System Fault Currents Research Articles

The Application of Active Superconducting DC Fault Current Limiter in Hybrid AC/DC Power Supply Systems

This paper presents a new topology of the active superconducting DC fault current limiter (DC-SFCL) applied in the hybrid AC/DC power supply systems. The proposed DC-SFCL is composed of superconducting transformer, DC chopper and voltage source converter (VSC). The primary winding of the transformer is connected in series with DC transmission line, and the second winding is connected with AC power system through the VSC and the DC chopper. The active DC-SFCL can suppress the fault current of DC system through power exchange between the DC and the AC system. Moreover, the DC-SFCL can act as an active power filter for both the DC system and the AC system to solve the problem of power quality. Using MATLAB SIMULINK, the simulation model of the hybrid AC/DC power supply systems with the proposed DC-SFCL is created. Simulation results validate the dynamics of system, and the performance of the active DC-SFCL is confirmed.

DSPとIGBTを用いた半導体型限流器の動作確認試験

This paper carries out the action confirmation test of a semiconducting-type fault current limiter (FCL) using the digital signal processor (DSP) to improve the instantaneous voltage drop and to reduce the fault current of power system. A insulated gate bipolar transistor (IGBT) is used as a commutation element of the FCL. The IGBT is a kind of the MOS-type gate power device. By using the IGBT, the high-speed operation of large current and high voltage can be realized. Next, the DSP is used in the FCL in order to detect the fault current at high speed. The DSP used in a test equipment is a starter kit (Texas Instrument TMS320C67). This is mainly used by the real-time processing, and it is suitable for the high-speed operation. The examination was carried out using computer simulation and a test equipment of small capacity in order to demonstrate the effectiveness of the technique using in this paper. Three kinds of FCLs are used in this paper. One is a resisted type and another is a reactor type. One of the remainder is the Z type which parallelly connected resistance and reactor. From computer simulation using PSCAD/EMTDC and small-scale experiment, three kinds of fault current limiter used in this paper confirmed moving within 1 msec from the fault detection to the action completion.

A wavelet-based technique for discrimination between faults and magnetizing inrush currents in transformers

This paper presents the development of a wavelet-based scheme, for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast, and computationally efficient tool. The operating time of the scheme is less than half the power frequency cycle (based on a 5-kHz sampling rate). In this work, a wavelet transform concept is presented. Feature extraction and method of discrimination between transformer inrush and fault currents is derived. A 132/11-kV transformer connected to a 132-kV power system were simulated using the EMTP. The generated data were used by the MATLAB to test the performance of the technique as to its speed of response, computational burden and reliability. The proposed scheme proved to be reliable, accurate, and fast.

Discrimination between faults and magnetising inrush currents in transformers based on wavelet transforms

Abstract This paper presents the development of a wavelet-based scheme, for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast and computationally efficient tool. The operating time of the scheme is less than half power frequency cycle (based on 5 kHz sampling rate). In this work wavelet transform concept is presented. Feature extraction and method of discrimination between transformer inrush and fault currents is derived. A 132/11 kV, transformer connected to a 132 kV power system were simulated using the EMTP. The generated data were used by the MATALB to test the performance of the technique as to its speed of response, computational burden and reliability. The proposed scheme proved to be reliable, accurate and fast.

A Wavelet-Based Technique for Discrimination between Faults and Magnetising Inrush Currents in Transformers

This paper presents the development of a wavelet-based scheme for distinguishing between transformer inrush currents and power system fault currents, which proved to provide a reliable, fast, and computationally efficient tool. The operating time of the scheme is less than half power frequency cycle (based on a 5 kHz sampling rate). In this work, the wavelet transform concept is presented. Feature extraction and method of discrimination between transformer inrush and fault currents are derived. A 132/11 kV, transformer connected to a 132 kV power system were simulated using EMTP. The generated data was used by MATLAB to test the performance of the technique as to its speed of response, computational burden, and reliability. The proposed scheme proved to be reliable, accurate, and fast.

