SWITCHING TRANSIENT PHENOMENA IN POWER SYSTEMS AT THE 400 KV HIGH VOLTAGE UNLOADED LINE

Transcription

1 8th WSEAS International onference on POWE SYSTEMS (PS 8), Santander, antabria, Spain, September 3-5, 8 SWITHING TANSIENT PHENOMENA IN POWE SYSTEMS AT THE 4 KV HIGH VOLTAGE UNLOADED LINE P. TUSALIU () M. PEPELEA () G. UANU (3) D.. TUSALIU (4) E. STOENESU (5) A. OZDEMI (6) ()(5) Electrical Faclty, University of raiova, OMANIA, () University of Piteşti, OMANIA (3) esearch Development and Testing National Institte Electrical Engineering raiova, OMANIA (4) ompter and Electronics Faclty, University of raiova, OMANIA (6) Istanbl Technical University, TUKEY Abstract: - This paper presents the transient phenomena, which appear, in Power Systems, at the nloaded line switching. As following of the switching transient phenomena in Electric Power System appear several distrbances, sometimes very dangeros for the electrical eqipment life, for the environment and for the hman life. Switching transient phenomena prodce in Power Systems overvoltages, overcrrents and electrical fields, which haven t to neglect. Ths was modelling and simlated the switching transient phenomena, conseqently the electric fields and the possible negative inflence abot electrical eqipment, environment and hman life. The simlation was performed sing the EMTD/PSAD software package, to obtain the transient overvoltages in the transmission line and in the bsbars. These compter programs present an efficient graphical ser interface integrated with a time domain integration tool, which can be sed sccessflly to simlate power system transients, inclding network control devices. It provides fast, accrate and flexible soltions, by applying the integration trapezoidal rle to solve the mathematical models. Also, the Math-AD Program evalates the electrical fields. After were analysed comparatively these reslts. The electrical field was calclated sing the IGE eqivalent charge model. The proposed simlation is applied for an nload transmission line connected between KEPEZ and YATAGAN in 38 kv Trkish National Power Transmission Systems, also for a 4 kv nloaded line in omanian Network. Key-Words: - Transient phenomena, power systems, high voltages, distrbances, electrical fields. Introdction The voltage stress in the switching devices depends on the network configration [-7]. Usally, the electromagnetic transient simlations are performed considering the nloaded line switching, also capacitor bank switching on the middle voltage part, sing the circit breakers [8-]. The most common approach is to se the T-model (the Freqency-Dependent model), which shold be considered in transient stdies in order to obtain accrate reslts. The T-model of line is based on the travelling wave s formlation, with the voltage distrbances reflecting the delay fnction and the waveshape attenation. This paper is devoted to the evalation of the transient recovery voltages, the overvoltages on each phases and the electrical field as a reslt of the nloaded line switching for different lengths of line. In this way, seven different length vales for the nloaded line were assmed. Analytical approach The analysis of transient phenomena at the nloaded line switching can be made analytically by sing the following mono-phase schematic circit proposed by [3, 4] (Fig. ). Fig.. Disconnecting of the nloaded line. ISSN: ISBN:

2 8th WSEAS International onference on POWE SYSTEMS (PS 8), Santander, antabria, Spain, September 3-5, 8 a ) Model-eqivalent b )Phasor-Diagram c )Instantaneos vales a ) Neglected esistance b ) Phasor-Diagram c ) Instantaneos vales or = + ( ) t 3 cos (6) L Where: both the general network and a redced network with neglected resistances are held. Switching transient phenomena of nloaded line can be expressed by figre and following eqations [3,4]: The maximm vale is: ˆ +, 594 ( ) = ˆ (7) 3 U i - t L Fig.. Electrical Model of nloaded line. = =,3 π = =,797 π L = =,67 L π The voltage can be calclated by [6-7]: () t di t = i dt = L + + i dt () 3 dt (3) where: and 3 are the voltage vales at the and 3 terminals in comparison with grond, in moment of crrent interrpting. By Laplace Transform: 3 L 3 L[] i = = (3) + L p L + p + L where: + = eslt: 3 t i = sin L L i (4) t 3 = t sin dt L L (5) Fig.3. Transient ecovery Voltage. The voltage Diagrams for, and the Transient ecovery Voltage are illstrated in figre 3. The maximm of the Transient ecovery Voltages will be: ˆ = max = Uˆ +,594 Uˆ Uˆ (8) r,594 (U - U ) ( ) ( ) 3 The circit breaker characteristics and the feeding network parameters inflence the transient phenomena. The growing speed of dielectric rigidity (U d = f (t)) and the raise of the transient recovery voltage (U r = f (t)), play also a very important role in this process [3-7]. 3 Application example In order to analyse the transient overvoltages at disconnecting of an nloaded line in a 38 kv Electric Power System the model from figre 4 has been stdied. This model was evalated sing the EMTD/PSAD software package. The 38 kv High Voltage Line of the Power Systems (fig.4) presents for analysis: the voltage generators; the transformer; the transmission line modelling by T-Line Model (Freqency-Dependent Model); the bsbar, the branch of capacitor bank, connected on generator, the circit breakers for the line and capacitor bank switching. The transient phenomena were simlated with the circit breaker on close position, followed by a disconnecting operation. The st time was.5 [sec] and the nd time was 3 [sec]. For capacitor bank it was assmed discrete capacitance vales from 3 μf ntil 5 μf with a step of μf, considering a star connection. ISSN: ISBN:

3 8th WSEAS International onference on POWE SYSTEMS (PS 8), Santander, antabria, Spain, September 3-5, 8 Table - Phase Voltages de to Switching Transient Phenomena in a 38 kv nloaded Line of Power Systems l V_AL[kV] 35,4 35,4 35,4 3, 3, 39, 336,8 V_BL[kV] 35,4 35,4 35,4 39, 39, 336,8 35,4 V_L[kV] 36,8 36,8 3,35 33,74 33,74 33,74 344,5 In table the phase voltages for different lengths of line are presented. Phase Voltages de to Switching Transient Phenomena in a 38 kv no-load Line of Pow er Systems Fig.4. Modelling and simlation of the switching transient phenomena sing PSAD Program. [kv] V_AL[kV] V_BL[kV] V_L[kV] Fig.6. The phase voltages for different lengths of line. 4 eslts The reslts are presented in the following tables and figres: Table - Transient ecovery Voltages de to Switching Transient Phenomena in a 38 kv nloaded Line of Power Systems l TV_A[kV] 687,8 698, 698, 7,8 7,85 7,5 7,3 TV_B[kV] 47,7 47,7 47,7 47,43 47,43 47,43 47,43 TV_[kV] 683,9 69,9 69,9 7,65 7,39 7,39 7, The table presents the transient recovery voltages for different lengths of nloaded line disconnecting. [kv] Transient ecovery Voltages de to Switching Transient Phenomena in a 38 kv no-load Line of Power Systems l TV_ A[kV] TV_ B[kV] TV_ [kv] Fig.5. Transient ecovery Voltages at switching of nloaded line for different lengths. Table 3 - Transient ecovery Voltages and the Phase Voltages de to Switching Transient Phenomena in a 38 kv nloaded Line of Power Systems l TV_A[kV] 687,8 698, 698, 7,8 7,85 7,5 7,3 TV_B[kV] 47,7 47,7 47,7 47,43 47,43 47,43 47,43 TV_[kV] 683,9 69,9 69,9 7,65 7,39 7,39 7, V_AL[kV] 35,4 35,4 35,4 3, 3, 39, 336,8 V_BL[kV] 35,4 35,4 35,4 39, 39, 336,8 35,4 V_L[kV] 36,8 36,8 3,35 33,74 33,74 33,74 344,5 The table 3 presents the transient recovery voltages and the phase voltages de to switching transient phenomena in a 38 kv nloaded line of power systems. [kv] Transient ecovery Voltages and the Phase Voltages de to Switching Transient Phenomena in a 38 kv no-load Line of Pow er Systems TV_A[kV] TV_B[kV] TV_[kV] V_AL[kV] V_BL[kV] V_L[kV] Fig.7. The Transient ecovery Voltages and the Phase. Voltages de to Switching Transient Phenomena in a 38 kv nloaded Line of Power Systems. ISSN: ISBN:

4 8th WSEAS International onference on POWE SYSTEMS (PS 8), Santander, antabria, Spain, September 3-5, 8 Table 4 - The Phase Voltages and the Electrical Field nder 38 kv Line to the crossing of the National Highway and ailway, at gronded level l V_AL[kV] 35,4 35,4 35,4 3, 3, 39, 336,8 V_BL[kV] 35,4 35,4 35,4 39, 39, 336,8 35,4 V_L[kV] 36,8 36,8 3,35 33,74 33,74 33,74 344,5 E_AL[ 8,5 8,5 8,5 8,7 8,69 8,88 9,8 E_BL[ 8,5 8,5 8,5 8,89 8,88 9,8 9,46 E_L[ 8,56 8,56 8,65 8,99 8,99 8,99 9,9 E_AL[ 3,4 3,4 3,4 3,7 3,7 4, 4,3 E_BL[ 3,4 3,4 3,4 4, 4, 4,3 4,9 E_L[ 3,49 3,49 3,64 4,7 4,7 4,7 4,66 In table 4 were presented the Phase Voltages and the Electrical Field nder 38 kv Line to the crossing of the National Highway and ailway, at gronded level. [ Electrical Field der a 38 kv Line 6, 4,,, 8, 6, E(x) 6 4 [ The Electrical Field nder a 38 kv Line to crossing of the National Highway and ailway, at gronded level E_AL[ E_BL[ E_L[ E_AL[ E_BL[ E_L[ Fig.9. The Electrical Field nder 38 kv Line to the crossing of the National Highway and ailway, at gronded level. The tables,, 3, 4 and 5 show the inflence of line length at nloaded switching regarding the Transient ecovery Voltages, Phase Voltages and Electrical Fields. There is noticed that vales obtained are very high. These can generate dangeros inflences on Electrical Eqipment, Environment and Life. It is necessary to improve the maintenance of Lines of Power Systems and of ircit Breakers switching in order to limit the maximm vales of the switching Transient Phenomena. Fig.. Electrical Field, Math-AD Program [, 6, 7]: 4,,, [m] Fig.8. The Electrical Field nder 38 kv Line to the crossing of the National Highway and ailway, at gronded level. Table 5 - Electrical Field nder 38 kv Line to the crossing of the National Highway and ailway, at gronded level l E_AL[ 8,5 8,5 8,5 8,7 8,69 8,88 9,8 E_BL[ 8,5 8,5 8,5 8,89 8,88 9,46 E_L[ 8,56 8,56 8,65 8,99 8,99 8,99 9,9 E_AL[ 3,4 3,4 3,4 3,7 3,7 4, 4,3 E_BL[ 3,4 3,4 3,4 4, 4, 4,3 4,9 E_L[ 3,49 3,49 3,64 4,7 4,7 4,7 4,66 The table 5 presents the Electrical Field nder 38 kv Line to the crossing of the National Highway and ailway, at gronded level, for different lengths of line. hi 9. m ri.47873m. q Ex( x) Y. ω. U ω U Y.37659ohm.. km. π. f 46.8kV. f 5. Hz = 5.5 kg m 5 s 7 A 3. U q =.3 6 kg m 3 s 4 A q. πε. Exx ( ) = m x d x d ( x d) ( y hi) ( x d) ( y hi) ISSN: ISBN:

5 8th WSEAS International onference on POWE SYSTEMS (PS 8), Santander, antabria, Spain, September 3-5, Ex( x) x Fig.. The Ex electrical field component for: d=m, x=5m and y=m. q Ey( y). y hi y hi πε. ( x d) ( y hi) ( x d) ( y hi) Ey( y) = m Ey( y) y Fig.. The Ey electrical field component for: d=m, x=5m and y=m. hi Ex ( ).. x hi. ln. hi U ri Ex ( ) =.4 4 kg m s 3 A Ex () x Fig.3. The electrical field at grond level. Analysing the reslts obtained concerning the intensity of electrical field, there is noticed that the maximm intensity of electrical field, nder the line, at grond level, appears at the maximal line length. These are:.4 kv/m for the crossing of the National Highway and 9.6 kv/m at the crossing of the National ailway. omparative with the limits recommended by the IGE and IEEE International norms [], these vales overtake the admissible limit [, 5]. Between the reslts obtained by modelling and simlation in PSAD and in Math-AD Programs significant differences don t appear. Generally, the vales obtained for the electrical fields are over the admissible limit, which were recommended of the International Norms [,5]. 5 Experiments on an nloaded line in omanian network In a 4 kv sbstation from omania were performed tests and measrements for following switching cases [9,]: a) nloaded disconnection line with trigger command of the circit-breaker from sbstation. b) nloaded connection of long line with breaking implse transmission to the circit-breaker from sbstation with remote protection from sbstation Line characteristics were the following: line length: 57.5 km steel-alminim condctor 45/75 mm 4 kv/6 A minimm oil circit-breaker Tests and measrements were necessary to establish the switching overvoltage level that appears at nloaded line connection and disconnection and to check the operating level of the maximal voltage protection de to the voltage growth at the end of the line. In case a) six tests with trigger command of the 4 kv/6 A minimm oil circit-breaker were performed in 4 kv sbstation, the command being given for different moments in the voltage reference crve with respect of the crrent passing trogh zero. In this way a half period was swept simlating the real exploitation conditions. In order to determine the switching overvoltages that appear in case b) of nloaded lines connection, three closing commands of the circit-breaker in sbstation with different moments by remote protection with different moments of the crrent connection were performed. Principle diagram of measring and command from Sbstation is presented in Figre 4. The following phenomena were recorded: circit-breaker command crrent, downstream and pstream voltages of ISSN: ISBN:

6 8th WSEAS International onference on POWE SYSTEMS (PS 8), Santander, antabria, Spain, September 3-5, 8 circit-breaker, switching overvoltages, time base. The error of measring chain is 3%. Within established program three connecting operations and three disconnecting operation of the nloaded lines were carried ot. Determination of switching overvoltages for nloaded lines by measrements shown that overvoltage factor is ks=.8 (p.) and this is below to that maximally admissible ks=.3 (p.) according to IGE recommendations. 3 B B B T B D losing implse A Fig.4. Test diagram at nloaded disconnecting B, B circit-breakers T crrent transformer D voltage divider A amplifier S transdcer AP programmable atomat P personal compter 3 point for overvoltages measrement P AP S 6 onclsion From the above reslts the following conclsions can be extracted: - De to the switching transients phenomena in Electrical Power Systems very dangeros distrbances for electrical eqipment and for arond environmental appear. Therefore, the electrical fields, in last days, are the concerning for many specialists, thanks to their negative effect abot eqipment, environment and life [, 5, 7, and ]. - De to the nloaded line switching in Power Systems, big overvoltages (transient recovery voltages, 3.8 [p..]; phase overvoltages,.59 [p..] appear, which all generate the electrical fields, with negative impact in Power Systems and arond Environment. - The reslts obtained for modelling and simlation are in according with theoretical soltions (.58 %). - The reslt obtained for the maximal electrical fields de to a 38 kv nloaded line switching in Power Systems from Trkey, nder line at gronded level (9.46 kv/m, at the crossing of the National Highway and 4.9 kv/m, at the crossing of the National ailway), show that they overtake the admissible limits recommended by the IGE and IEEE International norms [,5]. - Therefore it is necessary to make investigations and to impose the limited methods. P - Experiments on a 4 kv nloaded line in omanian network shown that the switching overvoltages did not overrn the maximm admissible vales so there is not necessary to limit them. Acknowledgment: Prof. Petre Tsali wold like to acknowledge NATO for the fellowship awarded and that allowed him to join the other co-athors in this research. eferences: [] Electric and magnetic fields prodced by transmission systems, Description of phenomenapractical gide for calclation. Working Grop (Interference and Fields) of Stdy ommittee 36 (Interference),, 98, IGE. [] Greenwood, A., Electrical Transients in Power Systems, Second Edition, John Wiley & Sons Inc, 99. [3] howdhri, P., Electromagnetic Transients in Power Systems, John Wiley & Sons Inc, 996. [4] A smmary of standards for hman exposre to electric and magnetic fields at power freqencies. Working Grop 36., Electra n 79, pp , 998. [5] Pinto, J.A., Tsali, P., oelho,.j., apacitor Bank Switching effects in an Electric Power System Using a Three-Phase Model, UPE 37 th International Universities Engineering onference, Vol., 9 th - th September, pp , Staffordshire University, United Kingdom. [6] Tsali, P., oelho,.j., Pinto, J.A., apacitor Bank switching in Electric power Systems nder balanced conditions, the Second IASTED International onference POWE AND ENEGY SYSTEMS (EroPES), Proceedings Jne 5-8,, pp. -6, rete, Greece. [7] Marinc, A., Greconici, M., The electromagnetic field arond a high voltage kv electrical overhead lines and the inflence on the biological systems, in Proc. of the 5 th International Power Systems onference, November 6-7, 3, Timisoara, omania. [8] Ngamsanroaj, K., Tayati, W., An analysis of switching overvoltages in the EGAT 5 kv transmission system. Power Engineering, 3 Large Engineering Systems onference on 7-9 May 3, IEEE, 3,pp [9] Vahidi, B., Farokhi, Sh., Electromagnetic interference on measring eqipments of HV sbstation de to switching. Transient Phenomena in Large Electric Power Systems, IGE Symposim, April 8-, 7, pp.9, Zagreb, roatia. [] Tsali, P.,a.o., Plenary speaker - Electromagnetic distrbances at 38 kv power systems operations de to nloaded line switching, the eighth IASTED International onference on POWE AND ENEGY SYSTEMS, Jne 3-5, 8, orf, Greece. ISSN: ISBN: