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Thursday, March 19, 2020 

Not the age, but the actual ageing should be at the forefront when replacing modular frequency converters, says Dutch company Bakker Sliedrecht.

Vessels with electric propulsion motors, as well as electrically driven cranes, pumps and similar equipment, all use modular frequency converters to control speed and power. Each frequency converter contains a capacitor bank, which is subject to ageing. Currently, capacitors are replaced at manufacturer-prescribed time intervals, e.g. 9 years. This replacement period is based on expectations of the most severe conditions rather than actual ageing of the capacitors. Thus maintenance is carried out at an early stage, often postponed so that downtime may be delayed. Replacing capacitors can involve 7 to 8 hours of work per module, with an average ship containing dozens of modules on board.

Bakker Sliedrecht therefore has started condition monitoring of modular frequency converters. The capacitor bank of one module per cabinet is inspected periodically, which enables the progression of aging o be determined, and to plan a replacement schedule based on the actual condition of the capacitors. Bakker Sliedrecht's experience shows how the ageing curve proceeds, so actual ageing over time can be predicted. Prolonged downtime of frequency converters also impacts on capacitor ageing, which is not taken into account in time-based maintenance schedules, but can be accounted for in condition-based predictive maintenance.

The company says that condition-based maintenance can save money and schedule work for the most convenient time. Such predictive maintenance has already been applied in the offshore crane vessel sector.

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