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The most important component of the cast-resin
transformer is the primary winding, which is composed of
aluminium foil interwound with insulating film over a
fibreglass support carried by a metal frame. |
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Both the conductor and the support have a coefficient of
thermal expansion that is closely matched to the epoxy
resin, thus ensuring mechanical strength and expansion
compatibility, which is required for compliance of the
product to class C2. |
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The support also binds the coils in such a way as to
allow handling and erection of the moulded winding
without any risk of misalignment. |
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Compared to wire or strip windings, where the voltage
gradients between the layers are much greater, causing
high dielectric stress, the use of foil conductor
assures extremely low and uniform internal stresses. |
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Furthermore, the flat surface of the foil ensures a
superior and more homogeneous resin penetration during
casting. This results in partial discharges below 10
pc. |
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The primary winding is equipped with voltage regulating
taps, normally set at +/-2 x 2.5%. |
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The insulating materials are of thermal class F with a
maximum temperature as allowed by the IEC
standards, that is, 140°C. (Average value, as
measured during a temperature rise test.) |
| The epoxy compound used is
self-extinguishing in compliance with class F1.
Should the transformer fail, self-extinction as well as
the absolute absence of toxic gases are both assured.
The opaqueness of the flue gas is also tightly
controlled, and the measured values are well below the
limits allowed by the safety standards in force. |
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