POWER SYSTEM BACKUP PROTECTION USING SYNCHRONIZED PMU

Transcription

1 POWER SYSTEM BACKUP PROTECTION USING SYNCHRONIZED PMU LAVUDYA JAYASREE 1 and GAIRABOINA NAGARAJU 2 1,2 Dept. of Electrical And Electronics, Engineering, Christu Jyothi Institute of Technology And Science,Yeshwanthapur, Jangaon, T.S Abstract- Calamity failures in power grid due to mal-function of traditional backup protection system was one of the main causes of unwanted cataract trips. The new technique based on synchronized PMU with fast communication network and GPS system for time transfer have a dynamic adaptation for back-up protection of power system. The goal of the protection scheme is to estimate a new wide area backup protection system to maintain the power system stable by isolating only faulty components from the healthy part of system. The purpose is to boost the overall effectiveness and consistency of the power structure for all power stages via significant dependence on WAPS as distributed intelligence agents with improved monitoring, control and protection capabilities of power network. Introducing the fastest and of course best technique for WAPS as synchronized Phasor measurement unit (PMU).This paper speculates recognition of fault site and protection of power system using PMU also clearance of fault. The protection scheme which is used in this paper depends on the concept of equating positive sequence quantities such as voltage and current angles for every lines connected to the bus to recognize and classify the faulted line. This paper emphasize simulation on 220 KV system by using MATLAB Simulink. Keywords-Phasor Measurement Unit,Backup Protection, Time Synchronization, Global Positioning System. I. INTRODUCTION Nowadays, power systems become very tough and challenging to manage due to fast development to satisfy enormous boost in load demands which leads the power system arrangement to become more complex. So, Electrical networks with adequate power quality and high reliability are preferred. With this admiration, new technologies suchlike smart grids has introduced a new standard for control, protection and monitoring system to improve reliability of electricity, safety of grids,decrease the unwanted blackouts, rapid response to interpretation in the electrical network, spotting of fault and recovery of electrical system as fast as possible. Wide area control, monitoring and protection system is the modern technique for management of electrical system [1].In electrical power system, the different fault occurs which results collapses of the electrical system [2].Collapse of power structure take place due to simple fault, load violation, power fluctuations and islanding. Lots of techniques are used in the power network for safety of transmission line. Distance protection is one of broadly used techniques, as in that protection the distance relay is used for protection purpose. The distance relays are depend on the standalone assessment and each relay operate autonomously corresponding to different region of protection.the distance relay is operating for fault taking place in between the connected relay position and the preferred position [3].Mal-operation of third zone distance protection in conditions such as power sway, voltage volatility and load encroachment may increase to wide area blackouts [4].In July 30th and 31st, 2012 two severe blackouts occurred in India. Here, new technique is provided for protection of wide area using synchronous PMU. This technique is depend on by comparing and equating positive sequence voltage magnitudes for specified areas and positive sequence current phase angles for every coupled lines between the two areas of the system network. The time synchronized phasor measurement technique is used, which gives a view of the dynamic power system and capable for controlling and monitoring of wide area protection. By using a fast GPS and modern conveyed system. DOI: /IJMTER HIIVJ 158

2 II. THE THIRD ZONE MAL-FUNCTION Usually, for the transmission lines the most important protection is done by first and second zones, while the protection done in third zone is recognized as the backup protection. About 80 to 85 percent part of the line without any time delay is covered by the first zone. First zone can be known as the chief protection. Second zone covers the whole length of the line plus 25 to 50percent of the succeeding shortest line and operation time is put about 0.25 to 0.4 seconds. The entire region confined by the both zones plus 25percent of the succeeding long line (third line) is covered by the third zone and for that the delay time is put among 0.6 to 1.5 seconds. The third zone is worked for backup protection. This structure is in general used to defend each line separately. The amplitude and the phase angle of quantities like voltage and current fluctuate, in this third zone, which is the reason of malfunction. Distance protection relays are ready with power sway recognition modules [4]. The very significant obsession in the power network is the need of reactive power and that is main reason of voltage volatility [5].The third zone relay which having a maximum area of protection as backup protection is the reason of Mal function of distance relay in provisions of voltage volatility [6]. When the dynamic load tries beyond the capacity of transmission network line or generation to be used that is most horrible instance of occurring the voltage instability [7]. The various number of methods are used for fault detection from voltage instability are presented. Voltage changes are not always reactive, as step- voltage increase due to switching of capacitors or load shedding.when the network is faulty, derived of voltage close to the voltage collapse is huge and negative. III. CONCEPT OF PMU The device named as PMU is worked to collect and provide instant phasor from desire areas of applications attracted with instantaneous day and time of the measuring called stamped data. Estimated phasor are called as synchro-phasors, here synchronized measurement technique plays very important roles, especially in backup protection. But to send information of PMU from distant parts of the network to main control system is consociated with delay of frequent tens of milliseconds. So it is not enough to use WAPS using PMU for main protection system. PMU measures positive sequence currents and voltages with accurate and exact time synchronization. The measurements are done by using GPS single pulse per second Synchrophasors, provide the phasor demonstration of voltage or current to complete time reference. This absolute reference is given in the form of a common timing signal by using high -accuracy clocks synchronized to corresponding universal time such as the universally used global positioning system (GPS).The synchronized clocks are used as a reference,so PMU creates the complex number of a constant sinusoidal signal phasor representation as presented in Fig. 1. The connection between the reporting moment and the phasor representation is that, the phase angle is equal to the angular division between the reporting peak and the period of the sinusoid. Though, if all PMUs works on the same timing reference, their measurements are comparable, and the differences among the phase angle of phasors are correct. As most applications look for to identify the differences between the phase angles of variety of phasors, the output of PMU provides a valuable input to monitoring, protection, and control operation in a power system. Figure -1 Phasor representation (a) Sinusoidal waveform (b) Phasor All rights Reserved 159

3 The synchronized phasor of ac signal is given as the complex quantities as below, x(t) = xr + jxi = ( xm / 2) e jø (1) = xm / 2 (Cos ø + j Sin ø ) (2) Where, xm = amplitude of synchronized vector, phase angle is denoted by ø and xi and xr are imaginary and real components of complex value. The general method for phasors calculation by using sample data is discrete Fourier transform. The high speed communications links used for WAPS are Fiber optic, microwave, PLC, Twisted pair. IV. THE PROJECTED TECHNIQUE The main purpose is to improve the interruption monitoring and system event analysis. Synchronous phasor measurements gives all revelatory state measurements that are phase angle, frequency and voltage magnitude. PMU is used to evaluate bus voltages and all revealing line currents next these measurements are given to PDC at control centre. The technique is WAPS which is accepted to find abnormal or faulty condition and to isolate the faulty area from the overall system. Two components are very important to distinguish the faults on transmission line. One is the drop of voltage and other is due to fault occurrence the change in flow of power direction. The fault current way to be able to resolve by using phase angle through reference to a base quantity. Direction of fault to be able to find out by with the assist of comparing the transmission line phase angle of current and voltage. The PMU, block diagram is as in Fig. 2 below. Figure -2 The block diagram of PMU The analog to digital converter, converts the analog signal from current and potential transformer to digital signal and passed through low pass filter. The GPS receiver detects the single pulse for each second synchronizing signal from GPS satellite. From these data the positive sequence quantities such as voltage and current are calculated. The voltage is viewed as reference polarizing quantity. The fault current Phasor lies inside forward and backward areas with reference to the reference phasor, corresponding to the fault situation [8,9]. Flow of Power in given direction is the effect of phase angle among voltage and current varying around its power factor angle while the power direction the current phase angle, with travels in opposite direction, reference to voltage will be[8]. At the main[8]. At the main place and current angles with supreme differences are measured for organized line with this affected region. By equating this angles with one another, the most value of complete difference is measured as faulted line. This process can be expressed mathematically as follows: Min { 1, 2 m n } (3) The positive sequence voltage magnitude is calculated by PMU for area 1, 2, 3, m, to n. When the fault take place on the network the output of positive sequence voltage magnitude becomes minimum. From this calculation the nearest faulted area can be determined. In this case this area is shown by m. Next there is need of comparing the accurate differences of current angles All rights Reserved 160

