Transormer Technologies Wind turbines require a grid connection where generation voltage is increased to medium voltage by a step-up distribution transormer . This transormer can be in- stalled outside the turbine in a substation or as a pad-mounted solution. For inside tower or nacelle installation, the wind turbine industry has the choice between dry type transormers and high temperature liquid-flled t ransormers. Dry type transormers have been installed in wind turbines because o their fre behaviour and compact dimensions. Recently high temperature liquid-flled transormers, such as SLIM ® , with fre retardant liquid have been developed or the multi-megawatt turbines because o their compactness, perormance and high reli- ability. The insulation system consists o a silicone liquid and a high temperature solid insulation NOMEX ® . Functional specifcations The electrical unctional specifcations or both technologies are the same, and both technologies can meet the requirements such as low voltage, h igh voltage, power, impedance, load losses, no-load losses that a multi-megawatt turbine needs. The high temperature design has more advantages : > On average the no-load loss es or liquid-flled transormers are 50% lower lead- ing to signifcant savings. > When high temperature insulation materials are used, the new tra nsormers can be designed much more compact and with improved thermal reliability. > Example : 4MVA SLIM ® step-up transormer with 2 low voltages 3300V and 690V, high voltage 33kV has dimensions o length 2800mm, wid th 1400mm and height 2100mm. Load losses can be as low as 23000W and no-load losses 6000W. Operating conditions The electrical environment o the step-up transormer is also dierent in a wind turbine: > more switching surges with as t transient overvoltages in windings and sys tem voltage drops; > higher harmonic content; > overuxing due to v oltage and requency uctuations. > For transormers with open insulation systems such as dry type transormers, fltering and drying o the cooling air and maintenance is suggested especially or transormers in a humid and salty environment. > For nacelle installations, vibrations with re quency range 5Hz up to 250Hz. Taking all this into account, the transormer industry perceives liquid-flled trans- ormers in general to be more reliable. Risk assessment and Standards The likelihood o a transormer ailure is extremely low. This statement is justifed by our own experience (more than 10000 transormers in wind turbines), general eedback and appreciation o users worldwide. The Mean Time Between Failures or liquid-flled transormers is > 500 years. International Standard IEC 60695-1-40 “Fire hazard testing: guidance or assessing the fre hazard o electro technical produ cts - insulating liquids” illustrates and confrms the good fre saety record o liquid-flled transormers and that such in- cidents are very rare. Conventional transormers have a mineral oil class O1 liquid (liquid with fre point < 300°C and a net calorifc value > 42 MJ/kg). The SLIM ® transormers use a silicone liquid and are classifed as class K3 (liquid with fre point > 300°C and a net calorifc value < 32 MJ/kg). The IEC-guide states that fres Fire behaviour o transormers Challenges or reliable step up transormers and substations or multi-megawatt turbines temp 20’ 40’ time fre radiation + radiation temperature profle applied to the transormers by fre and radiation freproo transormer: did not contribute to fre transormer partially contributed to fre, fre slowly dies out non freproo transormer: large contribution to fre, fre does not die out > High temperature liquid- flled transormer ater fre test. > Dry-type transormer ater fre test.