220KV变压器短路时线路距离保护分析

2010 China International Conference on Electricity Distribution Analysis of the 220kV line distance protection's measuring impedance when V IX traction transformer is in short circuit Tang Da-hail, Van Guo-ping2, Yi Xin2 I Zhenjiang Power Supply Company, Zhenjiang, Jiangsu, 212001; 2 Jiangsu Provincial Electric Power Company, Nanjing , Jiangsu, 210024 Abstract: Both of the traction transformers in the Shanghai-Nanjing intercity railway and Beijing-Shanghai high-speed railway connect two single-phase traction transformers as V/X wiring to form a complete traction transformer. One is operating, and the other one stand-by for it. First, the thesis analyzes the low-voltage side short current of V/V wiring traction transformer, and then calculates the measuring impedance of the interphase and grounding impedance components of 220kV distance protection which is in power supply side substation. Furthermore, it analyzes the measuring impedance of the interphase and grounding impedance components in V/X wiring traction transformer when its low-voltage side is in short circuit. The conclusion has been tested to be correct by simulation experiments. All of the analyses and experiments indicate that 220kV line distance protection's minimum measuring impedance in power supply side substation is much smaller than the minimum measuring impedance of regular transformer in grid when the short circuit takes place in the low-voltage side of traction transformer. So it should be paid attention to set protection values to avoid setting mistakes. This conclusion is also suitable for the V/X wiring traction transformers which use llOkV and 220kV including the above voltage grade railway power supply network. In conclusion, the thesis puts forward some important opinions which should be paid attention to setting 220kV line distance protection. Type the abstract using Times New Romar font with point size 9. The abstract is an essential part of the paper. Use short, direct, and complete sentences. It should be as brief as possible and concise. It should be complete, self-explanatory, and not require reference to the paper itself. The abstract should be informative giving the scope and emphasize the main conclusions, results, or significance of the work described. Do not use the first person; do not include mathematical expressions; do not refer to the reference, and try to avoid acronyms. Keys: 220kV line distance protection; traction transformer; V/X wiring; short circuit; measuring impedance; analysis Shanghai-nanjing intercity railway and Beijing-Shanghai high-speed railway are constructing now. The length of shanghai-nanjing intercity railway is 300.209km , and the traction power supply system adopts AT mode. The supreme speed of the trains in this line is designed to be 350km/h. In jiangsu Province, five 220kV traction substations are built new, each traction substation's power is supplied by two independently and reliable 220kV lines, both hot stand-by for each other. That the traction transformers are connected in V/X wiring has the advantages of saving space and investment[5l. So all of the transformers In shanghai-nanjing intercity railway and be�iing-shanghai high-speed railway adopt V/X wiring. According to the design which collocates four single-phase transformers for one substation, two single-phase traction transformers connected in V/X wiring to form a complete traction transformer for operation, the other V IX wiring traction transformer is fixed to stand-by. The two 220kV power supply lines collocate two complete optical fibre split-phase current differential protection and some back-up protections such as interphase and grounding distance protection, zero-sequence current protection and so on[1-3l. That adopting V/X wiring traction transformers makes the load of 220kV power supply system unbalanced. Other than the negative sequence current can effect the distance protection in peacetime[6-7l, it can also effect the measuring impedance and action characteristic of 220kV line distance protection in power supply side substation when the low-voltage side of the V IX wiring traction transformer is in short circuit. It is not same as short circuit situations of regular transformer in grid. So we can not 2 2010 China International Conference on Electricity Distribution set its protection values according to regular transformer methods, otherwise the setting will be wrong. Due to the V/X wiring is improved from V/V wiring, we first analyze the short current when V/V wiring transformer’s low-voltage side is in short circuit, and 220kV line distance protection’s measuring impedance. Furthermore, we analyze 220kV line distance protection’s measuring impedance when V/X wiring transformer’s low-voltage side is in short circuit. All the analysis can offer theoretical gist for the setting calculation of relay protection. 