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Three-terminal hybrid transmission lines (TTHTLs) are attractive from both environmental and commercial view. Hybrid transmission lines are growing due to urbanization, connecting an industrial load and renewable integration. A TTHTL comprises sections of both overhead lines and underground/subsea cables or overhead lines with different X/R ratios. Faulted section identification (FSI) is key for defining the adaptive/selective auto-reclosing scheme and estimation of the fault location for TTHTLs. In this paper, FSI and fault location algorithms are proposed without using the parameters of any line section. Novelty of the methodology lies in a two-stage approach to the problem. In the first stage, series impedance parameters of all the sections are calculated using closed loop formulae. These parameters are then utilized in identifying the faulted section. In the second stage, the above calculated line section parameters and faulted section are used to estimate complete line parameters including shunt capacitance and subsequently the fault location. The advantage of the proposed method is that it does not require an initial guess of the line section parameters, is non-iterative in the first stage, and provides correct fault section identification for TTHTLs. These features make it suitable for designing the selective auto-reclosing protection scheme for the TTHTLs within traditional protection relaying hardware. More importantly, the series impedance parameters calculated in the first stage constitute good initialization values for the non-linear problem of estimating the complete line parameters. This results in better convergence of the algorithm and accurate parameter estimation. The developed solution is verified using the PSCAD/EMTDC simulations for TTHTLs connected with conventional and different inverter-based renewable resources. The performance of the proposed solution is compared with commercially available solutions, and it is found to be accurate. This solution is amenable for implementation in line differential protection relays without additional infrastructural changes.

Distance protection is popular in transmission networks and constitutes a large installed base across grid systems. The most widely accepted implementation of distance protection is based on voltage and current phasors. Today the electric grids are becoming increasingly complex and dynamic in nature. With power electronic converter interfaced systems such as renewables, HVDC, FACTS, etc., there is a need for fast, secure and reliable protection decisions. The phasor-based distance protection is prone to reliability issues in such networks and is inherently limited in speed. Recently, ultra-fast protection solutions based on fault induced traveling waves are commercially available. Although promising, such solutions may miss faults near voltage zero-crossing, falsely detects nonfaulty disturbances as faults and as such lack wider acceptance in contemporary transmission lines where protection security is a non-negotiable requirement. In comparison, time-domain based distance protection solutions have appeal in terms of reliability and speed. In addition, an ideal time-domain distance protection should be applicable to various networks such as series compensated lines, lines connected to renewables and long underground/sub-sea cables. In this paper, we propose a method for time-domain based distance protection to meet these requirements. The method operates based on current based operating quantity and a novel dynamic restraining quantity which is calculated for the fault zone boundary point. The proposed method inherently overcomes influence of series compensation, renewable integration and provides a fast and reliable identification of in-zone and out-of-zone faults. It is tested for various networks using laboratory experimental data and field records. Further it is implemented in an IED platform and tested with RTDS simulations in hardware-in-loop mode. The method is found to work satisfactorily and consistently over the extensive test scenarios.

Locating fault precisely on power transmission line is highly beneficial to utilities and accurate fault location can expedite the repair of the faulted components, speed-up restoration, and reduce outage time. In this paper, a setting-free double ended fault location method for power transmission line is proposed using both end voltage and current measurements. This algorithm estimates the required setting parameters using pre-fault data and fault location is calculated using estimated parameters and during fault data. The proposed method is verified using the EMTDC simulations for lines connected with conventional and inverter-based renewable resources. The method is not affected by the error in line parameters and renewable integration. The method is implemented in Intelligent Electronic Device (IED) using 1kHz sampling rate and successfully installed on a 400 kV, 233.07 km line from Power Grid Corporation of India (POWERGRID), India and on a 220 kV, 265.6 km line from Svenska Kraftnat (SVK), Sweden. This paper presents laboratory test results as well as field experimental results in which line patrolling crews found the actual location. Pilot installation results match the performance demonstrated with laboratory experimental results. The method gives average fault location error of ~ 0.1 %. The method can locate the fault within two-tower span distance (~300m) which is comparable with traveling wave-based method that requires 1000 times higher sampling rate, high-cost hardware, more complex commissioning, and settings. These geographically diverse pilot installation results stand as testimony to the fault location accuracy of the proposed setting-free fault location solution.

Two-port equivalent model of the system around a transmission line is commonly used for various line protection related analyses. The main aim of the paper is to present methods that can be adopted in a decentralized manner at the substation level for estimating such an equivalent model. Firstly, the paper contributes to methods for estimation of simple two-source equivalents based on events such as fault on the line or shunt element switching at its terminals. The paper extends a discussion towards limitations of such models in the presence of a transfer path across the line terminals and proposes an extension of the estimation techniques to overcome the issue. Lastly, the paper proposes methods for updating the two-port equivalent model when network topology in the vicinity of the line of concern changes. This contribution differs in the aspect that it only seeks to update the two-port equivalent model, unlike the previous contributions wherein the aim is to estimate the equivalent model without assuming the availability of an initial solution. The methods for updating utilize the equivalent model parameters in a base network scenario and the measurements excited from a topology event. The proposed methods use only limited measurements of bus voltages and line currents, and model parameters of the line of concern and other neighboring apparatus (such as other incident lines or shunt reactors/capacitors). This is an advantage as the availability of the complete network model at any substation is always a challenge. Therefore, the methods can be deployed directly at substations in a decentralized manner. The proposed solutions are computationally easy and amenable for implementation in the framework of digital substations with advanced communication infrastructure. Testing and analysis are done using a simple two source transmission system and the IEEE 39 bus test system.

Locating fault position in a series compensated transmission line is a difficult task due to the non-linear characteristics of the metal-oxide varistor which is present in the protection system of the compensator. In this paper, a model-free two-terminal traveling wave-based fault location method for a series compensated line is proposed. The technique makes use of two subroutines which calculate the fault locations assuming that the fault position to be on the left and right side of the series compensator respectively. The method then selects the correct fault location of the two by a special logic based on faulted half-section identification. The first two traveling wave arrival times recorded at both the terminals of the line are used in the method. The proposed technique does not require model information of the series capacitor and transmission line. It has been verified using the PSCAD/EMTDC model of a 400-kV, 300 km transmission line which is compensated by a fixed series capacitor in the middle and line ends. The performance of the proposed method is compared with a commercially available classical two-ended techniques and setting-free method.