Use on the high seas

Stormy seas, salty air, snow or rain—how are cables of offshore wind turbines supposed to be tested? HIGHVOLT has found a solu­tion. It has now been used for the first time.

1. The chal­lenge

More offshore wind parks continue to be built at larger and larger sizes around the world. At the same time, the gener­a­tive perfor­mance of wind turbines is steadily increasing, and with it the oper­ating voltage of the connec­tion cables from the wind turbines to the collec­tion and connecting plat­forms, some­times at a distance of over 30 kilo­me­ters. A capacity of 66 kilo­volts has become common, and higher volt­ages up to 145 kV are being discussed. In 2019, the experts at the Inter­na­tional Elec­trotech­nical Commis­sion (IEC) there­fore decided to permit — along­side the soak test (a 24-hour test at nominal voltage) — only reso­nance testing for oper­ating volt­ages greater than 36 kilo­volts in the new IEC 63026 stan­dard for subma­rine cables up to 72.5 kV.

How do I get a testing system on the high seas? Many offshore wind park oper­a­tors face this ques­tion when they have to test their cables.(© HIGHVOLT)

For cables with a nominal voltage greater than 110 kV, this has been stan­dard for decades. But how do I get such a testing system to the switchgear and converter plat­form? In the middle of the ocean? And while dealing with wind and weather? The industry needed a solu­tion urgently for testing cables after instal­la­tion and finding the source of error in case of a later defect. Other­wise, elec­tricity will not reach the shore.

2. The Solu­tion

The testing experts at HIGHVOLT are working to make their proven reso­nance testing system fit for use at sea. First, there were exten­sive discus­sions with installers and oper­a­tors of wind parks, cable manu­fac­turers, service providers and certi­fi­ca­tion compa­nies in order to clarify the spec­i­fi­ca­tions and proce­dures for trans­port, setup and oper­a­tion. As a result, it was clear that the testing system needs to be much more rugged than its coun­ter­part on land because of the rougher condi­tions at sea. The require­ments for the mate­rials and oper­a­tion are also completely different due to the weather condi­tions.

The rendering shows all compo­nents of the reso­nance testing system: exciter trans­former, reac­tors, and the container for trans­porting acces­sories such as the control cabinet, oper­ating unit and divider.(© HIGHVOLT)

Another restric­tion is the load capacity of cranes at sea — 3.7 tons is the magic number up to which there are no restric­tions. Finally, there is also the DNV certi­fi­ca­tion, an impor­tant prereq­ui­site to allow the system to be trans­ported at sea, ferried to the plat­form and oper­ated there.

The engi­neers at HIGHVOLT reworked the testing system and divided it into several modules in order to meet the weight spec­i­fi­ca­tions. Reac­tors and exciter trans­formers have been inte­grated into the trans­port frame, which simul­ta­ne­ously protects them, and open high-voltage connec­tions are designed as shielded cables. To ensure that all mate­rials, paints and weld seams satisfy the special require­ments of maritime use, HIGHVOLT worked together with expe­ri­enced ship­building engi­neers and a special­ized ship­yard. Only twelve months after the initial sketch, the testing system at the HIGHVOLT plant in Dresden was ready for its first use in the field.

3. The first Appli­ca­tion

The HIGHVOLT test system saw its first appli­ca­tion by an offshore wind park oper­ator in the North Sea in November 2021. The wind park is almost finished, and the oper­ator has to check whether the cables were installed without errors. Expe­ri­ence tells us that more than half of all cases of faults can be traced back to faulty cable instal­la­tions.

HIGHVOLT experts have completed special training to be able to support customers on-site during the test. This takes place at night, as work is performed on the plat­form during the day.(© HIGHVOLT)

The weather on site showed off its full range, from sunshine to violent gusts of rain and ice — this appli­ca­tion had every­thing this time of year typi­cally has to offer. A HIGHVOLT service engi­neer was also on site in order to commis­sion the system and support the operator’s personnel during the elec­trical tests. To even be allowed on the plat­form, HIGHVOLT qual­i­fied three service engi­neers for offshore work assign­ments.

To be qual­i­fied, they needed to jump into the ocean from a height of twelve meters with a rescue device, free them­selves from a sinking heli­copter and prac­tice working at high alti­tudes. Because work on a plat­form is anything but safe. Since construc­tion work is still taking place during the day, the cable tests were carried out on the night shift. After­wards, the work of the HIGHVOLT service engi­neer was done for the time being and the oper­ator was able to bring the testing system to the next place where it is urgently needed.


Do you have any ques­tions about the testing system?
Dr. Mario Jochim would be glad to answer your ques­tions: