ABB Automation World 2012, V. Knazkins, 6 June 2012 Countermeasure of PSS4B for Low Frequency Oscillations PSS4B. ABB Group June 4, 2012 Slide 1

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1 ABB Automation World 2012, V. Knazkins, 6 June 2012 Countermeasure of PSS4B for Low Frequency Oscillations PSS4B June 4, 2012 Slide 1

2 Agenda Introduction Basic definitions: power system stability : The existing PSS types PSS IEEE PSS4B IEEE PSS4B Selected Results Conclusions June 4, 2012 Slide 2

3 Introduction Basic Definitions June 4, 2012 Slide 3 Rotor angle stability Small-signal stability which is concerned with the ability of the power system to maintain synchronism under small disturbances. The disturbances are considered to be sufficiently small that linearization of system equations is permissible for purposes of analysis Transient stability which is concerned with the ability of the power system to maintain synchronism when subjected to a large disturbance, such as a short circuit on a transmission line. Transient stability depends on the initial operating conditions of the system as well as the type, severity, and location of the disturbance Voltage stability.

4 Introduction Basic Definitions Electromechanical oscillations in a power system can be divided in 4 groups: - 4 : 1. 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 Hz Hz. 2. Inter-plant oscillations between two electrically close generation plants. Frequencies may vary from 1 to 2 Hz. 1 2 Hz. 3. Inter-area oscillations between groups of plants. Frequencies are in a typical range of 0.2 to 0.8 Hz Hz. 4. Global oscillation characterized by a common oscillation of all generators as found on an isolated system. The frequency of such a global mode is typically under 0.2 Hz. June 4, 2012 Slide Hz.

5 Introduction Theory Behind PSS PSS Oscillations in a simple power system: local mode. :. June 4, 2012 Slide 5

6 Introduction Theory Behind PSS PSS The Nordic power system: major transmission lines : June 4, 2012 Slide 6

7 Introduction Theory Behind PSS PSS The Nordic power system: oscillations at 0.29 and 0.59 Hz : Hz June 4, 2012 Slide 7

8 Introduction Theory Behind PSS PSS Thus, the main task of the PSS is to contribute a damping torque component to the generator at 2 different frequencies. In the Nordic power system these are oscillations at 0.29 and 0.59 Hz. PSS Hz. For large power systems, there can be more inter-area modes.. Also, there can be a global mode of oscillation with a very low frequency.. For conventional power system stabilizers it is a non-trivial task, since without examining of the complete power system is it difficult to know which generator participates in the inter-area modes. Thus, there is a need for a PSS which can contribute damping over a wide range of frequencies. June 4, 2012 Slide 8 PSS

9 The Existing PSS Types PSS There are a large number of power system stabilizers in existence. For instance, PSS1A, PSS2A/B, PSS3B, etc.., PSS1A, PSS2A/B, PSS3B,. The main focus is on the de-facto industry standard for PSS, namely, IEEE PSS2B. PSS IEEE PSS2B. These are widely accepted in Europe and North America as standard power system stabilizers. The properties of PSS2B are well understood and tuning rules are developed. PSS2B However, despite all the advantages of IEEE PSS2B, it is not very easy for it to achieve excellent damping of global modes of oscillations. IEEE PSS2B, June 4, 2012 Slide 9

10 IEEE PSS4B Since damping oscillations of very low frequency was a non-trivial task for existing PSS, Hydro Quebec developed a new type power system stabilizer, called Multiband PSS. PSS PSS. The Multiband PSS was standardized in 2005 and was named IEEE PSS4B. PSS 2005 IEEE PSS4B. PSS4B has 3 bands, each composed of 2 differential filters. PSS4B 3, 2 PSS4B is characterized by a large number of parameters which offer unprecedented tuning flexibility. PSS4B PSS4B can be tuned as follows: the low frequency band damps global oscillations, the intermediate band damps inter-area oscillations, and the high frequency band damps local oscillations. PSS4B :. June 4, 2012 Slide 10

11 IEEE PSS4B Transfer function of IEEE PSS4B IEEE PSS4B June 4, 2012 Slide 11

12 Selected Results For a simple power system with a lightly-damped local mode the following Bode plot was computed. fd No PSS PSS4B PSS2B 0.08 (f) / E fd (f) [pu/pu] June 4, 2012 Slide Frequency [Hz]

13 Selected Results Using the real HW implementation of UNITROL 6000 with PSS4B and a real-time simulator the following Bode plot was obtained. PSS4B UNITROL 6000 June 4, 2012 Slide 13

14 Conclusions A brief overview of power system stability and oscillatory modes was given. The problem of simultaneous stabilization of global, inter-area, and local modes of oscillations was outlined.. IEEE PSS2B is an excellent stabilizer; however, it is not very effective in simultaneous damping of multiple oscillations. IEEE PSS2B IEEE PSS4B was developed to alleviate the problem of simultaneous stabilization of multiple modes in a power system. IEEE PSS4B June 4, 2012 Slide 14 Simulation results and experiments with real-time simulator show that PSS4B has a great potential for addressing the problem of damping of electromechanical oscillations in power systems. PSS4B

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