Research_on_Secondary_Arc_for_UHV_Transmission_Lines.pdf

Research on Secondary Arc for UHV Transmission Lines

Xiang Song, Wen Jun, Zhang Hui-yuanSchool of Electrical and Electronic Engineering

North China Electric Power University Beijing, China

E-mail: [email protected]

Xiao Xiang-ningKey Laboratory of Power System Protection and Dynamic

Security Monitoring and Control (North China Electric Power University)

Ministry of Education Beijing 102206 China

E-mail: [email protected]

Abstract—A dynamic mathematical model—Johns arc model which could be used to simulate the dynamic secondary arc in the process of single-phase auto-reclosure after transient single-phase faults is presented and actualized in PSCAD/EMTDC. This model is used in the digital faults simulations of the first Ultra high voltage (UHV) transmission line of 1000kv class in China—the Jindongnan-Jingmen UHV single circuit transmission project under construction, the outcomes and influences of several known important factors, such as wind, manner of shunt compensation and other meteorological and geographical factors including temperature, humility, altitude and so on are discussed. According to the discussion, the preconcert reclosure interval of 1s is proved to be proper.

Keywords-UHV transmission line; single-phase auto-reclosure; dynamic arc model; secondary arc; secondary arc current (SAC); arc extinction duration.

0BI. INTRDUCTION

he faults on UHV transmission line are the studying hot points for the academic and engineer circles. Ninety percent of these faults are single-phase grounding ones,

and most of them are transient according to the statistics of the faults records [1]. Therefore, single-phase auto-reclosure has a widespread application as a method to improve the stability and reliability of the transmission lines. However, the success rate of the auto-reclosure in UHV systems is reduced in case of larger phase-to-phase capacitance and inductance-coupling as the consequences of higher voltage class and longer transmission distances. So the improvement of the success rate of single-phase auto-reclosure has become an important aspect of insurance of the system stability and security as well as an important technical issue of the application of UHV transmission system [2]. As principal precondition of reclosure that the faults must be removed before reclosure operation, so to fix the extinction duration of secondary arc has the very importance. The key to fix that duration is an accurate model of the secondary Farcs.

A simulation for the first UHV transmission project in China—Jindongnan-Jingmen transmission line (1000kV, 3000MW) under construction has been made on the basis of Johns arc model according to the comparison among the major

arc models. On the basis of the simulations the issues of coordination of the extinction of secondary arc and the action of single-phase auto-reclosure are discussed.

1BII. RESEARCH SITUATION

The arc on the faults point caused by the phase-to-phase capacitance and inductance-coupling of the two energized phases after the first operation of the breaks of the fault phase is called secondary arc and its current secondary arc current (SAC) which is the vectored superposition of the capacitance component and inductance component [3]. The extinction of the secondary arc can be explained by the conservation of energy in the arc gap which considers the energy balance among the arc and the transmission line and the surrounding environment as the chief reasons of the arc extinction [4]. And the condition of arc extinction can be present as the energy dissipation is more than energy injection in the arc column. The arc temperature dropping down with the increasing of the energy dissipation, and the arc resistance increasing in the meanwhile, which caused the final extinction of the secondary arc.

An engineering explanation is also presented to the arc extinction which ascribed it to the arc elongation caused by the air-flow and electromotive force generated by the interaction between the current of the arc and the energized phases. When the arc length is keeping on increasing, the potential per unit length reducing relatively, and the arc extinguishes when it reaches to a threshold value called maintain potential [1].

In the researches in early time, arc was crudely equivalent to a zero-resistance or a constant one, which may brought large deviation into the calculation and simulation.

In 1931, C. Warrington presented Warrington formula to formulate the Volt-Ampere characteristics based on the researches of the data from real faults, and several improvements had been presented after then [5, 6]. Warrington formula could formulate the relation among arc resistance, arc current and arc length crudely, namely larger arc current with smaller arc resistance and longer arc with larger arc resistance. But this model is usually used in the case of low-accuracy calculation because of the deviation and unfavorable extinction characteristic caused by the crude approximation [6].

T

This research was supported by “111 project” (B08013).

978-1-4244-2487-0/09/$25.00 ©2009 CrownAuthorized licensed use limited to: UNIVERSIDADE DE SAO PAULO. Downloaded on May 20,2010 at 15:35:04 UTC from IEEE Xplore. Restrictions apply.

In 30s and 40s of 20th century, two different approximations were presented by A. M. Cassie and W. Elenbaas relatively based on the theory of the conservation of arc energy which is known as Cassie—Mayr formula[7,8] and Elenbaas—Heller formula[9]. As the basis of current researches on plasma arc, these formulas could formulate the arc process with favorable accuracy in mathematics, but it difficult to be applied into engineering simulation because of the scarcity of many crucial parameters and its complicated calculation.