A practical method for evaluation of ground fault current distribution on double circuit parallel lines

The paper presents an original analytical procedure for quick and, for practical purposes sufficiently accurate evaluation of the principal components of the ground fault current. The procedure is valid for faults at any of the towers of a double 3-phase circuit line with an arbitrary number of spans. The method is obtained by application of relatively simple and exact equations for uniform ladder circuits of any size (for any number of pis, from one to infinity) and for any terminal conditions. The method can be applied to solve several practical problems: the evaluation of the maximum substation grounding system fault current, the selection of a ground wire capable of withstanding the fault currents and the prediction of step and touch voltages near the transmission towers. In the case of a double circuit 3-phase line, the solution of these problems is additionally complicated by the mutual inductive coupling between the two parallel lines.

Simulation study of unified power flow controller

The increasing complexity of ac power networks requires a high-performance power flow control system in order to obtain the desired power flow and enhance static and dynamic stability. One of the most effective power electronic systems to satisfy these requirements is a UPFC (Unified Power Flow Controller) employing self-commutated converters. This paper presents basic control strategies and simulation results for the UPFC using the EMTP (Electromagnetic Transient Program). The simulations were carried out for start and stop operations, power flow change operations in normal system conditions, as well as operations during system fault conditions. Thyristor-based bypass switches are used for the protection of the series compensator of the UPFC from system fault currents, and satisfactory protection capability was confirmed. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 23–30, 1999

Practical method for evaluating ground fault current distribution in station, towers and ground wire

The paper presents an original analytical procedure which enables a quick and, for practical purposes sufficiently accurate evaluation of the significant parts of the ground fault current, for a fault at any of the towers of a transmission line of an arbitrary number of spans. The advantages of the method are the simplicity and accuracy of the formulae for solving uniform ladder circuits of any size (from one up to an infinite number of pis) and any terminal conditions. The formulae are obtained by applying the "general equations of the line represented by discrete parameters" on a specific electrical circuit formed by a transmission line ground wire during ground faults. The presented method is suitable for analyses aimed at evaluating the maximum substation grounding system fault current, at selecting the ground wire capable of withstanding the fault currents and at the prediction of step and touch voltages near transmission towers.

Operating principle of a high Tc superconducting saturable magnetic core fault current limiter

An electrical fault current limiter (FCL) designed with a high Tc superconducting (HTS) dc bias winding is described. The winding is prepared by using a Ag-clad (Bi,Pb)2Sr2Ca2Cu3O10+x HTS wire. The limiting behaviour of this FCL is investigated and considered with respect to operation in a 6 kV power system. The results show that the FCL limits fault currents effectively, and is a possible solution for reducing power system fault currents.

Detection of and protection for internal low-current winding faults in overhead distribution transformers

Changing protection practices for overhead power distribution transformers involves mounting the arrester on the transformer tank and using lightning-surge-tolerant fuses to provide protection. Concerns about protecting transformers against low-magnitude internal winding faults as a result of this practice are addressed in this paper. An analysis of a high-power test involving primary and secondary winding faults is presented. The magnitude, duration, and signature of the winding faults are determined and categorized. An analysis of the response of surge-tolerant fuses shows that they often will not detect low-current winding faults before they propagate to the available system fault current. Testing also demonstrated the performance of current-limiters to effectively reduce the available system fault current, thereby minimizing stress to the transformer. The use of current limiters is recommended with surge-tolerant fuses. The pressure rise in the tank for primary winding faults is mainly caused by low-fault current and, when protected with current limiters, the relief device easily vents the gases. The pressure rise for secondary winding faults is more rapid and can exceed the capability of the relief device to limit the overpressure.

Electrical application of high T/sub c/ superconducting saturable magnetic core fault current limiter

A saturable magnetic core electrical fault current limiter (FCT) designed with a high T/sub c/ superconducting (HTS) DC bias winding is described. The HTS winding is prepared by using a Ag-clad (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub O10+x/ HTS wire. The limiting behaviour of this FCL is investigated, and its electrical application is considered in an electrical power transmission system. The results show that this FCL limits fault currents effectively and is a possible solution for reducing power system fault currents.

