Important Short questions and answers: Co-Ordination of FACTS Controllers

CO-ORDINATION FACTS CONTROLLERS

1. What is meant by controller interactions?

If two or more FACTS devices are connected in same transmission line then the operating variables between them must have better co-ordinated, that is called controller interaction. If FACTS devices are not co-ordinated, it creates unwanted oscillation in the transmission lines.

2. What are the types of controller interactions?

Multiple FACTS controller of a similar kind

Multiple FACTS controller of a dissimilar kind

Multiple FACTS controllers and HVDV converter controllers

3. What are the frequencies ranges of controller interactions?

0 Hz for steady state interactions

0 - 3/5 Hz for electromechanical oscillations 2 - 15 Hz for small signal or control oscillation

10 - 50/60 Hz for sub synchronous resonance (SSR) interaction

> 15 Hz for electromagnetic transients, high - frequency resonance or harmonic resonance interactions, and network resonance interactions

4. What is meant by steady state interaction?

Steady-state interactions between different controllers (FACTS-FACTS or FACTS HVDC) occur between their system related controls. They are steady state in nature and do not involve any controller dynamics. These interactions are related to issues such as the stability limits of steady state- state voltage and steady-state power, included are evaluations of the adequacy of reactive-power support at buses, system strength and so on. ( Eg) Steady state voltage control between FACTS-HVDC for ac voltage regulation.

5. What is the analysis method used to determine the steady state interaction?

To determine this interaction Load-Flow and Stability programs are used.

6. What is meant by electromechanical oscillation interaction?

Electromechanical oscillation interaction between FACTS controllers involve

synchronous generators, compensator machines and associated power system stabilizer control. The oscillations include local mode oscillations typically in the range of 0.8 - 2 Hz, and inter area mode oscillations, typically in the range of 0.2 - 0.8 Hz. The local mode is contributed by synchronous generators in a plant or several generators located in close vicinity, the inter-area mode results from the power exchange between tightly coupled generators in two areas linked by weak transmission lines.

7. What is the analysis methods used to determine the electromechanical oscillation interaction?

To determine this interaction Eigen value analysis programs are used.

8. What is meant by control or small signal oscillation interactions?

Controller interactions between individual FACTS controllers and the network or between FACTS controllers and HVDC links may lead to the onset of oscillations in the range of 2 - 15 Hz. These oscillations are largely dependent on the network strength and the choice of FACTS controller parameters, and they are known to result from the interaction between voltage controllers of multiple SVC’s, the series resonance between series capacitors and shunt reactors in the frequency range of 4 - 15 Hz and so forth. The emergence of these oscillations significantly influences the tuning of controller gain.

9. What are the analysis methods used to determine the control or small signal oscillation interaction?

These high frequency oscillation interactions are determined by frequency scanning programs, electromagnetic transient programs (EMTP’s), Physical simulators and eigen value analysis programs.

10.            What is meant by sub synchronous resonance interactions?

Sub synchronous oscillations may be caused by the interaction between the Generator torsional system and the series compensated transmission lines, the HVDC converters, the generator excitation control or even the SVC’s. Theses oscillations usually in the frequency range of 10 - 50/60 Hz, can potentially damage generator shafts.