Tests of the KGU-400/4.5 plant in non-standard operating modes

Results of experimental study of a commercial cryogenic helium plant of the KGU-400/4.5 type operating in the mode with time-varying heat load at helium temperatures and in the mode with excessive return flow rate are presented. It has been found, that at the heat load variation factor lower than 2 and with heat load step duration t < 1 min there is no cooling capacity change. When t > 1 min the plant operation is possible only with liquid helium consumption. Time behaviour of the second expander exit flow temperature is presented. It is shown, that with t > 5 min expander temperatures become too low and the plant is out of operation. One of the ways to achieve higher reliability in the expanders failure situation is considered. That is transition to the operating mode with excessive return flow rate. It is shown, that even when all expanders are out, the plant can work with cooling object for some hours provided enough liquid helium supply. This time can be used for repairs