Servo-systems

Highest precision for the actuator positioning

The development of hydraulic servo-systems controlling the steam flow or pressure in the thermal power plants is reckoned among the several applications realized by Duplomatic Oleodinamica in the electrical energy production sector. The different valve types, all of them with a linear actuation, are defined and dimensioned in order to guarantee the highest compliance with the requirements of functions such as pressure reduction, desuperheating, by-pass etc. Together with the actuator dimensioning, Duplomatic Oleodinamica has developed also the circuitry in order to meet the more and more pressing safety needs of the power plant staff.

The most advanced section of the system is represented by the control circuit of the driving actuators. This application foresees the use of DSE3G proportional valves with integrated electronics and shutting spool for the position control.

A special spool has been designed which is capable to control extremely low flow rates, in order to guarantee
the required positioning precision. The valves with integrated electronics have a central position spool with positive overlap: such dead zone is aborted by the electronics as soon as the regulation loop is enabled; as a consequence in case of break of the set point or power supply cable, the valve behaves as a normal closed centre proportional valve with positive overlap.

The programming flexibility of these new proportional valves allowed to take into consideration new solutions to be offered on the energy production market.

The new system allows the in-factory calibration and the recording of the data on the Pc; the advantage is the availability of a common data base which permits, in case of maintenance or replacement of the components, to parameterize the system again by inserting the same gain, dead band, offset data etc. available on the replaced version.

During the emergency or safety phases the easy management of the handling procedures with an off-condition actuator is therefore possible.

Because of the high reliability degree required by this application it has been advisable to apply a further hydraulic safety element. The hydraulic piloted sliding valves form the fast closing circuit and detach the proportional valve from the failsafe circuit. As a consequence the safety function is performed independently of the position acquired by the spool of the proportional valve.

The position transducer can be integrated inside the cylinder or it can be mounted externally with possible signal redundancy obtained by using the ERM electronic card by Duplomatic Oleodinamica. The positioning precision of these servo-systems is very high (some tenth of millimeter) in line with the requirements of the steam sector.