The ESS(energy storage system, here after) for a DC 1500V was developed in 2009. A ESS was installed on the track of Daejeon HRT in 2010. The advantage of the ESS is that it can save the energy and plus stable the catenary voltage. This paper presents the energy saved by the ESS in Daedong substation. When the ESS is on/off, the field tests are performed.