Characteristics of Large Hydro Generators of Dehar Power Plant

Studies for fixing capacity and unit size are outlined in chapter 2 Para 2.4. Considerations involved for fixing, Type and principal electrical and mechanical characteristics of 174 MVA Dehar Generators on Beas-Satluj Link project are given below:

Introduction

BEAS SUTEJ LINK项目的DEHAR发电厂于1976年至1980年委托，拥有六（四个第一阶段和两个第二阶段）半伞式垂直发电机0.95 PF，每次165兆瓦。该方案的纵向部分如图9.4所示。300rpm发生器耦合到282米（925英尺）的额定头帧涡轮机，其具有516rpm的涡轮机失控速度。为电厂选择的174个MVA的单位大小是该国最大的单位尺寸，而且可能是具有最高速度的机器，半遮阳伞结构。电厂将在第一阶段与印度北部区域网格相互联系，在Panipat的280公里长的单电路420 kV线和60km长时间

电路245 kv线在古武武武。沿两个第二级单元加入第二420 kV线。第一次在该地区推出了420 kV。脱离发电厂互连的主要互连传输系统（第1级）如图9.5和发电厂的互连（第一级）所示。经济的思考决定了要安装的发电装置的尺寸和类型，并在水电发电站提供传输网点。此外，在开发EHV系统的初始阶段，水电发电机的稳定性问题是由于系统弱，传输角度和在前导功率因数处的发电机的运行而致力于临界。由于长EHV线的电容负载，还存在自激励和电压稳定性问题的风险。此外，先进设计的现代机器的较小惯性常数也可能危及涡轮调速器齿轮的稳定性。这些问题被带出了和系统和其他考虑因素，用于修复脱离水电发电机和激励系统的经济尺寸，型号和主要电气和机械特性，保持在材料技术方面的推进，现代快速作用静态励磁设备和方法的可用性讨论了用于分析系统问题。 Dehar Power Station is located in the Himalayan region of India. This region and many other hilly areas

水力站所在的地方是地震区。还概述了在发电机中制造的规定，以保护防止地震部队。

兆瓦等级和发电机数量

Substantial economies in the cost of equipment and civil structure are obtained by the installation of lesser machines of bigger size especially in a high head power plant. Further, higher efficiency is associated with larger generating units. Limitation on the size of the unit is placed on the one hand by water turbine and on the other hand by system considerations. With the availability of better techniques and materials, hydraulic turbine design has undergone rapid advancement and very large sized medium and high head Francis turbine hydraulic turbines have been made or proposed, e.g., 8,20,000 HP hydraulic turbines for third power plant at Grand Coulee in USA. Accordingly the major constraint on unit size for medium and high head Francis turbine driven generators is system characteristics and other limitations. As the system grows bigger, larger size generating units can be installed. In general maximum economic unit size that can be installed in a system can be found out by evaluating the increase in system spare generating capacity required as a result of increase in unit size. Evaluation of system spare generating capacity for various unit sizes is dependent upon size and characteristics of the power plants in the system and spare capacity already available in the grid. Other considerations involved are part load operation and transportation of heavy and big single piece packages, The economic unit size at Dehar Power Plant was fixed keeping in view the maximum available working capacity of 583 MW as determined by water and power studies, the system spare generating capacity required to be provided at the power plant to meet forced outages in the system and the capacity outage required for scheduled maintenance of power units. Seasonal variation of load and available generating capacities was taken into consideration for fixing spare capacity. The spare generating capacity required for forced outages was worked out by probability methods.

运输也是在修复单位的最大尺寸时考虑。细节在第2章（段落2.5）中给出。因此，发电机的最佳数量和千瓦额定值固定为第一阶段的每个165 mW的四个单元。在动力屋中提出了两种相同的第二阶段单元，以处理网格中未来热电厂的峰值要求。

Power Factor and MVA Rating

The required MVA rating of generators is determined from the system reactive power requirements.Growth of system network and a better understanding of its behaviour has resulted in a definite trend towards specifying higher power factor rating especially for remotely located hydro generators,interconnected with the grid by EHV lines, so that the improvement in performance associated with the operation of generating unit nearer to its rated power factor can be realized. In case of Dehar Power Plant detailed load flow studies were carried out so as to find out the VARS (reactive power) fed into the system from Dehar generators for various interconnection alternatives. The reactive flow, megawatt load and consequently the actual power factor at which the machines operate in the study were found out. In the study total VARS of the system load were balanced by VARS from generators, capacitors already installed in the system and additional capacitors at load end adjusted so as to ensure tail end voltages at proper level. A typical study for an equivalent reduced network is shown in Figure 9.7. For various schedules of generation and transmission alternatives and line outage the reactive flow and power factor of operation at Dehar machines varies from 0.96 to 0.98. Consequently the power factor of the machines was specified as 0.95. Procurement of higher power factor machines resulted in saving in the cost of generators.

Type of Generators

通过采用伞式结构，采用带有组合的推力和引导轴承，可以节省发电机的成本，开销的起重机容量和民用结构。可以采用大型高速水电发电机采用伞式施工前所需的主要条件，如下所示：

a)The ratio of core length to rotor diameter be kept as low as possible and at the same time ensuring that a reasonably high output co-efficient is obtained consistent with the required winding temperature rises and transient reactances.

b)The required flywheel effect is incorporated in the rotor rim and poles with the stresses in the rotor at turbine runaway speed not exceeding two-third of the yield point of material.

c）在引导轴承上方的转子突出的转子突出充分减小，以确保组合发电机和涡轮轴系统的计算临界速度高于足够的余量的循环速度。

d)The radial width of air gap to be as high as possible so as to minimize the unbalanced magnetic pull on the rotor and thereby reducing the over-turning moment on the bearing.

e) Ample and adequate design of bearing and easy accessibility to the thrust bearing.

umbre为了满足上述条件lla construction for Dehar generators, it was necessary that the length of the rotor core (and hence rotor overhang above the guide bearing) be reduced. It is, therefore, obvious that umbrella generator construction would require large diameter rotors with ratio of core length to core diameter less than about 0.29 so that critical speeds are well above turbine runaway speeds. Large diameter rotors would mean higher speeds and consequently higher stresses. Quality of steel available for rotor fabrication was, therefore, one of the main factors which hitherto restricted umbrella construction to smaller sized medium and low speed Francis and Propeller or Kaplan turbine generators. Similarly the limit curve for hydro-generator of above 100 MVA rating did not exceed 200 rpm in Japan. It was now possible to adopt umbrella type construction for large high speed generators due to the advancement in material technology with special reference to higher tensile sheet steel for rotor rim punchings so as to obtain a minimumfactor of safety of 1.5 on the yield point at turbine runaway speed.For Dehar Power plant 173.8 MVA 300 rpm generators, high tensile sheet steel with a yield strength of 56kg/sq mm (36 tons/sq in.) was used which permits its operation on a turbine runaway speed of 510 rpm at a peripheral speed of 176 m/sec for its large diameter (6.8 m) rotors with the specified factors of safety. With the use of this high tensile sheet steel, it was possible to reduce the length of the core (and hence the rotor overhang above the guide bearing) sufficiently to satisfy the conditions for umbrella construction. A second guide bearing at the top, although not considered necessary by suppliers of generators, was got provided so as to provide better stability for the unit taking into consideration seismic zone of location.

制造商暗示伞机的成本低于传统顶部推力轴承和两个引导轴承装置的约12％至15％。实际提供的半伞发生器的更便宜约为10％。所计算的组合发电机和轴系统的第一临界速度与所提出的发电机的半伞布置约为涡轮机失控速度约为20％。