Harmonic Analysis of a High Speed Automatic Reclosing on a 400 kv Overhead Transmission Line

Transcription

1 Harmonic Analysis of a High Speed Automatic Reclosing on a 400 kv Overhead Transmission Line ANGELA IAGAR, SORIN IOAN DEACONU, CORINA DANIELA CUNTAN, IOAN BACIU Department of Electrotechnical Engineering and Industrial Informatics Politechnica University of Timisoara Revolutiei Street, No.5, Hunedoara, ROMANIA angela.iagar@fih.upt.ro Abstract: - Studies reveal that a vast majority of faults on overhead lines are transient in nature. For this reason are used automatic reclosing devices to maintain system stability and the continuity of the power supply. The paper analyzes a high speed automatic reclosing on a 400 kv overhead transmission line. For data acquisition was used a Compact Digital Recorder (CDR). The data stored in the internal CDR memory were extracted on a PC by CDR Link for Windows program. The fault analysis was performed with Focus for Windows program. Key-Words: - overhead line, single-phase-to-ground fault, automatic reclosing, data acquisition, harmonic analysis 1 Introduction The main function of the power line protections is to minimize the influence of faults on power system operation. On High-Voltage (HV) and Extra-High-Voltage (EHV) transmission lines the majority of faults are typically single-phase-to-ground and around 90% of them are temporary in nature [1, 2]. Transient faults can be successfully cleared by the proper use of tripping and auto-reclosing. This de-energizes the line long enough for the fault source to pass and the fault arc to de-energize, then automatically recloses the line to restore service [3]. The reasons for applying auto-reclosing function can be summarized as follows [1, 4-10]: - minimizing the interruption of the supply to the customer; - maintenance of system stability and synchronism; - restoration of system capacity and reliability with minimum outage and least expenditure of manpower; - restoration of critical system interconnections; - restoration of service to critical loads; - higher probability of some recovery from multiple contingency outages; - reduction of fault duration, resulting in less fault damage and fewer permanent faults; - relief for system operators in restoration during system outages. When applying high speed auto-reclosing (HSAR) to lines with distance protection, simultaneous tripping at the both ends of the line is important. This is normally accomplished using signaling channels [2, 3]. Another method is using zone 1 extension scheme. In this method, zone one reach is normally set to cover 120% of line. When fault occurs anywhere in the protected line breakers at both ends are tripped simultaneously without time delay and reclosed. A contact from reclose relay is used to reset the zone to 80% of line so that if the fault is permanent, the breakers will be tripped based on the respective zone timers when reclosed [3, 8]. Further is analyzed a HSAR on 400 kv overhead transmission line (OTL) Sibiu in Mintia station. At the 400 kv OTL the major protections and automations are unitary incorporated in advanced digital relays: line distance protection terminal REL 521 and distance relay LZ96a. Among the most important functions of REL 521 could be mentioned: distance protection (ZM); teleprotection; automatic switch onto fault logic (SOTF); local acceleration logic (ZCLC); instantaneous non-directional phase overcurrent protection (IOCph); time delayed undervoltage (TUV) and time delayed overvoltge protection (TOV); disturbance recorder (DR); fault locator (FLOC); trip value recorder (TVR); autorecloser 1- and/or 3-phase, single or double circuit breakers [11]. The distance protection zones can operate, independently of each other, in directional mode (forward - zones 1, 2, 4, or reverse - zone 3) or non- ISBN:

2 directional mode (zone 5) [11]. Zone 1, 2 and 3 can issue phase selective signals, such as start and trip. Distance protection zone 5 has shorter operating time than other zones, but also higher transient overreach. It should generally be used as a check zone together with the SOTF or as a time delayed zone with time delay set longer than 100 ms [11]. This variation is recorded by the Compact Digital Recorder during the period: t recording = t pre + t fault + t post, (1) where t pre is the pre-fault recording time, t fault represents fault recording time, and t post is the postfault recording time. Fig. 1. Schematic presentation of the operating characteristic for one distance protection zone in forward direction Fig. 1 presents the operating characteristic for one distance protection zone in forward direction, where: Xph-e represents the reactive reach for phase-to-ground (earth) faults; Xph-ph represents the reactive reach for phase-to-phase faults; Rph-e is the resistive reach for phase-to-ground (earth) faults; Rph-ph is the resistive reach for phase-tophase faults; Zline is the line impedance. Independent reactive reach setting for phase-tophase and for phase-to-ground measurement secures high selectivity in networks. Simplified setting parameters reduce the complexity of necessary setting procedures and make the operating characteristic automatically more adjusted to the needs in combined networks with off-lines and cables. In case of a fault located close to the Sibiu South station, (fig. 2) the distance protection from Sibiu South will frame the fault in step 1 (zone ZM1- adjustment Z1 ) and will issue an impulse by means of the high-frequency installation (IMP ZM1). The distance protection from Mintia station will frame the fault in step 2 (zone ZM2-adjustment Z2) and would trigger delayed ( s). But, at reception of the signal from Mintia (that applies to the input IMP CR) and by checking the framing into zone ZM2, it will command the breaker s rapid triggering. Thus, the fault is rapidly cleared. When a disturbance occurs in electric stations, it takes place a variation of the analogue and numerical parameters. Fig. 2. Principle of the teleprotection permissive scheme Fig. 3. Recording time of the disturbance The data stored in the internal CDR memory were extracted on a PC by CDR Link for Windows program. The fault analysis was performed with Focus for Windows program [12]. 2 Summary of the Fault Report Generated by Focus Program The quantities (analogue and numerical) acquired by CDR can be graphically visualized with Focus for Windows program. The program provides, also, the phasor diagrams of voltages and currents, and their harmonic analysis [12]. Further is presented a summary of the fault report generated by Focus program in case of a HSAR on the 400 kv OTL Sibiu, in Mintia station. 2.1 Values of Pre-fault Quantities The total time allocated to record the pre-fault quantities was ms. ISBN:

3 In fig. 4, at t=-30 ms, the phase differences between the phase voltages are a little modified against the normal operation. The homopolar voltage and the homopolar current have high values (U0=111.8 kv, I0=1.344 ka). Marker 2 (at t=-30 ms) catches the incipient stage of a phase-to-ground fault on phase 2 (L2). 2.2 Values of Fault Quantities Fig. 4. Marker 2: t=-30 ms (pre-fault). Phasor diagrams of voltages and currents Is noticed a slight decrease of the voltage on phase 2 (UL2=218.2 kv) compared with the voltages on the other phases (UL1=236.4 kv, UL3=240.8 kv). The current on phase 2 (IL2=1.314 ka) has a higher value (IL1=331.2 A, IL3=401.2 A). Fig. 5. Analogue quantities in the time period t= ms Fig. 6. Marker 4: t=17 ms (fault). Phasor diagrams of voltages and currents The values measured at the moment t=17 ms (fig. 6) are framed within the fault period of the recording. At this moment is recorded a maximum value of the current on phase 2 (IL2=2.93 ka) and a voltage decrease on phase 2 (UL2=70.02 kv). One can notice a significant increase of the homopolar quantities (I0=3.597 ka, U0=294 kv), up to the limit when the high-voltage breaker s protections of OTL Sibiu are triggered. Analogue quantities in the time period t= ms are presented in fig. 5, and numerical quantities are presented in fig. 7. Markers 1 (t=-60 ms, fig. 7) and 2 (t=-30 ms, fig. 7) show that the OTL protections are in stand-by (pre-fault period). Marker 3 (t=-8 ms, fig. 7) is close to the trigger limit. In fig. 7, marker 4 (t=17 ms) indicates the start of distance protections: START L2 RE 1:1 start for group 1 of protections through the line distance protection terminal REL 521, phase L2; GEN. START 1:1 general start of distance protection REL 521; GEN. TRIP R1:1 trigger impulse sent by the distance protection REL 521 to the highvoltage breaker of OTL Sibiu, in Mintia station; DIST. TRIP 1:1 trigger of distance protection REL 521; START L2 LZ 1:1 start for group 2 of protections through the digital relay LZ96a, phase L2; GEN. START 1:1 general start of digital relay LZ96a; DIST. TRIP 1:1 trigger of digital relay LZ96a. ISBN:

4 Marker 5 (t=34 ms, fig. 7) indicates: PLC REC CH 0:1 trigger impulse issued by the distance protection REL 521 of the teleprotection channel, that sends a trigger impulse to the high-voltage breaker of Sibiu station. frequency impulse through teleprotection. Fig. 8. Marker 7 (t=1065 ms): reclosing impulses to the breakers 2.3 Values of Post-fault Quantities Fig. 9. Marker 10: t=1184 ms (post-fault). Phasor diagrams of voltages and currents Fig. 7. Numerical quantities in the time period t= ms. Start of distance protections Fault locator of REL 521 terminal use for the distance to fault calculation a line modelling algorithm, that takes into account the sources at both ends of the line. In this way, the influence of the load current, the infeed from the remote end and the fault resistance, can be compensated, resulting in a highly accurate calculation. Taking into account the RMS values of the phase currents and voltages, the distance is quantified from the place where the protection is mounted up to the fault place, and is equal by 24.2 km. In fig. 8, marker 7 (t=1065 ms) indicates AR ON REL/R 1:1, with the following functions: - sending of a reclosing impulse to the Sibiu OTL s breaker in Mintia; - sending of a reclosing impulse to the Mintia OTL s breaker in Sibiu, by emitting a high- At the moment t=1184 ms (fig. 9) small differences between RMS values of the phase voltages (UL1=239.6 kv, UL2=242.5 kv, UL3=239.9 kv) and RMS values of the phase currents (IL1=375.8 A, IL2=394.3 A, IL3= A) are noticed. The RMS value of the homopolar quantities are low (U0=37.58 kv, I0=42.23 A). Fig. 9 presents the end of the successful reclosing (+): the breaker is connected, and OTL Sibiu is in operation. Fig. 10. Time variation of harmonic components of the faulted phase voltage (UL2) ISBN:

