Pre-insertion Resistors Research Articles

Pre‐insertion resistors temperature prediction based on improved WOA‐SVR

AbstractThe pre‐insertion resistors (PIR) within high‐voltage circuit breakers are critical components and warm up by generating Joule heat when an electric current flows through them. Elevated temperature can lead to temporary closure failure and, in severe cases, the rupture of PIR. To accurately predict the temperature of PIR, this study combines finite element simulation techniques with Support Vector Regression (SVR) optimized by an Improved Whale Optimization Algorithm (IWOA) approach. The IWOA includes Tent mapping, a convergence factor based on the sigmoid function, and the Ornstein–Uhlenbeck variation strategy. The IWOA‐SVR model is compared with the SSA‐SVR and WOA‐SVR. The results reveal that the prediction accuracies of the IWOA‐SVR model were 90.2% and 81.5% (above 100°C) in the ± 3°C temperature deviation range and 96.3% and 93.4% (above 100°C) in the ± 4°C temperature deviation range, surpassing the performance of the comparative models. This research demonstrates that the method proposed can realize the online monitoring of the temperature of the PIR, which can effectively prevent thermal faults PIR and provide a basis for the opening and closing of the circuit breaker within a short period.

Electrical-thermal coupling characteristics of pre-insertion resistors in AC filter circuit breaker for UHV grid.

The ultra-high voltage (UHV) AC/DC grid can provide a platform for sustainable power worldwide. To improve the bus voltage quality of the UHV AC system, AC filters are frequently switched into the UHV grid through circuit breakers with pre-insertion resistors. The pre-insertion resistors suppress inrush currents and operate over-voltage during switching. In this paper, we establish a macro and micro model of the pre-insertion resistor based on its temperature coefficient and micro-morphology. We simulate and analyze its electric-thermal coupling characteristics under standard closing and short-circuit faults. After the simulation model and physical comparison analysis, we find that under a usual closing surge, the electric field distribution of the pre-insertion resistor is uniform and undergoes a slight rise in temperature. However, under a short circuit fault, the temperature rise is drastic and exceeds the maximum allowable temperature, causing glassy melt in some parts of the resistor. Considering the volume ratio of each component of the resistor, a two-dimensional cross-sectional simulation model of the resistor is established to simulate the electric-thermal characteristics of the microstructure of the resistor, and insinuates that the current is concentrated in the carbon channel. That is mainly due to the uneven distribution of carbon material and may lead the local temperature to exceed the maximum allowable temperature and damage the resistor.

Energization Transient Suppression of 750 kV AC Filters Using a Preinsertion Resistor Circuit Breaker With a Controlled Switching Device

Different from typical circuit breakers, breakers used to switch AC filters in convertor stations have to operate frequently according to the real-time operation mode and daily load changes. Therefore, the performance of filter breakers decreases very quickly, which leads to frequent accidents. Both preinsertion resistors and controlled switching devices can suppress switching transients. In this paper, a comparative analysis of whether a controlled switching device and preinsertion resistor should be adopted is carried out using PSCAD. The transient is calculated as the combined result of the switching angle and preinsertion resistor value, and the optimal configurations are proposed. After determining the resistor value and whether a controlled switching device should be included, the reference voltage of the arrester should be reevaluated.

Virtual Resistance Control for Sequential Green-Start of Offshore Wind Power Plants

The changing energy landscape due to the large scale integration of renewable energy and shutting down of conventional thermal plants has opened up the potential of alternate sources in the blackstart services market. Grid forming wind turbines can do controlled islanded operation independent of an external grid voltage and thus participate in network restoration from the start. However, it is necessary to study the capability of wind turbines to deal with the demanding energization transients in a controlled and stable manner. This work investigates the feasibility of using virtual resistance in the wind turbine converter control to reduce transients during self-transformer inrush and sympathetic interaction from downstream string transformers. This can eliminate the need for pre-insertion resistors during sequential energization. The sensitivity of the AC current and voltage output along with DC link transient to the virtual resistance parameters has also been analyzed using PSCAD simulations. Finally the effectiveness of the proposed method for offshore network energization by a grid forming wind power plant has been tested by comparing to results for a pre-insertion resistor.

