Juan C. Ledezma Senior Staff Consultant juan.ledezma@siemens.com	Luis G. Pérez, Ph.D. Senior Staff Consultant luis.perez@siemens.com

Normal switching maneuvers in high voltage systems cause fast transient overvoltages and overcurrents which may be dangerously high. These electromagnetic transients (EMT) depend on a series of system characteristics such as the configuration of transmission lines and cables, transformer design, existence of capacitor banks, and other parameters. In order to predict the transients and to properly dimension the power system’s insulation characteristics, engineers simulate the electromagnetic transients using computer programs. These programs numerically solve a large number of algebraic and differential equations with partial and total derivatives with linear and non-linear parameters. PSS^®SINCAL can be used to perform such simulations by running the program system PSS^®NETOMAC in the background.

In addition to other well-known features of PSS^®SINCAL, the main advantages of using this program for EMT studies are these: (1) relatively simple migration of data from PSS^®E load-flow and sequence data files including the standard one-line diagram; (2) the entire transmission network or a large portion of it can be simulated with a minimal use of equivalents, for a more accurate representation; (3) the instantaneous interface between the simulation window and the graphic results window eases the engineering analysis; (4) when desired, results may be stored in IEEE COMTRADE format for subsequent analysis using SIGRA^® or sharing with other applications; and (5) instantaneous connection of the graphics with the document Windows^® environment for fast report writing.

The Houston office of Siemens PTI recently finished a study to determine the switching transients associated with the 500/220/110kV transmission system of Afghanistan. As a result of steady-state studies using PSS^®E, this system was found to require reactive compensation at several locations of the transmission network, including several 110kV and 220kV capacitor banks, and several 500kV and 220kV reactors. The transient electromagnetic study mainly included: (a) switching of capacitor banks and preliminary limiting inductor calculations; (b) line energization; (c) transformer energization; (d) reactor energization; and (e) single-phase-to-ground fault with three-phase clearing.

The study was carried out using the combined simulation and graphic capabilities of PSS^®SINCAL, which allowed a large number of simulations in a relatively short period of time, automatically producing the ready-to-insert standard graphic results used to create the written report. Figure 1 shows an example of the results obtained in this study, of one simulation of a single-phase-to-ground fault with three-phase clearing. This report was delivered on-time/on-budget to the customer in late May 2008.

Figure 1 - Simulation Example

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