Standard Technical Features of BTG System for Supercritical 660 ...

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Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Unitsvi)The sequence of startup mode shall be of the following types:a) Automatic modeIn this mode of operation, the sequence shall progress withoutinvolving any action from the operator. The sequence start/stopcommand shall be issued from the TFT/KBDs.b) Semi-automatic modeIn this mode of operation, once the sequence is initiated, the stepprogressing shall be displayed on the TFT. But the step executioncommand shall be prevented and shall be sent by the operator viathe keyboards. It shall be possible to bypass and/ or simulate one ormore criteria to enable the program to proceed. All the criteriabypassed shall be logged and displayed. It shall be possible to putthe system on the auto-mode after operating it on semi-automaticmode for some steps or vice-versa, without disturbance to thesequence operation.c) Operator test modeIt shall be possible to use the sequential control in operator guidemode/ test mode i.e. the complete system runs and receives inputfrom the plant and the individual push button stations (whereprovided)/ keyboards but its command output is blocked. Thewhole programme, in this case shall run in manual mode. Thismode shall allow the operator to practise manual operation usingstep and criteria indications. The actual protection should remainvalid during this mode of operation also.vii) For the HT and critical LT drives, the command shall be providedthrough redundant output module and inputs (status, switchgear &process) shall be acquired through input modules. The drive logic shallbe implemented in the redundant controller.The status for the 11 kV, 3.3 kV drives and other selected importantdrives shall also be wired in parallel to redundant input modules so thaton failure of the single input modules, the information regarding thestatus of the affected drive remains available in OLCS.viii) The output modules control module shall have the feature that ensuresthat in case of failure, all the outputs are driven to zero. The 24V DCcommand outputs to drives for on/open, off/close shall be separate andindependent and inverted outputs shall not be employed. For inchingtype of drives, position transmitter power supply and monitoring ofposition transmitter signal shall be provided.ix) The OLCS shall also include the control of electrical systems inaddition to the auxiliaries of boiler & turbine such as open/close oron/off etc. of various electrical systems such as generator, generatorauxiliary systems, breakers of 11kV, 3.3 kV, 415 V switchgears,144
Standard Technical Features of BTG System for Supercritical 660/800 MW Thermal Unitssynchronisation of unit etc. All the features and requirements asindicated above shall also be applicable for electrical system.17.2.5 Analog controls/closed loop controls system (CLCS) functionsThe CLCS shall continuously act on valves, dampers or other mechanicaldevices such as hydraulic couplings etc., which alter the plant operationconditions. The system shall be designed to give stable control action insteady state condition and for load changes in step/ramp over the load rangeof 50% to 100% MCR with variation or parameters within permissiblelimits. The system shall have the following minimum features:i) The controller capability shall, as a minimum, include (a) P, PI, PDand PID control functions and their variations (b) cascade control (c)feed forward control (d) state-variable based predictive control forSH/RH temperature control (e) on-off control, (f) ratio and biascontrol, (g) logical operation etc.ii)The loop reaction time (from change of output of the sensor of thetransmitter/temperature element to the corresponding control commandoutput) shall be within 500 milli seconds. However, for faster loopssuch as feed water, furnace draft, PA header pressure control loop etc.the same shall be based on actual process requirement but shall not bemore than 250 millisecond.iii) The controls shall be bumplessly transferred to manual mode onconditions such as failure of redundant control power supply, failure ofredundant controllers, field input signal not available, analog inputexceeding preset value, etc. as a minimum.iv) Any switchover from auto to manual and manual to auto shall bebumpless and without resulting in any change in the plant regulationsand the same shall be reported to the operator.v) Buffered analog output (positioning signal) of 4-20mA DC shall beprovided from CLCS to the respective E/P converters. For electricalactuators, pulse type output (bound less control) shall be preferred.vi)The system shall be such that when permissible limits are exceeded, anautomatic switchover from an operation governed by maximumefficiency, to an operation governed by safety and availability isaffected.17.2.6 Control system requirementsThe control system along with its measurement system shall performfunctions of closed loop control, sequence control, interlock & protection ofSG, TG and auxiliaries under all regimes of unit operation. Themeasurement system of control system shall perform the functions of signalacquisition, conditioning and signal distribution of various types of145
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