Losses in superconducting coils of 1 kWh/1 MW SMES

The in-situ measurements of pulse losses are carried out for the total system of ESK (Experimental SMES (superconducting magnetic energy storage) of Kyushu Electric Power Co.) with a capacity of 1 kWh/1 MW which was completed in 1998. ESK has six toroidal coils wound by Rutherford cables, each coil being contained in a fiber reinforced plastic (FRP) vessel set up in a Dewar. The loss was calculated by using a method of measuring the decrement of liquid helium (LHe) level in each vessel. The form of current variation for the measurement is a repeated triangular waveform. The charge-discharge rate was changed from 10 A/s to 140 A/s. Although there are considerable errors in the measurements, agreement between the measured results and theoretical calculations is satisfactory in view of the limited conditions of the in-situ measurement for the SMES coils of this scale. The origins of the loss are discussed in detail.