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• The future sample points are calculated using
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presentation.pptx
- 1. WELCOME
- 2. SYMMETRICAL FAULT DETECTION DURING POWER SWING
- 3. ABSTRACT • If a fault occurs during a power swing, it should be detected and the unblocking function should be invoked to clear the fault as soon as possible. • Distance relays are getting blocked during power swing to ensure reliability of the power system. • Due to the symmetric nature of signals during the power swing, symmetrical faults are difficult to be detected. • In this paper, a differential power-based fault detection technique is proposed for the detection of symmetrical faults during power swings.
- 4. Cont… • The differential power is calculated from the difference in predicted and actual samples of voltage and current. • The predicted voltage and current samples are obtained using the auto regression technique. • The proposed method is tested for different fault conditions and the results are compared with the available method. • The proposed method is found to identify symmetrical faults accurately during slow and fast power swings for different power systems.
- 5. Literature survey • Power Swing which is basically caused by the large disturbances in the power system which if not blocked could cause wrong operation of the distance relay and can generates wrong or undesired tripping of the transmission line circuit breaker. • To prevent unwanted distance or other relay operation during a Power Swing, we did fundamental studies of traditional and advanced detection and prevention methods. • However, many studies have shown that undesirable zone 3 distance relay operations have initiated tripping which lead to cascading events and finally wide-area voltage collapse (Jonsson and Daadler, 2003; Kim et al, 2005; Jin and Sindhu, 2008 ; Lim et al, 2008).
- 6. Cont… • To improve reliability of relay operation, adaptive scheme for distance protection has been introduced by many researches (Horowitz, Phadke and Thorpe, 1988, Thorpe et al, 1988: Jonsson and Daadler, 2003; Kim, Heo and Aggarwal, 2005; Lim et al, 2008). • In adaptive distance protection relaying, an important aspect to be considered is developing an indicator that can differentiate between faults and power swings. • The objective is to permit the trip signals during faults and block the trip signals during other events. • My enhancement to the topic is to clear or rectify the condition using The Fault Mitigation Technique.
- 7. LITERATURE REVIEW PAPERS Detection of Symmetrical Faults by Distance Relays During Power Swings. (IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 25, NO. 1, JANUARY 2010) • To maintain security of distance relays, power swing blocking is necessary to prevent unintended operation under power swings. • This paper presents a new method for detecting a symmetrical fault during a power swing, based on extracting components of the current waveform using the Prony method. • The merit of the proposed method was demonstrated by simulating various cases including solid faults and arc fault on a typical power system. • The ease of implementation as well as accuracy and high speed of fault detection are important advantages of the proposed method.
- 8. A Novel Approach to Detect Symmetrical Faults Occurring During Power Swings by Using Frequency Components of Instantaneous Three-Phase Active Power (IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012) • Based on the damping frequency component of 50 (or 60) Hz created on instantaneous three-phase active power profile after inception of a symmetrical fault, the proposed method will be able to detect the fault in less than one power cycle. • This detection method can be readily implemented, and is immune to the power swing slip frequency, fault inception time, and fault location. • The proposed method has several advantages that are superior to the existing methods. First, since it requires only three-phase active power, which can be simply calculated by production of instantaneous voltage and current, and FFT, which is coded in all digital relays, the new method can be readily implemented. Second, the new method is very fast.
- 9. Fast Distance Relay Scheme for Detecting Symmetrical Fault During Power Swing (IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 25, NO. 4, OCTOBER 2010) • The paper provides a fast detection scheme for symmetrical fault during power swing for distance relay, which is based on extracting the high- frequency component energy of forward and backward traveling waves induced by faults. • The multi resolution analysis based on wavelet transform has the ability to decompose the analyzed signals into different frequency bands. The selection of mother wavelet and the number of levels of wavelet transform are carefully studied. • The fault can be identified by feature extracting from the d1 component of Daubechies-8 (Db8) wavelet transform. • This proposed method can be used for distance relay operation blocking or monitoring.
- 10. A Classification Approach Using Support Vector Machines to Prevent Distance Relay Mal-operation Under Power Swing and Voltage Instability (IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 3, JULY 2012) • Distance relays, in the power transmission systems, are susceptible to the mal- operation under certain system events, such as power swings and voltage instability • The proposed scheme segregates the power system events into faults, power swings, and voltage instability. • This paper also proposes a new index, called the relay ranking index, for identifying the relays most vulnerable to the mal-operation due to power swings and voltage instability. • The scheme effectively discriminates the dynamic encroachment events and differentiates the system events into power swings and voltage instability by utilizing the transmission- line reactive power loss as a key indicator for the voltage-unstable situation.
