TURBINE GLAND STEAM CONDENSER

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Function of the Gland Steam Pressure Control System:
This system ensures the sealing of glands in HP, IP and LP turbine under various
Load conditions.
The Turbine glands are self seal type. Upto approximately 40% load steam from auxiliary
source (CRH/Aux.steam header) through gland steam valve is taken to seal all the HP, IP
and LP glands. During this period the steam leakage valve connecting this header to
condenser is kept closed. After approx. 40% of load, gland steam valve is closed and
steam leakage valve is opened. Pipings are so sized that the leak-off steam from Front
and Rear end of HP turbine goes to the condenser through steam leakage valve while
leak-off steam from the IP front and rear glands is utilised for sealing the LP glands,thus
ensuring proper temperature of sealing steam. The leak-off steam and air from the last
chambers of each rotor is sucked into a gland cooler.
Building up of vacuum in the condenser is the first step during start-up. For building up
vacuum it is necessary to seal the turbine gland by supplying steam to the shaft through
gland steam valve. The control system opens the gland steam supply valve until the
pressure in the header acquires a preset value. Subsequently when the set picks up Load,
the pressure of steam inside HP and IP turbine builds up resulting in the leakage of steam
from the Turbine into gland steam supply header which in turn would result in increase of
pressure. The controller gradually closes the gland steam supply valve and opens gland
leak-off valve, if required.
Electro-Hydraulic valve actuators:
The actuators of the two control valves are continuously under the control commands
from the electric controller through 2 Electro hydraulic converters.
The +ve voltage output opens the gland steam supply valve while the -ve voltage output
opens the gland leak-off valve.
Each hydraulic actuator has its own motor driven oil pump supplied from station AC system.
In the event of pump failure, the valve remains in stayput position. Subsequent operation
of the valve can be carried out locally though hand pump.
Pressure measurement:
The pressure in the header is measured by means of a pressure transducer. This
measurement is used for control as well as display purposes. The measurement range is -100
to +300mmWC
Control system equipment:
The control system is comprised of solid-state control system. The modules, including
power supply, operating and monitoring modules are arranged in a 3 tier group frame and
housed in a cubicle.
The pressure controller has PI characteristics. Its output is fed to electro-hydraulic
actuators via a PID position controller. The function of this controller is to set the
position of the valve as determined by the pressure controller as quickly and accurately
as possible.

The actuators incorporate magneto-resistor potentiometer to give contactless
non-wearing position indication. The output voltage of the potentiometer varies
proportionally with the valve position. The voltage is used to give an actual value
signal to the position controller as well as for valve position indication in the control
room. In order to ensure stable control characteristics during the transition period of
Gland steam supply valve closure to Leakage steam supply valve opening or vice-versa,
the valve travel of both the valves have got slight overlap.
The reference value for the steam pressure in the header can be set between 0-220mmWC
by means of potentiometer on the controller.
The pressure reference value is compared with the actual value supplied by the
transducer at the input to control of the deviation amplifier. The press controller is
given the progressive static characteristics so that its action is increased in the event
of large disturbance to the press control system eg., Load Trip. For small deviation
uptp +10mmWC, the characteristics is chosen to ensure stable control under all
operating conditions. The controller action is increased for larger deviations.
Progressive characteristics of the press controller indicates that it is possible to
adjust the amplifications between the press controller and position controller
independently for each valve. This feature enables to take care of any inaccuracies in
the sizing of the supply and leakage valves and the pipe lines.

n increase of

ion AC system.

nt range is -100

up frame and

0-220mmWC

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