Problem solved! Careful examination of the pictures will show that the wedges have been fitted incorrectly. This occurred 2+ months ago when the core was replaced. It was the cause of the overvolting, control box burnout, inverter capacitor blowing etc.
On the one hand I am disappointed that it took so long to discover and rectify, including not being noticed when the tower was lowered to replace the springs for the first time. However, on the other hand, I am very pleased that a definate fault has been found and rectified.
Now all that I need is some wind, once I have seen the turbine working well in a gale, I am sure that I will re-establish my confidence in the installation.
The installer's over voltage protection device has now been taken out. Turbine Services tell me that they are liaising Povern about developing an over voltage protector which may then be fitted as standard.
The lesson is: WHEN THE BLADES ARE FITTED CHECK AND DOUBLE CHECK THAT THE WEDGES ARE CORRECT!
Simon
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Simonridout