Induced Voltage and Induced Current on AC Same-tower Four-circuit Lines Comprised of Double-circuit 1 000kV Lines and Double-circuit 500kV or 220kV Lines

In order to select parameters of earthing switches on AC same-tower four-circuit(ST4C)lines comprised of double-circuit 1 000kV lines and double-circuit 500kV or 220kV(500kV/220kV)lines,we calculated the voltage and current on the lines induced between different circuits under different operation modes,different phase sequences and different lengths of the four-circuit lines,and established a model of AC ST4Clines in the electromagnetic transient program EMTP.Using the results,we studied the effects of three measures,i.e.installing coupling ground wires,increasing the distance between the conductors of the 1 000kV lines and the 500kV/220kV lines,and lowering the height of tower,for limiting the induced voltage and current.It is concluded that the 500kV/220kV lines are strongly affected by the 1 000kV lines,and the induced voltage and current are far beyond the ability of B-type earthing switches.However,all the three measures mentioned are considerably costly and ineffective:increasing the distance between the 1 000kV and 220kV conductors by 2mcan reduce the induction voltage and current on 220kV line by about 10%;adding coupling ground wires to 220kV tower decreases the induction voltage and current by only 6.7% ~20%;reducing the height of a tower lower 7mlowers the induced voltage and current by about 18%.As a result,we suggest installing auxiliary interrupters on the earthing switches to deal with the induced voltage and current on HVAC lines.