Turbine Governing System in Power Plant

8/10/2019 Turbine Governing System in Power Plant

1/113

Date 14th

July

Domain:HYDRO POWER

Knowledge Management System

Area:Hydropower

Keywords:Turbine governing,Hydraulic governing

Submitted by:Dr.Suparna Mukhopadhyay

[email protected],9650997786

POWER MANAGEMENT INSTITUTE


2/113

Turbine governing


3/113


4/113

steam technology

When wateris heated to the point of vaporizing, the

vaporized water takes up more space than the liquidwater did.

the liquid contents will vaporize and eventually expand tothe point where the can will explode to release thepressure inside.

When this pressure is used to perform a particular task -- like turning a turbine or causing a kettle to whistle --steam technology is harnessing steam power.

The methods of heating, containing, channeling and

using steam have changed A steam turbine is a device that converts the heat

energy in captured, pressurized steam, and convertsit to mechanical energy


5/113

The Components of a Steam

Turbine

A steam turbine uses steam, produced by theheating of water or other liquids, to generaterotational motion and energy. Most turbines have asort of l iquid tank, or boiler, with a heat source to

heat the liquid. All turbines must have an impeller, a fan-shapedobject that rotates in response to steam pressure.Many today have more than one impeller. Theimpeller is connected to a rotating generator, which

generates electrical power, or to some other rotatingmechanism that requires mechanical force tooperate, such as a wheel


6/113

The Heating of the Liquid and

Turning of the Impeller

The boiler of a steam turbine used to be powered solely by coal

fires. However, modern day technology has allowed other,more efficient heat sources to be used, such as nuclear or gasenergy. Once the liquid boils and releases a vapor, the vaportravels to the first impeller via a pipe.

This pipe increases the pressure of the steam until it is of highenough pressure to turn the turbine. The steam continues totravel past the impeller and into other pipes, provided thesteam turbine has more than one impeller.

These pipes direct the steam past other impellers, which thesteam also spins with kinetic energy. Each successive impelleris easier to turn than the last, because the steam has lessenergy after going through each impeller.


7/113

Generating Energy and Recycling

the Steam The result of all these turning impellers is a rotational force,

which can be used to generate electricity i f the rotating impeller

is connected to an electric generator. Usually, these electricgenerators generate electricity by turning a copper circuitinside of a magnetic field.

The turning of the copper inside the magnetic f ield generates

electrici ty, as stated by the law of induction. The steam left overinside the turbine must be recycled so that the turbine does nothave to be constantly f illed with more liquid.

To do this, the steam is allowed to condense back into a liquid

and is then pumped back into the boiler tank to be reheatedand sent back through the impellers, generating more power


8/113

Steam turbineturbine is a rotary engine that

takes energy from steam andtransfers the mechanical

energy to a generator to

produce electricity.


9/113

Classification of Steam turbines Reaction Turbines

Derive power from pressure drop

across turbine

Totally immersed in water Angular & linear motion converted to

shaft power

Propeller, Francis, and Kaplan

turbines

Impulse Turbines Convert kinetic energy of water jet

hitting buckets

No pressure drop across turbines

Pelton, Turgo, and crossflow

turbines

Propeller

Kaplan

Francis

Pump-as-

Turbine

Reaction

Crossflow

Crossflow

Turgo

Multi-jet

Pelton

Pelton

Turgo

Multi-jet

Pelton

Impulse

LowMediumHigh

Head Pressure


10/113


11/113

Turbine power

Turbine Power =( M,H, )Where, M=flow rate of steam (Kg/s)

H=Enthalpy drop (KJ/s)

= Efficiency of Turbine


12/113

INTRODUCTION

Governing system is an important control systemin the power plant as it regulates the turbinespeed, power and participates in the grid

frequency regulation. For starting, loading governing system is the

main operator interface. Steady state anddynamic performance of the power systemdepends on the power plant responsecapabilities in which governing system plays akey role.


13/113

What is Governing?TO GOVERN MEANS TO CONTROL AND REGULATETO GOVERN MEANS TO CONTROL AND REGULATE

CERTAIN PARAMETERS TO ACHIEVE EXPECTEDCERTAIN PARAMETERS TO ACHIEVE EXPECTEDFUNCTIONAL REQUIREMENTS .FUNCTIONAL REQUIREMENTS .


14/113

Need for governing system

The load on a turbine generating unit does notremain constant and can vary as per consumerrequirement.

The mismatch between load and generation

results in the speed (or frequency) variation.When the load varies, the generation also has tovary to match it to keep the speed constant.

This job is done by the governing system. Speedwhich is an indicator of the generation loadmismatch is used to increase or decrease thegeneration


15/113

Steam Turbines: Governors and

Controls Governor systems are typically speed-sensitive control systems. The

turbine speed is con-trolled by varying the steam flow through the turbine bypositioning the governor valve. Variations in the power required by thepump and changes in steam inlet or exhaust conditions alter the speed ofthe turbine, causing the governor system to respond to correct the operatingspeed.

Control systems, unlike governor systems, are not directly speed-sensitive

but respond to changes in pump or pump-system pressures and thenreposition the turbine "governor' 'valve to maintain the preset pressure.Consequently, changes in turbine steam conditions or in the power requiredby the pump result in a repositioning of the turbine governor valve or of aseparate steam valve only after the pressure being sensed by the controllerhas changed.

Even when a control system is furnished, a speed governor is also normallyfurnished.The speed governor is set for a speed slightly higher than thedesired operating speed in order to function as a pre-emergency governor;that is, prevent the turbine from reaching the trip speed when the controllercauses the turbine to operate at a speed above rated speed


16/113

Speed range is the percentage below rated speed for which thegovernor speed setting may be adjusted. For example, a turbinewith 4000 rpm rated speed and a governor system having a 30%range can be operated at a minimum speed of 2800 rpm:


17/113


18/113


19/113


20/113


21/113


22/113


23/113


24/113


25/113


26/113


27/113


28/113


29/113


30/113


31/113


32/113


33/113


34/113


35/113


36/113


37/113


38/113


39/113


40/113


41/113

BYPASS GOVERNING

It is employed in small capacity turbines runningon high pressure conditions and with smallblading dimensions.

Here the loading up to appx 80% ( Economic

loading ) is met by normal control valves feedingthe First stage. For higher loading , to supplymore steam which is not possible due to smallblading dimensions ( can lead to operational

problems) the extra quantity of the steam is fedto the intermediate section of turbine bypassingthe initial high pressure stages.


42/113

THROTTLE GOVERNING NOZZLE GOVERNIMG

All the valves in a set opens or

closes simultaneously / together

The Valves in a set opens or

closes consequentially or in asequence

It is a Full arc Admission

Turbine

It is a Partial Arc admission

turbine except at full Load.

It is most suitable for full load or

based Load plants

It is good for Low load or

variable load turbines.

No operational Problems May have operational Problem at

partial Loads

TYPES OF GOVERNING II


43/113

TYPES OF GOVERNING-II

Constant Pressure Mode: Here pressureupstream 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 pressureupstream of control valves varies

proportionately with the load requirement.

Response of Constant pressure Mode ismuch faster than Variable pressure mode, but

Constant pressure leads to more losses.

REGULATION


44/113

REGULATION

Regulation % of Turbine is defined as(No load Speed - Full Load speed) X 100 %

( Nominal Speed)

It varies from 2.5% to 8%

Normally it is 4 to 5 %

Turbine having less regulation will be moresensitive in the grid and hence will sharemore load and vice versa

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


45/113


46/113


47/113


48/113


49/113


50/113


51/113


52/113


53/113


54/113


55/113


56/113


57/113


58/113


59/113


60/113


61/113


62/113


63/113


64/113


65/113

Turbine Protection To Protect turbine from in admissible operating

conditions

It restricts failure to minimum

It consists of two type of protections.

1- Hydraulic Protection

2- Electrical Protection


66/113

Aux trip oil


67/113


68/113


69/113


70/113

660 MW SUPERCRITICAL UNIT


71/113

The turbine is a tandem-compound unit consisting of

high pressure cylinder (HPC) with a loop train of the

steam path, intermediate pressure cylinder (IPC) and 2 low pressure

cylinders (LPC).

IP and LP cylinders are double-flow. Steam reheat isarranged between the HP and IP cylinders.

The turbine is provided with nozzle steam admissionsystem. H.P., I.P. and L.P. rotors are solid forged rotors.

Moving blades of the H.P., I.P. and L.P. cylinders havethe integrally milled shrouds.


72/113


73/113

Purpose and construction


74/113


75/113

Control Fluid Circuit


76/113


77/113

The control fluid supply of the governing system should be inoperation from the Unit start-up to the shaft turning gear switching-on after the turbine rotor stopping after the turbine shutdown. During

the System operation one pump is on and supplies control fluid intothe governing system. The second pump is ready for switching-onand is in reserve. Gate valves at pumps' suction side are open, gatevalve on connection pipe between first pump discharge side andsecond pump suction side is closed.

