外文翻译冲压模具.doc

AN IMPROVED INSULARION SYSTEM FOR THE NEWEST GENERATION OF STATOR WINDINGS OF ROTATING MACHINESSummary:In recent years there has been a distinct trend to utilize machines with indirectly cooled stator windings also for the higher ratings, up to about 300 MVA with air cooling and about 450 MVA with hydrogen cooling. This imposed new demands on the well-known dielectric requirements, as this is a key item when laying out the machine.This report describes the modified structure of an improved synthetic resin insulation Matador-Plus. The most significant change was the introduction of powdered metaloxyde to the insulation structure used hitherto, which it enable the thermals conductivity to be doubled. The resulting characteristically changes are described relative to both short and long term behaviors of the insulation system.Based on the improved insulating qualities it was possible to reoptimize machine designs, which is fundamentally demonstrated.Key words:Turbo-generator, stator winding, insulation system, indirect conductor cooling, thermal conductivity.1:Introduction Over the last decades the development of turbo-generators with indirect conductor cooling in the stator winding has led to ever increasing ratings. Today, machines are being built with this technology for ratings which ,just a few years ago, were only possible with direct water or hydrogen cooling of the stator winding conductors.Aircooled machines with ratings of up to 130 MVA were already in service by 1970.With the development of gas turbines with larger unit ratings there is a trend today for air-cooled turbo-generators with ratings of 300 MVA. Hydrogen cooling in turbo generators permitted much higher unit ratings. By the of the 50s, machines with indirect conductor cooling had been realized up to 250 MVA and today the limit is above 350 MVA.Compared with direct conductor cooling used on larger generators , indirect cooling of the stator ending has the advantages that, bar production is simple and less expensive, the space needed for coolant flow with direct cooling is available for instance with water cooling.On the other hand, indirect cooling requires that the heat losses generated in the conductors ate dissipated via the insulation wrapping on the stator winding bars which is a poor thermal conductor. Depending on the case under consideration, the temperature drop involved represent 2040% of the total temperature rise.Besides the need to optimize the cooling technique on machines with indirect conductor cooling, there was also the continuous requirement to improve the insulation system which helped to make this course in development possible. The change in the 60s from thermoplastic mica-folium insulation system which helped to make thermoplastic mica-folium insulations to epoxy resin basesd synthetic resin insulation led to considerable improvement in the physical and particularly in the dielectric properties of the insulation material. A further step in the 70s saw the introduction of total immersion impregnation, also for large generator4/5 .The now further improved thermal conductivity allows a better dissipation of the winding heat losses and so a further increase in the ratings for indirect cooled machines.2.Effect of the improved insulation system on machine design 2.1 Cooling principle The laminated core is built up from varnish insulated, electrical sheet segments, and is subdivided into packets by radial duct spacers which form passages for the cooling gas flow. In one of the most common designs the core is split up into different cooling zones whereby the cooling gas is led in through axial tubes located in the stator housing.The gas flows radically through the core ducts and absorbs the iron losses produced in the core and the copper losses generated in the stator bars. The total temperature drop due to convection and thermal conduction. The gas absorbs other heat losses before reaching the cooling surfaces of the stator winding and therefore already has a certain temperature which increases further after absorbing the iron and copper losses. The winding