Offshore Wind farm HVDC Transmission System Protection against AC and DC Faults

Abstract

This   paper   develops   a   new   one-side,   non-communication  protection  algorithm  for  HVDC  transmission integrating  an  offshore  variable  speed  wind  farm  to a  public grid.  The  proposed  digital  relay  is  installed  at  the  AC  side  bus connecting  the  farm  with  the  HVDC  transmission  system.  The algorithm protects the HVDC system against DC faults along DC cables and AC faults on the AC sides before the rectifier and after the  inverter  stations.      This  algorithm  is  based  on  continuous tracking  of  autocorrelation  coefficient  between  the  sampled current  pattern  and  the  pre-cycle  stored  pattern  along  similar windows.  The  variation  in  coefficient  magnitude  indicates  the fault  incidence  while  its  sign  determines  the  fault  direction. Estimation  of  autocorrelation  from  one  side  for  the  same measured signal by  the relay  will eliminate the effects  of  fault resistance, harmonics and DC components associated with the fault  current.  To  validate  the  developed  algorithm,  the  HVDC transmission system fed by offshore farm is applied on real wind farm using the manufacture data.