Apparatus Subsection 67: Direct-current Commutating Machines: C. Commutating Machines
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Source Metadata
Section titled “Source Metadata”| Field | Value |
|---|---|
| Source | Theoretical Elements of Electrical Engineering |
| Year | 1915 |
| Section ID | theoretical-elements-electrical-engineering-section-67 |
| Location | lines 12084-12199 |
| Status | candidate |
| Word Count | 502 |
| Equation Candidates In Section | 0 |
| Figure Candidates In Section | 0 |
| Quote Candidates In Section | 0 |
Opening Source Excerpt
Section titled “Opening Source Excerpt”D. C. COMMUTATING MACHINES 203 It is evident that the inequality e > i<>r must be true, otherwise perfect commutation is not possible. If we have that is, the current never reverses, but merely dies out more or less, and in the moment when the gap G of the armature coil leaves the brush B the current therein has to rise suddenly to full intensity in opposite direction. This being impossible, due to the inductance of the coil, the current forms an arc from the brush across the commutator surface for a length of time depend- ing upon the inductance of the armature coil. Therefore, with low-resistance brushes, resistance commutation is not permissible except with machines of extremely low arma- FIG. 108. — Brush commutating coil A. ture inductance, that is, armature inductance so lowSource-Located Theme Snippets
Section titled “Source-Located Theme Snippets”Field language
Section titled “Field language”... hes proportionally to the load, or a commutating pole. In the preceding, the e.m.f. e.has been assumed constant dur- ing the commutation. In reality it varies somewhat, usually increasing with the approach of the commutated coil to a denser field. It is not possible to consider this variation in general, and e is thus to be considered the average value during commutation. 66. (b) High-resistance brush contact. Fig. 108 represents a brush B commutating armature coil A. 204 ELE ...Magnetism
Section titled “Magnetism”... armature coil. Therefore, with low-resistance brushes, resistance commutation is not permissible except with machines of extremely low arma- FIG. 108. — Brush commutating coil A. ture inductance, that is, armature inductance so low that the magnetic energy -7^—, which appears as "spark" in this case, is & harmless. Voltage commutation is feasible with low-resistance brushes, but requires a commutating e.m.f. e proportional to current z'o; that is, requires shifting of brushes proportion ...Chapter-Local Concept Hits
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