1.Analysis of the short current of V/V wiring traction transformer when its low-voltage side is in short circuit Due to the V/X wiring is improved from V/V wiring, we first analyze the short current of V/V wiring traction transformer and its influence to measuring impedance of line distance protection. Fig.1 shows the 220kV railway traction power supply system which adopts V/V wiring transformer, and the 220kV railway traction substation’s power is supplied by triphase alternate current. The traction transformer is connected by two single-phase traction transformers in V/V wiring to form a complete traction transformer. The traction transformer’s b phase of low-voltage side connects to rail, and a phase connects to the load of up-train electrification locomotive, c phase connects to the load of the down-train electrification locomotive. Figs. 1. Figure 1, V / V wiring diagram for railway traction power supply system Fig.2 shows the railway equivalent circuit diagram of traction power supply system, all the parameters have converted to high-voltage side of traction transformer. In the diagram, is the positive sequence equivalent impedance of system; is the positive sequence equivalent impedance of line; is the positive sequence equivalent impedance of monophase transformer (it has been converted to the high-voltage side) . 、 、 is the electric potential of the power; In the diagram, the part between A'B'C' and abc is the equivalent circuit of the traction transformer [4] . xtZ LZ BZ AE . BE . CE . Figure 2, V/V cable railway traction power supply system of the equivalent circuit 1.1 Two-phase short circuit of V/V wiring traction transformer’s low-voltage side In Fig. 2, supposing the power system is symmetrical, the equivalent impedances of system and the impedances of line are symmetrical, those are as follows: , thereinto， . Take traction transformer’s ab phase short circuit of low-voltage side for example, in the 220kV power supply line, those are as follows: ， , so 220kV line does not have zero-sequence current. According to the loop voltage, these can be concluded: . 2 .. CBA EaEaE == °= 120jea BA II .. −= 0. =CI ( ) ( LxtBBLxtABA ZZIZZZIEE +−++=− .... ) （1） ( ) BLxt j A BLxt A A ZZZ eE ZZZ aEI ++=++ −= ° 22 3 22 1 30 . 2 . . （2） BLxt j A B ZZZ eEI ++−= ° 22 3 30 . . （3） Because neutral point’s potential of the power is 0, the bus voltages of 220kV power supply substation are: xtAAA ZIEU ... −= ( )[ ] BLxt j BLxt j A ZZZ eZZjZeE ++ ++−= °−° 22 2 3030 . （4） xtBBB ZIEU ... −= ( )[ ] BLxt j BLxt j A ZZZ eZZjZeE ++ ++−= °−° 22 2 15030 . （5） CxtCCC EZIEU .... =−= In the same way, the current in 220kV line and the bus voltage of 220kV power supply transformer substation can be deduced as table 1 and table 2, when the low-voltage’s bc phase, ca phase of traction transformer is in short circuit. 2010 China International Conference on Electricity Distribution 3 Table I, VIV wiring short-circuit 220kV transformer low-voltage two-phase line current ab phase shorts be phase shorts out ca phase shorts out out IA .J3 E A eOo ' - J3 Ec e)lO° 2Zx1 + 2ZL + ZB 0 2ZXl + 2Z1. + 2Z In - .J3 E A e,jlOO .J3 E j300 .) R e 0 2Zxt + 2Z1. + ZR 2Z" + 2Z I. + Z R Ie J3EfJ e)lO° J3 Ec eOoo 0 - 2ZXl + 2ZL + 2ZB 2ZXl +2Z1. +ZR Table 2, V/V connection traction transformer substation low-voltage two-phase short-circuit power supply voltage on the 220kV bus UA UR U c ab E eJ3o ' [- Z + (2Z + Z )e -J3Oo ] phase A ] xl I, n E eJ3o' [- jZ + (2Z + Z )e -)1500 ] A xl I. H E c 2Z'1 +2ZI, +Zn 2Z'1 +2ZI. +ZR be phase EA j30° [. ( )e _)30' ] Ell e - JZxt + 2ZL +Zll E e)30' [- Z + (2Z + Z )e -)15O' ] R ] xl I. n 2Z" +2Zr. +ZR 2Z'1 + 2ZI. + Zn ca phase E. e)30 ' [- Z + (2Z + Z )e -)1500 ] ( ] xl I. R 2Z'1 + 2ZI, + 2Z R 1.2 Three-phase short circuit of VN wiring traction transformer's low-voltage side In Fig.2, supposing the power system is symmetrical too, that is as follows: E A = a E B = a2 Ec ' thereinto, 120' a = e1 . According to the loop voltage, these can be concluded: 1A (Zx, +Zr. +ZR )-lB (Zy, +Zr J =EA-Es (6) Is (Zx, +Zr J-1c (Zxt +Zr. +ZR ) =Es-Ec (7) 1A+h+h =0 (8) (9) According to the (8) formula, when V IV wiring traction transformer's low-voltage side is in three-phase short circuit, 220kV power supply line has no zero-sequence current. According to the 3 equations (7), (8) and (10) equations, these can be concluded: 1A = EA [3 (Zxt+ZJ+ (1-a2 )Zs ] (Zxt +ZL +ZJ(3Zxt +3ZL +ZJ (2) (11 ) ER E.eilOO [_ jZ +(2Z +Z )e -JJOo ] C xt L H 2Zxt + 2ZL + 2ZB Ie = aEA [3 (Zxt +Zr J+ (l-a)ZR l (12) (Zxt + ZL + Zs )(3Zxt +3ZL + ZJ Because neutral point's potential of the power