Utility Turbines

Electro-Hydraulic Governing System (EHTC)

EHTC: Advantages Safe Operation of Turbine in

conjunction with Turbine Stress Evaluator (TSC)

Excellent Operation Reliability and Dependability

Low transient and steady state speed deviations

EHTC: Advantages

Dependable control during load rejection

Reliable Operation in case of Isolated Grid

Critical Measuring Devices Speed Probes (3 Nos.) and

associated circuit elements Load Transducers (3 Nos.) Electro-hydraulic Converter housed

in Governing Rack (1 No.) Position Feedback Transmitter of

EHC

Control Loops

Speed Control Load Control Pressure Control

Speed Control: Main Functions PD Controller Start Up & Shut Down of Turbine Synchronizing with grid Providing Min. Load Operation of Turbine over entire

range of Load in case of Load Controller Failure

Load Control: Main Functions

PI Controller Provision of load reference

limiter Frequency influence option

Pressure Control:Main Functions

PI Controller Initial pressure control Limit pressure control

LOADCONT. PI

Governing Scheme for Typical Turbines

HYD

ELMIN

PRESSURECONT. PI

MAX

SPEEDCONT. PD

_

+

MINPrsu

m

++

+

_

+

PrtdPr

_

+NrtdNr

Nact

Pact

Pmax

Fact

Fref

_

+

_

+pREF

pACT

0

P

R

S

LIMIT PRES.

INIT. PRES.

MIN

MIN

HYD

HYD

HYD

EL

SPEEDERGEAR

STARTING DEVICE

MIN

FROM ELECCONTROLLER

TO CONTROLVALVES

Governing Scheme for Typical Turbines

Additional Functions

Tracking device option Load shedding relay Auto Synchronizer Isolated grid operation

Tracking Device Functions

The starting device keeps varying automatically with variation in the position of EHC. In case the EHC fails the starting device will restrict the raise in the load.

Load Shedding Relay Functions

During sudden load throw–off conditions, there will tendency for the speed to raise rapidly. To avoid such conditions the LSR gives a close command for closure of the control valves for a brief moment. The magnitude of load throw,time duration of closure of control valves are settable in the LSR.

Auto synchronizer Functions

The auto synchronizer accepts Gen and Grid Potential transformer signals. To match the frequency and voltage of the Generator, the auto. Sync. Unit gives Speed raise/lower command to EHTC and voltage raise/lower command to AVR.After parameter matching the auto sync. Unit generates a command for Synchronizing the unit

Auto synchronizer Functions

After parameter matching the auto sync. Unit generates a command for Synchronizing the unit

Turbine Stress Evaluator (TSE)

Turbine Stress Evaluator Compares thermal stress in the

monitored components with the permissible limits and generates margins.The temperature margin is fed to the set point controller – speed and load.

Derives start up criteria for ATRS

TSE: Components Monitored Emergency stop valve. HP control valve. HP casing. HP shaft. IP shaft.

TSE: Measuring Points Surface and mid wall temperatures of

ESV (Ti & Tm) Surface and mid wall temperatures of

HPCV Surface and mid wall temperatures of

HP casing. Derived value for HP and IP shaft

temperatures from specified locations in respective casings.

TSE: Operating Modes Three modes viz., fast, normal,

slow available. The increased fatigue rate

associated with fast mode can be compensated by more slow mode operation.

TSE: Margins For any component, the difference Ti –

Tm

represents the actual thermal stresses.

Depending on the value of Tm and operating mode the permissible value of thermal stress is determined.

From the difference between the permissible stress and prevailing actual stress the margin is derived.

TSE: Margins The margins of different

components are provided in the Bar graph form in the TSE monitor.

The reference variable derived from the minimum margin acts directly on the turbine control system.

LP Bypass Control System (LPBP)

LPBP system: Main FeaturesEnables alternative path for dumping steam from RH outlet to condenser bypassing IP and LP turbine.Maintains RH pressure from a criteria representing the HP turbine flow.Works in conjunction with HP bypass systems and when necessitated by the system.

LPBP system: Main FeaturesProvides fixed and variable set point.Protects the condenser by water injection.Hydraulically protects the system when the water injection press. is v low or condenser press. is v high

LPBP system: Pressure controlProcess variable for control loop is acquired from Press. Transmitter in RH line.Two set values viz. Fixed set point and variable set points are formed and maximum value is used as reference.

LPBP system: Pressure controlFixed set point is varied with push button in the control desk.Variable set point is derived from I stage pressure of HP turbine which is an indicative parameter of steam flow.Manual operation of valves is possible with push buttons in the control desk.

LPBP Scheme for Typical turbines

PTf(x)

Fixedsetpoint

MAX

PT

PICont.

Valve Lift PID

RH press

I stg. press

+

To EHC

From EHC LVDT

+

-

-

Gland Steam Control System (GSC)

Gland Steam Pressure Control Maintains the Gland steam header

pressure at required value. Provided with two control valves

viz. seal steam control valve and gland steam control valve.

Process variable is the header pressure from a transmitter.

Gland Steam Pressure Control The electro-hydraulic actuator

have inbuilt pump and it is powered by separate power supply.

In the event of pump failure,the valve remains stay put.

GSPC Scheme for Typical turbines

PT

PICont.

GS headerpress

+

-

Setpoint. f(x)

EHC

f(x)EHC

Seal steam valve

Leak steam valve

Cont.output 100

CommandTo

Valve

100

0

Seal steam valveLeak steam valve

Protection Systems

Protection Systems

Electrical Protection Systems

Hydraulic Protection Systems

Electrical Protection Systems Emergency PB (UCB) Lub Oil Pressure Very Low (2 out of

3) Fire Protection Trip Turbine Trip from ATRS Axial Shift Very High (2 out of 3) Over-speed Trip MFT Relay Acted from Boiler (2 out of

3)

Electrical Protection Systems

Generator Protection Trip Vacuum Low Trip HP Exhaust Temperature Very High(2 out

of 3) Generator Cold Gas Temperature Very

High Exciter Hot Air Temperature Very High Liquid Level in Generator Bushing Very

High (2 out of 3)

Hydraulic Protection Systems

Over-speed Trip 1 & 2 Vacuum Low Trip Axial Shift Hand Trip Lever 1 & 2

Features of Protection Systems Cyclic Test done periodically for each

Trip input Fault at input level will be annunciated Testing can be done online 2 out of 3 logic ensures reliability and

avoid spurious trippings 2 separate Processor Units realize the

Protection Logic with dedicated IOs.

Features of Protection Systems Data of both processors matched

through Serial Communication and discrepancy annunciated

2 separate Solenoids provided in Hydraulic System for redundancy

First cause of trip will be annunciated

Online Testing of Final Tripping elements through ATT

Utility Turbines

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