In traditional hydrodynamic automatic control systems (ACS) of power steam turbines (PT), the protection scheme (PS) of the turbine unit was used according to the rotation frequency "1 of 2". In modern electrohydraulic ACS, a "2 out of 3" or a "n-1 out of n" PS with a large number of channels is used, which makes it possible to implement a channel-by-channel check of the PS and identify the failure of one of the channels without stopping the PT. In ACS, the PS is implemented in an electrohydraulic device - a Protection Unit (PU). Valve PU is preferable to spool PU (SPU) in terms of cost and complexity of production. In valve PU, in case of failure of one of the channels during an emergency stop, the residual pressure remains in the protection line the greater the fewer valves (and, accordingly, channels) in the PU. In the case of PT UTMZ, the residual pressure of the 3-channel PU is unacceptably high (due to the characteristics of the Automatic Lock of the stop valve (ALSV)). During the reconstruction of the ACS PT UTMZ, 5-channel PU are used. It is proposed to carry out the reconstruction of the ALSV, which allows the use of 3-channel PU on PT UTMZ. This leads to an increase in the reliability of the PS operation by reducing the number of channels (and valves) of protection from 5 to 3 without increasing the cost of reconstruction of the ACS as a whole.