Search Results (10)

Current-limiting superconducting cable uses the quench resistance of superconductor under short-circuit current to improve the short-circuit impedance of the system. In this paper, the design of current-limiting 10 kV three-phase tri-axial superconducting cable is studied. The design methods of cable conductor layer, insulation layer and current-limiting characteristics are given, and one 5 m-long sample is fabricated for testing. The sample is made of stainless-steel-reinforced yttrium barium copper oxide (YBCO) tape, with an expected rated current of 2.5 kA and rated voltage of 10 kV. The test results show that the designed cable can transmit a maximum AC current of 3.0 kA at 77 K. The cable has passed the power frequency withstand voltage, partial discharge and lightning impulse tests. The current limiting characteristics under the action of DC pulse current show that the cable can quickly quench and produce resistance, and the corresponding equivalent resistance value also changes along with current amplitude and duration. Full article

The on-site measurement of transient voltages is of great significance in analyzing the fault cause of power systems and optimizing the insulation coordination of power equipment. Conventional voltage transformers normally have a narrow bandwidth and are unable to accurately measure various transient voltages in power systems. In this paper, a wideband parallel resistive–capacitive voltage divider is developed, which can be used for online monitoring of transient voltages in a 220 kV power grid. The structures of the high-voltage and low-voltage arms were designed. The internal electric field distribution of the high-voltage arm was analyzed. The influence factors and improvement techniques of the upper frequency limit were studied. The parameters of the elements of the divider were determined. The voltage withstand performances and scale factors under lightning impulses and AC and DC voltages, the temperature stabilities of scale factors and the step response and bandwidth of the developed voltage divider were tested. The results show that the deviations of the scale factors under various voltage waveforms and different temperatures ranging from −20 to 40 °C are within 3%. The withstand voltage meets the relevant requirements specified in IEC60071-1-2011. The step response 10~90% rise time is approximately 29 ns, and the 3 dB bandwidth covers the range of DC to 10 MHz. Full article

Transformer oil does not only serve as an insulating liquid, but also in removing heat from the windings and cores. Mineral oil (MO) has been widely used in transformers for more than 150 years. Recently, researchers have attempted to search for alternative insulating oils due to the possibility that MO will run out in the future together with the concern on fire safety and environmental pollution. Among the potential oils is rice bran oil (RBO). This work presents the studies of the lightning impulse (LI) of RBO behavior under various electric fields, gap distances and testing methods. The electrical performances of LI tests show that RBO and Palm Oil (PO) have lower LI breakdown voltage than MO under both uniform and non-uniform electric fields. However, the difference in LI breakdown voltages between RBO, PO and MO are slightly small which is less than 20%. In addition, there is no significant effect in the various testing methods under both uniform field and non-uniform field where the percentages of difference are less than 12% and 8% respectively. The data of LI breakdown voltage were statistically analysed to predict the withstand voltage and 50% breakdown voltage of oil samples by using Weibull distribution. The Weibull distribution of MO, PO and RBO has well fit with the fitting line. Finally, the relationship between LI voltages under a non-uniform field with various parameters of PO and RBO was obtained and proposed. From this work, it can be concluded that RBO shows promising results to be considered as an alternative to MO in transformer applications. Full article

With increased electrical energy demands projected in the future, the development of a hybrid solar photovoltaic (PV)–battery energy storage system is considered a good option. However, since such systems are normally installed outdoors and in open areas, they are vulnerable to lightning strikes and may suffer from malfunctions or significant damage to sensitive components, which may result in a major breakdown and loss of revenue due to equipment replacement costs and inefficient operation. Thus, the objective of this paper is to investigate the effect of lightning-induced overvoltage on a hybrid solar PV–battery energy storage system, considering indirect lightning strikes nearby the system. The presented hybrid solar PV–battery energy storage system and lightning-induced overvoltage are modeled in Electro-Magnetic Transient Program-Restructured Version (EMTP-RV) software. The lightning-induced overvoltage is simulated based on a lightning waveshape of 10/350 µs using the Heidler expression, whilst the Rusck model is used to simulate the lightning-induced overvoltage. Different lightning current amplitudes (3, 19, and 169 kA), lightning strike locations (20, 50, and 100 m), and cable lengths (5, 10, and 20 m) are used to investigate the induced effects on the system and on the impulse withstand voltage of 6kV, as stated in MS IEC 60664-1 for solar PV–battery systems and inverters at the DC side. The results indicate that as the lightning strike distance increases from 20 to 100 m, the percentage of strikes exceeding the impulse withstand voltage reduces from 67% to 54% at 19 kA. At 169 kA, the impulse withstand voltage is exceeded by more than 100%, regardless of the strike distance (from 20 to 100 m). Furthermore, differences in cable length do not have much impact on the lightning-induced overvoltage due to the small voltage drop across the short cable length. This study provides useful information for PV systems owners and will be useful in assigning appropriate lightning protection schemes for PV farms. Full article

Building Integrated Photovoltaic (BIPV) modules are a new type of photovoltaic (PV) modules that are widely used in distributed PV stations on the roof of buildings for power generation. Due to the high installation location, BIPV modules suffer from lightning hazard greatly. In order to evaluate the risk of lightning stroke and consequent damage to BIPV modules, the studies on the lightning attachment characteristics and the lightning energy withstand capability are conducted, respectively, based on numerical and experimental methods in this paper. In the study of lightning attachment characteristics, the numerical simulation results show that it is easier for the charges to concentrate on the upper edge of the BIPV metal frame. Therefore, the electric field strength at the upper edge is enhanced to emit upward leaders and attract the lightning downward leaders. The conclusion is verified through the long-gap discharge experiment in a high voltage lab. From the experimental study of multi-discharge in the lab, it is found that the lightning interception efficiency of the BIPV module is improved by 114% compared with the traditional PV modules. In the study of lightning energy withstand capability, a thermoelectric coupling model is established. With this model, the potential, current and temperature can be calculated in the multi-physical field numerical simulation. The results show that the maximum temperature of the metal frame increases by 16.07 °C when 100 kA lightning current flows through it and does not bring any damage to the PV modules. The numerical results have a good consistency with the experimental study results obtained from the 100 kA impulse current experiment in the lab. Full article

Lightning stroke on a transmission tower structure is one of the major reasons that results in high voltages at the tower arms due to the excessive lightning current flowing through the transmission tower to earth. The Surge voltage seen at the tower cross arm on the first tower close to a substation is the worst case. If this voltage is higher than the withstand level of the insulator string, the insulation of substation equipment will be exposed to transient over-voltage called fast front back-flashover (FFBF). The peak of this transient overvoltage is affected by the value of the system’s earthing resistance. This paper studies the effect of reducing the grounding resistance of both the surge arrestor (SA) and the first transmission line tower adjacent to a 66 kV substation on FFBF. Three case studies using PSCAD/EMTDC software are presented to simulate the variation of the potential sire at the substation equipment with different resistance values for the first tower and SA earthing resistance. The paper also addresses the economic protection system for solving the problem of transient overvoltage. The study proves that the proper design of the first tower grounding system enhances the safety of the system and reduces the cost for the grounding system to the minimum. Full article

The design, construction and characterization of a photonic voltage transducer with a lightning impulse protection for distributed measurements on medium voltage (MV) networks (11 kV) was presented in this paper. The sensor prototype, comprising a combination of a piezoelectric transducer and a fibre Bragg grating (FBG) as a core optical sensing element, and a dedicated lightning protection device comprising a set of reactive components, was evaluated through laboratory testing and its performance was assessed based on the accuracy requirements specified by the relevant industry standards. It was demonstrated that the sensor has the potential to meet the accuracy requirements for the 3P protection and 0.2 metering classes specified by the IEC 60044-7. The device successfully underwent lightning impulse withstand tests, satisfying the safety requirements applicable to 11 kV networks as specified by the standard. The usage of an FBG as a photonic sensing component enables the multiplexing of multiple such sensors to provide the distributed measurement of voltage along a power network. Full article

