WRITEUP ON EHTC

CONTENTS

1. Introduction

2. Electro Hydraulic Turbine controller General arrangement.

3. Tasks of the Turbine Controller.

4. Turbine Startup and Lift Limiter.

5. Speed/Load Regulation.

6. Main Steam Pressure Regulation.

7. Controller Selection Circuit, Formation of Valve Lift Set Points.

8. Trimming Function of HP/IP valves.

9. Valve Lift Controller.

10. Valve Closing Time Measurement.

11. Control Room Signals/Keys/Displays.

REFERENCE P&IDs.

LUBE OIL SCHEME DRG.NO. 2-131-00-90301

TO

INSTRUMENT AIR SCHEME DRG.NO. 2-131-00-90329

HYDRAULIC SUPPLY UNIT DRG.NO. 1-131-00-90309

HP/IP TURBINE SCHEME DRG.NO.1-131-00-90318

TSI SCHEME DRG.NO. 2-133-00-62027

1.0 INTRODUCTION:

The Electro Hydraulic turbine controller (EHTC) is the control system

which controls the steam flow supplied to the steam turbine via the Governor

valves. The controller modulates the requisite control variable (speed, load,

pressure, etc.) for each phase of operation in line with operating requirements.

The development of microprocessor technology makes it possible to equip

turbines with high-availability closed and open controls. Consequently,

mechanical-hydraulic control equipment – previously used very extensively – is

now implemented less and less frequently.

This type of turbine control system demands the use of modern

electrohydraulic actuator (EHAs). These actuators receive and process

electrical signals exclusively. Hydraulic actuators are employed to generate

the large positioning forces and achieve the short positioning times required.

Hydraulic power supply units supply the necessary high-pressure control fluid

(approx. 160 bar) to the actuators. Each power supply unit serves several

actuators.

2.0 ELECTRO HYDRAULIC TURBINE CONTROLLER (EHTC):

The steam turbine controller is a redundant digital control system

consisting of the following main components.

- Turbine start up and lift limiter.

- Speed controller.

- Load controller.

- MS pressure controller.

Valve lift setpoints for the valve lift controllers are formed from the output

of the master controller in controller selection and valve position setpoint

formation circuit.

A dedicated valve position controller, which is subordinate to the master

controllers, is used for each EHA.

The function of the EHTC is described in the following without regard to

redundancy.

3.0 TASKS OF THE TURBINE CONTROLLER:

- The turbine generator is run up from turning speed by the Speed

Controller within the temperature margins calculated by the turbine

stress evaluator (TSE). In addition, holding of turbine generator speed

within critical speed ranges is prevented.

- The turbine speed adjusted to the grid frequency during

synchronization.

- Loading of the turbine generator with the load controller from zero to

target load, in line with permissible load transients. The permissible

load transients are derived from the temperature margins calculated by

the TSE. Fixed transients for loading and unloading can be set.

- Limitation of the turbine generator load as a function of MS pressure

by the limit pressure controller to minimize life – limiting effects on the

boiler mode, so that output and thereby steam flow are set by the

steam generator.

- In case of faults in the steam generator of excessive load demands by

the turbine, the drop in steam pressure is counteracted by throttling

the turbine governor valves with the limit pressure controller.

- System frequency stabilization using a precise frequency-to-load

characteristic (droop) with provision for primary frequency control.

- Controlling full load rejection to zero-load and auxiliary load.

- Controlling step load changes resulting from grid faults and the

resultant new grid configuration. Islanding (operation in parallel to the

power supply system) is possible.

4.0 TURBINE START-UP AND LIFT LIMITER EQUIPMENT (TSL)

MYA01DG020/01,02,03,04,05:

The TSL can be operated from the main control room. The turbine startup

and limiting device (TSL) has the following tasks:

a) Holding and triggering of central tripping system.

b) Providing an analogous position value for each control valve for limiting

the valve position.

c) Providing blocking signals for the actuator unit HP/IP control for the

opening and closing of stop-valves.

The (TSL) guarantees during start-up the sequence: open stop vlv. Before

open cont. vlv and during shutdown the sequence: close cont. vlv before closing

stop vlv.

The TSL is of digital design. It is governed from the control room.

Pre-requisite for the control of TSL is that the system pressure of EHA oil

supply is built up.

The TSL corresponds, in its function, to a ramp generator. Output signal 0 –

100%.

The control is enabled by the two contact switches “Higher” and/or “Lower”.
The ramp-up time of ramp generator in the direction of closing and opening

amounts to T = 60 s for the output signal 0 – 100%.

The signal of the key TSL “Higher” is interlocked in AND with the signal of EHA

oil supply “ready for operation”. The limit signals are interlocked with the key

TSL “Higher” and “Not Lower” and/or “Lower” and “Not Higher”.

