Electric Transformers Transmission and Distribution Power Directory And Buyer's Guide at The Electricity Forum contains a listing of power and distribution manufacturers and suppliers of power, current, isolation, potential, auto, distribution, and step down. We also list testing, service and protection companies, monitoring equipment specialists.
It is a device used to transfer an alternating current or voltage from one circuit to another by means of electromagnetic induction. The simplest type consists of two coils of wire, insulated from one another and arranged so that a change in the current in one coil (the primary) will produce a change in voltage in the other (the secondary). In many types, the coils are wound on a core made of a material with high magnetic permeability; this intensifies the magnetic field induced by the current in the primary, increasing efficiency. Neglecting power losses (which are made small by careful design), the ratio of primary voltage to secondary voltage is the same as the ratio of the number of turns in the primary coil to the number of turns in the secondary coil. The primary and secondary currents are in inverse proportion to the number of turns in the coils. The primary and secondary impedances are in the same ratio as the squares of the numbers of turns in the primary and secondary coils. For example, if a 10-volt, 2-ampere alternating current were to flow through a 10-turn primary, theoretically a 20-turn secondary would exhibit a 20-volt, 1-ampere alternating current, with the output impedance four times as great. Power types are generally used to transmit power at a constant frequency. Audio types are designed to operate over a wide range of frequencies with a nearly flat response, i.e., a nearly constant ratio of input to output voltage. Radio frequency (RF) types are designed to operate efficiently within a narrow range of high frequencies.
Both oil filled and dry type devices convert voltages and phase configuration from one level to another, in most instances from higher voltages to lower voltages. They can accommodate features for isolation, distribution, as well as control and instrumentation applications. The design is fairly basic: they typically depend on the principle of magnetic induction between coils to convert voltage and/or current levels.
A few important specifications to consider include:
- maximum secondary voltage
- maximum secondary current
- maximum rating
- output type.
They may also provide more than one secondary voltage value.
These units have ratings that are determined by the sum of the VA (Volts x Amps) for all of the secondary windings. Output choices include AC or DC For AC waveform output, voltage the values are typically given in RMS values. Consult a manufacturer for waveform options.
Cores can be constructed as either a toroidal or laminated. Toroidal units typically have copper wire wrapped around a cylindrical core so the magnetic flux, which occurs within the coil, doesn't leak out, the coil efficiency is good, and the magnetic flux has little influence on other components. Laminated refers to the laminated-steel cores. These steel laminations are insulated with a nonconducting material, such as varnish, and then formed into a core that reduce electrical losses. There are many types. These include control, current, distribution, general-purpose, instrument, isolation, potential (voltage), power, step-up, and step-down. Mountings include chassis mount, dish or disk mount, enclosure or free standing, h-frame, and PCB mount.
Manufacturers in our directory include: Bel Volt Sales LTD., Bristol Park Ind. (BPI), Delta Group, Hammond, EECOL Utility Supply, Electronic Specialists Inc., Engineered Components Ltd., G.T. Wood Co. Ltd., Hammond, Innovelec, K-Tech Inc., Laprairie Inc., M.G.B. Electric Inc., Optima Systems Inc., Polycast International, R. E. Uptegraff Mfg. Company, Rondar Inc., SEEwater Inc., Tensor Resources Inc., Surplec Inc., Warco, Inc.
For more information consult any manufacturer listed in our Transmission and Distribution Product Directory and Buyer's Guide.
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