Transformer bushing is one of the most vulnerable substation devices during earthquake. To investigate the efficiency and cost effectiveness of base isolation for large transformers-bushing system

shaking table tests on a transformer-bushing system in the presence or absence of the double friction pendulum（FP） isolation bearings were conducted. Afterwards

in the seismic cost-effectiveness analysis

a ±200 kV and a ±800 kV converter transformers were taken as examples to calculate the expected expense of recovery construction after an earthquake by using the isolation efficiency obtained in the test and the fragility analysis. The research results show that the double FP isolation bearings can decrease by about 50% of the seismic strain responses of bushings and will not amplify the displacement when compared with the non-isolated system. Expense of the system with isolation can be less to 10% of that of the system without isolation. The analysis results from the two aspects show that the base isolation can significantly reduce the seismic responses and economically benefit for large transformer-bushing system in high seismic intensity areas

and it is deserving further development and applications.