After long-term operation and retrofit of digital electro-hydraulic(DEH) control system or flow path of steam turbine

the actual flow characteristic curve of the turbine's regulating valve will deviate from the design values

thus affecting the unit's primary frequency and load control ability. However

the field flow characteristics test has common shortcomings of severe test conditions

long duration and low precision. In this article

through analysis and excavation of the unit's historical operation data

two methods are proposed for different situations to identify the actual flow characteristics of the steam turbine's regulating valve. The flow characteristic curves of each valve are obtained by iteration calculation when the downstream pressure data can be achieved

or by the Freugel's formula when the downstream pressure data can not be achieved. The DEH valve management curve is optimized by simulation and piece-wise linearization to determine the reasonable valve overlap degree. The application of this method in a 660 MW unit shows that

in sequence valve operation mode

the linearity of the flow characteristics curve has been improved greatly

and the capability of the load variation and primary frequency regulation have been enhanced.