Research On The Monitoring Methods Of Hidden Failures In Relay Protection

Security and reliability of relay protection system are important factors for power system to operate safely. As the power system is becoming more large-scale and more complicated, relay protection devices are facing challenges. Hidden failure in relay protection devices is one of the main factors causing cascading power failure, and caused massive concern because of its invisibility and disastrous results after blackouts. But at present, there is no effective method for the monitoring and diagnostics of hidden failures in relay protection devises. Self-checking technique in traditional protection devices can not solve the problem of hidden failure entirely. So, research for new monitoring and diagnostics methods are of great practical significance to check out hidden failures.So,this paper have made a study on hidden failures in relay protection system, which are usually caused by hardware or software faults. A new monitoring and diagnostics method for hidden failures are given, considering possible hardware faults and unsuitable relay setting in relay protection system, based on performance characteristics of relay protection devices. In details, Research works are as follows:â‘ With theoretical knowledge on hidden failures, we made a research on the relationship between self-checking and hidden failures in relay protection , and get the conclusion that self-checking can not avoid hidden failures entirely, therefore a new monitoring method are needed.â‘¡The performance of starting elements, an important factor causing hidden failures, decides whether the relay protection devices could work normally. And now there is no useful on-line method to analyze and evacuate the performance of starting elements in relay protection devices. For this, a new method, using Fault Recorder Date and localized time-frequency wavelet transform, is put forward, to monitor the performance of starting elements in relay protection devices. An example is simulated to testify the rationality of the proposed method.â‘¢A way is shown as to how to diagnose the hidden failure in relay protection devices, based on working performance of relay protection devices. The phenomenon that when the measurement circuit works abnormally, the variance of sampling value will become extremely abnormal, will help to check out the hidden failure in the measurement circuit. For the hidden failure in the measuring and computing section, the information of measured and calculated value is used to diagnose the hidden failure in relay protection in dynamic process. And relatively, a necessary judgment criteria is set up. The results of simulation testify the effectiveness of the proposed method.â‘£The irrationality of setting value in protection is another reason causing hidden failure in relay protection devices. Concerning the case that inaccurate branch-coefficient selecting will cause irrational setting value, a method is proposed to monitor the setting value, based on wide-area information.