Intro powsys

• The electric power system consists of three principal divisions:
• Generating stations - convert energy available in different forms in nature into electrical energy
• Transmission systems - connecting links between generating stations and distribution systems
• Distribution systems - connect all the individual loads to the transmission lines at substations
• Thermal (coal, natural gas, oil)
• Hydro
• Nuclear
• Generating stations can be classified into four categories based on the type of primary source of energy employed:
• Non-conventional (wind, solar, geothermal, etc.)
• The sub-transmission system connects high-voltage substations through step-down transformers to distribution substations
• A distribution subsystem constitutes the part of the electric power system between the step-down distribution substation and the consumers' service switches
• Loads on a power system can be categorized as:
• Industrial
• Commercial
• Domestic
• Exchange of peak loads
• Advantages of interconnected grid systems:
• Use of older plants
• Increases diversity factor
• Economical operation
• Increases reliability of supply
• Reduces plant reserve capacity
• The first electric supply system was introduced by Thomas Edison in 1882 at the Pearl Street Station in New York, USA
• Electrical transmission and distribution is broadly categorized as:
• Overhead or underground
• AC or DC system
• Advantages of AC Transmission/Distribution:
• Power can be generated at higher voltages
• Maintenance of AC substation is easy and cheaper
• AC voltage can be stepped up/down by transformers with ease and efficiency
• Disadvantages of AC Transmission/Distribution:
• AC requires more copper than DC lines
• AC transmission line is more complicated than DC transmission line
• Skin effect in AC system increases the effective resistance of the line
• Continuous loss of power due to charging current in AC lines
• Technological developments in conjunction with AC transmission:
• High-speed relay system capable of detecting short-circuit currents within one cycle
• Suspension insulator
• High-speed, extra-high-voltage (EHV) circuit breakers capable of interrupting up to 63-kA three-phase short-circuit currents within two cycles
• High-speed reclosure of EHV lines for automatic return to service after a fault