Senvion issue means RWE retender

RWE Innogy is opening a new tender for turbines for its Nordsee 1 offshore project in the German North Sea, after a technical problem was detected at a number of Senvion machines of the model it plans to use at the wind farm.

Senvion – a unit of India’s Suzlon – faces a multi-million-euro repair bill to resolve the issue, which it says relates to spherical roller bearings and has been detected in less than 10 machines.

RWE is staging the new tender as a “fall-back option” even though it recently signed an updated contract with Senvion for the supply of 54 of its 6.2M-126 offshore turbines for the 332MW Nordsee 1.

That follows up on an initial contract from 2012 over the delivery of the turbines by REpower Systems – as Senvion was known until last year.

The new agreement adds a “conditions precedent” clause to the original 2012 supply contract, stipulating that it can be cancelled by the German utility.

The manufacturer said the problem was detected at “a single-digit” number of turbines – without disclosing where they are sited.

Senvion assured Recharge in an interview that it will have a fix for the technical anomaly ready before the end of RWE’s tendering process.

“We will have clearly defined counter-measures ready by the summer,” senior project manager Bernd Paulsen said. “RWE knows about our timing.”

Senvion also said that it is in close contact with all suppliers and clients affected by the technical problem.

“Not every turbine is affected, we are monitoring on a daily basis,” Paulsen stressed.

The manufacturer will exchange already-damaged roller bearings on the affected turbines at a cost of around €1m ($1.39m) per machine, which will be borne by Senvion.

The company will also install a so-called direct grease-injection system at the critical point in the roller bearing, once that system has been tested and is produced ready for installation, which is expected by September.

The manufacturer is monitoring all other machines and is ready to retrofit them with the direct grease-injection system, if a rise in temperatures indicates this is necessary to protect the bearing from damage.

RWE’s new tender for Nordsee 1 is for 54 offshore turbines with a capacity of between 5MW and 6.15MW and a rotor diameter of between 126 and 154 meters.

Interested companies need to submit their bids by May 7. The utility expects to complete the tendering process during the third quarter of 2014.

“We believe that Senvion will participate in the tender. In principle, we are optimistic that Senvion is delivering reliable machines,” a RWE Innogy spokeswoman told Recharge.

“But we need a fall-back option in order not to endanger the further course of the project.”

RWE Innogy says it expects to make a final investment decision on Nordsee 1 this year.

Senvion focuses on a solution

Senvion first spotted the problem of early wear in the spherical roller bearings – which support the main shaft in a drive-train to prevent damage-causing misalignment with the bearing housing – of “a single-digit number” of 5MW and 6MW machines last summer, writes Darius Snieckus.

Bearings have historically suffered a range of friction-related damage – including “micropitting” and “spalling” – when lubricants circulated through the componentry fail to provide a thick enough layer between surfaces, in this case between the rollers and raceway of the bearing between rotor hub and drive-train.

“These abnormalities have occurred all around the surface of inner and outer ring and to the rollers themselves caused by slight and slowly increasing temperature [in the component] leading to ‘starvation’ [of lubricants where the lubricant is ‘pushed out’ of contact areas in the bearings],” senior project manager Bernd Paulsen tells Recharge.

Various solutions to the problem have been tried by turbine makers, including using pre-tapered roller bearings and “super-finished” surface engineering of bearing parts.

Senvion has opted to retrofit the effected machines with “direct grease injection” technology, at a cost of €3,000-€4,000 a turbine. The alternative would be changing out the bearings, at a cost of €1m a unit

“From our monitoring we know that this is a problem that is borderline – sometimes we get a red flag, sometimes green,” stresses Paulsen.

Senvion’s 5M and 6M platforms – the largest of which is the 6.2MW 6.2M-152 model slated to be serial production in 2016 – are built around drive-trains with a three-stage planetary/spur gearbox and double fed induction generator.

Note: Amends earlier version to clarify in second paragraph that issue has been detected in less than 10 turbines.