Turbine Governing System

TURBINE GOVERNING SYSTEM (TGS) The TGS comprises of the of  the following sub‐systems: A.

Speed controller

B.

Load controller

C.

Pressure controller

D.

Control mode selection and Electro ‐ hydraulic converter (EHC)

E.

Mechanical hydraulic controller (MHC)

F.

Servo Motors of the of  the control valves.

The first four subsystems form the electro hydraulic controller. Both EHTC and MHC acts on the valve servo motors through selection criterion which ensures that MHC acts as backup to EHTC. Similarly selection circuit of  EHTC ensures that one of  the controllers influence the control action at a time. ELECTROHYDRAULC TURBINE CONTROL (EHTC) EHTC has the task to control the steam flow through the main control valves and accordingly the speed, as well as the load of  turbine generator for any operating condition i.e. startup, loading, operation under load, shutdown, and load rejection. EHTC consists of the of  the following basic control loops:‐ a)

Speed Control Loop

b)

Load Control Loop

c)

Pressure Control Loop

d)

Control mode selection & Electro Hydraulic Converter.

A. SPEED CONTROL LOOP The function of  speed Control Loop is to control the TG set during start up and during synchronisation with the distribution system. While the TG set is operating under load the speed controller serves as an overspeed limit controller.lt keeps the speed increase below the over speed trip setting. The speed increase generally results from partial or full toad rejection due to disturbance in grid. The setpoint to the speed controller is time dependent reference speed (Nr) and the feedback signal is the turbine speed (Nact).

The speed control loop consists of  i) Speed reference setter (SRS) ii) Speed reference limiter (SRL) iii) Speed controller i)

Speed reference setter

It accepts signal from manual push button in UCB, it can also have the provision of  accepting signal from F.G. control (functional group) during startup in auto mode and from synchroniser during synchronisation. Manual P.B signal has got first priority. Speed reference signal is an electronic module with a motorised setpoint setting facility.lts output Nr is proportional to 0‐10 volts which corresponds to 0‐3600 rpm. Nr is displayed in operators tile When turbine trips speed reference setter goes to follow up mode i.e., its output follows the actual turbine speed with a constant negative error. During normal operation when speed control not in active speed reference follows the actual speed by +15 rpm. ii)

Speed reference limiter

It determines the acceleration rate. It is basically an integrator. The integration can be stopped by a binary signal. The upper and lower limit of  the acceleration rate can be set by potentiometers in the electronic module Speed reference signal also gets influenced by the signal coming from TSE. Influence of TSE can be switched on or off from the EHC cabinet. When turbine trips SRL goes to fast modes, when TSE fault appears SRL stops integration (Provided TSE influence was on) stop reference limiter indication comes at the same time Output of SRL is known as N which is again 0 ‐ 10 volts signal is also displayed in operators tile and corresponds to 0 ‐ 3300 rpm iii)

Speed controller

It is a proportional type of  controller which requires a finite deviation (Nrtd ‐ Nact) to give an output signal. In case of  faults in the other control loops speed control loop may be used for load control of  TG. But due to proportional characteristics of  speed controller Nrtd should always be kept at a value more than the actual speed in order to keep the control valves open. For that purpose an adjustment is required which is known as droop. If required N is 3150 rpm in order to load the TG set fully at an actual speed of  3000 rpm, then droop is (3150‐3000)/3000*100 or 5%. During startup at different time the TG set may be synchronized at different throttle pressure. But in order to synchronies at lower throttle pressure the opening of  control valve should be more to get the required speed. So a corrective signal Known as “No load correction" is added to Nrtd as shown in the scheme. Actually Δn = f (p) [function of throttle pressure] This no load

correction is approximately 100 Bar = 20 rpm. This correction is high if  the pressure‐ is lower and vise versa. Output of speed controller goes to selection circuit. B. LOAD CONTROL LOOP Immediately after the synchronization of  the TG set to the grid, the load controller assumes control of the turbine. Its main components are i)

Load reference setter (LRS)

ii)

Load reference limiter (LRL)

iii)

Load controller

i)

Load reference setter

It is an electronic module with a motorized potentiometer setting arrangement. lt receives raise or lower command from UCB PB. When the unit is running in CMC, output of LRS follows the load demand signal from ACS ii)

