Electromagnetic Environment in a PWR Power Plant

Abstract

Electromagnetic disturbances have been measured in a 900 MW French nuclear power plant (34 plants of same type are being erected). Such a study is justified by the series of plants considered. The results presented have been obtained by syste­ matic measurements, in conducting and radiating modes, performed on the supply, control and measuring circuits at various operating powers of the plant. 1 INTRODUCTION Problems of electromagnetic compatibility we are faced with in nuclear power plants are particularly acute due to the intertwining of two factors : more powerful plants and greater number of distur­ bance-prone cut-off systems, higher sensitivity of measuring instruments and of monitoring/control systems. Actual tests have covered a span of four years to evidence all sources of disturbances in a nuclear plant and define them by a set of numerical values. They are justified by several facts : to take advantage of the notion of rating stage (34 similar power plants erected over about 10 years) to make a common map providing an overall view of a nuclear power plant on the EMC side, to know for each point the evolution of disturbances relative to the rating of the items of equipment installed by tests performed over a time interval of four years (from laying of first cables to 900 MW rated capacity), to obtain the data in order to determine the values within the equipment specifications and to define the typical disturbances for laboratory testing purposes. 2 CLASSIFICATION OF DISTURBANCES Disturbances may be divided into two classes, of different origin, and of different action on disturbed circuits together with the applicable protection means, but also by the measuring methods utilized. Such a classification breaks down to : Constant waves Such disturbances concern a given frequency wave which can be modulated, chopped or be assigned a slight frequency drift. They normally have a narrow frequency band spectrum. Impulse type disturbances Such disturbances generally originate in a sudden variation in the state of an electrical circuit, i.e. the opening of a contact. These sudden variations gene­ rate free oscillations in circuits, and the resulting disturbance is normally in the form of a highly damped wave. Such disturbances always have a very wide spectrum which can be from low frequencies up to several hundreds of MHz. According to their variation law versus time, two types of wideband disturbances must be distinguished : repetitive impulse type disturbances, recruring periodically within a certain repetition rate. Such are disturbances generated by rotating machines, at brush switching phases, non-repetitive impulse type disturbances, which, on the contrary, randomly appear at time ti. If the origin of such disturbances is known or not, times ti may be known beforehand or not, thus defining the applicable measuring methods to be used. Non-repeti­ tive impulse type disturbances maybe time-determined or random. Disturbances are exhibited via two main coupling modes, between the disturbing sources and the receiving equipment-prone. Measurements performed take two forms : conduction measurements made on cabling and wiring, electromagnetic radiation measurements made at various locations in the plant. 3 EQUIPMENT USED For these tests, a wide range of equipment has been used to cover the complete span of electromagnetic disturbances. Both tables further show a summary of such equipment with their bandpass limits.