EMVT 12 september - EMC and electrical safety - Imtech Marine


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Emc and electrical safety on board ships

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EMVT 12 september - EMC and electrical safety - Imtech Marine

  1. 1. EMC and electrical safety on board ships How EMI Filters undermine the protection against electric shock
  2. 2. Isolated Power Systems (applied on board) Earthed Power Systems (applied on land) Protection against electric shock • Traditionally, the unearthed system prevents an electrical loop • However, capacitances undermine this Protection against electric shock • 30 mA Residual Current Detector (RCD) detects current leakage and immediately switches off the power
  3. 3. Earth fault in IT system and electrical safety Disturbances in the power supply network • More Electronic equipment on board increases ElectroMagnetic Interference (EMI) • EMI-filters are needed to comply with regulations • EMI-filters reduce disturbances but undermine protection against electric shock
  4. 4. Electric shock effects on the human body
  5. 5. Earth fault currents I Three-phase filters applied in power electronic equipment
  6. 6. Single-phase filters applied in smaller equipment Earth fault currents II
  7. 7. How to ensure electrical safety on board In AC networks, an electrical loop occurs because there is a return path via parasitic capacitances of the conductors toward earth. Therefore it is very important to limit these capacitances How to limit disturbances Short the disturbance currents as close to their sources as possible. EMI-Filters do so by applying capacitors, which have low impedances for high frequency disturbance currents The filters to limit disturbance in the power supply networks counteract the measures to increase electric safety Contradicting demands
  8. 8. Suggested Remedies APPLY “MEDICAL TYPE” FILTERS • These filters don´t have capacitors connecting the active conductors to earth which limits the leakage currents to 10 µA. • The attenuation of common mode disturbances is significantly less than of the standard filters • The option is not available because the filters are integrated • APPLY TN-S / TT SYSTEM • Standard EMI-filters are intended to be applied in earthed systems. • Continuity of supply is no longer an issue due to better insulation materials and redundant systems in case of high availability demands APPLY RCDs • RCDs in isolated systems might not be able to measure the real earth fault current that a person is exposed to. Therefore 10 mA RCDs shall be applied for each socket • Many RCDs are needed
  9. 9. Conclusion Extended grids and filters create a safety risk in IT grids There are limited solutions available; like: – the use of RCD’s – special filters Real solution for the problem is to apply more TN grids, – continuity of supply can be arranged in other ways
  10. 10. Shared Success