Proceedings of 2018 IEEE International Conference on Applied Superconductivity and Electromagnetic Devices Tianjin, China, April 15-18, 2018
ID8284
Influences of SFCLs on the Incremental Power Frequency Relay of Transmission Line Qihuan Dong, Jianzhao Geng, Heng Zhang, Xiuchang Zhang, Boyang Shen, Jun Ma, Tim Coombs
W. T. B. de Sousa Institute for Technical Physics Karlsruhe Institute of Technology 76344 Eggenstein-Leopoldshafen, Germany
[email protected]
Electrical Engineering Division, Department of Engineering University of Cambridge Cambridge CB3 0FA, United Kingdom
[email protected]
applied widely in the power transmission lines. As the integration of SFCL to power grid change the fault transient characteristics, the reliability and sensitivity of the protection relays will be challenged. Therefore, it is important to study the effects of the SFCLs on protection relays to ensure the safe operations of the power system.
Abstract—The superconducting fault current limiter (SFCL) has been effective in coping with large fault currents and is expected to be widely used in the electrical power system. In order to maintain reliable operation of the transmission system with a SFCL, the influences of SFCLs on the incremental power frequency relay (IPFR) of the transmission lines are discussed in detail. In this paper a model of the real 220-kV transmission system with a resistive SFCL was built using Simulink/MATLAB software. Finally, numerical simulation tests have demonstrated the correctness and validity of theoretical analyses.
II.
When a short-circuit fault occurs in the transmission line, the whole system stays in the fault state, which could be decomposed into non-fault state and fault additional state by the principle of superposition. The electrical quantity of the fault additional state is called the fault component. SFCLs do not show any impedance in the normal operation, which would not affect the running of the power system. When a short-circuit fault happens, it rapidly turns into high impedance to limit the fault current. Therefore, due to the integration of the SFCLs, the extraction of the fault component will be influenced. However, the SFCL is negligible for the power system in the non-fault state, which directly leads to the deviation of the extraction of the fault component. This should be considered. Um, Im are the voltage and current of terminal m in the fault state, respectively; Um[0], Im[0] are the voltage and current of terminal m in the non-fault state, respectively; ᇞUm, ᇞIm are the voltage and current of terminal m in the fault additional state, respectively; and then Zsm and Zsn correspond to the equivalent system impedance of terminal m and terminal n, respectively. The protective relay is installed at terminal m and its end of protection range is x, so the setting impedance is Zset. And the measured impedance from terminal m to fault point is Zk.
Keywords-Superconducting fault current limiter (SFCL); incremental power frequency relay; transmission line
I.
INTRODUCTION
The expansion of the power grid and the growth of the installed capacities directly lead to the increase of the vulnerability of the power system. However, the circuit breakers (CBs) are not able to deal with the resultant increasing fault currents due to their limited interrupting capacity, which poses a big threat to the normal operation of the power system. Therefore, limiting short-circuit currents during the fault time has been significant to maintaining the safe and reliable operation of the power system. Superconducting fault current limiters (SFCL) have become one of the most ideal current limiting devices to solve the problem of the increasing fault current in power grids [1]. SFCLs have a negligible impedance during normal operation and can develop a considerably higher impedance within a very short time (less than a quarter of an AC cycle) after a fault occurs, thereby limiting the short-circuit current to a reasonable value without consuming extra power [2]. Despites of its merits, examples of real SFCLs being used in power grids are still rare because the practical application of the SFCLs has many problems, among which the coordination between the SFCLs and protective relay is a paramount one. Protective relay is applied to detect the fault and operate to trip the circuit breakers to isolate the fault. According to the electrical information used by protective relay, protective relay can be divided into over-current protection, impedance protection, directional protection, differential protection, and incremental power frequency type relay (IPFR). IPFR has been
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THEORETICAL ANALISIS
ΔU m'' = U m − U m[0] = U m − U m' [0] + U m' [0] − U m[0] = ΔU m + (U m' [0] − U m[0] ) = ΔU m + U A
ΔI m'' = I m − I m[0] = I m − I m' [0] + I m' [0] − I m[0] = ΔI m + ( I m' [0] − I m[0] ) = ΔI m + I A
(1)
(2)
where UA = U’m[0] - Um[0] and IA = I’m[0] - Im[0]. 1) When a positive direction fault for terminal m occurs in
1
the transmission line, the relationship between ᇞUOP and -Uf[0] is expressed by:
ΔU OP = ΔU m'' + ( − I m'' ) Z set = ΔU m − ΔI m + (U A − I A Z set )
inductive or resistive impedance increase. The fourth column shows the real protection distance after IPRF being modified to adjust for installation of SFCL.
