High impedance faults are rather difficult to detect, due to their inherent characteristics. However, in most cases high-impedance low-current faults evolve to low-impedance high-current faults, thus giving rise to life hazard situations and equipment damage. In this paper, a novel back up protection scheme for high impedance fault detection, based on synchrophasor measurement technology, is proposed. In fact, the presented detection method can be thought as the combination of a classic differential and a classic admittance relay. The protection device designated for high impedance fault detection, incorporating the proposed novel protection algorithm, permanently monitors transmission line’s shunt admittance thus being able to detect changes-increase in the resistive part of shunt admittance, namely the shunt conductance. Actually, a sudden rise of transmission line’s shunt conductance is a strong indicator of high impedance fault inception. Conducted computer simulations confirmed a high degree of selectivity and sensitivity of the proposed method. Moreover, the technical feasibility of the approach was tested considering real-world measurement data obtained for two 220 kV transmission lines. From the acquired data, measurement uncertainties of the monitored parameters in normal operating conditions, were calculated. The results demonstrate excellent sensitivity of the proposed method, even for the case of short transmission lines during low-loading conditions.

System integrity protection schemes (SIPS) are schemes that can, under potentially hazardous conditions, prevent a complete blackout of endangered parts of an electrical power system (EPS). The main objective of SIPS is to monitor the state of the power transmission network in real time and to react in emergency cases. This paper explores the use of phasor measurement unit (PMU) technology for the development of SIPS as a part of wide-area monitoring, protection, and control (WAMPAC) systems. A new SIPS development method is described using the experience from the real-time operation. The developed optimal bus-splitting scheme identifies potential actions that can eliminate or reduce power system overloads and protect the integrity of the power system. An optimal bus-splitting scheme based on a DC power flow model and PMU measurements is given as an example and is explained and tested on an IEEE 14 bus test system. Conducted simulations indicate that the described SIPS methodology supported by the PMU measurements can mitigate potential overloads of the observed network part.

Liberalization of the electricity market and inevitable control of the electric power system (EPS) on the edge of its stability as a result brings major changes in control and protection technologies. Control and protection systems are becoming increasingly complex, using even more process information and faster communication links. Intelligent electronic devices (IEDs) that perform control and protection functions are also becoming more complex. They are being developed on a daily basis, and just as you install the latest version of the device the newer model becomes available on the market. One of the newer technologies that is also rapidly evolving and can improve control of the EPS at the edges of its stability is the synchronized phasor measurements technology (SPMT). Implementation possibilities of SPMT are wide and they can be classified into three basic groups: system monitoring, control and protection. This paper describes initial phase implementation of an advanced control system of power transmission network around wind farm Vrataruša (42 MW) in the Croatian EPS based on SPMT. Among other things, it also describes guidelines and future use of system integrity protection schemes (SIPS) like adaptive underfrequency load shedding scheme based on real time measurements of loads, system protection against overloading of power transmission lines, system breaker failure protection and system busbar protection.

The monitoring and control of smart power transmission grid represents active infrastructure capable of obtaining increased transfer and distribution of electrical energy, with considerable rate of generation from renewable energy sources without compromising the stability, security and reliability of power grid in different operating conditions. The development concept of intelligent protection and control systems of the entire smart power transmission grid defines: (1) use of complex information and communication technology (ICT) system, (2) sending selected local information to a remote location where this information is processed and (3) implementation of accurately defined automated actions to neutralize and stop the spreading of major system disturbances. Wide area monitoring of electrical power system, which is the initial step in developing the smart power transmission grid has found its place around the world and it's expected increase of use in the daily work of system operators will result in more efficient and reliable use of ancillary functions during large scale disturbances. The intention of this paper is to point out the needs and developing possibilities of monitoring and control systems of the entire smart power transmission grid based on the System Integrity Protection Schemes (SIPS) and synchronized measurements technologies, to summarize accomplishments within ongoing projects and experience gathered worldwide, and to emphasize the need for making practical roadmap towards greater deployment of the technology. This paper will give the scheme of automatic transmission control system that aims to mitigate the possible overloading of existing transmission lines while maintaining the same rate of generation.