copper losses must be dissipated by thermal conduction via the insulation. In the regions of the cooling ducts heat transfer is by convection directly to the cooling gas flowing over the bar surfaces. The larger portion of the winding losses in the active part is first transferred to the stator teeth and then dissipated to the gas flowing through the cooling ducts.2.2 Example of an air-cooled turbo-generator In a typical example, dissipation by convection represents approximately 35% of the total temperature rise. This portion could theoretically be reduced by increasing the velocity of the cooling gas. However, from a certain flow velocity heat transfer can hardly be improved upon, and moreover, in order to achieve higher flow velocity of the cooling gas. However, from a certain flow velocity heat transfer can hardly be improved upon, and moreover, in order to achieve higher flow velocities excessive fan pressures and consequently fan performances are necessary, therefore this possibility does not offer much chance of reduction.The heat from the bar must be dissipated through the insulation by thermal conduction. For a first approximation the temperature difference between the copper and the core can be taken as beingTi=Pd/rs,Where: P=Losses to be dissipated D=Insulation thickness S=Hear transfer area R=Thermal conductivityThe insulation thickness is dependent on the rated voltage of the machine and therefore can nit be changed at all will. Nevertheless, the temperature difference between the copper and the core can be decreased thanks to an improved thermal conductivity of the insulation material. It is therefore possible to increase the losses to be dissipated from the winding while maintaining the total temperature rise. As an example, the temperature difference between copper and core decreases while the convection part between copper and core decreases while the convection part becomes more dominant.The possible increase in rating depends on various parameters. Increase voltage results in increased insulation thickness, and therefore the temperature difference copper to core has a greater part of the total temperature rise. The improved thermal conductivity of the stator insulation permits a possible increased rating for aircooled generators in the rrange of 510%. The rotor must be able to cover the higher back ampere-turns produced by the stator by higher field ampere turns.DCMACHINE PRINCIPLES1. Introduction Direct current machines as a class include those machines that either produce or utilize direct current. In either case the machine function as an energy conversion is from mechanical to electrical energy the machine is termed a generator. If the conversion process proceeds in the other direction the machine is a motor. There is no different principles involved in each case. There principles are now discussed.2. Generator and Motor Action Generator action is based upon the fact an e.m.f. (electromotive force) is induced in a conductor when the conductor moves in such a direction relative to a magnetic field that the conductor cuts the rate at which the conductor is moving relative to the magnetic field. Motor action is based upon the fact that a mechanical force is exerted on a current-carrying conductor in a magnetic field. The magnitude of the force is proportional to the product of the field strength and the current. There are definite relationships between the direction of the induced e.m.f. field and conductor motion in the case of a generator and the direction of the developed force, conductor current and field in the case of a motor.For a generator the relationship is summarized in what is termed “Flemings Right Hand Rule”.Where a motor is being considered, the basic rule is Flemings left Hand Rule.Where a machine operates as a motor or a generator in a given situation is largely independent of the machine conditions and parameters but depends on the direction of power flow between the machine and the electrical supply system. 