Novel pilot protection scheme for line‐commutated converter high voltage direct current transmission lines based on behaviour of characteristic harmonic impedances

Abstract

Transient behaviour of high‐voltage direct current transmission lines under direct current faults can be easily affected by many factors, namely, fault location, fault resistance and transmission line length. In order to design a suitable protective scheme, the impact of these factors should be thoroughly investigated. An impedance‐based analysis is more suitable in evaluating high‐voltage direct current system behaviour during direct current line faults, and consequently, in comparison to similar harmonic current or voltage‐based schemes, a characteristic harmonic impedance‐based protection is more capable in fault detection. Therefore, this paper presents a novel pilot protection method for line‐commutated converter based high‐voltage direct current transmission lines, which relies on continuous monitoring of characteristic harmonic impedances. The proposed method can accurately calculate location of faults along the line, and estimate additional valuable information, such as fault resistance. The validity of the proposed method is evaluated by a wide range of fault scenarios using the CIGRE high‐voltage direct current benchmark model, simulated in PSCAD/EMTDC and codes written in MATLAB software environments. It will be shown that the proposed protection method sounds promising, and can serve as an excellent backup option in the case of primary protection malfunction.

Fault-Location Accuracy of Natural Frequencies Using Incomplete HVDC Station Models

“…Line-commutated converter (LCC) stations present the largest smoothing reactors, in the range of 200 to 600 mH, while voltage-source converter (VSC) stations, and in particular modular multi-level converter (MMC) stations, require smaller reactors, typically below 50 mH. The importance of reactors in station models is witnessed by their inclusion in CIGRE models [23], even though those models were designed for benchmarking control strategies, rather than fault-transient propagation [14]. The value of the reactor inductance also plays a major role in identifying whether a fault is internal or external to the converter station [37].…”

“…As opposed to transmission lines, power-converter stations are highly non-linear active systems, for which numerical modeling of fault transients is far from trivial, a topic that is still debated even in low-frequency settings, where averagevalue models have been developed to better reproduce the dynamical response of converters [21], [22]. The widely applied CIGRE models have been used in fault-location analysis [23] but were in fact designed to benchmark the power dynamics of HVDC systems [24]. The possibility of deriving equivalent models of converter stations by means of direct measurements is clearly not an easier option when it comes to non-linear devices that need to be tested on-line under realistic operating conditions.…”

“…Bipolar lines would require to consider all possible fault configurations, with further complexity introduced by the coexistence of all-line and faulty-section sets of resonances, the former depending on the overall line length, while the latter only depends on the fault distance [31]. Previous works have indeed also resorted to equivalent monopolar descriptions [5], [23], [30], [32], [33].…”