GE 3687c SPEEDTRONIC™ MARK V STEAM TURBINE CONTROL SYSTEM

GE 3687c SPEEDTRONIC™ MARK V STEAM TURBINE CONTROL SYSTEM

Description

The SPEEDTRONIC Mark V is the latest version of GE’s long series of highly reliable electrohydraulic control (EHC) systems for steam turbines. Its heritage consists of a long list of successful control systems, including the first EHC Mark I steam turbine control built in the 1960s, and the SPEEDTRONIC Mark I-IV gas turbine control. The Mark V continues to combine the best turbine and generator design engineering with the latest electronic controls engineering to provide a modern, yet experienced controls package.

Some of the features are: 

• Common Architecture, Maintenance, and Spare Parts between steam turbine, gas turbine, and other controls 

• Very flexible, PC-based operator interface with Color Monitor and Logging Printer with alarm log, event log, historical trip log, etc. 

• Common operator training and controls for steam and gas turbines in combined-cycle STAGTM plants 

• Full Turbine-Generator Monitoring for all sizes of turbines can be included 

• High Resolution Time Tags including 1 ms time tags of contact inputs 

• New Communication Links to plant controls 

• Distributed Multiprocessor Control in each controller for maximum processing capability 

• Enhanced Diagnostics that can isolate a fault to the card level in any of the triple-redundant controllers 

• On-Line Repair of the triple-redundant controllers 

• Standard built-in Synchronizing Check Protection 

• Fully Digital Valve Positioning to provide a more linear response of the steam turbine 

• Direct Interface to Turbine Devices, including proximity monitoring equipment 

• Compact Packaging in half the cabinet size of the previous control system

CONTROL SYSTEM HISTORY

From their introduction in the late 1800s, steam turbines were governed by mechanical hydraulic control (MHC) systems. Speed was controlled by a flyweight governor of James Watt heritage, signals were transmitted by levers and links or hydraulic pressure signals, and motive power to control steam valves was provided by low-pressure hydraulics. Refined to the utmost, this technology was used through the mid-1960s, to control such sophisticated units as double-extraction industrial turbines, large double-reheat fossil units, and the first nuclear units incorporating pressure controls  for BWRs. The complexity of these later controls clearly showed that a new technology was needed.

ANALOG CONTROLS

GE introduced the electro-hydraulic control (EHC) system for steam turbines in the 1960s. The first medium-size unit went into service in 1961, and the first large reheat unit in 1968. The proportional controls used analog circuitry with dual redundancy for speed control and single channel for other controls. The logic and protective system was implemented with relays. 

The original Mark I system consisted of discrete component analog circuitry. In the 1970s, these circuits were modernized to take advantage of integrated circuitry (IC) technology as well as solid state logic circuits for some of the protection and logic. This resulted in the EHC Mark II, which had many IC components and a new cabinet arrangement, while the subsequent Mark III, used only on small- and medium-sized turbines, employed ICs throughout and also included electronic speed sensing and microprocessors for automation.

The main functions of a modern steam turbine control system are: 

• Speed and acceleration control during start-up 

• Initialization of generator excitation 

• Synchronization and application of load in response to local or area generation dispatch commands 

• Pressure control of various forms: inlet, extraction, back pressure, etc. 

• Unloading and securing of the turbine 

• Sequencing of the above functions under constraint of thermal stress 

• Overspeed protection during load rejection and emergencies 

• Protection against serious hazards, e.g., loss of lube oil pressure, high exhaust temperature, high bearing vibration 

• Testing of steam valves and other important protective functions