With the offshore wind sector experiencing impressive growth, Sam Fenwick hears from Semco Maritime about the use of TETRA to ensure workers’ safety and co-ordination

MoWhile critical communications deployments in the public safety sector are often driven by a combination of technology change and existing infrastructure reaching obsolescence or end of life, in many other sectors the main driver is growth in the form of new projects, be they airports, metro lines or offshore wind farms.

The global offshore wind industry had nearly 4GW of grid-connected capacity added in 2017, driven by record investment of more than $15bn, according to the International Energy Agency (IEA). It notes that in the EU, auction results have indicated that 30-50 per cent cost reductions are thought to be possible over the medium term, as larger turbines cut construction costs and larger products boost economies of scale (turbines at sea can dwarf those on land – the Vestas V164 has a rated capacity of 8MW, upgraded to 9.5MW, with an overall height of 220 metres).

However, the personnel involved in the construction, running and maintenance of offshore wind farms have to cope with a variety of hazards – simply moving from a boat onto a turbine in rough conditions can be daunting, and while there are means of making this easier, it presents more of a risk than just landing in a helicopter on a purpose-built platform (far more commonplace in the oil and gas industry).

Martin Søndergaard, product specialist, radiocom at Semco Maritime, a company that among its other activities provides integrated turnkey communication systems for the onshore and offshore energy industry, adds that as personnel on offshore wind farms are effectively lone workers, good communications together with fallback procedures are vital. In addition to the need to ensure workers’ safety, reliable communications are required due to the way in which operations are highly weather dependent – according to Søndergaard’s colleague, Russell Gallant, sales manager (telecom), this means they have to maximise their uptime.

“[It’s critical that they] make the most of their co-ordination of moveable activities across a very large area – there’s a lot of co-ordination that’s needed,” Gallant says. “We’ve done some calculations – renting a transfer vessel can cost €18-25,000 a day, so if you’ve got a cancelled trip, that’s going to hit you very quickly.”

Søndergaard says for a typical wind farm, Semco Maritime deploys a redundant TETRA base station, on a substation that consists of two transceivers from DAMM and two controllers. It decides, depending on the capacity required, whether to have two carriers or one with a hot standby, though it is typically the former. This TETRA system is integrated with “a lot of additional equipment [such as] VHF (AM and FM) implemented via a gateway”, with a PABX system (if required). The use of VHF (AM and FM) gateways, according to Gallant, means “they don’t have to have lots of different terminal types in the field and can just use a TETRA terminal for all voice communication applications”.

Redundant TETRA transceivers

While VHF FM (SOLAS) and AM (Helicopter) are mandatory, the use of gateways is not; however, he adds that the TETRA system offers a great deal of redundancy because if the backhaul to the land cuts out then “we can still work in trunked mode in the field, and if one transceiver goes down, we can still use the other, [while] if the whole base station goes down, we [can] still work in DMO mode”. To add extra value, Semco uses TETRA’s data capabilities to allow operators to track the movements of their workers, using its marine co-ordination system SemPAM.

To further ensure availability, the base station’s power supply can be backed up, as Søndergaard explains. “It depends on the client’s requirements, of course. Sometimes there is a UPS system available on the platform that we connect to. We also have the option of installing a small battery back-up inside the service boxes that we have from DAMM to provide two to four hours’ [running time, which depends] on the amount of transceivers and the load [that] we experience on the equipment. When we install repeaters inside the wind turbines, we typically also install a small UPS bank to support the repeaters in the event that the turbine needs to be shut down during maintenance.”

One added complication stems from the way wind farms have been developed and then sold on. “A lot of the bigger clients who have lots of fields have traditionally implemented a wind farm as a single entity, so everything is geared up to that one wind farm,” says Gallant. “[There’s a trend], certainly in some of the bigger players, to take all of that co-ordination between the different wind parks and try and make a hub for communications onshore from a marine co-ordination perspective, which gives them challenges – basically trying to bring all the different TETRA and VHF systems together.” He adds that they also want flexibility so that “if they [were to] sell the park off to somebody in the future, they still have the ability to cut that field out of a multisite solution”.

Søndergaard says one of the most important things to consider when deploying TETRA in this sector is “proper training of the users on the radio equipment, so they know how to operate the equipment when they are in the field [and] know the difference between trunked operation and direct mode operation”. In some cases, clients have reported that their systems aren’t working, only for the issue to be due to “the users not being fully educated on the system”.

There is also the harsh conditions and their potential impact on equipment, so Semco works to protect it as much as possible. Søndergaard adds: “Typically, we try to avoid all products that contain aluminium since it has been proven not to withstand a long time in a maritime environment. We try to mount the equipment inside [the] substations or we also put up environmental enclosures next to the antenna tower and so on, if we need to [shorten] the feeder runs.”

In addition, the risk of lightning strikes is a concern, so Søndergaard says it is important to spend more attention on ensuring adequate grounding compared with what would be needed “if it was just a non-critical onshore installation”.

He also emphasises the need for “good handcraft”, adding: “Most of this work that we supply to our end-clients is being installed at different yards all over Europe. Often the people installing antennas, cables and so on are not familiar with antenna cables and coax connectors. It requires the correct people to install this equipment [ie, the engineer or electrician needs to know what they are doing]. For instance, if a 7/8-inch cable is being installed and the electrician secures it to a tray with ties that squeeze that cable, then [the cable will need to be replaced soon afterwards], costing time and money.”

Gallant adds that quite often “if there’s a problem, it’s actually down to a bad installation on the antenna side of things, which can be avoided”.

Turning to handsets, Søndergaard says: “For offshore workers, it’s better to buy a little bit more expensive equipment from well-known manufacturers like Sepura, Motorola Solutions and so on because they just withstand [the offshore conditions] a lot better [than] some [of the] rather cheap equipment that you can buy from the Far East.”

Returning to the point about backhaul, Gallant says at the start of the construction phase “you might have nothing out there, it’s just blue water”, so a temporary TETRA base station with VHF with a satellite back to shore might be used. However: “If possible, we would try and see if there’s some sort of local infrastructure available. Typically, before a wind farm’s construction phase begins, there might be a metrology mast that would have been deployed beforehand to ensure that [the project placement will be economically viable]; so sometimes we can hook on the back of a metrology mast and set a temporary base. If it’s got fibre back to shore [then we use that], and if there’s a nearby platform we can [use its] fibre back to shore.” He adds that during the operation phase, the cables that conduct the electricity generated by the turbines back to shore include fibre, and it is this which is used for backhaul in normal operations.

Gallant says the approach to maintenance and ongoing support varies from customer to customer, with some allowing Semco to access their network, so it can remotely log onto the base stations, monitor for them and examine their log files to see if there are any problems brewing. Those clients that do not allow this require their own personnel to be more technically informed so they can do the work themselves.

Clearly, while ensuring reliable communications in tough maritime conditions is not without its challenges, these can be overcome with the right combination of expertise and planning.

Author: Sam Fenwick