自励式位相調整器の瞬時値解析による検討

The increasing complexity of ac power networks requires a high-performance power flow control system in order to obtain the desired power flow and enhance static and dynamic stability. One of the most effective power electronic systems to satisfy these requirements is a UPFC (Unified Power Flow Controller) employing self-commutated converters. This paper presents basic control strategies and simulation results for the UPFC using the EMTP (Electromagnetic Transient Program). The simulations were carried out for start and stop operations, power flow change operations in normal system conditions, as well as operations during system fault conditions. Thyristor-based bypass switches are used for the protection of the series compensator of the UPFC from system fault currents, and satisfactory protection capability was confirmed. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 23–30, 1999

Solid-state on-load transformer tap changer

Switching logic is defined for a single-phase transformer tap changer using thyristor switching. A laboratory model validates the theory and shows that tap changing is possible in less than one cycle over the whole power-factor spectrum. Waveform sampling and the use of a microprocessor based control system provides improved control and additional features such as data logging etc. Two schemes are considered for the application of thyristor tap changing to three-phase transformers. Economic viability is strongly dependent on the associated power system and its abnormal operating features, namely system fault currents and especially the degree of exposure of the transformer to lightning surges.

Analysis of the faults involving adjacent conductors of a six-phase transmission line together with a modelling of the phase conversion transformer

Abstract In a bulk power transmission system the amount of power transfer can be increased by converting the widely used three-phase double-circuit lines into six-phase single-circuit lines instead of upgrading the transmission voltage. In this conversion process only a phase conversion transformer at each end of the line is required while the existing conductors, towers and corridors of three-phase lines can be used intact. However, this conversion will have an effect on the system fault currents and fault levels. The well-known symmetrical component method is suitable for fault analysis in a three-phase system, but it has been found unsuitable for analysing the practical faults on a six-phase line and for modelling the phase conversion transformer. This paper illustrates the way the phase conversion transformer has been incorporated in the six-phase line fault modelling and also presents a new application of the straightforward loop current method by using it to determine the currents and fault MVA corresponding to the common and practical faults on a 132 kV six-phase line. The same method has also been applied to the fault analysis of a 132 kV and a 230 kV three-phase line and the results are compared with those for the six-phase line.

The truth about standby generator excitation support systems

Many who specify standby generators for critical applications assume that some type of excitation support system is required for self-excited generators. The rationale behind this thinking is that self-excited generators are not capable of producing enough short-circuit current to trip downstream overcurrent protection selectively. Field forcing schemes are used to produce 300% of rated current for at least 10 s to ensure that faults are cleared quickly enough and selectively enough to preserve the integrity of the power supply. This analysis of standby system fault currents shows the many variables to be considered and demonstrates that, except for the most unusual circumstances, self-excited generators do a good job of supplying short-circuit currents and clearing faults. The analysis is carried out in the context of a hospital.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Characteristics of Fault Currents on Distribution Systems

The results of a four-year study to determine the characteristics of distribution system fault currents are presented. Fault data from thirteen utilities was recorded on multi-channel digital fault recorders, with supplementary information recorded on utility questionnaires. Statistical distribution of such parameters as fault current magnitude, dc offset, X/R ratios, fault duration, and fault I2t values are included.

Calculation of system-fault currents due to induction motors

Calculation of system-fault currents due to induction motors

Calculation of system-fault currents due to induction motors

Calculation of system-fault currents due to induction motors

Reply: Calculation of system-fault currents due to induction motors

Reply: Calculation of system-fault currents due to induction motors

Calculation of system-fault currents due to induction motors

The paper makes recommendations for a standard method of determining the contribution made by induction motors to the fault currents in a power system. The need for such a method arises from the increasing number of large induction motors now being installed, and from the more rapid operating times of present-day switchgear. The basis of the proposals is that, for this purpose, an induction motor can be treated in the same way as a synchronous machine, using mainly the `subtransient reactance' of the induction motor. The recommendations are supported by a detailed theory of induction-motor transients, in which accurate formulas are derived for the current following a sudden short circuit. The `deep-bar effect' usually present in large squirrel-cage induction motors is dealt with in a similar manner to that adopted internationally for the `solid-pole effect' in synchronous machines, where the effect is theoretically simulated by two corresponding time constants appear in the formulas. An operational impedance function, similar to that of a synchronous machine, is used to obtain the transient parameters. The method is a simple one, and is particularly useful for determining switchgear ratings in a mixed system containing both synchronous and induction machines.