**2. Apparent reactance injected by series FACTS devices**

In general, FACTS compensator can be divided into three categories (Acha, E. al., 2004): Series compensator, Shunt compensator, and combined series-series compensator. In this chapter, we study the series FACTS devices.

#### **2.1. GCSC**

40 An Update on Power Quality

various parts of the world.

unified power flow controllers.

The FACTS concept is based on the substantial incorporation of power electronic devices and methods into the high-voltage side of the network, to make it electronically controllable. FACTS controllers aim at increasing the control of power flows in the high-voltage side of the network during both steady state and transient conditions. Owing to many economical and technical benefits it promised, FACTS received the support of electrical equipment manufacturers, utilities, and research organizations around the world. This interest has led to significant technological developments of FACTS controllers (Sen, K.K.; Sen, M.L., 2009), (Zhang, X.P. et al., 2006). Several kinds of FACTS controllers have been commissioned in

Popular are: load tap changers, phase-angle regulators, static VAR compensators, thyristors controlled series compensators, interphase power controllers, static compensators, and

The main objectives of FACTS controllers are the following (Mathur, R.M.; Basati, R.S., 2002):


The most Utility engineers and consultants use relay models to select the relay types suited for a particular application, and to analyze the performance of relays that appear to either operate incorrectly or fail to operate on the occurrence of a fault. Instead of using actual prototypes, manufacturers use relay model designing to expedite and economize the process of developing new relays. Electric power utilities use computer-based relay models to confirm how the relay would perform during systems disturbances and normal operating conditions and to make the necessary corrective adjustment on the relay settings. The software models could be used for training young and inexperienced engineers and technicians. Researchers use relay model to investigate and improve protection design and algorithms. However, simulating numerical relays to choose appropriate settings for the steady state operation of over current relays and distance relays is presently the most

In the presence of series compensators the system FACTS devices i.e. GTO Controlled Series Capacitor (GCSC), Thyristor Controlled Series Capacitor (TCSC) and Thyristor Controlled Series Reactor (TCSR) connected in high voltage (HV) transmission line protected by distance relay, the total impedance and the measured impedance at the relaying point depend on the injected reactance by compensators. So there is a reel impact on the relay settings zones.

This chapter presents a comparative study of the performance of MHO (admittance) distance relays for transmission line 400 kV in Eastern Algerian transmission networks


familiar use of relay models (McLaren et al., 2001).

**1.1. Problem statement** 

**1.2. Objectives** 

The compensator GCSC mounted on figure 1.a is the first that appears in the family of series compensators. It consists of a capacitance (C) connected in series with the transmission line and controlled by a valve-type GTO thyristors mounted in anti-parallel and controlled by an angle of extinction (γ) varied between 0° and 180°. If the GTOs are kept turned-on all the time, the capacitor *C* is bypassed and it does not realize any compensation effect. On the other hand, if the positive-GTO (GTO1) and the negative-GTO (GTO2) turn off once per cycle, at a given angle *γ* counted from the zero-crossing of the line current, the main capacitor *C* charges and discharges with alternate polarity (Zhang, X.P. et al., 2006), (De Jesus F. D. et al., 2007).

**Figure 1.** Transmission line in presence of GCSC

Hence, a voltage *VC* appears in series with the transmission line, which has a controllable fundamental component that is orthogonal (lagging) to the line current.

The compensator GCSC injects in the transmission line a variable capacitive reactance (*XGCSC*). From figure 1.b the expression of *X*GCSC is directly related to the controlled GTO angle (γ) which is varied between 0° and 180° as expressed by following equation (De Souza, L. F. W. et al., 2008), (Ray, S. et al., 2008) :

$$X\_{\rm GCSC}(\gamma) = X\_{\rm C\,max} \left[ 1 - \frac{2}{\pi}\gamma - \frac{1}{\pi}\sin(2\pi) \right] \tag{1}$$

Where,

$$X\_{\mathbb{C}\max} = \bigvee\_{\mathbb{C}\dots \alpha} \tag{2}$$

And,

**2.3. TCSR** 

(TCR).

al., 2006):

Impact of Series FACTS Devices (GCSC, TCSC and TCSR) on Distance Protection Setting Zones in 400 kV Transmission Line 43

(6)

(7)

<sup>1</sup> . . *XC j C*

.max

*C L*

*X X*

*X X*

*C L*

. 2 sin(2 ) ( )

.max

The compensator TCSR is an inductive reactance compensator at which its inductive reactance is continually adjusted through the firing delay angle (*α*) of the thyristors as shown in figure 3.a. It consists of a series reactor shunted by a thyristors controlled reactor

If the firing delay angle is 180°, the TCSR operates as an uncontrolled reactor (*L1*). When the angle decreases below 180°, the inductive reactance of TCSR decreases and at 90° it is given

From figure 3.b, the compensator TCSR injected in the transmission line a variable capacitive reactance (*XTCSR*). The expression of XTCSR is directly related to the controlled thyristors angle (α) expressed by the following equation (Acha, E. al., 2004), (Zhang, X.P. et

. . () 2 sin(2 ) ( ) // ( ) ( )

*X X X X*

2 1

*L L*

*L L*

2 1

2 1 max

*L L*

*X X*

*L L*

2 1 max

2 sin(2 )

 

(8)

 

From the equations (4), (5) and (6), the equation (3) becomes:

*TCSC*

*X*

by the parallel connection of the reactors (*L1*//*L2*).

**Figure 3.** Transmission line in presence of TCSR.

2 1

 

*X X X XX*

*TCSR L L*

 2 sin(2 )

 

> 

#### **2.2. TCSC**

The compensator TCSC mounted on Figure 2.a is a type of series FACTS compensators. It consists of a capacitance (C) connected in parallel with an inductance (*L*) controlled by a valve mounted in anti-parallel conventional thyristors (*T1* and *T*2) and controlled by an angle of extinction (α) varied between 90° and 180°.

