联合循环—05（GIS系统的主要电气设备）

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一、隔离开关 Insulation switchgear

母线上每回进出线都装有断路器和隔离开关
（1）由于隔离开关的作用之一是在设备检修时隔离电压，所以，当馈线的用户侧没有电源，且线路较短时，可不设线路隔离开关；
（2）如果线路较长，为防止雷电产生的过电压或用户侧加接临时电源，危及设备及检修人员安全时，也可装设；
（3）当电源是发电机时，发电机与其出口断路器之间不设隔离开关（断路器检修必然是在停机状态下）；
（4）双绕组变压器与其两侧的断路器之间不需要设隔离开关（也需停机)[1]

[1] 发电厂电气部分—姚春球，Chapter4，P161.

二、断路器 Breaker

断路器有灭弧装置，隔离开关没有，所以停电操作必须遵守操作顺序，即隔离开关必须在断路器断开的情况下或等电位情况下（有旁路连接隔离开关的两个触头）才能进行操作。

WL1线路检修后恢复送电操作：
先拉开QS14，检查QF1在断开状态，合上QS11(母线侧)、QS13，最后合上QF1；
WL1停电操作
先断断路器，检查断开状态，断开远离母线侧，靠近母线侧隔离开关。[1]
[1] 发电厂电气部分—姚春球，Chapter4，P161.

三、阻波器 Line trap

A line trap, also known as wave trap波的捕捉器, or high-frequency stopper高频阻波仪, is a maintenance-free parallel resonant circuit, mounted inline on high-voltage (HV) AC transmission power lines to prevent the transmission of high frequency (40 kHz to 1000 kHz) carrier signals of power line communication to unwanted destinations. Line traps are cylinder-like structures connected in series with HV transmission lines. A line trap is also called a wave trap.

The line trap acts as a barrier or filter to prevent signal losses. The inductive reactance of the line trap presents a high reactance to high-frequency signals but a low reactance to mains frequency. This prevents carrier signals from being dissipated in the substation or in a tap line or branch of the main transmission path and grounds in the case of anything happening outside of the carrier transmission path. The line trap is also used to attenuate the shunting effects of high-voltage lines.

The trap consists of three major components: the main coil, the tuning device, and the protective device (also known as a surge arrester). The protective and tuning devices are mounted inside the main coil. A line trap may be covered with a bird barrier, in which case there are four components.

The main coil is the outer part of the line trap which is made from stranded aluminum cable. The reactor coil, depending on the device, can be made up of several aluminum wires, allowing equal distribution amongst the parallel wires. The stranded aluminum coil is wound in one layer. However, when the application of more than one layer is necessary, separation between layers is required to provide a cooling duct between them to avoid overheating. The cooling duct is created with spacer bars made out of epoxy resin and fiberglass. The coil carries rated continuous power frequency currents, therefore this is the power inductor in this system. It provides a low impedance path for the electricity flow.[3] Since the power flow is rather large at times, the coil used in a line trap must be large in terms of physical size. Hence, a line trap unit is inserted between the busbar and connection of coupling capacitor to the line. It is a parallel tuned circuit containing inductance and capacitance. It has low impedance for power frequency and high impedance to carrier frequency. This unit prevents the high frequency carrier signal from entering the neighboring line.[4]

The next major component is the tuning device. This device is securely installed inside the main coil. It adjusts blocking frequency or bandwidth, and consists of coils, capacitors, and resistors. This smaller coil is attached to both ends of the main coil. Its purpose is to create a blocking circuit which provides high impedance. There are three types of tuning devices: wideband tuning, single frequency tuning, and double frequency tuning. The tuned circuit is usually a dual-circuit broadband type. If the traps are self tuned, they do not require the use of any tuning devices. With the use of a tuning device, a line trap can be tuned to a frequency of 1000 Hz.[4]

The last main component is the protective device, which is parallel with the main coil and the tuning device. It protects the main coil and the tuning device by lowering the over-voltage levels. The bandwidth of a line trap is the frequency range over which the line trap can provide a certain specified minimum blocking impedance or resistance.

Line traps are connected in series with power line and thus their coils are rated to carry the full line current. The impedance of a line trap is very low at the power frequency and will not cause any significant voltage drop.

