GESPEEDTRONIC™ MARK V STEAM TURBINE CONTROL SYSTEM

INTRODUCTION

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 (Figure 1).

The Mark V is the third generation of triple-redundant microprocessor-based turbine controls that originated in 1982, with the Mark IV1 and was followed in

1987, with the DCM2. GE has an installed base of 

over 1,000 running triple-redundant, steam and gas

turbine control systems. The Mark V family of turbine controls for the 1990s, offers a common control

architecture for small, medium, and large steam turbines, turbine-generator monitoring systems, generator excitation systems, and gas turbine controls.

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.

A major improvement for both medium and

large steam turbine controls was a reduction in

component count with a resultant increase in reliability. The EHC Mark II version for large steam turbines, in addition to integrated circuits, also introduced triple-redundant protection systems for the

functions that can cause a turbine trip, resulting in

further improvement in running reliability by virtually eliminating spurious forced outages.

The associated high-pressure hydraulic system,

using 1600 psig (110 bar) fire-resistant fluid, has

undergone gradual improvement through the

years. The basic technology is still in use for the

new electro- hydraulic controls.

The history of analog controls, as well as the

new digital controls, is summarized in Table 1.

The reliability of EHC systems developed

according to a classic learning curve shown in

Figure 2. The step change in reliability realized

with the EHC Mark II is attributed to two factors:

the superior reliability of integrated electronics

and the introduction of triple-redundant protection logic described above.

DIGITAL CONTROLS

While GE steam turbines were being shipped 

with these EHC systems through the mid-1980s, in 

the early 1980s, GE’s Gas Turbine Division introduced the very successful triple-redundant digital

control system – the SPEEDTRONIC Mark IV.

The first triple-redundant steam turbine control

system for utility turbines, the DCM system, was