Voltage levels
Different to industry standards in shipbuilding
- voltages of 1000VAC and above are considered “high voltage”
- voltages of less than 1000VAC are specified as “low voltage”
Typical voltage levels in shipbuilding are usually
- low voltage of 440VAC or 690VAC, which is being applied for an electrical power demand of typically up to 5-7 MW
- high voltage levels of 3300VAC, 6600VAC or 11000VAC are being applied when the electrical power demand exceeds 8 MW
For power demands of around 5-10 MW the selection of voltage levels may vary and depend on a combination of total power demand, different voltage levels in the distribution network, cable lengths, and safety and redundancy aspects.
Protection in electrical power distribution
Reliability aspects and classification requirements play a crucial role in selecting appropriate protection functionality, assuring adequate discrimination in case of failures.
For low voltage installations, classification societies define requirements in accordance with international standards, such as IEC61439-1 and 60092-302, and for circuit breakers according to IEC60947.
For high voltage installations the requirements are defined in accordance with IEC 62271-200, and for circuit breakers according to IEC 60470 and 62271-100/102/106.
Class requirements demand higher short circuit resistance and enhanced protection coordination with higher loads, which are more easily met with high voltage.
Consequently, classification societies demand protection devices independent from the high voltage arrangement and circuit breakers due to
- functional separation of main and control circuits and arrangements and independent control voltage supply
- possible redundancy and fail-safe operation
- more precise and selective protection settings supporting a clearer selectivity