The interlocking with TSL “Higher” is necessary, so that no counteracting

operation takes place in case of operating ATT valves. Thus, this interlocking

is provided even for the limit signals.

With the reaching of limit signal the ramp generator is stopped so long, until

the corresponding check-back signal is available.

Only then the next limit signal can be started by actuating further the

respective key (Higher/Lower).

Following Limit signals are generated from the ramp generator.

a) During Startup:

- Hold turb. protn chl 1/2 at 12.5%.

- Hold individual turb. protn. chl 1/2 for stop vlv. at 27.5%.

- Hold individual turb. protn. chl 1/2 for cont vlv. at 32.5%.

- Pilot valve to the stop vlv closed at 42.5%.

b) During Shutdown:

- Pilot valve to the stop vlv open at 37.5%.

- Trigger individual turb. protn. chl 1/2 for cont vlv. at 27.5%.

- Trigger individual turb. protn. chl 1/2 for stop vlv. at 17.5%.

- Trigger turb. Trip. chl 1/2 at 7.5%.

The output of TSL is provided for each HP/IP control valve and connected to

the pertinent position setpoint formation for processing in the position

setpoint formation the control range for the cont. vlv must be adjusted.

Standardization of the adjustment:

46% to 90% = - 10 to 105% cont. vlv

5.0 SPEED / LOAD REGULATION

5.1 SPEED SETPOINT FORMATION (MYA01DU001/02)

5.1.1 SPEED SETPOINT

The speed setpoint is set from the control room by manual control in the

control room or by the subgroup control (SG) “turbine control”, which controls
a speed ramp. A synchronizer is available for synchronizing the turbine speed

with system frequency. This adjusts the speed setpoint by means of manual

control. The manual interferences are preferred to automatic signals.

Setting range : 0 to 55 s-1.

The adjustable rate of change of speed ramp is converted in case of

transgression of a speed setpoint. Besides, a switch-over takes place in case

of generator circuit-breaker “ON” position.

Time constant of speed ramp:

- in the range of 0 to 49 s-1

Setting range : T = 25s for 50 s-1

Initial setting : T = 120s for 50 s-1

- In the range greater than 49 s-1 or gen. ckt. Brk “ON”

Setting range : T = 100s to 1000 s

Initial setting : T = 1000s for 50 s-1

By pressing the over speed test enable, PB, the upper limit of speed ramp

is increased.

5.1.2 CORRECTION OF SPEED SETPOINT:

The speed setpoint is corrected during response of following signals:

- Turbine trip “responded”.

to speed actual value minus an adjustable distance.

setting of distance

setting range : 0.5 s-1 to 2 s-1

Initial setting : 0.5 s-1

The response of turbine trip is stored. The resetting of memory takes place

by “enable” command from control room. During load operation above a

minimum load, the speed setpoint is automatically set to a higher value (50

rev/s + auxiliary power requirement). This results in speed control deviation

which is converted by the speed droop of the speed controller to a load level

corresponding to the auxiliary load requirement. In the event of load

rejection to aux. load, the turbine is regulated exactly to rated speed.

On response of speed gradient monitoring operation, the speed setpoint is

automatically decreased to holding speed. In all cases the speed ramp is

switched over from s=0 to s=1. The logic signal “s” has the following
significance.

s=0 -> integrated

s=1 -> output = input

5.1.3 SPEED TRANSIENT MONITORING:

In the limit range greater than 16.7 s-1 and less than 49-1 s-1, the

transient monitoring system responds, if the transient falls below a limit valve

dn/dt < 0.025 s-1/s.

In this case the speed setpoint is switched over to the holding speed.

The response of speed transient monitoring is indicated in the control room.

5.1.4 SETPOINT CONTROL:

The rate of change of speed setpoint is set by means of time constant of

setpoint control.

Setting range : T = 100 s to 1000 s for 50 s-1

Rate of change : 0.5 s-1/s to 0.5 s-1/s (at 100% input signal at integrator)

Initial setting: T=300 s. Rate of change = 0.167 s-1/s (at 100% input signal at

integrator)

If generator circuit breaker is “ON”, the time constant is changed to T=600s. If

there is no limitation of TSE the difference between un-delayed and delayed

speed setpoint is increased by the factor 100. Thus, the setpoint control runs

with maximum rate even in case of small setpoint changed (1%).

The output signal of the setpoint control generates the speed setpoint for the

speed/load control.

