ELECTRICAL ENERGY SYSTEMS HOMEWORK Atakan YERLI MUGLA,MUGLA SITKI KOCMAN UNIVERSITY Abstract Environmentally friendly technologies such as photovoltaics and fuel cells are DC sources. In the current power infrastructure, this necessitates converting the power supplied by these devices into AC for transmission and distribution which adds losses and complexity. The amount of DC loads in our buildings is ever-increasing with computers, monitors, and other electronics entering our workplaces and homes. This forces another conversion of the AC power to DC, adding further losses and complexity.In this study, an equivalent AC and DC distribution system are compared in terms of efficiency. 1. Advantages and Disadvantages of DC power transmission and distribution over the conventional AC power system Advantages of DC Transmission; • There are no Inductance and Surges (High Voltage waves for very short time) in DC transmission. • There is no concept of Skin effect in DC transmission. Therefore, small cross sectional area conductor required. • There are two conductors used in DC transmission while three conductors required in AC transmission. • Due to absence of inductance, there are very low voltage drop in DC transmission lines comparing with AC (if both Load and sending end voltage is same) • There is no concept of Skin effect in DC transmission. Therefore, small cross sectional area conductor required. Preprint submitted to Homework September 28, 2019 • In DC System, There is no interference with communication system and Corona losses are very low. • A DC System has a less potential stress over AC system for same Voltage level. Therefore, a DC line requires less insulation. • In High Voltage DC Transmission lines, there are no Dielectric losses. • DC system is more efficient than AC, therefore, the rate of price of Towers, Poles, Insulators, and conductor are low so the system is economical. • There is low insulation required in DC system (about 70 percent ). • In DC Supply System, the Sheath losses in underground cables are low. • DC system is suitable for High Power Transmission based on High Current transmission and the value of charging current is quite low, there fore, the length DC Transmission lines is greater than AC lines Disadvantages of DC Transmission: • Due to commutation problem, Electric power cant be produce at High (DC) Voltage and we can not step the level of DC Voltage (As Transformer can not work on DC) • Motor generator set is used for step down the level of DC voltage and the efficiency of Motor-generator set is low than transformer.so the system makes complex and costly.The level of DC Voltage can not be change easily. • There is a limit of DC Switches and Circuit breakers (and costly too) 2. COMPARISON OF OVERHEAD AND UNDERGROUND SYSTEM FOR DISTRIBUTION (AC) There is a debate because of both designs have advantages; • The major advantage of overhead circuits is cost.An underground circuit typically costs anywhere from 1 to 7 times the equivalent overhead circuit. The size of conductor for same amount of power is small on overhead system and shorter outage durations because of faster fault 3 finding and faster repair .Also long life durations are some of important advantages of overhead distribution lines.We can include ”Heat dissipation and insulation because of open atmosphere and hence air providing the necessary insulation” to the benefits of overhead distribution lines • Also Underground Distribution system has benefits too on its corner and they are; Public safety,no interference with the communication lines,not liable to the hazards from lightning discharges,significantly fewer short and long-duration interruptions,less voltage drop because reactance is lower but most important advantages of underground system we can use this it near to the submarine crossings and aesthetics is the main driver towards underground circuits. 3. USE OF DC FOR DISTRIBUTION SYSTEM Dc systems have inherent advantages over ac system like high overall efficiency, easier integration with renewable energy sources and energy storage systems. Moreover there is no reactive power and frequency stabilization issues so that results are reducing copper losses. Many loads like lighting systems, consumer electronics, and appliances using variable speed motor drives can be easily powered by dc distribution systems. Conventional dc distribution systems for telecom and data centers operate at 48 Vdc. it has been reported that Telecom New Zealand deployed a 220 Vdc system to replace the existing 48 Vdc system for increased power capacity. The new system has reportedly reduced the installation costs and copper costs. The proposed system uses 30-40 percent smaller batteries and maximizes available floor space 4 Table shows what type of different voltage levels are needed to power several types of applications. The voltage usage of these different appliances is shown because this offers an insight in what kind of appliances DC distribution can be used for. This also means that voltage standardizations should be adapted to be suitable for these applications to be able to utilize the DC distribution system. Dc distribution topologies are lvdc distribution systems ,mvdc distribution systems ,LVDC within households/buildings,LVDC distribution system/Test pilot and Due to increased requirements for reliability in Finland a test pilot for a unipolar point-to-point LVDC system was implemented by ABB and distribution system operator Elenia Oy in 2014. This was implemented to get further experience within the DC distribution systems field.Where therectifier converts the voltage from 400V AC to 570V DC, which is then boosted to 750V DC, to reduce the current. As an conclusion Dc distribution has advantages like improved efficiency and reduced costs compared to ac distribution. Major applications of dc distribution systems are in the field of telecommunications, data centers, dc buildings, and microgrids. For nowadays converting prices is high and 5 not recommended another one major challenge is selecting a suitable voltage level. Studies till date propose that a 380 Vdc system has both higher reliability and efficiency. Another critical challenge is the advancement in safety and protection technology for dc systems. Therefore, a suitable industry standard is needed to be developed to make such systems . 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