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A field-programmable gate array (FPGA) high-resolution time-to-digital converter (TDC) based on phase-wrapping, sorting, and selection to achieve an extremely fine bin size of 1 ps is proposed in this paper. Based on Nutt interpolation method, a wide measurement range with a high resolution can be realized at the same time. The input signal is fed into tapped delay lines (TDL) with regularized and automated cell placements to generate a multitude of delayed signals with plenty of regularized phase shifts. Due to periodicity, those phase shifts will be equivalently wrapped within a reference clock period and then phase sorting, ROM-based selection are applied to construct a merged TDL with uniform phase division across the reference clock period. The FPGA TDC was implemented successfully on both Altera Stratix IV to achieve a resolution as fine as 1ps with a measurement range of 1s. The short-range integral non-linearity errors (INL) are measured as −1.470– 1.676 LSB for Stratix IV to demonstrate its excellent linearity.

Inverter-interfaced renewable energy sources (IIRESs) are typically controlled during fault conditions to meet fault ride-through (FRT) requirements, e.g., reactive current generation (RCG) requirements specified by grid codes (GCs). However, fault currents generated by inverters are different from the traditional sources, i.e., synchronous generators. Consequently, phase selection methods (PSMs) used by protection relays could suffer from erroneous fault type classification. This paper develops a dual current controller (DCC) that regulates the inverter's negative- and positive-sequence currents to simultaneously meet phase selection and RCG requirements. First, the negative-sequence-current angle is obtained based on the angles of both zero- and positive-sequence currents to enable a correct operation for phase selection. Then, the positive-sequence current angle is adjusted to reach a trade-off between RCG requirements and phase selection achieved by the negative-sequence current. Lastly, the reference currents of the IIRES are generated in the stationary frame without violating the inverter's current limits. The proposed DCC supports the grid voltage by meeting the RCG requirements and enhancing the grid reliability and resilience by enabling correct phase selection. Comprehensive time-domain and real-time simulation verify the precise operation of the proposed DCC under various fault conditions and GCs. [ABSTRACT FROM AUTHOR]

Inverter-interfaced distributed generators (IIDGs) have fault current signatures that could jeopardize protective relaying. This paper unveils the failure of phase selection methods (PSMs) utilized by commercial relays in the presence of four-wire IIDGs, which adversely impacts the grid resiliency and reliability. A triple current controller (TCC) is proposed to regulate the inverter’s sequence currents during unbalanced faults to ensure accurate fault type identification. The negative- and positive-sequence components are extracted using a decoupled double synchronous reference frame (DDSRF)-based phase-locked loop (PLL). Further, a second-order generalized integrator (SOGI)-based PLL is employed for zero-sequence component synchronization. The negative- and zero-sequence reference currents are generated to force the angles of IIDG sequence currents to behave like those from synchronous generators (SGs) and abide by the inverter’s current limits. Consequently, commercial PSMs can correctly identify the fault type. The proposed TCC scheme pertains to four-wire as well as transformer-less IIDGs. A performance evaluation using time-domain simulations is conducted on a CIGRE benchmark system to confirm the success of the proposed control scheme under different fault conditions. [ABSTRACT FROM AUTHOR]

A method for fault type discrimination and faulted phase identification using instantaneous local current measurements is proposed. Seven current components are obtained from the measured three-phase instantaneous currents through a transformation and band passed filtered to remove the fundamental components and high frequency content. Upon detecting a fault, nine fault discrimination indices are computed taking different ratios of the maximum rates of change of these filtered current components. The indices are used to (i) separate ground faults from the phase-to-phase and three-phase faults, (ii) discriminate phase-to-ground from phase-to-phase-to-ground faults, (iii) differentiate phase-to-phase faults from the three-phase faults, and (iv) identify the faulted phases. As the indices are ratios, decisions are less affected by the fault resistance. The algorithm was validated using a power system simulated in PSCAD/EMTDC. Extensive testing involving more than 10,000 fault scenarios showed that fault type and faulted phases can be successfully identified. The algorithm found some difficulty in identifying the phases involved in phase-to-phase-to-ground faults at certain fault inception angles, and one of the thresholds can be affected by the transposition scheme. [ABSTRACT FROM AUTHOR]

