• Blackout prevention by power swing detection and out-of-step protection   [APPEEC 2014]
  • Author(s)
  • Joerg Blumschein
  • Any sudden load change in a power system, such as a fault, line switching etc. causes the system generators to adjust to the new condition. In that case a power swing may occur. Power swing can cause the load impedance to enter into the operating characteristic of the distance protection. Wrong operation of distance protection during a power swing may cause undesired tripping of transmission lines and possibly lead to cascading outages. The disturbances may also cause a loss of synchronism between two areas of a power system. In this case, it is essential that the asynchronous operating system areas are separated to avoid power outages. This paper describes a zero-setting power-swing detection method that is independent of network parameters and based on the verification of the impedance trajectories. Power swing can be detected up to 10Hz swing frequency, also during open pole condition and during asymmetrical operation. A blocking logic prevents unselective trips by the distance protection. Furthermore, this method can detect any kind of fault that may occur during power swing, so that the relay can trip quickly and selective in case of a fault during power swing. For unitable power swing a flexible out of step tripping function based on the shape of the impedance trajectory will be proposed. Using the shape of the impedance trajectory, the load flow direction, the voltage distribution and the position of the electrical centre are taking into account for the out of step tripping. According to the network structure the out of step trip can be issued at different severity of the out of step condition. During an out of step condition a controlled trip of certain transmission lines can separate the unstable grid into sub grids to prevent equipment damage and widespread power outages. The coordination of power swing detection, distance protection and out of step protection provides a reliable system protection. The risk of unwanted trips and cascating effects in the power system will be reduced.
  • Blackout prevention, out-of-step protection
  • References

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