Fault Current Path Research Articles

An Adaptive Overcurrent Protection Scheme for Distribution Networks

Distribution networks are evolving toward the vision of smart grids, with increasing penetration of distributed generation (DG), introduction of active network management (ANM), and potentially islanded modes of operation. These changes affect fault levels and fault current paths and have been demonstrated to compromise the correct operation of the overcurrent protection system. This paper presents an adaptive overcurrent protection system which automatically amends the protection settings of all overcurrent relays in response to the impact of DG, ANM, and islanding operation. The scheme has been developed using commercially available protection devices, employs IEC61850-based communications, and has been demonstrated and tested using a hardware-in-the-loop laboratory facility. A systematic comparison of the performance of the proposed adaptive scheme alongside that of a conventional overcurrent scheme is presented. This comparison quantifies the decrease in false operations and the reduction of mean operating time that the adaptive system offers.

Part II: Application Guidelines for High-Resistance Grounding of Low-Voltage Common AC-Bus and Common DC-Bus PWM Drive Systems

High-resistance ground (HRG) systems have gained popularity in process applications due to their ability to continue operation after a single line-to-ground fault and to limit the escalation of a single line-to-ground fault to a multiphase event. Part I of the companion paper has set the guidelines for designing safe and reliable HRG systems on industrial power systems used with linear loads and the effect of increased line-ground voltage stress on motor loads during fault conditions. However, literature on characteristics and pitfalls of HRG systems when used with nonlinear power converter systems is limited. Part II investigates anomalies of HRG systems used with nonlinear power converters such as neutral voltage shifting, increased line-ground transient fault voltages for both motor and ac source terminals and their voltage compatibility issues, increased neutral grounding resistor power dissipation, susceptibility of ground fault sensing equipment to nuisance tripping, and dc-bus voltage resonance on faults. Part II also investigates HRG zero-sequence fault current characteristics and paths observed under various fault locations in a common ac or a common dc-bus pulsewidth-modulated adjustable speed drive (ASD) system. Part II concludes with a summary of application guidelines when using ASD HRG systems.

Arc Flash Mitigation Using Active High-Speed Switching

One method of mitigating arc flash hazards associated with medium-voltage switchgear is the installation of active high-speed switch (HSS) systems. These systems are designed to detect and quench a burning internal arc in less than one-third of one electrical cycle. The internal arc is extinguished by the HSS's action of redirecting the fault current path from arcing through open air back to the intended current path of the switchgear bus. The new low-impedance current path provided by the HSS operation collapses the voltage at the point of the fault to near zero so that the arc is no longer sustainable. The system's high speed of operation compared to arc quenching via circuit breaker tripping translates directly to lower arc flash incident energy and minimal equipment damage. Another benefit of such active high speed systems could include switchgear compliance to the IEEE C37.20.7 guide for testing arc-resistant metal-enclosed switchgear without any arc by-product venting requirements. This paper explores application considerations of HSS systems relative to other available means of controlling and reducing the hazards of internal arcing faults in medium-voltage switchgear.

Improving the power supply reliability in resonant earthed systems by fault current path control established through Faulted Phase earthing Switch

This paper shows that appropriate manipulation of the Faulted Phase earthing Switch within the system using resonant earthed neutral, can be used to establish a controlled path for the fault current. In this way the arc extinguishes and the fault can be safely located without interruptions to the energy supply. The proposed current path control method is confirmed with simulations and extensive field-testing.

A LCC and MMC hybrid HVDC topology with DC line fault clearance capability

This paper proposes a LCC and MMC hybrid HVDC topology with dc line fault clearance capability suitable for bulk power transmission, in which the rectifier adopts a line commutated converter (LCC) and the inverters adopt two modular multilevel converters (MMCs). Resiliency to dc line faults can be achieved by alpha-retard of the LCC and the high power diodes installed in the overhead line close to the inverters. The start-up process is implemented in two stages. A hybrid HVDC system is modeled in PSCAD/EMTDC to demonstrate the effectiveness of the control system and the start-up scheme. Moreover, simulation results of a dc line fault confirm the feasibility that the fault current paths can be blocked by alpha-retard of the LCC and the installed high power diodes, and the whole system is able to restart after clearance of the transient dc line fault.

Controllable resistive type fault current limiter (CR-FCL) with frequency and pulse duty-cycle

In this paper a controllable resistive type fault current limiter (CR-FCL) is introduced. The CR-FCL inserts a pre-specified value of resistance based on a pre-defined function, by using a simple switching method, in series with the fault current path. When a fault occurs, a self turn off switch starts switching with a pre-specified frequency and duty cycle. By this switching pattern, the controlled value of resistance enters to the fault current path. So, the CR-FCL limits the fault current to the desired values. In addition, from transient stability point of view, by inserting the optimal resistance value, the CR-FCL is capable to enhance power system transient stability in a good manner. In fact, generation of the controllable resistance that depends on the duty cycle of the self turn off switch is the main idea of the CR-FCL. The variable duty cycle results the variable resistance and the fixed duty cycle results the fixed resistance. Analytical analyses of the proposed FCL are presented in details. Simulation results by power system computer-aided design/electromagnetic transients, including dc (PSCAD/EMTDC) software and corresponding experimental results are studied to validate the effectiveness of the CR-FCL. Considering error analyses, there is the good agreement between the simulation results and the experimental results.

Study on Coordination of Protective Relays Between Primary Feeder and Interconnecting Transformer Grounded by SFCL of Wind Farm

In this study, we analyse the coordination of protective relays between a primary feeder and an interconnecting transformer grounded by using a superconducting fault current limiter (SFCL) of a wind farm. Most wind farms and utility systems are interconnected by a transformer. The winding configuration of most interconnecting transformers is wye grounded-delta. Therefore, the utility-side grounding of the interconnecting transformer can support a new single line-to-ground fault current path. Because the coordination plan of a protective relay in a power distribution system does not consider the new fault path, an unintended relay operation can occur. To overcome this problem, an SFCL is applied to the ground connection of the interconnecting transformer. We analyse the effect of the resistive SFCLs on the coordination of the ground faults using time-domain transient simulation software (PSCAD/EMTDC).

Performance of optical ground wires during fault current tests

Optical ground wires (OPGW) must be able to fulfil the regular functions of a ground wire, such as lighting protection and fault current path, as well as provide secure communications by way of the optical fibers embedded inside. Fault current tests were performed on a loose-tube-design OPGW to evaluate the temperature and optical performance during and after fault current pulses or hits. Optical performance was found to be affected as early as the first rated fault current hit. Temperature gradient tests revealed much higher than expected optical core temperatures, with resultant buffer tube damage. A computer program for predicting the temperature gradient was developed and independently verified the measured temperatures. A redesign of the cable will be necessary to ensure adequate optical performance for rated fault current hits.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance of Optical Ground Wires During Fault Current Tests

Optical ground wires (OPGW) must be able to fulfil the regular functions of a ground wire, such as lighting protection and fault current path, as well as provide secure communications by way of the optical fibers embedded inside. Fault current tests were performed on a loose-tube-design OPGW to evaluate the temperature and optical performance during and after fault current pulses or hits. Optical performance was found to be affected as early as the first rated fault current hit. Temperature gradient tests revealed much higher than expected optical core temperatures, with resultant buffer tube damage. A computer program for predicting the temperature gradient was developed and independently verified the measured temperatures. A redesign of the cable will be necessary to ensure adequate optical performance for rated fault current hits. >