英文文献
Cirtcuit Breakers
A circuit breaker is mechanical switching device capable of making,and breaking currents under normal circuit conditions and also making.carring for a specified time ,and mediujm in which circuit interruption is performed may be designated by a suitable prefix, for example,air-blastcircuit breaker,oil circuit breaker.The circuit breakers currently in u can be dlassified into the following categories according to the arc-quenching principles:air swetches oel ciryit breakers,minmum-oil circuit breakers,air-blast circuit breakers,the magenetic air circuit breakers,minimum-oil circuit breakers,aer-blast circuit breakers,the by voltage,insulation levelcurrent,interrupting capabilities,transient recovery coltage,interrupting tiome,and trip delay.The nameplate on a circuit breaker usually indicates:１.The maximum steady-state current it can carry, 2. The maximum interrupting current,3. The maximum line voltage,4.The interrupting time in cycles, The interrupting time in may last form 3 to 8 cycles on a 60 Hz system. To interrubt large currents quickly, we hav
e to ensure rapid cooling. High-speed interruption lunits the damage transmission lines and equipment and, equally important,it helps to mainmain the stability of the system whenever a contingency occurs. The main parts of a circuit breaker are usually:arc-quenching chamber (or interrupter with moving and fixed contacts) operating mechanism and supporting structures.
Air Switches-With increasing currents and voltages, spring-action driving mechanisms were developed to reduce contact buring by faster-opening operation.Later,main contacts were fitted with arcing contacts of special material and shape,which opend after and clod before the main contacts.Further improvements of the air switch were the bursh-type contact with a wiping and cleaning function,the insulating barrier leading to arc chutes,and blowout coils with excellent arc-extinguishing properties.The features,as well as the horn gap contact,are still in u in low voltage as and de breakers.
Oil Circuit Breaker Around 1900, in order to cope with the new requirement for “interrupting capacity”,AC switches were immerd in a tank of oil. Is very effective in que
nching the arc and establishing the open break after current zero.Deion grids,oil-blast features,pressure-tight joints and vents,new operating mechanisims,and multiple interrupter were introucedover veral decades to make the oil circuit breaker a reliable apparatus for system voltage up to 362Kv.二胎孕前准备
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香港经典Types and Construction of Transformer
A transformer is a device that alternating current electric energy at one voltage level into alternating current electric energy at another voltage level through the action of a magnetic field.It consists of two or more coils wire wrapped around a common ferromagnetic core.The coils are (usually)not directly connected. The only connection between the coils is the common magnectic flux pren within the core.
One of the transformer windings is connected to a source of ac electric power,and the cond(and perhaps third) transformer winding supplies electric power to loads. the transformer winding connected to the power souce is called the primary winding or input winding.and the winding connected to the loads is called the condary winding or input
winding.If there is a third winding on the transformer,it is called the tertiary winding.
Power transformer are constructed on one of two types type of construction consists of a simple rectangular laminated piece of steel with the transformer windings wrapped around two sides of the rectangle.This type of construction is know as coreform .The other type consists of three-legged laminated core with the windings wrapped around the center leg .This type of construction is know as shell form.In either ca,the core is constructed of thin laminations electrically isolated form each other in order in order to reduce eddy currents to a minimum.
The primary and condary windings in a physical transformer are wrapped one on top of the other with the low-voltage winding innermost.Such an arrangement vers two purpos: 1.It simplifies the problem of insulating the high- voltage winding from the core.2.It results in much less leakage flux than would be the two windings were parated by a distance on the core.
包转发率 Power transformer are given a variety of different names, depending on their u in pow
樱花纹er systems.A transformer connected to the output of a generator and ud to step its voltage up to transformer levels is sometimes called unit transformer. The transformer ai the other end of the transformer line,which steps the voltage down from transmission levels to distribution levels,is called a substation transformer.Finally,the transformer that takes the distribution voltage and steps is down to the final voltage ai which the power is actually ud is called a distribution transformer.All the devices are esntially the same-the only difference among them is their intended u.
In addition to the various power transformer, two special-purpo transformers are ud with electric machinery and power systems.The first of the special transformers is a device specially designed to sample a high voltage and produce a low condary voltage directly proportional to it.Such a transformer is called a potential transformer.A power transformer also produces a condary voltage directly proportional to its primary voltage;the difference between a potential transformer and a power transformer is that the potential transformer is designed to handle only a very small current.The cond type of special transformer is a device designed to provide a condary current.much smaller t民族文化传承>08年属啥
han but directly proportional to its primary current.This device is called a current transformer.清除垃圾文件
