电力变压器的选择和冷却.docx

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1、T外文文献：Selection and Cooling of Power TransformerThe selection of the transformer can have a major impact on the cost a substation, since the transformer represents the major cost item. Nameplate rating is only a guide to transformer application, and should only be used as a first step in the selecti

2、on process. The transformer is available as a self-cooled unit, or it can be purchased with additional steps of forced cooling that use fan or fans and oil pumps. Transformer ratings can be increased from 25% to 66% by the addition of fans and pumps. The nameplate rating is based on a continuous loa

3、d producing a 55 to 65 conductor temperature rise over ambient. Since many transformers do not carry continuous loads, advantage can be gained from the thermal time lag to carry higher peak loads without exceeding the temperature limits .Transformer ratings are based on the assumption that only an e

4、xtremely slow deterioration of insulation will take place with normal operation. A substantial increase in rating can be achieved by accelerating the loss of insulation life. This increase in rating might approach 200% for an hour or two, and approximately 120% for 24 hours. For substations that are

5、 designed to carry full load under the outage of any one transformer, a high emergency rating for a 24-hour period (e.g. until the failed unit can be replaced) could mean the selection of smaller transformers and a substantial saving in substation cost.The selection of the transformer should involve

6、 a careful evaluation of a number of other factors ：(1 )Impedances should be selected considering their effect on short-circuit duties and low-side breaker ratings both for initial and future station developments. In addition, impedance is important to achieve a proper load division in the parallel

7、operation of transformers.(2)No load tap ranges should be selected to provide an adequate low-side bus voltage.(3)If the high-side or low-side voltages vary over a wide range during the load cycle, it may be necessary to provide bus regulation. The actual regulation can be calculated using the syste

8、m and load characteristics. If regulating equipment is needed, it may be desirable to provide it in the transformer by using load tap changer(LTC) equipment. If the need for bus regulation is not presently evident, but may be required in the future, it may be economical to leave space in the station

9、 for future regulators, and buy transformers without LTC equipment.A great many transformers, including all the large ones and all the high voltage ones are immersed in mineral oil which serves the double purpose of cooling and insulating the windings. Small transformers have enough tank surface to

10、radiate al 1 the heat caused by their losses without exceeding the permissible temperature rise. As size increases, the losses increase faster than the tank surface which soon becomes inadequate. Various methods have been developed to get the heat out of the tank more effectively. Large power transf

11、ormer being built today are commonly of the forced-oil-cooled type. In this design the oil is pumped both through the external cooling devices(air or water heat-exchangers)and through internal channels that are located nearest the points where the heat is generated. Thus the transfer of heat to and

12、from the oil is far more effective than in the plain self-cooled or fan-cooled unit where the oil is allowed to circulate by convection. When oil-to-air heat exchanger(a group fans on each radiator)is used, this cooling type is designated as type of FOA. While oil-to-water heat exchanger is used, it

13、 is called FOW.For applications where any liquid, even a nonflammable one, is objectionable, the dry-type transformer is used. The ventilated dry-type unit is cooled by a continuous natural draft of air and consequently is not suitable for locations where the air is wet or dirty. For these locations

14、 a completely enclosed unit, the sealed dry-type, is available, having a core-and-coil in a tank that is sealed and filled with an insulating gas. Dry-type transformers are completely nonflammable, using organic material such as epoxy resin.中文译文：电力变压器的选择和冷却变压器的选择对变电所的建造成本具有重大影响，因为变压器是主要的成 本项目。铭牌定额只是

15、变压器应用的指南,它只应该用作变压器选择过程的第一 步。变压器可以是自冷式单位，也可以购买额外的冷却装置,如强制冷却风机或机 组和柴油泵。根据额外的冷却机组和柴油泵，变压器评级可以从25%增加到66%O 铭牌评级是基于连续负荷产生超过环境55c到65c导体温升而评定的。？ ？ ？ 因为很多变压器不带连续负载,优势可以获得从热滞后时间进行更高的高峰负荷 而不超过温度限制。变压器的评级是基于假设：正常操作下的绝缘老化只是一个 极其缓慢的过程。通过加速绝缘老化的进程可以大幅度的提高评定等级。在一两 个小时左右评级可能增长接近200%,而在在二十四小时左右评级则增长大约 120虬因为变电站的设计要保证

16、在任何一个变压器断电的情况下都要满足全负荷 运行，为24变电站设计将满载在停机的任何一个变压器,因此在二十四小时内的 较高的紧急评级(例如直到失败的单位可以更换)可能意味着选择较小的变压器 和节约大量的变电所成本。变压器的选择应该涉及对其他影响因素的审慎评估：(1)阻抗应该被选择的考虑到他们对短路职责和下部断路器评级的影响对初 始和未来空间站发展。此外，阻抗在并行变压器的操作中获得一个合适的负载也 是十分重要的.无载分接范围应该选择提供一个足够的下部总线电压。(3)如果高压侧或低压侧电压在负载周期内变化很大的话，可能有必要提供总 线监管。通过系统和负载特性实际监管和控制是可以被计算和描绘的。如

17、果调节 设备是必要的，在变压器内使用负载抽头转换开关（LTC）设备来提供监管是可取 的。如果需要总线监管目前是不需要的,但可能在未来需要的，那么在变电站预留 未来安装设备的空间并且购买没有LTC设备的变压器是十分经济的。许多变压器,包括所有的大体积的和所有的高电压的变压器都是沉浸在矿物 油,矿物油有双重目的：冷却和绝缘绕组。小变压器有足够的容器表面辐射all 热引起的损失而不超过容许温度上升范围。随着体积的增加,损失增加的速度会 加快，这时容器表面会变得不适宜。很多的方法已经被改进以使的容器的散热更 有效。今天一般建造的大型电力变压器都是强制循环油冷却类型的。在这个设计 中矿物油通过油泵不仅流

18、进外部冷却设备（空气或水热交换器），而且流过内部最 靠近热源的凹槽。因此通过矿物油对热量进行转移的方式要比一般的自冷装置和 风冷装置要有效的多，因为油是允许通过对流循环的。当油空气热交换器（在每个 散热器有一组风机）被使用时，这种冷却类型被指定为FOA。当油水热交换器被使 用时,则被称为FOW。因为无论变压器是采用何种液体都是不受欢迎的，即使这种液体不易燃，所 以干式变压器得到普遍的应用。通风式的干式变压器通常是通过自然风来使变压 器冷却的，所以这种变压器不适于潮湿和恶劣的环境。如果铁芯和线圈是在一个 充满绝缘气体的封闭装置中则干式变压器在潮湿恶劣环境中是完全可以正常运 行的的。干式变压器是完全不燃烧的，因为它使用了有机材料如环氧树脂。