Research for the maintenance way of partial outage on 500 kV/220 kV four-circuit mixed-voltage transmission lines on the same tower

The multi-circuit transmission lines on the same tower can be considered for solving the contradiction between the growing electricity demand and the limited line corridor. Take the 500kV/220kV four-circuit mixed-voltage transmission lines as an example, the maintenance circuit would have high induced voltage and induced current because of the strong electrostatic coupling and electromagnetic coupling among the four circuits. Taking the length of lines into consideration, we adopt EMTP-ATP to calculate and analyze the induced voltage and induced current of the 220 kV one-circuit outage lines at different working conditions when the lower 220 kV one-circuit lines are in outage and the other three-circuit lines are in normal running. In the meantime, we analyzed the reason that the 220 kV I-circuit lines' induced voltage differed from the 220 kV Π-circuit lines' induced voltage by the capacitance model. The research conclusions are as follows: the maximum of the induced voltage reaches to 80.4 kV when the both ends of the outage lines are non-grounded and the maximum of the induced voltage reaches to 9.89 kV when the only one end of the outage lines are non-grounded. Therefore, we should regard the outage lines still as the live lines and carry out the maintenance by the live working way; the maximum of the induced voltage is 1.2 kV when the both ends of the outage lines are grounded and we can repair by the power-off maintenance way. As the phase sequence arrangement of the upper 500 kV lines is different, the electrostatic induction voltage of the 220 kV I-circuit lines is below that of the 220 kV Π-circuit lines.