Implementation of a Numerical Distance Relay for the 110kV Electric Lines

Transcription

1 Implementation of a Numerical Distance Relay for the 110kV Electric Lines GABRIEL NICOLAE POPA SORIN DEACONU CORINA MARIA DINIŞ ANGELA IAGĂR Department of Electrotechnical Engineering and Industrial Informatics Politechnica University Timişoara Str. Revoluţiei, no.5, Hunedoara ROMANIA gabriel.popa@fih.upt.ro Abstract: - In this article are presented the basic principles of the numerical protections used for protecting the high-voltage electric lines (110 kv). Is achieved a study for implementing a numerical distance protection DIPA 100, for a high-voltage line (an example from practice). For the numerical relay, is shown the protection characteristic of DIPA 100, characteristics of operation to faults phase-phase and characteristics of operation to faults phase-ground. By using of numerical protections for the high-voltage electric lines, is ensured an easy implementation in practice and a protection qualitatively superior compared with the classic protections. Key-Words: - Electric lines, High-voltage, Numerical protections, Distance protections 1 Introduction The protection systems are assemblies of simple or complex automatic devices, achieved usually with dynamic or static commutation relays, or with computing systems, installed on the energetic systems (ES) equipments, as generators, transformers, bus-bars, lines etc. The protection systems play the role to monitor their operation. In case of exceeding over certain limits the parameters that features their normal operation regime, the protection installations (PI) intervene in operative mode, actively, isolating the equipment where the fault appeared by the rest of ES installations if it s endangered the equipment s integrity or ES s normal operation. Usually, the insulation is achieved by disconnecting the switches through which the equipment is protected (EP) and is connected to ES. In case when the modification of the parameters against the normal values does not endanger immediately the EP or ES, PI signals the abnormal operation regime [1,2,3,4,5,6]. Automatic separation of the fault equipment of the rest of ES elements aims three main objectives: - to prevent the fault s development, respectively extension of its effects upon other installations from ES and its eventual transformation into a system emergency during the short-circuits. Due to the voltage s decrease and discharge of the active power synchronous generators (SG), can be disturbed the stability in operation of SG s and the power plants which operate in parallel, with all technical and economic consequences upon ES and consumers; - to re-establish a normal operation regime for the rest of ES, ensuring the continuity in supplying the consumers in conditions as better possible; - to limit the deterioration by the thermal and electro-dynamic effects of the short-circuit currents of the elements in which the fault was produced. These deteriorations can have extremely bad economic consequences due to the high costs of the actual ES equipments, especially generators and synchronous compensators and power transformers and autotransformers [7,8,9]. From the above, it results an important particularity of PI, e.g.: by monitoring the ES elements operation, out of the total possible states in which this can operate, PI should distinguish accurately two situations the normal operation regime and the fault regime. PI should act only in the last case and isolate the EP from the rest of the system [1,9,10]. PI contributes for ensuring the following ES operation requirements: continuity and safety in operation, high quality of the provided electric energy, as well as the integrity of the ES component equipment. For being possible the fulfilment of these requirements, PI should have a high safety degree and speed in operation, to ensure selectivity and to have an increased sensitivity. The above mentioned conditions can only be fulfilled by using relatively simple elements, with discontinuous action, e.g. relays with dynamic commutation (electro-mechanic relays) or static commutation (electronic relays or with magnetic ISSN: ISBN:

2 elements). In the last two decades appeared and developed numerical protection systems. 2 Protection installations principles 2.1 Operational block diagram of the protection installations PI and EP form together an automatic protection system, which is an automatic system in open circuit. From the set of possible values of the electric measures that feature the EP s operation, PI should select sub-sets characteristic to the abnormal or fault regimes and to elaborate, based on a logic algorithm, signalling or triggering controls. In fig. 1 is presented the operational block diagram of an automatic protection system of an ES (through a power station PS) [1]. The electric line may be: overhead line (OL) or underground cable (UC). by the processing and decision block, by amplifying or damping the measures; - Obtaining of symmetric components, reverse and homopolar, of the currents and voltages for the protections against non-symmetric faults, featured by an improved sensitivity against the one of the protections which controls directly the secondary measures. Processing and decision block (PDB), called also as PI s main block, receives the output measures from IB and processes them by an simpler algorithm, or more complicated depending on the PI s complexity degree. Further this processing, PI should establish accurately the moment when a fault appears, to locate the EP where the event was produced and to adopt a strategy to wipe it off, depending on its position. If the fault is located in EP, PDB elaborates the control signal to trigger the switches in the shortest time, and if the fault is exterior, PI should be prepared to intervene, with a certain delay, only if the fault was not wiped-off by the protection of that neighbour equipment. Execution block (EB) receives commands from PDB, transmits them to the switch s triggering (ST) coil and signals the transmission of the triggering command or appearance of an abnormal regime in EP. In certain situations, is necessary the information exchange between the PDB from the two EP s extremities, information with analogue character or logical character. Fig. 1. Block diagram of a protection installation The EP s operation regime is monitored by PI, which should contain such elements to distinguish the operation in normal, abnormal or fault regime. In order to be able to fulfil these functions, PI receives continuously information upon the EP s operation regime by measuring, by means of the current transformers (CT) and voltage transformers (VT), the fundamental electric measures currents and voltages - that features the EP s operation. PI contains also the following basic subassemblies: Input block (IB), or the measuring elements block, which receives the secondary measures of the measuring transformers and processes them in such way that the result of this processing to be applied to the next block. Processing in IB consists in: - Elimination of parasite signals, noises, harmonics, possibly of aperiodic components from the received information, by filtration, for obtaining the useful information; - Adapting the energetic level to the level required Fig. 2. Automatic protection system of an ES element with bilateral supply, situation which raises the most general problems regarding PI PI is mounted on al basic EP of ES, and the operational block diagram from fig. 2 is generally valid for all EP. The particularities that appear in the ISSN: ISBN:

3 blocks structure are determined by the type of EP, synchronous generator (SG), transformers, generator-transformer blocks, bus-bars, and lines. Supply source block (SB) is used foe supplying the PDB and EB blocks. 2.2 Principles of achieving the distance relays A particularity of the impedance protection, which is a complex protection with two input measures (current and voltage), is the fact that the measured impedance Z=R+jX is a circuit parameter dependent randomly both by the fault s location and the value electric arc s resistance. From this reason, is not sufficient to impose a simple operation condition, such as Z<Z pp (Z pp protection s start-up impedance), but a more rigorous condition, that should take into account the components ponderance R, X or Z, φ (the impedance s module and argument). This is possible by defining a domain D (fig.3) in the complex plan of R-jX impedances, where is located the impedance vector Z to faults, domain bounded by a contour C [1,2,11]. Fig.3. Defining the operation zone for a distance relay Contour C is called the operation characteristic of the impedance relay. The first achieved impedance relays (electromagnetic) were of induction or electromagnetic balance type. 3. Numerical distance relay DIPA Scope of utilization The complex protection digital relay DIPA-100 is equipment which includes practically all the protection-automation functions necessary for an electric line of 110 kv kv. By the complexity of the included functions, DIPA-100 lays in the category of the line terminals. The distance protection, as basic element, is conceived with six independent measuring elements which ensure the rapid, safe and selective removal of faults on electric lines with the neutral directly connected or by the small impedance connected to ground [11, 12]. The equipment can be used independently, or with integration in remote-controlling, due to the existence of DIPA-SCADA. DIPA-100 includes the following independent protection functions of the electric line [12]: - digital distance protection with the following extensions: blocking system at pendulum motions; tele-protection interface and logics; verification-blocking system from fusing of the voltage circuits, with optional commutation on the maximal protection of reserve current; - rapid protection at shutting-off the switch on fault; - directional homopolar protection; - reserve maximal protection. The following additional functions complete the protection/automation/integration needs in SCADA for an electric line of kv: - reserve s automatic reclosing; - human-machine interface; - special functions and integration in SCADA, which includes: monitoring interface of binary/analogue measures and communication with the SCADA remote-controlling system; SCADA line oscillo-perturbograph; optional, control extension in installation through SCADA; integration in the classic protection system; local measuring function (U, I, P, Q, f, Z, ϕ, etc.). 3.2 General technical characteristics The DIPA 100 equipment can be integrated both in classic solutions of protection-management electric stations and in new systems, e.g. the GALAXY distributed system of remote protection remote control, or in other systems. DIPA 100 is achieved in a multiprocessor structure, accumulating a calculation power of approximately 48 MegaFLOPS (48 mega-operations in mobile point per second) by using state-of-the-art DSP ISSN: ISBN:

4 technology. This allowed the implementation of some numeric algorithms for calculating of impedances and the various blocking conditions of a complexity and stability that should meet the safety conditions necessary to such equipment. The distance digital protection function has the following main characteristics [12]: - number of independent and simultaneous measuring elements: 6 ( R0, S0, T0, RS, ST, TR ); - number of triggering zones: 5 (each zone being of polygonal type); - front, rear or undirected protection: 3; - directed start-up: 1; - undirected start-up: 1; - the protection allows to adjust the compensation of the arc s resistance in any step, on R axis of plan Z, at detection of some faults with the ground; - typical triggering time in the rapid step, including the output relay with strong contacts: 25 ms; - maximum triggering time in the rapid step, including the output relay with strong contacts :30 ms; - the directional element has high sensitivity (has a good behaviour at the short-circuit protection with very low voltage); - adjustment range R, X on each step: 0.01 Ω Ω, in steps of 0.01Ω; - delays adjustment (for each zone): 0-6 s, from 10 to 10 ms; - accuracy of the impedance s measurement: ± 5 % for I = ( ) I n ; - accuracy of the delay s measurement: ±(1%), for t adjust > 30 ms; - reset coefficient: 5%; - minimum operation value in current: 0.2 I n ; - blocking to pendulums - internal (by the dz/dt criteria) and/or external; - verification functions for the plausibility of the measured units achieved in real time; - blocking to the lack of alternative voltage: internal (fusing, single-phased, bi-phased and three-phased )/external; possibility to switch automatically on the current maximal in two steps, as reserve element; single- and three-phased triggering; - selection of one tele-protection function; - protection s sensitization at connection on fault. The operation zone for protection terminal DIPA 100 are the dark areas from fig.4. Fig.4. Protection characteristic of DIPA Protection example of a 110 kv line with DIPA 100 Is presenting the protection of a simple-circuit line between two electric stations, symbolized by B and C, using the line protection terminal DIPA 100 in station B on aerial electric line (LEA) 110 kv Călan-Hăşdat, Romania (fig. 5). Fig.5. Diagram of the 110kV grid for setting the DIPA adjustments Technical data: - line s length B C: 15 [km]; - line s length A B: 10 [km]; - line s length C - D: 20 [km]; ISSN: ISBN:

5 - short-circuit power on station A bars: maximum= 4000 [MVA], minimum=1000 [MVA]; - short-circuit power on station D bars: maximum = 3000 MVA, minimum = 900 [MVA]; - maximum arc resistance to be compensated on the BC line: 50 [Ω]. Lines electrical characteristics: - specific direct impedance: z d L = j = [Ω/phase/km]; - specific homopolar impedance: z h L = j 1.34 = [Ω/phase/km]; h zl = ; d zl - current transformers ratio: k i = 600 / 5 = 120 ; - voltage transformers ratio: k u = 110 / 0.1 = 1100 ki kz = = ku Calculation of the distance protection adjustments [12]: - line s direct impedance: Z d L = 15 ( j 0.394) 0.109= j [Ω/phase]; - line s homopolar impedance: Z h L = 15 ( j 1.34) 0.109= j 2.191[Ω/phase]; - ground factor k H : 0 1 h Z 1 j e L k 1 H = = 1 = 0.8. d 0 3 Z 3 j68 L e Numerical protection adjustments DIPA 100: U n =57.8 [V]; I n =5 [A]; Line s length=15 [km]; Lines characteristics: X line direct = [Ω/phase]; R line direct = [Ω/ phase]; X line homopolar = [Ω/ phase]; R line homopolar = [Ω/ phase]; X line reverse = [Ω/ phase]; R line reverse = [Ω/ phase]; Step 1 adjustment Step 1 necessary adjustment: Z1 = 80% Z line (1) Z 1 = j = j 0. [Ω/phase] Arc resistance coverage: R arc = = 5.45 [Ω] X 1 = 0.51 [Ω/phase] R 1 = 0.2 [Ω/phase] ( ) 515 R 1p = 5.45 [Ω/phase] Direction rear: NO Primary impedance effectively adjusted: Z p p = j [Ω] (phase - phase) Z = 50 + j [Ω] (phase - ground) p g Step 2 adjustment Step 2 necessary adjustments: Z2 = ZBC ZCD (2) Z 2 = [ 15 ( j 0 394) ( j 0 394) ] 0 109= = j [Ω] Arc resistance coverage: X 2 = 1.07 [Ω/phase] R 2 = 0.43 [Ω/phase] R 2p = 5.45 [Ω/phase] Direction rear: NO Primary impedance effectively adjusted: Z p p = j [Ω] (phase - phase) Z = 50 + j [Ω] (phase - ground) p g Step 3 adjustment Step 3 necessary adjustments: Z 3 = 1.2 ( ZBC + ZCD ) (3) Z 3 = [ 15 ( j 0.394) + 20 ( j 0.394) ] = = j Step 3 X 3 = 1.8 [Ω/phase] R 3 = 0.72 [Ω/phase] R 3p = 5.45 [Ω/phase] Direction rear: NO Primary impedance effectively adjusted: Z p p = j [Ω] (phase - phase) Z p g = 50 + j [Ω] (phase - ground) Adjustment of steps 4 and 5, (start-up) Adjustment necessary for the start-up step - front: Z FD = j [Ω] Adjustment necessary for the start-up step - rear: Z RD = j 13.8 Step 4 Directed start-up X 41 = 10 [Ω/phase] X 42 = 1.5 [Ω/phase] R 41 = 7 [Ω/phase] ISSN: ISBN:

6 R 42 = 7 [Ω/phase] R 42p = 7 [Ω/phase] tgα= 0.58 tgα p = 0.58 Triggering time = 3500 [ms] Direction rear: YES Step 5 Undirected start-up Triggering time = 4000 [ms] With the above adjustments shall be obtained the characteristics from fig. 6 for phase phase faults, respectively the characteristics from fig. 7 for phaseground faults. Fig. 6 Phase-phase fault operation characteristics Fig.7 Phase-ground fault operation characteristics 5 Conclusion The numerical protections can achieve operation characteristics in accordance with the needs of the protected equipments and not against the technical possibilities, as in case of the classic protection systems. Utilization of hardware and software structures included in numerical protections allows the optimal adaptation to the protected equipment, without constructive modification of the protection equipment, but only by program s modification. The possibility to process a high data volume allows the integration of the functions of more classic devices into a single micro-computer and eliminates the adapters of different types. References: [1] J. Kock, C. Strauss, Practical Power Distribution for Industry, Linacre House, Jordan Hill, Oxford, U.K., [2] D.F. Warne, Newnes Electrical Power Engineer s Handbook, Linacre House, Jordan Hill, Oxford, U.K., [3] E. Kuffel, W.S. Zaengl, J. Kuffel, High Voltage Engineering. Fundamentals, Linacre House, Jordan Hill, Oxford, U.K., [4] J.E. Propst, D.R. Doan, Improvments in Modeling and Evaluation of Electrical Power System Reliability, IEEE Transactions on Industry Applications, Vol.37, No.5, September/October, 2001, pp [5] M. Pănoiu, C. Pănoiu, M. Osaci, I. Muscalagiu, Simulation Result about Harmonics Filtering using Measurement of Some Electrical Items in Electrical Installation on UHP EAF, WSEAS Transactions on Circuits and Systems, Issue 1, Volume 7, January 2008, pp [6] C. Pănoiu, I. Baciu, M. Pănoiu, C. Cunţan, Simulation Results on the Currents Harmonics Mitigation on the Railway Station Line Feed Using a Data Acquisition System, WSEAS Transactions on Electronics, Issue 10, Volume 4, October 2007, pp [7] R. Al.- Khannak, B. Bitzer, Developing Power Systems Reliability and Efficiency by Integrating Grid Computer Technology, WSEAS Transactions on Power Systems, Issue 4, Volume 3, April 2008, pp [8] H. Hamada, M. Marmiroli, J. Kubokawa, R. Yokoyama, Effective Optimal Power Flow Solution with Transient Stability Constraints based on Functional Transformation Technique, WSEAS Transactions on Power Systems, Issue 8, Volume 2, August 2007, pp [9] G. Parise, M. Adduce, Conductor Protection Against Short Circuit Current: Available I 2 t Evaluation, the 33 rd IEEE Industry Application Society Annual Meeting, St. Louis, Missouri, U.S.A., [10] M. Gavrilas, O. Ivanov, G. Gavrilas, REI Equivalent Design for Electric Power Systems with Genetic Algorithms, WSEAS Transactions on Circuits and Systems, Issue 10, Volume 7, October 2008, pp [11] M.P. Ransick, Numeric Protective Relay Basics, the 33 rd IEEE Industry Application Society Annual Meeting, St. Louis, Missouri, U.S.A., [12] ***, DIPA 100. Technical Documentations, Texas Instruments, USA, ISSN: ISBN: