why need 3 element system in power plant?
if it is not there then what l happen?

Answer Posted / 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

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