Basic Insulation Level Research Articles

Research and experiment the wireless passive surface acoustic wave technology for conductor temperature monitoring of high voltage equipment

This paper presents the research and design of a passive thermal monitoring system using wireless temperature sensors based on the principle of surface acoustic wave (SAW). The monitoring system is employed on components that need to be monitored for heat generation, including switch contacts, busbars, and cable connections at switchgears or ring main units (RMUs). The basic impulse insulation level (BIL), or voltage spike tolerance, of the wireless SAW temperature sensor utilised in this study, means that it is not necessary to power it with sensors that meet the high criteria for equipment installed in closed cabinets or medium voltage cabinets. The research team’s activities in this study included software development, data transmission design and manufacture, and sensor selection. The system functions steadily, with a temperature error of no more than 2oC, according to the test findings under laboratory settings.

Parallel Induction Analysis for Reduction of Interference Due to Lighting Strikes At 70 kV SUTT Parakan-Kadipaten

SUTT 70 kV Parakan-Kadipaten is one of the transmission networks located in areas with high lightning activity so that there is the potential for interference. If the voltage (V) caused by lightning > Basic Insulation Level (BIL) insulator, a backflash over will occur. One of the efforts made to minimize interference is by paralleling the tower inductance with NA2XSY cable which has a lower inductance than the tower. This study aims to determine the installation method and the effect of parallel installation of inductance to reduce interference due to lightning strikes. The research was carried out by performing calculations to determine the lightning Vimpuls before and after the parallel inductance and then comparing it with the BIL value of the insulator and network disturbance data. If the lightning Vimpuls > BIL insulator then a backflash over occurs and if the lightning Vimpuls < BIL insulator then there is no backflash over. From the calculation results, it is found that the value of lightning Vimpuls before parallel inductance > BIL insulator and after parallel inductance drops significantly to < BIL insulator. Meanwhile, when compared with the fault data 3 years before and 3 years after parallel, the fault inductance also decreased. In the year before the parallel inductance, namely 2015 there were 4 disturbances, in 2016 4 disturbances, in 2017 1 disturbance, and in 2018 the January-June period there were no disturbances. In the year after the parallel inductance installation, namely in 2018 for the July-December period there were no disturbances, in 2019 there were no disturbances, in 2020 there were 2 disturbances, and in 2021 the period (January-June) had 2 disturbances.

Analisis Perbaikan Sistem Pentanahan Tower 70 kV pada Transmisi Wlingi - Blitar

70 KV High Voltage Air Line (in Indonesian known as SUTT) is defined as part of an electric power transmission network that islikely to be struck by lightning. This condition may lead to back flashover (BFO) phenomenon if the grounding value in the transmission is found to be high (&gt;5 Ohms) and may also generate equipment failure. This research was intended to analyze the grounding improvement in tower T17, so that traveling-wave voltages may not result in failure of the main equipment at the substation, specifically the transformer. The value of the traveling wave at the substation was measured through simulation by means of the ATP Draw application in tower T17 to the substation. The grounding value may be reduced by increasing and widening the distance between the electrodes. The value obtained by modeling 4 electrodes with a distance of 0.5 meter was amounted to 1.73 Ohms. Furthermore, modeling 3 electrodes with a distance of 1 meter had successfully generated a value of 1.06 Ohm, and a value of 1.67 Ohm was also successfully obtained through modeling 2 electrodes with a distance of 2 meters. The ground resistance with a value of 67.05 Ohms that has not been repaired will lead to back flashover (BFO) caused by lightning strikes. However, this may be reduced properly with a lightning arrester which is capable of cutting the overvoltage at the substation, so that the voltage entering the transformer is below the BIL (Basic Insulation Level) value.

