Hi Direct approach: improving wind turbine drivetrain reliability.

Hi Direct approach: improving wind turbine drivetrain reliability.

Offshore wind turbines have been plagued by reliability issues that have driven up costs and damaged confidence in the technology. But could a new generation of drivetrain technologies change this?

For nearly a year, people gazing across Scotland’s Firth of Forth have been able to catch sight of an impressive feat of engineering: the world’s most powerful offshore wind turbine. The 7MW monster — the first of its kind — has blade tips that tower 196m above sea level, sweeping an area twice the size of the London Eye.

The majestic structure is part of a bigger plan to make use of the UK’s offshore wind capabilities. The total offshore generating capacity in UK waters provides around eight terawatt-hours (TWh) of electricity each year, enough to power around two million homes. Industry estimates suggest that by 2020, offshore wind will supply between eight to 10 per cent of the UK’s electricity annually.

One way to overcome reliability issues is to take the direct-drive route. That is what Alstom has beenm attempting with its 6MW Haliade WTG wind turbine.

The technology is giving the UK a chance to conquer a growing global market. Offshore construction costs are high, but fairly predictable. Without the same size constraints, wind turbines at sea provide economies of scale. They also produce far more energy than their land-based equivalent, with offshore turbines reaching 3–8MW of capacity. These energy gains, however, come at a cost when it comes to maintenance.

A wind turbine’s drivetrain provides the biggest headache for engineers. ‘They are a classic issue in the wind industry,’ said Daniel Castel, offshore platform director at Alstom. ‘Lots of effort has been made to improve the reliability of the gearboxes but the truth is that there are still some issues that prevent the achievement of a lifetime solution. This is especially critical for offshore where the operating expense is so high.’

’Haliade WTG is a direct-drive solution featuring our pure torque layout that allows for sharp control of the loads that go through the power train. 

Daniel Castel, Alstom.

To avoid excessive damage, Ricardo has come up with a solution dubbed MultiLife, which involves rotating the fixed inner components so that wear take place throughout the full circumference of the bearing rather than just on a small section.

Historically, gearboxes have suffered from failures in both the planet bearings and the high-speed shaft bearings. The high-speed shaft bearings, which undergo huge forces, can often be replaced on site, but any planet bearing failure requires removal of the gearbox from the turbine for repair elsewhere. The downtime this creates means that close to 25 per cent of a wind farm’s maintenance costs are linked to gearbox failures.

‘Individual offshore turbines are now pushing well above 5MW capacity, so it is crucial to design and build in the highest standards of reliability from the outset,’ said Paul Jordan, Ricardo’s global head of clean energy and power generation. ‘We need to avoid the risk of high costs of failure and remedial replacement of major components such as gearboxes.’

Jordan’s team has been working on a gearbox and drivetrain design for the Samsung Heavy Industries 7MW offshore wind turbine being tested in Scotland. The mammoth structure is designed to gather energy in some of the world’s roughest oceans. It has a rotor diameter of 171.2m with a hub that stands around 110.6m above sea level. The rotor tip moves at 95m/sec, meaning the drivetrain has to handle torque of 6.9MNm.

‘The most challenging aspect was the six degree of freedom dynamic analysis of the full drivetrain,’ said Jordan. This analysis allowed the team to subject each piece of the gearbox to finite element (FE) analysis testing. ‘It was important for us to consider gravitational and assembly loads as well as those due to operation,’ added Ricardo’s chief engineer for the project, John Stanton.

The team’s simulation revealed wear on the inner bearing concentrated over a small arc of around 40˚. The team came up with a solution — dubbed MultiLife — which involves rotating the fixed inner components so that the wear would take place throughout the full circumference of the bearing. This, the team claims, extends the life of the bearing by up to five times and avoids the bearing damage reaching a critical condition.

But to achieve more gains in reliability, Ricardo claims new innovations are needed. ‘There are limits to the optimisation of drivetrains that can be achieved through intensive simulation,’ said Jordan. ‘However, there are further step-changes that can be achieved through the adoption of advanced technologies that we have developed from our experiences in other, more mature industrial sectors such as off-highway equipment, motorsport and 

road vehicles.’

Ricardo’s TorqLife technology is claimed to improve wind turbine architectures susceptible to damage from loads such as strong gusts or emergency stops.

