外文翻译--风机刹车装置

1 Rotor Brake A mechanical breaking system is besides the aerodynamic breaking function of the rotor an unavoidable component of a wind turbine. It is part of the mechanical drive train. The first task is to keep the rotor of a wind turbine in position when it is at a standstill. Locking the rotor is a must for servicing and repair work and is generally common practice during normal down times. Moreover, most turbines have locking bolts between rotor hub and nacelle for bridging extended periods of standstill and for servicing and repair work. The rotor can thus be secured in one or more positions. Rotor brakes are almost always disk brakes. Suitable disk brakes can frequently be adopted cost-effectively from existing production runs intended for other machines or vehicles .Against this background, the design of the rotor brake itself poses few problems. Nevertheless, the rotor brake presents the systems designer of a wind turbine with issues which have consequences for the entire system. The first and most important question is, which task the rotor brake is to fulfill within the operating concept. In the simplest case, its role is restricted to a mere holding function during rotor standstill. In this case, the brake must be dimensioned for the required holding torque of the rotor during standstill. This is determined in accordance with the aerodynamic forces calculated to occur at the assumed maximum wind speeds (Chapt.6.3.2). Apart from its function as a pure rotor parking brake, the rotor brake can 2 also be dimensioned as a service brake. As long as the braking torque and braking power(thermal loading) can be absorbed, the mechanical rotor brake can be used as a second independent raking system in addition to aerodynamic rotor braking and the operational reliability of the wind turbine is considerably improved in this way. In small wind turbines, a mechanical rotor brake, which in cases of emergency prevents rotor runaway, has proved to be extraordinarily successful and is widely used today. With increasing turbine size, it becomes more and more difficult to meet this requirement. For a turbine with a rotor diameter of 60 to 80 m, the rotor brake takes on almost absurd dimensions if it is to brake the rotor torque and power during full-load operation. For this reason, the task of the rotor brake in large turbines is always restricted to the function of pure parking brake. Apart from the issue of the rotor brakes task with respect to operations, there is the question of where in the drive train the rotor brake is best installed. The alternatives are for the rotor brake to be on the” low-speed” or on the” high-speed” side of the gearbox. In most turbines, efforts to keep the brake disk diameter as small as possible lead to the rotor brake being installed on the high-speed shaft, i. e. between gearbox and generator(Fig. 8.31). Owing to the higher rotational speed, the torque is one or even two orders of magnitude lower than at the slower rotor shaft, depending on the gear ratio. However, mounting the brake on the high-speed shaft has at least two disadvantages. It is inferior from the point of view of safety, since the braking 3 function fails if the low-speed shaft or the gearbox break down. Moreover, the rotor must be held by the gears during a standstill. Gears react with increased wear of the tooth flanks to small oscillating movements, which are unavoidable in a stopped wind turbine due to air turbulence. In some turbines, it is attempted to solve this problem by no longer locking the rotor during standstill but by letting it” spin” at low speed. To avoid these disadvantages, the rotor brake was installed on the low-speed rotor shaft in some earlier systems. In small wind turbines a fully effective operating brake can be implemented with justifiable effort on the low-speed side, as long as design of the rotor shaft bearing assembly does not present an obstacle. The rotor brake on the low-speed side was a common feature of many earlier stall-controlled Danish wind turbines up to a power rating of about 100 kW in the Eighties. At that time it was considered to be an extra safety element even though the rotor brake was only designed as a parking brake. Installing the rotor brake on the slow side is much more problematic in large wind turbines, however. Even a parking brake already assumes a considerable size (Fig. 8.32).These disadvantages have led to the rotor brake being arranged on the high-speed side behind the gearbox in almost all new systems. 8.8 Gearbox The conversion of the greatly differing rotational speeds of the rotor and the electric generator has given the designers of the first wind turbines many headaches. This situation led to costly low-speed generator designs and to 4 hydraulic or pneumatic transmission systems to the generator (Chapt.8.1).Aerodynamicists made efforts to drive the rotor speed as high as possible in order to lower the gear ratio. It was assumed that costs would also increase considerably with increasing gear ratios, so that the development of rotors with extremely high tip-speed ratios was pushed forward. This situation has changed with the progress which has been made in gearbox technology. Today, high-performance gearboxes with gear ratios of up to 1:100 and more are available. In many areas of mechanical engineering, gearboxes are used which are suitable for deployment in wind turbines, as regards their technical concept, their efficiency and their operating life. The gearbox for the wind turbine has become a” vendor-supplied component”, which, with certain adaptations, can be taken from the standard product range of the gearbox manufacturers. Regardless of this favorable situation, the gearbox has been and still is a source of failures and defects in many wind turbines. The cause of these “gearbox problems” is not so much the gearbox itself, rather the correct dimensioning of the gearbox with regard to the load spectrum. In wind turbines, it is easy to underestimate the high dynamic loads to which the gearbox is subjected. Thus, in the early phase, many turbines had gearboxes which were undersized. Having learned their lessons, successful manufacturers equipped their turbines with ever stronger gearboxes and thus, in the course of development, empirically arrived at the right dimension. 5 8.8.1Gearbox Configurations Toothed-wheel gearboxes are constructed in two different forms. One is the parallel shaft or spur-gear system, the other is the technically more elaborate planetary gearing. The gear ratio per single reduction is limited, so that the difference in diameter between the small and the large wheel does not become too unfavorable. Parallel-shaft-gear stages are built with a gear ratio of up to 1 :5, whereas planetary stages have a gear ratio of up to 1 : 12. Wind turbines generally require more than one stage. Fig. 8.33 shows what effects different designs have on gearbox size, mass and relative cost 11. It is noteworthy that the three-stage planetary design has only a fraction of the overall mass of a comparable parallel shaft system. The relative costs are reduced to about one half. In the megawatt power class, the multi-stage planetary gearbox is, therefore, clearly superior. In smaller power classes, the comparison is not quite as unambiguous. In the range up to about 500 kW, parallel-shaft gear designs are often preferred for cost reasons. Small wind turbines are equipped with parallel-shaft gear systems.Theprevailingmodels are two-stage gearboxes which are commercially available from numerous manufacturers as modified universal transmissions (Fig. 8.34). In larger wind turbines, the planetary design definitely prevails. For outputs of several megawatts, two- or three-stage models are used (Fig. 8.35). Large gearboxes of this type are used, for example, in ship-building and several other 