7.2 kV Three-Port SiC Single-Stage Current-Source Solid-State Transformer With 90 kV Lightning Protection

This article proposes a multiport modular single-stage current-source solid-state transformer (SST) for applications like photovoltaic, energy storage integration, electric vehicle fast charging, data center, etc. The 7.2 kV 50 kVA current-source SST consists of five input-series output-parallel modules, each based on 3.3 kV SiC reverse-blocking <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> -plus-diode modules. The proposed SST has some unique features. First, compared with the voltage-source or matrix converter-based SSTs, the current-source SST has a unique advantage of single-stage isolated ac/dc or ac/ac conversion with an inductive dc link, but no medium-voltage (MV) ac experiments have been reported. This article for the first time demonstrates MV ac current-source SST up to 7.5 kV peak. Second, the multiport SST has a buffer port for active power decoupling (APD) or energy storage integration. The double-line-frequency power ripple from single-phase ac grid normally results in a large capacitor size in MV SSTs. The APD scheme is proposed in MV applications for the first time to enable a reduced dc link and the electrolytic capacitor-less SST with high reliability. Third, for a direct grid-connected converter without line-frequency transformer, insulation and protection are critical. A medium-frequency transformer design passes 55 kV basic-insulation level (BIL) and 60 kV high potential dielectrics withstand test with only 0.09% leakage inductance. Importantly, a lightning protection scheme is presented to protect the SST itself from 90 kV BIL impulse. Fourth, the proposed current-source SST topology is a modular soft-switching solid-state transformer (M-S4T) with full-range zero-voltage switching and controlled <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv/dt</i> for low electromagnetic interference. These concepts are verified in a three-port M-S4T prototype with forced oil cooling under single-module, stacked-module, steady-state, and dynamic operations.

A New Method to Distinguish between Nearby and Direct Lightning Strikes for Long Operational Medium Voltage Lines

Lightning strikes near Medium Voltage (MV) electricity distribution lines cause voltage transients to be induced onto the conductors of the power lines. The resultant Lightning Induced Overvoltage (LIOV) on the phase conductors may be estimated using computer models or measurements. Models and measurements are mostly limited to short floating lines to simplify calculations and to ensure accurate results that can be easily compared between different models. Existing measurement methods cannot be used to distinguish between nearby lightning and direct lightning strikes to an operational MV network by using only one instrument on a line that is more than 100 km long. The instrument needs to be less than a hundred meters from where the LIOV amplitude on the line is the highest. The new method described in this paper allows one to distinguish between nearby and direct lightning strikes to the line; by comparing the polarity of the current transient recorded at the substation to the lightning return-stroke polarity obtained from a lightning detection network. The new method also allows one to determine whether the LIOV of a particular lightning transient exceeded the Basic Insulation Level (BIL) of the line, by observing the power frequency fault current. The new method was applied to an operational 714 km network operating at 22 kV, and the results were compared with predictions in IEEE Std 1410-2010. Significantly fewer line faults due to nearby lightning were observed than predicted; the reason for this is explained.

Insulation Coordination Design for Grid-Connected Solid-State Transformers

The deployment of solid-state transformers (SSTs) in medium-voltage (MV) distribution systems is facing various challenges, especially the challenge of insulation coordination design against grid-originated lightning impulses. In this article, two challenges in existing insulation coordination designs for grid-connected SSTs are identified. One challenge is the mismatch between metal-oxide varistor (MOV) protective levels and SST insulation strength, the other challenge is the incompatibility of standard impulse test on SST protective structures. To address the MOV selection challenge, a novel lightning protection scheme is designed to protect a single-stage SST where the semiconductor modules are directly exposed to external lightning impulses. The in-lab lightning impulse tests are performed to verify the overvoltage attenuation performance of the prototyped lightning protection scheme. To address the impulse test challenge, the surge withstand capability of the protected SST is comprehensively evaluated with a complete set of insulation coordination design procedures beyond the basic insulation level (BIL) test. After these two challenges are addressed, a discussion is presented on substituting conventional transformers with the protected SSTs into insulation-coordinated distribution systems to facilitate the field deployment of SSTs.

