Realistic methodology for fault location and protection tests based on traveling waves

Session Title: Commissioning and testing procedures and tools (e.g. IEC 61850)

The interconnected electrical systems are day by day requiring faster and precise identification of faults to ensure its stability. Due to this need, more efficient location and protection algorithms are needed so that the impact of the defect is mitigated as quickly as possible. Among the various methods in the literature, algorithms based on traveling waves (TW) stand out for their high accuracy.

With the mastery of this technology, IED's manufacturers started to use TW not only for the identification of the fault location, but also to the protection, aiming to reduce the total TRIP time. Thus, it is necessary to use test systems capable of checking such functionalities through voltage and current waveforms that best represent the real behavior of the electrical power system, including fundamental frequency together with the TW. So, the use of software that performs simulations of transient conditions in conjunction with hardware capable of reliably reproducing the simu

Other test solutions capable to test functions based on traveling waves do not reproduce the complete behavior of the waveforms neither the real amplitude values. There are testers that just inject an artificial pulse of voltage or current to reproduce the arrival time of the traveling wave with limited quantity of pulses, others apply artificial pulses added to low frequency waveforms and there are also real-time simulators that reproduce the faithful waveform, but just at a low level, which is not suitable for connection with devices.

Artificial pulses are the ideal scenario for a TW algorithm to identify wave fronts, but they are not ideal for testing, as they do not represents the correct wave form and so do not guarantee  a deep evaluation of the IED algorithm. In the situation of a real fault, the signals measured by the TW devices are complex (non-periodic signals with a wide frequency spectrum and several reflections) and the TW are presented with amplitudes that are totally different from those applied by artificial pulses.

The present work will address a new methodology, a system composed of software and hardware that is capable of accurate modeling all the components of the electrical system, including the transmission lines, and later reproducing the very high frequency wave forms together with the fundamental frequency at secondary levels, thus contemplating all the necessary requirements for evaluating the device under test, without creating artificial pulses.

Commercial IEDs will be tested by the solution and the results will be presented for different fault types, incidence angles and fault locations. A practical comparison will also be made between fault locators based on impedance and locators based on traveling waves, demonstrating that the accuracy obtained by the TW algorithms is in the order of meters while the previous technology presents a range of kilometers.

The conclusion will emphasize the need for testing using realistic waveforms, concluding that the developed test system fits this reality, as it reproduces faithful waveforms in both its shape and amplitude.

lated signals is essential for testing the TW devices.