5.1.4.1 WT-INFLUENCE (TSE-INFLUENCE):

The time constant of setpoint control and thus the permissible rate of change

is limited as per TSE margins. The temperature margins holds good for the

following:

0 to 30 Kelvin (K) = 0 to 100% = kp = 0 to 1

0 to -30 Kelvin (K) = 0 to 100% = kp = 0 to –1

The following holds good in no-load operating for setpoint increase.

a) WT-influence “ON” :kp = dTu (turbine)

b) WT-influence “OFF” :kp = 1 (100%)

The following holds good in no-load operation for setpoint decrease:

a) WT-influence “ON” :kp = -1 (100%)

b) WT-influence “OFF” :kp = -1 (-100%)

In the load operation with speed controller the temperature-dependent load

margin is standardized to speed and it holds good for setpoint increase:

a) WT-influence “ON” :kp = dTu (turbine)

b) WT-influence “OFF” :kp = 1 (100%)

In the load operation, the following holds good for setpoint control.

a) WT-influence “ON” :kp = dT1 (turbine)

b) WT-influence “OFF” :kp = -1 (-100%)

The WT-influence can be switched on and off (See fig.3)

5.1.4.2 STOP OF SETPOINT CONTROL:

The setpoint control of speed is stopped during response of following signals:

- WT-influence “ON” and WT-influence “disturbed” or

- Generator circuit-breaker “OFF” and difference between delayed speed

setpoint and speed actual valve greater than + 0.34 s-1 and speed

setpoint “active”.

5.2 SPEED ACTUAL VALUE (Fig 4, MYA01DU001/04):

The speed actual value acquisition takes place in the overspeed protection. 3

speed actual values (KKS: MYA01CS014-16) are provided for speed regulation.

The effective speed actual value is generated by means of a selection of the

mean value from 3 (Mv3).

A monitoring of speed actual value also takes place by Mv3. In case of failure

of a channel, the channel with the maximum speed is connected to the output

of the Mv3. In case of failure of 2 channels, the proper channel as per the

monitoring is switched to output. The response of monitoring leads to a fault

signal “speed actual value recording DISTURBED”.

5.3 LOAD SETPOINT GENERATION (See Fig 3) MYA01DU001/03:

5.3.1 LOAD SET POINT

The load setpoint selection takes place by means of manual control in the

control room,

The time constant of ramp amounts to :

Setting range : T = 10 s to 200 s for 100% load

Initial setting : T = 60 s for 100% load

It is possible to set the load from external setpoint.

Automatic matching of speed and load setpoints is performed prior to change

over from load operation with speed controller to load operation with load

controller. This ensures bumpless transfer from load operation with speed

controller to load operation with load controller and vice versa.

5.3.1.1 CORRECTION OF LOAD SETPOINT:

In case the load control is switched “OFF”, the load setpoint is set to –10%.

On reactivation of load control, the load setpoint is set to the value of delayed

speed setpoint converted to an equivalent load level.

If the TSE influence is “ON” and it is “disturbed”, the load setpoint is stopped.

During Initial pressure operation, the load set point tracks the actual load.

5.3.1.2 SETPOINT CONTROL OF LOAD:

The rate of change of load setpoint is set by means of time constant of setpoint

control.

Setting range : T=200 s to 2000 s for 100% load.

Rate of change = 0.5% load set point/s upto 0.05% load setpoint/s (at 100%

input signal at integrator)

Initial setting: T=600 s for 100% load

Rate of change = 0.167% load setpoint/s

(At 100% input signal at integrator)

Thus, the setpoint control also runs with maximum rate in case of small

setpoint (1%). If there is no limitation of WT-free volume, the difference

between undelayed and delayed output setpoint is increased by the factor 100.

5.3.1.3 WT-influence (TSE Influence):

The time constant of setpoint control and thus the permissible rate of change

is limited depending on TSE margins.

Following holds good for the temperature margins:

0 to 30 Kelvin (K) = 0 to 100% ~ Kp = 0 to 1

0 to -30 Kelvin (K) ~ 0 to -100% ~ Kp = 0 to –1

In case of setpoint increase, the following holds good

c) WT-influence “ON” :kp = dTu (turbine)

d) WT-influence “OFF” :kp = 1 (100%)

In case of setpoint decrease, the following holds good:

a) WT-influence “ON” :kp = dT1 (turbine)

b) WT-influence “OFF” :kp = -1 (-100%)

The WT-influence can be switched ON and OFF (see Fig-3). The effective value

for Kp can be limited manually by means of a minimum and maximum value

selection. (ref pt 5.3.1.4)

5.3.1.4 MANUAL TRANSIENT SETTING:

The rate of change of setpoint control can also be limited manually for setpoint

increase and decrease (together). The transient setting takes place in the

control room by means of a manual control, which controls a speed ramp.

The ramp setting is T = 30 s for 100%.

The transient setting can be switched ON and OFF by means of a key

“transient setting ON/OFF” in the control room. The state is stored (OFF

precedes ON).

