scholarly journals Influence of Standard Lightning Impulse Front Time Tolerances on the Flashover Voltage of Suspension Insulators

2019 ◽  
pp. 76-81
Author(s):  
J Kluss ◽  
M Chalaki-Rostaghi ◽  
K Yousefpour ◽  
Z Ahmed ◽  
F Haque
Keyword(s):  
Systematic Approach ◽  
Discharge Voltage ◽  
String Length ◽  
Time Value ◽  
Double Exponential ◽  
Flashover Voltage ◽  
Field Homogeneity ◽  
Lightning Impulse ◽  
Maximum Tolerance ◽  
Glass Insulator

For high voltage impulse testing, a standard lightning impulse is defined in IEEE Std. 4 and IEC 60060-1 as a double exponential waveform having a front time T1 = 1.2 μs ± 30% and time to half-value T2 = 50 μs ± 20%. It has been noticed that for a given specimen, it is possible to successfully pass a flashover test at one end of the T1 tolerance range while failing the same test at the opposite end of the tolerance spectrum. Consequently, a systematic approach was adopted to investigate this observation. Up-and-down tests were performed to define the disruptive discharge voltage (critical flashover voltage CFO, U50) for 1, 5, 10, and 15 unit glass insulator strings standard lightning impulses using the minimum acceptance front time value (T1 ≈ 0.84 μs). Tests were repeated using the maximum tolerance value (T1 ≈ 1.56 μs) to investigate the degree of divergence in the flashover value. Particular attention is given to the steepness (voltage-time characteristics) of the applied impulse to consider if tolerance criteria amendment is merited in a future standard revision. As the steepness impact is more renowned in non-uniform geometries, field homogeneity as a function of string length is also incorporated into the analysis.

scholarly journals Evaluation of Filtered Spark Gap on the Lightning Protection of Distribution Transformers: Experimental and Simulation Study

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3799 ◽  
Author(s):  
Mahdi Pourakbari-Kasmaei ◽  
Farhan Mahmood ◽  
Michal Krbal ◽  
Ludek Pelikan ◽  
Jaroslava Orságová ◽  
...  
Keyword(s):  
Experimental Tests ◽  
Disruptive Effect ◽  
Protection Level ◽  
Spark Gap ◽  
Distribution Transformers ◽  
Double Exponential ◽  
Depth Analysis ◽  
Lightning Impulse ◽  
In Series ◽  
Experimental Laboratory

Protection of transformers, as one of the most expensive equipment in the power system, against lightning overvoltage impulses is a vital task. This paper, for the first time so far, investigates the effects of a filtered spark gap on the protection level of transformers against lightning overvoltage impulses. The filter is an inductor that is placed in series with the transformer and before the spark gap aiming to reduce the voltage at the connection point of the spark gap, and hence, enhancing the protection level of the transformer under lightning overvoltages. The experimental laboratory tests are accomplished on a 400 kVA, 22/0.4 kV, Delta-Star ( Δ − Y ) connection type transformer under 110 kV, and 125 kV overvoltage impulses, whereas the size of the spark gap is set to 80 mm and two inductors of 35 μ H and 119 μ H are considered. In order to perform a more in-depth analysis, a model that works reasonably close to the empirical case is developed in the EMTP-RV software. An optimization algorithm is used to determine the sensitive parameters of the double-exponential function, which is used to reproduce the applied laboratory lightning impulse voltages in the EMTP-RV environment. Moreover, the transformer is modeled according to the Cigre Guidelines (Working Group 02 of Study Committee 33). The behavior of the spark gap is simulated as close as the practical situation using the disruptive effect method. The preciseness of the simulated filtered spark gap model is verified by comparing the results of the simulated model in the EMTP-RV with the results of experimental tests. After verifying the model, different sizes of inductors are studied in the EMTP-RV environment to investigate whether larger or smaller inductors provide better protection for the transformer under lightning conditions. A comparison is performed among the conventional spark gap, surge arrester, and the filtered spark gap to provide a better analysis of the potential of the proposed device. The results indicate that proper sizing of the inductor, within an effective range, slightly enhances the protection level of the transformer.

scholarly journals Insulation Reconstruction for OPGW DC De-Icing and Its Influence on Lightning Protection and Energy Conservation

Energies ◽  
2018 ◽  
Vol 11 (9) ◽  
pp. 2441 ◽  
Author(s):  
Xiangxin Li ◽  
Ming Zhou ◽  
Yazhou Luo ◽  
Chao Xia ◽  
Bin Cao ◽  
...  
Keyword(s):  
Transmission Line ◽  
Power Loss ◽  
Energy Savings ◽  
Fiber Composite ◽  
Discharge Voltage ◽  
Lightning Strike ◽  
Lightning Protection ◽  
Induced Current ◽  
Lightning Impulse ◽  
Ac Transmission

In order to satisfy demands for DC de-icing of optical fiber composite overhead ground wire (OPGW) and solve questions such as those relating to circulating current loss and liability of suffering from lightning strike, the grounding method of OPGW must be changed from the current commonly used method of being grounded at every tower to being grounded at one tower. The OPGW would be connected to the tower by an insulator, which is often shunt connected with a protective discharge clearance. The recommended value of the discharge clearance is from 70 to 80 mm. The lightning impulse discharge voltage of such a clearance is generally not more than 100 kV. However, as the transmission line is struck by lightning, over-voltage on the clearance is 885 kV at least, even up to a few MV. The clearance can be broken down reliably. The influence of insulation reconstruction for OPGW on the induced current and the power loss of the AC transmission line was studied by means of theoretical analysis and simulation calculations. Results indicate that change of the OPGW grounding mode could reduce the induced current of the ground wire to below 1 A and reduce the power loss of the line to below 1 W/km. Power loss could be reduced by over 99%. Adoption of a suitable grounding mode for OPGW is of great significance for DC de-icing, lightning protection safety, and energy savings for UHV projects.

Test Research on Phase-to-Ground Air-Gap Discharge Characteristics of UHV Substation

2014 ◽  
Vol 492 ◽  
pp. 162-168
Author(s):  
Qi Ming Ye ◽  
Liang Xie ◽  
Xiao Qing Luo ◽  
Feng Huo
Keyword(s):  
Minimum Distance ◽  
Discharge Voltage ◽  
Air Gap ◽  
Test Results ◽  
Discharge Characteristics ◽  
Voltage Rise ◽  
Test Base ◽  
Impulse Discharge ◽  
Lightning Impulse

In order to optimize the design of UHV substation and reduce its construction investment, it is necessary to take further research of UHV substation air-gap discharge characteristics. In this paper, by using sub-conductor and tower to simulate UHV substation air-gap, lightning and switching impulse discharge characteristics tests of UHV substation are taken in the UHV AC test base of SGCC. The results show that, when the distance of conductor between tower is in range of 4m to 7m, the 50% lightning impulse and switching impulse discharge voltage rise along with the rise of air gap distance. As the air-gap increases, the switching impulse discharge voltage presents the trend of saturation. According to the analysis of test results, we can draw a conclusion that the gap factor of switching impulse discharge can be 1.22 when the minimum distance between conductors and tower is 5~8m.

Rigidité diélectrique d'un interface gaz–support avec contaminant métallique dans l'air sec et ses mélanges avec le SF6

2006 ◽  
Vol 84 (5) ◽  
pp. 381-398
Author(s):  
Adolphe Moukengué Imano
Keyword(s):  
Dielectric Strength ◽  
Partial Discharges ◽  
Dry Air ◽  
Voltage Stress ◽  
Flashover Voltage ◽  
Lightning Impulse ◽  
Conducting Particle ◽  
Series Of Experiments ◽  
Inception Voltage ◽  
Floating Electrode

In this paper, we conduct a series of experiments aimed at analysing the dielectric properties of compressed dry air, and some SF6–air mixtures up to 700 kPa, under application of AC 50 Hz and lightning impulse (LI) 1.2 μs/50 μs voltage. The investigations were carried out by using a cylindrical spacer model with an adhering particle on the surface under homogenous field conditions. We measure the partial discharges (PD) propagation characteristics under LI voltage stress, as well as the PD inception voltage and the flashover voltage for the contaminated particle. We also investigate the surface charge accumulation on the spacer surface under contaminated particle conditions. The results of the experiments reveal the influence a conducting particle has on the determined flashover field strength, for SF6–air mixtures compared with pure, compressed dry air. This influence is discussed for different particle lengths, but also for three different particle positions in the gap. Pure dry air achieves a higher dielectric strength when the particle gets into contact with the high voltage electrode, under negative LI voltage stress. The same result is obtained for the SF6–air mixtures, when the particle is located in the middle of the gap, as floating electrode on the spacer surface. The reported results contribute to the improvement of the models of breakdown through the interface gas–solid isolator. The application of these models should offer the possibility for considering the use of dry air, or its mixtures with SF6 which, normally have a lower relative global warming potential than pure SF6.[Traduit par la Rédaction]

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