Summary of Power Grid Operations and Voltage Classification

## Introduction Electric power grids deliver energy from generation plants to end consumers through a coordinated set of networks and devices. This material explains the main components, voltage classifications, and how transmission and distribution work. It breaks down concepts for a university-level understanding and highlights practical examples and applications. ## Main components of a power grid Figure 1.1 (described): Generation (1) → Transmission network (2) → Substation (3) → Distribution network (4) → Consumer (5). Each stage has specific equipment and voltage levels to optimise efficiency and reliability. > Definition: A power grid is an interconnected network for delivering electricity from producers to consumers, including generation, transmission, substations, distribution, and loads. ### Generation - Electricity is typically generated at **medium-voltage** levels in thermal, hydro, wind, solar, or other power plants. - Generators and step-up transformers increase voltage for efficient transmission. ### Transmission - High- and extra-high-voltage lines carry bulk power over long distances with reduced losses. - Transmission networks interconnect regions and balance supply and demand across large areas. ### Substations - Substations contain transformers, switching gear, protection, and control equipment to change voltage levels and route power. - Key functions: step-down for distribution, isolate faults, and maintain voltage regulation. ### Distribution - Distribution networks deliver electricity to industrial, commercial and residential customers at medium and low voltages. - Final step-down to consumer voltages occurs at distribution transformers near the load. ## Voltage classifications Electricity supply is subdivided to minimise losses and match equipment ratings. The classifications below follow the stated policy. | Classification | Voltage range (V) | | --- | --- | | Low voltage | Below $1\,\text{kV}$ | | Medium voltage | Between $1\,\text{kV}$ and $33\,\text{kV}$ | | High voltage | Between $33\,\text{kV}$ and $132\,\text{kV}$ | | Extra high voltage | Higher than $132\,\text{kV}$ | > Definition: **Voltage level** refers to a standardized range used to classify parts of the power system for design, operation, and safety. ## Why different voltages? (Loss and efficiency) - Power loss in a conductor is $P_{loss} = I^2 R$, so increasing voltage to reduce current lowers losses for the same transmitted power $P = VI$. - Example: For a fixed power $P$, doubling voltage halves current: if $P = V I$, then $I = P / V$. > Definition: **Transmission efficiency** is the ratio of delivered power to generated power, improved by using higher voltages to reduce current-related losses. ## High-voltage networks (overview) - Single high-voltage lines can carry large power amounts compared to medium- and low-voltage lines because of lower currents and losses. - Typical uses: long-distance bulk transfer, inter-regional ties, and backbone of the grid. ### Equipment and characteristics - Overhead lines, insulators, towers, series and shunt compensation devices, circuit breakers, and protective relays. - Higher voltages require larger clearances, stronger insulation, and more robust switching gear. ### Practical example - A power plant generates $500\,\text{MW}$ at $11\,\text{kV}$. A step-up transformer raises it to $220\,\text{kV}$ for transmission. At the receiving end a substation steps it down to $33\,\text{kV}$ for regional distribution. ## Distribution networks (details) - Industrial users may receive power at medium voltage (e.g. $11\,\text{kV}$ or $33\,\text{kV}$) depending on demand. - Residential customers typically receive low-voltage supplies (e.g. $230/400\,\text{V}$ three-phase systems in many countries). > Definition: **Distribution transformer** is a device that steps distribution voltages down to consumer levels while isolating and protecting the customer connection. ## Stability and reliability - Th