Abstract--This paper presents a modified distance protection

in the presence of Static Synchronous Series Compensator (SSSC), one of the series connected Flexible Alternating Current Transmission System (FACTS) devices. The presence of SSSC on a transmission line has a great influence on the measured impedance at the relaying point. The measured impedance itself depends on the power system structural conditions, pre-fault loading, and especially the fault resistance. In the presence of SSSC, its injected voltage as well as its installation point affects the measured impedance. Therefore, the conventional distance techniques do not fulfill the protective duties satisfactorily and new approaches are required.

Index Terms--Adaptive distance protection, Fault resistance, Measured impedance, Modified distance protection, SSSC.

I. INTRODUCTION

HE measured impedance at the relaying point is the basis of distance protection operation. There are several factors

affecting the measured impedance at the relaying point. Some of these factors are related to the power system parameters prior to the fault instance [1]-[3], which can be categorized into two groups: structural and operational conditions. In addition to the power system parameters and independent of the absence or presence of FACTS devices, the fault resistance could greatly influence the measured impedance, in such a way that in the case of zero fault resistance, the power system parameters do not affect the measured impedance. In other words, in the absence of FACTS devices, power system parameters affect the measured impedance only in the presence of the fault resistance, and as the fault resistance increases, the impact of the power system parameters becomes more severe.

In the recent years, FACTS devices are introduced to the power systems to increase the transmitting capacity of the lines and provide the optimum utilization of power systems capability. This is done by pushing the power systems to their thermal limits. It is well documented in the literature that the introduction of FACTS devices into a power system has a great influence on its dynamics. As power system dynamics changes, many sub-systems are affected, including the protective systems. Therefore, it is essential to study the

The authors are with the Center of Excellence for Power Systems

Automation and Operation, Department of Electrical Engineering, Iran University of Science and Technology (IUST), Narmak 16846, Tehran, Iran, (e-mails: sjamali@iust.ac.ir, kazemi@iust.ac.ir, and shateri@iust.ac.ir).

effects of FACTS devices on the protective systems, especially distance protection.

Unlike the power system parameters, the structural and controlling parameters of FACTS devices, as well as their installation position could affect the measured impedance in the case of zero fault resistance. In the presence of FACTS devices, the conventional distance characteristic are greatly subjected to mal-operation in the both form of over-reaching or under-reaching the fault point. Therefore, the conventional characteristics might not perform satisfactorily in the presence of FACTS devices.

The impacts of TCSC installation on the distance relay performance has been discussed in [4]. The impacts of the presence of TCSC on the protected line as well as the next line and the line behind have been introduced. In addition, the effect of instrument transformer connection point has been mentioned. The impacts of TCSC, SSSC, and STATCOM have been investigated in [5]. A soft computing tool has been presented in [6] for the compensated lines by TCSC based on fuzzy-neural networks. The impacts of the presence of TCSC on the protected line as well as the next line and the line behind have been studied in [7]. Based on the characteristics of TCSC, [8] has analyzed the influence of TCSC on fault component distance protection, and presented a solution for overcoming the aroused problems. In the case of communitarian aided distance protection, [9]-[10] have presented a technique for solving the problems caused by TCSC. A radial bias neural network has been implemented to evaluate the voltage across TCSC in [11] to mitigate its effect on the distance protection. A method for adaptive distance relay setting has been presented in [12] in the presence of SSSC, based on neural networks. Furthermore, the effects of series connected FACTS devices, or FACTS devices with the series branch including TCSC, TCPST, and UPFC, on the measured impedance at the relaying point have been presented in [13] and more detailed studies for UPFC have been presented in [14].

The presented solutions in [9]-[10] are based on unit protection or the data exchange between the relays at line ends, and that of [12] is biased on the artificial intelligence techniques. The other potential solution for problems caused by introduction of SSSC on a line could be adaptive or modified distance protection. In the adaptive or modified distance protection, the distance relay reach-point is adapted or modified due to the power system conditions and SSSC structural and operational parameters.

Modified Distance Protection in Presence of SSSC on a Transmission Line

S. Jamali, Fellow, IET, A. Kazemi, and H. Shateri, Member, IEEE & IET

T

978-1-4244-4241-6/09/$25.00 ©2009 IEEE

This paper investigates the measured impedance at the relaying point in the presence of SSSC. In addition to the power system conditions, the structural and controlling parameters of SSSC as well as its installation point affect the measured impedance at the relaying point. The measured impedance is presented for two cases of SSSC exclusion and inclusion in the fault loop. Here, an adaptive distance protection and then a modified distance protection are presented for distance relays at the ends of the compensated line by SSSC, based on the power system conditions and SSSC structural and controlling parameters.

II. SSSC AND ITS MODELING

As mentioned, Static Synchronous Series Compensator (SSSC) is placed in the group of series connected FACTS devices. As shown in Fig. 1, SSSC consists of a voltage source inverter connected in series through a coupling transformer to the transmission line. A source of energy is required for providing and maintaining the dc voltage across the dc capacitor and compensation of SSSC losses [15].

Fig. 1. Basic configuration of SSSC Fig. 2 shows the equivalent circuit of SSSC which consists

of a series connected voltage source in series with an impedance. This impedance represents the impedance of SSSC coupling transformer.

Fig. 2. Equivalent circuit of SSSC When energy source only has the ability of maintaining the

dc voltage and supplying the losses, SSSC only could compensate the reactive power. In this case the amplitude of injected voltage can be controlled due to compensation strategy, but the phase angle of the injected voltage would be perpendicular to the line current. The injected voltage could either lead or lag the line current by 90°.

Coefficients C1S and C0S are defined as:

L1SeS1 Z/ZC = (1)

L0SeS0 Z/ZC = (2)

III. MEASURED IMPEDANCE AT RELAYING POINT

Distance relays operate based on the measured impedance at the relaying point. In the absence of SSSC and for zero fault resistance, the measured impedance by a distance relay only depends on the length of the line section between the

fault and the relaying points. In Fig. 3 this impedance is equal to pZ1L, where p is per unit length of the line section between the fault and the relaying points, and Z1L is the line positive sequence impedance in ohms.

Fig. 3. Equivalent circuit for single phase to ground fault In the case of a non-zero fault resistance, the measured

impedance is not equal to the mentioned value. In this case, the structural and operational conditions of the power system affect the measured impedance. The structural conditions are evaluated by short circuit levels at the line ends, SSA and SSB. The operational conditions prior to the fault instance can be represented by the load angle of the line, δ, and ratio of the magnitude of the line end voltages, h, or EB / EA = he–jδ. In the absence of SSSC and with respect to Fig. 3 and Fig. 4, the measured impedance can be expressed by the following equations. More detailed calculations can be found in [2].

Fig. 4. Equivalent circuit of phase A to ground fault

L1SA1A1 ZpZZ += (3)

L1SB1B1 Z)p1(ZZ −+= (4)

L0SA0A0 ZpZZ += (5)

L0SB0B0 Z)p1(ZZ −+= (6)

B0A0

B0A0

B1A1

B1A1

ZZ

ZZ

ZZ

ZZ2Z

++

+=Σ (7)

B1A1

B11 ZZ

ZC

+= (8)

B0A0

B00 ZZ

ZC

+= (9)

L1

L1L0L0 Z3

ZZK

−= (10)

B1j

A1 ZehZDen += − δ (11)

Voltage Source Inverter (VSI)

Energy Source

ZSe + _

Vin re jγ Vin Vout

~ ~

A B F

EA EB Z1SA Z1SB p Z1L (1-p) Z1L

Rf

3Rf

A B F Z1SA Z1SB p Z1L (1-p) Z1L

Z2SA Z2SB p Z2L (1-p) Z2L

EA

Z0SA Z0SB p Z0L (1-p) Z0L

~ ~ EB

δjld eh1K −−= (12)

Den/K)R3Z(C ldfld += Σ (13)

)K31(CC2C

R3ZpZ

L001ld

fL1A +++

+= (14)

It can be seen for zero fault resistance, the measured impedance at the relaying point is equal to the impedance of the line section between the relaying and the fault points, and otherwise it deviates from its actual value.

Once SSSC is installed on the transmission line, depending on its exclusion or inclusion in the fault loop, the measured impedance would change. SSSC is installed at the length of i per unit from the relaying point. The following equations introduced due to SSSC presence on the line, independent of its exclusion or inclusion in the fault loop.

L1SA1AI1 ZiZZ += (15)

L1S1SB1BI1 Z)Ci1(ZZ +−+= (16)

L0SA0AI0 ZiZZ += (17)

L0S0SB0BI0 Z)Ci1(ZZ +−+= (18)

A. SSSC out of Fault Loop

Once SSSC is out of the fault loop, (3)-(6) and (11)-(12) should be modified, and some new equations are introduced:

L1SA1AF1 ZpZZ += (19)

L1IF1 Z)pi(Z −= (20)

AF1A1 ZZ = (21)

BI1IF1B1 ZZZ += (22)

L0SA0AF0 ZpZZ += (23)

L0IF0 Z)pi(Z −= (24)

AF0A0 ZZ = (25)

BI0IF0B0 ZZZ += (26)

BI1j

IF1j

AF1 Z)er1(ZehZDen +++= − γδ (27) δγ jj

ld eher1K −−+= (28)

Here, the measured impedance in the case of zero fault resistance is equal to the impedance of the line section between the relaying and the fault points.

B. SSSC in Fault Loop

When SSSC is in the fault loop, (3)-(6), (11) and (14) should be modified; (12) is changed to (28); and some new equations are introduced:

L1SB1BF1 Z)p1(ZZ −+= (29)

L1S1IF1 Z)Cip(Z +−= (30)

IF1AI1A1 ZZZ += (31)

BF1B1 ZZ = (32)

L0SB0BF0 Z)p1(ZZ −+= (33)

L0S0IF0 Z)Cip(Z +−= (34)

IF0AI0A0 ZZZ += (35)

BF0B0 ZZ = (36)

)er1(Zeh]Z)er1(Z[Den jBF1

jIF1

jAI1

γδγ ++++= − (37)

BI1j

AI1V ZehZKSe

+= − δ (38)

Den/er)R3Z(KC jfVV SeSe

γΣ +−= (39)

L1L00S1S0Z Z)K31(C)CC(CSe

+−= (40)

)K31(CC2C

R3CCZ)Cp(Z

L001ld

fVZL1S1A

SeSe

+++++

++= (41)

It can be seen that in the absence of the fault resistance, the measured impedance at the relaying point is not equal to the actual impedance of the line section between the relaying and the fault points.

IV. EFFECTS OF SSSC ON DISTANCE RELAY

IDEAL TRIPPING CHARACTERISTIC

The impacts of the presence of SSSC on a transmission line have been tested for a practical system. A 400 kV Iranian transmission line with the length of 300 km has been used for this study. By utilizing the Electro-Magnetic Transient Program (EMTP) [16] various sequence impedances of the line are evaluated according to its physical dimensions. The calculated impedances and the other parameters of the power system are:

Z1L = 0.01133 + j 0.3037 Ω/km Z0L = 0.1535 + j 1.1478 Ω/km Z1SA = 1.3945 + j 15.9391 Ω Z0SA = 7.4540 + j 27.8187 Ω Z1SB = 0.6972 + j 7.9696 Ω Z0SB = 3.7270 + j 13.9093 Ω h = 0.96 δ = 16º In the absence of SSSC, Fig. 5 shows the ideal tripping

characteristic of the distance relay, which is the measured impedance at the relaying point as the fault resistance varies from 0 to 200 ohms, while the fault location moves from the near end up to the far end of the line. The quadrilateral characteristic covering 80% of the line and the impedance of the transmission line, Z1L, are shown in Fig. 5. In addition, the dotted line is the measured impedance for the faults at the reach-point while the fault resistance varies from 0 to 200 ohms.

Fig. 5. Ideal tripping characteristic, without SSSC

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It can be seen that in the absence of the fault resistance, the measured impedance at the relaying point is the actual value. In other words, the left side of the ideal tripping characteristic is the impedance of the transmission line.

