Meliha Selak


Power System Protection Schemes in Smart Grid with Distributed Generation

Very complex power systems have been built to satisfy increasing demand of electrical power supply. With adding distributed generations (DG) of high capacity to the power grid endangers the normal operation of power system and might lead to outages and system collapse. With DG increases, distribution system is also becoming more like transmission system: double or multiple feed circuits having significant changes in operation; protection system becomes more complex due to changes in system behavior and power flow under short-circuit conditions.

The convention power system protection schemes, designed to detect the fault and signal circuit breaker to isolate the fault reliably and as fast as possible, but cannot prevent from the system collapse. Nowadays, the modernized networks and telecommunications infrastructure allow optimizing the existing electrical power system operation in addition to support the future innovation. The implementation of wide area special protection schemes (SPS) or remedial action scheme (RAS) which are designed to detect the system conditions that can cause instability, overload or voltage collapse can isolate faults in the direct area and/or in areas adjacent to the fault.

Power System Operation and Design

Very complex power systems have been built to satisfy increasing demand of electrical power supply. To design the power system that provides the secure power supply it requires to consider the different aspects including different studies: Steady State, Dynamic State Simulations and Electromagnetic Transients Study (EMTP). Distribution systems, with Distributed Generation (DG) increase, have been changed significantly in operation and safety of public and equipment. Therefore, power system protection schemes become more complex due to the changes in system behavior and power flow under short-circuit conditions.

Power System Line Protection

The power system protection schemes are designed to detect faults and then signal circuit breakers to isolate faulted parts from the rest of the electrical network reliably and as fast as possible. Relays are not required to operate during normal operation but must immediately activate to handle intolerable system conditions. The main components of protection systems and the operating principles of power system protection fundamentals are briefly introduced, focus on the implementation of power system protection of transmission line.

Transmission lines provide the connections between the various parts of the power system and the associated equipment. Just as these circuits vary widely in their characteristics, configurations, length, and relative impedance, their protection and techniques are different. The protective techniques commonly used for line protection are overcurrent, distance and pilot protection, depending of requirements. However, the most common practice to protect transmission lines is to equip them with distance relays. Distance relays are designed to respond change in current, voltage, and the phase angle between the measured current and voltage. Several fundamental factors influence the final choice of the protection applied to a power line: type of circuit (overhead, cable, single line, parallel lines, multi-terminals), line function and importance (effect of service continuity, realistic and practical time requirements to isolate the fault from the rest of the system), coordination and influence on power system stability. In addition to these four considerations, economic factors must be added. Those aspects will then be discussed.

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