The limitation of rate of change of setpoint control by WT-influence and

transient setting manually works in opening direction in minimum value

selection and in closed direction in maximum value selection.

5.3.1.5 STOP OF SETPOINT CONTROL:

The setpoint control of load is stopped during response of following signal:

- WT-influence “ON” and WT-influence “DISTURBED” or

- “Limit pressure reached”.

5.3.1.6 CORRECTION OF LOAD SETPOINT:

In initial pressure mode the load setpoint is set to the target load setpoint.

5.3.1.7 LIMITATION OF LOAD SETPOINT:

A manual control is available in the control room for the limitation of load

setpoint, which controls a speed ramp. Initial setting T = 60 s for 100% load.

5.3.1.8 LOAD SETPOINT ON/OFF (MYA01DU001/08):

An automatic switch-off of load setpoint takes place, if following criteria

respond in case of load rejection (e.g. due to a three-phase fault in the grid):

Generator actual load < 2 * auxiliary power (EB) and

Generator actual load > -1% PN (Reverse power) and

Deviation between load setpoint and generator actual load > 5%.

The reconnection of load setpoint, in case of generator circuit-breaker ON,

takes place automatically, if the generator actual load leaves the output range

between 2 * auxiliary power and –1% reverse power. The switching in at –1%
reverse power is necessary, so that the turbine generator unit can have

opposite effect to these in case of output swings in reverse power range.

During load rejection (load jump) greater than 70%, the load setpoint is

switched OFF. The input signal for setpoint control is changed over to –10%

on receipt of ‘Unload’ signal from automatic or by open signal from generator

breaker. This allows the Plant to be run down by the automatic with the

load controller to a level at which reverse power protection responds. The

output of setpoint control set to OFF on receipt of generator breaker OFF

signal.

5.5 LOAD ACTUAL VALUE:

The generated actual load (z channel) is acquired by means of load

transducers (KKS: MKA02FE001 A/B /C). The analog signals are signified for

further processing.

5.6 SPEED-LOAD REGULATOR (MYA01DU001/04):

The regulation of speed and load takes place by means of common speed-/load

regulator. Proportional gains (K2 and K3) are available parallel to common PIcontent

of speed-/load regulator for deviation of speed regulation and load

regulation. The input signal of the speed-/load regulator is generator from the

increased (K1) deviation of speed regulation plus effective load setpoint minus

load actual value. In the load operation, i.e. in generator circuit-breaker “ON”,

the frequency influence has effect on the speed/load regulator instead of

deviation of proportional speed regulations.

5.6.1 SPEED REGULATION DIFFERENCE (K1) FOR SPEED/LOAD CONTROLLER

AND LIMIT FREQUENCY INFLUENCE FOR SPEED – LOAD:

The difference from the effective speed setpoint minus speed actual value

forms the speed regulation difference for the speed-/load regulator by means

of an adjustable gain.

Setting gain

Setting range : K1 = 10 to 30

Initial setting : K1 = 20

During load operation, i.e. when load setpoint “ON” and load operation with

load controller, the speed difference is limited by limit frequency characteristic

and increased by proportional gain K1.

Limit frequency characteristic/Dead Zone : ± 0.25s-1(Setting range : 0 to ± 1s-1)

Gain : V=1

5.6.2 PRIMARY FREQUENCY INFLUENCE (Static):

For a frequency back-up control, the speed actual value is applied negative to

a fixed value of 100% (50 s-1) speed setpoint.

The difference through a non-linear filter effecters the speed/load regulator

by means of a static-characteristic in case of generator circuit-breaker “ON”.

The primary freq. component can be activated from control room.

5.6.3 SPEED/LOAD REGULATOR:

Transfer function : PI-action with adjustable parameters

1 + pTN

F(p) = Kp -----------------

PTN

Setting range Initial setting

Kp = 0.1 Kp = 0.1

TN = 1 s to 10 s TN = 1 s

5.6.3.1 LIMITING OF SPEED/LOAD REGULATOR:

In case the MS pressure controller or the Turbine startup and lift limiter

assumes control of the turbine, the upper limit of the speed/load controller in

changed over to the position setpoint signal +2%. This ensures that the upper

limit is tracked to the position setpoint signal with a constant margin of 2%,

for optimal transfer back to the speed/load controller a later time.

5.6.4 GENERATION OF POSITION SETPOINT OF SPEED/LOAD (See Fig 4)

MYA01DU001/04

An increased load setpoint (K3), increased speed difference (K2) is applied

positive to the output signal of speed/load regulator for the generation of

position setpoint of speed/load.

5.6.4.1 PROPORTIONAL INCREASE OF DIFFERENCE OF SPEED

REGULATION (K2):

The difference from effective speed setpoint minus speed actual value

influence the generator of position setpoint of speed/load by means of gain K2

Setting range : K2 = 5 to 20, Initial setting : K2 = 10

On switch over to load operation with load controller K2 is changed to K2=1.

5.6.4.2 PROPORTIONAL GAIN OF LOAD SETPOINT (K3):

The effective load setpoint influences the generation of position setpoint of

speed/load by means of gain K3

Setting range: K3 = 0.5 to 1, Initial setting: K3 = 0.9

6.0 MAIN STEAM PRESSURE REGULATION (MYA01DU001/05):

6.1 MAIN STEAM-PRESSURE SETPOINT:

The main steam pressure setpoint is provided by the boiler regulator.

6.2 INITIAL PRESSURE AND LIMIT PRESSURE OPERATION:

Corresponding keys are provided in the control room for the selection of initial

pressure or limit pressure operation. The state is stored (OFF precedes ON).

In limit pressure operation “ON”, the main steam pressure setpoint is trimmed

downwards by an adjustable amount (response threshold). The main steam

pressure regulator drifts into the 105% position and operates only in case of

pressure actual valve falls below an adjustable limit.

The application of response threshold takes place by means of a speed ramp.

The time constant of speed ramp:

Setting range : T = 20 s to 200 s for 100% main steam pressure.

Initial setting : T = 40s for 100% main steam pressure.

In case of initial pressure operation “ON”, the application of response

threshold is set to zero.

The resetting takes place by means of speed ramp.

6.3 MAIN STEAM PRESSURE VALUE:

The main steam pressure before main steam emergency stop valve is recorded

for MS-actual value generation by means of a pressure transducer. The

pressure actual value should be digitized for further processing.

In case for need, the pressure actual value can be applied to pressure

regulator by means of a lowpass filter. Hereby, fast pressure fluctuations are

smoothened.

6.4 MAIN STEAM PRESSURE REGULATOR:

Transfer function : PI – action with adjustable parameters.

F(p) = Kp 1 + pTN

-------------

pTN
Setting range Initial setting

Kp = 5 to 50 Kp = 5

TN = 3 s to 30 s TN = 10 s

Operating range : 0 to 105% position setpint of main steam pressure.

The output signal of MS-pressure regulator generates the position setpoint of

main steam pressure.

6.5 LIMITING OF MAIN STEAM PRESSURE REGULATOR:

When the pressure control deviation falls below minimum value, the limitation

of the pressure controller is tracked to the operating position setpoint of HPCV

+ 2%.

7.0 CONTROLLER SELECTION CIRCUIT, FORMATION OF VALVES POSITION

SET POINTS:

7.1 CONTROLLER SELECTION:

The output signals of the master controllers (speed/load controller, MS

pressure controller as well as the start-up and lift limiter) are minimum signal

selected such that only one controller is effective.

An identification module determines which controller is active and display

this.

Each governor valve can be individually closed and opened (lift limitation) from

the control console or by the automatic turbine tester (ATT).

7.2 FORMATION OF POSITION SET POINT FOR MAIN SEAM CONTROL

VALVES (MYA01DU001/09):

Following control equipment are selected in minimum value selection for the

formation of position setpoint of main steam control valves (HPCV).

- Position setpoint speed/load.

- Position setpoint main steam pressure.

- Position setpoint of TSL.

Finally a main steam pressure-dependent position setpoint correction and a

connection of trimming after free volume takes place. This position setpoint so

generated is taken for the generation of position setpoint of main control

valves 1 and 2.

7.2.1 MAIN STEAM PRESSURE-DEPENDENT POSITION SETPOINT

CORRECTION:
A position setpoint correction is available in order to facilitate the maintenance

of proportional allotment between steam flow through the turbine control

valves and position setpoint of turbine control st sliding main steam pressure.

The position setpoint correction takes place as per the following equation:

Hs turbine control

Hs turbine control = --------------------------------- A [%/(bar) bar]

Main steam pressure

A corresponds to the maximum main steam pressure.

7.2.2 An adjustable fixed valve is applied positive to the output signal of point 7.2.1

of a preference of HP-CV1.

Setting range : 0 to 10% position setpoint

Initial setting : 0% position setpoint

This position setpoint works as input signal of formation of characteristic by

means of a minimum/maximum value selection with the position setpoint of

drive individual control. The position setpoint of drive individual control is

applied to the maximum value selection only in case of control valve testing by

the ATT. The starting signal is made available by the ATT.

7.2.3 Position setpoint HP CV2 corresponds to that of position setpoint HPCV1

without preference.

7.3 POSITION SETPOINT FOR THE INTERCEPT CONTROL VALVES

(MYA01DU001/10):

For position generation of intercept control valves (IP-CV) the position setpoint

of HPCV of point 7.2.1 is matched in case of plants after trimming by means of

a characteristic for beginning of opening and OPEN-position.

7.3.1 CHARACTERISTIC FOR STARTING OF OPENING AND OPEN-POSITION:

The position setpoint main steam-CV is matched by means of a characteristic

for starting of opening and OPEN-position for the position setpoint formation

of intercept control valve.

- Setpoint of starting opening.

- Setting range : 0 to 100% turbine controller output.

- Initial setting : Value A ~ 10%.

- Setting OPEN-position.

Setting range : 0 to 100% turbine controller output.

Initial setting : Value B ~ 60%.

7.3.2 TRIMMING AS PER THE HP-EXHAUST STEAM TEMPERATURE

(MYA01DU001/14):

A signal for the application to position to position setpoint of intercept-control

valve is made available by trimming as per HP-exhaust steam temperature.

This signal is applied negative to the position setpoint of main steam control

valve.

7.3.3 POSITION SETPOINT INTERCEPT-CV (MYA01DU001/10):

The output signal of the characteristic or the minimum value selection

operates by means of a minimum value selection with the position setpoint

drive control as input signal of formation of characteristic. The position

setpoint of the drive individual control is applied directly only in case of

control valve testing by the ATT. The closing signal is made available by the

ATT.

7.4 ELECTRICAL CHARACTERISTIC COMPENSATOR FOR COMPENSATING

NON-LINEAR STEAM-VALVE CHARACTERISTICS (MYA01DU001/12):

The turbine control valve posses a non-linear, steady-state characteristic of

the steam flow through the valve stroke. This characteristic is compensated

by the characteristic compensator. It produces a linear relationship between

the steady-state conditions of its input variable and those of the steam flow.

A separate characteristic compensator is assigned to each positioning

regulator and thus to each turbine control valve.

The characteristic compensator a digital functional module with 10 divisions

in which the characteristic is accomodated. The pitch divisions should be

possible in varying lengths, so as to achieve smaller divisions in areas of

greater changes of amplifications.

8.0 TRIMMING FUNCTION FOR HP/IP VALVES(See Figure –14

MYA01DU001/14):

The valve lift configurations of the main steam valves relative to the reheat

valves depends on the correlation between steam condition in the main steam

system and in the reheater in various operating statuses (start-up, shutdown

and load rejection).

Normally, a configuration is calculated and this set. However, fixed

configurations result in longer start-up times due to con-optimal utilization in

terms of time for the margins from the TSE.

To obtain time-optimal response of the turbine generator during start-up, and

to keep the HP exhaust steam temperature below a permissible limit during

this process, an HP exhaust steam temperature limit controller is provided in

the turbine controller.

If HP exhaust steam temperature increases at an unacceptable rate, the

controller changes the valve lift configuration of the main steam/reheat valves

via a setpoint correction applied to the lift setpoint of the reheat valves,

thereby throttling the valves.

The HP exhaust steam temperature limit controller features PI action.

Activation of the controller is indicated in the control room by the

annunciation for HP exhaust steam temperature controller activated.

9.0 POSITION CONTROLLER (FIG-13) MAA12DG001 / MAA22DG001 /

MAB12DG001 / MAB22DG001 / MAA32DG001:

Each governor valve has a dedicated valve position controller.

The controller has following transfer functions:

F(p) = Kp (1+PTN)/PTN ; Kp = 0.01 to 1, σN = 1 to 100s

9.1 POSITION SETPOINT:

The following position setpoint corresponds to the output signal of the

characteristic curve formation.

9.2 POSITION ACTUAL VALUE:

9.2.1 POSITION ACTUAL VALUE ACQUISITION:

For acquiring the position actual value, the piston position of the EHA is

recorded by means of analog position transducer.

The position transducer is so selected that maximum drive lift is obtained.

The maximum drive lift is larger/equal to the valve lift plus a negative and

position over travel.

Before the digitization of position transducer signal, the current signal of

position transducer is converted through an I/U-converter into a voltage

signal.

9.2.2 A/D-CONVERTER:
The analog position transducer signal is converted through a A/D-converter

into a digital signal.

9.2.3 POSITION ACTUAL VALUE MATCHING:

For matching the position transducer signal with the valve lift-valve lift is

always smaller than the measuring length of position transducer – a

characteristic curve is available.

Signal Adjustment: 0 to 50 mm (for HPCV), 0 to 95 mm (for IPCV) position

transducer = 0 to 100% valve lift = 0 to 100% position actual valve.

9.2.4 MONITORING OF POSITION TRANSDUCER SIGNAL:

In case of failure of position transducer signal at 4mm –no more operating

area of valve lift - a closing signal for the servo-valve of –2% constant is

specified. Besides, a fault signal “position actual value distributed” is given.

The response of monitoring is stored (OFF has priority over ON), it can be

restored through an acknowledgement key. So that the acknowledgement key

has no priority over the disturbance, a bypass of memory is available.

9.3 ACTUATOR:

9.3.1 TRANSFER FUNCTION:

P-characteristics with adjustable parameters

F(p) = Kp

Control range Initial adjustment

Kp = 10 to 40 Kp = 20

Operating area : -100 to 100% actuator output.

9.3.2 ACTUATOR LIMIT:

A limit of maximum positive and negative actuator output signal and of the

servo-valve current is available. Besides, the actuator output is limited to 10%

during transgression of an adjustable position actual value by 90%.

9.3.3 CORRECTION OF THE ACTUATOR:

Thanks to the high actuator gain in case of small errors in digitization of

actual value in an actuator, it results in large differences of the 3 actuator

output signals. To avoid this, difference from Mv3 of the 3 actuator output

signals and the output signal of actuator is applied to the actuator input,

through an amplification adjustment (V=1/Kp) as a synchronous correction

signal.
9.4 DITHER SIGNAL:

A dither signal, adjustable in amplitude and frequency, is applied to the

actuator output signal.

9.5 D/A-CONVERTER:

The digital output Signal of actuator is converted through a D/A

- converter into an analog signal.

Signal conversion:

-100 to 100% actuator output = -10 to 10V actuator output

9.6 CONTROL SERVO VALVE:

The 3 analog delayed actuator output signals controls a U/I – converter

through an Mv3. The output signal of U/I – converter is restricted to

maximum control coil current through the servo-valve.

Mode of working of Mv3:

The Mv3 selects the mean signal and connects it to the output. Depending

upon the output signal, if an input signal transgresses a specified tolerance

band, the this input signal is disconnected within the Mv3 and it is replaced

by a constant of 0%. This way the Mv3 works like a minimum value selection

for the two remaining signals. The failure of a channel in indicated by a fault

signal “actuator disturbed” Tolerance band: means actuator output ± 2V.

9.6.1 U/I-CONVERTOR:

The voltage signal is given by the U/I converter is an impressed current.

Signal conversion: -10 to 10V = -20 to 20 mA.

9.6.2 LIMIT OF CONTROL COIL CURRENT:

The control coil current is limited to ± 18 mA of the maximum control coil

current. This takes place through the diodes in the supply lines.

9.6.3 SERVO-VALVE:

The servo-valve (KKS:.MA.AA012) is designed with 2 control coils, which are

connected in parallel (for reasons of availability).

rated current per coil : 7.5 mA

resistance per coil : 200 Ohm

inductance per coil : 2 Henry

9.7 HIGH SPEED CONTROL:

If the difference from the position setpoint before the valve characteristic curve
and the position actual value led through a reciprocal valve characteristic

curve in the closing direction falls shorts of an adjustable limit signal, then the

pertinent partial turbine tripping control valve is actuated.

Limited signal:

Control range : -10 to –40% Xd

Source adjustment : Xd < -25% (release position Xd > -25%)

From the response of the high speed control of live steam control valve 1, the

high speed drive is actuated by the intercepting control valve 1 and from the

live steam control valve 2 the high drive is actuated by the intercepting control

valve 2 in parallel.

For the partial Trip release mechanism, the 3 signals of 3-channel actuator are

combined in 2-of-3 circuit arrangement (relay technique).

By changing-over to the manual setpoint, the actual control difference (signal

before the actuator) becomes effective for controlling the high sped drive. This

signal is combined with a minimum valve position (source adjustment) = 3%

opening actual value) in AND-function.

9.8 CONTROL “ACTUATOR OUTPUT +100%”:

From the program outage (pressure relief) the subgroup EHA oil-supply

turbine valves, the actuator output is switched to +100%.

9.8 CONTROL “ACTUATOR OUTPUT –100%”:

In partial trip control valve K1 or K2 TRIPPED, the actuator output of the

pertinent actuator is connected to –100%.

9.9 SIGNAL “TURBINE GOVERNING SYSTEM DISTURBED”:

The generation of the control room signal “Turbine governing system

disturbed” results for the following individual signals:

- Fault signal “position actual value disturbed”.

- Fault signals “actuator disturbed”.

- Fault signal “internal 15-V power supply disturbed”.

From the failure of each internal 15-V power supply a fault signal each is

indicated “internal 15-V power supply actuator disturbed”.

9.10 VALVE LIFT DISPLAY:

The valve lift display is obtained from the adjusted position actual value.

9.11 SIGNAL FOR ATT VALVES (FIG-20 MAA12DG010 / MAA22DG010 /

MAB12DG010 / MAB22DG010 / MAA32DG010):

From the position actual value, the signals larger than 98% and smaller than

2% are available for automatic turbine testing facility.

10.0 VALVE CLOSING TIME MEASUREMENT (FIG-21: MYA01DK080):

In the course of the test program for the automatic turbine tester (ATT), the

closing times of the emergency stop and governor valves are measured

sequentially.

11.0 CONTROL ROOM SIGNALS/KEYS/DISPLAYS (MYA01DU001/07):

11.1 FAULT SIGNAL:

The generation of fault signal “turbine governing system DISTURBED”, which

is indicated in the control room, takes place from following individual signals.

- Speed actual “DISTURBED”

- Load actual “DISTURBED”

- Pressure actual “DISTURBED”

- Pressure setpoint “DISTURBED”

- WT-influence “DISTURBED”

- Position controller (MV3) HP-CV “DISTURBED”

- Position controller (MV3) IP-CV “DISTURBED”

- Position controller (MV3) OL-CV “DISTURBED”

11.2 CONTROL ROOM:

Following displays, operating keys and signal are provided in the control room

for turbine governing system.

11.2.1 DISPLAYS / INDICATIONS FOR THE FOLLOWING:

- For delayed and undelayed speed setpoint (total range)

- For speed setpoint (magnifying lens in rated speed range and load

operation)

- For speed actual value.

- For un-delayed and delayed (Effective) load setpoint.

- For limit load setpoint.

- For load setpoint transient.

- For generator actual load.

- For MS-pressure setpoint.

- For deviation of MS-pressure control.

- For position setpoint of MS-cont. vlv

- Display per manual position setpoint. (For each drive control)

- For position setpoint TSL.

- For main steam control valve lift.

- For IP control valve lift.

- For HP Exhaust Temp setpoint and actual value.

- For overload control valve lift.

11.2.2 OPERATING KEYS & STATUS SIGNALS:

- Keys for TSL “higher” and “lower”

- Keys for speed setpoint “INCREASE/DECREASE”

- Keys for limit load setpoint “INCREASE DECREASE”

- Keys for load setpoint transient “INCREASE DECREASE”.

- Keys for load setpoint transient “ON/OFF”.

- Key for manual load setpoint “INCREASE/DECREASE”.

- Key for initial pressure operation “ON”.

- Key for limit pressure operation “ON”.

- Key for Frequency influence “ON”.

- Key for WT-influence “ON/OFF”.

- Key for load for load opn. with spd/load controller (Operation mode

selection).

- Key for setpoint enable (reset stop setpoint).

- Key for Overspeed test enable.

- Key for initial pressure operation ON/OFF.

- Key for lift limit setpoint “INCREASE/DECREASE”.

- Key for HP exh. Temp. limit controller “ON / OFF”.

- Initial pressure operation ON/OF.

- Status signal “external load setpoint ON/OFF”.

- Status signal “Load setpoint of system regulation ON/OFF”.

- Status signal “Load setpoint ON/OFF”.

- Status signal “WT-influence ON/OFF”

- Status signal “MS-pressure WITH/WITHOUT FILTER”.

- Status signal “Initial/limit pressure operation ON”.

- Signal “Speed difference > max”.

- Status signal per MS-ESV CLOSE/OPEN.

- Status signal per IP-ESV CLOSE/OPEN.

- Signal “Speed/regulator active”.

- Signal “TSL Control active”.

- Signal “Load regulator active”.

- “Main-steam pressure regulator control active”.

- Signal “Load operation with speed controller ON”.

- Signal “dn/dt monitoring RESPONDED”.

- Signal “setpoint control of speed STOP”.

- Signal “limit pressure reached”.

- Fault signal “turbine governing system DISTURBED”.

- Status signal “Initial pressure “ON/OFF”.

- Signal for “HP Exhaust Temp limit regulator “DISTRUBED”.

- Status signal “All stop valves opened”.

- Status signal “All stop valves closed”.

- Status signal “Part trip vlv ch1 1/2 triggered”.

- Status signal “Part trip control vlv ch1 1/2 triggered”.

- Status signal “Part trip vlv ch 1/2 hold”.

- Status signal “Part trip vlv ch11/2 hold”.

- Status signal “Reheat min. pr. control active”.

- Status signal “HP exhaust temp. limit control in operation”.

11.3 ALARM ANNUNCIATIONS:

Faults in sensors, cabling, power supply or I & C equipment are monitored.

Fault alarm are gated in the cabinet to output a group alarm for turbine

controller fault and indicated by the cabinet alarm lamp. The message is also

output to the power plant alarm annunciation system in the form of a static

and a dynamic alarm.

A pushbutton is located in the control room. Stored alarms can be reset by

pressing this button.