Usually SSSC injected voltage is adjusted according to its controlling strategy. Therefore, SSSC injected voltage would vary as the power system loading is changed. But in this study the operational conditions of the power system are assumed to be constant and it is assumed these conditions are achieved by the different SSSC operational parameters.

The ideal tripping characteristic for SSSC installation on near end, mid-point, and far end of the line are investigated in [17]. In the case of SSSC out of fault loop, it does not affect the measured impedance for zero fault resistance. Therefore, the cases of SSSC at the near end and mid-point are investigated.

Fig. 6 shows the effect of SSSC installation at the near end of the transmission line. Here, the amplitude of the injected voltage takes the magnitudes of 0.00 and 0.10 in both leading and lagging modes. In Fig. 6 the tripping characteristic without SSSC is shown in the dashed form for comparison.

Fig. 6. Ideal tripping characteristic, SSSC at near end

It can be seen that in the case of an inactive SSSC, with

zero injected voltage, it would affect the measured impedance at the relaying point. This is due to the presence of the coupling transformer in series with the line. It can be seen that the tripping characteristic transfers upward. The measured resistance increases as well as the measured reactance.

As the injected voltage amplitude increases in the leading mode, the measured resistance decreases for high fault resistances, and increases in the case of low fault resistances, while the measured reactance decreases. Generally, it can be said that in the presence of SSSC in the leading mode at the near end of the line, the tripping characteristic shrinks and turns in clockwise direction.

Once the injected voltage amplitude increases in the lagging mode, the measured resistance increases for high fault resistances, and decreases in the case of low fault resistances, while the measured reactance increases. Generally, it can be said that in the presence of SSSC in the lagging mode at the near end of the transmission line, the tripping characteristic expands and turns in anticlockwise direction.

Fig. 7 shows the effect of SSSC installation at the mid-point of the transmission line. Here, the amplitude of the injected voltage takes the magnitudes of 0.00 and 0.10 in both leading and lagging modes.

Fig. 7. Ideal tripping characteristic, SSSC at mid-point

In the presence of SSSC at the mid-point, tripping

characteristic is split into two parts. The lower part is for the faults on the near half of the line, while the upper part is corresponding to the faults on the far half. The location of two parts according to each other, overlapping or separation, depends on SSSC injected voltage.

It can be seen that an inactive SSSC affects the measured impedance at the relaying point. In the lower part, the measured resistance decreases slightly for the faults close to the near end and increases slightly for the faults close to the mid-point, while the measured reactance increases slightly for the faults close to the near end and decreases slightly for the faults close to the mid-point. The tripping characteristic is very close to that of in the absence of SSSC. In the upper part, the measured resistance increases as well as the measured reactance and the tripping characteristic transfers upward.

In the lower part and SSSC in the leading mode, as the injected voltage amplitude increases, the measured resistance decreases as well as the measured reactance. On the other hand and for SSSC in the lagging mode, as the injected voltage amplitude increases, the measured resistance increases slightly as well as the measured reactance. For zero fault resistances, the measured impedance is the actual impedance of the line section up to the fault point.

In the upper part and SSSC in the leading mode, as the injected voltage amplitude increases, the measured resistance decreases in the case of high fault resistances and increases for low fault resistances, while the measured reactance decreases. Otherwise for SSSC in lagging mode, as the injected voltage amplitude increases, the measured resistance increases for high fault resistances and decreases for low fault resistances, while the measured reactance increases.

Generally, it can be said that in the presence of SSSC in the leading mode at the mid-point of the line, the tripping characteristic splits into the two separated parts, with overlapping in the case of the high injected voltage amplitudes, the lower part is approximately fixed, while the

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upper part shrinks and turns in clockwise direction. On the other hand and in the case of SSSC in the lagging mode, the tripping characteristic splits into the two separate parts, the lower part is approximately fixed, while the upper part expands and turns in anticlockwise direction.

V. ADOPTIVE DISTANCE PROTECTION

Knowing the structural and operational conditions of the power system, as well as the structural and controlling parameters of SSSC, the measured impedance for a solid fault at the reach-point can be calculated. The required information could be provided via SCADA system, after each updating. There is no need for online data from the other side of the line, as it is required in unit protection based approaches. Once the measured impedance at the relaying point for a solid fault at the reach-point has been calculated, the quadrilateral characteristic would be adopted due to this value. Therefore, distance relay would operate correctly and its covering region in the first zone does not reduce.

