Distribution Network Protection Schemes formed from Wirelessly Connected Directional Agents

This paper outlines a proposal to implement wide-area protection of SMART electrical distribution networks using wirelessly-communicating Directional Agents.  Directional Agents combine measurements of system currents and voltages to provide directional indications of power flows on a protected network.  Wireless communication between measurement transducers and Directional Agents, coupled with wireless interconnection of Directional Agents, offers ‘plug-and-play’ possibilities for implementing unit protection schemes based on directional information.

Increasing quantities of dispersed electrical generation from renewable resources are being embedded into distribution networks to respond to the challenge of combatting carbon di-oxide emissions.  Embedding generation into distribution networks can cause unusual power flows, compared to those experienced on conventiional passive radial networks:  Power flows can change direction, and fault current levels may be so low as to make them almost indiscernible from operational load values.   Accordingly, widely deployed distribution network protection techniques based on system magnitudes (such as time-graded overcurrent protection) may no longer be effective.  Combining other measured system quantities as well as currents allows more sophisticated techniques to be implemented.   For example, combining system voltages and currents in Directional Agents can provide indications of magnitudes and directions of power flows across networks.  This addition of directional assessments to existing magnitude measurements can provide better selective differentiation between faulted, and un-faulted, network conditions.    Further, the increasing widespread availability of wireless communications affords new opportunities for the information to be shared across networks to facilitate informed wide-area decision making about their health.    Employing Directional Agents in conjunction with wireless communications to acquire and share power flow information in wide-area schemes could provide unit protection, with expansive network coverage, for fast selective fault clearance. 

This work considers the requirements of such unit protection schemes.  The feasibility of wirelessly implementing the necessary communications to form the wide-area unit protection schemes is researched.  In particular, the wireless communication of GOOSE messages for command transfer, and wireless communication of Sampled Analog Values (SAV) for data transfer, both in accordance with IEC 61850, are studied for suitability to realise aided directional schemes.

The studies indicate that wireless Ethernet communications are suitable to connect Directional Agents to provide unit protection for wide-area schemes using directional measurements.