To study the speed change of expander rotor during the load rejection of liquefied air energy storage(LAES) system

a dynamic model of expander unit of 500 kW LAES system is established. The load rejection process of the expander unit with different closing times of adjustment valve and time constants of rotor is simulated and analyzed. The results show that

when the closing time of adjustment valve is 5 s and the time constant of the rotor is 15 s

the over speed ratio of expander 1's speed to expander 2's speed is 142.2%

and the load rejection time is 7 071 s. The over speed ratio of expander 3's speed to expander 4's speed is 141.2%

and the load rejection time is 4 550 s during the load rejection. When the closing time of adjustment valve is shortened to 0.5 s and the time constant of the rotor is reduced to 6 s

the over speed ratio of expander 1's speed to expander 2's speed reduces to 120.9%

and the load rejection time shortens to 2 552 s. The over speed of expander 3's speed to expander 4's speed is 120.3%

and the load rejection time is 2 200 s during the load rejection. Thus

during the load rejection of the LAES system

shortening the closing time of adjustment valve can make the maximum speed of expander rotor within the safe range. Moreover

to shorten the time of load rejection

the time constant of the rotor should be appropriately reduced.