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Combination of wavelet transforms and artificial intelligence in HV shunt capacitor banks: Fault and inrush currents classification
(2020-01-01)
Patcharoen, Theerasak
;
Ngaopitakkul, Atthapol
The installation of HV substation shunt capacitor bank in a substation and transmission system affects both the capacitor inrush currents and fault currents. This is led to mal-operation of the overcurrent protection relay (50/51) and unbalance current protection relay (60C, 51NC) to classify whether it is the inrush current or fault current. The protective relay may be tripped due to transient inrush currents during a capacitor energizing. This paper presents a new detection and classification technique by using a combination of the discrete wavelet transform (DWT) and probabilistic neural network (PNN). The DWT on the measured three-phase current signals was employing the effective time-frequency analysis for detection. The detail wavelet coefficients of level-1 to level-30 of currents signals are extracted by DWT using 'db4' mother wavelet. The suggested PNN technique uses to classify those transient. The two classification techniques such as 1) only DWT and 2) combined DWT and fuzzy inference system (FIS) are compared with the proposed method. The performance of the proposed technique is found to be accurate for the detection and classification of power system transient in a capacitor bank which it has high accuracy by 100% for detection and more than 98% for classification.
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Discrete wavelet transform for improving the accuracy of an unbalance current protection relay due to transient fault and inrush current signals
(2019-05-01)
Patcharoen, Theerasak
;
Ngaopitakkul, Atthapol
An unbalance current protection relay (60C, 51NC) cannot operate fast enough to avoid catastrophic failure against high system fault currents within capacitor units because traditional unbalance current protection relays are not capable of distinguishing and classifying transient fault current and switching inrush current. This paper proposes a new algorithm for the detection and classification of such current signals. The program used for the simulation was PSCAD/EMTDC. The current signals output was used as discrete wavelet transform (DWT) input. The wavelet-based fault and inrush current detection and classification unit received the various captured transient current signals, and used DWT to detect and analyse various cases studies. The actual inrush current signals from both the experimental setup and testing on an actual 115 kV HV shunt capacitor bank were used to verify the proposed algorithm. Results show that the proposed algorithm is effective at accurately identifying fault and inrush currents.
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Simulation analysis of the switching of 230kV substation shunt capacitor banks with a 6% series reactor for limiting transient inrush currents and oscillation overvoltage
(2018-06-01)
Patcharoen, Theerasak
;
Ngaopitakkul, Atthapol
;
Pothisarn, Chaichan
;
Leelajindakrairerk, Monthon
This paper presents the simulation and investigation of switching large shunt capacitor banks in a 230kV Thailand substation system. Simulations are performed using PSCAD/EMTDC to determine the peak of the transient inrush currents, the oscillation overvoltage and the frequency of the inrush current. The inrush current is generated by energizing the 4 × 72 Mvar, 230kV shunt capacitor banks. The purpose is to observe and investigate the behaviour of transient inrush currents and oscillation overvoltages to ensure the safe and successful operation of shunt capacitor banks. The methodology of inrush current transient analysis and transient reduction control was studied. The proposed method for controlling system transients during capacitor energization is through the use of a switching shunt capacitor bank with a series 6% reactor. The simulation cases for transient mitigation are numerically conducted for six different cases: a base case, with a pre-insertion resistor, with a pre-insertion inductor, with a current-limiting reactor, with a series 6% reactor and using synchronous closing control. The effects of parameters such as the sizing of the current-limiting reactor, the capacitor bank rating and the short-circuit impedance of the system are investigated. The simulation results demonstrate that the switching shunt capacitor bank with a series 6% reactor is effective in reducing the high transient inrush currents and oscillation overvoltages.
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Investigation and reduction of effects of transient signals for switching capacitor into a power system by using an experimental test set
(2018-01-01)
Yoomak, Suntiti
;
Pothisarn, Chaichan
;
Jettanasen, Chaiyan
;
Ngaopitakkul, Atthapol
This paper aims to investigate switching capacitor bank of the 115 kV Nong Chok substation under the Electricity Generating Authority of Thailand (EGAT). The substation comprises of 3 steps capacitor banks with reactive power of 48 Mvar in each step. In case study, the substation is downscaled to be an experimental unit with 415 V and 5 Mvar in each step in laboratory. Inrush currents, the behavior of transient signals, that occurs when capacitors are switched into the system are studied and analyzed. To reduce the effect of switching capacitors, current limiting reactors connected in series with the capacitors are proposed. In addition, a zero-crossing circuit is designed to control switching angle of the capacitors, since it has a significant effect on the inrush currents. The results of experiment are compared with two case studies: switching capacitors without integrated 7% of reactors and switching capacitors with integrated 7%. It can be summarized that the switching capacitor without integrated reactors has inrush currents change based on the switched angles of the capacitors. However, the switching capacitor with integrated reactors gives inrush current values are almost approximate in each angles of switching and they are lower the case of the switching capacitor without integrated reactors. Nevertheless, reactor integration into the system leads to high current values at the steady states.