One way to overcome the reliability issues is to take the direct-drive route. That’s what Alstom has been attempting with its 6MW wind turbine, dubbed Haliade WTG. ‘We do not have any gearbox in the drive train,’ said Castel. ‘It is a direct-drive solution featuring our pure torque layout that allows for sharp control of the loads that go through the power train.’ With no gearbox coupled to the generator, the turbine consists of fewer rotating parts, increasing reliability.

Ricardo has also developed a technology, named TorqLife, which it claims improves wind turbine drivetrain architectures susceptible to non-torque loads transmitted into the gearbox. The same potentially failure-inducing mechanism can also affect the generator for direct-drive architectures. This load can be created under certain operating conditions such as gusts or turbulent wind conditions and fault conditions such as grid loss and emergency stop.

TorqLife uses a dual-function coupling that avoids drivetrain overloads. It is based on an arrangement of hydraulic cylinders between the rotor shaft and gearbox, or direct-drive generator, which are able to isolate non-torque loads. Ricardo claims this innovation offers the prospect of enabling wind turbine drivetrains to survive in the harshest conditions for their full lifetime.

‘What makes our job really rewarding is that our endeavours will help ensure that a much greater proportion of renewable power is delivered to the grid, and at a much lower cost than would otherwise be the case,’ said Jordan. If the UK is to make the most of its offshore wind power potential, then technologies such as this will be vital to ensuring investors’ support for the industry. Addressing concerns over reliability could also help win over those who remain on the fence over renewable’

Hi' Ah-ram Online Reader: Renewable energy is Egypt's raft out of crisis: Experts.

Hi' Ah-ram Online Reader: Renewable energy is Egypt's raft out of crisis: Experts.

Power-generating windmill turbines of The Zafarana project, Egypt (Photo: Al-ah-ram).

"The solutions are known, but the will to implement them is absent, say energy experts discussing Egypt's energy crisis";

Scarcity of financial resources and the lack of a solid plan are the main reasons behind the perpetuation of Egypt's energy crisis, according to experts who attended the Cairo Energy Conference.

"The energy problem is well known. Its solutions are also well known, but there is no will to solve it," says Mohamed Shoeb, former president of the Egyptian Natural Gas Holding Company.

Shoeb and other experts, some of which are former officials, believe an advance can be achieved if the government thinks out of the box.

Many believe solar energy is a viable option for Egypt. "Some countries, like Germany, have a plan to generate all their electricity needs from renewable energy by 2050, and so should we," says Gala Othman, president of the Association of Wind Energy.

"Solar energy is no longer expensive. The cost of it has decreased by almost 90 percent during the last 10 years," says Shoeb.

Many experts say smart electricity meters that can reduce consumption in peak hours can help reduce electricity cuts. Instead of cutting off power, the government can reduce the consumption of households who have several air conditioners or power-hungry electrical devices in operation in peak hours.

Experts add that energy saving LED lightbulbs can reduce power consumption by 20 percent and would cost less to widely distribute than fuel imports.

"There are several ideas that can be studied and implemented, but we have been very slow," says Mohamed Moussa Omran, undersecretary of the Ministry of Electricity.

"We were the first in the region to start using solar energy, but were left behind. Countries like Bahrain, the United Arab Emirates and Saudi Arabia are introducing smart meters," he said.

"Transparency is missing, and that is a problem that needs to be solved. The government thinks the people are not capable of understanding the problem," says Shoeb.

Different parts of the government do not speak frankly to each other about the issue, he adds. 

"The discourse inside a governmental administration would most probably change if they interact with another one in a different ministry," he said.

Differences between the Ministry of Electricity and the Ministry of Petroleum over the issue have led to an exchange of accusations between previous ministers.

In a speech Saturday, Egyptian President Abdel-Fattah El-Sisi said that the production and distribution of electricity were not developed to catch up with consumption.

He estimated that Egypt needs 2,500 Megawatts annually for the upcoming five years to meet rising demand, at a cost of $2.5 billion a year.

In addition to funds needed to build power stations, El-Sisi said that fuel needs would amount to $700 million per station per year.

He invited private investors to develop power stations as well as the power grid.

Power cuts have become frequent since August 2008, but were generally confined to summer months when air conditioning use increases the demand for power. In winter 2012/13, blackouts became common.

Close to 80 percent of Egypt's electricity is generated by natural gas, the production of which has lagged behind in recent years as political unrest and mounting government debts have discouraged foreign energy firms from developing new gas fields.

Hi Energy! Wind Power in Canada series, focusing on the O&M of wind turbine blades, gearboxes and generators!.

Hi Energy! Wind Power in Canada series, focusing on the O&M of wind turbine blades, gearboxes and generators!.

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