What is used for?

SIGMA SLP is an object-oriented software package for computation of transmission and distribution line lightning performance. In short, it calculates the number of outages to expect based on configurable system parameters and lightning activities. It allows simple application of Line Surge Arresters (LSA’s) to define optimum quantities and placement of LSA’s. SIGMA SLP helps utilities, grip operators, engineering companies and LSA manufacturers to address lightning performance.

Advanced modeling and simulation

Phase-to-ground(tower) and phase-to-phase flashovers using a leader propagation flashover model can be simulated. Each tower in the simulated line section can include different flashover ratings. Line insulation flashover voltage are randomly selected in the Monte Carlo simulations. Soil ionization tower footing resistance model are automatically implemented. Counterpoise or constant resistance tower footing model can be also implemented. Linear and non-linear tower footing resistance representation, counterpoise, leader propagation flashover model, linear or upward concave stroke front, initial voltages etc. are standard features used into simulations. Each line span is divided into short segments to accept strokes between towers and to consider corona influence. Transients on the conductors separately computed from that on the towers. Corresponding interconnections done in each time step using Thevenin equivalents. This enables extremely fast electromagnetic transients simulations.

Simplicity above complexity

The software is based on simplicity and does not require advanced knowledge in circuit modeling like other EMTP-based software. The software does its own complete modeling for electromagnetic transients simulations. The user specifies only readily available data as line geometry, system parameters LSA's main ratings (catalogue values), grounding conditions, number of towers for the simulated line section, insulation critical flashover voltage, etc.

Possibility of complex structures

Simulations can be performed either on shielded or unshielded lines since the user can build quickly its own structure. Standard configuration and compact lines can be analyzed. For multi-circuit lines, each three-phase system can have different voltage levels. Multi-circuit outages are directly obtained. Unbalanced (differential) insulation can be simulated.

Ground wires or neutral conductor can have different connections along the simulated line section (insulated or grounded at different towers). Transients on the tower top can be represented. Influence of the underbuilt ground wires or guy wires with separate grounding can also be simulated. Each tower can have different phase-to-ground and phase-to-phase insulation characteristics. Nearby objects in the electro-geometric simulations are considered.

Method & Models

A Monte Carlo statistical method is used for the simulation of lightning activity, while a three-dimensional electro-geometric model is adopted for the determination of stroke terminations. Electromagnetic transients on the line are computed by the multiphase travelling wave method. Transients are computed separately from the towers' ones while corresponding connections are being performed by Thevenin equivalents. 

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Line Surge Arresters application

The software is specifically designed to enable quick and easy determination of optimum LSA’s installation scheme. A specific and limited quantity of LSA can be applied methodically on towers and phases to determine the optimal configuration for a specific budget. Ideally it is often required to define the minimum amount of LSA to achieve the best lightning performance improvement by reducing the number of outages to a negligible value. Placement can be made arbitrarily but an automatic tool for LSA’s placement is integrated in the Sigma SLP software. Line Surge Arresters, connected in parallel with the line insulation can be gapless (NGLA) or with external series gap (EGLA). 

The software provides a statistical representation of LSA’s discharge currents, thermal energy and charge transfers to be compared with LSA’s ratings. It helps to define maximum expected charge/energy and therefore analysis the failure rate of your installation.

A standard stroke distribution can be used for the simulation of lightning activities (Two lines CIGRE stroke distribution from CIGRE TB 63 / 1991) or a customized stroke distribution can be defined by the users to reflect better its own situation.