3. Generator Construction The following descriptions and explanations apply to both motors and generators .In the descriptions, a material having good magnetic characteristics is one that can be worked at high values of flux density without saturation occurring and with a low hysteresis loss. Where an alternative name for a component is common it is given in brackets.3.1 (Frame, B Yoke ody) This is the base on which the machine is built. It has the following functions and characteristics. (1). The yoke completes the magnetic circuit comprising the poles air gaps and armature and gives a return path for the field flux. (2). Modern practice is to make the yoke of steel plate or cast steel of a good magnetic characteristic. In this instance a low hysteresis loss is not important as the flux can be assumed to be constant. (3). The yoke also acts as a rigid frame to which piles and end shields are bolted and to which holding down feet are welded. These are all an integral part of the yoke when the yoke is cast. 3.2 Main pole System (1). Each main pole is an assembly of steel laminations of good magnetic characteristics, between 1.0 and 1.5 mm thick riveted together and of the same length as armature core.(2). Each pole provides a level seat for supporting a main field excitation coil. The body of the pole is reduced to keep the mean length of turn of a main field coil to a minimum thereby reducing the coil resistance and losses.(3). Generally a given number of poles covers a given output range. It will be appreciated that the number of poles will be an even number. In general the larger the out put the greater the number of losses.3.3 Inter poles (Commutating Poles) (1). Inter poles are fitted in the inter polar arc between the main poles and there are generally the same number of inter poles as main plows. In some cases, however, only every alternate pole carries an excitation winding. (2). The poles can be either rectangular in shape and solid construction or alternatively they can be of laminated construction, similar to the main pole.(3). Where steel bar parallel construction is used the inter pole coil held in position by clips or a similar device.3.4 Armature Core (1). This is made up of iron laminations, with very good magnetic characteristics and low iron loss, since, as will be seen later, the armature winding carries an alternating current. In addition each lamination is insulated to reduce eddy current losses further.(2). Slots are notched on the periphery of the core to take the coils-the armature coils are fitted into these slots.(3). The cote is clamped firmly between two endplates and is keys to the shaft and on large machines pole vents are provided in the core to allow cooling air to pass through.3.5 Commutator The commutator bars (or segments) are made of hard drawn or silvered copper held in place by steel vees, which are rather of cast steel or machined from a bar. The segments are insulate from the holding vees. Insulation vees are made of mica. In order to make the connections each bar is dotters in the riser portion and armature conductors ate then soldered in. Commutators must be machined to a very high degree of accuracy to ensure a smooth true surface for brushes to run on at all speeds.3.6 BrushesThe function of the brushes is to collect current from, or supply current to, armatures. Depending on the purpose of the machine, the brushes are made of special types of carbon. Ideal carbon has long life, negligible wearing effect on commutators and good commutating properties.3.7 Brushes Holder (Brush box) The brush holder holds the brushes is the brush in position in contact with the commutator allowing it to slide up and down but without allowing side movement. In order to maintain the correct pressure aspiring arrangement presses the brush firmly on to the commutator.The brush holder is clamped to the rocker arm. 3.8 Brush Rocker The brush rocker consists of two parts, a rocker ring and a rocker arm. The rocker arm is clamped into position on to the rocker ring and is insulated from it. The bruch rocker generally fits on a spigot inside the end shield, enabling the brushes to be rotated round the commutator until the best brush position is obtained. The rocker is clamped in this position and very often dowelled to the end shield.3.9 End shiled (1). The end shield is bolted to the frame and held true by spigot Ensiled. (2). It holds the armature bearings in position and also provides a base for the brush assembly.