Power Plant Products

1 October 2004

Protection at lightning speed

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UK power engineering specialist EA Technology has launched a package of services to protect windfarm operators, developers and their insurers against lightning damage.

“Lightning strikes account on average for half of insurance claims to wind turbines and up to 0.4% of assets installation costs per year,” says EA Technology’s Benoit Dal Ferro.

“Wind turbines are inherently vulnerable to lightning because of their height and location. The need to reduce damage will become increasingly critical, both in terms of the direct cost and its effect on reliability ... operators and their insurers also need accurate methods for assessing and reducing risk.”

The service is an extension of techniques developed in 20 years of protecting high voltage cables and equipment in the UK power industry. They include a lightning location system which gives windfarm operators two hours’ warning of approaching storm activity.

The package also includes risk assessment in existing and proposed windfarm sites, using detailed records of historical lightning activity, optimising earthing and protection systems in existing and proposed windfarm developments to reduce damage to turbines and ancillary equipment, validating insurance claims for lightning strike damage, investigating lightning damage incidents, both to establish the causes and help prevent future occurrences, and helicopter surveys of remote and offshore windfarms to report on damage and vulnerability to future incidents.

Rechargeable for renewables

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Saft has developed an extended performance version of its Sunica.plus range to make it suitable for renewable energy applications, in particular solar photovoltaic and windpower. A new optimised electrode design is combined with Saft’s internal partial gas recombination process developed originally for the company’s Ultima range.

Saft claims the new batteries are highly efficient, absolutely reliable and capable of operating in extreme temperatures (-50 °C to +70 °C) and at any state of charge with low maintenance requirements. Under such conditions the service life offered is 20 years.

The batteries contain a stable alkaline electrolyte which does not change during charge and discharge. This enables them to provide good cycling ability in the unstable charging conditions found in renewable applications. They also operate efficiently irrespective of the charge level and are unaffected by accidental overcharge, deep discharges or inversion. During the critical winter months for photovoltaic applications the charge efficiency of these batteries is claimed to be close to 100 %.

They offer a capacity of greater than 80 % for a typical 120 hour discharge at -40 °C. And when operating for extended periods at +30 °C they suffer only a 20 % decrease in life, compared with a 50 % reduction for lead-acid batteries.

The alkaline electrolyte used does not react with steel and, since the battery remains electrochemically stable during charge and discharge cycles, the structure of the battery stays intact and unchanged throughout its life. Most importantly, the battery’s performance is completely predictable over its service lifetime, with no risk of the ‘sudden- death’ failure found in lead-acid batteries. At +20°C, one of these batteries can achieve up to 8000 cycles at 15 % depth of discharge during its lifetime. Topping-up with water at intervals of between one and four years is required, depending on the application.

Transforming conditions

CC Jensen has produced a new system to condition transformer oils which it claims can more than double the life of transfomers and even help achieve high operating efficiencies.

According to Jensen, a major problem in power transformers is the degradation of the cellulose insulation used in the transformer core. Degradation is caused by oxygen introduced through the venting pipe, water and acid that builds up in the transformer oil and is absorbed by the cellulose, and the transformer operating temperature which can accelerate oxidation. The result is a shorter life for the transformer and an increased possibility of breakdown. De-gassing and filtering of the oil to remove particles and water helps to alleviate all these factors.

The V30 vacuum filtration and de-gassing unit consists of a vacuum chamber and a filtration insert. A vacuum pump maintains the pressure in the chamber at a low enough level to vaporise water, so the gas content of the oil can be drawn off. The patented filter element eliminates particles from the oil down to 3 micron absolute.

When the oil is pumped back into the transformer it is clean and absolutely dry with water content down to as low as 4 ppm. The dry oil gradually draws water out of the cellulose, to be removed when it next enters the vacuum chamber. This can only be done when the transformer is functioning, as the temperature needs to be sufficiently high for the water to move freely from the cellulose into the oil. The longer time allowed for the dehydration process the better the result, which is why continuous de-gassing is very advantageous.

In most cases where the V30 has been used, including 2 years of successful field trials, the oxygen level was reduced to a point where the transformer became chemically inert. This means in practice that the life expectancy of the transformer was increased by a factor of between 2 and 10 depending on the operating conditions. De-gassing also increases the chargeability of the transformer, enabling higher power outputs with no negative consequences to the serviceable life of the equipment.

The most advanced version of the V30 provides on-line monitoring of gas emissions, allowing condition data be displayed and linked to an alarm system that will shut down the transformer if certain conditions exist. This protection is claimed to have a considerably quicker response than the traditional Bucholz relay.

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