We recently had the opportunity to service Siemens Robicon Perfect Harmony VFDs on a LNG Carrier (Ship) in the middle east. When natural gas is cooled to minus 259 degrees, it assumes a liquid state. Liquefied Natural Gas (LNG) is much more efficient to transport than compressed natural gas (CNG). It is particularly suited for large LNG Transport Ships.
The problem is keeping it cool. Many LNG Ships use large compressors to lower nitrogen to around minus 321 degrees where it becomes a liquid. The liquid nitrogen is then used to keep the LNG in liquid form for transport. The Siemens Robicon Perfect Harmony VFDs, in this case, actually control the compressors. The typical size of the Siemens Robicon Perfect Harmony VFDs used in this ship are around 8000 HP. At this horsepower the medium voltage power cells are generally liquid cooled to conserve space. That’s especially important when mounting the Siemens Robicon Perfect Harmony VFDs in the limited space available aboard a LNG Transport ship.
Siemens Robicon Perfect Harmony VFDs aboard a LNG Carrier ship face the same issues medium voltage drives do anywhere else. The problems are exacerbated by the fact that the ship is often at sea and not easily reached. This makes performing predictive maintenance a bit more critical than many other applications.
In particular, over time the bus capacitors can begin to age and fail (See Robicon Perfect Harmony Preventive Maintenance) . It’s important that the state of the bus caps be carefully monitored by routine maintenance. And, when the time comes, the Siemens Robicon Perfect Harmony VFD bus caps should be replaced. These problems can be exacerbated by environmental issues such as moisture and heat. Both of which are always an issue on LNG Transport Ships.
The market for LNG is expanding, and consequently, we expect to see more of these applications. IF spare power cells for the Siemens Robicon Perfect Harmony VFD are stocked on the LNG Transport Ship, we can actually repair and refurbish the medium voltage VFD power cells in our facilities. We have complete test and load stands to do this, and often this makes more sense than having technicians actually aboard. That’s not to suggest that we don’t place people aboard when it makes more sense to do so. EMA regularly services off shore applications.
In addition to the power cells, other components that need maintenance inspection are the phase shifting transformers. These can be a particularly nasty failure under certain conditions. We’ve actually seen fires as a result of this. The failures usually occur on power up. The Siemens Robicon Perfect Harmony drive does not use a “pre charge” circuit, so power up usually results in relatively large currents through the input transformer. (see Precharge on Robicon VFDs for more information.)
IF you have Siemens Robicon Perfect Harmony VFDs on a LNG Transport Ship or any other application, give us a call at 770-448-4644 OR use any of the convenient contact methods on this site. No One, Anywhere, is Better at Drives than we are.