IEEE Electrification Magazine - June 2015 - 62

Simulators

Currents

1,000
800

Generator 1
Generator 2
Generator 3
Starboard Propulsion 1
Starboard Propulsion 2
Port Propulsion 1
Port Propulsion 2

500
400

0
06:48:00

06:51:00
Time

Figure 15. The experimental record of generator (1,000-A scale) and
propulsion (800-A scale) currents during the incident leading to blackout.

in idle waiting for possible maneuvers, some air-conditioning compressors, and low hotel load (the ship was mainly
unoccupied). The resulting power factor was quite low. One
of the generators suddenly failed because of a lubrication
fault, causing an automatic removal of one of the harmonic
filters to avoid reactive power overcompensation. In a short
amount of time, another generator failed because of the
same lubrication problems (the lubrication circuit is in common to a group of generators). This caused the automatic
removal of the remaining harmonic filter (along with its
power factor correction function), which, in turn, caused
overexcitation in the remaining generator. The PMS automation did not detect the reactive overload because of a sensor
fault on the remaining generator, so it did not react to the situation. Moreover, it allowed a propulsion power increasing
command, worsening the situation.
The increase in the reactive power required from the
propulsion brought the remaining generator to saturation,
and, as a consequence, the system voltage progressively
dropped. At this point, protections operated, leading the system to the blackout. Analyzing what happened, it is obvious
that the basic cause of the incident was the poor integration
between the ship's control and protection systems. Indeed,
the technological limitations of the equipment employed
make it impossible to realize effective system integration.
Fortunately, in the last few years, the trend is to increase the
PMS managing functions, sensors, and actuators, acquiring
more data from the system and acting more and more as
an integrated platform management software, but there is
still a long way to go.

I E E E E l e c t r i f i c ati o n M agaz ine / j un e 2015

Today, system design is done by decomposing the IPS in little, noninteracting subsystems. As previously stated, this
procedure can sometimes lead to incorrect design, discovered only when the ship is assembled, and then to expensive
modifications to be done after the installation on board.
Software tools capable of simulating the behavior of
the whole system are proving to be more and more a key
feature that is essential for the IPS's accurate design. Obviously, the creation of an entire shipboard power system
simulator is a difficult and time-consuming operation.
Nevertheless, the possibility to experiment with different
settings for the system's regulators and protections, and
also to try different logic procedures to manage the loads,
is worth the cost that the simulator creation implies.
In particular, it should be noticed that the use of a simulator permits one to know the system's responses when it
is not yet assembled, in a short amount of time, and permits the same test conditions to be applied in every trial.
The latter point is important because when tests on real
systems are done, it is not possible to fix exactly the same
conditions, meaning that sometimes the results are not
comparable to each other. Moreover, the most relevant
advantage of using a simulator is the possibility to run tests
that would bring the system into dangerous conditions. In
this way, it is possible to analyze particular situations (such
as fault transients) without damaging the devices or creating harmful situations for the crew and the surroundings.
Realizing a single simulator that is capable of modeling
the entire IPS function in every condition and for both
short- and long-term dynamics is a harsh matter. A shortterm-dynamics-tailored simulator will take a very long
time to perform a long-term-dynamics simulation because
of the computation of fast transients, which did not affect,
to an appreciable extent, the long-term behavior. Likewise,
a long-term-dynamics-tailored simulator cannot perform
short-term simulations because of the removal of the fast
dynamics, which is done with the aim of reducing the
computational work. Accordingly, it is important to accurately define the scope of the simulator and then build it by
applying the appropriate simplification hypotheses.
The proper solution could be the realization of a certain
number of different simulators tailored to the needs of the
designer. For example, short-term-dynamics simulators
could be realized with the aim of studying the single component's behavior, while long-term-dynamics simulators could
be realized to study an entire IPS's behavior. As an example,
given the typical bandwidth of voltage control, a simulator
customized for this study could be created using the
hypothesis to consider only electromechanical transients. In
doing so, several simplifications could be accomplished
(some of them strong, e.g., totally algebraic load's network) to
obtain a simplified simulator, which is faster than a complete one that is dynamic.
Before being used, a simulator must necessarily pass
through a tuning and validation procedure. The mathematical

Table of Contents for the Digital Edition of IEEE Electrification Magazine - June 2015