电力专业英语阅读-作业六

1、作业六:将下列段落翻译成中文Overhead alternating-current transmissionOverhead transmission lines distribute the majority of the electric energy in the power system. A typical high-voltage line has three phase conductors to carry the current and transport the energy, and two grounded shield conductors to protect t

2、he line from direct lightning strikes. The usually bare conductors are insulated from the supporting towers by insulators attached to grounded towers or poles. Lower-voltage lines use post insulators, while the high-voltage lines are built with insulator chains or long-rod composite insulators. The

3、normal distance between the supporting towers is a few hundred feet.Transmission lines use ACSR (aluminum cable, steel reinforced and ACAR (aluminum cable, alloy reinforced conductors. In an ACSR conductor, a stranded steel core carries the mechanical load, and layers of stranded aluminum surroundin

4、g the core carry the current. An ACAR conductor is a stranded cable made of an aluminum alloy with low resistance and high mechanical strength. ACSR conductors are usually used for high-voltage lines, and ACAR conductors for subtransmission and distribution lines. Ultrahigh-voltage (UHV and extrahig

5、h-voltage (EHV lines use bundle conductors. Each phase of the line is built with two, three, or four conductors connected in parallel and separated by about 1.5 ft (0.5 m. Bundle conductors reduce corona discharge.The power that a line can transport is limited by the line's electrical parameters

6、. Voltage drop is the most important factor for distribution lines; where the line is supplied from only one end, the permitted voltage drop is about 5%.Conductor temperature must be lower than the temperature which causes permanent elongation. A typical maximum steady-state value for ACSR is 212

7、76;F (100°C, but in an emergency temperatures 1020% higher are allowed for a short period of time (10 min to 1 h.Corona discharge is generated when the electric field at the surface of the conductor becomes larger than the breakdown strength of the air. The oscillatory nature of the discharge g

8、enerates high-frequency, short-duration current pulses, the source of corona-generated radio and television interference. Surface irregularities such as water droplets cause local field concentration, enhancing corona generation. Thus, during bad weather, corona discharge is more intense and losses

9、are much greater. Corona discharge also generates audible noise with two components: a broad-band, high-frequency component, which produces crackling and hissing, and a 120-Hz pure tone. Transmission-line conductors are surrounded by an electric field which decreases as distance from the line increa

10、ses, and depends on line voltage and geometry. At ground level, this field induces current and voltage in grounded bodies, causes corona in grounded objects, and can induce fuel ignition. Utilities limit the electric field at the perimeter of right-of-ways to about 1000 V/m. An ac magnetic field aro

11、und the transmission line also decreases with distance from the line.开销交流电传输架空输电线分布大部分电能在电力系统中。一个典型的高压线路具有三相导体携带的电流和输送的能量,以及两个接地屏蔽导体,以保护免受直接雷击的行。在通常的裸导体从支撑塔由连接于接地的塔或极绝缘体绝缘。低电压线用支柱绝缘子,而高电压线都建有绝缘体链或长棒复合绝缘子。支撑塔之间的正常距离为几百英尺。输电线路用钢芯铝绞线(铝合金电缆,钢筋和ACAR(铝电缆,铝合金加固导体。在一个ACSR导体,绞合钢芯承载机械负载,并滞留铝层包围芯携带的电流。一个ACAR导体

12、是由铝合金制成具有低电阻和高机械强度的绞合缆线。ACSR导体通常用于高电压线,以及用于变速和配电线路ACAR导体。超高压(特高压和extrahigh电压(超高压线使用分裂导线。线的各相是建立与两个,三个或四个导体并联连接并通过大约1.5英尺(0.5M分离。分裂导线减少电晕放电。该线可以传输的功率是由线的电气参数的限制。电压降是配电线路的最重要因素;其中线只从一个端提供,则允许的电压降是约5%。导体温度必须高于导致永久伸长的温度低。对于ACSR的典型最大稳态值是212°F (100,但在紧急情况下的温度更高的10-20%被允许为短时间(10分钟至1小时。当电场在导体的表面变得比空气的击穿强度较大的电晕放电产生的。放电的振荡性质产生高频率,持续时间短的电流脉冲,电晕产生的无线电和电视信号干扰源。表面不规则如水滴引起局部电场集中,提高电晕的产生。因此,在恶