电力专业英语4--继电保护2

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2013-5-1
Grounding System
• Formerly, many power systems were ungrounded systems using delta-delta transformers. Ungrounded systems suffer form several problems, including transient overvoltages that necessitate the use of two surge arresters for a single-phase transformer (one on each side of the winding), and trouble with rapid, automatic clearing of the very common phase to ground short circuit. • 以前，许多电力系统采用角型接线变压器，为不接地系统。 不接地系统会带来很多严重的问题，包括暂态过电压，因 此，即使是单相变压器，也需要分别在原边和副边绕组各 安装一个避雷器。而且对于非常常见的相接地故障的快速 自动切除非常困难。
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• If the neutral is grounded, the bank tries to ground the feeder, and when ground faults occur on the primary side, the distribution banks will supply ground current. This usually causes a large number of blown fuses on wye-delta distribution transformers with grounded neutrals. • 如果中性点接地，….，当在原边侧发生接地故障 时，配电变压器组中有接地电流流过。这会导致 星型中性点接地接线的配电变压器的保险熔断。
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• Floating the bank neutral alleviates the problem, but may cause overvoltage problems such as ferroresonance. Wye-wye banks avoid the ferroresonance problem since they invariably have grounded neutrals on both sides. • 变压器中性点浮地能减轻这一问题，但可能造成 过电压问题，例如铁磁共振。星星连接变压器组 不会产生铁磁共振问题，因为在原边和副边中性 点均接地。
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• Instrument transformers 仪用（或测量用）互感器
• Instrument transformers are the input transducer for protective relays, but also metering (both fro revenue metering and for data acquisition). The two main types of instrument transformers are current transformers (CTs) and potential transformers (PT’s). The latter are also called voltage transformers (VT’s), with no difference intended. • 测量用互感器指的是保护继电器的输入传感器，也指计量 仪表（例如电费计量和数据采集）的输入传感器。两种主 要的测量用互感器为电流互感器（CT）和电压互感器 （PT）,后者也简称VT。
电力专业英语4 -- 继电保护2
电气工程学院
继电保护2
• • • • • • • • • Distance Relay 距离保护 Undervoltage Relay 低电压保护 Overvoltage Relay过电压保护 Blocking Relay闭锁继电器 Phase Angle or Out of Step Relay失步保护 Frequency Relay频率继电器 Directional Power Relay方向功率继电器 Instantaneous Overcurrent Relay瞬时过流保护 Differential Relay差动保护
2013-5-1
11Βιβλιοθήκη • The CT acts to step the current down, say from 1000A on the primary to 5A on the secondary. This would give a CT ratio of 1000:5A or 200:1A, and would require 200 turns on the secondary (assuming one primary “turn”). • CT的作用是降低电流，例如将原边1000A的电流 降至副边的5A。则CT的变比为1000:5A 或200:1A， 副边绕组的匝数为200（假设原边绕组匝数为1）
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• Generator step-up transformers and step-down transformers serving four-wire distribution system are usually connected delta on the primary and wye on the secondary. Remember primary means input and second means output, so a step-up transformer primary is the low-voltage side but a step-down transformer primary is the high-voltage side. • 发电机 升压变压器和向四线配电系统供电的降压变压器通 常在原边侧为三角型连接，在副边侧位星型链接。需要注 意的是原边指输入，副边指输出，因此升压变压器的原边 为低压侧，但降压变压器的原边为高压侧。
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• Current transformers for relaying purposes are given accuracy class ratings, such as C400 or T400 (sometimes written as 10C400 or 10T400). The letter C indicates that its performance may be calculated from its magnetization curve. The letter T indicates that its performance must be determined by test. • 保护用电流互感器均给出其（测量）精度等级， 例如C400或T400（有些标为10C400或10T400）。 字母C表示其特性通过其磁化曲线计算出来。字 母T 表示其特性由实验决定。
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• The number following the letter C or T is the voltage rating: the secondary voltage produced by 20 times rated secondary current (maintaining a ratio error less than or equal to 10%). The 10% ratio error will not be exceeded for any current from 1 to 20 times rated current at lesser burdens. • 字母C或T之后的数字指出电压等级：所产生的副 边电压是额定副边电流的20倍（以维持变比误差 等级小于等于10%）。只要副边电流小于20倍的 额定电流，变比误差就不会超过10%。
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• An ungrounded system is connected to ground only by stray capacitances, so a single phase to ground short circuit draws very little fault current. • 不接地系统通过隔离电容接地，因此单相接地故障会产生 非常小的故障电流 • To allow rapid detection and automatic clearing of ground faults, and to reduce insulation and arrester costs, grounded systems have become more common than ungrounded ones. • 为了快速检测和清除接地故障，并且降低投资在隔离设备 和避雷器上的费用，接地系统的应用越来越广泛。
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• In many cases, the power transformers in a grounded system are connected delta wye, with the wye neutral grounded to the substation ground mat. • 很多情况下，接地系统中的电力变压器的连接方 式为三角星型接线，星型接线的中性点和变电站 的接地网相连。 • Generators and step-down transformers serving only three-phase loads are often grounded through a resistance to limit the ground fault current to low values. • 发电机和只带三相负荷的降压变压器一般通过电 阻接地，以降低接地故障电流的大小。 2013-5-1