Research on operation and fault diagnosis technology for EHV/UHV SF6 circuit breakers pre-insertion resistors

Pre-insertion resistors (PIR) are critical components for suppressing the closing inrush current and operating overvoltage during the closing process of the circuit breaker. And it is widely adopted in 800kV and above transmission lines and alternating current filters of converter substations. These special application environments lead to higher failure rates than other electrical components. However, in the daily operation and fault diagnosis of PIR, there is no systematic method to analyze whether there are defects in PIR and the cause of failure after the PIR fails. Based on two PIR failure in series and parallel structures, this paper proposes methods such as dynamic resistance fitting, acoustic and vibration signal detection, insulation performance test, and heat capacity test during operation. In the aspect of fault diagnosis, methods such as PIR splicing based on Iterative Closest Point , stress analysis, and electric field simulation are proposed. Finally, proposed methods can be adjusted to estimate the operating state of PIR through the disassembly inspection to avoid the GIS breakdown accident during the operation of the circuit breaker.

Study on pre‐charging process and pre‐insertion resistors selection of VSC‐HVDC system with different MMC topologies

Here, the uncontrolled rectification pre-charging characteristics of the VSC-HVDC system with different modular multilevel converter (MMC) topologies such as full-bridge, half-bridge, and hybrid topologies are proposed based on theoretical analysis and PSCAD/EMTDC simulations. Different MMC topologies have a great impact on the selection of pre-insertion resistors. The surge energy of pre-insertion resistors is the lowest with the full-bridge sub-module (FBSM) MMC, while much higher with the half-bridge sub-module (HBSM) MMC. In order to prevent start-up failure caused by extremely non-uniform voltage between FBSM and HBSM of hybrid MMC, the FBSM should be turned to half-bridge state by valve control system as soon as possible so as to carry out the second charge, and then balance the sub-modules voltage by bypass certain high-voltage sub-modules. The half-controlled charging process has a great influence on the absorbed energy of the pre-insertion resistors of hybrid MMC. The research results can be used to guide the selection of VSC-HVDC pre-insertion resistors and start-up strategy making.

Controlled switching technique for minimization of switching surge during energization of uncompensated and shunt compensated transmission lines for circuit breakers having pre-insertion resistors

Controlled Switching Device (CSD) is considered to be the replacement of Pre-Insertion Resistor (PIR). Moreover, tie Circuit Breaker (CB) used in One-and-a-Half-Breaker (OHB) scheme as well as in line connected with non-switchable reactor scheme are employed with PIR and CSD. In this paper, a new methodology has been proposed using CSD with PIR-CB for further mitigation of the switching surge during energization/re-energization of Un-compensated Transmission Line (UCTL) and Shunt reactor compensated Transmission Line (SCTL). Unlike the existing methodology (both for UCTL/SCTL) which requires line side voltage signatures, the proposed methodology does not necessitate the same for SCTL and requires only the polarity of line side voltages for UCTL. The performance of the proposed methodology has been evaluated by generating diversified cases on 400 kV UCTL and SCTL using PSCAD/EMTDC software package. The proposed switching strategy is able to mitigate the switching surge of the order of 33% for UCTL and 20% for SCTL. Comparative evaluation of the proposed methodology with usual PIR methodology clearly shows its effectiveness with reference to statistical variations of CB. The proposed methodology has been validated during effects of various parameters such as weather conditions, insulation resistance, change in closing phase sequence, and Surge Arrestor (SA).

