Transient Overvoltage Studies Research Articles

Study of transient overvoltages on CSI adjustable speed drives under arcing SLGF in the industrial cable grid

Single line to ground fault (SLGF) in MV ungrounded networks is often accompanied by arcing. Most of these arcing faults are unstable and cause transient overvoltages that can exceed the insulation withstand limits of grid equipment. This problem has become especially troublesome in industrial grids widely using power electronics devices, which tend to have lower insulation margins than other power equipment. Typically an arc suppression coil is used to compensate the SLGF capacitive current and reduce the likelihood of arcing in this case. However, as the operating experience shows, arcing ground faults were also recorded in compensated industrial cable grids. This article proposes an original algorithm based on known arc burn theories to simulate the maximum overvoltage values during arcing SLGF. The purpose of this article is to examine the effect of an arc suppression coil on the nature and magnitude of transient overvoltage. The study of transient overvoltages is carried out on the example of an industrial cable grid containing AC adjustable speed drives under arcing SLGF caused by cable insulation breakdown. Simulation results for various grid operating configurations show that the suppression coil can reduce the transient voltage rise intensity but cannot affect the initial voltage pulse during an SLGF. The presented model allows sizing the minimum insulation margins and selecting thresholds of overvoltage protection triggering for grid equipment to ensure its reliable operation.

Cable Surge Arrester Operation Due to Transient Overvoltages Under DC-Side Faults in the MMC–HVDC Link

The dc cables of the voltage-sourced converter-based HVDC link, including the modular multilevel converter (MMC) configuration, must be protected by surge arresters against transient overvoltages. The selection of the appropriate surge arresters requires a comprehensive understanding of the phenomena that cause the overvoltages and accurate calculation of energy discharged in the arresters. This paper investigates the mechanism that causes transient overvoltages, due to dc-side line-to-ground faults, in a cable-connected MMC–HVDC link. This paper also evaluates the impacts of various system parameters, for example, the prefault power transfer level, the MMC arm inductance, the transformer leakage inductance, the fault location, the ac system short-circuit capacity, the cable inductance, and the MMC blocking delay, on the peak transient overvoltages and the amount of energy discharge in the cable surge arresters. The transient overvoltage studies are also conducted when the dc cable is replaced by an overhead line. The studies are performed in the PSCAD platform. The studies conclude that the prefault power transfer level and the MMC blocking delay have the most significant impacts on the surge arrester energy discharge under dc-side line-to-ground faults in the MMC–HVDC link. The study results also provide essential information for the design of the MMC–HVDC link components.

Methodology for Cable Modeling and Simulation for High-Frequency Phenomena Studies in PWM Motor Drives

The analysis of the transient overvoltages in a pulsewidth modulation (PWM) motor drive system comprises a wide frequency range, which starts with the low values corresponding to the motor speed, includes the switching harmonics, which can reach up to few hundreds of kHz, and also the cable resonance frequency, which value can be in the MHz range, depending on the cable length. In this context, this work presents a time domain methodology for cable modeling able to represent the cable parameters variation due to skin effect in this broad range of frequencies. The proposed technique reproduces accurately the wave propagation and reflection phenomena, thus showing to be very appropriate to transient overvoltage studies in PWM motor drives. A new alternative to represent the frequency-dependent cable earth-return path is also included, allowing the computation of the zero-sequence currents generated by the common-mode voltage produced by the inverter. Simulations using the proposed methodology are conducted and the obtained results are compared with measurements, showing good agreement.

High‐frequency behavior of power inductor windings using an accurate multiconductor transmission line model: input impedance evaluation

AbstractThis research and tutorial paper is the second part of a work dedicated to the analysis and computation of the electromagnetic behavior of inductor windings operating at high‐frequency regimes—a critical issue for very fast transient overvoltage studies. The inductor winding, wound around a ferromagnetic core, containing a total number of N dielectric coated cylindrical turns, is modeled by using a multiconductor transmission line (MTL) approach (proximity effects being accounted) whose constitution and characterization was presented in a former paper. In the present work, we make use of the R, G, L, and C constitutive matrices of the structure in order to develop a modal analysis technique‐based formulation aimed at the evaluation of the winding's input impedance in the frequency‐domain. Results obtained show that the input impedance critically depends not only on the number of layers of the winding but also, and, more importantly, on the frequency, where resonance phenomena play a key role. Frequency‐domain analysis is complemented with simulation results in the time‐domain that clearly illustrate how critical and sensitive the system response can be under minute changes of the winding's excitation current. Copyright © 2007 John Wiley & Sons, Ltd.

Evaluation of the constitutive parameters of a multiconductor transmission line model aimed at the representation of inductor windings at high frequencies

AbstractThis paper is the first part of a work dedicated to the analysis and computation of the electric and magnetic behavior of inductor windings (e.g., power transformer windings) operating at high‐frequency regimes; a recognized key issue for very fast transient overvoltage studies. Here, the inductor winding, containing a total number of N turns, is modeled as a system of N‐coupled parallel conductors resembling a uniform inhomogeneous multiconductor transmission‐line structure (MTL) where proximity effects cannot be neglected. The characterization of the winding's equivalent MTL structure requires the specification and evaluation of its constitutive parameters, namely, the per‐unit‐length (PUL) capacitance and inductance matrices, and also the PUL resistance and conductance matrices, the latter two associated with losses. Close proximity between inductor turns together with the consideration of dielectric‐coated turns prevents the utilization of closed‐form expressions for the evaluation of most of the inductor constitutive parameters. Here we employ a harmonic expansion method (HEM) primarily aimed at the construction of the capacitance matrix from where the inductance and conductance matrices can be derived. A new theory based on Dubanton's approach but taking into account proximity effects related to eddy currents in the inductor core is also proposed and developed. This research paper provides, in a tutorial fashion, a comprehensive explanation of the details and approximations involved in the evaluation of the constitutive parameters of the MTL structure under analysis––an aspect that unfortunately is lightly tackled or even ill‐treated in the literature of winding models. Copyright © 2007 John Wiley & Sons, Ltd.

Hybrid modelling of inhomogeneous transformer winding for very fast transient overvoltage studies

This paper presents a novel approach for the modelling of transformer windings, which is valid in the frequency range of 10 kHz to a few MHz. It is a hybrid model; coil-by-coil detailed plus inter-coil black box model. The parameter estimation of the detailed model and the synthesis of the black box model is based on frequency domain measurements. The technique is applied to a high-voltage transformer winding. The comparison of the measurements and the frequency domain simulation of the model with EMTP confirms the validity and accuracy of the model for the intended frequency range. Experiments in the frequency range of several MHz reveal that remarkable overvoltages appear at the connecting point of the inverted and interleaved part of this winding. It is shown that the reason of the VFTO (very fast transient overvoltage) in the MHz range is the inhomogeneity of the winding parts.

Transient overvoltage study and model for shell-type power transformers

In order to calculate winding resonances of shell-type power transformers under lightning impulses, an accurate RLC model of the transformer taking into account frequency dependence, is presented. RLC parameters are calculated using analytical and finite element methods. An interactive computer model has been developed and allows automatic generation and calculation of the network elements. The classical network method is used for the frequency study. Transient overvoltages of the transformer are calculated from the frequency response by Fourier transform. Good agreement between experimental and numerical results shows that the model is well adapted to predict windings overvoltages. >

Analysis and Control of Transient Overvoltages on UHV Transmission Systems

The results of a comprehensive study of transient overvoltages on a UHV transmission network are presented. In the study, the expected magnitudes of switching overvoltages due to the energization and reclosing, operations were evaluated for a conceptual 1500-kV system. Fault initiation and fault clearing overvoltages were also studied. The sensitivity of transient overvoltages to network configuration and to key system parameters was examined. The effectiveness of various means of overvoltage control was evaluated. It is demonstrated that the overvoltages can be reduced to a practical level depending on the type and complexity of the control technique utilized.

Transient overvoltage studies of AC filter systems for HDVC treminals

Many ac filter configurations have been implemented on various hvdc installations thoughtout the world. This paper attempts to make an initial documentation of the transient overvoltage studies performed during the various design stages of the ac filters for the Sylmar Terminal of the Pacific Intertie. Included in the paper are the results of these studies made to determine the transient voltage levels. The application of arresters is considered utilizing two application criteria based on the duty the arresters would experience in various locations for the particular filter configurations.

Fault Surge Versus Switching Surge A Study of Transient Overvoltages Caused by Line-to-Ground Faults

When the improvements in extra-high- oltage power circuit breakers now being studied are realized in practice, over- voltages caused by energization or reenergization of lines can be made so low that the limiting factor determining how much the line insulation may be reduced might become the overvoltage produced by single line-to-ground faults. On lines insulated for levels below twice the normal line-to-ground crest voltage, such faults could develop into double line-to-ground faults, which would be particularly objectionable if single-pole switching were to be employed.