Design of transformers: structure


Design of transformers

Transformers are used in the radio-electronic equipment working in the most various conditions: in stationary and land mobile objects, onboard the ships, airplanes and rockets, on space objects.

Устройство трансформатора

Transformer device.

In use transformers are exposed to different mechanical influences (accelerations, vibration, blows); they are used in very severe climatic conditions: at change of ambient temperature in wide limits (from — 65 up to +250 °C), at high   relative air humidity (up to 98% at the temperature up to 40 °C) and with the lowered atmospheric pressure (up to 5 mm Hg.).

The design of transformers has to ensure their reliable functioning during all set service life.

Therefore impose the following main requirements to the design: mechanical durability, heat stability, moisture resistance and breakdown strength.

Схема включения трансформатора

Scheme of turning on of the transformer.

Besides, depending on assignment of the equipment in which transformers are used the last have to have either the smallest weight, or the smallest volume, or the smallest cost. These technical and economic requirements significantly influence the design of transformers.

And, at last, one more important requirement — technological effectiveness of the design of transformers, i.e. the possibility  of their production using the most economic technology processes.

The design bodies defining the electromagnetic basis of the transformer - the core (magnetic conductor) and windings with isolation.

Magnetic conductors are intended for creation of the zamknuyoty way for the magnetic flux with perhaps smaller magnetic resistance. Therefore they are produced from materials, oblayodayushchy by high magnetic conductivity in strong alternating magnetic fields and having small losses on magnetic reversal and whirling currents.

For magnetic conductors of transformers of industrial and povyyoshenny operating frequency magnetosoft materials are used: electrotechnical transformer became, there were with the increased magnetic conductivity, nickel and cobalt alloys (peryomally, perminvar, the permendur, etc.). For magnetic conductors of vysokoyochastotny transformers magnetodielectrics, ferrite of different structures are used (alsifer, oksifer, etc.).

The main sizes of the magnetic conductor depend on the rated moshchyonost of the transformer, the maximum induction and operating frequency and are defined in the course of calculation of the transformer.

Трехфазный трансформатор

Three-phase transformer.

Windings are intended for creation of electric circuits on primary and secondary parties of the transformer and for the preobrayozovaniye together with matnitoprovody to electrical energy in electromagnetic (this function is performed by primary winding) and back — from electromagnetic in electric (these are preobrazovayony secondary winding carries out).

For production of windings the wide nomenclature of winding wires and the large amount of various izolyayotsionny materials is used.

Winding wires represent the wire of krugyoly or rectangular section covered with isolation, predoyokhranyayushchy from turn-to-turn fault or the thin tape, the foil.

The main material for production of the winding wire is copper as it has small unit resistance. Recently aluminum as less defitsityony and having small specific weight began to be applied. To reduce the weight of the welding machine, windings can be reeled up the aluminum wire.

The domestic industry releases the round wire with enamel isolation, for example: for work at the temperature up to 105 °C — PEL, PEV-1, PEV-2 with the diameter on copper from 0,05 to 2,44 mm; for work at the temperature of +120 °C — PEVTL-1 and PEVTL-2 with the diameter on copper 0,06 - l, 56 and 0,06 - 2,44 mm respectively; for work at the temperature of +220 °C — PNET — имид on the basis of polyimide with the diameter on copper from 0,125 to 1,38 mm, Make also wires with fibrous (the design and estimate documentation, PSDK, etc.) and enamel and fibrous (PELShO, PEPLO, etc.) isolation.

The copper foil is produced from 0,015 to 0,05 mm thick with the width of tape from 20 to 150 mm. Aluminum foil is produced from 0,005 thick to. 0,2 mm with the width of tape from 10 to 600 mm. The copper foil is covered with insulating varnish, and aluminum — oxidized.

There are 2 essentially different ways of production of windings. The first way consists that the wire in the form of integral multi-layer winding have on the sleeve or the coil along all length of the rod of the magnetic conductor or its part. At the second way the winding is carried out in the form of set of separate eleyoment (ship's biscuits), each of which represents the finished design. Ship's biscuits string on the core rod one by one and connect among themselves electrically posledovatelnoyoparallelno for providing required currents and tension. Ship's biscuits can be made of the foil that is very perspective.

The set of windings and the system of isolation (the inter-turn, mezhdusloyevy, mezhduobmotochny and external) represents the transformer coil.

Except the magnetic conductor and windings, transformers contain the number of additional elements: parts for assembly of separate parts of the core and fastening of the assembled transformer; parts for connection of the transformer to the scheme; parts for cooling of the magyonitoprovod and coils; external electrical insulation, moisture protection and mechanical protection.

Designs of these additional elements are defined by type of the magnetic conductor and coils and environmental conditions.

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