In the case of the conventional distance protection, setting the first zone of the relay at 80% of the line length, the first zone would be a quadrilateral as follows. The upper side is parallel with R axis and its reactance is equal to the reactance of the reach-point. The left and right sides are parallel with the impedance of the reach-point with the distance of 0.6 of the magnitude of the reach-point impedance. The lower side crosses the impedance of the reach-point at the origin and makes a right angle with it.

In the proposed adoptive distance protection, setting the first zone of the relay at 80% of the line length, the first zone would be a quadrilateral as follows. The upper side is parallel with R axis and its reactance is equal to the reactance of the calculated impedance for a solid fault at the reach-point. The left and right sides are parallel with the impedance of the calculated impedance for the solid fault at the reach-point with the distance of 0.6 of the magnitude of the reach-point impedance, i.e. 0.8Z1L. The lower side crosses the calculated impedance for the solid fault at the reach-point at the origin and makes a right angle with it.

Fig. 8 shows the close up of ideal tripping characteristic around quadrilateral characteristic in the presence of SSSC at the near end of the line. Here, the amplitude of the injected voltage takes the magnitudes of 0.00 and 0.10 in the both leading and lagging modes. The conventional quadrilateral characteristic and the impedance of the line are plotted with solid lines. The adopted quadrilateral characteristic is shown with dotted line. The ideal tripping characteristic in the absence of SSSC is plotted with dashed line for comparison. The measured impedance for the fault at the reach-point is shown for all cases.

It can be seen that in the case of an inactive SSSC presence at the near end, the region covered with the adopted quadrilateral characteristic is more than that of in the case of conventional quadrilateral characteristic. In the case of the adopted quadrilateral exactly 80% of the line is covered in the first zone, and the protected region is not reduced.

Fig. 8. Adoptive distance protection, SSSC at near end

On the other hand, in the case of SSSC in the leading

mode, the region covered with the adopted quadrilateral characteristic is more than that of in the case of conventional quadrilateral characteristic. When comparing this region with that of in the case of an inactive SSSC, only a slight shrinking could be observed, as well as a clockwise turning.

Otherwise, in the case of SSSC in the lagging mode, the region covered with the adopted quadrilateral characteristic is more than that of in the case of conventional quadrilateral characteristic. When comparing this region with that of in the case of an inactive SSSC, only a slight shrinking, less than that of in the case of leading mode, could be observed, as well as an anticlockwise turning.

Fig. 9 shows the close up of ideal tripping characteristic around quadrilateral characteristic in the presence of SSSC at the mid-point of the line. Here, the amplitude of the injected voltage takes the magnitudes of 0.00 and 0.10 in the both leading and lagging modes. The conventional quadrilateral characteristic and the impedance of the line are plotted with solid lines. The adopted quadrilateral characteristic is shown with dotted line. The ideal tripping characteristic in the absence of SSSC is plotted with dashed line for comparison. The measured impedance for the fault at the reach-point is shown for all cases.

Fig. 9. Adoptive distance protection, SSSC at mid-point It can be seen that in the case of an inactive SSSC presence

at the mid-point, the region covered with the adopted

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quadrilateral characteristic is more than that of in the case of conventional quadrilateral characteristic. In the case of the adopted quadrilateral exactly 80% of the line is covered in the first zone, and the protected region is not reduced.

On the other hand, in the case of SSSC in the leading mode, the region covered with the adopted quadrilateral characteristic is more than that of in the case of conventional quadrilateral characteristic. When comparing this region with that of in the case of an inactive SSSC, only a slight shrinking could be seen, as well as a clockwise turning.

Otherwise, in the case of SSSC in the lagging mode, the region covered with the adopted quadrilateral characteristic is more than that of in the case of conventional quadrilateral characteristic. When comparing this region with that of in the case of an inactive SSSC, only a very slight expansion could be observed, as well as an anticlockwise turning.

