The Analysis And Processing Of Frequency AC Mixed With DC System Maloperation

With the progress of the times and the rapid development of China’s economic strength,people on the electricity market requirements are growing more and more stringent.The DCsystem in power system protection and control is not only used as control power for circuitbreakers and disconnectors in power plants,but also used as power supply and action powerfor computer protection. Therefore, the domestic requirements for DC system operation havebeen clearly stipulated at home and abroad. A dedicated set of DC system bus insulationmonitoring device must be ensured,and the DC system is not allowed to be grounded or to beconnected with other grounded nature outside power supply in operation. How to ensure thestable operation of the DC system is equivalent to how to improve the operational reliabilityof relay protection devices.This paper analyzes the case that two transformers simultaneously tripped caused byrelay equipment maloperation.The maloperation was caused by false wiring that industrialfrequency AC was wired into DC system in the construction process. Since the failures hasnot be detailed recorded by wave-recording device, the following work must be done.Atfirst,the fault must be searched in the field.Secondly, the act of recorder and the record data inDC insulation monitoring unit must been analyzed. PSCAD software aslo be used to simulatean accident transient processes for the analysis process provides a more intuitive analysis relyon. At last, the effects on protection and control devices of wiring the frequency AC into DCsystem for computer must be analyzed and evaluated. In this paper,during developingappropriate corrective action,reasons from design,construction,drawings,equipmentselection,engineering supervision and other aspects are analyzed,and correspondingpreventive measures are proposed.