Placement and rating planning of feeders & transformers for LV/MV distribution networks

Allocation and Sizing of Distribution Transformers and Feeders

Distribution network planning is largely characterized by the allocation and sizing of distribution transformers. The location of these transformers directly dictates the length and route of medium - voltage (MV) and low - voltage (LV) feeders. Therefore, the location and rating of transformers, along with the length and size of MV and LV feeders, need to be determined in a coordinated manner.

To achieve this, an optimization process is essential. It aims to not only cut down the investment costs for transformers and feeders but also minimize the loss costs and maximize system reliability. Constraints like voltage drop and feeder current must be kept within their standard ranges.

For low - voltage (LV) network planning, the key tasks are determining the placement and rating of distribution transformers and LV feeders. This is done to reduce both the investment in these components and the line losses.

Regarding medium - voltage (MV) network planning, it focuses on pinpointing the location and sizing of distribution substations and MV feeders. The goal here is to minimize investment costs, along with line losses and reliability metrics such as SAIDI (System Average Interruption Duration Index) and SAIFI (System Average Interruption Frequency Index).

During the planning process, several constraints must be met.

Bus voltage, as a key constraint, should be kept within a standard range. The actual feeder current must be lower than the feeder's rated current. Enhancing the voltage profile, reducing line losses, and improving system reliability are primary concerns in distribution network planning, especially in semi - urban and rural areas.

Installing capacitors is another way which highly increases the voltage level and reduces the line loss. The Voltage Regulators (VRs) are also common elements for covering these problems.

Reliability is a key concern in distribution network planning. Long - span distribution lines raise the likelihood of line failures, thereby reducing system reliability. Installing cross - connections (CC) is an effective measure to mitigate this issue.

Distributed generators (DG) can inject active and reactive power, which helps lower reliability indices and improve the voltage profile. However, their high investment costs deter power engineers from widespread adoption.

Given the discrete and nonlinear nature of the allocation and sizing problem, the resulting objective function has multiple local minima. This highlights the significance of choosing an appropriate optimization method.

Optimization methods are mainly classified into two groups:

• Analytical - based methods.

• Heuristic - based methods.

Analytical methods are computationally efficient but struggle to handle local minima effectively. To address the local minima issue, heuristic methods have been widely used in the literature.

In this research, both analytical and heuristic methods will be implemented in Matlab. Discrete Nonlinear Programming (DNLP) will be used as the analytical approach, and Discrete Particle Swarm Optimization (DPSO) as the heuristic approach.

Accounting for load growth and peak load levels is another crucial factor that needs to be considered during the planning process.