Analysis of Transient Behavior of Mixed High Voltage DC Transmission Line Under Lightning Strikes

Abstract

Growing urbanization coupled with increased power demands have led to increasing use of mixed power transmission lines with sections of overhead lines (OHL) and underground cables. Due to differences in surge impedance of cables and OHL, voltage surges experience reflections and refractions at their boundaries which make the transient behavior of mixed high voltage direct current (HVDC) line quite peculiar. Lightning strikes on overhead sections of lines induce voltage surges that travel along OHL and enter the cable section. Lightning overvoltage can cause OHL insulators to flashover and stress cable insulation or cause its permanent breakdown. In this paper, we simulated a fast front model of a mixed HVDC transmission line using an electromagnetic transient simulation program (PSCAD) to analyze its transient behavior under a lightning strike. The leader progression model has been used to predict the dielectric performance of OHL insulators. It has been shown that transition towers adjacent to the cable section are much less vulnerable to flashover than subsequent towers. The length of a riser section (connecting OHL and cable) and tower footing impedance have shown to significantly influence the flashover performance of OHL insulators. In addition, the length of cable segments and sheath grounding impedance has been found to influence cable overvoltage. This paper can be used to evaluate the insulation coordination and overvoltage protection requirements for a mixed HVDC transmission line.

Assessment of Overvoltage and Insulation Coordination in Mixed HVDC Transmission Lines Exposed to Lightning Strikes

“…Many researchers have studied the impact of lightning strikes on mixed transmission lines since the 1990s and several resulting articles have attempted to address various aspects of lightning transients in mixed HVDC as well as HVAC lines [6][7][8][9][10][11][12][13][14][15][16]. Many of these studies focused on specific design aspects such as the shunt reactor on cable terminal, presence of surge arrester/sheath voltage limiter, OHL geometries and tower footing impedance.…”

“…Others focused on the modelling details such as corona, frequency dependent sheath grounding impedance as well as tower footing impedance. In our previous study [15], we presented a thorough theoretical analysis supported by fast front transient simulation regarding the transient behavior of mixed HVDC transmission lines. The insulators of OHL most vulnerable to flashover were identified and the reason for their high vulnerability was explained.…”

A Comprehensive VSG-Based Onshore FRT Control Strategy for OWFs With VSC-MT-HVDC Transmission

“…Moreover, significant power imbalance occurs between the reduced active power exported by ON-HVDCCs and the wind power in-feed by OF-HVDCCs which will be stored as an electrical field in the respective capacitors of VSCs and HVDC lines. Accordingly, transient direct over-voltage might appear due to the limited stored EPRP of VSCs that might cause equipment failure/aging in turn [2].…”

Accurate Evaluation of Steady-State Sheath Voltage and Current in HVDC Cable Using Electromagnetic Transient Simulation

“…It has been successfully applied in three phase AC cables to suppress circulating currents in the sheaths [11,[21][22][23]. In DC cables, sheath grounding at terminals is applied to suppress the sheath voltage in [7,[24][25][26]. However, the steady state sheath voltage and losses have not been discussed by any of these papers.…”

“…However, the steady state sheath voltage and losses have not been discussed by any of these papers. The need for investigating steady state sheath voltage and losses in DC cable considering various sheath grounding schemes has been emphasized in [1,26,27].…”