Optimal Design Software for Substation Grounding

Abstract

Different types of substations in an electric power system play different but crucial role in functioning of power system. In a substation design, the attention is paid for the design of grounding system as gaffe in it proves dangerous to the system and working personnel. Design of an effective grounding system is key to the substation performance because it deals with personnel safety and also operation and protection of equipment.

Responsibility of keeping the substation safe is upon the grounding system installed within it. The absence of reliable and effective grounding system in any substation, can result in malfunctioning or non-operation of control and protective devices and may prove hazardous for persons working therein. Therefore, the grounding system design is a task that must be performed critically.

This report is aimed at describing the development of and functioning of software for optimal design of substation grounding systems for square and rectangular areas. IEEE standard 80 - 2000 is widely accepted document pertinent to safe practices to be followed while designing grounding systems for electrical substations. Using equations there in (i.e. IEEE Std. 80 2000) blended with finite element (FE) methodology is implemented for the design of grounding system. A software named \ Ground Grid Designer (GGD) " has been developed using MATLAB as mathematical computing tool as well as GUI programming platform. GGD can be deployed as a standalone application using MATLAB run time compiler add-on, so that it can be used on the computer even where MATLAB is not installed. Designing substation grounding employing FE technique results into a 3D graphical representation indicating potential at any point within and (slightly) outside the grid area. It is also feasible to find the area of high potential on the ground during abnormal / fault condition. The information availed thus helps in modifying the ground design as per the standard requirements.

The GGD is designed to cater to design of grounding grid of any rating of substation, however limited to two basic shapes and single soil layer. The software offers three possibility, of which optimal design can be justified. Two methods out of three has a Variation as opposed to the designs of a literature.

In addition to grounding system analysis and optimization, GGD allows derivation of soil model from available Earth Resistance Testing (ERT) data. It can extract uniform soil models from available test data, to be used in further calculations. Performance of the software is evaluated by comparison with Ground Grid Systems (GGS) module of ETAP and IEEE 80-2000 design. Sample design problems solved with the help of both the software produce quite comparable results in majority of the cases. Thus by such software testing, technical soundness of the software is proved. In certain cases GGD is found to be superior than ETAP and IEEE 80-2000 design. Some standard designs available in the literature has been tested and optimal design is thus proposed. Typically, a new approach is suggested for a grounding grid design.