| Rotary Converter |
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The rotary converter can be thought of as a motor-generator where the two machines share a single rotating Armature and set of Field Coil s. The usual practice, in fact, was to have two Commutator s, one at each end of the armature (or, for AC-to-DC machines, a set of Slip Rings and a commutator). The advantage of the rotary converter over the discrete motor-generator set is that the rotary converter avoids converting all of the power flow into mechanical energy and then back into electrical energy; some of the electrical energy instead flows directly from input to output, allowing the rotary converter to be much smaller and lighter than a motor-generator set of an equivalent power-handling capability. (One way to envision what is happening in an AC-to-DC rotary converter is to imagine a rotary reversing switch that is being driven at a speed that is synchronous with the power line. Such a switch could Rectify the AC input waveform with no magnetic components at all save those driving the switch! The rotary converter is somewhat more complex than this trivial case because it delivers near-DC rather than the pulsating DC that would result from just the reversing switch, but the analogy may be helpful in understanding how the rotary converter avoids transforming all of the energy from electrical to mechanical and back to electrical.) Rotary converters have essentially been made obsolete by smaller, cheaper, far more reliable Semiconductor Rectifier s. For railway electrification via a catenary wire there has also been a tendency to switch from medium-voltage DC or low-frequency AC to high-voltage, mains-frequency AC, thus eliminating the need for any rectification or frequency conversion. SEE ALSO EXTERNAL LINKS |
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