Steam Turbine Electro-Hydraulic Control

Emerson’s Mark Stratton and Tori Winter presented Steam Turbine Electro-Hydraulic Control (EHC) Systems at the 2023 Ovation Users Group Conference. They opened by sharing a description of a steam turbine EHC system.

electro-hydraulic controlFluid power components and electronic controls operate the primary steam valves on a steam turbine and includes utility, extraction, and auxiliary turbines.

The EHC components consist of a hydraulic power unit (EH skid), accumulators, filters, actuators, trip manifolds, and instrumentation. Typical operating pressures are 400 psi to 2500 psi.

The steam turbine EHC system components bridge the control and hydraulic systems with servo and proportional valves, solenoid-operated directional valves, position feedback, temperature & pressure measurements, and speed probe.

Common issues with these systems are servo valve failures, valve calibration, heat or vibration component failures, seal compatibilities, leaks, fluid chemistry, obsolete parts, operational testing anxiety, and turbine work equipment damage.

From a maintenance standpoint, monitor for EHC fluids, perform system flushing, perform periodic refurbishment, maintenance, and systems equipment upgrades.

EHC System upgrades can include electronic overspeed protection. The Ovation Electronic Overspeed with EH retrofit can dramatically improve performance over a mechanical overspeed system from 340 to 490msec.

Next, they discussed trip functionality with a testable dump manifold. Key capabilities include Triplex design, fault tolerance, testable with turbine on-line, 2 out of 3 voting in the hydraulic circuit, on-line diagnostics, failsafe  (de-energize to trip) operation, options for variable trip flow, and sub-plate & tube connection options.

Ovation system testable dump manifold

A manual turbine trip handle enables a local shutdown and directly interfaces to the hydraulic system. A proximity switch monitors the position of the trip handle.

A pressure status manifold (PSM) triple analog inputs replace lube oil trip, vacuum trip, and thrust bearing trip. 2 out of 3 voting on A/I’s  will trip the turbine.

Position feedback provides continuous position monitoring, redundancy, and integration with Ovation valve positioning—valve positioner (RVP) modules and the servo driver (RSR) module.

Here is a summary of the EHC individual mechanical component upgrades.

Visit the Steam Turbine Control section on for more information on these components for more efficient, reliable and safe operations.

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