Electricity is generated at power plants and transmitted to different substations from where it will be distributed to individual customers. The interconnected lines, which facilitate this movement, are known as a transmission network. This is distinct from the local wiring between high-voltage substations and customers, which is typically referred to as electric power distribution. Most transmission lines are high-voltage three-phase alternating current and high-voltage direct current technology is usually used for greater efficiency over very long distances. The transmission at high-voltage reduces the energy loss, which occurs in long-distance. The electric power distribution is the final stage in the delivery of electric power; it carries electricity from the transmission system to individual consumers. The distribution substations lower the transmission voltage with the use of transformers. De Lorenzo, also here, has designed a specific trainer where three-phase transformers (for step-up and step-down stages), transmission lines (overhead power lines with different length), busbars and power circuit breakers are used to achieve a system that allows the end user to evaluate and to carry out an almost real trainer but lower power. It is supplied with SCADA (Supervision and Control software Data Acquisition) software that communicate with all the active devices to provide real-time measurements, system status and control. It is dedicated to high schools and first years of university.
Today, the public electric power is supplied almost exclusively using three-phase systems with frequency of 50 or 60 Hz, depending on the country.
The major advantage of AC three-phase over DC power systems is that the electrical power is generated economically in large power stations relatively far from the end users, transported at high voltage over long distances with very little power loss and finally made available to the consumers providing them with two different levels of voltage depending on the application needs.
The major components of electric power transmission and distribution systems are:
• Transformers: step up transformers increase the generated voltage to values suitable for high voltage transmission systems, isolation transformers are used to exchange power between networks, and step-down transformers decrease the voltages to medium voltage level and further down to low voltage to be distributed to the consumer.
• Transmission lines: overhead power lines are mainly used to transmit electrical energy from the power stations to the consumers.
However, in densely populated areas the power can only be supplied through cables.
Various voltage levels are used for transmitting power; the levels are determined by the amount of power and the distance; the higher the transmission voltages, the lower the currents as well as the transmission losses.
However, it must also be considered that network investment costs increase with the voltage.
• Busbars, disconnectors and power circuit breakers: they are the main components found in a switching station used for power distribution.
To evaluate the optimum network configuration, complex calculations have to be carried out.
In this laboratory the basic circuits of power engineering, series and parallel connections of operating equipment (lines, transformers) as well as circuits involving the conversion of delta connections to star connections and vice versa, are analysed.