VI. MODIFIED DISTANCE PROTECTION

As mentioned, the adoptive distance protection is based on the information about power system conditions and SSSC parameters. If the required information is not available, the adoption procedure could not be performed. In this case, distance relay should utilize a fixed pre-determined characteristic. This characteristic could be conventional quadrilateral characteristic, but the modified characteristic is a better alternative.

Here, it is suggested that the adopted quadrilateral characteristic in the case of an inactive SSSC is selected for the modified characteristic. When the required information is not available, this characteristic would be activated.

The lack of information would be in two stages of lack of SSSC information and lack of the whole system information. The modified distance protection is investigated in the both stages of information unavailability.

A. Lack of SSSC Information

In this case, the information of SSSC is not available but the information of the power system is known. Fig. 10 shows the close up of ideal tripping characteristic around quadrilateral characteristic in the presence of SSSC at the near end of the line. Here, the amplitude of the injected voltage takes the magnitudes of 0.00 and 0.10 in the both leading and lagging modes. The conventional quadrilateral characteristic is shown by dotted line; and the modified characteristic and the impedance of the line are plotted with solid lines. The measured impedance for the fault at the reach-point is shown for all cases.

It can be seen that the modified quadrilateral characteristic for SSSC at the near end covers larger region than the conventional quadrilateral characteristic. In the case of the modified quadrilateral characteristic, approximately 80% (and a little more in the case of the high amplitudes of the injected voltage in the both leading and lagging modes) of the line is covered in the first zone, and the protected region is not reduced as severely as the case of conventional quadrilateral characteristic. In the case of SSSC in the leading mode, due to

ideal tripping characteristic clockwise turning, the maximum tolerable fault resistance decreases, while for lagging SSSC, due to ideal tripping characteristic anticlockwise turning, the maximum tolerable fault resistance increases.

Fig. 10. Modified distance protection, SSSC at near end

Fig. 11 shows the close up of ideal tripping characteristic

around quadrilateral characteristic in the presence of SSSC at the mid-point of the line. Here, the amplitude of the injected voltage takes the magnitudes of 0.00 and 0.10 in the both leading and lagging modes. The conventional quadrilateral characteristic is shown by dotted line; and the modified characteristic and the impedance of the line are plotted with solid lines. The measured impedance for the fault at the reach-point is shown for all cases.

Fig. 11. Modified distance protection, SSSC at mid-point

It can be seen that the modified quadrilateral characteristic

for SSSC at the mid-point covers larger region than the conventional quadrilateral characteristic. In the case of the modified quadrilateral characteristic, approximately 80% (and a little more in the case of the high amplitudes of the injected voltage in the both leading and lagging modes) of the line is covered in the first zone, and the protected region is not reduced as severely as the conventional quadrilateral characteristic. In the case of SSSC in the leading mode, due to ideal tripping characteristic clockwise turning, the maximum tolerable fault resistance decreases, while for lagging SSSC, due to ideal tripping characteristic anticlockwise turning, the maximum tolerable fault resistance increases.

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B. Lack of Whole System Information

In this case, the information of the power system, including SSSC information, is not available. Fig. 12 shows the close up of ideal tripping characteristic around quadrilateral characteristic in the presence of SSSC at the near end of the line. Here, the amplitude of the injected voltage is 0.10 in the both leading and lagging modes for two different operational conditions. The first operational condition is the case of increase in the transmitted load trough the line, load angle of 22º and voltage ratio of 0.94. Otherwise, the second operational condition is the case of decrease in the transmitted load, load angle of 10º and voltage ratio of 0.98. The conventional quadrilateral characteristic is shown by dotted line; and the modified characteristic and the impedance of the line are plotted with solid lines. The measured impedance for the fault at the reach-point is shown for all cases.

Fig. 12. Modified distance protection, SSSC at near end It can be seen that in the case of solid faults, the power

system conditions does not affects the measured impedance considerably. It can be concluded that the impact of SSSC controlling parameters on the measured impedance for faults with zero fault resistance is more considerable than the power system conditions. Therefore, the mentioned tips in the previous section are also valid in this case.

