A Straightforward Method for Wide-Area Fault Location on Transmission Networks

Local practices in fault location require measurements from one or more terminals of the faulted line to be available. On the other hand, the nonlinearity of circuit equations associated with wide-area fault location makes their solving process iterative and computationally demanding. This paper proposes a non-iterative method for wide-area fault location by taking advantage of the substitution theorem. Accordingly, a system of equations is constructed which can be easily solved using the linear least-squares method. The distributed-parameter line model is considered to provide a highly accurate estimation. Besides, due to inherent errors of current transformers, the current data is not taken into account to preserve the accuracy. In order to avoid uncertainties in relation with construction of zero-sequence network, just positive- and negative-sequence networks are exploited. Nonetheless, the method still is capable of pinpointing all types of short-circuit faults by using a restricted number of synchronized pre- and post-fault voltage phasors. Numerous simulation studies conducted on the WSCC 9-bus and New England 39-bus test systems verify the effectiveness and applicability of the proposed fault location method, even with limited coverage of synchronized measurements

A Modified Formula for Distance Relaying of Tapped Transmission Lines with Grounded Neutrals

Protection of tapped transmission lines with grounded neutrals has been always a challenging problem, usually resulting in compromise solutions. This type of lines may be protected by pilot relaying requiring dedicated and reliable telecommunication links. This paper proposes a modified distance relaying for protection of tapped lines with grounded neutrals under single-phase-to-ground (1-ph-g) faults. The proposed method uses only local measurements similar to conventional distance relays. Nonetheless, it facilitates fast fault clearing from both line ends over a wider portion of the protected line length. Regardless of whether or not the tapping transformer is in service, the method performs desirably with no need for signaling. The proposed method is extensively tested on a large number of test-systems using the sinusoidal steady-state analysis. It is also implemented into the National Instrument Compact-RIO embedded hardware that has been suitably coupled with the RT-LAB real-time digital simulator by Opal-RT. This setup is used to conduct extensive hardware-in-the-loop (HIL) testing. The improved performance together with simplicity of the proposed distance relaying makes it an attractive option to include in numerical protective relays

From Available Synchrophasor Data to Short-Circuit Fault Identity: Formulation and Feasibility Analysis

This paper proposes a novel formulation for determining the short-circuit fault identity, that is the fault type, faulted line and exact fault distance on it, by using available synchrophasor data. A simple and yet quite effective procedure is developed to model the fault area as a stand-alone sub-system. Thanks to phasor measurement units (PMUs), the proposed technique does not require the operating point and model of the portions being replaced. This greatly alleviates the complexity and technical problems involved in modeling the entire power system, as enforced by existing wide-area methods. A couple of effective theorems in Circuit Theory are exploited in a way as to make the pre-fault bus impedance matrix applicable in the post-fault condition. The obtained fault equations are readily solved by the least-squares method to provide a closed-form solution for the fault distance. Two necessary and sufficient conditions are introduced to assess the fault location feasibility by a given set of PMUs. High accuracy is achieved since the calculations merely involve sound equations remaining after removing erroneous measurements of instrument transformers. The proposed method is successfully validated by more than 10000 simulation cases conducted on the New England 39-bus and 118-bus test systems

A Traveling-Wave-Based Methodology for Wide-Area Fault Location in Multiterminal DC Systems

While in many applications, multiterminal dc (MTDC) systems are potentially appropriate substitutes for their ac counterparts, their protection problems still require more attention. This paper proposes a novel traveling-wave-based methodology for fault location in MTDC systems. The traveling-wave principle, along with two graph theory-based lemmas, is deployed to locate the fault by sectionalizing the graph representation of the MTDC system. Accordingly, the system of equations relating the fault inception time, fault point, and first arrival time at different converter locations would be derived and solved. The method merely needs the first surge arrival times, thereby eliminating the practical problems in relation to identifying subsequent traveling waves. More important, it successfully determines the fault location, regardless of the network topology complexity, that is, the number of its meshes and radial lines. To demonstrate the effectiveness of the method, it is applied to some complicated MTDC systems containing meshes and radial lines. Numerous simulation studies carried out for different conditions verify high accuracy, robustness against fault impedance, and noise immunity of the proposed method