In 1976, A. T. Johns presented an engineering dynamical arc model on the basis of the theory of the conservation of arc energy and the analysis and summary of the faults date [10-12].This model is widely accepted and used in engineering simulation of SAC because of its advantages on accurate approximation, simple calculation, precise outcome and accessible parameters.

2BIII. JOHNS ARC MODEL

8BA. Introduction Johns arc model is a dynamic arc model based on energy

conservation, namely, the arc resistance changes with the energy afflux [10]. According to the energy conservation,

dq dt e i p= ⋅ − 1

Where, dq/dt is the variance ratio of energy in the arc column per unit length; is the power afflux of the arc per unit length where e is the electric field strength in the arc column and i is the arc current; p is the energy loss of the arc per unit length.

Set ( ) ( )x x xT g dq P dg= ⋅ ⋅ , (1) could be transformed into

( )x x x xdg dt G g T= − 2

Where g is the arc conductance, G is steady arc conductance.

Equation (2) can be used on the simulation of primal arc and secondary arc.

Set ( )p p pG i V l= ⋅ , p p pT I lα=Where Vp is the steady voltage gradient, Ip is the peak

value of steady primary arc, when the current value is in the range of 1.4~24kA, Vp approaches to 15V/cm, lp is the arc length, =2.8 , when the formula is used on the simulation of primal arc;

Set [ ]( )s s s rG i V L t= 1.4 ( )s s s rT I L tβ=Where Vs is the steady voltage gradient of secondary arc, Is

is the peak value of steady primary arc, when the current value is in the range of 1~55A, Vs can be obtained from formula 0.475s sV I −= , Ls is the dynamic arc length can be obtained from (3)

0

1 ( 0.1 )( )

10 ( 0.1 )r

s rr r

t sL t L

t t s≤

=>

3

Where tr is the arc lasting duration, L0 is the initial length of the arc, =2. when the formula is used on the simulation of secondary arc [10,12] .

is -the transient value of SAC, can be calculated by (4)

s s si u g= ⋅ 4

Where us is the transient potential drop of the arc column.

9BB. Simulation and Verification Johns model is used in the simulation of 750kV

Vinnitsa-Dnieper transmission system, and a comparison among the outcomes and measuring data in [13] is made in order to verify the accuracy of this model.

The structure of the system is shown in Fig. 1, where L1, L2,L3 are the shunt reactors of 300Mvar, LN1, LN2 are the neutral reactors of 300 . Other line parameters are given in [13].

ABC

1L 2L3L

2NL1NL

Vinnitsa Dnieper417km

Figure 1. Diagram of Vinnitsa-Dnieper transmission line

Three typical cases as follow are simulated, 1) L3 is absent, and L1, L2 are grounded directly;

2) L3 is absent, L1 is grounded directly, and L2 through LN2;

3) L3 is absent, and L1, L2 are grounded through LN1, LN2relatively.

Comparisons between simulation and measuring are shown in Fig. 2 and TABLE I.

The data of simulation and measuring are mainly coincided according to TABLE I. Some differences of the waveform between simulation and measuring are presented in (2) and (3). These differences are due to the different direct components induced from the shunt reactors when the line breakers act in different time points.

TABLE I. COMPARISIONS OF SIMULAT ION AND MEASUR ING

Case 1 2 3

ED (s) simulation 0.14 0.28 0.67measuring 0.13 0.26 0.63

SAC (A) simulation 3 26 49measuring 5.3 27.5 49.4

SAC=RMS value of SAC; ED=extinction duration of secondary arc.

Authorized licensed use limited to: UNIVERSIDADE DE SAO PAULO. Downloaded on May 20,2010 at 15:35:04 UTC from IEEE Xplore. Restrictions apply.

Figure 2. Comparison between simulation and record of SAC

3BIV. SIMULATIONS OF ARC MODEL IN UHV SYSTEM

10BA. Calculate Conditions The equivalent circuit of Jindongnan-Jingmen transmission system is shown in Fig.3, Jindongnan-Nanyang and Nanyang-Jingmen are 1000kV transmission lines of the length of 350-365km and 282-291km relatively; Jindongnan is connected with Huabei 500kV system and Jingmen with Huazhong 500kV system. Shunt reactors which grounded through neutral reactors are installed on both sides of Jindongnan-Nanyang and Nanyang-Jingmen transmission lines. All above are shown in Fig. 3. Other line parameters are given in [14].

B. Simulation and Calculation Simulations have been made to the Jindongnan-Nanyang

and Nanyang-Jingmen transmission lines relatively; faults points locate on the head, the middle and the end of each phase. The outcomes are shown in TABLE II.

