Renewable energy generators(REGs)are integrated into the grid via power electronic devices and their fault current characteristics are greatly influenced by the control strategies. This may cause malfunction of the traditional relays. The transmission line emanating from the renewable energy power plant(REPP)is usually the only power transmission channel

so the operation performance of its primary protections such as current differential protection plays an important role in the utilization efficiency of renewable energy and operation safety of the grid. Here an analysis of current differential protection is demonstrated for such transmission lines connected to inverter-interfaced REPPs. The fault current of the inverter-interfaced REGs is calculated and its angular characteristics are analyzed. Based on this

the operation performance of the current differential protection is discussed under asymmetrical faults facing both a strong grid and a weak grid. It is revealed that for internal phase-to-phase faults

line current differential protection may refuse to operate for the weak grid and will operate reliably with a low sensitivity for the strong grid. And for internal ground faults

current differential protection will operate reliably both for the strong and the weak grid owing to the appearance of zero-sequence current. Simulations based on the real-time digital simulator(RTDS)verify the conclusions. The findings of this study can provide advice about protection configuration of transmission lines connected to the inverter-interfaced REPPs. This work is supported by National Key Research and Development Program of China(No. 2016YFB0900503)

State Grid Corporation of China(No. 5211JY16000U)

and Fundamental Research Funds for the Central Universities(No. 2016ZZD01).