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Analysis and investigation on the behavior and performance of single phase grid connected induction generators system
(2017-10-02)
Nuttapong, P.
;
Sawetsakulanond, B.
;
Kinnares, V.
This paper presents an inrush current reduction method for a 1/2 HP (0.4 kW), 220 V, 4.8 A, 4 poles single phase split-phase type induction generator when connected to a grid using single-phase voltage control with power electronic equipment. A study and analysis of relationship between voltage, current and real power by laboratory tests under direct on line and soft connection conditions are given. Simulation and experimental results are in good agreement. According to testing results, it is found that the proposed voltage control is able to reduce 75-80 % of the inrush current when starting the connection. Research results will be guidelines in applications of effective single-phase induction generators for wind energy.
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The application of a 6% reactor in high-voltage capacitor bank switching
(2016-01-01)
Chiradeja, Pathomthat
;
Ngaopitakkul, Atthapol
The switching of capacitor banks at high voltage for power-factor improvement and voltage support can generate significant transients. Such switching transients are produced by inrush currents and transient overvoltages in systems to which the capacitor bank is connected. These switching transients can cause damage to insulation and mal-operation of protective relays. This paper presents the simulation and investigation of a switching large-shunt capacitor bank in a 230kV Thailand substation system. A computer simulation using PSCAD/EMTDC was performed to determine the peak of the transient currents, the oscillation overvoltage and the frequency of the inrush current. The transient inrush current is generated by energizing of the 4×72 MVAr, 230 kV shunt capacitor banks. Methods of inrush current transient analysis and reduction were evaluated. Limiting the transients with a 6% reactor in series was simulated. The simulations indicate that the 6% reactor can significantly reduce the magnitude of the transients.
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Analysis of transient signals in a substation capacitor bank system using an experimental setup
(2016-01-01)
Patcharoen, Theerasak
;
Ngaopitakkul, Atthapol
The capacitor bank system is one of the important systems in an electric utility, with the benefit of power factor correction and reactive power compensation for transmission and distribution systems. Installation of a capacitor bank system in a substation causes transient signals when switching occurs. The aim of this research is to study the transient signals that occur when the capacitor bank is switched in each step. A capacitor bank-switching experimental test unit has been built to create a downscale capacitor bank system in a distribution-level substation. This unit was modelled after the NongChok substation under the Electricity Generating Authority of Thailand (EGAT). The impact on the distribution system when the capacitor bank is switched has been studied, and phenomena such as inrush currents, voltage transience, and frequency oscillation are taken into consideration. A method to reduce transient issues has been discussed and implemented in the test unit to evaluate the performance impact of these methods on a switching capacitor bank system.
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A discrete wavelet transform approach to discriminating among inrush current, external fault, and internal fault in power transformer using low-frequency components differential current only
(2014-01-01)
Ngaopitakkul, Atthapol
;
Jettanasen, Chaiyan
This paper proposes an algorithm based on discrete wavelet transform (DWT) for discriminating among inrush current, internal fault, and external fault in power transformers. Fault conditions are simulated using the Alternative Transients Program/Electromagnetic Transients Program (ATP/EMTP). Daubechies4 (db4) is employed as the mother wavelet to decompose low-frequency components from fault signals. The ratio between per unit (p.u.) differential current and p.u. time is suggested as an index. The numerator of the ratio is the difference between the maximum differential current and the minimum differential current in terms of p.u. with a base value selected at the transformer-rated current. The ratio is calculated for all three phases, and from a trial and error process the indices for the separation among the internal fault condition, the external fault condition, and inrush condition are defined. The results obtained from the proposed technique show good accuracy for discriminating faults in the considered system. In addition, the proposed algorithm uses data of the differential current with a time of quarter cycle under the analysis. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

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