Adaptive load shedding scheme to preserve the power system stability following large disturbances

Following large disturbances, the conventional under frequency load shedding (UFLS) relays may not operate properly, as they are designed to merely preserve the frequency stability of the system, independent of its voltage stability. In this study, an adaptive load shedding scheme is proposed to maintain the power system stability when the conventional scheme fails. In doing so, the frequency and its falling rate along with a properly defined voltage falling rate are exploited to determine closeness to the disturbance area and its severity. Accordingly, a proper amount of load is shed from the locations with the highest influence on the system stability. The proposed scheme exclusively utilises locally measured quantities and does not require a communication link. The associated logic is practical and can be easily appended to the existing UFLS relays to enhance their performance. To demonstrate the efficiency of the proposed UFLS scheme, it is applied to two large-scale power systems where the exact load model is taken into account. The obtained results verify that a large number of blackouts because of inappropriate operation of conventional UFLS relays can be prevented using the proposed scheme

Locating Faults on Untransposed, Meshed Transmission Networks Using a Limited Number of Synchrophasor Measurements

The method of symmetrical components is not effective for fault location in the case of untransposed lines, due to potential couplings between the sequence circuits. This paper proposes a non-iterative algorithm in the phase-coordinates for wide-area fault location on untransposed transmission networks. In doing so, first, an improved two-terminal method is suggested to accurately locate faults on untransposed lines. Next, an algorithm is proposed to infer voltage and current phasors at the faulted line ends without direct measurements, by taking advantage of the data provided by phasor measurement units (PMUs). Accordingly, the adverse effect of close instrument transformers transients on the estimation accuracy is minimized. Being highly nonlinear in terms of fault distance and impedance, the fault equations are derived and made linear in this paper by defining six suitable auxiliary variables. The resulting system of equations is solved using the least-squares method to obtain three-phase voltages and currents at the faulted line ends. A main feature of the proposed algorithm is that it only requires a limited number of current and voltage synchrophasors. An additional advantage of the proposed algorithm is that the faulted line is not required to be known a-priori. The proposed algorithm is validated using extensive simulation studies on the New England 39-bus test system, accounting for different fault locations, types and resistances

Fault location on multi-terminal DC systems using synchronized current measurements

Multi-terminal dc transmission systems are suitable substitutes for their ac counterparts, once the associated costs are justified. This paper proposes a new traveling wave-based fault location method for multi-terminal dc (MTDC) systems. In doing so, the fault section and its included lines are specified using a straightforward algorithm. Then, an evaluation index is developed to determine the faulted line amongst all included ones in the fault section. Finally, a system of linear equations taking into account the fault inception time, the fault location and the first arrival times at different detector locations are constructed and solved. The method merely needs the first current surge arrival times, thus eliminating the practical difficulties in relation with identifying other traveling wave features. Besides, the fault is easily located despite the complexity of the network topology, i.e., the number of its meshes and radial lines. To examine the effectiveness of the proposed method, a large number of simulation studies are conducted on a complicated MTDC system. Obtained results verify the high accuracy, noise immunity and fault impedance robustness of the proposed method

A new algorithm to stabilize distance relay operation during voltage-degraded conditions

This paper deals with the possible operation of distance relays during impending voltage instability and presents a new method to prevent its maloperation in power system voltage-degraded conditions. The proposed method successfully discriminates between fault occurrence and system incidents during stressed voltage conditions, even for the most severe cases such as sudden equipment outages and high impedance faults. The proposed scheme successfully blocks maloperation of relay zone 3 where the degraded condition is detected. It is based on the rates of change of voltage and current magnitudes. These values are different during fault occurrences in comparison with the corresponding values during stressed conditions system incidents. Simulation results verify the effectiveness of the proposed method