Research On Contact Degradation And Load Capacity Evaluationof GIS Circuit Breaker

As an important power system primary equipment,the load and breaking capacity of GIS circuit breaker is the key to protect the normal operation of power system.The adjustment of the grid structure and the change of the system operation mode require that primary equipments of power system have good load capacity.The load current that GIS circuit breaker itself can sustain,determines the limit value of series circuit current for dynamic capacity-increase.As the most frequently operated switch devices,the contact material of GIS Circuit breaker works in high temperature and high pressure of the SF6 gas for long-term,and that lead it to the contact degradation phenomenon,which is one of the important factors to limit its load capacity.Therefore,to study the contact degradation of main contact and evaluate the load capacity of GIS circuit breaker,helps to improve the running level of GIS circuit breaker equipment and provides safeguard for the operation and development of power system.This paper combines with subtopics of the national high technology research and development program(863 program),based on the basic electrical contact performance(electrical performance,mechanical properties and thermal performance)and the stress relaxation under the temperature rise caused by the load current of the GIS circuit breaker main contact,has carried out the research and analysis of the contact degradation and load capacity of the main contact of the GIS circuit breaker.This paper has discussed the stress relaxation and relaxation law of the main contact alloy of GIS circuit breaker firstly,introduced the basic theory of contact resistance,and analyzed and revealed the contact mechanism of the contact failure and the contact resistance of the GIS breaker under the stress relaxation based on the influence of stress relaxation on the contact pressure and the equivalent calculation method of the contact pressure contact resistance.The temperature-rise of GIS circuit breaker touch finger is a key factor affecting its load capacity.In this paper,a finite element model of structure-thermo-electric coupling has been established for the main contact in the arcing chamber of the GIS breaker which is responsible for the main load current.This paper has dealt with the results of structure field calculation equivalently using electrical contact theory and the theory of mechanics of materials.By taking the calculation results into heat-electricity coupling calculation model through the conductive bridge model,the structure field and thermal field calculation have been done with the normal contact status of main contact,contact switch does not reach the designated position,angular deviation of main contact,which will lay the foundation for analyzing the degradation of main contact and the load capacity of GIS circuit breaker.Stress relaxation phenomenon is the important reason that lead to the release of contact stress and increase of contact resistance of self-elastic contact.The stress relaxation of contact alloy material will affect the contact degradation and temperature rise of GIS circuit breaker contact finger directly.Based on the finite element calculation of the main contact of the GIS circuit breaker,the influence of the load current,contact resistance and ambient temperature on the temperature rise has been analyzed by this paper.According to the temperature limit specified in the regulations,the correspondence between the maximum load current and the change of the contact resistance has been calculated.Based on the stress relaxation characteristics of the contact alloy material under the load current and temperature rise,a method of assessing the contact degradation and load capacity of GIS circuit breakers based on stress relaxation has been put forward,which will provide the theoretical basis and technical support for the dynamic capacity-increase of power system.