Distributed Low-Voltage Measurements for use in Electrical Distribution Networks’ Protection...

Distributed Low-Voltage Measurements for use in Electrical Distribution Networks’ Protection, Control, and Automation Schemes.

This paper introduces a proposal for compact AC voltage measurement units.   The units should provide a cost-effective pathway to make improvements to commonplace protection practices found on traditional electrical distribution networks.   The improvements should particularly benefit networks transitioning towards SMART grid operation with the inclusion of dispersed generation.

The amount of electricity that consumed from clean renewable sources is increasing significantly.  Often the supplies of this renewable energy are dispersed within electrical distribution networks.  This causes disruptions to traditional power-flow patterns on the networks.  A proven approach to protecting traditional radial networks uses time-graded overcurrent protection to detect high current levels associated with faults.  This method, however, is jeopardised when dispersed sources of generation are embedded into the network, since fault-current levels may drop, and currents may flow in different directions.   With dispersed generation in the network, different protection techniques are required to ensure safe and efficient network operation.

Protection techniques that take into account system-voltage conditions offer potential solutions to the dilemma.  Whether the protection is in the form of conditioned overcurrent protection (voltage-restrained or, voltage-dependent), impedance measuring (Distance) protection, or directional protection, some knowledge of the system voltage as well as system currents is needed for the techniques to be implemented.     At the distribution level, a full complement of measuring current transformers is usually available for protection.  Due to cost and space limitations, however, voltage transformers are not commonplace on distribution networks.  This has often precluded the provision of protection techniques that are dependent upon system voltage measurements.  

This paper presents a conceptual model for a compact, low-cost, device for acquiring voltage measurements at the consumer supply level to overcome the oppositions.  This research covers acquisition of consumer-voltage measurements and communication of the measurements to conventional relaying points, to afford voltage-influenced protection for the network.  

A study of compact, low-cost, voltage acquisition devices confirms the feasibility of providing a signal suitable for protection purposes.    Wireless conveyancing of the voltage measurements is demonstrated.  In combination, the concept of a consumer-side-resident voltage-measurement device suitable for augmenting electrical distribution network protection is confirmed.  Rudimentary field-testing demonstrates successful voltage data acquisition along with effective wireless communication to devices such as Directional Agents to provide protection.  

The demonstration offers a compact, low-cost, proof-of-concept, model that is ripe for industrialisation.  Such a component lends itself to combination with Directional Agents to provide wide-area protection of SMART distribution networks.