Electrical power can be produced in many ways, including chemical reactions, heat, light, or mechanical energy. Most electrical power produced today is through hydroelectric plants and nuclear energy, and by burning coal, oil, or natural gas. Fossil fuel and nuclear-fission plants use steam turbines to deliver the mechanical energy required
Year: 2014
In addition to the basic components of a synchronous generator (the rotor, stator, and their windings), auxiliary devices are used to help maintain the machine’s operation within acceptable limits. These devices include the following: GOVERNOR The function of the governor is to control the mechanical power input to the generator.
The process of interrupting the current in an ac system is aided by the fact that ac current goes through zero every half-cycle, or approximately every 8 ms in a 60 Hz system. The absence of a natural current zero in dc makes it difficult to develop a dc circuit
In cases where HVDC is selected on technical considerations, it may be the only practical option, as in the case of an asynchronous interconnection. However, for long-distance power transmission, where both ac and HVDC are practical, the final decision is dependent on the total costs of each alternative. The total
High-voltage dc (HVDC) transmission offers several advantages over alternating current for long-distance power transmission and asynchronous interconnection between two ac systems, including the ability to precisely control the power flow without inadvertent loop flows that can occur in an interconnected ac system. HVDC transmission can be classified into one of
Distribution systems are designed to maintain service voltages within specified limits during normal and emergency conditions. Typical voltage limits are: • For service to residential customers, the voltage at the point of delivery shall not exceed 5% above or below the nominal voltage. This is equivalent to the band between
The circuit breaker scheme used at a substation provides for varying degrees of reliability and maintainability on both the input and output sides. Each additional circuit breaker provides greater reliability and flexibility in maintaining the bus energized during a fault or during maintenance. However, the cost also increases with each
Specialized hardware is necessary to interconnect the elements of a power-distribution system. Utility control and switching systems operate under demanding conditions, including high voltage and current levels, exposure to lightning discharges, and 24-hour-a-day use. For reliable performance, large margins of safety must be built into each element of the system.
The effective resistance offered by a conductor to high frequencies is considerably greater than the ohmic resistance measured with direct currents (dc). This is because of an action known as the skin effect, which causes the currents to be concentrated in certain parts of the conductor and leaves the remainder
The connection of several generating stations in parallel is known as interconnected grid system. The various problems facing the power engineers are considerably reduced by interconnecting different power stations in parallel. Although interconnection of station involves extra cost, yet considering the benefits derived from such an arrangement, it is gaining
