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DESIGN CRITERIA FOR LP BYPASS SYSTEM OF ... - Bhelpswr.co

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DESIGN CRITERIA FOR LP BYPASS SYSTEM OF ... - Bhelpswr.co Powered By Docstoc
					 Design Criteria for

LP BYPASS SYSTEM
 LP Bypass system provide a very
effective means of controlling
reheat –steam flow during



üStartup
üLow-load / part load
 operation
üSudden load rejection
 It enhances fast starting
capability of turbines from
all initial conditions e.g.


 üCold condition
 üWarm condition
 üHot Condition
LP steam-bypass system operate in
     parallel with the turbine



 Protect Condenser from excessive
  temperature and pressure that
could result from sudden injection
       of superheated steam
 Ensure coordinated control between
HP and IP turbine control valves and
the steam bypass systems to operate at
any remaining load

Subsequently reloaded in a controlled
manner
Schematic Diagram of Bypass System
• The controls for LP Bypass system
  are combination of electrical and
  well proven hydraulic system

• Electro-hydraulic converter
  provides the necessary link
  between hydraulic actuator and
  electrical system
• The LPBypass Controller acts as a
  maximum pressure Controller

• It regulates the reheater pressure
  either to the fixed set value or
  suitably derived variable set value

• If the reheater pressure exceeds
  this set value, the Controller
  causes the electro-hydraulic
  converter to operate and initiate
  bypass operation
          Set Value formation

üThe Two set values – fixed and
variable are formed for the LPBypass
control system
üset value to be used is determined by
a maximum value selector
üFor the formation of variable set
point, a pressure transducer is used to
measure the steam pressure in HP
turbine
  SEQUENCE OF EVENTS RESULTING
      FROM LOAD REJECTION
  Upon receiving load rejection signal from
  electrical system:
ü Turbine Speed Controller assumes
  control of the TG set

ü It initiates fast closure of HP & IP
  turbine control valves through position
  controller

ü Fast closure of turbine control valves
                                           st
  cause an immediate decrease in HP 1           .
  Stage pressure
  SEQUENCE OF EVENTS RESULTING
      FROM LOAD REJECTION

ü Pressure increases in main and
  reheat steam systems

ü These pressure changes are sensed
  by HP and LP Bypass controllers

ü Respective bypass valves are
  opened
If LP steam- bypass system
  fails or the condenser
 cannot accept LP bypass
steam , Safety Valves open
    and dump steam to
         atmosphere
       Hydraulic Mode of Operation




• The controller controls plunger coil of Electro
  Hydraulic Converter
• With increase in voltage, the jet pipe is deflected
  towards right
• Converter piston moves downwards leading to
  generation of LPB signal oil through Follow-up
  pistons provided in the hydraulic control system
    Hydraulic Mode of Operation




• Two Follow-up Pistons actuate and open first
  stage of water injection valve

• Remaining two Follow-up Pistons generate signal
  oil for opening LPBypass stop and control valve
ADJUSTMENT
     OF
LPBYPASS
CONVERTER
Design of LPBypass Valves for 210
       MW Steam Turbine




                          • Controlled
                            by 8 bar
                            mineral oil
Design of LPBypass Valve for 500 MW
           Steam Turbine




                        • Controlled by
                          36 bar FRF
       Protection Devices




ü Low Vacuum Condensor Protection
ü Spray Water Pressure Switch
ü Condensor Temperature Protection
  Protection Devices cause closure of
  bypass station in case of following
              eventualities


a) Condensor vacuum is low ( > 0.6 bar
   absolute )
b) Spray water pressure is low ( < 8.5 /
   9.5 bar )
c) Temperature of condenser body is
   high (> 90° C )
 Water Injection Valves operate in
             two stages




• Second stage Water Injection Valves
  open when steam flow through
  LPBypass Valves increases more than 45
  %
CURVE FOR LPBYPASS CONTROLLER
• Damping device

				
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posted:5/3/2014
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