6 fields of mechanical engineering, so that suitable gearboxes for large wind turbines can be derived from these production sources. Gearboxes with one planetary stage and two additional parallel-shaft stages are used in many late-model turbines (Fig. 8.36).With the additional parallel shaft, the primary and secondary shafts are no longer coaxial. This has the advantage that a hollow through shaft can be implemented more easily. In this way, power supply lines supplying power to the blade pitch drive, as well as measurement and control signals for the rotor, can be routed through the gearbox. In larger gearboxes, an auxiliary rotor drive is frequently flanged to the gearbox housing. Using this electric motor, the rotor can be turned slowly. Such an auxiliary unit is indispensable for assembly and maintenance work in large rotors. Gearbox lubrication is usually carried out via a central oil supply in the nacelle. As a rule, it also contains an oil cooler and a filter. In spite of indisputable advances having been achieved in the durability of the gearboxes, there is still “trouble with the gears” being experienced even in the latest wind turbines. Although it is possible to adapt gearboxes for wind turbines from other types of machine, they are subject to special demands which are often not encountered in other applications. Much negative experience in recent years has provided important insights into this issue: Special attention must be devoted to the smooth running of the tooting. Particularly prominent gear meshing frequencies can cause resonances in the drive train.“Cheap” transmissions with simple tooting are unsuitable for use in 7 wind turbines. Oil leaks in the transmission are a particular problem. Labyrinth seals have proven more reliable than slipping type seals. In many cases, the housing flanges also showed leaks after some time. A box design with a top flange is apparently more advantageous than gearbox housings with flanges on the input and output side. The quality of the lubrication has been found to be a decisive factor for the service life of the gearbox. Oil temperatures which are too high cause just as much damage as does contamination in the oil. Oil coolers and filters are indispensible for large gearboxes ands is the careful observance of oil change intervals. The stiffness of the gearbox housing is an important criterion for its service life if the housing is integrated into the static design of the nacelle. Apart from these constructional measures, of course, the correct dimensioning has a decisive influence. 8 风机刹车装置 机械制动装置作为主传动链的一部分，同具有气动刹车功能的转子一样，是风力发电机一个不可或缺的组成部分。其首要任务是当风机停转时，使风机转子处于适当的位置。在维修工作的过程中，锁定主轴是必须的，而且在正常的停工期间，锁定主轴也是惯常的做法。更为重要的是，为了渡过持续的主轴停转时期以及维修工作的进行，大多数风机都会在轮毂和机舱之间安装锁紧螺栓，从而使主轴在一个或者多个位置得到保护。 主轴刹车通常采用盘式刹车，适当的盘刹可以频繁采用为其它的机器或装置设计的现存的生产线，这样就可以节约成本。在这样的背景 下，主轴刹车的设计本身不会产生很多问题。然而，主轴刹车也会给风机系统的设计者带来一些问题，而这些问题可能给整个系统带来一些后果。 最为重要的问题是，在经营理念之内，刹车装置要完成哪项任务。在最简单的情况下，在主轴停转的情况下，刹车装置的尺寸必须满足所需的支持转矩。这是由假设风速达到最大时所计算的空气动力所决定的（第 6.3.2 节）。 刹车装置除了单纯地具有主轴驻车制动功能外，尺寸合适时，其也可以作为停车制动装置。只要制动力矩和制动力（热负载下）能够被吸收，主轴机械刹车也可以用作除了气动主轴刹车外的第二独立刹车 系统，这样一来，风机的运作可靠性得到大幅提高。对于小型风机，在紧急情况下，主轴机械刹车会防止主轴失控，这一点被证实是非常成功的，并得到了广泛的应用。 随着风机尺寸的增大，这一需求会越来越难以得到满足。对于主轴直径为 60 米到80 米的风机来说，如果是在满载运转期间制动主轴转矩和主轴功率，主轴刹车装置几乎承担了离谱的规模。因此，在大型风机中主轴刹车装置的作用总是被限制在单纯的进行驻车制动的上。 除了主轴刹车装置的运转任务的问题外的另一个问题是，刹车装置安装在主传动链的哪个位置是最合适的。两种可以选择的方案分别是安 装在齿轮箱的低速轴和高速轴。在大多数的风机中，为了使得刹车盘的直径尽可能地小，常将刹车装置安装在高速轴上，比如安装在如齿轮箱和发电机之间（图 8.31）。根据齿轮的传动比，由于转速较高，转矩会比在低速轴上低一个甚至两个数量级。 然而，将刹车装置安装在高速轴上至少有两点缺点。由于如果低速轴或者齿轮箱出现故障时，刹车功能就会失效，所以从安全的角度上，这种方案是处于劣势的。再者，在主轴停转的过程中，其必须由齿轮支撑。随着齿轮齿侧的逐渐磨损，齿轮会产生一些小的震动，由于空气扰动，对于一个一个停止工作的风机来说，这一点 是不可避免的。在有些风机中，为了试图解决这一问题，主轴停转时，不再锁定主轴，而是允许它在低速下转动。为了避免以上缺点，早期的主轴刹车系统被安装在低速轴上。在小型风机中， 9 只要主轴轴承装置的设计不会出现问题，也可以通过无可非议的努力在低速端实施一个完全有效可操作的刹车方案。 80 年代，丹麦许多功率高达 100kw 的失速控制型风机普遍采用主轴刹车安装在低速轴的方案。那是，即使主轴刹车装置仅仅被设计为驻车刹车装置，这一方案也被看作是一个额外的安全因素。然而，在大型风机中，将主轴刹车装置安装在低速轴是非常有争议的。即使假 设刹车装置有一个相当大的尺寸（图 8.32）。在几乎所有新的系统中，这些缺点已经引导主轴刹车装置被安装在齿轮箱后部的高速轴上。 图 8.31N