One fan for control fluid vapor extraction is also in operation, thesecond fan is switched off, gate valves at fan suction side are open.One control fluid cooler is in operation, the control fluid coolercooling water outlet and inlet gate valves are open. The secondcontrol fluid cooler is off - cooling water outlet and inlet gate valvesare closed. Gate valve on control fluid supply from unstabilized

pressure discharge header to fine filter is open. Control fluid transferpump is switched off; gate valve on control fluid supply line fromcontrol fluid transfer pump to fine filter is closed.

Starting of Control Fluid Pumps


78/113

S a g o Co o u d u ps

The operator switches the control fluid governing system in use byswitching-on of the governing pump pre-selected as a working one.

After mounting, repair or standstill the working pump starts with thegate valve closed on the discharge side. Upon switching the pumpin use, the gate valve opens little by little on the discharge side forfilling the System piping.

During normal operation and after the downtime without discharging

of the control fluid system, the working pump starts with the gatevalve open on the discharge side. The working filter and control fluidcooler are selected by the operator locally by means of hand-operated gate valve. Following the working control fluid pumpstarting, the governing system fan preselected by the operator as aworking one and the governing system control fluid temperature

regulator are switched in use.

System Stopping


79/113

Sys e S opp g

The control fluid governing system is stopped by

the operator if the Turbine is shutdown - theturbine stop valves are closed and the generatoris disconnected from the grid.

To stop the control fluid governing system it isnecessary to switched off all the working controlfluid pumps. Following the governing systempump stopping, the governing system controlfluid temperature regulator is switched in useand with 15 minutes time delay the governingsystem fan stops.

Abnormal Situations in Control


80/113

Fluid System Control Fluid Pressure Drop

1. control fluid pressure decrease downcontrol fluid standby pump starts

automatically.

2. For the period of standby pumpchange-over and turn, pressure in the

system is kept by weight-loaded

accumulator

Other abnormalities


81/113

1. Level Decrease in Control Fluid Tank

control fluid should be added to the tank during turbine operation toreach normal level through the line

2.Governing System Control Fluid Temperature Increase

the inching valve opens automatically on the control valve bypass oncooling water line.

3.Filter Foulingthe corresponding filter or strainers should be cleaned or replaced bythe personnel during the plant operation.

4.Tripping of Governing System Fan

the standby fan inlet gate valve should be open and then the standby

fan should be switched in use5. Fire

control fluid pump starting automatics are blocked and the workingpumps stop automatically when the turbine stop valves are closedand the generator is disconnected from the grid


82/113


83/113

Hydraulic Protection System


84/113

The protection system of the turbine is

intended for fast closing of stop andgoverning valves,

Striker

electomagnetic switchesturbine trip

Protection system performance


85/113

testing

Hydraulic Part of Governing system


86/113


87/113


88/113

Governing system controls the steam flow to the turbinein response to the control signals like speed error, powererror.

It can also be configured to respond to pressure error. Itis a closed loop control system in which control actiongoes on till the power mismatch is reduced to zero.

As shown in the basic scheme given in Fig. 1, the inlet

steam flow is controlled by the control valve or thegovernor valve. It is a regulating valve.

The stop valve shown in the figure ahead of control valveis used for protection. It is either closed or open. In

emergencies steam flow is stopped by closing this valveby the protective devices


89/113

The steam flow through the control valve is proportionalto the valve opening in the operating range. So whenvalve position changes, turbine steam flow changes andturbine power output also changes proportionally.

Thus governing system changes the turbine mechanicalpower output.

In no load unsynchronized condition, all the power is

used to accelerate the rotor only (after meeting rotationallosses) and hence the speed changes.

The rate of speed change is governed by the inertia ofthe entire rotor system. In the grid connected condition,

only power pumped into the system changes whengoverning system changes the valve opening


90/113

When the turbine generator unit is being started, governing systemcontrols the speed precisely by regulating the steam flow. Once theunit is synchronized to the power system grid, same control system

is used to load the machine. As the connected system has very large inertia (infinite bus), one

machine cannot change the frequency of the grid. But it canparticipate in the power system frequency regulation as part of agroup of generators that are used for automatic load frequencycontrol. (ALFC).

As shown in the block diagram, the valve opening changes either bychanging the reference setting or by the change in speed (orfrequency). This is called primary regulation.

The reference setting can also be changed remotely by powersystem load frequency control. This is called secondary regulation.Only some generating units in a power system may be used forsecondary regulation

PERFORMANCE ASPECTS


91/113

Regulation or droop characteristic

Whenever there is a mismatch in power, speed changes.As seen earlier, the governing system senses this speedchange and adjusts valve opening which in turn changespower output.

