Parts of static converter

85.04 - Electrical transformers, static converters (for example, rectifiers) and inductors. - Ballasts for discharge lamps or tubes - Liquid dielectric transformers : 8504.2 1 - - Having a power handling capacity not exceeding 650 kVA 8504.10 8504.22 - - Havin 8504.23 - - Having a power handling capacity exceeding 10,000 kVA a ower handling capacity exceeding 650 kVA but not exceeding 1O,OO% k ? ~ - Other transformers : - - Having a power handling capacity not exceeding 1 kVA 8504.32 - - Having a power handling capacity exceeding 1 kVA but not exceeding 8504.31 16 kVA 8504.33 - - Havin a power handling capacity exceeding 16 kVA but not exceeding soo ~ Q A - - Having a power handling capacity exceeding 500 kVA 8504.40 - Static converters 8504.50 - Other inductors 8504.90 - Parts 8504.34 (I) ELECTRICAL TRANSFORMERS Electrical transformers are apparatus which, without having any moving parts, transform, by means of induction and using a preset or adjustable system, an alternating current into another alternating current of different voltage, impedance, etc. These usually consist of two or more coils of insulated wire wound in various confi ations on laminated iron cores, although in some cases (e.g., radio-frequency transformers) ere may be no magnetic core, or the core ma be of agglomerated iron dust, ferrite, etc. An AC in one coil (the primary circuit) induces an A usually at different values of current and voltage in the others (the secondary circuit). In certain cases (auto transformers) there is only a single coil, part of the winding of which is common to the primary and secondary circuits. In shell type transformers, there is a shell of laminated iron round the transformer. 8F E Certain transformers are designed for particular p oses, e-g., matching transformers for matching the impedance of one circuit with that of ano er, and instrument transformers (current or voltage transformers, combined insfxument transformers) used to step down or step up voltages or currents to the level of the connected equipment, e.g., measuring instruments, electricity meters or protective relays. %' for the control of the amount of The power-handling capacity of a transformer is the kilovolt-ampere (kVA) ou ut based on continual use at the rated secondary voltage (or amperage, when applicable) an at the rated frequency without exceeding the rated temperature limitations. !' Transformers for electric weldin equipment presented separately without their welding heads or welding a pliances are c assified in this heading. However, they are excluded (heading 85.157 when presented together with their welding heads or welding appliances. f The headin also covers induction coils, a kind of transformer in which an intermittent or induces a corresponding current in the secondary. They recticurrent in the pri fluctuating % can be used either to step up the vo tage to a higher value or, in the case of tele hony, to reproduce in the secondary circuits a small fluctuating current corresponding to the ff'uctuation imposed on a steady DC in the primary. The heading covers induction coils of all kinds, other than ignition equipment for internal combustion engnes (heading 85.11). ""Y (11) ELECTRICAL STATIC CONVERTERS The ap aratus of this group are used to convert electrical ener in order to ada t it for further use. T!I ey incorporate converting elements (e.g., valves) of%fferent types. h e y may also incorporate various auxiliary devices (e.g., transformers, induction coils, resjstors, command regulators, etc.). Their operation is based on the principle that the converting elements act alternately as conductors and non-conductors. The fact that these apparatus often incorporate auxiJiary circuits to re late the voltage of the r oes the fact that they are emerging current does not affect their classification zn this group, nor C sometimes referred to as voltage or current regulators. This group includes : (A) Rectifiers by which alternatin current (single or polyphase) is converted to direct current, generally accompanied by a (B) Inverters by which direct current is converted to alternating current. (C) Alternating current converters and cycle converters by which alternating current (single or polyphase) is converted to a different fiequency or voltage. (D) Direct current converters by which direct current is converted to a different voltage. Electrical static converters may be divided into the following principal categories according to the type of converting element with which they are equipped : (1) Semiconductor converters based on the one-way conductivity between certain crystals. Such converters consist of a semiconductor as the converting element and various other devices (e.g., coolers, tape conductors, drives, regulators, control circuits). These include : (a) Monocrystalline semiconductor rectifiers using, as a converting element, a device containing silicon or germanium crystals (diode, thyristor, transistor). (b) Polycrystalline semiconductorrectifiers using a selenium disc. (2) Gas discharge converters, such as : (a) Mercury arc rectifiers. Their converting element consists of a glass envelope or a metal tank having a vacuum and containing a mercury cathode and one or more anodes through which the current to be rectified passes. They are equipped with auxiliary devices, e.g., for priming, charging, cooling, and sometimes to maintain the vacuum. There are two categories of gas discharge rectifiers identifiable according to the mechanism of the primer, viz., " excitrons " (with charging anodes) and " ignitrons " (with igniters). (b) Thermo-ionic rectifiers with incandescent cathodes. Their converting element (e.g., a thyratron) is similar to that of mercury arc rectifiers except that it contams an incandescent cathode in place of the mercury cathode. (3) Converters with a mechanical converting element based on the one-way conductivity of various contacts, such as : (a) Contact rectifiers (e.g., those using camshafts) with a device whose metal contacts open and close in synchronisation with the frequency of the alternating current to be rectified. @) Mercury-jet turbine rectifiers with a rotating jet of mercury, synchronised with the frequency of the alternating current, which stnkes a fixed contact. (c) Vibrator rectifiers with a thin metal tongue, oscillating at the frequency of the alternating current, which touches a contact so placed that the current IS drawn from the source. (4) EIectrolytic rectifiers based on the principle that the combination of certain roducts used as electrodes in combination with certain liquids used as electrolytes wi 1 only allow current to flow in a single direction. P Electrical static converters may be used for different purposes, e.g. : (1) Converters to supply electricity to drive stationary machines or electric traction vehicles (e.g., locomotives). (2) Supply converters, such as accumulator char ers (which consist essentially of rectifiers with associated transformer and current contro apparatus), converters for galvanising and electrolysis, emergency power packs, converters for installations which su ply high-tension direct current, converters for heating purposes and for the current supp y to electro-magnets. P Also classified here are converters known as high-tension generators (used particularly with radio apparatus, emission tubes, microwave tubes, ion-beam tubes) which convert the current from any source, usually the mains, into the direct high-tension current necessary for feeding the equipment concerned by means of rectifiers, transformers, etc. This heading also includes stabilised suppliers (rectifiers combined with a regulator), e-g., uninterruptible power supply units for a range of electronic equipment. However, hi h-tension generators (or transformers) s ecifically desi ed for suppl ing radiological apparatus falfiin heading 90.22. Automatic voltage regu ators are classi? f ed in heading 66.32. P These consist essentially of a sin le coil of wire which, inserted in an AC circuit, limits or prevents by its self-induction the ow of the AC. They vary from small chokes used in wireless circuits, instruments, etc., to large coils often mounted in concrete, used in power circuits (e.g., for limiting the flow of current in the event of a short circuit). Inductors or inductances obtained in the form of individual components by a printing process remain classifiable in this heading. Deflection coils for cathode-ray tubes are classified in heading 85.40. PARTS Sub'ect to the general provisions regarding the classification of parts (see the General Exp anatory Note to Section XVI), parts of the goods of this heading are also classified here. In particular, metal tank mercury arc rectifiers, vvlth or without a pump, are always classified as parts. I However, most of the electric components of the devices of this heading are to be found in other headings of the Chapter, for example : (a) Various switches of heading 85.36 (for example, those used with multiple contact transformers). a (b) Vacuum or mercury va our rectifying tubes and valves (other than the metal tank type) and thyratrons (heading 85.4 ). (c) Semiconductor diodes, transistors, and thyristors (heading 85.41). (d) Articles of heading 85.42.