Emc and electrical safety on board ships

1. EMC and electrical safety on
board ships
How EMI Filters undermine the protection
against electric shock

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. 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. Electric shock effects
on the human body

5. Earth fault currents I
Three-phase filters applied in power
electronic equipment

6. Single-phase filters applied in
smaller equipment
Earth fault currents II

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. 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. 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. Shared Success