The resonance overvoltages in nonsinusoidal modes of extra high voltage transmission lines

Due to the rising role of overhead lines extra high voltage there is a need of application of modern electronic devices that allow controlling modes of bulk electricity system. Durable resonance overvoltage may cause damage of electrical power equipment. This kind of overvoltage is caused by properties of the network and can be eliminated by changing the ratio between the parameters of the network and its mode. Unlike switching overvoltage that exist centiseconds, resonance overvoltage not only occur unexpectedly, but they may go on for a long time until the automatic action or action of personnel will not change electrical schemes or operation modes. The resonance overvoltage are neglected when selecting insulation or parameters for high-voltage surge arrester as this protective measure is calculated to limit switching overvoltage, not to extinguish a long resonance process. Therefore, the probability and development of system accidents due to resonance overvoltage is significant. One of the main causes of equipment failure in the main electrical network is overvoltage. Overvoltage are the values which according to the technical requirements exceed the maximum value of normal operating voltage. The reason is that the relatively small insulation reserve provides for the equipment of the electricity grid because of its high cost for a given voltage. Generally, cost of power systems insulation is a significant factor in capital investment. The main source of distortion in extra high voltage networks is nonlinearity of volt-ampere characteristic of magnetic shunt in unloaded power autotransformer. This mode causes the conditions for the significant overvoltage on even harmonics. It should be noted that the processes of the second harmonic overvoltage are generally known, but their specific occurrence conditions depend on many factors of abnormal mode. That is why the aim of the article is developing measure for reduction and prevention of overvoltage in accordance with conditions for their existence. In investigations residual magnetization is neglected because capacitance between autotransformer and circuit breaker is large enough. In the article the features of the operation of SF6 switches that should be considered when introducing them to the power lines of 750 kV. The switching control unit Switchsync F236 is one of such devices which enables to connect and disconnect contacts of poles circuit breakers at required time. This function of Switchsync F236 can be used not only for interruption of short circuit. One of the objectives of application Switchsync F236 is prevention of resonance overvoltage occurrence at closing extra high voltage line on no-load autotransformer. The analysis of electromagnetic switching transients when operating a three-phase auto recloser with really existing power transmission lines has been implemented. The influence of initial conditions of electromagnetic transients based on simulation has been analyzed. Based on the research it is proposed to use suppression equipment components with aperiodic current line switches. The research of recommended exposure settings of the controlled switching device on duration of current aperiodical component has been done. Recommendations on the use pre-insertion resistors and switching units controlled have been proposed. The importance of application and prevention of resonance overvoltage caused research area which is presented in article. Ref. 11, fig. 6.

Power Testing of Preinsertion Resistors: Limitations and Solution

Preinsertion resistors (PIR) are used in combination with circuit breakers to absorb switching transients and come into effect during the “closing” operation of the breaker. It is mainly used for rated voltages equal to or higher than 420 kV for line lengths above 200 km. Although it is an important component, power testing of complete PIR is very complicated and not well defined. Therefore, an attempt has been made in this paper to provide alternative test methods for power testing of PIR without compromising its important parameters. Due to high energy requirements and limitations of the test laboratory, a multipart testing of PIR is necessary to prove its thermal capability and dielectric behavior. Before proceeding with the complete PIR test, the critical parameters of PIR, such as mechanical insertion time, rate of decay of dielectric strength of the interrupter, and PIR switch, etc., should be verified with testing. These test procedures are also explained in detail along with a method to theoretically evaluate electrical insertion time for different network conditions. The series PIR configuration for the metal-enclosed ${\mathrm{SF}}_{6}$ system has been considered in this paper.

Evaluation of controlled energization of shunt reactors for minimizing asymmetric DC component of charging current with circuit breaker having pre-insertion resistors

Generally, Controlled Switching Device (CSD) is used during de-energization as well as energization operations of shunt reactors. However, for substations configured with One-and-Half Breaker (OHB) or line connected to non-switchable reactor scheme, the Pre-Insertion Resistor Circuit Breaker (PIR-CB) might be used during switching of shunt reactor. This paper presents optimized controlled switching strategy to minimize the level of asymmetric dc component of charging current during energization of a shunt reactor using CSD with PIR-CB. This is achieved by optimizing the insertion instant, value and Electrical Insertion Time (EIT) of PIR. The validity of the proposed technique has been evaluated by generating a large number of simulation cases in PSCAD/EMTDC software package by changing rating & configuration of shunt reactor, EIT, insertion & removal instant and the value of PIR. The simulation results suggest that the proposed methodology maintains the level of asymmetric dc component in charging current of the order of 1.02, 1.11, 1.11 p.u. for grounded star (Yg), un-grounded star (Y) and delta (Δ) configuration of shunt reactor. At the end, field results of energization of 240 MVAr shunt reactor with PIR-CB for line application at 765kV have been presented which clearly depicts mitigation of asymmetric dc component.

