723PLUS/Analog Load Sharing Manual 02879
86 Woodward
• Gain is too low. If the preceding procedure does not improve the slow
periodic cycling of the engine speed, the control may be limiting cycling
through the low gain control region set by the Window Width set point.
Increase the Gain set point to minimize the cycling. If actuator
movement becomes excessive, reduce the Compensation set point
until movement is acceptable. In some cases, Compensation may be
reduced to zero and only the Gain and Reset adjustments used. This
should be done only if necessary to eliminate excessive actuator
response to misfiring or other periodic disturbances. Reduce the
Window Width set point until the limit cycle amplitude is acceptable
without excessive rapid actuator movement.
2. Full Load Adjustment
Do these adjustments at the speed and load at which the engine is most
often operated.
If operation in this range is satisfactory, no further dynamic adjustments are
necessary. If during changes in load or an actuator bump, excessive speed
errors occur, increase the Gain Slope adjustment until engine performance
is satisfactory.
If excessive actuator movement again occurs, do procedure 3, then repeat
procedure 2. If the settling time after a load change is too long, reduce the
Reset set point slightly and increase the Gain slightly. If slow-speed hunting
occurs after a load change but decreases or stops in time, increase the
Reset set point slightly and reduce the Gain set point. See Figure 4-4.
WARNING—OVERSPEED
The use of negative Gain Slope should be considered carefully. Low gain at
high fuel levels will result in poor load rejection response or possible
overspeed. To prevent possible serious injury from an overspeeding engine,
the Maximum Fuel Limit must be set near the full load output current
demand to prevent excessive integrator windup and a subsequent low gain
condition.
3. When significant load changes occur, the control should switch
automatically to high gain (gain x gain ratio) to reduce the amplitude of the
speed error. Reduce (or increase) the Window Width set point to just
greater than the magnitude of acceptable speed error. A value of Gain Ratio
too high will cause the control to hunt through the low-gain region. This
normally will occur only if the Window Width is too low. If necessary to
decrease the Window Width to control limit cycling (identified by the engine
speed slowly cycling from below to above the speed setting by the amount
of Window Width), the Gain Ratio may be reduced for more stable
operation.
NOTE
When paralleled to the utility, speed error is created when corrective bias
signals following load changes are applied to the speed reference by droop
or the Load Sharing Control inputs. Speed errors are manifested as load
transients instead of speed transients. An actuator bump is recommended
to test dynamic settings when operating in parallel with the utility.
4. Verify that performance at all speed and load conditions is satisfactory and
repeat the above procedures if necessary. Full load rejection testing is
recommended as part of the performance testing.
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