**Figure 2.** Transmission line in presence of TCSC

From figure 2.b, the compensator TCSC injected in the transmission line a variable capacitive reactance (*XTCSC*). The expression of *XTCSC* is directly related to the controlled thyristors, angle (α) which is varied between 90° and 180° and expressed by following equation (Acha, E. al., 2004), (Sen, K.K.; Sen, M.L., 2009):

$$X\_{\rm TCSC}(a) = X\_{\rm C} \; / \, X\_{\rm L}(a) = \frac{X\_{\rm C} X\_{\rm L}(a)}{X\_{\rm C} + X\_{\rm L}(a)} \tag{3}$$

$$X\_L(\alpha) = X\_{L\max} \left[ \frac{\pi}{\pi - 2\alpha - \sin(2\alpha)} \right] \tag{4}$$

Where,

$$X\_{L\max} = L.o.\tag{5}$$

And,

42 An Update on Power Quality

Where,

**2.2. TCSC** 

Where,

Souza, L. F. W. et al., 2008), (Ray, S. et al., 2008) :

max

of extinction (α) varied between 90° and 180°.

**Figure 2.** Transmission line in presence of TCSC

equation (Acha, E. al., 2004), (Sen, K.K.; Sen, M.L., 2009):

The compensator GCSC injects in the transmission line a variable capacitive reactance (*XGCSC*). From figure 1.b the expression of *X*GCSC is directly related to the controlled GTO angle (γ) which is varied between 0° and 180° as expressed by following equation (De

2 1 ( ) 1 sin(2 ) *X X GCSC C*

max <sup>1</sup> . *XC <sup>C</sup>*

The compensator TCSC mounted on Figure 2.a is a type of series FACTS compensators. It consists of a capacitance (C) connected in parallel with an inductance (*L*) controlled by a valve mounted in anti-parallel conventional thyristors (*T1* and *T*2) and controlled by an angle

From figure 2.b, the compensator TCSC injected in the transmission line a variable capacitive reactance (*XTCSC*). The expression of *XTCSC* is directly related to the controlled thyristors, angle (α) which is varied between 90° and 180° and expressed by following

. () ( ) // ( ) ( )

 

max ( ) 2 sin(2 )

max . *X L <sup>L</sup>*

*TCSC C L*

*X XX*

*X X L L*

*C L*

(3)

(4)

(5)

*C L X X*

> 

*X X*

 

 

(2)

(1)

$$X\_{\mathbb{C}} = \bigvee\_{\mathbf{j}, \mathbf{C}, \alpha}^{\prime} \tag{6}$$

From the equations (4), (5) and (6), the equation (3) becomes:

$$X\_{\rm TCSC}(\alpha) = \frac{X\_{\rm C} X\_{L,\max} \left[ \frac{\pi}{\pi - 2\alpha - \sin(2\alpha)} \right]}{X\_{\rm C} + X\_{L,\max} \left[ \frac{\pi}{\pi - 2\alpha - \sin(2\alpha)} \right]} \tag{7}$$

#### **2.3. TCSR**

The compensator TCSR is an inductive reactance compensator at which its inductive reactance is continually adjusted through the firing delay angle (*α*) of the thyristors as shown in figure 3.a. It consists of a series reactor shunted by a thyristors controlled reactor (TCR).

If the firing delay angle is 180°, the TCSR operates as an uncontrolled reactor (*L1*). When the angle decreases below 180°, the inductive reactance of TCSR decreases and at 90° it is given by the parallel connection of the reactors (*L1*//*L2*).

**Figure 3.** Transmission line in presence of TCSR.

From figure 3.b, the compensator TCSR injected in the transmission line a variable capacitive reactance (*XTCSR*). The expression of XTCSR is directly related to the controlled thyristors angle (α) expressed by the following equation (Acha, E. al., 2004), (Zhang, X.P. et al., 2006):

$$X\_{\rm TCSR}(a) = X\_{L2} \; / \, / X\_{L1}(a) = \frac{X\_{L2} X\_{L1}(a)}{X\_{L2} + X\_{L1}(a)} = \frac{X\_{L2} X\_{L1-\max} \left[ \frac{\pi}{\pi - 2\alpha - \sin(2\alpha)} \right]}{X\_{L2} + X\_{L1-\max} \left[ \frac{\pi}{\pi - 2\alpha - \sin(2\alpha)} \right]} \tag{8}$$

Where,

$$X\_{L1-\text{max}} = L\_1.o\tag{9}$$

Impact of Series FACTS Devices (GCSC, TCSC and TCSR) on Distance Protection Setting Zones in 400 kV Transmission Line 45

The power system is divided into protection zones defined by the equipment and the available

Most of these zones are illustrated in figure 4. Although the fundamentals of protection are quite similar, each of these six categories has protective relays, specifically designed for primary protection, that are based on the characteristics of the equipment being protected. The protect ion of each zone normally include s relays that can provide backup for the relays protecting the adjacent equipment (Zellagui.M; Chaghi.A. 2012.a ). The protection in each zone should overlap that in the adjacent zone; otherwise, a primary protection void would occur between the protection zones. This overlap is accomplished by the location of the CTs

circuit breakers. Six categories of protection zones are possible in each power system:

**3.2. Principles of relay application** 

 Transformers, Bus bars,

**3.3. Protection zones** 

Generators and generator-transformer units,

 Utilization equipment (motors, static loads, or other), Capacitor or reactor banks (when separately protected).

the key sources of power system information for the relays.

Lines (transmission and distribution),

**Figure 4.** Protection zone on power system

And,

$$X\_{12} = \text{j.} L\_2.o$$
