Active distance protection schemes for asymmetrical faults of renewable energy stations transmission line

The limited fault current amplitude and uncertain phase of inverter-interfaced renewable energy stations (IIRES) lead to the risk of malfunction of traditional distance protection. In order to solve this problem, based on the idea of control and protection coordination, this paper proposes an active protection scheme for transmission lines combining the IIRES current control strategy and distance protection. Firstly, the negative sequence current of the specified phase angle is injected during the fault period through the IIRES negative sequence current control loop, and the current phase of the fault point is obtained by using the local negative sequence fault component. Secondly, combined with the different characteristics of the phasor plane of voltage and current in the internal and external faults, a fault identification criterion based on the phase difference between the operating voltage and the fault point current is proposed. Finally, to distinguish reverse faults that may cause misjudgment of internal and external faults identification, the additional harmonic current is injected through the IIRES during the fault, and the direction protection auxiliary criterion is formed according to the amplitude characteristics of the harmonic current signal. This scheme leverages the high controllability of IIRES and only requires single-ended information for fault identification. RTDS simulation analysis verifies that the proposed protection scheme exhibits high reliability under various transition resistances, different asymmetric faults, and developing faults.