Systematic Approaches and Analyses on Voltage Uprating of 132 kV Transmission Lines: A Case Study in Malaysia

With the ageing infrastructure and fast-growing demand faced by utilities worldwide, voltage uprating is one of the most effective solutions and strategic approaches in asset management decisions. In this study, a systematic voltage uprating method is used to propose the new voltage level, based on the existing transmission lines’ physical structure, by utilising appropriate techniques. Prior to work conducted, the existing 132 kV transmission line was first examined in terms of the clearances and the components attached, and a technical issue on the clearance under still air was found to be a significant concern, particularly on phase-to-earth arrangements. Next, the proposed techniques and processes, by increasing the insulation strength and improving air conductor clearances, were used for the individual existing 132 kV transmission tower. The proposed voltage uprating of the 132 kV transmission tower comprehensively examines phase-to-earth under normal and extreme wind conditions based on electrical clearance requirements for 275 kV transmission lines. The proposed uprating model was then simulated using the Finite Element Method (FEM)-based commercial software under several lightning conditions, i.e., various basic lightning insulation levels (BIL) and different flashover mechanisms, taking into consideration still air and wind conditions for the voltage profile and its insulation strength analyses. The study found that the voltage profile condition for the proposed voltage uprating model was able to withstand its BIL under all conditions and thus satisfied the electrical requirement needed.

Investigation of the impact of a standard lightning impulse on the structure of an 11/0.415 kV distribution transformer

In this paper a model has been proposed to investigate the effect of Standard Lightning Impulses at voltages below the Basic Insulation Level (BIL) on winding geometry, based on the extraction of resistances, inductances, capacitances and conductance using Finite Element Method (FEM) and the resultant structural movement. The winding and insulation in a transformer can be subjected to overvoltage surges i.e. lightning strikes and switching events. If the frequency component of the incoming transient surges matches the resonance frequency zone of the transformer windings, the amplification and attenuation of the overvoltages along the windings may result in abnormal voltage stress on the conductors of the winding. Hence, the monitoring of electromagnetic forces and the resultant mechanical stresses are of paramount importance in the minimization of the occurrence of mechanical failure in transformers. The Standard Lightning Impulse (SLI) was induced at the outermost layer of the High Voltage (HV) winding of the 11/0.415 kV transformer and resultant electromagnetic forces acting in axial and radial directions were computed. The computed directional forces were in turn induced to the winding structure to observe the structural behavior. The FEM model was tested using an SLI with a voltage, 35 kV, below the BIL of this class of transformer. The modeling showed that the axial and radial forces impinge a mechanical stress in the outer column supports of the winding structure. This model will allow the investigation of buckling within windings at elevated voltages above the BIL.

Design of a Lightning Protection System for an Overhead 3 kV DC Electrified Railway Line: A Case Study from South Africa

A protection scheme is proposed for the 3 kV DC railway, in Kwa-Zulu Natal province, a region with a high lightning occurrence density. The surge protection was sought by implementing three metal-oxide surge arresters and an overhead ground wire. The purpose of these arresters is determined by their location in the circuit and the points that are vulnerable to adverse lightning effects: an arrester is installed to protect insulators between overhead lines and the supporting metallic mast, an arrester is installed to protect the point of contact between a stationary power supply wire and the train, and an arrester is installed to protect apparatus associated with the running tracks (return rail). An isolated earthing system is explored, and the effects of surge impedances and footing resistances are discussed. The voltage dropped across relevant vulnerable components and energy absorbed by the system components are determined by the simulation software Simulink. These results are compared with a railway system outfitted with the designed lightning protection mechanisms. Lightning currents are injected into the system using Heidler function where the parameters are in compliance with lightning protection standards. It is observed that the protection mechanisms defend susceptible components to a specified level. This demonstrates the success of the design in accordance with arrester protection levels (73.3 kV) and equipment withstand capabilities (a basic insulation level of 143 kV). This offers a protection margin of 95%. The largest percentage overshoot in the system is 39%, and this value is substantiated using reflection phenomena.

Modeling of transient caused by lightning strike at Nias high voltage substation using ATP-EMTP case study

Lightning has always been a dangerous threat to power system equipment consisting of: power plants, substations, transmission lines and distribution lines. Commonly, the overhead high voltage transmission line is subjected to lightning strikes. Therefore the protection level against lightning is determined based on the level of insulation of equipment. To prevent damage due the equipment due to a lightning strike, an arrester is used. In this study, three models of arrester are used as comparison viz. IEEE arrester model, Micaela arrester model and Karbalaye arrester model. The system were simulated by using the Alternative Transients Program (ATP) software. The results show that the lightning arrester is declared successful in protecting the transmission system, where the three lightning arresters have Margin Protection (MP) arrester which reaches 28%. In the simulation, it is known that the IEEE and Karbalaye arrester successfully breakdown the lightning current in transmission system so that the transient overvoltage recorded on the transformer does not exceed the Basic Insulation Level (BIL) value of the transformer. While the Pincenti arrester has also succeeded in reducing the voltage on the system but its value is greater than the transformer BIL of the substation, Teluk Dalam, Nias

Voltage stress reduction for distribution line covered conductor

Interruptions due to vegetation frequently occur at the distribution line in Indonesia. Follows to that, the distribution utility decided to replace the bare conductor with the one-layer XLPE cable. However, new problems occurred mainly at the link between the XLPE cable and the post insulator on each of distribution pole. The high permittivity material of XLPE and the ceramic insulator enhance the local electric field that produces pinholes on cables. In the later phase, the pinholes become more extensive and if there is a lightning strike that causes a voltage that exceeds the Basic Insulation Level of the insulator, then the electric arc will flow from the conductor to the ground isolator through the pinhole. This paper proposed a novel design to cover the cable, including its accessories. Based on a simulation using a finite element analysis, the electric field stress is reduced by the following steps: 1. Add a semiconductor layer on the XLPE layer, 2. Replace the ceramic insulator with the polymer one, 3. Modify the binding between the cable and the post insulator by using a unique clamping method.

Reinforcement Learning Based Recloser Control for Distribution Cables With Degraded Insulation Level

Utilities continuously observe cable failures on aged cables that have an unknown degraded basic insulation level (BIL). One of the root causes is the transient overvoltage (TOV) associated with circuit breaker reclosing. To solve this problem, researchers propose a series of controlled switching methods, most of which belong to deterministic control. However, in power systems, especially in distribution networks, the switching transient is buffeted by stochasticity. Since it is hard to model transient overvoltage due to its complexity, we propose a model-free stochastic control method for reclosers under the existence of uncertainty and noise. Concretely, to capture high-dimensional dynamics patterns, we formulate the recloser control problem by incorporating the temporal sequence reward mechanism into a deep Q-network (DQN). Meanwhile, we embed our physical understanding of the problem into the action probability allocation and develop an infeasible-action-space-elimination algorithm. Through PSCAD simulation, we first reveal the impact of load types on cables' TOVs. Then, to reduce the training burden for the proposed reinforcement learning (RL) control method in different applications, we establish a post-learning knowledge transfer method. After the validation with our industrial partner, we exhibit several learning curves to show the enhanced performance. The learning efficiency is proved to be outstanding due to the proposed time sequence reward mechanism and infeasible action elimination method. Moreover, the results on knowledge transfer demonstrate the capability of method generalization. Finally, a comparison with conventional methods is conducted. It illustrates the proposed method is most effective in mitigating the TOV phenomenon among three methods.