(3)
TABLE I. SIMULATION RESULTS OF IPFR WITH RESISTIVE SFCL Protection Distance (km)
Z sm + Z set =− U f [0] + U B Z sm + Z k + Z SFCL
Impedance of R-SFCL (ohms)
2) When a reverse direction fault for terminal m occurs in the transmission line, the relationship between ᇞUOP and -Uf[0] is expressed by:
ΔU OP = ΔU m'' + (− I m'' )Z set = ΔU m − ΔI m + (U A − I A Z set ) =−
(4)
Z + Z SFCL − Z set U f [0] + U B Z + Z k + Z SFCL ' sn ' sn
III.
CASE STUDY
With SFCL
Without SFCL
With SFCL (Zset not contains RSFCL)
(Zset contains RSFCL with fault components correction)
1.8
83
78
83
2.8
83
72
83
3.8
83
65
83
4.8
83
57
83
5.8
83
74
83
TABLE II. SIMULATION RESULTS OF IPFR WITH INDUCTIVE SFCL
A. Simulation The simulation process for the following case studies is showed in Fig. 1. The precise fitting function to represent the impedance of the R-SFCL is obtained according to the working principles and the real impedance characteristics of SFCLs. Therefore, 220 kV transmission system with different SFCLs can be simulated by using MATLAB software. And the total length of the transmission line is 100 km and the expected protection distance of IPFR is 85 km. The current-limiting effect of different SFCLs and the response of the IPFR were evaluated and examined for the transmission lines with and without the presence of the SFCLs.
Protection Distance (km) Impedance of X-SFCL (mH)
Without SFCL
(Zset not contains XSFCL)
(Zset contains XSFCL with fault components correction)
1.8e-2
83
64
83
2.8e-2
83
52
83
3.8e-2
83
41
83
4.8e-2
83
29
83
5.8e-2
83
18
83
With SFCL With SFCL
IV.
CONCLUSIONS
In this paper, investigations were carried out to determine the impacts of different kinds of SFCLs on the incremental power frequency relay of transmission lines. The resistive and inductive SFCL respectively adds resistive or inductive value to the impedance of the transmission line, which affects the relationship between the voltages and currents. This will result in rejecting operation when a fault occurs in the protection zone, which largely affects the safe operation of the power transmission system. So the setting values of the IPFR for transmission lines and its coordination with the SFCLs must be regulated correspondingly.
Figure 1. Simulation process for case study.
REFERENCES
B. Results Table I and Table II shows how the effective protection distance shrink as the resistive and inductive impedance of the SFCL increase when a resistive type and an inductive type SFCL operates in the grid respectively. It is clear that for both types of SFCL, protection distance decrease significantly when
[1]
A.Wolsky, “HTS from Precommercial to Commercial: A Roadmap to future use of HTS by the Power Sector,” Int. Energy Agency (2013). [2] M.Noe, M.Steurer, High-Temperature Superconductor Faut current limiters: Concepts, Applications, and Development Status, Supercond. Sci. Technol. 20(2007) 15-29. Author, B. C. Author, and D. Author, “The tit
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