The invention discloses a multi-terminal flexible DC
power grid line direction
pilot protection method. The method comprises steps:
DC current and
voltage at two ends of a DC reactor are measured and a
DC current mutation rate di / dt and a
voltage mutation rate du / dt are calculated; when the di / dt or the du / dt is larger than a threshold value K1-set and K2-set, a protection
algorithm is started instantly; fault
voltage at two sides of a DC reactor at a protection terminal is measured, and corresponding transient components UM_line and UM_
bus (UN_line and UN_
bus) are extracted; r1=UM_line / UM_
bus (r2=UN_line / UN_bus) is calculated, and a fault direction is judged: if r1>1+epsilon (r2>1+epsilon), epsilon is a reliable margin,
positive direction fault is judged and a direction
signal RM is equal to 1 (RN=1), or otherwise, reverse direction fault is judged, and a direction
signal RM is equal to 0 (RN=0); when RM&RN=1, internal fault is judged; and when RM&RN=0, external fault is judged. The method of the invention has the advantages that
data synchronization is not needed; a sampling rate is lowly required; the
fault resistance withstanding ability is strong; influences from line distributed
capacitance do not exist;
engineering implementation is facilitated; and the hardware
investment cost is reduced.