5 Focus program allows the harmonic analysis of the voltages and currents up to 10-th order. Harmonic analysis of the faulted phase voltage (UL2) reveals the presence of the even and odd harmonics in the waveform (fig. 10 and fig. 11). currents per phases 1 and 3 (IL1 and IL3, fig. 12 and fig. 13) have great values. Fig. 13. Time variation of harmonic components of current IL3 Fig. 11. Time variation of harmonic components of the faulted phase voltage (UL2) Harmonic components of the faulted voltage are sudden increases at the time moments: t=-30 ms (fault occurrence), t=17 ms, t=34 ms (triggering of the line breakers), t=77 ms (secondary arc initiation), t=123 ms, t=320 ms (final arc extinction) and t=1083 ms (closing of the line breakers). In the time periods t= ms and t= ms all harmonics of faulted voltage exceed the compatibility limits [13]. The non-linearity of the electric arc distorts the voltage and current signals on the sound phases, because of electromagnetic and capacitive couplings of the faulted and the sound phases. Fig. 14. Time variation of THD[%] for currents waveforms In the time period t= ms Total Harmonic Distortion (THD) of currents IL1 and IL3 (fig. 14) exceed the compatibility limits [13]. Fig. 12. Time variation of harmonic components of current IL1 In the time period t= ms all harmonics of Fig. 15. Time variation of THD[%] for phase voltages waveforms ISBN:

6 Fig. 15 show that THD of phase voltages UL1 and UL3 have small values; THD of the faulted phase voltage UL2 has very great value, and exceed the compatibility limits, during the time periods t= ms and t= ms [13]. 3 Conclusion Fast clearing of EHV faults is essential to maintain power quality in an area, because events on the EHV system affect the underlying transmission and distribution systems. Benefits of successful high speed reclosing on EHV overhead transmission lines are: improved system stability, reducing the duration of fault arc, respectively disturbance time, and economics in system design. Are noticed especially the facilities offered by Focus program in analyzing the analogue and numerical quantities; the visualization of RMS values, phasor diagrams and harmonic analysis are in real time. Further the analysis of the disturbance report issued by the Focus program, can be determined the causes, amplitude and consequences of the appeared disturbance. References: [1] ***, Automatic Reclosing Transmission Line Applications and considerations ( [2] IEEE Power System Relaying Committee Working Group, Single phase tripping and auto reclosing of transmission lines-ieee Committee Report, IEEE Transactions on Power Delivery, Vol. 7, January 1992, pp [3] G. Kobet, et al., Justifying pilot protection on transmission lines, 63rd Annual Conference for Protective Relay Engineers, College Station, TX, March 29 -April , pp [4] Z. Radojevi, J. Shin, New digital algorithm for adaptive reclosing based on the calculation of the faulted phase voltage total harmonic distortion factor, IEEE Transactions on Power Delivery, Vol. 22, Issue 1, 2007, pp [5] M. E. Hamedani Golshan and N. Golbon, Detecting secondary arc extinction time by analyzing low frequency components of faulted phase voltage or sound phase current waveforms, Electrical Engineering, Vol. 88, 2005, pp [6] M. Jannati, B. Vahidi, S.H. Hosseinian, S.M. Ahadi, A novel approach to adaptive single phase auto-reclosing scheme for EHV transmission lines, International Journal of Electrical Power & Energy Systems, Vol. 33, Issue 3, March 2011, pp [7] R. Aggarwal, A. Johns, Y. Song, R. Dunn, D. Fitton, Neural-network based adaptive singlepole auto re-closure technique for EHV transmission systems, IEE Proceeding on Generation, Transmission and Distribution, Vol. 141, Issue 2, 1994, pp [8] E. A. Frimpong and P. Y. Okyere, A Review of Adaptive Autoreclosure Techniques, Indian Journal of Computer Science and Engineering, Vol. 1, Issue 3, 2010, pp [9] N. Sh. Rasool, M. F. Al-Kababjie, ANN Adapting Auto_Reclosing Relay In a Simulated Iraqi Super Grid, Proceedings of the 11th WSEAS International Conference on Automatic Control, Modelling and Simulation, (ACMOS '09), Istanbul, Turkey, May 30 - June 1, 2009, pp [10] N. Svigir, S. Tesnjak, An Approach to Selection of Basic Parameters Relevant for Automatic Reclosing Technique in Electric Power Systems, 7th WSEAS International Conference on Electric Power Systems, High Voltages, Electric Machines, Venice, Italy, November 21-23, 2007, pp [11] ***, REL 521 Line distance protection terminal, ABB Technical brochure, [12] ***, Focus for Windows v2.0, TELECOMM, [13] IEC/TR , EMC, Part 3-6: Limits Assessment of Harmonic Emission Limits for the Connection of Distorting Installations to MV, HV and EHV Power Systems (revision), ISBN: