Proceedings of the 13th WSEAS International Conference on SYSTEMS

Study about Numerical SEL-387 for Overcurrent and Differential Protections of 110/20 kV

ANGELA IAGĂR1, GABRIEL NICOLAE POPA1, CORINA MARIA DINIŞ1, GHEORGHE MORARU2 1Faculty of Engineering Hunedoara, Politechnica University Timişoara Str. Revoluţiei, no 5, Hunedoara, 331128, ROMANIA {angela.iagar,gabriel.popa,corina.dinis}@fih.upt.ro, http://www.fih.upt.ro

2SMART Sibiu Bd. Corneliu Coposu, no 1-3, Sibiu, 550245, ROMANIA [email protected]

Abstract: - Nowadays, the main problems of the relay protections result from the fact that in the modern electric systems the performances imposed to the protections operation became very severe, enhancing the difficulty in their simultaneous satisfaction. In these conditions, the numerical relays are used more and more for the electrical installations protection. This paper presents a study regarding the establishment of the protection, measuring and automation functions necessary for the numerical relay SEL-387 concerning the protection of the 110/20 kV transformers from the national energetic system (Romania). In this purpose, were calculated the adjustable settings of the protection functions, and after setting, the numerical relay was verified in laboratory conditions.

Key-Words: - Numerical protection relay, Differential protection, Overcurrent protection,

1 Introduction of current and transformers, and introducing In the last decades a strong development of the of some filters that should allow the relays supply energetic installations was registered, as regards the only with sinusoidal quantities (the fundamental quantitative parameters (intense increase of harmonics of current and voltage) [4,5]. transmission capacity of lines, lines total length The second problem in the relays protection etc.), but also the qualitative ones (increasing the technique is related to the increase of faults installed capacity utilization time, very high clearance safeties and preventing their for the transmission lines, increasing the grids transformation into system failures. looping degree, improvement of maintaining the In this respect, a special attention shall be given and voltage values, increasing the safety to the back-up protections. Also, for safety increase, and the continuity of the consumers power supply the protection operation is combined with the etc.) [1-3]. automations of system [4,6,7]. However, once with the energetic systems Another problem in the relays protection development, maintaining of their stability became technique is related to the necessity of ensuring more and more difficult. simultaneously the selectivity and speedily operation The condition for maintaining the stability for the faults appeared on the entire protected line. imposed the achievement of some protections with a Thus, in the modern electric systems the very reduced pickup time (20-30 ms). performances imposed to the protections operation But, within a short interval from the appearance became more severe, enhancing the difficulty in of a fault, the transient components of the electric their simultaneous satisfaction. quantities that supply the protective relays are very In these conditions, the numerical relays (relays) large. are used more and more for the protection of Hence, one of the current problems of the relays electrical installations [8-10]. protection technique consists in elaboration of some The numerical protection relays present measures that should eliminate the influence of the important advantages compared with the transient components upon the protection operation. electromechanical or static relays. Among these, Here is framing the achievement of some new types communication in the local dedicated area network

ISSN: 1790-2769 265 ISBN: 978-960-474-097-0 Proceedings of the 13th WSEAS International Conference on SYSTEMS

at bay level and at the substation level, respectively ƒ Through-Fault Recording and Monitoring the human-machine communication interface would Through-fault duty is recorded and accumulated be the most important[8-10]. for use in SELOGIC® control equations or manual The self-supervision function is extremely monitoring. important for the optimization of the protections ƒ Protection and Control Logic maintenance [9-11]. Restricted Earth Fault (REF) logic provide a Integration of multiple protection, control and sensitive grounded-wye winding ground fault self-supervision functions, at the same level, provide protection. SELOGIC Control Equations with reduced size of wires in the substation, reducing the SELOGIC variables, timers, latch bits, and remote probability to appear human mistakes and improving control elements customize advanced protection and the electromagnetic compatibility [3,9]. control schemes. One can notice also the possibility of integrating SEL-387 includes local programmable control the numerical relays in any application [3,10,11]. elements and programmable text display points for However, is imposed the correct setting of the advanced local operator interface. numerical relay and its testing in laboratory ƒ Metering and Reporting conditions. Oscillographic event reports (up to seven 60- Further is presented a study concerning the cycle reports), Sequential Events Recorder (SER) establishment of the protection, measurement and reporting, and accurate metering eliminate or reduce automation functions necessary for the numerical external recorder and metering requirements. relay SEL-387 concerning the protection of the ƒ ACSELERATOR® QuickSet™ Software 110/20 kV transformers from the national energetic Develop relay settings off-line, program system (NES) and its experimental checking. SELOGIC control equations, and analyze post-fault event reports. Automatically captures and stores 23 most recent 2 SEL-387 numerical protection relay eleven-cycle, oscillographic reports detailing SEL-387 is a current differential and overcurrent current, voltage, contact I/O, and protection element numerical relay. conditions during events. The main features of SEL-387 are [12]: Sequence-of-events recording captures, time- ƒ Two-, Three-, and Four-Winding Current tags, and stores 512 latest state changes of contact Differential Protection inputs, contact outputs, control points, and Sensitive current differential protection (with protections elements. programmable single- or dual-slope percentage ƒ SEL-387 relay includes a sophisticated thermal restraint) is supervised by a choice of second and model to monitor temperatures and insulation aging fourth-harmonic blocking or restraint elements, plus of mineral oil immersed transformers. fifth-harmonic and dc blocking elements for secure ƒ Additional local and remote control and protection of up to four windings. binary SER messaging. Phase current harmonic blocking is set for either ƒ Distributed Network Protocol (DNP) 3 Level 2 common or independent winding basis. Slave communications protocol. Unrestrained high-set differential elements ƒ SEL-387 is certified to a wide range of electrical provide fast operation for high-magnitude internal noise, temperature cycling, and seismic tests. faults. "Around the clock" phase angle compensation settings and automatic tap calculations simplify 3 Setting of SEL-387 for a three- settings. phase transformer ƒ Individual Winding Overcurrent Protection The basic data of the transformer that should be Torque-controllable overcurrent elements, protected are: including one instantaneous, one definite-time, and - = kV110U , = kV20U , = MVA25S ; one inverse-time element each for phase, negative- 1 2 - vector group of the transformer: YD11. sequence, and residual ground currents, provide comprehensive overcurrent protection on each • Selection of the current transformers (CTs) for winding input. the differential protection Combined current feature sums current from two Is used a procedure based on the standard CTs for ring-bus and breaker-and-a-half overcurrent ANSI/IEEE C37.110-1996, Guide for the applications. Application of Current Transformers Used for Protective Relaying Purposes.

ISSN: 1790-2769 266 ISBN: 978-960-474-097-0 Proceedings of the 13th WSEAS International Conference on SYSTEMS

Windings 1 and 2 are validated for differential excitation current of the transformer. Is requires: protection, and windings 3 and 4 for overcurrent MIN ≥ N TAP/I1.0P87O MIN . (2) protection. and: = ÷11.0P87O (3) Settings will be: = Y1W87E , = Y2W87E , O87P - Restrained Element Operating Current = N3W87E , 4W87E = N . Minimum Pickup, per unit of TAP. The setting labels have the following definitions: = 3.0P87O (4) E87Wn - Enable Winding n in Differential; = 4,1n • Then, is set the percentage restraint characteristic (n is the number of winding); Y – Yes; N – No. in order to make the difference between the internal • The following settings refer to the CTs and external faults. connection and to the current ratio for each winding: Considering that the CT error is 1%, it can be set: = =1501CTR;YCT1W (110 kV) = 251SLP , = 31IRS , = 552SLP . = = 8002CTR;YCT2W (20 kV) SLP1 - represents Restrained Element Slope 1, [%] SLP2 - represents Restrained Element Slope 2, [%] The setting labels have the following definitions: IRS1 - Restrained Element Slope 1 Limit. WnCT - Winding n CT Connection, = 2,1n . SLP2 improves the sensitivity in the region The CTs are connected in a Wye (Y) configuration. where the CT error is small and ensures the security CTRn - Winding n CT Ratio (IPRI/IN), = 2,1n ; at high current in the region where the CT error is

