Oscillatory and Transient Phenomena in Dynamo Circuits

MacFarlane, James W (1937) Oscillatory and Transient Phenomena in Dynamo Circuits. PhD thesis, University of Glasgow.

Abstract

It has been indicated by mathematical analysis and proved, in some cases, by experiment that: (1) A dynamo, the field of which is excited through a transformer, will produce and maintain low frequency oscillations of controllable magnitude and frequency. (2) A shunt wound dynamo, having a mutual inductive link between the load and field circuits will self-excite, produce, and maintain low frequency oscillations of controllable amplitude and frequency. (3) A plain shunt dynamo, although capable of oscillatory discharge, will not maintain oscillations without external aid. (4) A plain series dynamo can neither produce an oscillatory discharge nor maintain oscillations without external aid. (5) In a compound dynamo the fields of which are mutually linked, the tendency to maintain oscillations through the presence of mutual inductance is balanced, or partially balanced, by the impulse from the series winding. (6) In a compound dynamo the fields of which are not mutually linked, the tendency to produce and maintain oscillations is present due to the impulse from the series winding. Analysis indicates that this impulse must be positive, that is, obtained from cumulative series coils, and in Chapter 6, would appear that a further condition is necessary for the maintenance of oscillations. This is that although the dynamo is cumulatively wound, the field must fall with increase of load current. (7) A separately excited dynamo can produce and maintain oscillations if either the transformer or series impulse method is correctly applied. In testing the above statements 6 generators of various types and sizes were examined, some of these having completely laminated field structures and compensating windings, others with salient poles and solid yokes, and one having neither compensating nor interpole windings. These generators varied in output from 6 to 320 Kw, in speed from 1000 to 3000 r. p. m. and all have been known or caused (for the purpose of this investigation) to self-excite, produce and maintain low frequency oscillations under various conditions of excitation. These results indicate that any shunt dynamo-electric machine may self-excite under suitable conditions and that there exists a value of M which can be inserted between the load and field circuits to cause this condition, For the compound wound dynamo it will not be so easy to arrange for an oscillatory condition because of the difficulty of providing a series winding without interfering with the shunt winding and at the same time assuring that the dynamo is naturally capable of oscillatory discharge. It has been further indicated by theory and proved in some cases, by experiment, that: (a) The linear theory, under the quoted assumptions, gives reasonably good results for the Chapter 6. transient values of current and voltage during switching. (b) The linear equation, although giving a good indication that maintained oscillations may be expected under certain conditions, does not correctly predict either the wave shape or the frequency of the resulting oscillation. (c) To obtain rapid response to sudden changes of load it is necessary that the magnetic energy stored in the armature and field circuits must be kept as low, and that in the load circuit relatively as high as possible. (d) For extreme rapidity of response in larger dynamos, the use of high ceiling voltage exciters and injector transformers are indicated. Concluding, the oscillograms taken from the three welding dynamos of recent but quite different design, indicate that the criteria evolved for good welding performance are reasonable.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Electrical engineering
• Date of Award: 1937
• Depositing User: Enlighten Team
• Unique ID: glathesis:1937-80032
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 03 Mar 2020 10:05
• Last Modified: 03 Mar 2020 10:05
• URI: https://theses.gla.ac.uk/id/eprint/80032