功率因数英文文献翻译课件.docVIP

电气专业本科毕业设计英文翻译 学院(部)：电气与信息工程学院 专业班级： 电气09-6班 学生姓名： 李 鼎 指导教师： 李红月副教授 年 月 日 POWER FACTOR The power factor of an AC electric power system is defined as the ratio of the real power flowing to the load to the apparent power in the circuit, and is a dimensionless number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 pf = 50% pf). Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power will be greater than the real power. In an electric power system, a load with a low power factor draws more current than a load with a high power factor for the same amount of useful power transferred. The higher currents increase the energy lost in the distribution system, and require larger wires and other equipment. Because of the costs of larger equipment and wasted energy, electrical utilities will usually charge a higher cost to industrial or commercial customers where there is a low power factor. Linear loads with low power factor (such as induction motors) can be corrected with a passive network of capacitors or inductors. Non-linear loads, such as rectifiers, distort the current drawn from the system. In such cases, active or passive power factor correction may be used to counteract the distortion and raise the power factor. The devices for correction of the power factor may be at a central substation, spread out over a distribution system, or built into power-consuming equipment. Power factor in linear circuits . Instantaneous and average power calculated from AC voltage and current with a unity power factor (φ=0, cosφ=1). Since the blue line is above the axis, all power is real power consumed by the load. Instantaneous and average power calculated from AC voltag