Basler Electric DECS-400 - Manual (Page 160)

148 9369700990 Rev R
Closed-Loop Voltage Regulator Response Measurements
Proper operation of the automatic voltage regulator and exciter are critical to the performance of the PSS.
Step response measurements of the voltage regulator should be performed to confirm the voltage
regulator gain and other critical parameters. A transfer function measurement between terminal voltage
reference and terminal voltage should be performed with the unit operating at very low load. This test
provides an indirect measurement of the PSS phase requirement. As long as the unit is operating at very
low load, the terminal voltage modulation does not produce significant speed and power changes.
Input Signal Measurements
Tests should be performed at various load levels to confirm that the input signals are calculated or
measured correctly. Since the PSS uses compensated terminal frequency in place of speed, the derived
mechanical power signal should be examined carefully to ensure that it does not contain any components
at the electromechanical oscillation frequencies. If such components are present, it indicates that the
frequency compensation is less than ideal, or that the unit inertia value is incorrect.
Stabilizer Step Response Measurements
A standard technique for verifying overall system response is through step response measurements. This
involves exciting the local electromechanical oscillation modes through a fixed step change in the voltage
regulator reference. Damping ratio and frequency of oscillation can be measured directly from recordings
of generator speed and power for different operating conditions and settings. Normally this test is
performed with variations of the following:
•
Generator active and reactive power loading
•
Stabilizer gain
•
System configuration (e.g., lines out of service)
•
Stabilizer parameters (e.g., phase lead, frequency compensation)
As the stabilizer gain is increased, the damping should increase continuously while the natural frequency
of oscillation should remain relatively constant. Large changes in the frequency of oscillation, a lack of
improvement in damping, or the emergence of new modes of oscillation are all indications of problems
with the selected settings.
Large Disturbance Measurements
Depending on the location, tests may be performed to measure the response of the system to large
disturbances. These disturbances can include line switching, load rejection, or generation runback. For
example, on hydroelectric units, high mechanical power rates of change (in excess of 20% per second)
may be possible. This requires an examination of the terminal voltage excursion that can be caused in
dual-input stabilizers that band limit the mechanical power signal.
Disturbance Recording
The DECS-400 is equipped with a power data recorder that can capture several quantities. Some of these
quantities include terminal voltage, field voltage, active power, reactive power, speed, generator current,
and stabilizer output. The recorder can be set to trigger automatically for a system disturbance and save
the captured data. This feature allows the user to obtain direct recordings of actual system disturbances
for comparison with simulated responses. This can be very important since it may not be possible to
configure the system to perform staged tests of worst-case configurations and contingencies.
Commissioning DECS-400