(3). Generally end shields contain suitable openings for servicing of brushes and have inlets and outlets for cooling air if required.3.10 Main Field Winging The purpose of the magneto motive force produced by this winding is to establish the magnetic field through which the armature conductors move. It is possible to construct a curve showing the relationship between field current and magnetic flux for a given magnetic circuit. This is termed the magnetization curve and usually applies to a given specified speed. 3.11 Inter pole Coil This coil produces a magnetic field which helps the armature coil current to reverse or commutate. It also helps to overcome the magnetic field produced by the armature and is connected in series with the armature. The number of turns on this coil are related to the number of turns and type of connection used on the armature winding and to the number of compensating poles relative to main poles.3.12 Compensating Winding This winding is generally only used on large, highly rated machines. Very simply, it compensates for and cancels out the detrimental effect of the armature magnetic field on the main magnetic field. The shoe portion of the main field pole lamination is made deeper and slots are punched in the pole face facing the armature to take the compensating winding. 3.13 Armature Windings The e.m.f. or the force produced by one conductor in a motor or generator is insufficient for practical purposes and as a result armatures in practical machines require many conductors to perform effectively. The method of interconnection of these conductors and the connection to the commutator to enable the necessary transfer of electrical energy form to armature system to the external circuit to be effected are termed the armature winding. The two types of windings are termed lap windings and wave wondings.最新一代旋转电机定子绕组改进的绝缘系统摘要 近几年有一个明显的趋势：对于较高额定功率（空冷电机功率高达300MVA，氢冷电机功率大约为450 MVA）的电机，也采用定子绕组绝缘系统提出了新的要求，因为这在设计电机时是主要的一项。本文论述了改良合成树脂绝缘的改进结构Micadur-Plus。其最大的改变是在至今使用的绝缘的结构中加入金属氧化物粉末。这可使导热系数提高1倍。还叙述了由此产生及提高绝缘系统短期和长期的性能变化。在提高绝缘质量的基础上可重新优化电机设计，这一点从根本上得到证实。关键词 汽轮发电机，定子绕组，绝缘系统，导体间接冷却，导热系数1：前言 在过去的几十年里，由于对定子绕组导体间接冷却汽轮发电机进行研究，已使其功率得到提高。目前，针对几年前用绕组导体直接水冷或氢冷才能实现的单机额定功率，正在制造采用上述间接冷却技术的电机。1970年投入使用的输出功率为130MAV的空冷电机一直在运行。随着具有更大单机额定功率的燃气轮机的发展，目前的趋势是300MAV功率的空冷汽轮发电机。汽轮发电机采用氢冷允许更高的单机额定功率。50年代末，导体间接冷却的电机功率已达250MAV，而目前可达到350MAV以上。与在较大发电机使用的导体直接冷却相比，定子绕组间接冷却的优点为：一：线棒制造简单而且费用较少；二：直接冷却时，冷却剂需占用的空间可用于绕组铜线；三：不再需要辅助设备（例如水冷却时所需的）。另一方面，间接冷却却需要通过绕包在定子绕组线棒的绝缘，把导体产生的热损失散逸出去。定子绕组为热不良体。根据下面的研究情况，所涉及的温降为整个温升的20%40%。对导体间接冷却的电机，除了要选择最佳的冷却技术外，还需要不断的改进绝缘系统。这将助于这一课题的发展，60年代，从热塑性云母箔绝缘到以环氧树脂为基的合成树脂绝缘的变革，大大改进了绝缘材料的物理性能，特别进一步，大型发电机也采用了整体浸渍。热导体系数的进一步改善，使绕组的热耗更好地散逸，所以进一步提高了间接冷却电机的功率。2.改进绝缘系统对电机设计的影响2.1冷却原理碟片铁心是由涂绝缘漆的电工硅钢片叠成的。径向通风糟钢把铁芯分成若干段。在最普通的设计中，把铁心分成不同的冷却区域，通过固定在定子机座中的轴向管道引入冷却空气。气体径向流经铁心通风槽，吸收铁心产生的铁损和定子线棒产生的铜损所放出的热量。定子绕组的总温升包括冷却剂温升和对流，热传导产生的温降。气体在冷却定子绕组表面之前，就吸收了其它热损，已具有一定的温度。该温度在吸收铁损和铜损之后又进一步升高。通过绝缘的热传导将必须散逸的绕组铜损散发掉。在风道区，利用冷空气直流流过线棒表面产生的对流进行热传导。带电部件的大部分绕组损耗首先被传递到定子齿上，然后散逸到在流经通风道的气体中。2.2 空冷汽轮发电机的实例在一个典型的实例中，对流损耗大约占总温升的35%。理论上通过冷却气体的速度可减少这部分损耗。但是，借助于一定的流速很难改善热传导。此外，为了获得更高的流速，需要非常大的风机压力和很好的风机性能，所以这项措施不可能为减少损耗寄予较大的希望。 利用热传导将线棒产生的热通过绝缘发散掉。首先，铜和铁心之间的温差可近似表示为Ti=pd/rs式中p=散逸耗损d =绝缘厚度r=导热系数s=热传导面积绝缘厚度取决于电机的额定电压，因此不能随便更改。不过改进绝缘材料的热导系数可减少铜和铁芯之间的温差。因此，就能在保持温升不变的情况下增加绕组的散逸损耗。做为实例，当对流占主导地位时，铜和铁心之间的温差将下降。此外的实例可从绕组中散逸大约14%的热损耗。铜损耗随负载电流的平方增加，因而线电流密度大约可以增加7%，电机功率与线电流密度成正比，所以电机功率也以同样比例增加。增加额定功率的可能性取决于各参数。提高电压就要增加绝缘厚度，因此铜和铁心之间的温差占总温升的份额较大。改善定子绝缘的热导系数，可使空冷发电机的额定功率提高5%-10%。由于较高的励磁安匝，转子必须能够承受定子产生的较高反安匝。直流电机的原理1. 概述 作为电机中的一类，直流电机包括发出直流电或使用直流电的电机。不管是哪种情况电机都是能量转换装置，当转换是由机械能到电能时，装置叫发电机，如果转换从另一个方向进行，装置便叫做电动机，在发电机和电动机的基本结构细节之间不存在差异，但两种情况下的原理都各不相同。下面就对这些原理进行讨论。2. 发电机和发电机的作用发电机产生作用的基础是这样一个事实，当导体相对于磁场作切割力线（磁场）的运行时，导体中就感应出一个e.m.f. （电动力）,电动力的大小取决于导体在磁场中的运动速度。电动机则以下述事实为基础，磁场对处于其中的载流导体施加一个机械力。这个机械力的大小与磁场强度与电流的乘积成正比，在发电机中所感应出的电动力场与导体