Load reference limiter

It accepts signal from LRS. lt determines the rate of load change. The load changing rate is set from UCB PB in turbine operators desk. Allowable load rate change signal from TSE also influences the LRL. In fact, the minimum of  load changing rate set by the operator and that allowed by TSE determines the actual rate of change. There is one absolute load limit setter in EHC cabinet. Whatever be the load set by the operator or that allowed by TSE the load cannot exceed the setting of  the absolute load limit setter. Load ref. limiter (LRL) is basically an integrator with adjustable time of integration. In case of the following LRL stops integration: a)

TSE influence ON & TSE fault appeared

b)

Pressure control active in limit pr. mode & load ref > pr lim by some adjustable setting (20 MW or so),

c)

During auto startup of turbine if "Block speed & load ref integration" signal comes from FGC. After load reference limiter, two signals are added to the load reference

a)

A pressure influence signal Pr Δp

b)

A frequency influence signal Pr Δf 

The magnitude of  frequency deviation from rated frequency is a measure of  the ratio of  load generated to the load demand. In case of load deficit load frequency will drop. In load control loop there is an electronic circuit which compares the grid frequency with the rated one and

generates a corrective signal which is added to the load reference. This takes care of  the deviation in grid frequency. The frequency influence can be switched ON or OFF from EHC cabinet. Now frequency influence of power (Pr Δf) can change the load set point if frequency goes over 3020 rpm and this set point change can be 15 MW maximum, so set point will reduce by 15 MW at rate which can be set from cabinet. Similarly if  frequency goes below 2980 then machine will load by maximum 15 MW, set point will change by 15 MW and rate can be set from cabinet. Over above this frequency correction, there is a limit frequency influence which comes into effect only when the speed is in the higher range and when the RPM goes above 3078. If  rpm goes over 3078 then machine is unloaded at the rate of  3.3 MW / rpm and this unloading is due to droop of  machine (5%) & if  machine rpm goes over 3228 then machine is unloaded fully. This unloading is through reducing the output of  the load controller and hence load set point does not change it remains where it was. So if  frequency falls and comes below 3078 machine will pick up load. Pressure influence on load (Pr ΔP) is added when pressure is more or less than set pressure 2 then load will vary depending upon deviation. If  the pr set point is deviated by 10 kg/cm then MW is reduced by 15 to maintain boiler pressure either in higher or lower side. However, this setting has been set to zero. Load Gradient : In auto means it will follow operators set load rate (at turbine desk) and in manual means it will follow internal set rate ( 60MW/min ). It can be made ON/OFF when p & Pr lim difference is minimum. iii)

Load controller :

It is a PI action controller so it maintains the load very close to the load reference. The characteristics changes during isolated operation. During isolated grid condition Load Controller becomes P ‐ Controller (gain changes). Isolated grid comes under following condition: 1. Speed & Pr Controller Not in service & 2. Load Controller ON & Load controller active & 3. f >3024 rpm There are two following circuits which are taking input from speed controller and pressure controller to make load controller to follow the above two controllers which ever in service. If  Speed Controller is active then load controller follows 100 mV below Speed controller output.

If  pressure controller is active then load controller follows 150 mV above pressure controller output. Here one thing is noticeable that controller set point does not change. Only controller output is made to track as near as possible to the active controller (speed or pressure ). If  it was not made so then Load controller would have gone to saturation and then for bringing back to service more time would have required. When Load controller in service then one should not make it OFF because that time toad controller is controlling turbine so if  Load Controller is made off  means ‐10V supply is directly given to it which means turbine load may be thrown off. So it is advisable to make load controller off  when Speed controller is in service if  required so. Of  course Load controller can be scheduled off  from UCB. This is indicated by the blinking yellow on lamp in the panel. Scheduling off  stops the tracking of  speed set point and the speed set point now can be manually increased until the speed controller becomes active. When speed control becomes active the load controller is scheduled off and the yellow lamps become steady. C.

PRESSURE CONTROL LOOP

The error signal for this controller is obtained from CMC. The pressure controller controls the turbine load with respect to main steam pressure deviation and prevents a pressure drop during a quick load increase. There are two possible modes of  control in pressure control loop. i)

Limit pressure control

ii)

Initial or Throttle pressure control.

i)

Limit pressure control

When unit is running in load control mode, due to some disturbances in boiler, throttle pressure may decrease. As a result pressure deviation (prref  ‐ pract) will increase. Pressure controller is basically a PI controller but its characteristic is such that its output will decrease when deviation increases. Thus when deviation goes on increasing, at certain point, output of pressure controller comes below load controller. Hence pressure controller will take the control of  the unit from the load controller because there is one MIN gate at the final phase of  the selection circuit i.e. it is the controller having minimum output that will take the control. But if  limit pressure mode is selected by the operator at the desk, the pressure controller will not take any corrective action until delta P goes above a definite value (i.e. 15 2 kg/cm ). When actual pressure touches this limit value the pressure controller takes corrective action and modulates the control valves to keep the pressure at this limit. ii)

Initial pressure mode:

If this mode is selected by the operator, the pressure controller, if selected by the selection ckt

keeps the throttle pressure very close to the pressure reference value. Initial pressure mode is automatically selected if there is run back or if turbine follow mode is selected. D.