- 11. Mitigating the Impacts of CCVT Subsidence Transients on the Distance Relay (IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 27, NO. 2, APRIL 2012) • The paper presents a comprehensive time-domain model of the coupling capacitor voltage transformer (CCVT) to investigate the effect of CCVT subsidence transients on the distance relay. • The studies show that voltage-zero subsidence transients can adversely impact the performance of the distance relay and result in the overreach problem. • The method is based on improving the degree of accuracy of the voltage Phasor estimation during the CCVT subsidence transients. • The proposed method is not affected by harmonics and high- frequency transient distortions of the voltage, and prevents the relay overreach problem.
- 12. Review of existing methods • In a power system disturbance-like faults, generator disconnection and change in the large block of loads are the main reasons for power swing. • Large variations in voltage and current causes undesired tripping of distance relay which may lead to subsequent line outages. • The power swing blocking (PSB) function is used to prevent mis-operation of distance relays during swing.
- 13. • If a fault occurs during the power swing, it should be detected and suppressed. • Conventional fault detection techniques may fail to distinguish fault during the power swing. • Symmetric nature of phase voltages and currents during the swing makes this task tedious.
- 14. PROPOSED METHOD • Full-cycle sample points of voltage and current are predicted using auto regression technique for any phase. • It models the nth value of a variable as a function of previous values, where k is the order of the model. • The accuracy of the prediction technique improves with a higher value of k.
- 15. PHASE 1 - CASE STUDY • The method is tested for various fault conditions during the power swing for a 400-kV double- circuit transmission system (i) • A 230-kV WSCC 3-machine, a nine-bus system (ii) • Simulation and analysis are going to be done through PSCAD/EMTDC
- 16. • i) • ii)
- 17. ANALYSIS WITH AUTO REGRESSION PROGRAMME • Auto regression is a special technique for regression analysis. • The technique models nth values of the system as a function of K previous values. • Higher values of K improves the system prediction accuracy.
- 18. Cont… • The expression for the Kth order auto regression model is • where a1,a2….aK are the auto regression coefficients and i’s are the samples of the variable. • The calculation of coefficients are done by considering the P available samples of the system.
- 19. Cont… • matrix form of the system can be written as • It can be further written as • The future sample points are calculated using available samples and [A]
- 20. Cont… • The expression for obtaining future samples (next q samples) is • The accuracy of prediction decreases with length of q. • The accuracy of the technique depends on the selection of k, p, q.
- 21. Cont… • The coefficients of the auto regression technique are calculated using previous samples of a variable and these samples gives a clear picture of the future disturbances and system oscillations. • The difference between the predicted and actual values of the variable is found to be negligible when there is no external disturbance with the selected system.
- 22. Cont… • The differential components of voltage and current at any sampling instant of time are calculated as follows:
- 23. Cont… • The rms values of differential voltage and current are calculated over a period of one cycle Where N is the number of samples per cycle
- 24. Cont… • The differential power ΔP is calculated from the rms voltage and current as
- 25. RESULTS FOR THE DOUBLE-CIRCUIT LINE • The system is simulated using PSCAD/EMTDC software with a distributed transmission-line model. • A three-phase fault is created in Line-2 at point F at 0.5 s, which is cleared after 0.1 s by the opening of breakers B3 and B4. As a result, the distance relay R1 in line-1 experiences a power swing. • Any fault in line-1 during the swing has to be detected by relay R1.
- 26. FLOW DIAGRAM FOR THE PROPOSED DOUBLE CIRCUIT LINE
- 27. Results Differential component of voltage
- 28. Differential component of current
- 29. • Differential power for the 3Phase fault at 3.65s during power swing.
- 30. Inference • The difference in the actual and predicted samples of the voltage and current during the power swing followed by a three-phase fault at 3.65 s are shown. • The wave forms obtained are clearly showing the predicted and actual samples of voltage, current and power during the swing and fault. • Difference in predicted and actual samples of voltage and current is less during the power swing and high for the fault period.
- 31. • The differential power can be obtained directly from the current – voltage waveforms. • The magnitude of ΔP is negligible for the power swing and high for the fault period. • The algorithm identifies the fault if the magnitude exceeds the threshold value of ΔP. • The selection of threshold value is much important to get a more accurate fault detection. • The threshold value should be greater than the maximum differential power during the swing condition.
- 32. CONCLUSION • Detection of symmetrical fault during power swing is actually a threat to power system protection. • The base paper is hereby proposing an auto-regression based study of symmetrical fault components during the swing period. • But mitigating a fault is much beneficial than making a tripping with the CBs. • The thesis is thus proposing a fault mitigation scheme to assure an improved reliability with the power system.