4 positive sequence of interrelated lines associated with this area m which is faulted with the interrelated close to area and then by selecting maximum one. This can be expressed as, Max { m1, m2, m3,. mn } (4) Where, m and n are the organized part which shows the positive sequence current angle difference for the transmission network. This can be specified as follows, mn = mn- nm (5) V. SIMULATION AND RESULTS As presented in fig. 3 the five bus network is employed for case study. The interconnected network is taken of 220 KV, 100 km transmission line, one side is connected with generating station and other with load through interconnected lines. Matlab Simulink software is applied to simulate various faults and investigations. As discussed in the paper, lack of a proper technique for the solution of Mal operation in the third zone on 230 KV lines and above [10]. In this way in paper, the projected technique is tested. As displayed in fig 4 the simulation is performed by using the MATLAB Simulink software for five bus test system. The standards given are in per unit at 50Hz on 100MVA base [11]. Figure -3 The five bus system network taken for study The values for system are given in per unit on 100 MVA (base ) in table no.1 Table- 1 The transmission line parameters. 1 Generator MVA,220Kv,50Hz,Synchronous generator pu model 2 Transformer 220 KV/13.8 KV,100 MVA 100 Synchronous KV,100 MVA machine 4 LOAD Kv,50MW,24Mvar,RL load 5 LOAD Kv,100MW,48Mvar,RL load 6 LOAD Kv,80MW,38Mvar,RL All rights Reserved 161

5 7 LOAD Kv,120MW,58Mvar,RL load 8 LOAD Kv,150MW,RL load When different fault appeared on the given transmission line, the faulted signals can be recognized from results. Similarly, various fault situation are simulated on the system using the proposed technique. Type of Fault can be detected and observed by using Fault Analysis Block given in fig. 6 for three phase to Ground Fault but same can be obtained for single line to ground fault and double line to ground fault. Figure- 4 SIMULINK model of 5 Bus 220 kv system Figure -5 MATLAB/Simulink block diagram responsible of the selection of the type of fault & its clearance. Figure- 6 Fault analysis block for three phase to Ground Fault Figure All rights Reserved 162

6 Figure -8 Three phase current signals for entire lines connected to the fault affected area (i.e. area 2). The fault is situated on line 1 connecting area 1 and area 2. When fault occurs, line connected between area 1 and area 2 is exaggerated. Fig. 7displays the output of three phase to ground voltage, whereas fig. 8 shows output of three phase current of the lines linked to faulted part. As well, different fault conditions are simulated on the system with projected procedure Figure -9 Positive sequence voltage magnitudes five different areas during fault on the network Fig. 9 shows the output from the five PMUs, the graph shows the five positive sequence voltage magnitudes (PSVM) for five different areas during fault. The minimum value is selected which is showing the nearest area to the fault (area 2 ). Fig. 10 shows the perfect difference of all positive sequence current angles (PSCA) for every lines interconnected with the faulted region (area 2) with the other adjacent areas (areas1, 3, 4) and the maximum ultimate difference of positive sequence current angle with line 1. Figure- 10 Positive sequence current angle absolute differences for interconnected lines to the faulted All rights Reserved 163

7 REFERENCES [1] Terzija Vladimir, Valvrde Gustavo, Cai Deyu, Regulski Pawel,Madani Vahid, Fitch John, SkokSrdjan,Miroslav M.Begovic & Phadeke A Wide-Are Monitoring,Protection, and Control of Future Electric Power Networks, Presented At Proceedings of the IEEE,VOL. 99, NO. 1, Jan 2011, PP [2] Machowski J, W Bialek J, R Bumby J, Power System Dynamics- Stability & Control, 2 nd Edition2008, Press John Willy & Sons Ltd. [3] S. Horowitz and A. Phake, Power System Ralaying. Taunton, Somerset, U.K., Research Studies Press, 1992 [4] A.R.Motavalian, N.Moadabi and G. B. Gharehpetian, Reliability Assessment of Power [5] System Backup Protection between Smart Grid Control Center Using Phasor Measurement Units International Conference on Renewable Energies and Power Quality ICREPQ 13 [6] Kundur Prabha, Power System Stability and Control, March 1994, Press McGraw-Hill Inc, Chapter 2& 14. [7] Grenor Verbic, Ferdinand Gubina, A New Concept of VoltageCollapse Protection- Based on Local Phasors,IEEE Transactions on Power Delivery, Vol.1 9 No.2, Apr.2006, PP [8] Jonsson Mattias, E. Daalder Jaap, An Adaptive Scheme to Prevent Undesirable Distance- Protection function During Voltage Instability IEEE Transactions on Power Systems Delivery, VOL. 18, NO. 4, Oct 2003, All rights Reserved 164