Woodward 505XT, Инструкция по установке и эксплуатации, Страница: 67 / 242

Manual 35018V1 505XT Digital Control System for Steam Turbines
Woodward 65
The Speed PID operates in the Frequency control mode when the generator breaker is closed and the
utility tie breaker is open. In the Frequency control mode, the unit will operate at the same speed or
frequency regardless of the load it is supplying (up to the unit’s load capability). Refer to Figure 3-8.
When breaker positions result in the Speed PID switching to Frequency control, the speed set point is
instantly stepped to the last turbine speed (frequency) sensed before Frequency control was selected.
This allows a bumpless transfer between modes. If the last speed sensed was not at the ‘Rated Speed
Set Point’ (synchronous speed) setting, the speed set point will ramp to the ‘Rated Speed Set point’
setting at a defaulted rate of 1 rpm/s (tunable through the Service mode).
In the Frequency control mode the speed set point can be varied with the Speed Set Point Raise/Lower
commands, as desired, to allow manual synchronization across a tie breaker to an infinite bus. See the
Synchronization section in this Chapter.
For indication purposes, a relay can be programmed to energize when the unit is in Frequency control.
Unit Load Control
The 505’s Speed PID can control two independent parameters when the generator breaker is closed;
frequency when the generator is isolated, and unit load when the generator is paralleled with an infinite
bus. When the generator breaker and utility tie breaker inputs are both closed, the Speed PID operates in
a Unit Load mode. This method of allowing a PID to control a second parameter is referred to as Droop.
Giving the Speed PID two parameters to control allows it to control unit load and act as a stabilizing effect
for any change in bus frequency. With this configuration, when bus frequency decreases or increases,
unit load increases and decreases respectively, based on the unit’s droop setting. The net effect is a
more stable bus. See Figure 3-9 for a frequency and load relationship diagram.