Design of an improved distribution substation in the city of Ethiopia

Power distribution problem in the city

The main objective of this thesis work is to investigate and address the problems that consumers face due to the present state of the power distribution problem in the city, and recommend ways to better the situation through a design of the power distribution system.

Statement of the Problem

Ethiopian Government is currently making all rounded effort to change the country’s economic status from the current least developed level to a medium income level. Of the many aspects of this effort, expanding and strengthening of the electric power supply sector is one among the most emphasized economic dimensions.

Since Bishoftu city is one of selected areas as the industry zone by the government and is near to the capital city (Addis Ababa) this makes the city a preferred location for most of the industries in the country, and hence considerable share of the electric power supply is supplied to the city.

Methodology

Due to the nature of the study, it is started by reviewing literatures related to power distribution and reliability issues. The data collected from the field work is then analyzed. For the evaluation of the system, power simulation software (like dig silent, auto cad, Visio etc.) are utilized.

Generally the following methodology is followed in conducting the thesis work:

1. Site visit
2. Technical data collection at selected substation Investigation of power distribution problems and reliability problems for power distribution systems in the city
3. Estimate the load of the system
4. Design of power distribution substation
5. Analyzing the economic feasibility of the designed system
6. Simulation of the reliability improvements

Simulation Software Dig Silent Power Factory

The calculation program Power Factory, as written by Dig SILENT, is a computer aided engineering tool for the analysis of transmission, distribution, and industrial electrical power systems. It has been designed as an advanced integrated and interactive software package dedicated to electrical power system and control analysis in order to achieve the main objectives of planning and operation optimization.

The name Dig SILENT stands for “Digital Simulation and Electrical Network calculation program”. Dig SILENT Version 7 was the world’s first power system analysis software with an integrated graphical single-line diagram interface.

The following key-features are provided by the program:

1. Integrated interactive single line graphic and data case handling
2. Power system element and base case database
3. Integrated calculation functions (e.g. line and machine parameter calculation based on geometrical or nameplate information)
4. Power system network configuration with interactive or on-line access to the SCADA system
5. Generic interface for computer-based mapping systems

Description of Bishoftu Substation II

Bishoftu city is now supplied from national grid that is, interconnected system (ICS). Ethiopian Electric Power Corporation (EEPCO) is a provider of electric power in the country.

A 132 kV transmission line is stretched into the substation. Then, the distribution system in the city has a primary voltage of 33 kV and 15 kV. And also, this voltage value is stepped down to 380 and 220 volts to customer’s level.

It is not preferred for major substation and it lack operational flexibility and in case of bus fault or CB failure the entire bus has to be de-energized, but it is low cost, simple to operate and requires simple protection.

Figure 1 above illustrates the current (old) arrangement of the distribution substation of Bishoftu town.