The new medium voltage power drive from Wärtsilä enables ice breakers and ice-going vessels like arctic shuttle tankers to take advantage of the power and space savings of the Low Loss Concept
Wärtsilä’s electrical systems capability is being enhanced with the development of an in-house designed medium voltage variable speed drive[ds_preview], which is, amongst others, covering the power demand for vessels with electric propulsion such as ice breakers, arctic shuttle tankers or LNG carriers. It greatly expands on the success of the low voltage power drive introduced in 2005 by meeting power needs from 5.5 MW up to 25 MW. The drive can be used as a control device in applications such as marine main propulsion, thrusters, large fans, pumps, compressors and hoists. Furthermore, it can control asynchronous, synchronous and permanent magnet machines in generator or motor mode.
The development work for the medium voltage drive has been carried out at Wärtsilä’s R&D facilities in Norway, and Wärtsilä is now conducting validation tests including operation at full power of the drive and associated Low Loss Concept (LLC). Performance has met and exceeded expectations. The new drive will be ready for delivery to customers in the first quarter of 2014. In recognition of the benefits it provides, most particularly the ability to reduce energy consumption and therefore save on fuel and operating costs, Frost & Sullivan has presented Wärtsilä with the 2012 »Europe Customer Value Enhancement Award in Electric Power Drives for the Marine Industry«.
Lower weight and size
The power electric unit is wholly focused on maritime applications, featuring rugged construction and easy maintenance access in confined spaces. According to Wärtsilä, also the size and weight of the new drive is significantly lower than other products on the market today, saving valuable space on board. The design is compliant with IEC, marine classification societies, IACS and NORSOK requirements. »Every design decision was made with marine conditions and the safety of ships’ crew in mind,« says project manager Jakob Bjelland.
The drive is water cooled and the cooling water cabinet, including the de-ionising unit, can be delivered as an integrated or stand-alone solution; so that all shipyards need to do is connect the ship’s cooling water. All control and power electronics are located in the upper section of the cabinet sealed from dust and contamination during operation and commissioning, whilst the power and water connections are located in the lower section easily accessible for maintenance and commissioning. The medium voltage power drive features three level pulse-width modulation (PWM) inverter control and the latest press-pack insulated gate bipolar transistor (IGBT) technology. The modular IGBT design has large overload capacity, integrated gate driver boards and a plug-in bus bar connection. »This is the first time that IGBT technology has been introduced to a direct 6.6 kV feed in a marine application. The advantage is that with a true 6.6 kV input, there is no need to have transformers between the switchboard and the drive, giving it the most compact footprint on the market,« Bjelland says.
In the core of Low Loss Concept
To extend the compact solutions, the power drive can be installed as part of a Wärtsilä Low Loss Concept (LLC). The LLC solution is based on a transformer in which the main windings are phase shifted by 30° by rectifying bridges to cancel the 5th and 7th harmonic currents. These bridges are supplied from the two phase-shifted sides of the LLC transformer with each providing 50 % of the required power. With the use of ready-built plug-and-play filters, total harmonic distortion levels of less than 5 % are achieved and the majority of the harmonic currents pass through the transformer, not into the generator. LLC therefore eliminates the need for propulsion transformers and genset power can be applied directly to the frequency converters used for speed control. The low loss transformers can be located flexibly in the system giving greater freedom to designers to optimise the use of the limited available space on board.
In most cases to date Wärtsilä’s low voltage power drive has been delivered as part of a LLC and used for electric propulsion applications in the offshore support vessel market. LLC has already been installed on around 70 vessels including such high profile offshore support vessels (OSVs) as »Viking Lady«, retrofitted with fuel cell technology, and two LNG-fuelled vessels, owned by Harvey Gulf. Another important motivation for these operators to select the LLC is the possibility to achieve an environmental rating number (ERN) of 99.99.99.99, showing maximum probability that a vessel will keep position even at worst case single failure, while still allowing for additional fuel savings, because fewer gensets need to be in operation to reach the required level of redundancy.
System efficiency of the Low Loss Concept is 2–4 % higher than in traditional transformer-based systems, and the current supplied from the switchboard to the frequency converter is 10 % lower. Shipowners can therefore achieve fuel savings of between 30,000 and 100,000 € per year.
»The scaling up of LLC to medium voltage means the benefits can now be offered to larger installations as well benefitting cargo, passenger and offshore markets,« says Patrick Baan, director of R&D for Wärtsilä’s electrical & automation business. »Additionally, both systems can be integrated with Wärtsilä’s integrated Control and Communication Centre (Wärtsilä 3C) to create further synergies in delivery, construction, operation and maintenance.«
