts. Lower voltages in secondary AC networks are got due to stepdown transformers.
There are 3 types of ship electric power stations – main, emergency and
special ones. The main SES’s provide all the consumers of electrical energy
in the normal operating regimes such as navigation, maneuvering, stop while
loading, stopping and also emergency regime.
There are 2 emergency regimes on the ship One of them is fire, another one
is ship hull hole accompanied by filling it with water. Emergency SESs are
operating just in at these unfavorable regimes.
Emergency SES begins to operate and provide by electric energy the
consumers responsible for ship’s safety at fails of main SES.
Special SESs are used in some ships to provide high power electrical
installations (drilling equipment, lifting crane etc).
Ship generators
Generator unit is the main electrical energy source on the ship. It consist of
machine-generator and engine driving this machine-generator. There are used
diesel, steam and gas turbines to drive the machine-generator. The engine
driving a rotor of machine-generator is called the primary engine. The rotor of
machine-generator may also be driven by the ship’s main engine. Such kind of
generators are called shaft generator (a green one).
The main parameters of ship generator (add efficiency, time to start,
lifetime, overloading ability etc) depend on kind of primary engine (unit). Some of
them are presented in the Table 1.
The indicators with * sign correspond to use of fuel-oil.
Meaning of abbreviations used in the Table 1 is consistently:
DG – diesel-gеnеratоr;
TG – turbоgеnеratоr;
GTG – gas turbine gеnеratоr.
Table 1
№
Indicator
1.
Power range, kW
Time to major overhaul, per 1000
hours
Efficiency, %
Specific fuel consumption,
grams/kW*hour
Kilograms per kilowatts, kg/kW
Time to start, minutes
a) re-start
b) from the resting position
Overloading ability, %
Noise made by unit
Labor costs, hour per day
2.
3.
4.
5.
6.
7.
8.
9.
Type of unit
DG
TG
GTG
30…1500 100…3200 600…1500
15…30
25…50
20…25
25…30
30…40
20…25
<250
300*
470…550*
30…50
14…65
10…18
<1
4…7
10
Loud
0,5…1,1
20
2…3
30
2…5
–
20
Not too loud Too loud
0,5…1,0
–
The most widely used kind of ship’s primary engines is diesel-generator. It is
conditioned by their economic advantages in comparison with others and higher
mobility i.e. little times to start.
If the main engine used in the ship is a steam turbine then there are used
generators driven by steam turbine. An advantage of use such group of primary
engines is their high reliability. They can also provide reliable parallel operating of
generators. Unfortunately, they have also some disadvantages especially lower
mobility i.e. higher times to start (needed to heat turbine) and lower economic
indicators.
The generator units driven by primary gas turbine contain properties of
diesel-engines and steam turbines, but they have higher levels of specific fuel
consumption and noises.
There are used both DC and AC generators independently on type of
primary engine. Synchronous generators driven by diesel-engines are widely
used in the ships.
Determination of AC frequency
Use of higher AC frequencies for ships’ electric supply systems is one of
the most appropriated ways to optimize (minimize) mass indicators of electrical
installations.
As known the rated frequencies used for ships’ AC systems are 50 Hz or 60
Hz. Consider influence of rated frequency used on mass-dimension indicators of
electrical equipment and installations.
Increasing of AC frequency from 50 Hz to 400 Hz leads to a little (about 10
%) increasing of the cable network’s weight.
The frequencies 200 – 250 Hz are the best (optimum) for asynchronous
motors with turns per minute no more than 1000. Just at these frequencies they
have the minimum best (optimum) mass-dimension indicators.
The frequencies 200 – 400 Hz are the best for ship generators. Their massdimension indicators at these frequencies are very preferably. Thus, increasing
of ship generators’ rated frequency from 50 Hz to 400 Hz leads to decreasing
their volume and mass by 3.5 times. In the same time, it leads also to significant
decreasing volume and mass of primary engines.
Building the ships with higher AC frequency networks begun in some
countries about 40 – 50 years ago gives optimistic results.
There has been stated due to researches that the best technological
performance of ship electrical equipment is possible to be reached at supply
frequency 200 – 400 Hz (at corresponding increasing of voltage). Unfortunately,
practical application of higher frequencies faces with some difficulties. The main
of them is absence of industrially produced electrical machines, switching
equipment and protection apparatus with higher rated frequencies and voltage.