LV-MV marine step-up transformer series for subsea utilities
This particular use has been confirmed today after several years of research and development, making it possible to consolidate for the purpose various design choices validated first by Italweber Elettra technicians and then by the end customer, with the prerogative of obtaining compatibility with the naval regulations.
Each transformer is intended for the power supply of a single medium voltage submarine engine, which by driving a pump provides mechanical energy to the entire oil platform, this through a centralized pressurized oil system.
The entire power supply block is therefore composed of the series of transformers, which, being installed in a dedicated container, can be transported and used around the world according to the user's needs.
It was therefore required to power the power part (motors) and the auxiliary part (instrumentation and lighting), therefore the supply allowed the development of two different types of transformer with different characteristics.
Each type was tested in our test room in the presence of RINA technicians, thus obtaining certification for naval use.
Power transformers have the following characteristics:
| Rated power | 450 kVA |
| Primary voltage | 380 - 440 - 4400 V |
| Secondary voltage | ynD5 |
| Connection group | 50/60 Hz |
| Frequency | 6 |
| UK % | 6 |
| Primary insulation class | 1.1 / 3 / – kV |
| Secondary insulation class | 7.2 / 20 / 60 kV |
| Thermal class | F |
| Operating Ambient Temperature | 45°C |
Auxiliary power transformers have the following features:
| Rated power | 10 kVA |
| Primary voltage | 380 - 440 - 480 V |
| Secondary voltage | 2450 - 2550 - 2650 V |
| Connection group | ynD5 |
| Frequency | 50/60 Hz |
| UK % | 4 |
| Primary insulation class | 1.1 / 3 / – kV |
| Secondary insulation class | 3.6 / 10 / 20 kV |
| Thermal class | F |
| Operating Ambient Temperature | 45°C |
There were many choices made for this type of application:
- Multiple primary and secondary control sockets: the voltage drop caused by the 7 km of the submarine cable, combined with the dispersion reactance of the transformer and the load itself, were the reason for the insertion of the medium voltage switching sockets.
The primary (low voltage) sockets have been installed in view of different mains voltages based on the location of the system in the world.
- Low inrush current: the numerous switching on and off of the transformers during the 24 hours, added to other restrictive parameters imposed, meant that the design had to take place while maintaining a very low inrush current.
- Installation inside OFF-SHORE containers: since the structure can be transported around the world according to needs, the transformers are installed by the end customer inside a pre-wired container, which is constantly subjected together with the transformers to the critical environmental conditions caused by the marine environment combined with the mechanical stresses due to repeated handling.
In order to avoid damage due to the latter aspects, the transformers are built with the following precautions:
– Reinforcement of the transformer's load-bearing structures
– C5M treated steel reinforcements against corrosion
– Dedicated natural rubber anti-vibration mounts and 316 stainless steel frame
– Forced ventilation to counteract any overloads or temperature increases due to climatic conditions
– PT100 temperature probes on both low voltage and medium voltage windings
– Earthing balls on the medium voltage windings for the safety of the systems