Network Protection Systems Considering the Presence of STATCOMs

Abstract

STATCOM is a shunt type Flexible AC Transmission System (FACTS) device that maintains the voltage at the connection point by injecting/absorbing the reactive power. With the presence of STATCOM, the current magnitude during fault is modulated and the performance of available overcurrent relay is constrained. Distance relay, in such a situation, finds problem due to the compensation effect during the dynamic performance of STATCOM. The dynamic response time of STATCOM may overlap with the operating time of distance relay. The control action associated with the STATCOM also affects the performance of distance relay during line faults. The chapter presents the analytical and simulation studies for demonstrating the performance of Mho and quadrilateral type distance relay protecting a line with STATCOM. The performance of Inverse Definite Minimum Time (IDMT) overcurrent relay is also discussed.

Appendices

Appendix 1

The least error square algorithm is a powerful tool for estimation of phasors of power system signals. The fault current signal in a series compensated line can be modelled as

$$ i_{k} = I_{1} \sin (k\omega_{0} T_{s} + \phi ) + I_{S} \sin \left[ {k(\omega_{0} - \omega_{m} )T_{s} + \phi_{s} } \right]\,\, + k_{0} e^{{\frac{{ - kT_{s} }}{\tau }}} \, $$

(21.6)

where,

$I_{1}$ :

the peak of the fundamental component,

$I_{S}$ :

the peak of the subsynchronous frequency component,

$\omega_{0}$ :

the fundamental frequency, rad/s

$\omega_{m}$ :

the subsynchronous frequency, rad/s,

$T_{s}$ :

sampling interval, s,

$\phi$ :

the phase angle of the fundamental frequency component,

$\phi_{s}$ :

the phase angle of the subsynchronous frequency component,

$k_{0}$ :

the magnitude of the decaying DC component,

$\tau$ :

the time constant of the decaying DC component, s.

The above equation can be written in a linear form as

$$ i(k) = a_{11} x_{1} + \,a_{12} x_{2} + a_{13} x_{3} + \,a_{14} x_{4} + \,a_{15} x_{5} + \,a_{16} x_{6} $$

(21.7)

where,

$$ \begin{aligned} & a_{11} = \sin (k\omega_{0} T_{s} ),a_{12} = \cos (k\omega_{0} T_{s} ),a_{13} = \sin (k(\omega_{0} - \omega_{m} )T_{s} ), \\ & a_{14} = \cos (k(\omega_{0} - \omega_{m} )T_{s} ),a_{15} = 1,a_{16} = - kT_{s} , \\ & x_{1} = I_{1} \cos \phi ,\,x_{2} = I_{1} \sin \phi ,\,x_{3} = I_{S} \cos \phi_{S} ,\,x_{4} = I_{S} \sin \phi_{S} ,\,x_{5} = k_{0} ,\,x_{6} = \frac{{k_{0} }}{\tau } \\ \end{aligned} $$

The above linear equation can be written as,

$$ \left[ A \right]\left[ X \right] = \left[ B \right]\,\,\,\,\,\,\,\,\, $$

(21.8)

where, $\,\,\left[ A \right]\, = \,\left[ {\begin{array}{*{20}c} {\sin(\omega_{0} T_{s} )} & {\cos (\omega_{0} T_{s} )} & {\sin((\omega_{0} - \omega_{m} )T_{s} )} & {\cos ((\omega_{0} -\omega_{m} )T_{s} )} & 1 & { - T_{s} } \\ {\sin (\omega_{0}2T_{s} )} & {\cos (\omega_{0} 2T_{s} )} & {\sin ((\omega_{0}- \omega_{m} )2T_{s} )} & {\cos ((\omega_{0} - \omega_{m})2T_{s} )} & 1 & { - 2T_{s} } \\ \vdots &\vdots &\vdots&\vdots &\vdots & \\ \vdots&\vdots &\vdots &\vdots&\vdots & \\ {\sin (\omega_{0} NT_{s} )} & {\cos(\omega_{0} NT_{s} )} & {\sin ((\omega_{0} - \omega_{m} )NT_{s})} & {\cos ((\omega_{0} - \omega_{m} )NT_{s} )} & 1 & {- NT_{s} } \\ \end{array} } \right] {\text{and}} \left[ B \right] = \left[ {i(t_{0} + T_{s} )\,\,i(t_{0} + 2T_{s} )\,\,...i(t_{0} + NT_{s} )} \right]\,^{'}$ and $\left[ B \right] = \left[ {i(t_{0} + T_{s} )\,\,i(t_{0} + 2T_{s} )\,\, \ldots \;i(t_{0} + NT_{s} )} \right]^{'}$.

In the above relation, N represents for number of sample points per cycle. The unknown vector becomes, $\left[ X \right] = \left[ {x_{1} \,x_{2} \,x_{3} \,x_{4} \,x_{5} \,x_{6} } \right]^{'} \,$.

To estimate $\left[ X \right]$, following equation is used and fundamental component is obtained thereafter.

$$ \left[ X \right] = \left[ {\left[ A \right]^{T} \left[ A \right]} \right]^{ - 1} \left[ A \right]^{T} \left[ B \right]\,\,\,\,\,\, $$

(21.9)

For (A4), $\omega_{m}$ is obtained. The electrical resonance frequency of a series compensated line is described by

$$ \omega_{e} = \omega_{0} \sqrt m \,\,\,\, $$

(21.10)

where $\omega_{0}$ = the fundamental frequency, rad/s and $m$ = degree of compensation. The perturbation frequency is,

$$ \,\omega_{m} = \omega_{0} - \omega_{e} \,\,\,\, $$

(21.11)

Appendix 2

21.2.1 System Data

• The parameters of each line (Line-I-200 km, Line-II and Line-III-300 km);

• Positive sequence impedance = 0.03293 + j0.3184 Ω/km,

• Positive sequence capacitance = 0.01136 μF/km

• Zero sequence impedance = 0.2587 + j1.1740 Ω/km,

• Zero sequence capacitance = 0.00768 μF/km

• The parameters of each source are;

• Positive sequence impedance = 0.06979 + j1.99878 Ω,

• Zero sequence impedance = 0.2094 + j5.9963 Ω.

21.2.2 STATCOM Specifications

• 1. STATCOM Specifications: Thee-phase, two-level 24-pulse GTO-based VSC, 300 MVA rated power, 11 kV rated bus voltage. PWM switching frequency, 500 Hz.

• 2. Coupling transformer: Two transformers Y-Y (115 kV:11 kV, 50 MVA) and Y-Δ (115 kV:11 kV, 50 MVA).