A criterion for non‐voltage directional elements applied in AC networks connected with VSC‐based interconnection devices

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Abstract

The application of voltage source converter (VSC)‐based interconnection devices or distributed generators (DGs) in an AC distribution system makes the network change from a single‐terminal power supply network to a multi‐terminal power supply network. However, traditional three‐section current protection applied in AC distribution networks is not capable of identifying the direction of the fault, and therefore it is necessary to install directional elements to ensure the reliability of the three‐section current protection. The phase relationships among negative‐sequence currents under phase‐to‐phase faults that happen at different locations in the AC distribution network connected with back‐to‐back VSC‐based interconnection device are derived first in this paper. Then a novel criterion based on the phase relationships among the negative‐sequence currents flowing through the protected line and the other two branches emanating from the same bus is proposed for fault direction identification. The proposed directional criterion is applicable to multi‐terminal power supply networks containing VSC‐based interconnection devices or VSC‐interfaced DGs, with three or more branches emanating from each bus. The proposed directional criterion does not require potential transformers (PTs), and is hardly affected by transient resistance. Under a symmetrical fault, negative‐sequence current can be obtained by delaying the filtering data window of any one of three phases, and the dead zone of traditional directional elements when the fault happens at the outlet of the relay can be avoided. The validity of the proposed criterion is verified by several PSCAD simulation results. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

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