Directional, phase-selection, and distance elements of a relay are prone to misoperation in the presence of inverter-based resources (IBRs). To address these problems, modifications of relay elements as well as new control schemes for IBRs have been proposed in the literature. These methods focus mainly on addressing the misoperation of only one of the above relay elements. The available solutions that are based on a new control system focus only on the negative-sequence current loop. Thus, they work only for unbalanced faults. This paper proposes a comprehensive dual current control scheme for IBRs during all types of faults such that all of these relay elements operate correctly. The proposed method controls the IBR to operate as a voltage source behind a virtual impedance in the positive-sequence circuit, and a single impedance in the negative-sequence circuit, thereby emulating the phase angles of a synchronous generator's (SG's) fault current. The proposed method also maximizes the active, and reactive current generation of the IBR during faults, and emulates the incremental sequence current magnitudes of an SG. The proposed method does not require altering the relay elements. Moreover, correct operation of the relay elements is achieved regardless of the fault type, resistance, and location. The effectiveness of the proposed method is verified through not only simulation studies, but also hardware-in-the-loop testing of commercial relays. [ABSTRACT FROM AUTHOR]

Inverter-based resources respond differently than synchronous generation sources during power system faults, challenging line protection reliability. Part I of this paper presented cases that challenge line protection schemes. In this paper (Part II), we provide solutions that can be applied to gain a substantial improvement in reliability. [ABSTRACT FROM AUTHOR]

The unique fault current signatures of inverter-interfaced renewable energy sources (IIRES) hinders the correct operation of the existing phase selection methods (PSMs) that operate based on the sequence currents. As a result, the system resilience during unbalanced faults is imperiled. In this paper, a new dual current controller is developed to regulate the relative angles of the IIRES sequence currents during unbalanced faults to enable accurate identification of the fault type by the existing PSMs. The proposed method consists of three design stages. In Stage I, the IIRES control system identifies the fault type using the sequence voltages at its terminal. Stage II aims at generating the appropriate reference angle for the IIRES negative-sequence current. In Stage III, the IIRES sequence currents are controlled in the double synchronous reference frame to track the reference angle. The proposed controller makes the existing PSMs immune against fault conditions and reactive current generation requirements imposed by grid codes. Consequently, the protection system can select and trip only the faulted phase(s), and thus, the system reliability is considerably enhanced. Time-domain simulations are used to confirm the successful operation of the proposed controller under different fault conditions and grid codes. [ABSTRACT FROM AUTHOR]

In this paper, a practical rule-based guideline has been presented for on-line detection of partial discharge (PD) defected phase (i.e., phase selection) followed by discriminating PD defected cable section (i.e., localization) in cross-bonded single core cable networks. Both goals are met by relying on the proposed rules that take the advantages of an energy-based index, calculated/measured at different junctions of cable network. The whole process provides practicability needs, as it requires neither synchronized measurements at different junctions of a network nor any PD pulse detection. Moreover, the proposed procedure derives the required indices from the measurements out of the link boxes, which provides enough safety in practical applications. Simulating and investigating four popular cross-bonding schemes (including sectionalized and continuous by coaxial cable and single core cable) as well as various characteristics of PD sources, different source locations, and noisy condition have proven acceptable performance of the proposed method in both tasks of phase selection and localization. [ABSTRACT FROM AUTHOR]

In order to accurately measure the impedance, the residual current for impedance measurement in ground distance relay is compensated in a fixed manner. It has been shown that the above compensation manner may have negative impact on the phase selection in mho elements in a single-pole trip scheme. A new residual current compensation method based on the magnitude of current of each phase for mho elements is presented in this paper. The performance of this new method is analyzed under all kinds of fault conditions. Simulation studies are carried out to investigate the new compensation method based fault component impedance relay in a typical transmission system. The relay has shown satisfactory performances under various fault conditions especially for the close-in ground fault and cross-country fault. This new compensation method can also be used in phase selector based on impedance measurement. [ABSTRACT FROM PUBLISHER]

In long line applications that involve tripping the faulted phase in case of LG faults, single-pole autoreclosure is extensively used. Traditional phase selectors can suffer some deficiencies in their performance due to varying system and fault conditions. However, the advent of wavelet transform techniques with their ability to focus on system transients provides an effective and reliable method for accurate and fast phase selection. This work describes the design and implementation of a new technique using wavelet transform algorithms. The technique is based on utilizing sharp transitions generated on the faulted phase. The paper presents the wavelet transform concept and its value in classification techniques and feature detection schemes. Feature extraction principle is derived. Generated data from the simulation of 400 kV power system using EMTP were used to test the performance of the technique. [ABSTRACT FROM PUBLISHER]