GESPEEDTRONIC™ MARK V STEAM TURBINE CONTROL SYSTEM

separately driven from each controller, and the

position feedback is provided by three LVDRs.

The normal position of each steam valve is the

average of the three commands from <R>, <S>,

and <T>, respectively. The resultant averaging circuit has sufficient gain to override a gross failure

of any controller, such as a controller output

being driven to saturation. Diagnostics monitor

the servo coil currents and the D/A converters in

addition to the LVDRs.

The third form of voting for the trip solenoids

is discussed under OVERSPEED.

OVERSPEED

The <P> protective controller contains three

independent cards <X>, <Y>, and <Z> with their

own processors and power supplies. This separate

set of triple-redundant electronics with its associated three separate speed pickups replaces the

mechanical overspeed governor. <R>, <S>, and

<T> use the first three pickups for speed control

and the primary overspeed protection, while <X>,

<Y>, and <Z> monitor the second set of three

pickups for emergency overspeed protection

(Figure 3).

In addition, the <X>, <Y>, and <Z> cards contain separate relay drivers and magnetic relays that

perform a final contact vote prior to driving the

turbine trip solenoids. Diagnostics monitor the

status of the output ports, relay drivers, and relays

to initiate maintenance alarms if a failure occurs.

Standard on-line and off-line primary and emergency overspeed trip tests are built in to facilitate

testing all hardware and software. Figure 8 illustrates hardware logic voting of an output from

each of three controllers.

SYNCHRONIZING

Automatic synchronization is performed by the 

<X>, <Y>, and <Z> cards in conjunction with the

<R>, <S>, and <T> controllers. The controllers

match speed and voltage and issue a command to

close the breaker based on a predefined breaker

closure time. Diagnostics monitor the actual breaker closure time and self-correct each command.

Redundant sets of primary and backup phase-slip

windows eliminate the need for the traditional GXS

synchronizing check relay in the generator control

cabinet. Another feature is the ability to synchronize manually via the Mark V operator interface

instead of using the traditional synchroscope on

the generator protective cabinet. Operators can

choose one additional mode of operation by selecting the monitor mode, which automatically matches speed and voltage, but waits for the operator to

review all pertinent data on the CRT display before

issuing a breaker close command.

POWER LOAD

UNBALANCE – PLU

Large steam turbine applications use another

module similar to <P> which is designated <PLU>

for power load unbalance. This provides power

load unbalance protection and interface to the

fast closing feature on control and intercept valves

via three independent cards <U>, <V>, and <W>.

COMMON I/O <C>

A significant amount of I/O on turbines and

generators is used only for monitoring. This nonredundant I/O is monitored by the <C> module.

For example, thermocouples can be used for control and protection or just for monitoring.

Thermocouples which are used for rotor stress calculations are connected directly to the <R>, <S>,

and <T> controllers, while thermocouples that are

used for monitoring only, e.g., the thrust bearing

oil drain temperature, connect to <C>. 

OPERATOR INTERFACE <I>

The interface work station <I> consists of a PC,

color monitor, cursor positioning device, keyboard, and printer. It can be used as the sole operator interface or as a local maintenance work station with all operator control and monitoring

coming from communication links with a plant

distributed control system (DCS). Figure 9 shows

the operator interface schematically. 

Operators use the monitor, cursor positioning

device, and keyboard. The keyboard is not necessary. However, the keyboard is convenient for

accessing displays with dedicated function keys

and adjusting setpoints by entering a numeric

value such as 1,000 rpm rather than issuing a

manual raise/lower command. Set point and

logic commands require an initial selection, such

as the command to engage the turning gear,

which is followed by a confirming execute command. The monitor is available in various sizes

and types, and it can be used for desktop mounting, packaged as a drop-in insert for a control

room console, or mounted in a separate freestanding cabinet. The keyboard is primarily used