Transient Overvoltage in 10kV Hybrid OHL-Cable System during Energization

With increasing number of cables adopted in 10kV distribution system, numbers of OHL-cable hybrid lines occur in distribution networks. The power supply is interrupted frequently due to insulation breakdown of cables caused by transient overvoltage in distribution networks. Accordingly, characteristics of transient behavior during line energization are investigated in this paper. The amplitude and frequency of transient overvoltage with different cable shares in hybrid line are studied. In the meantime, 100 simulations are performed considering the randomness of closing timings of circuit breakers (CB). Statistical results reveal that the most severe overvoltage occurs when cable share in hybrid line is 20%. This is due to the fact that characteristics of energy redistribution during line energization are different when impedance and admittance of transmission lines change. Moreover, the dominant frequency 19.6kHz is observed. Furthermore, different load rates are considered since CB exists only at the sending end of line. Statistical results reveal that transient overvoltage is lower while load rate is higher. And the dominant frequency 15.1kHz is observed, which corresponds to the circle time 0.066ms. This work has important value for investigation of electromagnetic transient phenomenon and insulation coordination of hybrid line in 10kV networks.