The electricity supply industry is undergoing a profound transformation worldwide. Market forces, scarcer natural resources, and an ever-increasing demand for electricity are some of the drivers responsible for such unprecedented change. Against this background of rapid evolution, the expansion programs of many utilities are being thwarted by a variety of well-founded, environment, land-use, and regulatory pressures that prevent the licensing and building of new transmission lines and electricity generating plants.
The ability of the transmission system to transmit power becomes impaired by one or more of the following steady state and dynamic limitations:
These limits define the maximum electrical power to be transmitted without causing damage to transmission lines and electrical equipment. In principle, limitations on power transfer can always be relieved by the addition of new transmission lines and generation facilities.
Alternatively, Flexible Alternating Current Transmission System (FACTS) controllers can enable the same objectives to be met with no major alterations to power system layout. FACTS are alternating current transmission systems incorporating power electronic-based and other static controllers to enhance controllability and increase power transfer capability. 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 various parts of the world.
Popular are: load tap changers, phase-angle regulators, static VAR compensators, thyristors controlled series compensators, interphase power controllers, static compensators, and unified power flow controllers.
The main objectives of FACTS controllers are the following (Mathur, R.M.; Basati, R.S., 2002):
Regulation of power flows in prescribed transmission routes,
Secure loading of transmission lines nearer to their thermal limits,
Prevention of cascading outages by contributing to emergency control,
Damping of oscillations that can threaten security or limit the usable line capacity.
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 familiar use of relay models (McLaren et al., 2001).
1.1. Problem statement
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 compensated by three different series FACTS i.e. GCSC, TCSC and TCSR connected at midpoint of a single electrical transmission line. The facts are used for controlling transmission voltage in the range of ±40kV as well as reactive power injected between -50 MVar/+15 MVar on the power system. This chapter studies the effects of GCSC, TCSC and TCSR insertion on the total impedance of a transmission line protected by MHO (admittance) distance relay.
The modified setting zone protection in capacitive and inductive boost mode for three forward zones (
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.
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
Hence, a voltage
The compensator GCSC injects in the transmission line a variable capacitive reactance (
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 (
From figure 2.b, the compensator TCSC injected in the transmission line a variable capacitive reactance (
The compensator TCSR is an inductive reactance compensator at which its inductive reactance is continually adjusted through the firing delay angle (
If the firing delay angle is 180°, the TCSR operates as an uncontrolled reactor (
From figure 3.b, the compensator TCSR injected in the transmission line a variable capacitive reactance (
3. Power system protection
Fault current is the expression given to the current that flow in the circuit when load is shorted i.e. flow in a path other than the load. This current is usually very high and may exceed ten times the rated current of a piece of plant. Faults on power system are inevitable due to external or internal causes, lightning may struck the overhead lines causes insulation damage. Internal overvoltage due to switching or other power system phenomenon may also cause an over voltage which leads to deterioration of the insulation and faults. Power networks are usually protected by means of two main components, relays that sense the abnormal current or voltage and a circuit breaker that put a piece of plant out of tension.
Power system protection is the art and science of the application of devices that monitor the power line currents and voltages (relays) and generate signals to deenergize faulted sections of the power network by circuit breakers. Goal is to minimize damage to equipment that would be caused by system faults, if residues, and maintain the delivery of electrical energy to the consumers (Horowitz, S.H.; Phadke A.G. 2008), (Blackburn, J.L.; Domin, T.J. 2006).
Many types of protective relays are used to protect power system equipments. They are classified according to their operating principles; over current relay senses the extra (more than set) current considered dangerous to a given equipment, differential relays compare in and out currents of a protected equipment, while impedance relays measure the impedance of the protected piece of plant.
3.1. Principal characteristics of protection system
Reliability : assurance that the protection will perform correctly in presence of faults on electrical transmission and distribution line,
Selectivity : maximum continuity of service with minimum system disconnection,
Speed of operation : minimum fault duration and consequent equipment damage and system instability,
Simplicity : minimum protective equipment and associated circuitry to achieve the protection objectives,
Economics: maximum protection at minimal total cost.
3.2. Principles of relay application
The power system is divided into protection zones defined by the equipment and the available circuit breakers. Six categories of protection zones are possible in each power system:
Generators and generator-transformer units,
Lines (transmission and distribution),
Utilization equipment (motors, static loads, or other),
Capacitor or reactor banks (when separately protected).
3.1. Protection zones
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 the key sources of power system information for the relays.
4. Setting zones for MHO distance relays
Distance protection is so called because it is based on an electrical measure of distance along a transmission line to a fault. The distance along the transmission line is directly proportional to the series electrical impedance of the transmission line.