Such conclusions could be drawn out from the comparison above that the RMS value and the extinction duration of the secondary arc have a trend of reduction as the increasing of the faults distance to the head of each phase. It is different to the general recognition of the trend of the SAC which reduces from the head to the middle and increases from the middle to end, namely, the SAC has a minimum value in the middle of the line. It could be explained as follow that the SAC is the vector sum rather than the algebraic sum of the inductance component and the capacitance component, which brings about the different trend of the SAC along the line in the lines of different parameters.

Figure 3. Equivalent circuit of Jindongnan-Jingmen transmission system

TABLE II. SIMU LAT ION OUTCOMES OF JINGDONGNAN-JINGME N TRAN SM ISSION LINE

J-N N-J

phase Distance (km) SAC A ED s Distance

(km) SAC A ED s

A20 31.6 0.79 20 27.7 0.52

170 24.3 0.72 160 21.5 0.44 320 18.8 0.52 270 18.9 0.43

B20 31.9 0.8 20 25.8 0.45

170 25.6 0.71 160 21.2 0.46 320 20.0 0.51 270 19.1 0.38

C20 31.1 0.79 20 27.0 0.52

170 23.5 0.73 160 24.6 0.46 320 19.4 0.52 270 19.2 0.43

J-N=Jindongnan-Nanyang transmission line; N-J=Nanyang-Jingmen transmission line


4BV. THE INFLUENCES TO EXTINCTION DURATION

12BA. Influence of Faults Location Simulations have been done in phase A of

Jindongnan-Nanyang and Nanyang -Jingmen transmission system and the faults distance changes with a unit length of 50km from the head to the end in the precondition of other situations above unvaried. The outcomes are shown in TABLE III and Fig. 4.

Such a conclusion could be drawn out from TABLE III and Fig.6 that the value of SAC and extinction duration of the secondary arc have a trend of reduction on both transmission lines of J-N and N–J as the distance to the head increasing.

TABLE III. SACS AND EDS WIT H DIFFERENT FAU LT S LOC AT IO NS

Distance (km) 20 70 120 170 220 270 320

SAC (A) J-N 31.6 29.0 27.2 24.3 22.5 21.2 18.8 N-J 27.7 25.6 23.0 21.5 20.4 18.9 —

ED (s) J-N 0.79 0.77 0.73 0.72 0.66 0.57 0.52 N-J 0.52 0.48 0.47 0.44 0.43 0.43 —

Figure 4. SACs and EDs with different faults locations

13BB. Influence of Initial Arc-Length Simulations have been done to the same faults on the head

of phase A, and the initial arc-length changes in the range of 600cm~1400cm in the precondition of other situations above unvaried. The outcomes are shown in TABLE IV and Fig. 5.

Such conclusions could be drawn out from TABLE IV and Fig. 5 that both of SAC and ED have a same trend of reduction with the increasing of the initial arc-length which is in accordance with the practical situation.

TABLE IV. SACS AND EDS WIT H DIFFERENT IN IT IALARC- LENGTHS

Initial arc-length (cm) 600 800 1000 1200 1400 SAC (A) 33.7 31.5 30.1 28.8 29.1 ED (s) 1.09 0.89 0.75 0.67 0.58

Figure 5. SACs and EDs with different initial arc-length

14BC. Influences of Wind Wind is recognized as one of the most important factors

which influence the extinction of secondary arc. It’s generally recognized that the arc extinguished more rapidly in winds of larger velocity [3]. However, the practical situation is that influence of wind is not only decided by its velocity but also by its direction. Because that most of the arcs ground through towers and insulator stings, when arc flashover though suspension insulator stings, wind blows the arc horizontally which elongates the arc and accelerates its extinction, but when stain ones, wind blows the arc longitudinally which prevents the elongation of the arc and retard the extinction of the arc or even make it unable [15], as shown in Fig. 6.

11

2 2

Figure 6. The influence of wind direction

So the influence of wind is a synthesis of the influences of


wind velocity, wind direction and form of insulator stings. Such conclusions could be drawn out from the discussion above [15].

1) Wind is an advantage of arc extinction in the situation of the application of suspension insulator stings. In that case, wind with larger velocity leads to shorter extinction duration;

2) Wind is a disadvantage of arc extinction in the situation of the application of strain insulator stings. In that case, wind with larger velocity may leads to longer extinction duration or even the situation of un-extinguishable.

15BD. Influence of Other Factors There are obvious influences to the extinction of SAC

from those environmental factors such as environmental humidity, temperature, atmospheric pressure, altitude, magnetic field and so on. These conclusions below could be drawn out on the basis of the theory of the plasma arc and the researches and investigations of the practical arc processes.