Fig. 13 shows the close up of ideal tripping characteristic around quadrilateral characteristic in the presence of SSSC at the mid-point of the line. Here, the amplitude of the injected voltage is 0.10 in the both leading and lagging modes for the two previously mentioned different operational conditions. The conventional quadrilateral characteristic is shown by dotted line; and the modified characteristic and the impedance of the line are plotted with solid lines. The measured impedance for the fault at the reach-point is shown.

It can be seen that in the case of solid faults, the power system conditions does not affects the measured impedance considerably. It can be concluded that the impact of SSSC controlling parameters on the measured impedance for faults with zero fault resistance is more considerable than the power system conditions. Therefore, the mentioned tips in the previous section are also valid in this case. In the case of the faults up to the mid-point, the measured impedance is the actual value in the all cases.

Fig. 13. Modified distance protection, SSSC at mid-point

VII. CONCLUSION

This paper evaluates the measured impedance at the relaying point in the presence of SSSC on a transmission line; and presents the distance relay ideal tripping characteristic. The variation of the tripping characteristic due to the changes in SSSC controlling parameters is studied in the case of its inclusion in the fault loop, installation at the near end and the mid-point of the line. An adoptive approach is presented for distance protection in the presence of SSSC, due to SCADA based information about SSSC controlling parameters and the power system conditions. According to the results of adoptive approach, a modified distance protection is presented, for durations with the lack of the system information.

In the case of SSSC inclusion in the fault loop, the measured impedance for the faults at the reach-point deviates from its actual value which leads to decrease in the covered region in the distance relay first zone. In order to solve this problem, the reach-point of the distance relay is adopted due to the power system conditions and SSSC structural and controlling parameters.

Comparing the adopted quadrilateral characteristic with the conventional one, it can be seen that the adopted quadrilateral characteristic changes considerably, increase in the covered region. On the other hand, comparing the adopted quadrilateral characteristics in the various cases, it can be seen that the characteristic does not vary severely due to changes in SSSC controlling parameters, turning clockwise or anticlockwise rather than variation of the covered region.

As mentioned, once SSSC controlling parameters are changed, the adopted characteristic turns clockwise or anticlockwise, and its covering region does not vary considerably. Applying the adopted characteristic for an inactive SSSC as the modified one, only the maximum tolerable fault resistance of the distance relay is affected, and its covering region is not affected considerably.

On the other hand, as the power system conditions are changed, the measured impedance in the case of the faults with zero fault resistance is not affected considerably. Therefore, the modified quadrilateral characteristic performs satisfactorily once the power system conditions are changed.

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Resistance, R (Ohms)

Rea

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ce,

X (

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s)

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( 0.10 , Leading , 2 )

( 0.10 , Lagging , 1 )( 0.10 , Lagging , 2 )

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VIII. REFERENCES [1] Zhang Zhizhe and C. Deshu, "An adaptive approach in digital distance

protection", IEEE Trans. Power Delivery, vol. 6, no. 1, pp. 135–142, Jan. 1991.

[2] Y. Q. Xia, K. K. Li, and A. K. David, "Adaptive relay setting for stand-alone digital distance protection", IEEE Trans. Power Delivery, vol. 9, no. 1, pp. 480–491, Jan. 1994.

[3] S. Jamali, "A fast adaptive digital distance protection", in Proc. 2001 IEE 7th International Conference on Developments in Power System Protection, DPSP2001, pp. 149–152.

[4] Wang Weiguo, Yin Xianggen, Yu Jiang, Duan Xianzhong, and Chen Deshu, "The impact of TCSC on distance protection relay", in Proc. 1998 IEEE International Conference on Power System Technology, POWERCON '98, vol. 1, pp. 382–388.

[5] M. Khederzadeh, "The impact of FACTS devices on digital multifunction protective relays", in Proc. 2002 IEEE Conference and Exhibition on Transmission and Distribution, Asia Pacific IEEE/PES T&D 2002, vol. 3, pp. 2043–2048.

[6] P. K. Dash and M. V. Chilukuri, "Soft computing tools for protection of compensated network", in Proc. 2003 National Power Engineering Conference, PECon 2003, pp. 52–61.

