Combined real-time hardware-in-the-loop simulations and modeling of communication networks (co-simulation platforms) is a powerful testbed for development and validation of relay protection schemes utilizing communication links especially for applications in Smart Grids. This paper introduces laboratory tests in such environment of a new protection scheme for medium voltage networks with distributed generation. It is based on impedance measurements with compensation of remote infeed currents and high fault resistances. Since the scheme utilizes multi-terminal measurements, a communication network emulator has been developed to model Ethernet network impairments. The test method uses Monte-Carlo approach for evaluation of protection dependability. The results demonstrate enhancement of impedance relay performance compared to the conventional protection. Moreover, fault location capability is preserved with sufficient accuracy. Nevertheless, communication network imperfections, such as jitters and data loss, deteriorate scheme functionality.

Earth fault detection and location are very important issues in distribution networks. Current methods for faulty feeder selection are based on measurements of steady-state or transient signals. The work presented here identifies and gives analyses of scenarios when ground protection based on these methods is prone to misoperation in resonance grounded systems. It is shown that the traditional watt-metric approach can malfunction depending on network and fault parameters. The admittance methods help to eliminate many issues, however they might have complex settings depending on network configurations. Special attention is paid to approaches based on transient signals as the most promising alternative solution. The current work considers methods utilizing zero sequence current, angle, power, energy and admittance transients. The paper reveals limitations for their application mainly due to presence of electrostatic asymmetry, cables in a network, fault resistance and inception angle. Nevertheless, dependability of these methods is higher than the steady-state especially for intermittent faults. It is also found that analysis of prefault information is important both for the steady-state and the transient methods. The obtained results can be used to enhance reliability of protective schemes and as drivers

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