Use on the high seas

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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.

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.

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.

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.

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YOUR CONTACT

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