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

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 threesection 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, negativesequence 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.

A Novel Single-Terminal Fault Location Method for AC Transmission Lines in a MMC-HVDC-Based AC/DC Hybrid System

“…The converter and its system behind can be equivalent to a controlled positive-sequence current source . I dev , which is not influenced by its working state in a rectifier or inverter [29]. Meanwhile, whatever the fault ride through control strategy adopted by the converter, the equivalence exists.…”