为了提高大型水轮发电机的运行可靠性，设计人员对电机的冷却系统作了不少改进，基中包括线圈采用液态介质内冷系统等。蒸发冷却技术已在中国数个电站的几台立式水轮发民机中得到应有和，并经历了长时间的商业运行考验。为了验证这种新型冷却系统的优越性，应对电机内的温度场进行深入的分析。该文以有限元法计算了采用蒸发冷却系统的大型水轮发电机定子三维温度场，以包括导体、端部绕组及通风沟在内的定子半个齿距全轴向长度为计算域，并考虑蒸发冷却的特点，建立了物理和数学模型。论文以李家峡电站一台400MW蒸发冷却发电机为实例，计算了不同工况下的定子温度分布，计算结果与现场实测数据进行分析比交，验证了计算方法的正确性。论文得出了一些有助于设计和运行的结论。

考虑水轮发电机端部结构的物点，计入材料的各向导性和非线性，以电路和磁路等效原理导出定子铁芯叠片边段和分瓣压圈的等效电导率及磁导率。计算了一台725MW水轮发电机在各种工况下的端部磁场，结果与实测值非常吻合，证明了所提出方法的正确性。计算了李家峡400MW水轮发电机在欠励工况下的端部磁场，并与现在进相工况进行时的实测数据对比，结果满足工程要求，为预测水轮发电机进相能力和充电空量提供了依据。

Impedance character as well as relevant impedance criterion is important in thesmall-signal stability analysis of multi-sgage dc distributed power systems, where subsystems are integrated. At the same time, we usually approximately simplify a tightly controlled load-converter as constant power load. In this paper, we focus on the impedance character and impedance criterion in two-stage dc distributed system, which is in fact criterion in two-stage dc distributed system, which is in fact inter-dependent dynamical system with both interaction loop and many individual regulation loops. We verify that minor loop gain method can be directly extended to inter-dependent subsystems, while original impedance criterion cannot. Furthermore, we develop a substitutional stability analysis. With this substitutional impedance criterion, we discuss the influence of regulation loop gain, load resistance, input voltage and various duty-cycle ration on system small-signal stability. In additon, we analyze the impedance shift process of the imput impedance of load-converter and build the relationship between it and rgeulation loop gain. Negative rgsistor approximation of load-converter is only regarded reasonable when high regulation-loop gain is assumed and low-frequeney character of load-converter is considered. Simulation results illustrate the validity of the substitutional impedance criterion.