中文摘要：

大型超临界汽轮发电机组将是我国的主力机组，电抗的增大和定子绕组电阻的减少将使短路电流水平下降，保护灵敏度降低。同时由于结构设计的原因，综合性能较好的一些保护方案如横差保护和不完全纵差保护等将不能应用于大型超临界汽轮发电机。文中重点讨论了匝间短路后各电气量的变化对继电保护的影响。研究表明，发电机发生匝间短路故障后，随着短路匝数的增加，转子二次谐波电流以及单元件横差电流均有较大的变化，以此构成的相应保护方案将能够可靠动作。在此基础上，提出故障分量负序功率方向保护可以作为一重主保护方案，并就该方案在实际应用中所涉及的主要问题提出了看法和建议。

英文摘要：

The protection schemes for large ultra-supercritical turbo-generators, the leading units in the near future in China, will suffer from the low sensitivities because it has the high reactance and low resistance. Several sorts of protection schemes with good performance such as transverse differential protection and incomplete longitudinal differential protection can not meet the requirements of ultra-supercritical turbo-generators. This paper investigates the laws governing the generator internal faults. And the second harmonic current in the field winding and the unit-transverse differential current of the faulty generator are also analyzed after the occurrence of asymmetrical faults. The results show that both of them have the similar changing trends and can be used to achieve the reliable action. According to that, a new directional relay based on the negative sequence power and the second harmonic current in the field winding is presented as one of the main protections. It can provide high performance at different conditions.