Pressure control mode of 250 mw BHEL make steam turbine

Hi Engineers,

I need some knowledge about Pressure control mode in BHEL make steam turbines. As far as I understand in Pressure control mode Main Steam control valves try to keep the turbine inlet pressure at set value. So load might fluctuate but it does not matter in Pressure control.

But in this mode we have two sub modes. Initial Pressure Mode and Limit Pressure Mode. What are these and what is the difference between the two?

Can anybody help?
 
Hi Engineers,

I need some knowledge about Pressure control mode in BHEL make steam turbines. As far as I understand in Pressure control mode Main Steam control valves try to keep the turbine inlet pressure at set value. So load might fluctuate but it does not matter in Pressure control.

But in this mode we have two sub modes. Initial Pressure Mode and Limit Pressure Mode. What are these and what is the difference between the two?

Can anybody help?
Hi

Would you tell us the type /size /model of TURBINE/CONTROLS SYSTEMS...

I got a document with a BHEL make steam turbine as following:
Turbine and Auxiliaries:
Main Turbine:
Make: BHEL, Hyderabad
Rated Speed: 3000 rpm
No. Of Cylinders 3 (HP, MP, LP)
At 110 MW- steam flow at inlet is 364.5 t/hr (pressure -130 atm., Temp. 535°C R/H
535°C cooling water 32°C)

And now I suggest you the following notes from this very interesting document:
Pressure control can be operated on initial pressure control mode or limit
pressure control mode by selection from desk. When the pressure controller is not
effective, its output corresponds to maximum valve opening . As the steam working
condition approaches the working range of controller, tracking to a preset take over
margin is effected, so that the pressure controller can rapidly assume control of the
valve. When the pressure controller controls the valves the load controller is tracked
as per pressure controller. The power delivered by the Turboset is decided by the
boiler steam pressure.
In the initial pressure control mode the set pressure is predetermined with
respect to load in a characteristic form. During initial startup, for example, for a
pressure of 30kg/cm2 20MW load is maintained and for change of 30kg/cm2 to
150kg/cm2 a change of load from 20MW to 150 MW is envisaged. Any deviation
between the reference pressure valve and actual pressure valve is corrected by
regulating the power output.
In the limit pressure control mode, the pressure controller influences the main
steam control valve to support boiler pressure control, only if a preset MS pressure
deviation is exceeded say by 10kg/cm2 as per the characteristics. This provision
allows the load controller to handle small quick load variations until the pick up limit
of limit pressure control is reached.
When the turbine is in operation, one of the three controllers (Speed, Load and
pressure) will be exercising the control and other will be matched continuously for
quick transfer. The speed and load controllers are tied up to a maximum selector
circuit. The output of this circuit is compared with the sum of speed and 100% load
signal via a Min selection circuit to avoid erroneous load control signal. The speed/
load control signal is compared with pressure control via a Min selection circuit.
In case of sudden separation of the loaded Turboset from grid the output of the
load controller is immediately reduced below the output of the speed controller which
is set at station load. Due to maximum selection the speed controller assumes control
and returns the turbine back to the reference speed. This provision improves the
dynamic response of the closing of the main stream control valves and keeps the
turbine speed form rising along the droop characteristic.

Do not hesitate to give us your feedback!
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You need assistance ? We can assist you !

ControlsGuy25.
 
Initial steam pressure control Mode:

MW is controlled by Boiler and Steam pressure is maintained by Turbine Controls.


Limit Pressure Control Mode:

Normally Load Controller maintains TG power output and boiler controller maintains steam pressure.
But when pressure falls to a preset value, EHTC controls steam flow through Control valves only to maintain steam pressure. MW is not controlled.
 
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