turbine

governing

DEH

To regulate the speed of the Turbine at various loads in a isolating set

To regulate the load as per the frequency demand when working in a grid network.

To prevent and protect the turbine from over speeding.

To allow on line testing of various safety protections .

To enable the tripping of TG set in the event of actuation of protections.

Safe and healthy loading of the TG Set

Nozzle Governing Throttle governing Bypass Governing

Governing is effected by varying the amount of steam which is further done by changing the positions of control valves.

Any Throttling of Steam will lead to losses . In governing system along with the change of quantity of steam the quality of the steam also changes. Therefore Throttling should be minimum

THRO

TTLE

GO

VER

NIN

GN

OZZ

LE G

OV

ERN

IMG

All the valves in a set opens or closes simultaneously / together

It is a Full arc Admission Turbine It is most suitable for full load or based

Load plants No operational Problems

The Valves in a set opens or closes consequentially or in a sequence

It is a Partial Arc admission turbine except at full Load.

It is good for Low load or variable load turbines.

May have operational Problem at partial Loads

It is employed in small capacity turbines running on high pressure conditions and with small blading dimensions.

Here the loading up to appx 80% ( Economic loading ) is met by normal control valves feeding the First stage. For higher loading , to supply more steam which is not possible due to small blading dimensions ( can lead to operational problems) the extra quantity of the steam is fed to the intermediate section of turbine bypassing the initial high pressure stages.

Constant Pressure Mode: Here pressure upstream of control valves is kept constant and change is made by changing the position of control valves.

Variable Pressure mode: Here control valves are in full open position and pressure upstream of control valves varies proportionately with the load requirement.

Response of Constant pressure Mode is much faster than Variable pressure mode, but Constant pressure leads to more losses.

Mechanical: Transducer is mechanical centrifugal speed governor which actuates controls valves through mechanical linkages.

Hydro mechanical: Here transducer is a centrifugal speed governor .It is connected to a Hydraulic system where the signal is amplified so that Control valves servomotor can be actuated.

Hydraulic: Here speed transducer is a centrifugal pump whose discharge pressure is proportional to square of speed. This signal is sent to hydraulic converter which generates a signal which is proportional to valve opening/Closure is required. Before applying it to control valves servomotor this signal is suitably modified.

Electro Hydraulic : Here transducer can be electrical or Electronic. The generated signal after processed electronically and electrically is fed to a Electro-hydraulic converter which converts electrical signal into Hydraulic signal. Hydraulic signal before applying to control valve servomotor is suitably amplified

With continuous development of computer technology, microprocessor based DCS control has been widely used.

This 150 MW Digital electro-hydraulic control system jointly developed by Dongfang steam turbine works and SYMPHONY

Regulation % of Turbine is defined as (No load Speed - Full Load speed) X 100 % ( Nominal Speed) It varies from 2.5% to 5% Normally it is 4.5 % Turbine having less regulation will be more

sensitive in the grid and hence will share more load and vice versa

Normally base load plant has high regulation and Peak load plant has small regulation.

Turbine latching means the process to make the protection system of steam turbine entering into security mode.

Allowable conditions for turbine latching Steam turbine is tripped. All main steam valves are full closed. When condition is satisfied, allow to latching. After DEH receives the

order of turbine latching, relay is energized to close, so resetting solenoid valve

1YV is energized for switching into flowing. Turbine lube oil enters into emergency tripping device, to push levers

moving. The MSV & RSV oil supply solenoid energized 15YV,16YV,21YV and

22YV. The return oil of HP safety oil to the oil tank is shut off, PS1, PS2, and

PS3 will send out signals, and the pressure of HP safety oil is built up. At the same time, HP tripping solenoid valve 5YV,6YV, 7YV, 8YV are

energized

PS-1 PS-2 PS-3

1YV

2YV

ZS-1

ZS-4ZS-5

4YV

ZS-2

ZS-3

This turbine's mode of start is HIP START In 150MW Unit, two HP MSVs and four HP CVs are used for

controlling HP steam admission, and two RSVs and two IP CVs are used for controlling IP steam admission. Hydraulic actuator mechanisms are used for driving the above CVs to ensure rapid action and high positioning accuracy.

The working speed of ST is 3000r/min. The speed of ST will vary with the load in grid. After the speed measurement loop of ST regulation system measures the actual speed of ST and compares it with rated speed (3000 r/min), the opening of HP and IP CV and ICV will be controlled.