IPRI - primary current; IN - secondary current. big. • Further, will be achieved the internal • Setting the unrestrained current instantaneous compensation of the current transformers. protection. Because the windings of the transformer to be This protection has the purpose to operate protected are wye- (Y) and delta- (D) connected, and speedily at a very high current, which clearly the windings of the current transformers are all wye, indicates an internal fault. it should be made an adjustment of the phase angle. The operation level is set to approximately 10 The necessary settings for the internal times TAP: compensation of the current transformers are: =10P87U (TAP multiples) = 0CTC1W ; CTC2W =11( 330° around the clock U87P represents Unrestrained Element Operating compensation), Current Pickup Level. where: • Second-harmonic blocking W1CTC - Winding 1 Connection Compensation; Second-harmonic current can be used to identify W2CTC - Winding 2 Connection Compensation. the inrush currents and to avoid the protection relay • Relay calculates the Winding n Current Tap misoperation. (TAPn) based on the following equation: Is set = %252PCT (the restrained differential ⋅1000MVA protection is blocked if the second harmonic is TAPn = ⋅ C (1) higher than 25% from fundamental). VWDGn3 ⋅⋅ CTRn PCT2 - Second-Harmonic Blocking Percentage of where: Fundamental =1C , if the CTs are connected in a Wye • Fifth-harmonic blocking configuration ( WnCT = Y ); According with the industrial standards MVA - is the Maximum Transformer Capacity (ANSI/IEEE C37.91, C37.102) the overexcitation (Three-Phase MVA). occur when the ratio between voltage and frequency VWDGn – represents Winding n Line-to-Line applied to the transformer increases by 1.05 per Voltage, [kV]. completely loaded unit, or by 1.1 per unloaded unit. With MVA = 25, 1VWDG =110 , 2VWDG = 20 , The transformer overexcitation produces odd result: = .01TAP 875 A , = .02TAP 902 A . harmonics in the exciting current. These produce If MVA=OFF, the user must define TAPn. false differential currents that could cause relay TAPMAX/TAPMIN must be less than or equal to misoperation. 7.5. Otherwise, the numerical relay warns the user Is set = 355PCT % (the operation is blocked if upon this. the fifth harmonic is higher than 35% from • Setting of the operating current. fundamental) and TH P5 = OFF (the 5th harmonic Operating current is set to a minimum value, but alarm is deactivated). high enough to avoid the operation at a stationary PCT5 - Fifth-Harmonic Blocking Percentage of regime error of the current transformers and at the Fundamental TH5P - Fifth-Harmonic Alarm Threshold

ISSN: 1790-2769 267 ISBN: 978-960-474-097-0 Proceedings of the 13th WSEAS International Conference on SYSTEMS

• Independent Harmonic Blocking The independent blocking is not activated: = NIHBL (any harmonic blocking element blocks all 87R elements).

4 SEL-387 laboratory tests (a)

4.1 Instantaneous Overcurrent Protection The connection diagram used for checking the SEL- 387 relay in case of the instantaneous overcurrent protection is presented in figure 1. For checking the SEL-387 relay was used an OMICRON test system (TEST UNIVERSE) (fig.1).

(b)

(c)

Fig.2. Results of checking the instantaneous overcurrent protection on winding 1

¾ 50P22P – The instantaneous overcurrent protection on winding 2 The adjustable settings of SEL-387 for the instantaneous overcurrent protection on winding 2 are presented in Table 2; the experimental results are shown in figure 3 (a, b, c). Table 2

Adjustable settings for the instantaneous overcurrent Fig.1. The connection diagram used for checking the protection on winding 2 instantaneous overcurrent protection Phase R S T ¾ 50P12P – The instantaneous overcurrent I, t protection on winding 1 Iact [A] 2.8 2.8 2.8 The adjustable settings of the SEL-387 relay for tact [s] 0.03 0.03 0.03 the instantaneous overcurrent protection on winding 1 are presented in Table 1. ¾ 50P32P – The instantaneous overcurrent Table 1 protection on winding 3 Adjustable settings for the instantaneous overcurrent The adjustable settings of SEL-387 for the protection on winding 1 instantaneous overcurrent protection on winding 3 are presented in Table 3. The experimental results Phase R S T are shown in figure 4 (a, b, c). I, t I [A] 2.8 2.8 2.8 Table 3 act Adjustable settings for the instantaneous overcurrent t [s] 0.03 0.03 0.03 act protection on winding 3

The experimental results obtained by checking Phase R S T the instantaneous overcurrent protection on winding I, t 1 are shown in figure 2 (a, b, c). Iact [A] 2.8 2.8 2.8 tact [s] 0.03 0.03 0.03

ISSN: 1790-2769 268 ISBN: 978-960-474-097-0 Proceedings of the 13th WSEAS International Conference on SYSTEMS

¾ 50P42P – The instantaneous overcurrent protection on winding 4 The adjustable settings for the instantaneous overcurrent protection on winding 4 are in Table 4; the experimental results are in figure 5 (a, b, c).

