英文资料及其翻译
Transformer
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.These coils are (usually)not directly connected. The only
connection between the coils is the common magnectic flux presen within the core.
One of the transformer windings is connected to a source of ac electric power,and
the second(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 secondary
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 of cores.one 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 case,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 secondary windings in a physical transformer are wrapped one
on top of the other with the low-voltage winding innermost.Such an arrangement
severs two purposes: 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 separated by a distance on the core.
Power transformer are given a variety of different names, depending on their use
in power systems.A transformer connected to the output of a generator and used 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 used is called a distribution transformer.All these devices
are essentially the same-the only difference among them is their intended use.
In addition to the various power transformer, two special-purpose transformers are
used with electric machinery and power systems.The first of these special transformers
is a device specially designed to sample a high voltage and produce a low secondary
voltage directly proportional to it.Such a transformer is called a potential transformer.A
power transformer also produces a secondary 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 second type of special transformer is a device designed to provide a
secondary current.much smaller than but directly proportional to its primary
current.This device is called a current transformer.
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 use 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-oilcircuit
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 have 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
ter,main contacts were fitted with arcing contacts of special material and
shape,which opend after and closed 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
