A Pilot Protection Scheme for Transmission Lines in VSC-HVDC Grid Based on Similarity Measure of Traveling Waves

Abstract

The voltage-source converter (VSC)-based high-voltage direct-current (HVDC) grid is an effective means for large-scale integration of renewable energies. This paper proposes a pilot protection scheme as the backup protection for transmission lines in the VSC-HVDC grid. The traveling wave (TW) propagating processes and waveform characteristics at both ends of the transmission line are analyzed under different fault conditions. Based on the different characteristics between internal and external fault conditions, the protection is formulated utilizing similarity measure of TW waveforms. A four-terminal VSC-HVDC grid is modeled on PSCAD/EMTDC platform to test the performance of the proposed protection. Various simulation results demonstrate that the proposed protection is able to accurately discriminate internal faults from external faults and identify the faulty pole. The protection performance analysis shows that the protection is insensitive to the fault resistance, the protection sampling rate, and the inductance value of the reactors at the end of lines. The protection algorithm is simple with small calculation amount and does not require data synchronism. Furthermore, the proposed protection has superiority in the fault resistance withstand ability compared with other backup protections.

Impact of Propagation Losses on Fault Location Accuracy in Full Transient-Based Methods

“…As opposed to TWM, an alternative group of location methods has more recently been developed, using the entirety of transients recorded by a single probe. They can therefore be referred to as full transient-based methods (TBM) and share the idea of locating a fault by measuring the similarity between measured and reference (typically simulated) transients signals [12]- [21]. TBM have been shown to present some advantages compared to TWM, as discussed at the end of [13].…”

Surge Compression for Improved Fault Location Accuracy in Full Transient-Based Methods

“…In TBM a single-ended recording is commonly used, and the synchronization is no longer needed for estimating the fault position, but rather in order to accurately overlap measured and reference transients before computing their similarity [20]. No timestamp is required in this case: the alternative to transient synchronization in TBM would require computing their cross-correlation function, which would be a clearly more computationally expensive solution.…”

“…Another class of TWM exploits transients more thoroughly, by including later echoes and potentially the full transient [4], [12]- [20], resulting in a more accurate fault location according to [13], [14], [20], [21]. The reasons for their higher location accuracy were discussed in [22].…”

“…These reference data are most of the time based on numerical simulations, but can also make use of experimental data [13]. TBM are found throughout the literature to implement either direct transient correlation [13], [14], [20] or indirect comparison involving normalized projections. This last case has been mostly given consideration under the electromagnetic time-reversal (EMTR) technique [15], [17], [21], [23], [24].…”

“…The most practical impact could be expected for lines with high-frequency propagation losses: in this case a higher sampling rate may paradoxically reduce the location accuracy, as proven in [25]. It is therefore of practical interest to be able to increase the location accuracy without relying on higher sampling rates, a standard solution adopted in TWM [14], [20], [26]. Moreover, in legacy protection relay systems transients may be sampled at rates well below 1 MHz [13], [20], [27], [28], limiting the ability to accurately locate faults with other methods.…”