Impedance is defined as the ratio of voltage to current. Therefore, distance protection measures distance to a fault by means of a measured voltage to measured current ratio computation (Zigler, G., 2008), (Zellagui, M.; Chaghi, A., 2012.b). The philosophy of setting relay at Sonelgaz Group is three forward zones and one reverse zone to protect EHV transmission line between busbar
4.2. Setting zones
4.2.1. First zone
In practice it is normal to adjust the first zone relays (
This unit is not set to protect the entire line to avoid undesired tripping due to over reach. Over reach may occur due to transients during the fault condition.
4.2.2. Second zone
It is set to cover about 20% of the second line (BC). The main object of the second zone unit is to provide protection to the end zone of the first section which is beyond the reach of the first unit. The setting of the second unit is so adjusted that it operates the relay even for arcing faults at the end of the line. To achieve this, the unit must take care beyond the end of the line. In other words its setting must take care of under reach caused by arc resistance (Dechphung, S; Saengsuwan, T., 2008), (Zellagui, M.; Chaghi, A., 2012.b).
Under reach is also caused by intermediate current sources, errors in CT, and VT and measurement performed by the relay. To take into account the under reaching tendency caused by these factors, the normal practice is to set the second zone reach up to 20% of the shortest adjoining line section. The protective zone of the second unit is known as the second zone of protection. The second zone unit operates after a certain time delay. Its operating time is 0,3 sec.
4.2.3. Third zone
It is provided for back-up protection of the adjoining line. Its reach should extend beyond the end of the adjoining line under the maximum under reach, which may be caused by arcs, intermediate current sources and errors in CT, VT and measuring unit (Zellagui. M.; Chaghi. A., 2012.b). The protective zone of the third stage is known as the third zone of protection.
The characteristic curve on MHO (admittance) relay for setting zones is shown in figure 6.
Figure 7 represents the tripping time
The total impedance of transmission line AB measured by MHO distance relay is:
Where, ZAB is real total impedance of line AB, and KVT and KCT is ratio of voltage to current respectively.
The presence of series FACTS systems in a reactor (
4.3. Measured impedance by relay in presence fault
Distance relaying belongs to the principle of ratio comparison. The ratio is between voltage and current, which in turn produces impedance. The impedance is proportional to the distance in transmission lines, hence the distance relaying designation for the principle.
This principle is primarily used for protection of high voltage transmission lines. In this case the over current principle cannot easily cope with the change in the direction of the current flow, which is common in the transmission but no so common in radial distribution lines. Computing the impedance in the three-phase system is a bit involved in each type of the fault produces a different impedance expression. Because of these differences the settings of the distance relay are needed to be selected to distinguish between the ground and phase faults.
In addition fault resistance may create problem for distance measurement because of the fault resistance may be difficult for predict. It is particularly challenging for distance relays to measure correct fault impedance when the current in feed from the other end of the line create an unknown voltage drop on the fault resistance (Kazemi, A. et al., 2009), (Kulkami, P.A. et al., 2010).
This may contribute to erroneous computation of the impedance, called apparent impedance ‘seen’ by the relay located at the end of the line and using the current and voltage measurement just from the end. Once the impedance is computed, it is compared to the settings that define the operating characteristics of the relay. Based on the comparison, a decision is made if a fault has occurred, if so in what zone.
The principle behind the standard distance protection function is based on measured apparent impedance (
5. Case study and simulation results
The power system studied in this paper is the 400 kV, 50 Hz eastern Algerian electrical transmission networks at group SONELGAZ (Algerian Company of Electricity and Gas) which is shows in figure 8 (Sonelgaz Group/GRTE, 2011). The MHO distance relay is located in the bus bar at Ramdane Djamel substation in Skikda to protect transmission line between busbar
The figure below represents a 400 kV transmission line in the presence of a series FACTS type GCSC, TCSC and TCSR installed in the midpoint of the transmission line protected by a MHO distance relay between busbar A and B.
5.1. Characteristic curve of installed series FACTS devices
Figure 9 shows the characteristic curves of the different compensators used GCSC, TCSC and TCSR installed on transmission line in this case study.
5.2. Impact on the impedance of a protected transmission line.
The impact of the angle variation
The impact of the angle variation
The impact of the angle variation
5.3. Impact on setting zones
5.3.1. Impact of GCSC Insertion
Figures 10 and 11 show the impact of the variation extinction angle
5.3.2. Impact of TCSC Insertion
Figures 12 and 13 is show the impact of the variation extinction angle of
The results are presented in relation to a typical 400 kV transmission system employing GCSC, TCSC and TCSR series FACTS devices. The effects of the extinction angle
Therefore settings zones of the total system protection must be adjusted in order to avoid unwanted circuit breaker tripping in the presence of series FACTS compensator.
Acha E Fuerte-esquivel C. R Ambriz-pérez H Angeles-camacho C 2004 FACTS Modelling and Simulation in Power Networks,John Wiley & Sons Ltd Publication, 978-0-47085-271-2London, England.
