Symmetrical Short-circuit Current Research Articles

Estimation Method of Short-Circuit Current Contribution of Inverter-Based Resources for Symmetrical Faults

This paper proposes a practical approach to estimate the symmetrical short-circuit current (SCC) levels in overcurrent protection devices (OCPDs) installed on radial feeders for any penetration level of inverter-based distributed energy resources (DERs). The proposed method restores the lost phase protection coordination by estimating SCC values and changing the TMS of OCPDs accordingly. The method is validated by comparing the results with simulations on the IEEE 34-Node Test Feeder using MATLAB/Simulink, which shows an average error of 1.5% and a maximum error of 3.0%. For a 100% penetration level, the SCC variation through OCPDs installed on the main fault trunk (MFT) exceeds ± 10%, leading to compromised phase protection coordination. The SCC flowing reversely through OCPDs on lateral branches and the fault on the MFT could cause improper tripping. Higher SCC levels are estimated and measured for fault impedances equal to zero. The phase protection is restored by changing the TMS of OCPDs using the estimated values. The study proposes two phase protection schemes to accommodate inverter-based DERs injecting 1.2 pu and 2.0 pu of SCC for a 100% penetration level. This study contributes to improving the protection coordination of distribution networks with high penetration levels of DERs. The findings have practical implications for distribution system operators and planners to maintain safe and reliable operation of distribution feeders.

The Analysis of the Symmetrical Short-Circuit Currents in Backup Power Supply Systems with Low-Power Synchronous Generators

This paper presents an analysis of the short-circuit currents of a synchronous generator with a rated power of 16 kVA. For this purpose, the authors carried out measurements of real short-circuit currents during laboratory tests. Additionally, a simulation model of the generator was developed according to the individual machines data from the catalog and field calculations in ANSYS Maxwell software. Based on the mentioned research, the authors compared waveforms of the symmetrical short-circuit currents. In this paper, the last compared family of short-circuit current waveforms was obtained using analytic calculations. As the presented comparison shows, the assumed method of selecting short-circuit waveforms impacted their values. However, the difference in energy related to short-circuit currents did not influence on the selection of the short-circuit protections, especially at low values of steady-state short-circuit currents and short time constants characteristic for the generators, performing the functions of an alternative power supply. Regardless of the research method, the results presented in the article show that the selection of the short-circuit protections is complicated in case of hybrid electrical systems equipped with low power generators.

Three-phase Making Test Method for Common Type Circuit Breaker

The synthetic short-circuit making test to adequately stress the circuit breaker has been specified as the mandatory test duty in the IEC 62271-100. The purpose of this test is to give the maximum pre-arcing energy during making operation. And this requires the making operation with symmetrical short-circuit current that is established when the breakdown between contact gap occurs near the crest of the applied voltage. Also, if the interrupting chamber of circuit breakers is designed as the type of common enclosure or the operation is made by the gang operated mechanism that threephase contacts are operated by one common mechanism, three-phase synthetic making test is basically required. Therefore, several testing laboratories have developed and proposed their own test circuits to properly evaluate the breaker performance. With these technical backgrounds, we have developed the new alternative three-phase making circuit.