In view of the problem that ZnO varistors are often subjected to thermal breakdown and deterioration due to lightning strikes in low-voltage power distribution systems, this article used a 8/20 µs multi-pulse surge current with a pulse time interval of 50 ms to perform shock experiments on ZnO varistors. SEM scanning electron microscope and an XRD diffractometer were used to analyze the structure of the grain boundary layer and the change of the crystalline phase material of ZnO varistor under the action of a multi-pulse current. The damage mechanism of ZnO varistor under the multi-pulse current was studied at the micro level. The results show that the average impact life of different types of ZnO varistor is significantly different. It was found that the types of trace elements and grain size in the grain boundary layer will affect the ability of ZnO varistor to withstand multi-pulse current. As the number of impulses increases, the grain structure of the ZnO varistor continues to degenerate. The unevenness of internal ion migration and the nonuniformity of the micro-grain boundary layer cause the local energy density to be too large and cause the local temperature rise to be too high, which eventually causes the internal grain boundary to melt through, and the local high temperature may cause the Bi element in the ZnO varistor to change in different crystal phases. Full article

As one of the key technologies to solve the problem of high short-circuit current, the fault current limiter (FCL) has become a research hotspot in China and abroad. The overvoltage and protection measures of the FCL are the key technologies for its application. Therefore, this paper studies the lightning intruding overvoltage and protection measures for a 500 kV FCL based on a high coupled split reactor (HCSR). Firstly, according to the main topology of the system and the 500 kV HCSR-FCL structure, the lightning intruding overvoltage simulation model of the 500 kV station, including the nearby transmission lines, is established on the PSCAD (Power Systems Computer Aided Design) program. Secondly, the lightning overvoltage of the equipment in the station and the components of the HCSR-FCL are simulated and analyzed when the transmission lines nearby are subjected to lightning shielding failure and back flashover. Meanwhile, the influence of the HCSR-FCL on the lightning overvoltage of the equipment in the station are compared and analyzed before and after the HCSR-FCL is installed. The simulation results show that the overvoltage of the equipment in the station and the components of the HCSR-FCL is more serious when the shielding failure occurs in the transmission lines nearby. The HCSR-FCL can reduce the lightning overvoltage of the equipment in the station, but the maximum inter-terminal and inter-arm lightning overvoltage of the HCSR can reach 1064 kV and 790 kV, respectively, under the current limiting state and the current sharing state. Finally, methods of increasing the arresters on the transmission lines side of the HCSR-FCL and shunt capacitor between each module of the HCSR-FCL are proposed to reduce the lightning overvoltage. The lightning impulse withstand voltage of each component of the HCSR is also proposed: The inter-terminal lightning impulse withstand voltage of HCSR is 170 kV. The inter-arm lightning impulse withstand voltage of HCSR is 200 kV. The terminal-to-ground lightning impulse withstand voltage of the HCSR-FCL is 1550 kV. Full article

This paper presents lightning (1.2/50 µs) breakdown voltages of palm oil (PO), coconut oil (CO) and mineral oil (MO) in a quasi-uniform sphere to sphere electric field at two gap distances. The type of PO used in this study is Refined Bleached Deodorized Palm Oil (RBDPO) Olein type. The effect of voltage polarities (positive and negative) and testing methods (rising voltage, up and down and multiple level) on the lightning breakdown performance were investigated. The results indicated that lightning breakdown voltages of CO and RBDPO are comparable to those of MO under various test conditions. The results indicated that there is no polarity effect for lightning impulse breakdown tests in a quasi-uniform field. The testing methods, including rising voltage method, up and down method and multiple level method have a notable influence on the breakdown voltages. The effect of the 50% breakdown voltage on rising voltage method, up and down method and multiple level method for RBDPO and CO is comparable to MO. The withstand voltage at 1% and 50% breakdown probabilities were obtained using the Normal distribution fitting on the cumulative probability plot of impulse shots. Based on a normal distribution fitting, withstand voltages 1% breakdown probability of POA were close to the MO. Finally, based on statistical studies and simulation using ANSYS software, the prediction formulas for breakdown voltage for larger gap distances for all samples were derived. Full article