[7] M. E. Erezzaghi, P. A. Crossley, and R. Elferes, "Design and evaluation of an adaptive distance protection scheme suitable for series compensated transmission feeders", in Proc. 2004 8th IEE International Conference on Developments in Power System Protection, DPSP2004, vol. 2, pp. 453–456.

[8] Liu Qing, Wang Zengping, and Xu Yan, "Study on the influence of TCSC on fault component distance protection", in Proc. 2005 IEEE/PES Transmission and Distribution Conference and Exhibition: Asia and Pacific, T&D2005, pp. 1–4.

[9] T. S. Sidhu and M. Khederzadeh, "TCSC impact on communication-aided distance-protection schemes and its mitigation", IEE Proc. Generation, Transmission and Distribution, vol. 152, no. 5, pp. 714–728, Sept. 2005.

[10] M. Khederzadeh and T. S. Sidhu, "Impact of TCSC on the protection of transmission lines", IEEE Trans. Power Delivery, vol. 21, no. 1, pp. 80–87, Jan. 2006.

[11] A. N. Abdel-Latief, A. F. Abdel-Gawad, and M. E. Mandour, "Mitigation the effect of TCSC on the transmission lines protection devices", in Proc. 42nd International Universities Power Engineering Conference, UPEC2007, pp. 556–561.

[12] H. Rastegar, and A. P. Khansaryan, "A new method for adaptive distance relay setting in the presence of SSSC using neural networks", in Proc. 2006 1ST IEEE Conference on Industrial Electronics and Applications, ICIEA2006, pp. 1–8.

[13] P. K. dash, A. K. Pradhan, G. Panda, and A. C. Liew, "Digital protection of power transmission lines in the presence of series connected FACTS devices", in Proc. 2000 IEEE Power Engineering Society Winter Meeting, vol. 3, pp. 1967–1972.

[14] P. K. dash, A. K. Pradhan, G. Panda, and A. C. Liew, "Adaptive relay setting for flexible AC transmission systems (FACTS)", IEEE Trans. Power Delivery, vol. 15, no. 1, pp. 38–43, Jan. 2000.

[15] A. T. Johns, A. Ter-Gazarian, and D. F. Warne, Flexible ac transmission systems (FACTS), Padstow, Cornwall: TJ International Ltd., 1999.

[16] H. W. Dommel, "EMPT reference manual", Microtran Power System Analysis Corporation, Vancouver, British Columbia, Canada, August 1997.

[17] A. Kazemi, S. Jamali, and H. Shateri, "Effects of SSSC on distance relay tripping characteristic", in Proc. 1st International Power and Energy Conference, PECon2006, pp. 623–628.

IX. BIOGRAPHIES

Sadegh Jamali, was born in 1956 in Tehran, Iran. He received his BSc from Sharif university of Technology in Tehran in 1979, MSc from UMIST, Manchester, UK in 1986 and PhD from City University, London, UK in 1990, all in Electrical Engineering. Dr. Jamali is currently an Associate Professor in the Department of Electrical Engineering at Iran University of Science and Technology in Tehran. Dr. Jamali is a Fellow of the Institution of Engineering Technology (IET) and the IET Council Representative in Iran. His field of

interest includes Power System Protection and Distribution Systems.

Ahad Kazemi, was born in Tehran, Iran, in 1952. He received his MSc degree in electrical engineering from Oklahoma State University, U.S.A in 1979. He is currently an associate professor in electrical engineering department of Iran University of Science and Technology, Tehran, Iran. His research interests are reactive power control, power system dynamics, stability and control and FACTS devices.

Hossein Shateri (M’07) was born in 1979 in Karaj, Iran. He received his BSc and MSc from Iran University of Science and Technology in Tehran in 2001 and 2003, respectively all in electrical Engineering. He is currently working towards a PhD degree in the Department of Electrical Engineering at Iran University of Science and Technology (IUST) in Tehran, Iran since Sep. 2004. He has published over 120 papers in international conferences and journals.

H. Shateri is a Member of the Institution of Electrical and Electronic Engineers (IEEE) and a Member of the Institution of Engineering Technology (IET). His field of interest includes Power System Protection, and Distribution Systems Protection and Automation.