ehtc

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Prepared by:

L.V.A.B

Checked by: Approved by:

P.S.V.S P.S.V.S

Date:

31.12.09REF-DOC HINDALCO-

EHTC-R00.DOC

COPYRIGHT AND CONFIDENTIAL The information on this document is the property of BHEL. It must not be used

directly or indirectly in any way detrimental to the interest of the company.

TITLE: WRITE-UP ON EHTC.

OWNER: HINDALCO INDUSTRIES LIMITED (UNIT: MAHAN AND ADITYA ALUMINIUM) 2X (6X150) MW CAPTIVE POWER PLANT BARGAWAN, DISTT: SINGRAULI & LAPANGA, SAMBALPUR

CUSTOMER:

DEVELOPMENT CONSULTANTS PVT. LTD. CONSULTING ENGINEERS KOLKATA, CHENNAI, MUMBAI, NEW DELHI

REF. DRG. EHTC BLOCK DIAGRAM 3-133-00-62113

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C O N T E N T S

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

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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.

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- 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.

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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

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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

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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

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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”.

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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.

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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”.

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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 PI-content 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.

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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.

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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.

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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.

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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.

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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.

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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

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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

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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

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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.

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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”

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- 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).

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- 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.

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RECORDS OF REVISION

REV.NO.

DATE REVISION DETAILS REVISED APPROVED

00 31.12.09 ISSUE P.S.V.S

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