Capacitor Bank Energization Research Articles

High-impedance fault modeling and classification in power distribution networks

This work presents a novel method for the classification of high-impedance faults (HIFs) in power distribution networks based on the association of higher-order statistics (HOS) and a multilayer perceptron (MLP) artificial neural network (ANN). An alternative model is developed to represent the HIF phenomenon considering five different contact surfaces with the ground. A broad analysis comprising six types of typical events that occur in distribution networks is performed in the Alternative Transient Program (ATP) software, including several conditions such as: normal operation; single-phase faults; two-phase faults; three-phase faults; energization of transformers and capacitor banks; switching of inductive loads; as well as faults involving five modeled surfaces. HOS is combined with Fisher’s discriminant ratio (FDR) to extract the best characteristics. At the end, the MLP-type ANN is used to recognize the specific patterns of each event aiming to identify each event accurately, especially HIFs. The obtained results demonstrate that the proposed technique proves to be a reliable and accurate tool, achieving classification hits above 98%.

Cause identification of electromagnetic transient events using spatiotemporal feature learning

This paper presents a spatiotemporal feature learning method for cause identification of electromagnetic transient events in power grids. The proposed method is formulated based on the availability of time-synchronized high-frequency measurements and using the convolutional neural network as the spatiotemporal feature representation along with softmax function for the classification. Despite the existing threshold-based, or energy-based events analysis methods, such as support vector machine autoencoder, and tapered multi-layer perceptron neural network, the proposed feature learning is carried out with respect to both time and space. The effectiveness of the proposed feature learning and the subsequent cause identification is validated through the Electromagnetic Transients Program (EMTP) simulation of different events such as line energization, capacitor bank energization, lightning, fault, and high-impedance fault in the IEEE 30-bus, and the real-time digital simulation of the WesternSystemCoordinating Council (WSCC) 9-bus system.

Probabilistic Assessment and Evaluation of Transients in a Medium-Voltage Three-Phase Capacitor Bank Energized by Unsynchronized Vacuum Switchgears

This paper presents a case study of a medium-voltage three-phase capacitor bank (CB) energization, based on an unsynchronized switching scheme using three independent pole vacuum switches simultaneously commanded. The motivations are cost reduction and simplification of the switching scheme. The maximum current and voltage peaks during transients caused by connection of CB with three independent pole switches or a three-phase mechanically coupled switch are compared. A probabilistic assessment for the overcurrents and overvoltages based on Monte Carlo simulation is also performed. The obtained results show that three single-phase unsynchronized switches could be used in a CB, with good transitory response.

Intelligent Transient Overvoltages Location in Distribution Systems Using Wavelet Packet Decomposition and General Regression Neural Networks

Overvoltages are the main causes of damages and accidents in electric power grids. The traditional approach is to install some static protection devices that are passive and cannot identify the overvoltage types or locate where the overvoltage event occurs. In recent years, with the development of smart grids, some online overvoltage monitoring systems have been developed. However, the approaches to data processing still need further development. A novel technique for identification and location of overvoltages in power distribution systems is proposed, which uses capacitor bank energization overvoltages (CBOVs) and ground fault temporary overvoltages (TOVs) as the study cases. The wavelet packet decomposition (WPD) theory is used for frequency band decomposition, and a general regression neural network (GRNN) is used in identification and location. Simulation results based on real-world power distribution systems show that the method is accurate and fast.

Energization of long HVAC cables in parallel – Analysis and estimation formulas

The installation of long HVAC cables has recently become more common and it will likely increase during the next years. Consequently, the energization of long HVAC cables in parallel is also a more common condition.The energization of HVAC cables in parallel resembles the energization of capacitor banks in parallel and high inrush currents are associated to both energization phenomena.The existing IEEE standard C37.012-2005 for capacitive switching proposes a formula that can be used to estimate the peak magnitude and frequency of the inrush current. However, for sake of simplicity, the formula has several simplifications and it does not always provide accurate results. This paper proposes a new formula that can be used for the estimation of these two quantities for two HVAC cables in parallel.

Study of Transformer Resonant Overvoltages Caused by Cable-Transformer High-Frequency Interaction

Power transformers can fail from dielectric stresses caused by electromagnetic transients. In this paper, we focus on a special phenomenon where excessive overvoltages arise due to resonance. This situation can take place when a transformer on the high-voltage side is connected to a cable and the low-voltage side is unloaded. Very high overvoltages can then result on the low-voltage side from transient events that cause a weakly attenuated overvoltage on the cable with a dominant frequency matching a resonance peak in the transformer voltage ratio. Laboratory tests on a 11-kV/230 V distribution transformer show that a step voltage excitation on a 27-m cable produces 24-p.u. overvoltage on the open low-voltage side. The voltage waveforms are accurately reproduced by a black-box model obtained from frequency sweep measurements. Simulations show that overvoltages as high as 43 p.u. could occur with the most unfavorable cable length. It is further shown that the following situations can lead to high overvoltages on an unloaded transformer low-voltage side: 1) ground fault initiation at the far cable end, 2) cable energization from a busbar with several other cables connected, 3) cable energization from another cable with the same length, and 4) capacitor bank energization at the far cable end.

BACK-TO-BACK CAPACITOR ENERGIZATION TRANSIENTS MITIGATION: COMPARISON OF PRE-INSERTION INDUCTORS VERSUS SURGE REACTORS ON A 46 kV SUBTRANSMISSION SYSTEM

ABSTRACT Two devices that are used to reduce back-to-back capacitor bank energization transients, pre-insertion inductors and surge reactors, are investigated in this paper. The Alternative Transients Program (ATP) was used to develop a computer model of a 46-kV system. A parametric study, varying the switched capacitor size and the system strength, was completed to determine the effectiveness of the two methods. Pre-insertion inductors reduced the peak inrush current better than the surge reactors. However, both of these devices generated peak overvoltages greater than the case containing neither of them. The optimum inductor size is highly system dependent. A thorough study of the system should be completed before the choice is made to use pre-insertion inductors or surge reactors.

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. >

Consideration of Phase-to-Phase Surges in the Application of Capacitor Banks

The energization of capacitor banks can result in high phase-to-phase surges at locations in a power system other than the substation where the capacitor bank is being switched. The probability of obtaining high phase-to-phase surges is greater for ungrounded capacitor banks than for grounded banks. These surges are highest at a substation which is fed radially from the bus with the capacitor bank. The phlase-to-phase surges are a threat to the insulation of three-phase transformers in the radial substation. Plhase-to-ground surge arresters on the transformers are not very effective in protecting them from these surges because the surges are comprised of line-to-ground components which are approximately equal in magnitude and opposite in polarity. Therefore, the phase-to-phase surges could only be limited by arresters to two times the arrester protective level. Closing resistors in the switching device used to energize the capacitor banks are very effective in reducing the phase-to-phase surges.

Control of Overvoltages on Energizing Capacitor Banks

Transient voltage phenomena occurring during the energization of shunt capacitor banks, due to prestrike and temporary interruption in the switching device of inrush currents have been considered. An analysis is made of a generalized capacitance circuit and energization transient voltage pattems are shown for a range of circuit permutations. An application guide is discussed for reduction of overvoltages during capacitor bank energization by proper choice of circuit elements. The influence of circuit resistance on the bus voltage patterns is reviewed.

Station Capacitor Switching Transients - Analytical and Experimental Results

Station capacitor bank energization transients predicted by a circuit model are compared to field test results. Selection of a suitable model is discussed. A computer solution of the model is presented.