Luiz Cera Zanetta

Fault location in transmission lines using one-terminal postfault voltage data

A new algorithm for fault location in transmission lines, with fault distance calculation based on steady-state measured phasors in local terminal is presented. For the postfault, only voltage phasors are required, avoiding possible errors due to current transformer saturation; the current phasors are required only in prefault time, when saturation does not occur. The algorithm does not use simplifying hypothesis but requires system equivalent data at both line terminals and the fault classification, considering fault resistance purely resistive. In order to verify the algorithm performance, a parametric analysis of variables that influences short-circuit conditions is developed, including an analysis of remote equivalent setting. The results show that the algorithm is very accurate, even in cases when the remote equivalent is not well fitted.

Optimization algorithm for fault location in transmission lines considering current transformers saturation

This paper deals with fault location calculations that use voltages and currents during transient conditions and pre fault values. The method uses transmission line measurements at both terminals and its main contribution is the possibility of fault location even with the lack of some current measurements as in the case of current transformers saturation or even when data acquisition process fails. The equations are based on two-port line representation that can be applied to transposed or untransposed lines and equivalent impedances at the terminals are not needed. With the proposed formulation, the algorithm does not use simplifying assumptions to calculate the fault distance and the fault resistance simultaneously. For phase-to-ground faults, the possibility of lack of accurate current measurement in one CT is assumed. For double phase-to-ground faults and three phase faults, the lack of measurements in two or three CTs, respectively, is also assumed. The results, considering different line configurations and fault types, are presented, showing the accuracy and efficiency of the proposed method.

Multirate Simulations With Simultaneous-Solution Using Direct Integration Methods in a Partitioned Network Environment

Multirate simulation of electric networks exhibiting a wide variety of time constants decreases the simulation runtimes by exploiting the property of circuit latency. The fundamental idea is to use different integration steps for different network subsystems, according to the requirements of accuracy of each subsystem. Programs that exploit circuit latency are usually based on relaxation methods that require iterations among the different subsystems of the original networks. These methods lack the numerical robustness of direct implicit integration methods used in circuit simulators and are not adequate for real-time simulation due to their non-uniform solution times. This paper proposes circuit latency exploitation without iterations making use of the concept of interlinked Multi-Area Thevenin Equivalents (MATE). Results are presented showing the efficiency and accuracy of the method

A current based model for load flow studies with UPFC

This paper deals with an alternative proposition for the steady state modeling of unified power flow controller (UPFC). Since current limitations are determinant to FACTS apparatus design, the proposed current based model (CBM) assumes the current as variable, allowing easy manipulation of current restrictions in optimal power flow evaluations. The performance of the proposed model and of the power injection model (PIM) are compared through a Quasi-Newton optimization approach. Two operating situations of a medium size network with 39 busbars were studied from the point of view of optimization and current limits, observing the performance of the UPFC modeling.

Medium voltage SF6 circuit-breaker arc model application

Abstract This paper presents an arc model used to evaluate the SF6 circuit-breaker interruption capacity on non-completely standardized conditions. A method is shown to calculate the arc parameters and their application on an electromagnetic transients program. Tests and simulations were carried out concerning transformer fed fault and short-line fault.

Application studies of line arresters in partially shielded 138-kV transmission lines

The application of arresters on transmission lines has been one of the most effective alternatives for the reduction of lightning flashover rates. This paper reviews previous methods for evaluating lightning performance of lines with arresters. Improved calculation of line outage rates are developed to include power freuency voltage and arrester failure rate evaluations, based on field experience. The transmission lines are modeled in full detail in the ATP program and the outage rates are calculated with Monte Carlos method. Probability energy stresses on arresters are evaluated for strokes on conductors and shield wires as a function of tower footing resistance.

Fault Location in Multitapped Transmission Lines Using Unsynchronized Data and Superposition Theorem

Lines with several taps are frequent and involve a large number of small towns and customers. With the need for costs reduction, this solution has been adopted in Brazilian utilities, with measurements only at the two terminal substations of the main line. The relevance of the problem is related to the long time for fault location when there are several secondary tap lines, depriving a large number of customers of energy during this period. Since there is not yet an adequate approach for this configuration, without additional hardware and measurements in tap lines, this paper presents a low-cost solution focusing on the synchronization of data measurements and the fault location in the main line or in the tap lines. The algorithm can handle the critical condition of zero-sequence infeed of star-delta transformers connected to tap lines, detecting the faulty section through the superposition theorem and finally obtaining the fault distance. Simple and accurate enough expressions were developed for fault location in order to help computer implementation of the algorithm. The algorithm also enables fault location in double-circuit main lines with several tap lines. The results, considering various line configurations and fault types, are presented, showing the accuracy and efficiency of the proposed method.

Evaluation of line surge arrester failure rate for multipulse lightning stresses

This paper develops a method to analyze energy stresses on transmission line surge arresters. The approach computes the failure rate of arresters due to energy stresses, convolving the density probabilities of first and subsequent pulses. Multipulse stroke effects are considered in a 138 kV line case study, typical of single circuit lines, located in regions with high densities of ground flashes, in SE Brazil. The proposed method provides an improved insight into energy stress evaluation for selection of line surge arresters.

Compensation strategy of autotransformers and parallel lines performance, assisted by the UPFC

In this paper, reactive power compensation through the tertiary winding of an autotransformer, is proposed. Such an approach emerges as an alternative to support the significant voltage variation present over two parallel connected autotransformers, in the South Eastern Brazilian system. The above proposal will also help in controlling the line voltage variation due to the UPFC series converter action. A detailed steady-state analysis of the series voltage and the shunt reactive current when supporting line voltage, is realized. Such analysis is based upon the d-q coordinates. The UPFC effect over an uncompensated parallel line, is also studied. The waveform simulations performed to control each transformer terminal voltage, were obtained utilising the ATP/EMTP program. Results concerning the effectiveness of the autotransformer tertiary winding reactive power injection by the UPFC shunt converter, as well as the load flow control over the referred transformers, are also presented.

Steady-state multiline power flow control through the generalized IPFC (interline power flow controller)

The interline power flow controller (IPFC) is one of the newest devices within the FACTS group. By utilizing this device, an enhanced controllability over independent transmission systems or those lines whose sending-end are connected to a common bus can be obtained. As an extended version of the UPFC (unified power flow controller), the IPFC appears as an excellent solution for the control of multiline systems, but it also presents its own complexities whilst operating under certain system conditions. The steady-state response and performance of a generalized IPFC controlling two independent AC systems, is in this paper evaluated. None-the-less, the study can be extended to systems having more than two transmission lines. In order to observe its dynamic behavior and simultaneously validate the previous steady-state analysis, an IPFC model was also built in the ATP program. The results obtained validated the IPFC model built and ratified its capability for controlling the power flow over the compensated transmission lines.