is 0, the bus voltages of 220kV power supply substation are: UA = EA-IAZ,t _ Ej3Zx, +ZH )(Zxt +ZI. +ZH )+ (2+a2 )ZHZJ (3Xxt +3ZL +ZB )(Zxt +ZL +ZB ) (13 ) U H = E H -1H Z xl EAa2 (3ZL +Zs ) 3ZYt +3ZL + Zs Uc = Ec-1c ZXI ( 14) EA a[(3Zxt +ZB )(Zxt +ZL +ZB )+ (2+a)ZBZJ (3Xx, +3ZI. +ZH )(Zxt +ZI. +ZH ) CIS) 2. Analysis of the measuring impedance when V N wiring traction transformer is in short circuit 2.1 Analysis of the measuring impedance 4 2010 China International Conference on Electricity Distribution when VN wlrmg traction transformer is in two-phase short circuit In Fig. 2, according to the short current analysis conclusion above, take ab phase short circuit for example to analyze measuring impedance of 220kV power supply line protection. According to the conclusion of table I and table2, the AB phase measuring impedance of 220kV power supply line protection can be deduced as follows: Z = UA -UR AR lA-h 1 A (z J + Z H) -1 H Z J. 21 A ( 16) In the same way, measuring impedance of BC and CA are as follows: _ ( )e/600 ' r::; Zsc - 2Zr. +Zs + J-v3Zx/ (17 ) (IS) Using the same analysis method, according to the short current analyzed in Table I, Table 2 above, the measuring impedance of 220kV power supply line's grounding distance protection can be deduced as follows: VA ZA= ---- IA+K3/o = �[- jZxt + (2ZL +ZB)e-i300] Zs = � [jZxt + (2ZL +ZS)e/30] Zc = 00 ([9) (20) Similarly, the measuring impedance of 220kV power supply line's interphase and grounding distance protection can be deduced as follows in table 3 when the line is in bc phase or ca phase short circuit. Table 3, V/V cable traction railway traction low-pressure side of two-phase short-circuit 220kV line impedance measurement of distance protection component ZAS Zsc: ZCA ZA ZS Zc: ab-phase short circuit ZL+ZsI2 ( ) ;600 'J3 2ZI. + Z s e + J 3Zxt (2ZL +ZS)e- J600 - jJ3zxl Z (2Z Z )e-;30O -Jxt+ L+B J3 ( )eJ30° jZxl + 2ZL + Zs J3 00 bc -phase short circuit (2Z L + Z B )e -J60° - jJ3z,1 Z;. +Zs 12 ( )e 16OO 'J3 2ZL +Zs . + J 3ZxI 00 Z (2Z Z )e-.J3O° -J xl + L + S J3 ( )eJ300 jZ,t + 2Z L + Z B J3 ca -phase short circuit ( )eJ600 J3 2ZL +2Zs + j 3ZxI (2ZI. +2Zs)e-;60° - jJ3zxt ZL +Zs . ( ) ;300 JZ,t + 2ZL +2ZB e J3 00 - jZ,t + (2ZL + 2Z B )e-J30O J3 2.2 Analysis of the measuring impedance when VN wiring traction transformer is in three-phase short circuit 1 A(ZJ +ZH)-l H ZJ lA-Is In figure 2, according to the above analysis results about short current, we analyze the action of 220kV power supply line protection. According to the analysis of three-phase short current, the AB phase measuring impedance of 220kV power supply line protection can be deduced as follows: Z = __ R_+Z r 1-� lA (2[) In the same way, measuring impedance of BC phase, CA phase are as follows: 2010 China International Conference on Electricity Distribution 5 Z/lC (22) Using the same analysis method, according to three-phase short current analysis above. the A phase measuring impedance of 220kY power supply line's grounding distance protection can be deduced as follows: UA ZA= ---- I A+K3Io EA-IAZYI Z'I +Zr +ZR - -----''''--------'-'-2 ------''------ -Z xl 1- a ZB 3ZxI +3Zr+ZR (24) Similarly, the B phase and C phase measuring impedance can be deduced as follows: Z B = Z L + Z B /3 (25 ) (Zxt +Zr. +ZR ) Zc = -'-----''-------''------''-'-- - Zxt 1- aZR 3ZxI +3Z r+ZR 2.3 Analysis of 220kV protection's measuring impedance (26) line distance That can be found out in Table 3, when ab phase or bc phase short circuit takes place in low-voltage side of the railway traction transformer, the distance measuring impedance of 220kY line interphase distance protection is always be Z L + Z B / 2, and it is the minimum value, the other two interphase measuring impedances both are greater than this value. When ca phase short circuit takes place in low-voltage side of the railway traction transformer, the distance measuring impedance of 220kY line interphase distance protection is Z L + Z B ' and it also is the minimum value, the other two interphase measuring impedances both are greater than this value. Because the system impedance is much less than ( 2Z I. + Z R ) when two phase short circuit takes place in low-voltage side of the railway traction transformer, the measuring impedance of 220kY line grounding distance protection IS equal to the 2/.J3 minimum measuring impedance of interphase distance protection, and it has a 30oexcursion angle. Because (Z xl + Z L) is much smaller than Z B ' (Z xl + Z I. ) can be ignored, according to the formula (21 ) and (22) , AB phase and BC phase's minimum measuring impedance are as follows: ZB ZAR � 2 +Zr. 1- � 1- a 2 ZB +Z 1 - .J3e -JISO" r - J7 Z j19.IC Z -- Be + L 7 (27) So when three-phase short circuit takes place in low-voltage side of the railway traction transfonner, the two measuring impedances of Z AB and Z Be both are greater than(ZL +ZB/3) ,and close to the(ZL +ZB/3),but less than (Z L + Z B) . Because (Z xl + Z L ) IS much less than Z B ' (Z xl + Z L) can be ignored, according to the formula (23 ) and (25) , A phase and C phase's minimum measuring impedance are as follows: ZR 1 300 ZA�1_a 2+ZI.