Ingeteam has designed and accomplished the commissioning of the following two DP3 Accommodation Vessels for the Mexican shipowner PEMEX.
These vessels have the particularity of having only one retractable thruster powered at the same time from both DP zones (DP1 and DP2).
The main electrical plant Single Line Diagram is as follows:
Due to this configuration DNV requires to perform a “live” short-circuit test in order to prove that in case of a failure (fire, flooding, short circuit, …) in the common area it will not be propagated to the DP1 and DP2 main switchboards. As well it is necessary to ensure that in the event of a failure in one zone (DP1 or DP2) it will not be transfered to the other zone through the retractable frequency converter DC bus. The short-circuit test must fulfil the DNV rules “For DYNPOS-AUTR and DPS 3.
SHORT-CIRCUIT LIVE TEST CONFIGURATION
The following scenario, during DP mode operation, was tested and approved by DNV and the FMEA. The vessel was operated in DP with:
Both 690V bus-ties were in closed position.
A three phase short-circuit was done in MSB 690V closing the CB of the short-circuit box which was connected directly to the MSB.
The box was designed and manufactured by INGETEAM MARINE SYSTEMS and used in both vessels.
SHORT-CIRCUIT SIMULATION AND RESULTS
The goal of the test was to check that with the settings of the systems involved (breakers settings, AVR settings, governor settings,…) only the selected breaker (the one that produced the short-circuit and identical to the retractable thruster) was tripped and all the main consumers continued working.
To check the performance of the plant and the ride through capability the following measurements were checked:
On the other hand, the input voltage and frequency resulted equal were the same in the four running frequency converters.
The coasting mode was correctly accomplished in the four frequency converters in operation, according to the following graph DC bus voltage which resulted within the limits all the time:
DC bus voltage:
CONCLUSIONS
As conclusion of this test it should be demonstrated that in case of a short-circuit: