The Principle and Analysis for the Incorrect Pickup of SIEMENS Electrode Bus Differential Protection

Earth electrodes are an essential component of the monopolar HVDC (high voltage direct current) transmission system, since they carry the operating current on a continuous basis. Earth electrodes are also found in all bipolar HVDC systems. As in any high voltage system, the power circuit of the HVDC system requires a reference point for the definition of the system voltage as the basis for the insulation coordination and overvoltage protection. According with this, protections (electrode bus differential protection especially) for the earth electrode are very significant. With the knowledge of the actual configuration of the Gui-Guang HVDC project and principle of the electrode bus differential protection, the present article tried to thoroughly analyze the differential current arithmetic and the action criterion in different HVDC transmission mode. The relation between the electrode bus differential protection and DC station control system, and pole control system were also introduced. DC station control system performs all the control functions as well as protection and communication tasks in the DC traction power supply. The tasks of the pole control systems are pole and converter related control functions. This includes mainly the closed loop control function for the converter control. Nevertheless all other pole related open loop control functions are included as well. Moreover, based on the operation of the Gui-Guang HVDC project, the HVDC system operation mode being incorrect identified is the possible reasons for the incorrect pickup of electrode Bus differential protection was analyzed and discussed. Furthermore, corresponding countermeasures and improvements of HVDC system operating mode identifying were presented.