In order to ensure safe operation of ST, the hydraulic system is also fitted with several sets of redundant protection assembly:

Emergency tripping device and testing solenoid valve HP and LP tripping solenoid valves

Over speed limiting solenoid valves

Automatic Judgment of Thermal State Start-up of ST is a process during which ST and rotor are heated. In order

to reduce the thermal stress during start-up procedure, different starting curves are adopted for different initial temperature.

DEH will automatically identify the thermal state of unit according to the temperature (T) of inner upper wall of HP inner casing at regulation system each time closing switch. In case the temperature of upper wall is bad, it will automatically be replaced by the one of lower wall.

T≤150°C Cold state 150°C<T<300°C Warm state 300°C≤T<400°C Hot state 400°C≤T Excessive hot state 2 Start-up mode The start-up mode of the unit-HIP combined start

Before grid-connection of steam turbine-generator units, DEH is speed closed loop isochronous control system. Its set point is a demand speed. The difference between the demand speed and actual speed, after calculated with PID regulator, by controlling the opening of oil servo motor by means of servo system, enable the actual speed to follow the variation of the given speed.

After target speed is set, the given speed will approach to the target speed at a specified raising speed rate. When it enters into the critical speed zone, the raising speed rate will be automatically changed into 400r/min/min to pass through the critical speed zone quickly. During raising speed, the steam turbine normally needs to be warmed up at moderate speed or high speed, in order to reduce thermal stress.

Target speed Except that operators set target speed through OIS, DEH may automatically set target

speed under following conditions: When steam turbine is just latched, the target is current speed When breaker open, the target is 3000r/min; When steam turbine is tripped, the target is zero. When the target exceeds the upper limit, it will be changed into 3060 or 3360r/min;

When the unit is at ATC mode , the target speed is determined by ATC During synchronization, the target will change with synchronization increasing or

decreasing signals (change rate：60r/min/min); If the target is set by mistake at the critical zone, it shall be changed as a specified critical value.

Grid-connection & increasing load and normal control load Synchronization After the units come to constant speed, with the interface with auto synchronization

device, DEH can receive increase or decrease signals from the auto synchronization device, and control the speed of units to realize a quick synchronization.

In case one of following conditions occurs, the auto synchronization mode will Exit Speed < 2985 or > 3015r/min;

Grid-connection with initial load When all grid-connection conditions are met, DEH will immediately increase the set value,

to have the generator operated with initial load to avoid reverse power. Since the load feedback is not put in use at the beginning of grid-connection, the pressure

of main steam shall be used to correct the set value to be increased. Set value ＝original value＋3＋f（P0） At the beginning of synchronization, the

target is equal to this set value.

Load rate If set by operators, the load rate is within (0~100) MW/min; Under self starting mode, the load rate is within (1.5~30) MW/min, with step length of

0.5MW/min; When switching over single valve/sequence valve or switching over valves, load rate is

5.0MW/min

When certain fault occurs with steam turbine-generator unit, you may quickly reduce the opening of valve and release partial load, to prevent from deterioration of fault. After RUNBACK function is put in use, when DEH receives the signal of opening and putting in RUNBACK, the total valve position reference value will decrease at a relevant change rate based on original value, till the signal of opening and putting in RUNBACK disappears, or the RUNBACK function is switch off, or the reference value is reduced to the lower limit at corresponding level. At the same time, the target and set point i.e. equivalent to total valve position reference, will decrease accordingly.

The conditions for switching off RUNBACK:

The load is less than 25%; Steam turbine tripped;

Grid-disconnected. Based on different faults, RUNBACK may be classified as three levels, which will be

triggered by on-off input signals from No.1#, 2# and 3# RUNBCK switches. When RUNBACK is acted, it will automatically switch off Load feedback or main

steam pressure feedback, and exit CCS mode.

Load limitation is high load limitation and low load limitation ， it’s limitation value is setted by operator in OIS default high load limitation value is 145MW，default low load limitation value is0MW.

High load limitation If it is not desired to have too high load on the steam turbine-generator unit for certain

period for some reasons, the operators may set high limitation value within (low limitation value ~165 MW), so that the load point of steam turbine is always lower than the limited value. The high load limitation value mustn’t be lower than the low load limitation value.

When the actual load is higher than high load limitation value high load limitation is actived cut off load feedback automatically exit CCS mode.

Low load limitation If it is not desired to have too low load on the steam turbine-generator unit for certain

period for some reasons, the operators may set low limitation value within (2MW~ high limitation value), so that DEH set point Is always higher than the value relating to the limitation.