Table 4 (a) Adjustable settings for the instantaneous overcurrent

protection on winding 4 Phase R S T I, t Iact [A] 2.5 2.5 2.5 tact [s] 0.03 0.03 0.03

(b)

(a)

(c)

Fig.3. Results of checking the instantaneous overcurrent protection on winding 2

(b)

(a)

(c)

Fig.5. Results of checking the instantaneous overcurrent protection on winding 4

(b)

4.2 Differential Protection The connection diagram used for checking the numerical SEL-387 in case of the differential protection is presented in figure 6. For checking the SEL-387 relay was used an OMICRON test system (TEST UNIVERSE) (figure 6). The experimental results are presented in Table

5. (c) Further the experimental tests was found that the Fig.4. Results of checking the instantaneous SEL-387 relay corresponds to the norms specified overcurrent protection on winding 3 by the manufacturer.

ISSN: 1790-2769 269 ISBN: 978-960-474-097-0 Proceedings of the 13th WSEAS International Conference on SYSTEMS

energetic system (Romania).

References: [1] L. Hewitson, M. Brown, B. Ramesh, Practical Power Systems Protection, Elsevier Science&Technology Books, 2004. [2] K. R. Padiyar, Power System Dynamics: Stability and Control, John Wiley & Sons (Asia) Pte. Ltd. and Interline Publishing Pvt. Ltd., Singapore, 1995. [3] G. Ziegler, Numerical Differential Protection: Principles and Applications, Siemens, Berlin, 2005. [4] R. C. Dugan, M. F. McGranaghan, S. Santoso, H.W. Beaty, Electrical power systems quality, Second Edition, McGraw-Hill, 2004. [5] R. Al-Khannak, B. Bitzer, Developing Power Systems Reliability and Efficiency by Integrating Grid Computing Technology, WSEAS TRANSACTIONS on POWER SYSTEMS, Vol. 3, Issue 4, 2008, pp.226-236.

[6] F. Muzi, Real-time Voltage Control to Improve Fig.6. The connection diagram used for checking the Automation and Quality in Power Distribution, differential protection WSEAS Transactions on Circuit and Systems, Vol. 7, Issue 1, 2008, pp.173-183. Table 5 [7] T. Miki, The Efficient Offline Search System for Results of checking the differential protection High Risk Events of Power Systems Caused by Natural Disasters, WSEAS TRANSACTIONS on I1 I2 I3 ∠ t Il If POWER SYSTEMS, Vol. 3, Issue 5, 2008, [A] [A] [A] [s] [A] [A] [°] pp.267-276. 0.87 0.9 0.87 48 0.0510 0.313 1 [8] A. Oonsivilai, B. Marungsri, Stability 1.741 1.8 1.741 45 0.0532 0.522 2 Enhancement for Multi-machine Power System 2.611 2.7 2.611 45 0.0544 0.783 3 by Optimal PID Tuning of Power System 3.48 3.6 3.48 49 0.0354 1.321 4 Stabilizer using Particle Swarm Optimization, 4.351 4.5 4.351 52 0.0326 1.908 5 WSEAS TRANSACTIONS on POWER SYSTEMS, 5.22 5.4 5.22 54 0.0526 2.495 6 Vol. 3, Issue 6, 2008, pp.465-474. 6.09 6.3 6.09 55 0.0332 3.031 7 [9] G. F. Johson, Reliability Considerations of 6.96 7.2 6.96 56 0.0558 3.6 8 Multifunction Protection, IEEE Trans. On Industry Application, Vol. 38, No. 6, November 2002, pp 1688-1700. [10] H. M. Soliman, M. F. Morsi, M. F. Hassan, M. 5 Conclusions A Awadallah, Power System Reliable SEL-387 numerical relay ensures security for Stabilization with Actuator Failure, Electric external faults, inrush, and overexcitation conditions Power Components and Systems, Volume and provide dependability for internal faults. 37, Number 1, January 2009, pp. 61-77. This relay combines harmonic restraint and [11] H. Ito, G. P. Baber, I. Shuto, H. Sugiura, blocking methods with shape recognition technique. Technology and Experience of Fully Numerical Even harmonics of the differential current provide Differential Protection Communicating over restraint, while the fifth harmonic and dc component Metallic Pilot-Wire, 2006 IEEE PES block relay operation. Transmission and Distribution Conference and Further the experimental tests was found that the Exposition Latin America, Venezuela, pp.1-6. SEL-387 relay corresponds to the norms specified [12] *** SEL, Technical Documentations SEL-387, by the manufacturer and can be used for the Pullman-Washington, SUA, 1996-1997. protection of 110/20 kV transformers from national

ISSN: 1790-2769 270 ISBN: 978-960-474-097-0