Short Circuit Current Contribution Research Articles

Novel estimation framework for short-circuit current contribution of type IV wind turbines at transient and steady-state of the faults

Given the increasing penetration of converter-interfaced resources in power systems, properly estimating the short-circuit current (SCC) contribution in large networks has become a growing challenge and necessity to ensure the security and stability of the systems and assets. This paper presents two novel methods to estimate the SCC contribution of type IV wind turbines at both the transient and steady-state stages of unbalanced and balanced faults: (1) a machine learning-based method trained with electromagnetic transient (EMT) simulations and capable of estimating some of the initial peak and transient current magnitudes; (2) an analytical approach to estimate the steady-state SCC based on the voltage and grid code dependency of the converter during the fault. The methods are coupled into a single framework and compared to field-validated EMT models of a real turbine. The results show that the majority of the estimated currents in the transient stages present errors below 5%. In steady-state, the errors are not greater than 1.21%. Given the complexity of the problem, these margins may be deemed acceptable for short-circuit studies.

DC Switchyard Configurations for the Integration of Distributed Energy Resources

HVDC supergrid must grow in an organized way. The objective of HVDC substations will be to integrate generation groups and occasionally connect them to the AC network. That way, all substations will not be identical and their relevance will not be the same. In AC substations, network topological changes are made to limit the short circuit current contributions, perform load distributions and allow maintenance work when the application of restrictions is necessary, without compromising generation. These maintenance tasks should allow the exploitation of the network without making concessions on the stability of the system. DC networks do not require topological changes in the network to distribute loads, its utility would be reduced to facilitate maintenance tasks and minimize the possible effects of faults. However, it must be discussed which is the most suitable switchyard or whether more than one switchyard are required such as in AC networks. In the paper the usual topologies and switchyard configurations are analyzed and compared to determine if the architectures inherited from the AC grids can be used in the future HVDC supergrid. Several DC switchyard configurations are also discussed. Finally, the most suitable configurations are compared and applied to a study case.

Dynamic Investigations of Grid Connected Fixed-Speed Wind Turbine During Grid Faults

Especially during grid faults, grid code requirements for wind power integration have become a key element in improving grid efficiency and reliability. Under severe problems for network operation, wind turbines are expected to continue operating and supporting the grid during frequency restoration. This paper presents simulation results of a fixed-speed grid-connected wind turbine under various short-circuit current contributions. Fault analysis is carried out by studying the grid side line to ground fault, double line fault, double line to ground fault, and three phase fault involving ground and without ground. The obtained current waveforms are analyzed to explain the behavior, such as the rate of decay and peak values. Variations of active and reactive power during post-fault conditions and faulty conditions are investigated. Moreover, recommendations for switchgear and protection equipment are performed.

Analysis of short-circuit current contribution at offshore platform in a HVDC-OWF system

Analysis of short-circuit current contribution at offshore platform in a HVDC-OWF system

Faulted phase selection multicriteria algorithm implemented in generic hardware for centralized P&C in smart grids

The integration of devices based on renewable energies and power electronics makes it necessary to rethink some of the methods used for protection and control in distribution and transmission grids. The difference between short circuit current contributions from renewable and conventional generators may affect protection system operation. Fault phase selection is one of the elements to be analyzed under renewable generation scenarios due to its importance in protection functions such as distance protection.The digitization of substations presents new opportunities in control and protection systems, such as functionality increase, reliability improvement, cost reduction of the installation and capacity for remote maintenance. This paper proposes a multi-criteria fault phase selection algorithm developed to be implemented in digital substations. The proposed faulted phase algorithm combines the results provided by four independent protection algorithms and has been designed to be applied in transmission power systems. Depending on the electrical variables measured in each event, quality criteria are defined to consider the strengths and weaknesses of each independent algorithm. The proposed algorithm has been implemented and tested on the centralized protection and control platform called EPICS, obtaining very satisfactory results.

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.

Concerning Short-Circuit Current Contribution Challenges of Large-Scale Full-Converter Based Wind Power Plants

Concerning Short-Circuit Current Contribution Challenges of Large-Scale Full-Converter Based Wind Power Plants

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

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

Experimental study on short-circuit current characteristics of a photovoltaic system with low voltage ride through capability under a symmetrical fault

Large number of photovoltaic (PV) power plants connected to a power grid can bring significant impacts to fault currents and the operation of protection systems. In this paper, short-circuit current characteristics of a PV system with low voltage ride through (LVRT) capability under a symmetrical fault is studied. PV system short-circuit experiments with different voltage dips at high and low output power levels are designed and conducted. The experiment results provide useful and valuable references for researches of PV system short-circuit current characteristics, modeling and PV system short-circuit current contribution to a power grid. Then, based on the experiment results, steady-state values, peak values and steady state short-circuit currents harmonic characteristics at different conditions are obtained and analyzed. It is found that, the DC component amplitude of a PV system short-circuit current is almost negligible compared with that of the power frequency component, which is different from conventional synchronous generator short-circuit current. Meanwhile, based on the LVRT control strategy and experimental results, the expression of steady-state short-circuit current RMS value is derived and verified, which provides an important basis for short-circuit current calculation of power system with large scale of PV plants.

CALCULATION METHOD FOR THE CONTRIBUTION OF HVDC STATIONS WITH LINE-COMMUTATED CONVERTES (LCC) TO THE AC SHORT-CIRCUIT CURRENT

Short-circuit currents are a key measure for the planning of AC high voltage electrical networks. In this paper, the short-circuit current contribution of a HVDC system with line-commutated converters (LCC) to the short-circuit current in the AC system is investigated. Based on simulations in PSCAD/EMTDC the influence of different factors on the short-circuit current contribution is studied. These factors include the rating of the HVDC system, its operating point, different DC links such as back-to-back links, cables and overhead lines with varying DC line lengths and the type of short circuit and its distance from the HVDC converters. Based on the findings relevant factors are identified. On the basis of the simulation results a simplified analytical approximation for the short-circuit current contribution is derived, which takes into account the identified relevant factors.

SSR Alleviation in SCIG-Based Wind Power Plants Using Resistive Bridge-Type FCL

Series-Compensated Transmission Lines (SCTLs) are widely used for connection of large scale wind power plants (WPPs) to the power system to transmit the active power generated from WPPs. However, it can lead to sub synchronous resonance (SSR) phenomena in WPPs connected with SCTLs. Also, capacitive compensation of transmission lines reduces the line impedance, which leads to increasing short circuit current level in WPPs. This study proposes the resistive bridge-type fault current limiter (RBFCL) for SSR mitigation and limiting short circuit current in WPPs connected with SCTLs. Also, its performance is compared with the static synchronous compensator (STATCOM) and thyristor controlled series capacitor (TCSC) to demonstrate the effectiveness of the RBFCL in terms of SSR mitigation. The WPP used in this paper is modelled based on an aggregated squirrel-cage induction generator (SCIG) derived by an aggregated wind turbine (WT). The PSCAD/EMTDC software and the IEEE first benchmark model are used for this study. Simulation results demonstrate that the RBFCL not only limits the short circuit current contribution of WPPs, but also effectively damps the SSR oscillations due to IGE as well as TI, when the WPP is subjected to a large disturbance.

Short-Circuit Current Contribution of Doubly-Fed Wind Turbines According to IEC and IEEE Standards

The calculation of short-circuit currents is critical for the design of protection systems and electrical equipment rating. The short-circuit current contribution of traditional synchronous generators, which depends on common machine parameters, has been validated in recent decades. In this sense, the increasing penetration of wind power generation in current power systems means that network operators need to evaluate the response of wind turbines when a fault occurs. The recent publication of Edition 2 of IEC 60909-0 in 2016 defined a formulation to represent the short-circuit contribution for modern wind turbines, such as doubly-fed and full-converter technologies. Nevertheless, both the IEC and the ANSI/IEEE guidelines are based on new parameters that must be provided by the wind turbine manufacturer. This paper develops a methodology to calculate the parameters that define the short-circuit contribution of doubly-fed wind turbines for both international guidelines, IEC 60909-0 Ed. 2 and ANSI/IEEE. Field measurements and simulations are used for the validation of the developed method. Furthermore, some of the shortcomings of the IEC short-circuit calculation method are identified and alternative approaches are proposed and evaluated.

A Robust Adaptive Overcurrent Relay Coordination Scheme for Wind-Farm-Integrated Power Systems Based on Forecasting the Wind Dynamics for Smart Energy Systems

Conventional protection schemes in the distribution system are liable to suffer from high penetration of renewable energy source-based distributed generation (RES-DG). The characteristics of RES-DG, such as wind turbine generators (WTGs), are stochastic due to the intermittent behavior of wind dynamics (WD). It can fluctuate the fault current level, which in turn creates the overcurrent relay coordination (ORC) problem. In this paper, the effects of WD such as wind speed and direction on the short-circuit current contribution from a WTG is investigated, and a robust adaptive overcurrent relay coordination scheme is proposed by forecasting the WD. The seasonal autoregression integrated moving average (SARIMA) and artificial neuro-fuzzy inference system (ANFIS) are implemented for forecasting periodic and nonperiodic WD, respectively, and the fault current level is calculated in advance. Furthermore, the ORC problem is optimized using hybrid Harris hawks optimization and linear programming (HHO–LP) to minimize the operating times of relays. The proposed algorithm is tested on the modified IEEE-8 bus system with wind farms, and the overcurrent relay (OCR) miscoordination caused by WD is eliminated. To further prove the effectiveness of the algorithm, it is also tested in a typical wind-farm-integrated substation. Compared to conventional protection schemes, the results of the proposed scheme were found to be promising in fault isolation with a remarkable reduction in the total operation time of relays and zero miscoordination.

A calculation method for the short-circuit current contribution of current-control inverter-based distributed generation sources at balanced conditions

When a grid-connected inverter-based distributed generation (IBDG) source behaves as a current source that can limit its magnitude in current loop control, the contribution from the inverter to the short-circuit current (SCC) is not as significant as those from conventional synchronous generators. However, the increased IBDG sources can change the magnitude and phase angle of the SCC, so they should not be ignored in SCC calculation. The objective of this study is to present a method for calculating the SCC of an IBDG source of acting as an internally either limited or unlimited current source at balanced conditions. For this purpose, negative- and zero-sequence networks are transferred to a positive-sequence network with balanced IBDG sources. Subsequently, SCCs and zero-, negative-, and positive-sequence induced voltage are determined by using zero- and negative-sequence current injection matrices. Then, new SCC calculation equations for a single line-to ground, line-to-line ground, line-to-line, or three-phase fault are also derived. As a result, the proposed method improves the conventional method in terms of taking the contribution from a balanced IBDG source to SCC into account.

Impacts of Placement of Wind Turbine Generators with Different Interfacing Technologies on Radial Distribution Feeder Fuse-Fuse Protection Coordination Scheme.

The ever increasing demand on the electrical energy has led to the diversification on the electrical energy generation technologies especially from the renewable energy sources like the wind and the solar PV. Micro-grids powered by distributed generators utilizing renewable energy sources are on the increase across the globe due to the natural abundance of the resources, the favorable government policies and the resources being environmentally friendly. However, since the electrical power distribution networks have always been passive networks, the connection of the distributed generations (DGs) into the network has associated several technical implications with distribution network protection and Over-Current Protective Devices (OCPDs) miss-coordination being one of the major issues. The need for a detailed assessment of the impacts of the wind turbine generation (WTGs) on the distribution networks operations has become critical. The penetration of the WTGs into a distribution network has great impacts on the short circuit current levels of the distribution network hence eventually affecting the OCPDs coordination time margins. The factors which contribute to these impacts are: The size of the WTG penetrating the distribution network, the location at which the WTG is connected on to the network and the Type of the WTG interfacing technology used. An important aspect of the WTGs impacts studies is to evaluate their short circuit current contribution into the distribution network under different fault conditions. The magnitudes of these short circuit currents, both the three phase and the single-line-to-ground (SLG) faults, are needed for sizing the various Over-Current Protective Devices (OCPDs) utilized in protecting the distribution network. The sizing of the OCPDs entails among other procedures coordinating them with both the upstream and the downstream OCPDs so that there is sufficient time margin between their Time Current Characteristic (TCC) curves. For Fuse-Fuse protection coordination, the ANSI/NEC rules stipulate that a minimum of 0.025seconds or more time margin should be maintained between the primary/downstream fuse and the secondary/upstream/back-up fuse. Due to the topological and operational differences between the different types of WTGs interfacing technologies, the electrical generators design industry has divided wind turbine generators into four different types labeled as Type I, Type II, Type III and Type IV. This paper presents a detailed study of the impacts brought upon by integrating wind turbine generators on a conventional Fuse-Fuse protection coordination scheme. A conventional Fuse-Fuse protection coordination scheme was modeled in Electrical Transients Analysis Program (ETAP) software and WTG with different interfacing technologies connected. A study of the impacts brought by the integration of the WTGs on Fuse-Fuse Miss-coordination was performed. IEEE 13 Node Radial Distribution Test Feeder was used for the study.

Impacts of Placement of Wind Turbine Generators with Different Interfacing Technologies on Radial Distribution Feeder Fuse-Fuse Protection Coordination Scheme.

The ever increasing demand on the electrical energy has led to the diversification on the electrical energy generation technologies especially from the renewable energy sources like the wind and the solar PV. Micro-grids powered by distributed generators utilizing renewable energy sources are on the increase across the globe due to the natural abundance of the resources, the favorable government policies and the resources being environmentally friendly. However, since the electrical power distribution networks have always been passive networks, the connection of the distributed generations (DGs) into the network has associated several technical implications with distribution network protection and Over-Current Protective Devices (OCPDs) miss-coordination being one of the major issues. The need for a detailed assessment of the impacts of the wind turbine generation (WTGs) on the distribution networks operations has become critical. The penetration of the WTGs into a distribution network has great impacts on the short circuit current levels of the distribution network hence eventually affecting the OCPDs coordination time margins. The factors which contribute to these impacts are: The size of the WTG penetrating the distribution network, the location at which the WTG is connected on to the network and the Type of the WTG interfacing technology used. An important aspect of the WTGs impacts studies is to evaluate their short circuit current contribution into the distribution network under different fault conditions. The magnitudes of these short circuit currents, both the three phase and the single-line-to-ground (SLG) faults, are needed for sizing the various Over-Current Protective Devices (OCPDs) utilized in protecting the distribution network. The sizing of the OCPDs entails among other procedures coordinating them with both the upstream and the downstream OCPDs so that there is sufficient time margin between their Time Current Characteristic (TCC) curves. For Fuse-Fuse protection coordination, the ANSI/NEC rules stipulate that a minimum of 0.025seconds or more time margin should be maintained between the primary/downstream fuse and the secondary/upstream/back-up fuse. Due to the topological and operational differences between the different types of WTGs interfacing technologies, the electrical generators design industry has divided wind turbine generators into four different types labeled as Type I, Type II, Type III and Type IV. This paper presents a detailed study of the impacts brought upon by integrating wind turbine generators on a conventional Fuse-Fuse protection coordination scheme. A conventional Fuse-Fuse protection coordination scheme was modeled in Electrical Transients Analysis Program (ETAP) software and WTG with different interfacing technologies connected. A study of the impacts brought by the integration of the WTGs on Fuse-Fuse Miss-coordination was performed. IEEE 13 Node Radial Distribution Test Feeder was used for the study.

Short-Circuit Model for Type-IV Wind Turbine Generators With Decoupled Sequence Control

The power system planning and protection studies are becoming more challenging due to the rapid increase in penetration levels of converter-interfaced renewables. Type-IV wind turbine generators (WTGs) and photovoltaic panels are interfaced to the grid through a full-scale converter, and their short-circuit current contributions are mainly designated by the converter control and associated current limits. This paper proposes a new phasor domain modeling approach for the wind parks (WPs) with Type-IV WTGs, using the concept of control-based equivalent circuits. The proposed model precisely represents the detailed electromagnetic transient (EMT)-type model in steady state, and is able to account for the fault-ride-through function of the WTG control as well as its specific decoupled sequence control scheme in addition to the traditional coupled control scheme. Although the collector grid and WTGs inside the WP are represented with their aggregated models, the overall reactive power control structure of the WP is preserved by taking the central WP controller into account. The accuracy of the proposed model is validated through detailed EMT simulations.

A Comprehensive Review of Power Quality Issues and Measurement for Grid-Integrated Wind Turbines

Background: Renewable energy generation using wind energy has emerged worldwide and has opened up significant new markets in electrical power generation. However, different factors that affect power quality performance of Wind Turbine (WT) applications such as wind speed fluctuation and use of power electronic based devices have been presented due to the rapid increase of WT installations. Methods: Accordingly, it is worth to measure, assess and evaluate the quality of the generated power of these WTs in order to ensure their compliance with the grid-integration conditions. In this work, first, a general classification of WTs and their operating principle is reviewed. Because variable speed WTs are frequently used in today’s power systems, much attention was paid to this type of turbines. Second, the various power quality aspects caused due to the integration of the wind energy systems into the grid were presented and discussed. Flickers, harmonic distortion, response to voltage dip, active power, and reactive power requirements, fault-ride through and short-circuit current contribution were the addressed power quality problems. Results: Further, the study pointed out the need for a unified evaluation process to assess the power quality performance of the grid-connected wind systems. Conclusion: Also, it was concluded that success in integrating more wind energy systems hinges on accurate power quality performance assessment.

LVRT Test data analysis of converter‐interfaced wind turbines

Doubly Fed Induction Generator (DFIG) and Permanent Magnet Synchronous Generator (PMSG) are converter-interfaced wind turbines, which have much more complex short circuit behaviour after grid voltage drops. The research on short circuit current contributions provided by the wind turbines is very important for power system planning and relay protection's setting. Here, the Low Voltage Ride Through (LVRT) test data in north China are used to study the short circuit behaviour of DFIGs and PMSGs. The characteristics of two featured quantities, fundamental frequency component and peak current, are investigated. Unlike simulation or theoretical analysis, the field test data of real wind turbines from different manufacturers help utility operators to better understand the fault characteristics of converter-interfaced wind turbines.

Comprehensive Study on Different Possible Operations of Multiple Grid Connected Microgrids

This paper proposes an efficient strategy for control of multiple grid connected microgrids (MGs) through converters, to improve network management during normal, islanding, and fault conditions. In normal condition, the converters control the bidirectional power flow between the MGs (downstream) and the main network (upstream). When the upstream is disconnected from downstream, if one of the MGs cannot handle its local loads, the deficit of power is provided by the other MGs. Transferred powers of the MGs are controlled regarding power quality (PQ) preserving criteria of the network. If PQ in a point of common coupling of an MG degrades, its converter goes into semi-isolated mode. Furthermore, in case of fault occurrence in the upstream, the converters limit fault current contribution of the MGs, in order to preserve the MGs PQ. However, in case of fault occurrence in the MG, the converters are bypassed by the relevant static switches. Therefore, short circuit current contribution of the upstream will be maximized to improve the MGs PQ. This strategy can also overcome the problems related to the system short circuit capacity increment in case of a newly added distributed generation unit, such as loss of the over current relays coordination.