If Turbine does not maintain the load as per set load, then this condition is called load hunting.Following are the some potential reasons for load hunting
1-Problems associated
with actuators:
These are related to leakages in actuators, piston stuck up,
oil holes elongation etc. Because of these issues there will interruption or
fluctuation of secondary oil flow through actuators, this creates the problems of
actuator miss-operation & eventually load hunting.
2-Improper
calibration of actuators:
This results into mismatch of actuator opening & given
set point or valve demand
3-Lower control oil
pressure than required:
Actuators are designed for specific pressure of control oil,
if the control oil pressure at actuator inlet becomes less, then there will be
more chances of mal function of actuator.
4-Fluctuation of
control oil pressure/flow:
Fluctuation of control oil pressure or flow due to
malfunction of pump or line PRV may lead to actuator misoperation & hence
creates load hunting.
5-Control oil line
leakage:
Leakages in control oil line welding & flange joints
will lead to fluctuation of flow & pressure causing actuator malfunction
& load hunting.
6-Contamination in control oil
Foreign particles present in oil lead to improper
functioning of actuators, which causes load hunting
7-Burs or scoring
marks on actuator spindle & control valves spindles:
Burs or any rough scoring marks on spindles will lead to
improper operation of actuator & valves
8-Passing of control
valves:
This is the major reason for load fluctuation & Turbine
over speed
9-Improperly set
control valve cones:
During turbine HP valve assembly after maintenance, HP
control valve cones should be set as per factory set readings, if it is
disturbed, then there will be issues related to load hunting, low load at more
HP demand or over speed.
10-Damage or broken
control valves spindle & discs (cones):
Spindle damage or disc damage makes uncontrolled operation,
as there will be wrong response from control valves to governor.
11-Wrongly tuned P&IDs in Governor: The disturbed values in P&ID tuning will result
into heavy load hunting
12-Malfunction of
Governor: This is very rare, but certainly results into load fluctuation of
Turbine trip
13-Sudden changes in
inlet steam pressure & extraction steam pressure
14-Fluctuation of
grid frequency
15-Failure of Turbine inlet & extraction pressure sensor
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