Control Mode Selection and Electro‐hydraulic Converter

Selection ckt consists of  mainly MIN and MAX gates, these controllers are meaningfully connected to the "Position controller" The selection ckt automatically selects which one of the controllers should be in service at a time. Output of the controller selected by the selection ckt goes to the position controller as the position set point. The position controller actually controls the position of  the plunger of  the EHTC coil. Thus EHTC converts electrical signal to secondary oil pressure. The actual value of  the plunger coil position is measured by two transmitters. Minimum value of  positions given by the two transmitters is taken as the actual value. E. MECHANICAL HYDRAULIC CONTROL (MHC) The MHC comprises the following: i)

Starting device (Starting & load limit)

ii)

Speeder gear (Reference speed & load adjustment)

iii)

Hydraulic speed governor

iv)

Hydraulic amplifier

Starting device is used to run up turbine up to the speed of  2500 rpm. After synchronization the same device is used as load limiter. For every position of  the starting device there is a corresponding auxiliary secondary oil pressure. The speeder gear takes over the control action after the speed of 2500 rpm. The speed error acts on the bellow which modulates the aux. sec. oil pressure. The minimum of the aux. sec oil pressure from starting device and speeder gear is sent as an input to hydraulic amplifier. F.

SERVO MOTORS OF CONTROL VALVES:

Effective sec. oil pressure of HP and IP control valves are computed as the minimum secondary oil pressures due to EHTC and MHC. HYDRAULIC SPEED TRANSMITTER The MOP shaft carries the hydraulic speed transmitter. The hydraulic speed transmitter operates on the same principle as a centrifugal pump impeller. The variation of the pressure in the primary oil circuit due to speed variation serves as a control impulse for the hydraulic speed governor.

ELECTRICAL SPEED TRANSMITTER The electrical speed signals originates from the electrical speed transducers which consist of  three Hall generators and a non‐magnetic aluminum disc with 120 permanent magnets arranged around its circumference located on the MOP shaft. When the disc rotates with the pump running, the permanent magnet of the aluminum disc act upon the three stationary Hall generators, two of  which supply a voltage pulse to the pulse converter each time a magnet passes. Third is a spare. For safety reasons, the actual speed is sensed and processed via two separate channels. In the event of failure of one channel the second is automatically switched in and an alarm given. The voltage pulses are amplified and converted to a measurable DC voltage which is proportional to speed in the pulse converter and then fed to the speed measuring unit of EHTC. From speed measuring unit speed signals are also provided to the TSE, ATT and recorders. FIRE PROTECTION OF TURBINE If  any fire occurs in the turbine floor then turbine is to be stopped and put on barring depending on the severity of fire. If fire occurs away from the turbine then it is less dangerous (means it is not required to put all oil pumps off) so turbine can be kept rolling on barring gear. But if  fire is near the turbine then it is dangerous as fire may catch oil there by endangering turbine so all oil pumps are to be stopped and only oil supply is to be given for bearings. So for that purpose fire protection 1 and fire protection 2 push button have been provided on the turbine desk. Logic sheet is attached .

UNIT OPERATION MODES The Unit can be operated in four different modes 1. 2. 3. 4. 1.

Coordinated mode Boiler follow mode Turbine follow mode Runback mode COORDINATED MODE

BOILER MASTER AND GENERATION OF FUEL / AIR SET POINT The function of the boiler master auto / manual station on UCB is to provide a set point for fuel and air flow i.e. fuel demand and air demand signals. In co‐ordinated mode it is equal to sum of  boiler load set point and master controller (PID) output. In this mode master controller acts on DP error. The fuel demand as generated is compared with actual air flow and a minimum of the two is selected as the fuel set point. The air demand as generated is compared with ∑ fuel flow & 30% of  air flow and maximum is selected as air set point. This MIN / MAX selection ensures an air rich furnace. When fuel / air demand increases the MAX gate first increases the air set point and when fuel has decreased the MAX gate permits reduction of air flow also only after fuel has decreased. Fuel control error Oil flow to burners and feeder speed (which is the measure of  coal flow) along with C.V corrections added to get total fuel flow. Cabinet adjustments are provided to take care of  individual calorific values to obtain total fuel flow as fuel oil equivalent (FOE). The total fuel flow (FOE) is compared with fuel set point to generate fuel control error. This control error is fed through (PI) Controller (Master Fuel Controller) to all feeders in parallel and each feeder is provided with a bias and an auto / manual station. Secondary Air Flow Control As mentioned earlier, air demand is generated as the MAX of the following: a. b. c.

