GB239881A - Improvements in or relating to the feeding of alternating current systems by asynchronous generators - Google Patents

Abstract

239,881. Siemens - Schuckertwerke Ges. Sept. 13, 1924, [Convention date]. Alternating - current induction machines.- An asychronous generator is made to supply energy at constant frequency independently of variations in its own speed by being excited through a cascaded, compensated commutator machine which acts as a frequency transformer between the induction generator and a supply circuit of which the voltage and frequency are independent of the circuit fed by the induction generator. In the form shown in Fig. 1, the asynchronous generator 1, which is driven by a motor 2 and feeds a system 5, is excited through its rotor by a mechanically coupled commutator machine 3 fed through its rotor from an independent constant frequency system 4. The frequency given by the machine 1 is independent of its speed. The machine 3 may be excited through its stator, as shown in Figs. 2 and 3, in which case it is arranged to give a variable frequency to correct changes in the speed of the asynchronous generator. In Fig. 2, the commutator machine 3 is stator-excited from a mechanically-coupled frequency converter 6 which is fed from constant frequency mains 4. In Fig. 3, the stator excitation of the machine 3 is derived from a so-called " electrical differential gear " comprising a synchronous type of machine of which the stator member 8 is mechanically coupled to the asynchronous generator group and the rotor is independently driven by a motor 7 and excited from a continuous current supply 9. It is shown in the Specification that with connections as described above the machine 1 has a compounding property at hyper-synchronous speeds whereby its voltage is kept up with increasing load, but independent regulating means of known type may be used for regulating the voltage or the wattless energy generated by the machine 1. When several asynchronous generators working in parallel are excited from separate sources, synchronizing conductors or mechanical arrangements may be employed for keeping the sources in synchronism, and means may be employed for distributing the load among the generators. Where several generators work in a common system, they are preferably arranged so that any one may act either as a " time giving " machine for the others or independently. For example, in an hydro-electric plant the exciting machine is arranged to be driven either by a water turbine at constant speed for time-marking or, alternatively, by a synchronous motor forming part of the system if the time marking is to be transferred to another member of the plant, the constant-speed turbine running light in these circumstances.