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THD - Total Harmonic Distortion

Power quality with frequency drive applications for maneuvering and propulsion systems - simulation for the ship power network.

SER offers the simulation of the harmonics of the complete power network. Our simulation software makes it possible to simulate big power grid networks on the basis of the components and the true circuit diagrams of the equipment.

Our engineering services include:

  • Power grid simulation for newbuildings
  • Simulation for existing vessels with too high THD with recommandations for the THD reduction
  • Simulation of the complete ship power network for classification approval

Our comprehensive model library contains models of:

  • Generators
  • Transformers
  • Linear and non-linear consumers
  • 6-, 12-, 18- and 24-pulse frequency converters with phase shift transformers of different vector groups and voltage levels
  • Active Front End (AFE) converters
  • Active- and passive harmonic filters

A complete simulation model of the ship’s power network is established on the basis of the given information on generators, the single-line diagram and the consumer- and frequency converter lists.

The simulation is made for different typical scenarios of ship’s operation such as:

  • Normal sea operation
  • Berthing manoeuvres
  • DP operation
  • Split bus-bar modes

The result of the simulation is the harmonic analysis of the voltage and the currents in the grid. The power quality in power networks regarding the harmonic distortions is ruled by the IEC 61000. The power supply on board of ships is, unlike the power supply on shore, very limited and matched to the power of the onboard consumers. In case of diesel electric propulsion systems, the frequency converter load of the generators can be up to 85% of the total generated power of the ship. Therefore, the problem of the THD (total harmonic distortions) must be very carefully taken into account. The limit of the voltage distortion THD-V is ruled by classification societies – in normal case by 5% … 8%, with diesel electric propulsion systems up to 10%.