Risk Analysis Of Differential Protection Caused By The Communication Delay And Error

With the development of smart grid, mutual penetration between power system and electric power communication system, has been gradually merge into a highly integrated composite power system. Therefore, the security and stability of power system should not only consider the effects of power a device and external hazards, but also consider the influence of communication system. The present research for composite power system has just started, to study the effect of communication delay and error on power system is the key part. Based on the analysis of the process that the communication delay and error affect the power system, the risk evaluation method of relay protection caused by communication delay and error is proposed.Firstly,the requirements on the communication delay and error that the relay protection communication channel must satisfy is made clear from the optical fiber protection channel itself and relay protection business demand. This can be used for the study of the effects that the communication delay and error have on differential protection.Considering the characteristics of relay protection services, the optical fiber protection channel delay and error is divided into large disturbance(channel switching) and small disturbance to be studied respectively. For the large disturbance, transferring the time delay and bit error probability into the failure rate of the fiber channel, the real time and long-term communication delay and error probability distribution models are proposed. The models not only consider the internal structure of channel and the communication equipment, but also consider the effects of the real time delay and error on channel failure rate, which overcome the shortcomings of the two states(normal or fault) based on statistical data method and improve the accuracy; For small disturbance, the main considerations are environmental minor changes, external disturbances or measurement error. Based on the uncertainties, assume the communication delay and error obeys certain distributions, which is more reasonable than traditional method dealing with it as constant value.Through the analysis of the process of the communication delay and error affecting relay protection, the mechanism of the communication delay and error affecting relay protection is revealed. Based on the existing qualitative analysis method, combined the error introduction and relay protection principle, the false trip probability model caused by inconsistent delay and refuse-operation probability model caused by consistent delay and bit errors are proposed. The models quantitatively evaluate the mal-function probability of the relay protection caused by communication delay and error. The results of the evaluation can reflect the effects that the communication delay and error have on relay protection device.Based on the traditional evaluation method about the mal-operation consequence of the relay protection, the risk theory is used to evaluate the mal-operation risk of the relay protection caused by communication delay and error. According to the evaluation results, the level of risk is classified and the related mitigation and avoidance methods are put forward.