IEEE Electrification - September 2020 - 37

220 V, 50 Hz

400 V/200 V
400 V/200 V

400 V, 50 Hz

Hotel Load ac Bus 400 V, 50 Hz

G

Emergency DG

Hotel Load
Tx 1
630 kVA
690 V/400 V
50 Hz
dc
ac

Main
M Propulsion 1
0-1,000 kW
3 ac 0-665 V
0-120 rpm
M

ac
dc

Side Propulsion
0-300 kW
3 ac 0-690 V
0-1,500 rpm

dc
ac

dc
ac

ac
dc
dc Bus Starboard Side 1 kV

220 V, 50 Hz

Hotel Load
Tx 2
630 kVA
690 V/400 V
50 Hz
dc
ac

dc Bus
System
G

1,100 kW
3 ac 690 V
1,200-1,500 rpm
DG1

	

IEEE Elec trific ation Magazine / S EP T EM BE R 2 0 2 0

Figure 9. A single-line schematic of the dc bus system of the Shen Kuo (2,100 tons). (Source: Wuxi Silent Electric System (SES) Technology Co., Ltd.; used with permission.)

M
Main
Propulsion 2
0-1,000 kW
3 ac 0-690 V
0-120 rpm

ac
dc
dc Bus Port Side 1 kV
ac
dc

G
DG2

G

Performance on a Real Mission
For the Shen Kuo, the cruising mode
means the total power required by the
propulsion motors is more than 1 MW,
thus each DG in the vessel needs to
generate more than 50% of its rated
power. When the main propulsion
motors are lightly used for the maneuver and DP modes or in idle for the
docking mode, the DGs are lightly
operated at less than 50% of the rated
output. The advantage of dc bus system in fuel savings and emissions
reduction is mainly evident in the partial- and light-loading conditions of
the DGs.
From 17 November 2018 to 8 January 2019, the Shen Kuo conducted a
mission from the Southeast China
coast to the Mariana Trench; its
course is illustrated in Figure 11.
During this 53-day voyage, the Shen
Kuo operated only about 20% of the
time in cruising mode; the rest of

dc
ac

1,100 kW
3 ac 690 V
1,200-1,500 rpm
G
DG4
400 kW
3 ac 690 V
1,200-1,500 rpm
DG3
400 kW
3 ac 690 V
1,200-1,500 rpm

counterpart for the same purpose. The
footprint reduction is mainly due to
the absence of the ac switchboard and
the rectifying transformers. The considerably smaller footprint and weight
benefit the ship owner with more
space and higher payloads. Not only
are the footprint and weight reduced,
but also the cabling and manifolds,
which means installation and maintenance become simpler. System simplification and footprint reduction are
illustrated in Figure 10.
An assessment of the cost of the dc
bus IEP system as compared with the
ac counterpart for the same system
specifications as the Shen Kuo is shown
in Table 1. While there are cost savings from switchboard and propulsion
transformers, the overall cost of the dc
bus system is modestly higher,
which is attributed to additional
power electronic devices used in
forming the high semiconductor dc
bus system. However, it is expected
that the dc bus system will become
more cost-effective in the future as a
result of continuous cost reductions
related to power semiconductors and
more uptake of dc bus systems in
other applications.

37



IEEE Electrification - September 2020

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