! zyxwvutsrqpon IEEE Transactions on Power zyxwvutsrqpo Delivery, Vol. 7. zyxwvutsrqp No. zyxwvutsrq 3, July 1992 1121 MICROPROCESSOR-BASED UHS RELAYING FOR DISTANCE PROTECTION USING ADVANCED GENERAT~ON s IGNAL PROCESSING P. K. Dutta P. B. Dutta Gupta Department of Electrical Engineering Indian Institute of Technology Kharagpur-721302, INDIA Abstract UHS refers to operating times ofless thail 5 millisec.on 50 Hz power systems. Three d i F - tinct types of UHS relaying realisation in dis tance protection via advanced generation digi- tal signal processing, possible with cheap and readily available VLSI chips, have been consi- dered. Type I is the correlator detector,Type 11 and -111 are the spectrum and cbpstrum analysers respectively. Performance of these detectors is evaluated with respect to varying system configurations that complicate the post fault signals. Microprocessor implementation of these techniques show that 5 msecs limit is achieved in Type I and I1 detectors where- as Type I11 detector can operate in 3 msecs. Keywords : Relay,Signal Processing, pProcessor Introduction UHS distance relays are necessary for . fast circuit breaking to improve stability in large EHV power grids. Conventional digital relays compute the impedance to the fault , based on fundamental components of post fault voltage and current for which some form of filtering is necessardlt2) .The post fault transient signals are initially dominated by electromagnetic travelling waves and therefore not easily amenable to fundamental componeRt extraction with fast convergence. This delay is unacceptable in terms of UHS relaying and so the solution is sought in the information content of the transients themselves (3) .The post fault transients are corrupted by multi- ple reflectionsfrom system terminals and dis- conttnuities and are very complex in character leading to maloperation and inaccuracy in some of the installed schemes. A deeper insight in- to the behaviour of the transients is possible via advanced generation signal processing that is feasible with cheap and readily available VLSI chips. Three distinct possibilities, via correlator detection, spectrum analysis and cepstrum analysishave been investigated with respect to microprocessor-based relaying. A comparative evaluation of their performance with respect to varying system configurations e.g. line length and compensation, fault dis- tance and inception angle and source impedance is interesting from the point of view of UHS relaying .. zyxwvutsrqp 90 IC 572-8 ?;XD A ,.?-per recorii::enci.ed .mil cl);roved by tho IKG Power 3ystsn 2ela:;-ins Co:lriittee of t:le gineerin: Jociety Por pi-ese:ltstion st ,'PES International Power ::eeting-Inciia., 3ew :)elhi, India, October 2 ; - 3ove::ijer 1, 1:?3. &.nuscript subritteci February 9, 1990- r~aiie :iveilaLle for printin;, kugust 13, lg?U. Basic Relaying Principle If the super-position theorem is valid, the post fault voltage vf+ and current if+ can be written as v = v +v. f+ ' zyxwvuts f- fo - i i f+ f- fo = i where vf- and if- are the prefault voltage and current respectively and vfo and ifo are the voltage and current corresponding to the pseudo-voltage source at fault point on fault. Transients v fo , ifo are best obtained by assuming distributed parameter loss-less trans mission lines in terms of forward and backward travelling waves fl (t-ax) and f (t+ax) res- pectively where t is time and a zyxw =E, 1 and c being the true inductance and capacitance per unit length respectively and x is the propaga- ting distance vfo = v(x,t) = D.5 [f (t-ax) + f2 (t+ax)]l(c) 1 ifo = i(x,t) = 8.5/Zo[f (t-ax)- f2 (t+ax)]l(d) 1 where Zo is the line surge impedance. Signals for travelling wave based relay- ing are taken as follows : SF = v(x,t) + Zo i(x,t) SR = v(x,t) + 2, i(x,t) The distance relaying algorithm consists of two parts - first fault detection and then fault distance calculation. Since distance cal- culated is dependent on travelling wave speed, aerial mode components,which are frequency invariant,are considered and are obtained through modal transformation matrices. Since single location distance relaying is better than two-location directional relay- ing necessitatingintercomnunication channels, distance relays with signals derived at a single location are only considered. The correlation detection type of relay- ing has been considered earlier. Crossley and McLaren (8) used cross correlation between SF and SR to detect the arrival of SR and its application has been extended to Teed circuits Ibe and Cory (12) consider the sudden change in the wave as a function of space and time; however, an averaging process is involved that results in time delay. Further investigation (20)has shown that various di scriminativechec!t 0885-8977/92/$3.0001992 IEEE