Air demand from Boiler Master Fuel flow A safe minimum 30% air setting

Actual air flow is measured at the suction of  each one of  the FD fans (Piezometric ring) Two transmitters per fan are provided, sum of the two selected transmitters give the secondary air flow. Primary air flow is added to this to give total airflow which is used for combustion control, purge logic, SADC. Secondary air flow is measured in aerofoil near the windbox (left

and right). Now, this actual air flow is compared with the air set point and then modified by O2 trim to generate the air flow control error. This signal is doubled in case only one out of  two running fans available for automatic control. An equalizing and biasing signal is added to equalize and bias the individual fan air flows. Control signal thus formed operates on the individual controller (for each fan) whose output fires the thyristor drives of  the 415 V AC motors for blade pitch control. An auto / manual station is provided for each fan. O2 TRIM A selection station and a setter for oxygen set point are provided to achieve the desired excess air. If variable O2 set point (SP) is selected, set point is generated by a function generator which is a function of max (air flow SP and total air flow). In other mode SP is set from UCB. O2 in flue gas is compared with this SP and error is fed to PI controller, output of  which is limited between 0.8 and 1.2% of  total air flow. O2 ‐ PI controller output multiplied by total air flow (actual) makes the FD fan blade pitch controllers look at the air flow as if  it is more or less depending on O2 ‐ PI controllers output on higher side or lower side. O2 probes are provided at the outlet of economizer and average of any two of the four can be selected for control. These probes are zirconium oxide probes working on the principle of partial pressure of oxygen. Generation of  Δ P / Δ MW Signals The pressure set point is compared with actual throttle steam pressure to obtain the control error signal DP. Three pressure transmitters are provided for redundancy along with deviation monitoring and middle of  the three is selected as actual pressure. In case of  two transmitters fault, the control is put to manual. The pressure set point generated in this circuit is also sent to HP Bypass Control. Actual MW signal (middle of 3 transmitters) is sent from turbine cabinets to CMC cabinet where AMW signal is formed as the difference between load demand to actual MW. Generation of Load Demand Signal Load Demand is the MW set point signal for boiler combustion control and turbine (EHC). This signal is generated as follows : Target Load (MW set point) for the unit is set either by UCB operator or in auto mode by ADS mode. Digital display is provided for target load. This target load is subject to MIN & MAX Limits, set by the UCB operator. After this limiting, target load is subjected to a rate control which varies the MW set point signal at the rate set by the UCB operator or as permitted by the TSE whichever is lower. As in CMC both turbine and BM are on auto input to the rate controller will be the target load set point. To this rate controlled set point a frequency influence correction signal is added and Load Demand signal is formed. To ensure that the unit is following the load set point closely, an inhibit increase/decrease feature is provided. If  any of  MW, steam pressure, FW flow, fuel flow deviates from set point significantly or has reached the MAX/MIN limits, the load demand is inhibited from increasing

or decreasing as the case may be. Similar signals for air flow & turbine load limit active are two additional signals to inhibit increase of load demand. Selection of CMC 1. 2. 3. 4. 5. 6.

7. 8.

Put air control on Auto ( at least one FD fan ) Put feeders speed control on auto after varying Fuel Master (FM) output and making feeder speed controller error zero. Vary Blr master output so that FM error becomes zero. Then put FM on auto. Make throttle pr. set point and actual pr. difference zero Put BM on auto increase / decrease unit master output so that it becomes equal to actual load. [wait until load set value and load actual value matches as shown in the CMC panel digital indicator] From TG desk put turbine control on auto. Press coordinated push button along with manual release on CMC desk.

BOILER FOLLOW MODE In this mode turbine is in manual and the load is set at the turbine desk. The Boiler in auto follows the turbine and fires to maintain the throttle pressure. It means boiler master has to be on Auto. If  for any reason or the other the Load demand set point signal is not available the turbine load has to be set manually and the system can be switched to boiler follow mode. In boiler follow mode set point = sum of  boiler load index and Master controller output (PID) acting on ΔP. In boiler follow mode as turbine is on manual so input to SPCM wilt be turbine load set point, i.e. ∑Pr Selection of Boiler Follow Mode 1. 2.

Put all AIR, FW, Fuel Master Controller on Auto. Put Boiler Master Controller on Auto.

If  the unit is in turbine follow or coordinated mode automatic change over to boiler follow occurs under following conditions Turbine goes to manual because of any reason or operator action . (Pr CMC ‐ Pr lim) > 60 MW TURBINE FOLLOW MODE It means turbine control has to be on Auto. On turbine follow mode the unit load is controlled through boiler, acting on the firing rate in the same manner as the steam pressure control

described in CMC mode. The pressure is controlled by EHTC system utilizing the pressure deviation formed in the boiler master control system. In turbine follow turbine operates in initial pressure mode. In TFM set point = Sum of boiler load set point and master controller output (acting on Δ MW Error) Selection of Turbine follow mode 1. 2. 3. 4. 5.

Boiler master on manual Confirm that Throttle pressure deviation is zero Put turbine in Auto from turbine desk Press " Turbine follow " push button along with manual release on CMC desk and turbine goes to initial pressure mode from LMT Mode by itself. Now load set point can be changed by varying the boiler master manually.

RUNBACK MODE Under runback conditions the firing rate for the boiler must be reduced to preset values, as close as possible to the tolerable limits. Therefore the swings of firing rate caused by the action of  the PID controller must be avoided. As consequence of  this condition the system has to be switched to pure feed forward control, where the firing rate set point is directly proportional to the load capability signal. To avoid any mismatch between steam production of the boiler and the turbine load, the turbine has to be switched to initial pressure control, as with TFM. RUNBACK RESETTING Let the boiler master be in Auto Reduce load set point from the turbine desk to a value slightly less than "Load set point" so that " Runback in Operation" resets,

HP ‐ LP BYPASS LP BYPASS CONTROL The function of  this controller is to control the pressure of  R/H system. The steam which cannot be accepted by the medium pressure and low pressure turbine stages are bypassed to the condenser during start up and shutdown of  the turbine on partial load below boiler minimum load in case of load rejection, turbine trip etc. The LP turbine bypass controller (LPB) comprises: 1. 2. 3. 4.

Pressure control loop Valve position control loop Tracking unit Automatic control interface

Pressure control loop consists of: 1. 2. 3.

Set point derivation equipment Pressure controller Actual pressure derivation equipment

Two pressure set points are derived for the LPB and' are gated in an auctioneer. One is the fixed set point and the other is the variable set point. The variable set point is obtained with the aid of  a pressure transducer upstream of  the HP blading (Refer to as wheel chamber pressure). This provides a load dependent set point and hence reflects the dependence of the actual pressure signal on steam flow. The variable set point is limited to an upper value by an adjustable limiting function which is kept well below the response pressure of  the reheat safety valves. During start‐up and shut‐down the variable set point is suppressed by a fixed set point. The fixed set point can be adjusted between 0 and 120 % of  the maximum reheat pressure from the control room. Actual pressure is obtained by means of  a pressure transducer in the reheater outlet. A PI action pressure controller acts on the deviation between the actual pressure and the higher of the variable and fixed set point signals. Valve Position Control Loop The pressure controller output signal acts as the set point signal for the connected valve lift controller. The valve lift controller acts as a slave controller for the pressure control loop. This subordination improves both the stability and the dynamic response of the control system as a whole. The input signal for the valve lift controller is the deviation between the actual valve lift and the valve lift set point received from the pressure controller. The lift of  the LP turbine bypass control valve is governed by the position of  the servo piston in the electro‐hydraulic converter. The spray valve and the LP bypass valve are actuated in accordance with the pre‐set characteristics.

The LPB can be transferred from governing (auto) to manual control by depressing the controller on/off  push button. It is thus possible to adjust the valves by directly pressing the open and close push button. There is also an automatic transfer from governing to manual control during certain fault condition to prevent incorrect control action. Tracking Unit Continuous tracking of  the controlling variable which is not in action is provided to ensure bump less transfer between control system and manual at all times. In the" automatic governing" mode the manual set point adjuster is automatically tracked to the controller output signal. In the" manual mode " the valve lift controller signal is automatically tracked with the manual set point. However, zero deviation between the pressure set point and the actual pressure would be required for bump less transfer from manual governing to automatic governing, if the transfer is made in spite of an existing control deviation, this is compensated subsequently by the controller, which reposition the control valves as appropriate, Automatic Control Interface This acts as a centralized control for the proper operation of the LP Bypass controller. When AC I is switched on, the fixed pressure set point is set to a value of 3 bar above the actual pressure as soon as the light up signal is given at the start up sequence. A minimum opening of  25% is applied which causes the desuperheating spray, bypass stop and control valve to be opened during start up. This is to ensure minimum flow through reheater. To achieve a rapid pressure build up, the bypass valves are retained at this opening till the actual reheat pressure crosses 12 bar. This is known as "hold process". In this process the fixed point is automatically tracked to the actual pressure (tracking mode). Control is transferred to automatic governing only when reheat pressure is above 12 bars. The fixed set point is thus maintained at 12 bars. When a bypass valve lift of 35% is reached, the ACI for the fixed set point is switched off. The variable set point takes over from the fixed set point through the auctioneer and thus governs the reheat pressure set point. The fixed set point of 12 bar is reached at the unit shut down also. In this manner sufficient flow through reheater is ensured at all time, as also optimum rising of  the reheat pressure is achieved. Condenser Temperature Protection The purpose of  the condenser temperature protection is to protect the condenser from excessively high steam inlet temperatures. Thermocouples output temperature signals are converted into limit signals in an analog temperature conditioning module. The limit signals are passed to an interlock circuit which locks out the LP turbine bypass station. Following points are to be kept in mind before charging LP bypass.

2

1) Condenser vacuum should be > ‐0.7 kg/cm 2 2) Spray water pressure > 25 Kg/ cm 3) Temperature solenoids should be in reset condition given on the turbine console. Remember: If any of the above conditions is not present during LP bypass operation trip close command will be issued for LP bypass. HP BYPASS Purpose of HP bypass system: 1. 2. 3.

During boiler start up, it diverts the steam to the reheater thereby ensuring cooling of  reheater tubes. During turbine start up phase, it controls the live steam pressure. At each phase, it monitors and prevents excessive live steam pressure at boiler outlet.

In HP bypass system, there are two pressure control valves, two temperature control valves (spray water valves) and one spray water pressure control valves. PRESSURE CONTROL Pressure set point for opening of bypass pressure control valves is derived from actual pressure itself. It is normally kept to 8 to 10 kg above throttle pressure set point. There is provision for setting this value from UCB manually. The set point and actual value are compared and the difference between the two fed to the PI action controller. When actual throttle pressure exceeds the set value, the pressure control valves open. After PI controller there is one valve position controller which receives valve position feedback and make correction for accurate positioning There are certain criteria called fast opening criteria any one of these criteria is present the BP valves quickly open fully by a quick stroking device. Provided no closing criteria is present. TEMPERATURE CONTROL Temperature controller is a P‐PI action controller. An additional P‐Part is there because : a)

Whenever there is one fast opening command to a pressure control valve, the temperature control valve will open without delay.

b)

Whenever BP1 valve opens, spray valve (BPE) will open without delay. In the P‐l part actual temp down stream of  BP valves and temp set point are compared. The output of PI controller forms the position set point of the valve. This valve is compared with the actual valve position and a signal proportional to the error is issued to position the valve accurately.

REHEATER PROTECTION LOGIC ARMING OF REHEATER PROTECTION This protection gets armed after Boiler Load index >200 T and HP/LP opening > 2 % BOILER WILL TRIP. WHEN ANY ONE OR MORE OF THE FOLLOWING CONDITIONS OCCUR 1.

2.

3

TURBINE TRIPPED OR GEN CB OPENED AND HPBP OR LPBP IS IN < 2% POSITION AND LPBP NOT STARTS OPENING WITHIN 5 SECS i.

TURBINE WORKING AND

ii.

LOAD SHEDDING RELAY ACTED MEMORY STORED FOR 11 SECS AND

iii.

HPBP OR LPBP CLOSED < 2 %

i.

BOILER WORKING AND

ii.

TURBINE NOT WORKING AND

iii. HPBP OR LPBP CLOSED < 2 % THIS IS TO TRIP THE BOILER DURING STARTING WHEN THE HPBP OR LPBP CLOSED DUE TO SAFETY INTERLOCKS IN HP‐LP BYPAS SYSTEM SUCH AS DOWN STREAM TEMP V HIGH. VACCUM LOW ETC.