为了机组首次启动的安全顺利进行，需要正确选择临时励磁电源的电压等级、容量，并进行保护定值核算。结合某电厂1号机组的启动试验，对自并励机组启动试验励磁电源的选择及保护定值计算进行了论述，分析了非全压冲击励磁变压器的励磁涌流的产生机理，指出非全压冲击变压器的励磁涌流远小于全压冲击值，与变压器额定电压下空载合闸产生的励磁涌流截然不同，并通过现场事故录波证实。在此基础上，并结合现场事故实例指出：励磁临时电源速断保护定值整定过大，会导致励磁变压器低压侧短路时保护拒动，据此，给出满足启动试验要求的临时继电保护定值整定方法。

The voltage level and capacity of the temporary excitation power should be correctly choosed and the protection setting for the safe and smooth first-starting of units should be calculated. According to the starting test of No.1 unit in a power plant, in this paperthe selection of excitation power and the calculation of the protection setting for the self-shunt units are discussed, and the generation mechanism of magnetizing inrush current is analyzed in the case of non-full voltage impaction on excitation transformer. The results show that the magnetizing inrush current generated by non-full voltage impaction is far less than that by full voltage impaction, which is totally different from the magnetizing inrush current generated by the transformer no-load closing with nominal voltage, and is verified by the incident wave records. On that basis, combined with the incident instance, the conclusion that the large protection setting values for excitation temporary source could cause the protection failure under short circuit conditions of excitation transformer at the low voltage side is pointed out, and a correct protection setting value method for temporary relay is suggested, which could meet the requirements of starting test.