GB1390403A - Electricity generating arrangements - Google Patents

Abstract

1390403 Electricity generating arrangements; control of several A.C. motors SIEMENS AG 6 March 1972 [6 March 1971 12 Feb 1972] 9635/72 Headings H2H and H2J An electricity generating arrangement comprises a turbine-generator set, the generator G of which is driven by the turbine during normal generating operation of the arrangement, a static semi-conductor frequency changer including an inverter U2 and a rectifier U1, a rotor position sensor p for controlling the inverter in dependence on the instantaneous position of the generator rotor, and a current control device U10 for controlling the rectifier in dependence on a desired value of the current fed to the generator by the frequency changer. The generator is initially driven as a motor by closing switches al connected to a mains network N, a3-a8 and a10, the excitation winding E being energized by an auxiliary, valve rectifier U3. An armature voltage controller U14 limits the armature voltage U LA to a permissible value U LA * whilst a current limiting controller U15 ensures that the excitation current I FA cannot exceed a permissible value I FA *. The sensor p supplies signals to thyristors in the inverter U2 via a pulse divider U5 and to a frequency/voltage converter U6 which acts as a speed sensor. A start control system U7 supplies a desired armature current signal which is compared with the actual armature current provided by a current transformer U and enables the control of the rectifier U1 via a control unit U8, a switch U9 and the current control device U10. When the generator speed reaches approximately half its rated speed the converter U6 enables the system U7 to change over the switch U9 so that the rectifier U1 is controlled by an armature voltage control U12 which receives an actual armature voltage signal from a sensor S. The switches a4-a6, a8 and a10 are opened and then the switches a9, a4 are closed so that the rectifier U1 supplies the winding E. The turbine then drives the generator up to its rated speed and the generator output is synchronized with the mains network N, the switch a2 being closed. A standby supply system Sch for use if the mains system N fails is provided and includes an auxiliary generator HG coupled to a diesel drive D. Fig. 6, shows a system in which a number of generators G1-G4 are successively run-up to a predetermined speed. A selector switch d and switches a51-a54 are controlled by the control system U7 so that each generator is run up to the predetermined speed measured by its respective sensor P1-P4 and is then disconnected from the output of the frequency changer U1, U2. The operation of the switches is cyclically repeated so that each generator is re-energized before friction losses have reduced the generator speed to a minimum value.