This article analyzes parameters of stability of the secondary electrical circuits of the variable speed pump storage unit. The differential equations in Laplace transformation are describing operation equations and transfer functions of dynamic mathematical model of the exciter and control system. The additional factors and transferring units are installing in the structure circuit of the dynamic model. The dynamic mathematical model of the variable speed pump storage unit is comparing with standard mathematical models of IEEE. Investigation for stability and instability of the secondary electrical circuits of the variable speed pump storage unit are created the methodology of testing.