A novel approach for basic insulation-level (BIL) enhancement of vacuum interrupters

This article introduces a newly developed design method that may be utilized in modern high-voltage vacuum interrupter (VI) design. At first, a typical 24 kV vacuum chamber is modeled using finite-element method. Potential and electric field profiles are derived and analyzed in detail. To continue, the proposed approach which consists of twin metallic rings placed in the porcelain tubular insulator is added to the previous model and the new model is analyzed in three steps: short-, medium- and long-course scenarios. The achieved patterns illustrate the severe reduction in electric field value of the contacts' surface especially for long-course prototype (up to 74.2%). This phenomenon is discussed in detail. Considering the Fowler–Nordheim quantum tunneling equation; a reduction in electric field intensity brings to lower field emission current value which is the most important factor of breakdown during BIL tests. It is important to note that any reduction in electric field value results in decrease in micro-discharge value and microparticle movement, which are the additional reasons for vacuum insulator failure during high-voltage pulse insertion. This means that the inception voltage of the proposed VI can be increased so that higher BILs like 63 kV insulation high voltage requirements are achieved. The reduction rate of field emission current density is reduced to 4.9% of its initial value for or 120-mm course which expresses the effectiveness of this new approach.

Closed-Form Expressions for the Estimation of the Minimum Backflashover Current of Overhead Transmission Lines

The minimum backflashover current, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BF</sub> , of typical overhead transmission lines is estimated through ATP-EMTP simulations considering the tower ground resistance and AC voltage phase angle as parameters. Several single- and double-circuit lines are investigated with operating voltage from 66 kV to 765 kV and Basic Insulation Level from 325 kV to 1950 kV. The backflashover rate, BFR, of the investigated lines is obtained using an expression that accurately considers lightning incidence to the line for prospective currents higher than I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BF</sub> ; the relevant CIGRE expression underestimates BFR. BFR can be easily estimated using solely the phase angle values corresponding to zero AC voltage of the phase conductors. Based on the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">BF</sub> and BFR results, simple expressions are introduced for the calculation of an equivalent minimum backflashover current as a function of insulator length and tower ground resistance or impulse impedance. These expressions enable straightforward estimation of BFR without the need for time-consuming simulations or laborious analytical methods adopting simplifying assumptions.

Extended Application for the Impulse-Based Frequency Response Analysis: Preliminary Diagnosis of Partial Discharges in Transformer

Frequency response analysis (FRA) with low impulse voltage signals (IFRA) is useful in diagnosing faults like the mechanical displacements and inter-turn shorts in transformers. However, they fail to diagnose the presence of any source of partial discharges (PD) across the oil-paper insulation. PD is happening only above its inception voltage level for the applied signal, thereby changing the loading effect of the insulation system and becoming detectable. If FRA tests are extended carefully up to high voltages, they can be even useful for the preliminary diagnosis of the potential sources of PD. Investigations were not carried out so far to get an insight into this aspect. Motivated by this, an investigation was done, first time, on a 315 kVA, 11 kV/433 V transformer. IFRA was carried out carefully at various voltage levels, up to 50% of the Basic impulse insulation level. The IFRA results of the transformer under its healthier condition, under the emulated inter-turn shorts and, the PD sources across the major-insulation were, observed and compared. Low-voltage IFRA is found sufficient, only for diagnosing the inter-turn shorts. When IFRA is extended to moderately high voltage, it is found useful in the preliminary diagnosis of the PD sources.

Protection of 25 kV electrified railway system

Improving the reliability of an electrified railway operation system requires protection against overvoltage, particularly those of atmospheric origin. The most serious threat to the traction system is lightning when it strikes the mast or conductors. The ZnO arresters are used to protect a system from this phenomenon. In the present investigation the system under study is developed and each element is represented by a model corresponding in EMTP program and some elements are modelled using the models section in ATP EMTP. Protective effect of the surge arrester and discharge current which passes through it is analysed and discussed in case lightning strikes a mast. The simulation results have shown that the surge arrester reduces overvoltage in primary power transformer traction below the basic insulation level, under critical conditions.

