GB1187691A - Improvements in or relating to Gas Circulatory Drives for Nuclear Reactors - Google Patents

Abstract

1,187,691. Cooling reactors. NUCLEAR POWER GROUP Ltd. 18 Dec., 1968 [10 Jan., 1968], No. 1477/68. Heading G6C. A gas circulator drive for a gas-cooled nuclear reactor comprises for each circulator a variable frequency A.C. motor coupled to the circulator, means connecting the motor under normal operating conditions to a mains or an internally-generated electrical supply and, in a situation where the supply fails, is interrupted or is not available, to at least one auxiliary variable frequency A.C. generator adapted to supply electrical power to the motor at a frequency that is automatically varied in response to a fall in load on the circulator. The or each generator is connectable to a group of motors and control means are provided which, on sensing a fault in the normal electrical supply, disconnect all but one of the motors of the group from this supply, start up the auxiliary generator and connect the said one motor to the generator when this has reached a predetermined speed less than full speed (e.g. halfspeed), the control means further detecting the current flow from the generator and subsequently connecting, if required, further motors of the group to the generator in turn as determined by the current flow from the generator. Alternatively, the connection between the motor and generator may be made when the speed of the motor equals that of the generator since the motor may still be running with a falling speed following disconnection of the grid or internal supply. The need for further motors of the group being connected to the generator may arise if in addition to loss of grid supply there is a reduction in pressure in the reactor due, for example, to a leak in the reactor vessel. With a falling pressure, the power required by each motor and consequently the current which they draw falls. When all the motors have been connected, provision must be made to limit the speed of the motors and generators in the event of further reduction in the coolant pressure. This limitation is achieved by setting the governors of the prime movers driving the auxiliary generators to full speed when all the motors have been run to half speed.