现有的测定中压平衡活塞汽封漏汽量的变汽温试验法存在一定的误差且不能实现在线监测。分析变汽温试验法存在的误差，并考虑中压平衡活塞汽封漏汽的影响，对某300 MW汽轮机进行变工况详细计算。结果表明，中压缸效率基本不受再热蒸汽流量、中压平衡活塞汽封漏汽量及再热蒸汽温度的影响。基于相邻两工况下中压平衡活塞汽封间隙一定及中压缸相对内效率相等的原理，提出中压平衡活塞汽封间隙、漏汽量及中压缸相对内效率的计算方法。利用变工况详细计算数据进行检验，以及与变汽温试验法测定结果进行比较，证明所提出的计算方法的有效性。利用所提出的计算方法，对某高中压合缸汽轮机在某一运行时段内的中压平衡活塞汽封间隙、中压平衡活塞汽封漏汽量、再热蒸汽流量及中压缸相对内效率进行实例计算。

The existing method of measuring intermediate pressure(IP) balance piston seal leakage by temperature variation test exists some errors and cannot achieve on-line monitoring. The errors of the temperature variation test method are analyzed, and the detailed variable condition calculations which considering IP balance piston seal leakage for a 300 MW steam turbine are performed. The results show that the IP turbine efficiency is basically not influenced by reheated steam flow, IP balance piston seal leakage and reheat steam temperature. The new calculation methods of balance piston seal clearance, IP balance piston seal leakage and IP turbine efficiency are put forward which based on the balance piston seal clearance and IP turbine efficiency are equivalent at two adjacent working conditions. By the detailed variable condition calculations results and temperature variation test results, the effectiveness of the new calculation methods is proved. The IP balance piston seal clearance, IP balance piston seal leakage flow, reheated steam flow and IP turbine efficiency for a steam turbine in a certain period are computed.