Impulse dielectric behaviour of dry air in sphere‐plane gap

The dielectric strength of dry air is lower than that of SF6, so it is very difficult to use dry air in extra-high-voltage-class gas-insulated equipment. However, due to its environment-friendly property, dry air is expected to be an alternative to SF6 in low-voltage level gas-insulated equipment. In order to study the possibility of dry air to be applied in equipment in the power distribution system, streamer and breakdown phenomena of dry-air need to be carefully investigated. This study carried out an experimental study of impulse breakdown phenomena of dry air under a quasi-uniform electric field. Results showed that the impulse breakdown voltage of dry air is higher under the positive polarity. Under the gas pressure of >0.4 MPa, the impulse breakdown voltage of minus 50% (V 50%) of dry air is >150 kV, which satisfies the basic impulse insulation level of the power distribution system equipment. Further, in the quasi-uniform electric field, once streamer discharge appears, it always triggers an electrical breakdown. The development mechanisms for the breakdown of dry air under both positive and negative polarities are well discussed in this paper.

KAJIAN PEMASANGAN LIGHTNING ARRESTER PADA SISI HV TRANSFORMATOR DAYA UNIT SATU GARDU INDUK TELUK BETUNG

Generally, The power centers are connected to the air transmission line, and the airborne transmission channel is susceptible to disturbances that are affected from outside the system, one of which is a lightning strike. Lightning strikes are harmful to the components present in the central power supply. And therefore, the protection from the lightning strikes is required, so that the components in the power center is not damaged when exposed to lightning surges. In this research we discussed the power transformer protection (60MVA) on the Teluk Betung substation so that the power transformer is safe from the over voltage caused by the lightning surge. The specification of the arresters mounted on the HV side of the power transformer unit one of Teluk Betung substation with nominal voltage of 144 kV has been in accordance with the system requirements. The maximum distance between the arrester and the allowable power transformer is 28.5 meters. Distance in the field is 3 meters, the voltage that arrives at the power transformer is 480 kV and still below the Basic insulation level of the transformer, so that the protection of the power transformer against the lightning surge is very good.

Effect of High Voltage Impulses on Surface Discharge at the Oil-Paper Interface

High voltage transients in electrical power systems are mainly caused by lightning strikes and switching operations. The high voltage transients above the basic insulation level (BIL) would degrade the electrical insulation of the equipment.In this work, the effect of high voltage impulses on the trend of the surface discharge at the oil-paper interface was investigated. The partial discharge patterns were recorded by the Insulation Condition Monitoring (ICM) system. The HV impulses were generated by a standard 1.2/50 μs HV impulse generator. The measurement results presented in this paper seem to show that surfacedischarge would cause complete breakdown (continuous flashovers) at the oil-paper interface much faster when the test sample is first aged by HV impulses comparedto when it is unaged.

Covered conductor burn-down prevention for distribution line in Indonesia

Covered conductor (CC) is used to resolve temporary line to ground fault in the distribution line. However, some cases of CC burn down were found in Indonesia. These phenomena were triggered by lightning strikes that cause transient overvoltage with a magnitude greater than basic insulation level (BIL) of insulator. Consequently, short circuit current will flow through the pinhole on CC. Burn down phenomena will create high impedance fault that is unable to be detected by protection relay, thus the conductor will remain energized and harmful to the surroundings. Therefore, this paper presents study about CC burn down prevention. The study was performed using transient simulation to find the effect of earth wire utilization against the transient overvoltage due to lightning strike. In addition, finite element simulation and laboratory testing were also performed to analyze the effect of power arc device on burn down prevention. The results show that the lightning strike with negative polarity will not cause transient overvoltage with a magnitude greater than the insulator BIL. However, if the lighting strikes have positive polarity then the insulator BIL will be potentially exceeded. Furthermore, the utilization of power arc device will prevent the CC burn down.