= .J3 ZRe-J +ZI. (28) (29) Therefore, when three-phase short circuit takes place in 6 2010 China International Conference on Electricity Distribution low-voltage side of the railway traction transfonner, the two measuring impedances of Z A and Z c: both are greater than (Z[" + Z HI 3) , and the other one Z H is equal to(Z[ +ZH 13). 3. Analysis of the line distance protection's measuring impedance when V IX wiring traction transformer is in short circuit 3.1 Analysis of the V/X wiring traction transformer's winding Generally, there are two traction transformers in intercity railway substation, one is used to supply power, and the other one stand-by for it. Each transformer is made up of two single-phase transformers connected in VIX wiring (Fig. 3). T and F of one single-phase transformer are connected to up-trains and down-trains towards nanjing, T ' and F ' of the other single-phase transformer are connected to up-trains and down-trains towards shanghai. Each single-phase transformer has one primary winding and two secondary windings, the primary winding and the two secondary windings are symmetrical in structure, the polarity of T and F are reverse. The other head of the two windings are connected together to the ground and the rail, so the parameters of the two windings are symmetrical. The typical nameplate parameters of single-phase voltage transformer are: DQY-40000/220, rate capacity is 40/25/25 MVA, rate voltage is 220/2x27.5kV, Wiring group is liOiO, short circuit impedance is 1O.38-1O.42%' L.... Sl Gl t-- I- Figure 3, connection of V I X wiring traction transformer diagram 3.2 Short circuit types of VI X wiring traction transformer The main short circuit types of V IX wiring traction transformer are as follows: (l) one secondary winding or leading wire of the monophase transformer shorts out to ground, this is the most common type; (2) two monophase transformers both have one secondary winding or leading wire shorts out to ground at the same time, but this type is uncommon; (3) two secondary windings or leading wires of one monophase transformer short out to ground at the same time right C this type is short for monophase transformer short circuit) , such as power lines which across over railway, or communication lines break and drop on the traction line or on the ground; (1) two secondary windings or leading wires of the two monophase transformers all short out to ground in C this type is short for all short circuit), this kind of situation mainly takes place in that someone forgets to remove the earth connecting line when the transformer inspection has finished; (5) short circuit between two secondary windings or leading wires in one monophase transformerC this type is short for short circuit between the leading wires of monophase transformer), such as power lines which across over railway, or communication lines break and drop on the traction line, but don't drop on the ground; (6) both of the two monophase transformers short out between two secondary windings or leading wires, this kind of short circuit is uncommon too. 3.2 Analysis of short circuit in V IX wiring traction transformer Analyzing short circuit type (l) and (2) of V/X wiring traction transformer, the equivalent circuit shows in figure 2, and the conclusion is similar to the VN wiring transformer. Analyzing short circuit type (3) and (1) of VI X wiring traction transformer, the equivalent circuit is also similar as figure 2 because winding parameters of each monophase transformer are symmetrical, the only difference is that Z H is replaced by Z� . And Z� = ZI + Z2 II Z3 (Z\, Z2' Z3 are the equivalent impedance of monophase transformer's one primary winding and two secondary windings which have been converted to high-voltage side). So the analysis of V N wiring transformer short circuit and measuring impedance of 220k V line distance protection are also applicable to V IX wiring transformer system, the only difference is that Z B is replaced by Z� . Analyzing short circuit type(5) and (6) of V IX wiring traction transformer, the equivalent circuit is also similar as figure 2 because winding parameters of each monophase transformer are symmetrical, the only difference is that Z H is replaced by Z� And Z� = ZI + (Z2 + Z3) X 0.52 (two secondary windings is connected in series, the voltage is 55kV, videlicet, the per-unit value of single-ph