考试在即，急求高手帮忙翻译
文章出自中国电力出版社 电气工程及其自动化专业英语网上找了很久实在找不到翻译 所以想请高手帮忙。谢谢~ 刚打出来得。。如果有错误 还请原谅~
Differential Proteetion
The general idea involved in the differential
protection scheme is to compare the operating quantity
(voltage or current) at the input and output ends,i.e.
terminal of the equipment being protected .This is a
vector comparison since the quantity being compared has
the magnitude and the phase angle associated with it.
Tripping is initiated if the magnitude of the difference
exceeds a pre-determined constant value(i.e. base
value).
For a transformer, the differential protection scheme
is shown in Fig.7-5.The CTs have been connected at the
two sites (i.e. primary and secondary side.)By properly
choosing the turn ratios of CTs and reversing its
connections to that of the main transformer being
protected,CTs secondary currents are made nearly the
same during normal load conditions or external faults.
However, during internal fault in the transformer, the
current I1 on the primary side of the transformer will
differ from the current I2 on the secondary in magnitude
and/or in phase.The trip signal is given if the vector
difference of these currents flowing in the operating
coil exceeded in the base value. Hence for tripping
/I1-I2/ >=K
where K is a constant (i.e. base value) .-%-80505-%--%-80493-%- NO.2
When two or more synchronous machines are interconnected, the stator voltages and currents of all the machines must have the same frequency and the rotor mechanical speed of each is synchronized to this frequency. Therefore, the rotors of all interconnected machines must be in synchronism. In a generator, the electromagnetic torque opposes rotation of the rotor, so that mechanical torque must be applied by the prime mover to sustain rotation. The electrical torque (or power) output of the generator is changed only by changing the mechanical torque input by the prime mover. The effect of increasing the mechanical torque input is to advance the rotor to a new position relative to the revolving magnetic field of the stator. Conversely, a reduction of mechanical torque or power input will retard the rotor position. In a synchronous motor, the roles of electrical and mechanical torques are reversed compared to those in a generator. 第三部分
progressive drop in bus voltages can also be associated with rotor angles going out step. For example ,the gradual loss of synchronism of machines as rotor angles between tow groups of machines approach or exceed 180' would result in very low voltage at intermediate points in the network . in contrast , the type of sustained fall of voltage that is related to voltage instability occurs where rotor angle stability is not an issue
voltage instability is essentially a local phenomenon of beats; however ,its consequence may have a widespread impact . voltage collapse is more completely than simple voltage leading to a low-voltage profile in a significant part of the power system . voltage instability may occur in different ways . for purpose of analysis, voltage stability is usually classified into the following tow subclasses :
large-disturbance voltage stability is concerned with a system's ability to control voltage
following large disturbance such as system fault,loss of generation,or circuit contingencies .this ability is determined by the system load characteristics and the interactions of both continuous and discrete controls and protections . a criterion for large- disturbance voltage stability is that , following a given disturbance and following system-control actions ,voltages at all buses reach acceptable steady state levels
2
small disturbance voltage stability is concerned with a system's ability to control voltage following small perturbation such as incremental changes in system load . this from of stability is determined by the characteristics of load, continuous controls and discrete controls at a given instant of time . a criterion for small disturbance voltage magnitude increase as the reactive power injection at the same bus is incressed . a system is voltage unstable if , for at least one bus in the system the bus voltage magnitude decrease as the reactive power injection at the same bus is increased.
Voltage instability does not always occur in its pureform .Often the angle and voltage instabilities go hand in hand .One may lead to the other and the distinction may not be clear.However, a distinction beween angle stability and voltage stability is important for understanding of the underlying causes of the problems in order to develop appropriate design and operating procedures. 大家帮个忙。。谢了~~~ 呵呵，这个忙很难帮啊 好多啊。。。有心无力了。
不过还是建议楼主提供原稿，因为别人在翻译的时候，有时候你输入的文字中有一点小错误，都会使整个意思发生变化，翻译的时候就会更加头疼了。
页:
[1]