Power line carrier communication (PLCC) technology has been frequently used since 1950 by the grid stations to transmit information at high speed. Transmitting information along high-voltage lines, at high frequency, has been one of the main means of communication in electric power for over fifty years. The data collected from different sensors is transmitted on power lines thereby reducing the maintenance cost of the additional wiring. In some countries, this technology is also used to provide Internet connection. In order to communicate, high-frequency line traps are used as they allow substations to communicate with each other through the power lines at the same time as they transmit electrical power. In order to separate power from messages being sent, different frequencies are used. Electrical power has a frequency of 50 Hz or 60 Hz in most places, and the communication waves use frequencies such as 150 kHz and 200 kHz. Line traps consist of filter circuits that allow only power frequency waves to travel to that of electrical equipment. They also stop communication waves from traveling to equipment.

Communication is crucial for substations.

[2] WIKIPEDIA——Line trap

见联合循环—03（高压电引出方式，主要设备）（1）

四、限流电抗器 Currant limiting reactor

In electrical engineering, current limiting reactors can reduce short-circuit currents, which result from plant expansions and power source additions, to levels that can be adequately handled by existing distribution equipment.[1] They can also be used in high voltage electric power transmission grids for a similar purpose. In the control of electric motors, current limiting reactors can be used to restrict starting current or as part of a speed control system.

A current limiting reactor is used when the prospective short-circuit current in a distribution or transmission system is calculated to exceed the interrupting rating of the associated switchgear. The inductive reactance is chosen to be low enough for an acceptable voltage drop during normal operation, but high enough to restrict a short circuit to the rating of the switchgear. The amount of protection that a current limiting reactor offers depends upon the percentage increase in impedance that it provides for the system.[4]

Current limiting reactor
The main motive of using current limiting reactors is to reduce short-circuit currents so that circuit breakers with lower short circuit breaking capacity can be used. They can also be used to protect other system components from high current levels and to limit the inrush current when starting a large motor

A line reactor is an inductor wired between a power source and a load. In addition to the current limiting function, the device serves to filter out spikes of current [7] and may also reduce injection of harmonic currents into the power supply. The most common type is designed for three-phase electric power, in which three isolated inductors are each wired in series with one of the three line phases.[8] Line reactors are generally installed in motor driven equipment to limit starting current, and may be used to protect Variable-frequency drives and motors

五、接地开关

普通的接地开关配置在断路器两侧隔离开关旁边，属于隔离开关的一种，能在一定时间内承载非正常条件下的电流（如短路电流），不要求它能承载正常条件下的电流，检修时手动操作合上，恢复时手动操作拉开，仅起到断路器检修时两侧接地的作用。

六、快速接地开关

快速接地开关是具有一定关合短路电流能力的一种特殊用途的电动操作接地开关。快速接地开关配置在出线回路的出线隔离开关靠线路一侧，当线路接地故障被切除后，由相邻运行线路供电形成故障线路的潜供电流，利用快速接地开关关合，可消除潜供电流，再快速开断接地开关，确保线路自动重合闸能成功。
例如线路发生单相故障时，故障线路两侧开关断开，但是由于正常相与故障相之间存在电磁耦合，由正常相向故障相提供潜供电流，不利用故障点去游离，熄弧时间会拉长，甚至不熄弧，为了减少潜供电流，在两侧开关断开时，自动装置动作立即合上两侧的快速接地开关，根据一个整定的熄弧时间，再断开快速接地开关，然后再单相重合闸，可以提高重合闸的成功率。

七、电流互感器

A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.

Current transformers, along with voltage or potential transformers, are instrument transformers. Instrument transformers scale the large values of voltage or current to small, standardized values that are easy to handle for measuring instruments and protective relays. The instrument transformers isolate measurement or protection circuits from the high voltage of the primary system. A current transformer provides a secondary current that is accurately proportional to the current flowing in its primary. The current transformer presents a negligible load to the primary circuit.[1]

Current transformers are the current-sensing units of the power system and are used at generating stations, electrical substations, and in industrial and commercial electric power distribution.

八、电压互感器

Voltage transformers (VT), also called potential transformers (PT), are a parallel-connected type of instrument transformer. They are designed to present a negligible load to the supply being measured and have an accurate voltage ratio and phase relationship to enable accurate secondary connected metering.

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