Patent GB-211570-A (GB)
Title: Improvements in or relating to the rapid regulation of the voltage of alternating current generators
IPC: H02P9/36
Filed: 1922-11-21
Abstract: 211,570. Rushen, P. C., (Siemens-Schuckertwerke Ges.). Nov. 21, 1922. Exciting; regulation of exciting machines. - The voltage of an alternating- current generator is rapidly regulated to a constant value for changes of load by changing the excitation of a series exciter in accordance with changes in the exciting current which occur automatically by magnetic reactions caused by the change of load. As shown by the time curves of current and volts, Fig. 1, if the alternator load current fall from B to C it is found that the excitation current i falls also, by reaction from G to K, the terminal volts E concurrently rising slightly from N to 0 through the addition of a voltage due to the changed armature leakage flux. Without special provision, the exciting current would rise slowly, as at KL, with a corresponding increase in the terminal volts, as at OP. According to the invention, the excitation is automatically held at or about the value K, as at KR, which it assumes when the load changes and the volts are accordingly held at OS instead of increasing as at OP. Converse actions occur with increase of load. The exciter is designed with small magnetic reaction throughout its circuit so that its B-H curve is substantially a straight line and it works in neutral equilibrium, i.e. its terminal volt-ampere load characteristic XY, Fig. 3, is straight and coincides approximately with the B-H curve. This machine also has high hysteresis as shown by the partial loop Q, T, U, Z, within which the line XY lies. The change in excitation may be effected in many ways. Fig. 4 shows an alternator b with a series exciter p working in neutral equilibrium, the series coil q of the exciter being shunted by a resistance r. The resistance is changed in accordance with the volts of the mains a bv means of a rectifier and an auxiliary motor. In this case, instead of following the lines KR, OS, Fig. 1, the exciting current and machine volts mav be held to the values KV, OW, thus giving absolute volt regulation to the value MN. Auxiliary excitation may be used in a coil o, Fig. 5, in addition to a constant excitation supplied at r. The coil o takes, through a rectifier g, a current which varies in proportion to the volts on the mains a. To prevent magnetic reaction between the series coil q and the coil r these coils may be in series with the windings of a transformer having equal inductances and connected in opposition to the two coils. Alternatively, a choking coil may be used in series with the winding o. The speed of regulation may be increased by the use of an intensifying device between the mains and the exciter, e.g. by employing thermionic tubes or by making the transformer d, Fig. 5, so highly saturated that its secondary voltage increases more than proportionally to the voltage under regulation. A transformer for this purpose is described with two mesh-connected secondaries in series. Fig. 8 shows a form in which the difference between the voltage of the regulated machine b and a constant voltage is used to excite the regulating winding o. The constant voltage is given by a synchronous generator 2, motor-driven at 3 on the mains and feeding one primary winding y of a transformer z, the other and opposing winding x of which is fed from the mains. The secondary feeds the regulating coil o of the exciter through a rectifier g, the coils q and r acting as in Fig. 4. The motor 3 and generator 2 are so coupled that the generator volts are always in phase with those of the mains a. In an alternative form, the coil o is excited from a thermionic tube, the grid volts of which are controlled by the generator 2 and rectifier g of Fig. 8. In the form shown in Fig. 10, a single coil o, fed by the difference between the volts of the mains and a constant voltage derived from a battery 6, replaces the separate coils o, r, Figs. 5 and 8. Normally, the rectifier and battery volts are equal, and the direction of current in the coil o varies in accordance with fluctuations of the volts at a under regulation. To allow for the unidirectional conductivity of the rectifier, a ballast resistance 7 loads it permanently with at least the maximum current which the coil o takes and so ensures that the difference between the battery and rectifier currents never becomes negative. In the case of unavoidable departure of the exciter characteristic from the neutral equilibrium condition, for example owing to heating effects, a supplementary regulation may be employed, as shown in Fig. 12. in which a volt-operated relay 10 controls a motor 11 for cutting out cells when deviation from the standard value occurs. This Figure also shows means for changing from automatic to hand-regulation, this being done by shortcircuiting the series coil q at 12 and changing the regulating coil o on to the hand-controlled resistance 14 bv means of a switch 13. The method of regulation may be made dependent on variations in the alternator current or output, in place of voltage, and it may be combined, as a rough adjustment, with known methods of rapid regulation for fine adjustment.