Valve position limitation If it is not desired to have too high opening of valves on the steam

turbine-generator unit for certain period for some reasons, the operators may set valve position limitation value within (0~120) %. The load reference value or this limitation value, whichever is smaller, shall be taken as the set value for DEH total valve position.

In order to prevent valve position from jumping, the valve position limitation value is provided with change restrictions, and the change rate is 1%/second

Modern turbine generating units are intermediate reheat unit system ones, namely, one boiler operates with one steam turbine, therefore, in order to accomplish secondary frequency regulation, load set point of ST control system is not only properly changed but also the load set point of boiler control system is properly changed so that sufficient energy and safe operation of boiler can be ensured, this is called coordinated controloperator can press "CCS" button in the "AUTO CONTROL" graphic to make it set 'IN's, in other words, the function of CCS control is enabled El. 2 Under the CCS control, the function of load control can' t be input, the unit' s target load value is determined by CCS, the load rate is 100MW/min .The operator is prohibited to operate high, low load limitation value, the value is set to 165MW and.OMW automatically. (Note: the value of load rate and load high, low limitation is determined in the field)

When the boiler system can not maintain main steam pressure due to certain fault, the decrease of main steam pressure can be slowed down by reducing steam flow by means of closing down the opening of control valve, so as to assist in stabilizing the combustion in boiler

The conditions for switch off TPC modeGrid-disconnected , Pressure signal failed , High/low load limitation acted , RUNBACK actedSystem is at “MANUAL” mode.

The conditions for putting TPC in useGrid-connected; In auto modeMain steam pressure higher than 90% rated value; Main steam pressure signal is normal Main steam pressure limitation power-up default value is 10MPa, and the operators may set this limitation value within (3~13) MPa when switch off TPC mode.

During TPC mode being put in use, if the main steam pressure is lower than the specified value, the main steam pressure limitation will be acted. When it is acted, the set point will decrease at a change rate of 1%/second based on the point where the action is started. At the same time, the target and set point i.e. equivalent to total valve position reference, will decrease accordingly. If the main steam pressure rises again above the limitation value, the set point will stop decreasing. If the main steam pressure failed to return back, the set point will stop decreasing when the total valve position reference is less than 20%. When main steam pressure limitation is acted, automatically switch off Load feedback and main steam pressure feedback, and quit CCS mode

Overspeed limitation The method that is used to prevent the speed of steam turbine from jumping into steam turbine tripping speed is called as overspeed limitation.

Load rejection Because the time constant of rotor of large capacity steam turbine is small and the time constant of volume of steam cylinder, when load rejection takes place, the speed of steam turbine will fly swiftly upward, if it is controlled with the speed feed back of the system only, the highest speed may be over 110%, thus emergency tripping of steam turbine may occur. the overspeed limitation solenoid valve should be acted quickly, HP&IP control valves are closed, and the target speed and the given speed should be changed into 3000r/min. After a period of time, the overspeed limitation solenoid valve is de-energized, the control valves are controlled by the servo valves again, speed closed-loop control is restored, and finally the speed of the steam turbine is stabilized at 3000r/min. in this way, the synchronization can be carried out quickly after the accident is eliminated.

103% overspeed If overspeed occurs, the life of the steam turbine will be influenced negatively. Except the speed can exceed 103% speed only during the overspeed test of steam turbine, it is allowed to exceed 103% speed at any time (103% means network frequency up to 50.5Hz). When not in overspeed test, once the speed exceeds 105%, act up the overspeed limitation solenoid valve, close HP&IP control valves. After the speed is lower than 103%, the overspeed limitation solenoid valve is de-energized, and the control valves are controlled by the servo valves again. Note: when performing overspeed test, the function of 103% overspeed limitation is invalid.

KEY FASHER

FORK

CAVITY RING

SPRAY OIL

Overspeed protection If the speed of steam turbine is too high, the steam turbine may be damaged

due to action of centrifugal stress. In order to prevent from overspeed of steam turbine, the DEH system is provided with overspeed limitation function, but if it is failed to control the speed, and the preset speed is exceeded, turbine tripping should be carried out immediately, to close all main steam valves and control valves.

