Fault Clearing Overvoltages on Long Transformer Terminated Lines

Electromagnetic transients are the tidal waves of electric power systems. These momentary voltage surges generally lasting only fractions of a second can be powerful enough to disrupt normal operations and even cause serious damage to major pieces of equipment, such as transformers. Created by lightning, line faults, substation switching functions, and other sudden events along a utility network, transients must be taken into account both in choosing equipment ratings for a power system and in setting its operating parameters. Like the builders of a seawall that must withstand the highest expected waves from the ocean, engineers trying to guard against damage from transients face an extraordinary design task. Most of the huge computer simulation codes related to power systems either model steady-state conditions or deal with system stability problems. The analysis of electromagnetic transients, on the other hand, requires a much more detailed examination of how some critical portion of a power system will react to conditions that can change greatly in microseconds. For many years, simulation of transient effects was performed by special-purpose analog computers called transient network analyzers (TNAs). These machines, which are still in use, recreate a portion of the power system in miniature, complete with voltage sources representing generators and various kinds of capacitive or inductive loads. TNAs are generally adequate but relatively inflexible, tedious to set up, and cumbersome to use. Once a system configuration is modeled, many simulations can be performed. Given the need to manually reconfigure TNA circuits to represent changes in a system, however, the analyzers can also be quite expensive to use. During the late 1960s, Herman Dommel of the Bonneville

Emergency transmission line switching to suppress power system inter-area oscillation

Transient study of two 500 kV coupled lines in a transient network analyzer

The increasing penetration levels and stochastic characteristics of renewable energies and aging of transmission equipment bring potential negative impact on the economic and reliable operation of power grid. Therefore, the realistic and cost-effective choice for the utilities is to tap the potential of existing transmission infrastructures. Some smart grid technologies can leverage the potential transmission capacity and offer a flexible way for the power system operation. The dynamic thermal rating can evaluate the maximum transmission capacity of lines dynamically based on the environmental data. The optimal transmission switching can change the transmission topology and remove the transmission congestions. These technologies should be considered in the network-constrained unit commitment problem systematically to study their impact on the power system scheduling. However, the dynamic thermal rating incorporated network-constrained unit commitment studies are all based on the fixed transmission topology. So the overall influence of dynamic thermal rating and transmission line switching on network-constrained unit commitment has not been studied as yet. In this paper, the line switching technology and dynamic line rating according to multi-regional environmental information are incorporated in the network-constrained unit commitment framework. Case studies are implemented on a modified RTS-79 system. The simulation results verify the effectiveness of the coordination of two technologies in the reduction of generation cost and wind curtailment.

Purpose This paper aims to survey the need for full capacity utilisation of transmission lines in power systems network operations. It proposes a review of the N-1 security criterion that does not ensure reliable dispatch of optimum power flow during outage contingency. The survey aims to enlarge the network capacity utilisation to rely on the entire transmission lines network operation. Design/methodology/approach The paper suggests transmission line switching (TLS) approach as a viable corrective mechanism for power dispatch. The TLS process is incorporated into a constraint programming language extension optimisation solver that selects the switchable line candidates as integer variables in the mixed integer programming problem. Findings The paper provides a practical awareness of reserve capacity in the lines that provide network security in outage contingency. At optimum power flow dispatch, the TLS is extended to optimal transmission line switching (OTLS) that indicates optimal capacity utilisation (OCU) of the available reserve capacity (ARC) in the network lines. Practical implications Computational efficiency influenced the extension of the OTLS to optimal transmission switching of power flow (OTSPF). The application of OTSPF helps reduce the use of flexible AC transmission systems (FACTS) and construction of new transmission lines.. Originality/value The paper surveys TLS efforts in network capacity utilisation. The suggested ARC fulfils the need for an index with which the dispatchable lines may be identified for the optimal capacity utilisation of transmission lines network.

Steady-state overvoltages can occur on EHV transmission systems during various system operating conditions. The voltage waveforms are characterized by a periodic waveform which may be distorted by harmonics if iron saturation of equipment on the lines occurs. This paper discusses the results of digital and transient network analyzer (Anacom) studies which analyzed system parameters with respect to their effect on harmonics in steady-state overvoltages. Special emphasis was focused on the factors influencing harmonic distortion of the steady-state voltages.