Inrush Current Parameters Associated with Back-to-Back Switching of Capacitors in a Bank

Back-to-back switching of 50 kVAr capacitors, in a capacitor bank of 200 kVAr is investigated experimentally. The switching inrush currents in a three-phase, 200 kVAr, 415 V Automatic Power Factor Correction panel at power frequency are captured in the laboratory. The characterizing features of inrush current are reported and analyzed. The commercially available two makes of switches (contactors) are used to compare the inrush currents with and without their pre-insertion resistors (PIR). The inrush current scenario of the experimental setup is modeled in EMTDC/PSCAD to ascertain the results. The ratio Ipeak/IN for both the contactors without PIR exceeded the limit mentioned in IEC 60831-1 Ed 3.0 : 2014.

Investigation and Analysis of Temporary Overvoltages Caused by Filter Banks at Onshore Wind Farm Substation

Parallel resonance generated by capacitive elements on the wind farm amplifies the current distortion caused by harmonic emission from the wind turbines and results in high voltage and current distortion through the transmission equipment connected to the grid. Similarly, series resonance amplifies the harmonic voltage distortion from the HV bus to MV bus, causing the same effect. Harmonic filters are used to screen out the unwanted harmonic effects on the wind farm. The switching activities of the harmonic filter bank may cause overvoltages on the onshore wind farm substation, thus, they are investigated in this paper with the aid of ATP/EMTP software. Temporary overvoltages caused by energising and de-energising of the filter were investigated to understand whether they exceed the withstand limits of the system. It was found that the overvoltages for both energization and denergization were beyond the power frequency withstand level. By then using statistical studies on the mitigation methods, it was found that the use of pre-insertion resistors and surge arresters greatly mitigated the overvoltage caused by energization.

Input filter pre-charge scheme for high-power PWM-current source rectifiers connected to a weak utility supply

High-power PWM current source rectifiers are normally connected to the ac grid by means of a lightly damped LC input filter. Pre-charge schemes employing pre-insertion resistors are typically used to mitigate the over-voltage across the filter capacitors during the connection to the grid. However, noticeable distortion of the grid voltage may still occur during the insertion of the input filter to the grid. This is particularly true at low ratios of the supply fault level to the converter-rated power and cannot be avoided when conventional pre-charge schemes are used. This study proposes a pre-charge scheme that yields a smooth and controllable connection of the input filter to the grid along with total absence of both over-voltage across the input filter capacitors and voltage distortion on the grid. This is novel and it is of particular interest whenever PWM-CSRs are connected to relatively weak grids. Pre-charge is carried out by the main PWM-CSR converter, which is in turn supplied on its dc-side by a small low-power low-voltage pre-charge converter. This completely eliminates the need for any pre-charge components on the ac-side [which can be bulky and expensive at medium voltage (MV) levels]. Experimental results obtained from a 150 kW PWM-CSR are included in the study.

Chaveamento controlado de linhas de transmissão: uma abordagem em tempo real via RTDS™

O objetivo deste trabalho é apresentar um método para chaveamento controlado de disjuntores de linhas de transmissão e desenvolver um dispositivo para controlar o fechamento dos seus contatos. A estratégia de chaveamento consiste em encontrar um instante apropriado para o fechamento do disjuntor e é baseada em um algoritmo simples de detecção de passagem por zero. Pela primeira vez, o método é avaliado em tempo real usando um RTDS TM (Real Time Digital Simulator) e sua implementação se dá de duas formas: na primeira, utiliza-se a ferramenta CBuilder do RTDS TM e na segunda, utiliza-se um DSP (Digital Signal Processor) como dispositivo de controle. Dados do sistema elétrico da CHESF são utilizados para estudos de caso. Diferentes operações de chaveamento são analisadas: energização e religamento de linhas com compensação em derivação, considerando os efeitos da carga residual. O desempenho do método proposto é comparado com o método de resistores de pré-inserção. As simulações confirmam a eficiência do chaveamento controlado, o qual é economicamente mais atrativo.

