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Wind Turbine Services: Detect the problems of the wind turbine cooling systems in time

06.07.2017

By Kalle Jalonen, Project engineer, KL-Lämpö Oy

We detect the problems of the wind turbine cooling systems with laboratory analyzes, before the problems cause high maintenance or repairing costs. By implementing the analysis data we can solve possible problems in advance.

Though the coolant of wind turbine cooling system may already be in bad shape the turbine may still work adequate. If the cooling ability is good enough the general condition of the cooling system and the coolant may be forgotten. When the first heating alarm occurs the system is often already in a state in which it should never be. The time from the starting point of corrosion to a leaking system can be surprisingly short even though the system hadn´t given any signs of the problems. By frequent monitoring the condition of the coolant much of the problems can be avoided.

Configuration vulnerable to corrosion

The materials used in wind turbine cooling systems are commonly aluminium, plastic and rubber. Rubber hoses are inexpensive, light-weight and easy to install, but unfortunately they let oxygen through in time, little by little. This is why these systems often contain small amounts of air. Air is bad for heat transfer abilities, but it also predisposes the system to phenomenon we know as corrosion.

Aluminium is very vulnerable material to corrosion and it is used in crucial parts of the cooling system. In addition stainless and acid-proof steels are used in the system but these materials are strong and durable. Sometimes also black iron is used and it is also vulnerable to corrosion.

Against corrosion with inhibitors

Inhibitors alias corrosion protection chemicals are used in order to prevent corrosion. Inhibitor is added to the glycol solution (coolant) already in the manufacturing stage. As time goes on the amount of inhibitor in coolant can decrease; the inhibitor slowly disintegrates to the system because the coolant in under great mechanical stress. This weakens the corrosion protection ability.

The amount of inhibitor in the coolant should be constantly observed and added if found necessary. If this is not done and the amount of inhibitor decreases too low the result can be corrosion. In worst case scenario the corrosion becomes so bad that the system starts to leak. If there is a leak in the radiator or even worse, inside the converter cabinet, the damage and the repairing operations can become very expensive and laborious. And at the same time the turbine will be off-line and thus unprofitable.

Deposits

When corrosion starts to appear in the cooling system different materials from the system surfaces will start to dissolve into the coolant. These materials and the disintegrated inhibitor can form deposits. Even though the amount of the inhibitor has been kept on a good level the disintegrated amount will not vanish from the system by itself. All of these impurities can form so bad deposits that the system can even clog in certain parts.

The cloggings and the deposits significantly reduce heat transfer abilities of the system: sometimes so badly that cooling is no longer efficient enough. At that point the energy production of the wind turbine can start to suffer from overheating alarms and downtimes.

Different inhibitors have different structures and features: they are often completely different chemicals. Sometimes there have been situations where the type of the coolant used in a cooling system has not been certain, or it has not been clarified. In this uncertain situation, a coolant with different kind of inhibitor has been added to the system. This is a terrible mistake: different inhibitors can form very bad deposits when mixed together. After this kind of mistake, the system usually needs a thorough cleaning operation to get it back to its proper performance level.

However, the deposits and the possible corrosion will age the coolant in every wind turbine cooling system to a point, where the system has to be cleaned and the coolant has to be replaced to restore the original heat transfer ability.

How to inspect the coolant?

Regular laboratory analyzes are easy and informative ways to examine not only the coolant, but also the condition of the cooling system. In this analysis the most common metals which weaken heat transfer abilities are defined as well as the most crucial physical abilities of the coolant.

If there are also deposits to examine the composition can be clarified with separate EDS-analysis. If some impurities appear in the analysis the surfaces of the system are deemed to have deposits as well. On system surfaces even the smallest amounts of impurities will decrease the heat transfer ability. The possible corrosion in the system can also be detected by the analysis. In wind turbines the possible deposits and corrosion are in very important position because the cooling systems are constantly under very high mechanical stress.

On basis of the analysis proper maintenance operation plans can be made to improve the decreased cooling ability.

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