Analysis and Damping of Subsynchronous Oscillations Using STATCOM

Abstract

Series compensation of long transmission lines is an economic solution to the problem of enhancing power transfer and improving system stability. However, series compensated transmission lines connected to the turbo generator can result in Subsynchronous Resonance (SSR) leading to undamped Subsynchronous Oscillations (SSO). The advent of Flexible AC Transmission System (FACTS) controllers using high power semiconductors has made it possible to apply these controllers in conjunction with fixed series compensation, not only to improve system performance, but also to overcome the problem of SSR. FACTS controllers based on Voltage Source Converter (VSC) are emerging controllers that have several advantages over the conventional ones using thyristors. STATCOM is a shunt FACTS controller suitable for voltage regulation and damping of oscillations. This chapter describes the analysis and simulation of a series compensated system with STATCOM connected at the electrical center of the transmission line. The SSR characteristic of the combined system is discussed. A new technique of SSR damping is presented in which a STATCOM injects subsynchronous current.

Appendices

Appendix

System Data

The technical data for the case studies are summarized below.

IEEE FBM

The system data is the modified IEEE First benchmark model. Data are given on 892.4 MVA, 500 kV base. The base frequency is taken as 60 Hz.

Generator Data

$$x_{d} = 1.79, \quad x_{d}^{'} = 0.169, \quad x_{d}^{''} = 0.135, \quad x_{q} = 1.71, \quad x_{q}^{'} = 0.228,\quad x_{q}^{''} = 0.20, \quad R_{a} = 0$$

$$\begin{aligned} T_{do}^{'} & = 4.3,\;T_{do}^{''} = 0.032,\; T_{qo}^{'} = 0.85, \;T_{qo}^{''} = 0.05,\;T_{d}^{'} = 0.4, \\ T_{d}^{''} & = 0.0259,\;T_{q}^{'} = 0.1073,\;T_{q}^{''} = 0.0463 \\ \end{aligned}$$

Multimass mechanical system

The self damping of 0.20 is considered for HP, IP, LPA and LPB turbines. The mutual damping between HP-IP, IP-LPA, LPA-LPB and LPB-GEN are taken as 0.30 whereas for GEN-EXC it is taken as 0.005 (Table 17.A.1).

Table 17.A.1 Multimass mechanical system data

The fractions of total mechanical torque T _m for HP, IP, LPA and LPB turbines are takes as 0.30, 0.26, 0.22 and 0.22 respectively.

Transformer and transmission line data

$$R_{t} = 0.00, \;X_{t} = 0.14 ,\; R_{L} = 0.02, \;X_{L} = 1.0, \;X_{SYS} = 0.06$$

Excitation System

$$K_{A} = 200, \;T_{A} = 0.025, \;E_{{fd{ \hbox{max} }}} = 6, \;E_{{fd{ \hbox{min} }}} = - 6$$

Power System Stabilizer

$$T_{w} = 10, K_{PS} = 6 , T_{1} = 0.10, T_{2} = 0.01, \xi = 0.5,\omega_{n} = 22 \text{rad/s}$$

$$V_{{PS { \hbox{max} }}} = 0.10, V_{{PS { \hbox{min} }}} = - 0.10$$

• Data for Analysis with STATCOM

Transformer and transmission line data

$$R_{t} = 0.00, \;X_{t} = 0.14 , \;R_{1} = 0.016, \;X_{1} = 0.8, \;X_{C} = 0.6$$

$$B_{C} = 0.25213, \;R_{2} = 0.004 , \;X_{2} = 0.2, \;X_{SYS} = 0.06$$

STATCOM Data

$$R_{s} = 0.0381, X_{s} = 0.5711 , b_{C} = 0.2984, R_{P} = 299.66$$

Voltage controller

$$K_{s} = 0.15, K_{p} = 0.0 , K_{i} = - 100, i_{Rmax} = 0.1681, i_{Rmin} = - 0.1681$$

Type II Controller

$$K_{1} = 0.175, K_{2} = 3.5, SSDC: X_{th} = 0.16,\,Limits\;on\;SSDC\;output = \pm 0.00285$$