ABB UNITROL 1020 - Page 80

Chapter 3 - Device Overview 
72 3BHS335648 E82 UNITROL 1020 User Manual
Kp
Setting of derivator gain
None
Upwer@Nolad
Adjustment of kceiling depending on input
voltage
None
HIR Controller
High initial Response controller:
Fast proportional exciter current regulator,
processing the output AUTO PID regulator as an
input to fast exciter current regulator.
Improves stability for very high ceiling factors
None
Ve Limiter
Limits PWM output
Improves stability for very high ceiling factors
None
Non-linear error of AUTO
PID
Non-linear error amplification depending on
configurable threshold
None
FRT Testing
Manipulating voltage measurement signal by
multiplication of time profile
Attention: The machine will boost and deliver
extensive Q to the network
None
3.4.5.4 Power System Stabilizer (PSS)
The PSS is used to improve the damping of possible oscillations in large transmission
networks by adding a signal to the voltage regulator of the existing excitation system.
It is also used to attenuate local rotor oscillations in synchronous generators through
additional influencing of the excitation. The main application is in excitation systems in
single or multi-machine power plants.
Electromechanical oscillations can be classified into four main categories:
 Local oscillations between a unit and the rest of the generating station and
between the latter and the rest of the power system. Their frequencies typically
range from 0.8 to 2.0 Hz.
 Inter-plant oscillations between two electrically close generation plants.
Frequencies may vary from 1 to 2 Hz.
 Inter-area oscillations between two major groups of generation plants.
Frequencies are in a typical range of 0.2 to 0.8 Hz.
 Global oscillation characterized by a common in-phase oscillation of all
generators as found on an isolated system. The frequency of such a global mode
is typically under 0.2 Hz.
The IEEE Std. 421.5-1995 PSS 2A/2B/2C type model functionally represents the PSS.
This model is shown in the figure below.
The object of the power system stabilizing (PSS) equipment is to increase the generator
exciter‘s contribution in order to improve the stability of the highest possible operating
range of the generator. The PSS derives additional signals from the generator internal
frequency, which considerably improves the stability of the power transmission.