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Due to the increasing complexity of electrical and control systems on-board ships, maintenance of ship electrical installations has become a major issue. Reactive maintenance, i.e. repairing after a failure, is even more critical on ships. This is because that the maintenance teams on-board are limited in number. They need to be trained and competent on many different systems, products and technologies. In order to ensure correct operation of these systems, it is necessary to follow manufacturer recommendations regarding regular verification, testing and replacement of critical parts when needed.
Preventive maintenance is the common strategy in the shipping industry. According to manufacturer recommendations and classification society requirements, maintenance plans are scheduled in advance so as to reduce downtime. It makes it easier to anticipate and plan resource availability (material, dock, human resources).
However, this preventive approach is not perfect and cannot guarantee zero failure when shipping. In addition, due to the increasing pressure on costs, maintenance operations are under scrutiny and reducing the downtime. It has become a major challenge.
Condition-based maintenance for ships
Condition-based maintenance (CBM) is a different strategy. While preventive maintenance relies on manufacturer and classification society requirements, CBM is adapted according to the actual service conditions. Ships are generally designed to operate in certain configurations, typically at an average given speed. All components are sized according to these requirements. In particular, electrical installations are supposed to operate at a rated voltage, with pre-determined load profiles. It helps maximize the efficiency ratio of this equipment. However, the actual use may be different. For example, introduction of a slow steaming operation has modified the operating point of the main engine and propeller. Although this practice aims to reduce fuel consumption, in many cases it does not correspond to the forecasted use of system as it was designed.
In this approach, the technical parameters of the equipment are measured and combined with environmental parameters relating to system usage. This information will then be used either to detect early signs of failure or to adjust maintenance plans.
Measurements and analysis
One of the key considerations is how to gather the data needed for monitoring. The shipping industry is starting to take advantage of the global Internet of Things (IoT) trend. CBM is all about leveraging the fast growing connectivity of devices. Most electrical equipment on-board includes embedded sensors or provides data such as temperature, pressure, current power (medium voltage), switchboards. They are equipped with protection relays, current and voltage transformers or power meters providing comprehensive data. Power transformers can be equipped with embedded temperature sensors. This data is primarily used for ship control and monitoring systems. However, it could easily be made available for external monitoring. The analysis of different parameters is combined with environmental data like external temperature or relative humidity. They can lead to detection of imminent failures or give relevant information relating to the misuse of equipment.
One of the most critical examples relates to busbar joints and cable connections. Poor connections can result in serious damage – from over-heating to fire, causing large losses. It is estimated that about 25% of all major electrical failures are due to loose or faulty connections1. To prevent such events, a preventive approach would typically consist of regularly checking tightening torque on every single power connection point. However, it can take a lot of time on a large ship. In the predictive approach, one solution is to monitor the conductor temperature next to the connection point. Furthermore, it is to detect abnormal values, either individually or by comparing other values, (temperature on other phases). In these conditions, it is possible to point out connections needed to verify instead of checking all individually. This saves time and avoids unnecessary work.
Other applications related to CBM on electrical installations include circuit-breaker monitoring, (low and high voltage), environmental monitoring, etc. Of course, CBM is not limited to electrical equipment. Vibration analysis methods are used to detect component failures such as defective bearings, misalignment of equipment like gearboxes, motors, etc.
Such monitoring demands well-adapted IT infrastructure on-board vessels. While data has to be collected locally, they should be available for analysis preferably on shore, for example in ship operators’ service offices. Different solutions exist, but cloud-based architectures are suitable. Data loggers are installed on-board to collect the data and send it to the remote server through an Internet connection. They most likely use satellite communication. The configuration of this communication system will be highly dependant on the number of monitored assets and on the frequency of data exchange. We can keep in mind that the available bandwidth is expected to be limited to approximately 200k bytes/second. Megabyte size communication lines are very unlikely to be used for such purposes, for cost reasons. Finally, all this data should be securely stored so as to be analyzed and saved for future reference. Implementation of this infrastructure should be made taking appropriate measures regarding cyber security, the dedicated IT solutions and data loggers.
Key benefits and challenges
The benefits of CBM for ship operators are multiple. First it will improve the overall system reliability and significantly reduce downtime. It will also make it possible to adjust and optimize the maintenance plan frequency based on actual figures. Therefore, it leads to significant cost reductions. Data analysis can also be used to compare similar vessels inside a fleet. Moreover, it is also to examine trends over longer periods, typically energy consumption on critical loads, efficiency levels, etc. This data and related reports may be used to determine areas for optimization in the ship’s design and retrofit requests. Spare parts management is also simplified, especially because the need for emergency spare parts is reduced.
On the other hand, some challenges should be taken into account. CBM can lead to modifications in the frequency of maintenance operations. However, ship operators should manage these unpredictable maintenance periods from a logistical viewpoint and justify these changes towards classification societies. In any case, there will always be a need for preventive maintenance. The first reason is that some operations need to be performed on a regular basis. Secondly, certain ageing components cannot be easily monitored. The initial cost of the installation needed to perform CBM can be quite high. The best approach is to include the technical requirements linked to CBM as early as possible in the vessel’s design. When it is not feasible, the best solution is to maximize the use of non-invasive technologies. They can be embedded in easy-to-install devices, such as wireless, battery-free sensors.
The shipping industry is facing challenges regarding energy efficiency and cost optimization. In order to optimize the investments, CBM is taking on a greater significance in terms of key implementation strategies to consider in the coming years.
1: Source: NETA (InterNational Electrical Testing Association)
