Answer / pramod d.gaur

Three element means to control three parametes,i.e.
feedwater flow in to the drum, steam flow and level
control of drum,now in a three element, the set point of
level control track the ratio of steam flow to the
feedwater flow,i.e, as much as amount of steam flow flow
out of drum or in other word steam consume by process
equall amount of feedwater flow in to the drum.In such
cases there is very least chances that water from the drum
get carried away with steam in to the turbine when there is
load fluctuation

Regards

Pramod D.gaur

Answer / ajeet pal singh

As steam flow and feed water flow effects the level of
boiler drum these two are taken as two elements in three
element control system to achieve smooth control on drum
level ideally these two are capable to maintain the drum
level but the third element as drum level actual itself is
taken to compensate various leakages etc. As we know the
controller doesn't respond unless it senses some error
between PV and SV and if drum level actual is taken alone to
control the drum level, controller will respond only if
level goes up or down to its set point and this will
maintain always a pulsating drum level instead of a straight
line. Steam flow and feed water flow consideration gives a
feed forward effect to controller hence a smooth control on
drum level can be achieved

Answer / kmns kiran

Three element control is just for better controlability of drum level with feed water incoming flow, steam output flow & drum level
In case of any bad signal from feed water & steam flow (BDQ) , then control will go to single element drum level control.
Plant will not trip

Answer / ramachari

three element is between the feed water flow,steam flow and drum level.Mainly it is decides the how much of amount feed water is required with steam flow and vice versa with no variation of the drum level and will take the compensation of the temp and pressure.means it will maintain the drum level with the three parameters level,presuusre,temp also.

Answer / kul bhushan emecon controls

In Power Plant three element control is always required
because when Load changes then steam flow will change vice
versa drum level & flow of feed water will change to manage
the action between all three perameters we require three
element control.Otherwise due to any mismanage between all
three plant will trip.

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