Comparative analysis of techniques for control of switching overvoltages during transmission lines energization

The energization of long transmission lines can cause high overvoltage stresses not only along the transmission line, but also in the rest of the network. The traditional method of limiting switching overvoltages to acceptable levels is the use of circuit breakers equipped with pre-insertion resistors. The present paper describes a study comparing this traditional method with two other alternatives for the limitation of switching overvoltages during line energization in an actual 500 kV transmission system: the use of metal oxide surge arresters at both line closing of circuit breaker poles. Digital simulations were made with PSCAD/EMTDC software and the degree of shunt compensation is considered as an independent parameter.

Circuit-breaker requirements for alternative configurations of a 500 kV transmission system

This paper describes a study made to assess the electrical stresses imposed on line circuit breakers of a new 500 kV AC expansion of the FURNAS transmission system, to be possibly installed in the Brazilian central region. The study has considered three configurations of the transmission lines, two of which assume the use of compact towers. In one of these two cases, the lines would have high surge-impedance loading. Digital simulations have been made with the aid of the Alternative Transients Program (ATP) to calculate the switching transients appearing as a result of line energization and reclosing, clearing of terminal and short-line faults, no-load line opening in normal and faulted conditions and out-of phase switching. Four alternatives have been considered for the limitation of overvoltages on closing, assuming either the sole use of surge arresters on each line end or the use, in addition to the arresters, of pre-insertion resistors, synchronizers or time relays to provide a staggered closing of the breaker poles. The stresses obtained were compared with those applied by the standard IEC tests or with the maximum admissible levels usually considered by the utility for its transmission branches at the planning stage.

Evaluating capacitor-switching devices for preventing nuisance tripping of adjustable-speed drives due to voltage magnification

Nuisance overvoltage tripping of pulse-width modulated adjustable-speed drives, due to switching of shunt capacitor banks at a utility's substation and the subsequent voltage magnification which can occur at an industrial customer's utilization-voltage bus, is discussed. Adjustable-speed drive design considerations affecting transient overvoltage ride-through capability are identified and discussed. A comparative evaluation of three switching devices equipped with transient overvoltage control, namely, circuit breakers with pre-insertion resistors, circuit switchers with highly damped pre-insertion inductors, and controlled closing devices, is presented.

Effectiveness of pre-insertion inductors for mitigating remote overvoltages due to shunt capacitor energization

Pre-insertion inductors have been introduced as a cost-effective alternative to pre-insertion resistors for controlling capacitor bank energization overvoltages. The results of a system study investigating remote overvoltage mitigation methods for shunt capacitor switching show that pre-insertion inductors are not always as effective as pre-insertion resistors. A parametric study is performed to determine the effectiveness of pre-insertion inductors for controlling remote overvoltages, such as those at the end of open-ended lines or transformer-terminated lines. The results show that the pre-insertion inductors used for controlling remote overvoltages may become completely ineffective for certain system conditions. This finding is explained in terms of the physical phenomena. >

Energization of large shunt reactors near static VAR compensators and HVDC converters

A case study is presented involving the switching of large reactors on a power transmission system including an HVDC terminal and static VAR compensator in close proximity. Switching the subject reactor without preinsertion resistors led to field problems with harmonic distortion and offset currents. The study provides insight to the system behavior for reactor switching events. The results provide a sound basis for selecting control and equipment modifications to permit normal reactor switching.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transmission Line Insulation Design at High Altitude

The Public Service Company of Colorado plans to initiate 345-kV transmission at altitudes of 1250 to 3680 m. Compared to sea-level designs, the increase in the required tower strike distance has been predicted at about 50% for altitudes of 3600 m [1]. However, by use of surge arresters at station entrances and preinsertion resistors in the circuit breakers, the tower insulation design is comparable to present lower altitude designs.