Blackburn J. L Domin T. J 2006 Protective Relaying: Principles and Applications,rd Edition, Published by CRC Press, 978-1-57444-716-3USA.
De Jesus F. D De Souza L. F. W Wantanabe E Alves J. E. R 2007 SSR and Power Oscillation Damping using Gate-Controlled Series Capacitors (GCSC)IEEE Transaction on Power Delivery, 22N°3, (Mars 2007), 1806 1812
De Souza L. F. W Wantanabe E. H Alves J. E. R 2008Thyristor and Gate-Controlled Series Capacitors: A Comparison of Component Ratings, IEEE Transaction on Power Delivery, 23 2May 2008), 899 906
Dechphung S Saengsuwan T 2008Adaptive Characteristic of MHO Distance Relay for Compensation of the Phase to Phase Fault Resistance, IEEE International Conference on Sustainable Energy Technologies (ICSET’ 2008), Singapore, Thailand, 24 27November 2008.
Gérin-lajoie L 2009A MHO Distance Relay Device in EMTP Works, Electric Power Systems Research, 79(3), March 2009, 484 449
Horowitz S. H Phadke A. G 2008 Power System Relayingrd Edition, Published by John Wiley & Sons Ltd, 978-0-47005-712-4England, UK.
Jamali S Shateri H 2011 Impedance based Fault Location Method for Single Phase to Earth Faults in Transmission Systemsth IET International Conference on Developments in Power System Protection (DPSP), United Kingdom, 29 March- 1 April, 2010.
Kazemi A Jamali S Shateri H 2009Measured Impedance by Distance Relay with Positive Sequence Voltage Memory in Presence of TCSC, IEEE/PES Power Systems Conference and Exposition (PSCE’ 09), Seattle, USA, 15 18March 2009.
Khederzadeh M Sidhu T. S 2006 Impact of TCSC on the Protection of Transmission Lines
Kulkami P. A Holmukhe R. M Deshpande K. D Chaudhari P. S 2010Impact of TCSC on Protection of Transmission Line, International Conference on Energy Optimization and Control (ICEOC’ 10), Maharashtra, India, 28 30December 2010.
Liu Q Wang Z 2008Research on the Influence of TCSC to EHV Transmission Line Protection, International Conference on Deregulation and Restructuring and Power Technology (DRPT’ 08), Nanjing, China, 6 9April 2008.
Mathur R. M Basati R. S 2002 Thyristor-Based FACTS Controllers for Electrical Transmission SystemsPublished by Wiley and IEEE Press Series in Power Engineering, 978-0-47120-643-9New Jersey, USA.
Mclaren P. G Mustaphi K Benmouyal G Chano S Girgis A Henville C Kezunovic M Kojovic L Marttila R Meisinger M Michel G Sachdev M. S Skendzic V Sidhu T. S Tziouvaras D 2001Software Models for Relays, IEEE Transactions on Power Delivery, 16 12April 2001), 238 245
Ray S Venayagamoorthy G. K Watanabe E. H 2008 A Computational Approach to Optimal Damping Controller Design for a GCSCIEEE Transaction on Power Delivery, 23 3July 2008), 1673 1681
Sen K. K Sen M. L 2009 Introduction to FACTS Controllers: Theory, Modeling and Applications",Published by John Wiley & Sons, Inc., and IEEE Press, 978-0-47047-875-2New Jersey, USA.
Sonelgaz Group/GRTE 2011Topologies of Electrical Networks High Voltage 400 kV, Technical rapport published by Algerian Company of Electrical Transmission Network, 30 December 2011, Sétif, Algeria.
Zellagui M Chaghi A 2012a). Distance Protection for Electrical Transmission Line: Equipments, Settings Zones and Tele-Protection, published by LAP Lambert Academic Publishing, 0000-9783Saarbrücken- Germany.
Zellagui M Chaghi A 2012.bMeasured Impedance by MHO Distance Protection for Phase to Earth Fault in Presence GCSC, ACTA Technica Corviniensis : Bulletin of Engineering, Tome 5, Fascicule 3, (July-September 2012), 81 86
Zellagui M Chaghi A 2012.cA Comparative Study of FSC and GCSC Impact on MHO Distance Relay Setting in 400 kV Algeria Transmission Line, Journal ACTA Electrotehnica, 53 2July 2012), 134 143
Zhang X. P Rehtanz C Pal B 2006 Flexible AC Transmission Systems : Modelling and ControlSpringer Publishers, 978-3-64206-786-0Heidelberg, Germany.
Zigler G 2008 Numerical Distance Protection : Principles and Applicationsrd Edition, Publics Corporate Publishing, Wiley-VCH, 978-3-89578-318-0Berlin, Germany.