The reliability of the electrical system is a fundamental study that is carried out to determine the possible deficiencies that an electrical system can have in case of failures, since a failure can cause disturbances, power cuts, and load disconnections. For this reason, Optimal Transmission Switching (OTS) with Optimal AC Power Flows (OPF-AC) is used to reduce disturbances when faults occur and minimize equipment load and disconnections, but OTS offers possible switches in order to make it possible to reduce the damage that can be done for a fault with operating limitations in voltage, power, and angular deviation. However, to have a complete study, it is proposed to use a reliability analysis through contingency ranking to know the risks that a switched system may have at the time of simultaneous or consecutive failures. In addition, a load capacity investigation is conducted to determine if the transmission lines are within their operating limits. The study presents an analysis of the behavior of the switched system and an adequate operation for the mitigation of failures in the system through the switching of transmission lines with analysis of load capacity and reliability. The results presented by the proposed methodology will be compared with Matlab’s Matpower simulation package.

A cryogenic power cable is expected to be capable of carrying bulk power as a main transmission line in a future metropolitan electric power system. It is important to establish a strategy of how to sustain power supply when such a highly densified power supply route trips from the network due to contingency. It is proposed here that the bulk power transmitted by the cryogenic cable could be distributed into the parallel conventional transmission lines by suitable circuit breaker operations in the system. In this process, power‐flow routes are forced to be changed with a remarkable modification in the system configuration. In this paper, the power swings associated with the large power‐flow change following contingent faults are analyzed by means of a transient network analyzer. It is found that the proposed system modification could be realized without any harmful power swing if the parameters in generators as well as in control devices have conventional magnitudes. It is shown also by simulations that the margin to occurrence in an unstable power swing is left sufficient even if the parameters deviate somewhat from the present magnitudes.

Loading margin calculation with line switching: A decomposition method

AC filter group (ACF) circuit breaker is an important part of the AC filter group field of UHV DC engineering, which realizes the control, measurement, protection, and switching of transmission lines. In this paper, the arc extinguishing chamber electric field simulation of the AC filter group circuit breaker is carried out. The dynamic process simulation analysis of the zero zone arc is carried out according to the working condition requirements of the filter group circuit breaker. The research results show that the cause of arc reignition is the low velocity of the airflow field inside the arc extinguishing chamber, and the arc contacts of the arc extinguishing chamber are severely ablated under multiple operations, resulting in the distortion of the internal electric field distribution and multiple breakdown discharges.

An electronic arc model has been developed which simplifies the study of harmonic phenomena in are furnace power systems on a transient network analyzer (TNA). The model helps insure the proper magnitude and phase relationship of the harmonies at each loading condition. The simulation procedures and arc model characteristics are described. Also, some examples of typical study results are given.

As an industrial customer of the utility, electrical arc furnace (EAF) is the major flicker source that degrades the grid power quality. As a possible solution, STATCOMs with high bandwidth can be used. In this paper, the normalized model of a CMC-based STATCOM and an EAF model are introduced, and then a DQ-model based control strategy is proposed for flicker mitigation. Case studies are conducted for STATCOM applying to a 40 MVA EAF arc furnace. Simulation results verify the controllers' stability and performance. A transient network analyzer (TNA) is developed to experimentally test the developed controller.

Overall critical evaluation of the dynamics of EHV dc-power transmission requires that a variety of system conditions and effects of many parameters be studied. Problems can be strictly electrical or electromechanical. In general, those that fall in the former category are of short time duration, while those in the latter may be either of intermediate duration, on the order of 1 second, or of long duration, from 2 to 40 seconds. The approach used, whether it be 1) a physical model such as a transient network analyzer; 2) an analog computer, sometimes called an electronic differential analyzer, or 3) a digital computer, will depend upon the specific problem at hand. The capabilities and limitations of the analog computer in providing solutions to electromechanical problems are outlined in this paper, and the results reported give insight into the dynamic performance characteristics of a dc link under constant current or power control, with or without a parallel ac line.

A comprehensive state-space model of two-stage grid-connected PV systems in transient network analysis

A static VAr compensator (SVC) was installed at the Eddy County substation near Artesia, New Mexico. It was put into commercial operation in April 1992. Before the commissioning period, a phase of extensive testing and analysis of the digital closed loop control was undertaken. This work was done using the actual control hardware and software in conjunction with an analog TNA and with digital simulation models of control and power systems. Results of this work were checked with the power system during field commissioning of the SVC. This paper gives an overview of the closed loop control design. It presents some results from the TNA tests, digital simulation and commissioning field tests of the SVC operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>