Servo motor shows improved control behaviour

Voith Turbo has developed new servo motors where the stroke has been shortened, to build high-pressure steam turbine compact servo motors for individual application in a compact format

High-pressure steam turbine compact servo motors (H-DAKS) for individual application can now be built as even more compact units.

Voith Turbo has developed new servo motors where the stroke has been shortened from 120 to 60 millimeters.

As a result, the plate valve which had been necessary for high oil flow volumes can be eliminated, a saving in components, which increases the availability of the servo motor.

Instead of the spiral spring needed for stroke reduction, in future cup springs with increased spring ratings and lower tolerances can be used.

Additionally, Voith Turbo has also improved the control behaviour and the fast closing function.

High-pressure servo motors are also suitable for applications on larger steam turbines.

In steam turbines, electro-hydraulic Voith servo motors precisely and dynamically control the steam supply and, when necessary, also the steam bleed.

On a load increase during the turbine operation (trip), the control valve of a medium-size steam turbine need to shut safely within 300 milli-seconds.

Larger steam turbines require even shorter closing times due to higher mass flows.

The control valve with the newly developed high-pressure servo motor is shut far below the required time of 300ms.

This fast reaction occurs without undershooting, which reduces the load on the valve seat.

Additionally, applications with gas turbines, where extremely precise fuel dosage is required, are now also possible.

For the first time, an improved pilot control has been implemented into the new Voith servo motors.

This pilot control which has been tested in numerous trials has a higher magnet force, while the current uptake stays the same.

Consequently, a harder control spring with higher energy storage can be used.

The result: especially in the small signal range, is that the control behaviour is more dynamic and more stable against friction influences and reactions of the hydraulic fluid.

The adherence to even closer production tolerances for the components of the hydraulic pilot valve has led to a considerable reduction of oil leakages from 4 to 2.5 l/min.

This pays off for the operator, because it means that the hydraulic pumps can be designed with lower dimensions.

Another innovation is the possible operation with flame-resistant hydraulic fluids which results in more favorable premium payments for fire insurance.

As an option, the new high-pressure servo motors are also available in an explosion-proof design.

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