Potential faults in electrical equipments and secondary circuits of large and medium 300 MW and 600 MW genera‐tor‐transformer units with unit‐typed connection mode are hard to be discovered before alarming and tripping ,while stability of calculating data about the main transformer power loss rate (MTPLR) is sensitive to these faults .Research indicates that when the main transformer is in normal operation ,positive correlation of MTPLR with its average load coefficient is weaker and as daily average load coefficient of the main transformer is within 0.6 and 1.0 ,its MTPLR is close to some intrinsic con‐stant .When electrical equipments and secondary circuits break down such as non‐sudden abnormalities in electric energy me‐ters ,voltage transformers (VT) ,current transformers (CT) ,fuses ,secondary circuits and so on ,calculating value of MT‐PLR will change a lot which is obviously deviated from the intrinsic constant .Generation enterprises can make statistics and analysis on calculating value of transformer loss rate according to above characteristics so as to survey states of electrical e‐quipments and secondary circuits and pre‐judge abnormalities and faults .%300 MW、600 MW等大中型单元式接线的发电机–变压器组电气设备和二次回路的潜在性故障，在告警和跳闸之前难以被发现，而主变压器变损率计算数据的稳定性对该类故障表现敏感。研究表明，主变压器正常运行时，变损率与其平均负载系数的正相关性较弱，当主变压器日平均负载系数为0.6～1.0时，其变损率趋近于某个固有常数。当发电机–变压器组电气设备和二次回路故障，如电能表、电压互感器、电流互感器、熔断器和二次回路等发生非突发性异常，主变压器变损率的计算值将大幅度变化，与正常运行时的固有常数形成明显偏差。发电企业可据此特性，统计和分析各主变压器的变损率计算值，监测电气设备和二次回路的状态，预判其异常和故障。
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