A national grid network is a network of cable that connects all the power stations in a country to transmit electricity to the consumers throughout the country. Electricity is in demand just about everywhere in the civilized world, and in Great Britain the network for supplying this electrical power is known commonly as the National Grid. The National Grid is an electric power transmission network which connects the substations and power stations. This is so that any electrical energy generated in Great Britain, can be utilized and help meet energy demands elsewhere. This grid system also includes interconnections that run under the sea to Northern Ireland HVDC Moyle, the Isle of Man and France HVDC Cross-Channel. The electrical energy generated for the National grid needs to be moved around all parts of the country to supply the demand. There are two methods available for the transmission and distribution of electric power and these are: * Underground Insulated Cables
* Overhead Cables (Bare Conductors Suspended at a Safe Height Above Ground) The overhead lines are generally used for high-voltage long distance transmission, because the cost is lower than underground cables, especially at higher voltages. In British practice, high voltage transmission lines carry voltages ranging from 66kv to 132kv, and extra high voltage lines carry voltages from 220kv to 380kv. In all cases the power is transmitted in the form of three-phase alternating current at 50cycles/sec, and the cost of an overhead line depends largely on conductor size and voltage [Cheesman, 2007].
Figure 1: General layout of electricity networks (Diagram taken from: http://en.wikipedia.org)
Structure of distribution grids
The structure or "topology" of a grid can vary considerably. The physical layout is often forced by what land is available and its geology. The logical topology can vary depending on the constraints of budget, requirements for system reliability, and the load and generation characteristics. A typical topology of a grid is shown in figure 2 below.
Figure 2: Schematic representation of a radial system (Diagram taken from: http://www.transanatolia.eu)
Figure represent a classic electricity distribution grids-simple radial tree, sending power from a source (point A representing power generation or a substation) to delivery points (other points representing homes, businesses, or other sub networks).
The cheapest and simplest topology for a distribution or transmission grid is a radial structure. This is a tree shape where power from a large supply radiates out into progressively lower voltage lines until the destination homes and businesses are reached. Most transmission grids require the reliability that more complex mesh networks provide. Other topologies used are looped systems and tied ring networks.
National grids are composed of many smaller electrical networks that are linked together into a larger network called a Wide Area Synchronous Grid, also known as an interconnection. A Wide Area Synchronous Grid allows all the independent electrical networks in a particular area to be connected by synchronizing the electrical frequency between them. United Kingdom interconnections are synchronized at 50Hz.| |
Task 2: describe the basic topology of the ring and radial feeder system. Radial Feeder System
In a radial configuration, lines branch out sequentially and power flows strictly in one direction, only one path is connected between each customer and the substations. The electrical power flows from the substation to the customer along a single path. If this path is interrupted, it will result in a complete loss of power to the customer. The loading of a distribution feeder is inherently unbalanced because of the large number of unequal single-phase loads that must be served. An additional imbalance is introduced...