Patent Number: 047479949
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates in general to the control of switchgear mechanisms which supply power to process control apparatuses, and more specifically to the control of reactor trips in a pressurized light water nuclear reactor, including sensing the condition of power supplied to devices which position control rods in the reactor. 2. Description of the Related Art The most important step in the shutting down of a nuclear reactor is the insertion of control rods into the reator core. Conventionally, the control rods in a pressurized light water nuclear reactor are positioned by spring-loaded mechanical grippers which hold the control rods only while supplied with electrical power. When the power is cut off, the mechanical grippers release the control rods which fall into the reactor under the force of gravity. A switchgear mechanism is connected to the power supply line for the rod positioning grippers to interrupt the supply of power when an unsafe condition is sensed by the reactor control and protection systems. Typically, the rod positioners are supplied with alternating current (AC) power at 480 volts. Conventional switchgear mechanisms utilize low resistance, direct current (DC) shunt trip coils which respond quickly but require that the power supplied thereto be cut off shortly after activation of the switchgear to prevent overheating and resultant burnout of the shunt trip coils. Conventionally the trip coil is powered by a DC battery which supplies, e.g., 125 volts under the control of a manually or automatically activated switch. Auxiliary contacts on the switchgear are connected in series with the battery and trip coil to break the circuit between the battery and trip coil after the shunt trip coil is activated. Thus, de-energization of the shunt trip coil conventionally depends upon the mechanical operation of the switchgear, which can be tested only by activation of the switchgear. SUMMARY OF THE INVENTION An object of the present invention is to eliminate the use of an externally supplied DC power to activate a trip coil in switchgear to control reactor trips in a pressurized light water nuclear reactor. Another object of the present invention is to ensure deactivation of a trip coil in switchgear controlling the supply of power to a process control device. A further object of the present invention is to provide electrical isolation of a power condition signal generated by a control system which controls the supply of power to a process control device. Yet another object of the present invention is to provide a control system which controls and monitors the condition of power supplied to a process control device. The above-mentioned objects are obtained by providing a control system for a trip coil in switchgear receiving power at a first level from a power source and supplying the power at the first level to a process control device. The control system includes a transformer, supplied with power by the switchgear, for reducing the power from the first level to a second level and a trip device for supplying the power at the second level to the trip coil of the switchgear only when interruption of the power supplied to the process control device is desired. A control system according to the present invention may include a voltage/optical converter for converting the power at the second level to a light signal and an optical transmitter for transmitting the light signal to a monitoring device. These objects, together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hererinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like reference numerals refer to like parts throughout.