High temperature and humidity are the disadvantages of the extinction of secondary arc, scilicet, humid summer climate or atmosphere of fog is detrimental to the extinction of secondary arc;

1) Areas of suspended particulates, industrial estates, areas of seashore and areas of chemical rain are detrimental to the extinction of secondary arc;

2) The probability of the occurrences of arc faults in areas of high altitude is lower than areas of low altitude, and the average extinction duration is shorter in the areas of high altitude too.

5BVI. CONCLUSIONS

According to the discussion above, such conclusions can be drawn out:

1) The method of grounding the shunt reactors through neutral reactor could inhibit the secondary arc effectively. The SAC reaches it minimum value when phase-to-phase capacitance is compensated completely. The effect of compensation of the measure of which grounding the shunt reactors of both ends of the line through the neutral reactors is better than the measure that grounding the shunt reactor of one end through the neutral reactor and the other end directly.

2) The extinction of the secondary arc is a complex of many factors. System and line parameters, compensate-situation, and meteorological and geographical conditions are the effective factors of the arc extinction which caused the complicated phenomena of secondary arc. And the velocity and

direction of wind is the most factor of influence among the meteorological ones, of which the effect on the extinction of arc is partly determined by the form of the insulator stings applied.

3) All the extinction durations of the simulation outcomes of Jindongnan-Jingmen transmission system are less than 1s, so to adjust the reclosure-duration of the single-phase auto-reclosure to 1s is suitable for engineering practice.

6BREFERENCES

[1] Ding-xie. Gu, Pei-hong. Zhou. “Secondary Arc and Reactive Power Compensation in UHV AC Transmission System”. High Voltage Engineering. 2005,11,21-25(in Chinese)

[2] Hao. Wang, Yong-li. Li, Bin. Li. “Secondary arc extinction methods for 750 kV and UHV transmission lines”. Electric Power. 2005,12,29-32(in Chinese)

[3] Ji-ying. Liu, Fu-rong. Wang, Kang. Zhang. “Study on Potential Supply Current Based on UHV Electric Network”. Electric Switchgear.2007,5,30-34(in Chinese)

[4] G. Ban, L. Prikler, G. Banfai. “Testing EHV Secondary Arcs”. IEEE Porto Power Tech. Conference 10th -13th September, 2001,Porto, Portugal

[5] A. R. Van and C. Warrington, “Reactance relays negligibly affected by arc impedance,” Elec. World, pp. 502–505, Sept. 19, 1931.

[6] M. Djuric and V. Terzija, “A new approach to the arcing faults detection for auto-reclosure in transmission systems,” IEEE Trans. Power Delivery, Vol. 10, pp. 1793–1798, Oct. 1995.

[7] A. M. Cassie. “Arc ruptures and circuit serverity: A new theory.” CIGRE Rep Paris, France. 102, 1939

[8] King-Jet Tseng, Yaoming Wang, D. Mahinda Vilathgamuwa, “An Experimentally Verified Hybrid Cassie–Mayr Electric Arc Model for Power Electronics Simulations,” IEEE Trans. Power Electronics, Vol. 12, No. 3, pp. 429–437, 1997.

[9] L. Van der Sluis. “Comparison of test circuits for high voltage circuit breakers by numerical calculations with arc models”. IEEE Trans. Power Delivery, Vol. 7, No. 4, pp. 2037–2045, 1992.

[10] A. T. Johns, A. M. Al-Rawi. ” Developments in the Simulation of long distance single-pole-switched EHV Systems”, IEE Proceedings, Vol. 131, Part C, No.2, March 1984.

[11] A. T. Johns, W. M. Ritchie, “Applications of an Improved Technique for Assessing the Performance of Single-Pole Reclosing Schemes”, IEEE Trans. Power Apparatus and Systems, Vol. PAS-103, No. 12, December 1984.

[12] Johns. A. T, Aggarwal RK, Song YH. “Improved techniques for modeling faults arcs on faultsed EHV transmission system”. Proc IEE—Gener Trans. Distrib 1994: 141(2):148–54.

[13] H. N. Schnerer, B. R. Stperling, J. W. Chadwick, el. “Single-phase Switching Tests On 765 kV and 750 kV Transmission Lines”. IEEE Trans. Power Apparatus and Systems, Vol. PAS-104, No. 6, June 1985

[14] Ling. Cheng, Yu-qin. Xu, Zi-lin. Song. “Single-phase adaptive auto-reclosure of EHV transmission line based on the arc characteristic”, Relay, 2007, 22, 18-22(in Chinese)

[15] Zeng-yuan. Guo, Wen-hua. Zhao. Electric Arc and Thermal Plasma.Science Press, Beijing, 1985.


Research_on_Secondary_Arc_for_UHV_Transmission_Lines.pdf

Documents

Transcript of Research_on_Secondary_Arc_for_UHV_Transmission_Lines.pdf