For safety and reliability, many overspeed protections are set in the system: DEH electric overspeed protection 110% Mechanical over speed protection

Mechanical over speed energized HP trip test module solenoid valve5YV,6YV,7YV,8YV, HPCV oil supply solenoid 9YV to 12YV, IPCV oil supply solenoid 17YV, 18YV and HP trip solenoid 27YV, 28YV

Electrical trip energized electrical trip solenoid 3YV, HPCV & MSV oil supply solenoid 9YV to 14YV, IPCV & RSV oil supply solenoid 17YV to 20YV and HP trip solenoid 27YV, 28YV

28YV

27YV

PS-5PS-4

7YV

8YV

6YV5YV

ELECTRICAL TRIP DEVICE

3YV

MECHANICAL TRIP DEVICE

ELECTRICAL TRIP DEVICE

During startup, in order to reduce the thermal stress of HP cylinder, startup in single valve mode shall be used normally. During normal operation, sequence valve mode shall be used normally, in order to reduce the throttling loss of HP control valve. Normally, the single valve mode is mandatory when the load is < 30%. While it is started at hot state and extreme hot state, due to small thermal stress and high steam parameter, the opening of valve will be too small if it is started in single valve mode, which will result in instable control, so it can be switched into startup in sequence valve mode. Set value for CV = single valve coefficient X set value for single valve + (1-single valve coefficient) X set value for sequence valve Under single valve mode, single valve coefficient is 1. After the operators send out the order of switching to sequence valve mode, it will take 10 minutes for single valve coefficient to become from 1 to 0, and finally keep as 0, which is known as sequence valve mode. During the switchover of valve control modes, the main steam pressure feedback or Load Back shall be put in use normally to maintain the load constant.

In order to guarantee that the fly loop of emergency overspeed governor can quickly fly out once the overspeed of units occurs to trip the steam turbine, the flyball should be tested for free movement.

During such a movement test, oil may be sprayed in the fly loop to increase centrifugal force, so that it can fly out. The flyout of flyball due to oil injection test shall not result in tripping. In order to improve the reliability, test isolation valve is added.

Allowable conditions for oil injection test: Test soft button in allowable position; The speed within (2985~3015) r/min; HP expansion differention is lower than 3mm. During the test, 4YV energized, 2YV energized, oil is sprayed into emergency

tripper, fly ring strikes out, and ZS2 sends signals, 2YV is de-energized, after a while, 1YV latch automatically,when latched, the isolation valve is de-energized, which means a successful test.

After the steam turbine is installed for the first time or after an overhaul, the precision of overspeed protection action must be verified, and each loop of overspeed protection shall be tested for verification. When doing overspeed protection test, set the target speed of DEH as 3360r/min, and slowly increase it to the speed of steam turbine. When the action speed of one loop of overspeed protection under test is met, this loop of overspeed protection will be acted to trip the steam turbine. For this reason, overspeed test is also called as raising speed test. DEH can automatically record steam turbine tripping speed and the highest speed.

a) DEH electric overspeed test The test can be carried out by setting target value as 3360r/min and the

rate as 180r/min/min on OIS. b) Mechanical overspeed test In OIS, set target speed to 3360r/min ，the turbine’s speed raise from

3000 r/min speed that fly ring fling out tripped turbine. the speed that fly ring fling out should be between at 110%～111% .

During normal operation of the unit, action test for HP and IP main steam valve and HP and IP regulating valve can be carried out regularly to prevent steam admission valve from blocking. Full travel action test can be carried out to HP and IP main steam valve and regulating valve.

Allowable conditions for action test of valve: All main steam valves fully opened. Load larger than 65 MW but less than 135MW; Automatic mode； Not in CCS mode Grid-connected

DEH can control the unit to conduct MSV leak test and CV leak test in case ST idles at rated speed and boiler steam pressure meets certain requirement.

Allowable conditions for valve leak test: Latched； Speed is higher than2990r/min；

The breaker is off； Auto mode.

HP tripping solenoid valves can be tested on OIS Under normal conditions, 5YV, 6YV, 7YV and 8YV solenoid valves are energized,

and pressure switches PS4 & PS5 are in normal positions. During test, 5YV is

de-energized, 6YV, 7YV and 8YV are energized, and PS5 sends signals, which means a successful test of 5YV. 7YV may be tested in the same way with 5YV. 6YV is de-energized, 5YV, 7YV and 8YV are energized, and PS4 sends signals, which means a successful test of 6YV. 8YV may be tested in the same way with 6YV.

If the solenoid valve is acted, and pressure switch signal is not correct within 15 seconds, the test can be considered failed

Loading and unloading piston

MOOGOn-Off Solenoid