This action stops once the power mismatch is madezero. But the speed error remains. What should be thechange in power output for a change in speed is decidedby the regulation.

If 4 % change in speed causes 100 % change in power

output, then the regulation is said to be 4 % (or in perunit 0.04).

Transient performance


92/113

The governing system, as noted earlier is a closed loop

control system. Stability is an important parameter in anyfeedback control system.

Stability and speed of response depend on the signalmodifications done by various blocks in the loop.

The closed loop gain depends on the individual blockgains and the adjustable gains provided in the speedcontroller and load controller.

The gain at the steady state and during the transient isimportant in deciding the performance. If the gain is not

proper there can be hunting in the system as shown inFig

Lift- flow characteristic


93/113

An important characteristic that decides the loop

gain is the valve lift versus flow characteristic.Due to the nature of design, this characteristic isnonlinear.

Though linearization is done either in theforward path or reverse path using mechanicalcam, the gain introduced is different at lowopenings. The effective closed loop gain is lessresulting in less damping capability at low loads.

Transient speed rise


94/113

Governing system maintains the turbine speed as set by thereference. When there are disturbances, the response should be

quick otherwise speed may continue to deviate. Transient speed rise(TSR) is one important criterion that is used to judge the responsecapability of the governing system. Load throw off or load rejection isa major disturbance. When the TG unit is running at full load, if thecircuit breaker opens, load is cut off. The full load steam flow causesthe rotor to accelerate. The steam inflow is to be cutoff as soon aspossible. It cannot be done instantaneously as the hydro mechanicalelements take certain time to respond. Speed shoots up and thenfalls gradually due to the closure of control valve, as shown in Fig. 8.The peak value of speed is called transient speed rise (TSR).


95/113

Even when the control valves are closed steam remaining in thesteam volumes of reheater piping, turbine cylinders (entrainedsteam) continue to do the work and increase the speed for few

seconds. There is an emergency governor provided to stop the turbine if thespeed crosses its setting, usually 112 %. The standards specify thatthe TSR value should be less than the emergency governor setting.That means when there is a full load throw-off, governing systemshould act fast so that turbine does not trip.

There are other devices provided in the governing system whichhelp in minimizing transient speed rise like load shedding relay(LSR) which cause feed forward action to close governing valvesbefore speed variation is sensed by the speed transducer

Governor insensitivity or dead band


96/113

The governing system action depends onspeed sensing. There is a minimum value

of speed which cannot be picked by the

sensing mechanism and hence mayremain uncorrected. This minimum value

is called governor insensitivity or dead

band.

Mechanical hydraulic governor as

backup


97/113

backup

As mentioned earlier mechanical hydraulicgovernor comprising hydraulic speed

sensor, primary amplification devices

(called follow up pistons) are provided asbackup to the electro hydraulic governor

(EHG)


98/113

The EHG system and MHG system will becontinuously generating command signals for

the governor valve opening. Normally both willhave the same value. There is a minimum logicprovided hydraulically (called hydraulicminimum).

According to this whichever calls for lesservalve opening will prevail. In this way in casethere is a failure in electronic part mechanical

governing system will take over. The turbine canbe run with MHG alone


99/113

Preparation of the governing

system for the turbine starting


100/113

system for the turbine starting

Before turbine start-up the control gear (CG)

should be in the position "closed". At that all stop

and governing valves are closed. At start-up CG

should be set in the position "opened".

At that position at first oil is supplied to cock the

overspeed governor slide valves, after that head

pressure is applied to SV servomotors and

electro-hydraulic


101/113

converter-adders. Stop valves open but

governing valves remain closed untilcontrol action from turbine controller is

applied to electro-hydraulic converter-

adder

Turbine control during start-up, load variation,

and synchronization


102/113

Functional Group Control: Start-

up / shutdown of Governing Oil

System


103/113

System The governing oil system is started into operation by operator

provided that the level in the governing oil tank is higher than

nominal value by 200 mm. In this case according to the group start-up program the following sequence of operations is carried outautomatically:

control oil pump is started The fan duty is started;

The control valve which maintains the oil temperature to control of

the turbine is switched over to automatic control mode. The governing oil system is stopped the turbine stop valves areclosed and the generator is disconnected from the grid. Runningcontrol oil pumps are stopped;

The control valve) which maintains the oil temperature to control of

the turbine is disconnected from controller and fully closed; In 15 minutes after control oil pumps stopping all running fans ofgoverning oil system are stopped.


104/113


105/113


106/113


107/113


108/113


109/113


110/113


111/113


112/113


113/113

THANK YOU

Turbine Governing System in Power Plant

Documents