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.
According to NEC 240.101 regulations each and every component of a power system distribution network has to have an over-current protective device (OCPD) for its protection. The OCPDs must coordinate with other devices both upstream and downstream for a reliable operation and protection of the power systems distribution network. There are four equipment/components for the IEEE 13 node radial test feeder each modelled in this paper to be protected by fuses. These components are namely the nodes, the underground cables, the overhead distribution lines and the transformers. Equipment protection is an important and necessary exercise of performing power systems protection coordination processes. The equipment and their over-current protective device’s time-current characteristic (TCC) curves are important tools used to show and to indicate the protection requirements, landmark points and damage curves for all power systems equipment. Individual equipment protection requirements and limitations are described and identified by use of their various landmarks and damage curves. These damage curves and the landmark points are all superimposed with the Time-Current Characteristic curves of the Over-Current Protective Devices used in protecting the equipment on one composite TCC graph. Equipment damage curves which fall to the right and above the Over-Current Protective Device’s TCC curves with sufficient margins are considered to be protected by the OCPDs. Equipment damage curves which fall to the left and below the OCPD’s TCC curves are considered not to be protected by the OCPDs. IEEE Standard 241 states that on all power systems, the OCPDs should be selected and set to open before the Ampacity mark, the short circuit damage curves, and both the thermal and the mechanical damage curves limits of the protected components are exceeded. This paper presents a detailed Fuse-Fuse protection scheme for the IEEE 13 node radial test feeder as modeled on the Electrical Transients Analysis Program (ETAP).
With the global increase in the number and the capacity of the distributed generators (DGs) penetration levels in the power systems networks', there is need for a detailed assessment of the impacts the DGs have on the power systems operations. The distribution network topology, control and protection philosophies are all designed to extract power from the transmission network and distribute it to the loads. The distribution network is not designed to have generators directly connected into it hence its power flow is unidirectional from the main utility grid to the loads. During a short circuit, the presence of DGs in a distribution network creates an increase in the short circuit current levels of the distribution network and a bi-directional power flow. A wind turbine generator (WTGs) is one of the most commonly utilized form of renewable energy largely integrated into the distribution networks. An important aspect of theWTGs impacts studies is to evaluate their short circuit current contribution into the distribution network under different fault conditions. The IEEE 13 node radial test feeder was modelled for the short circuit study in electrical transient analysis program (ETAP) software. The short circuit study was then performed on the radial test feeder firstly without WTGs connected and secondly with different WTG interfacing models connected at various nodes on the 13 node radial test feeder. Four models utilizing either the induction machines or the synchronous machines were simulated in ETAP for the WTG interfacing. The four models were classified as Type I, Type II, Type III and Type IV WTGs. Placement of the four models of the WTGs, Type I, Type II, Type III and Type IV WTGs created an increase in both the three phase and the SLG short circuit fault currents levels of the test feeder. Of the four models the Type I, Type II and Type III WTGs displayed similar characteristics in the increase in both the three phase and the SLG fault currents levels hence the three models were represented as one WTG model and referenced as a doubly fed induction generator (DFIG) machine. The Type IV WTG model was the only unique machine in how it impacted on the fault currents hence it was studied alone. The two WTG models, that is the DFIG machine and the Type IV machine, were then broadly classified as the two main interfacing technologies utilized in the WTG modelling from either the induction machines or the synchronous machines. This paper presents a detailed investigation on the impacts the two WTG interfacing technologies, the DFIG and the Type IV WTG models with their capacities being varied from 1MW to 3MW have on both the three phase fault currents and the SLG fault currents occurring at selected nodes of the IEEE 13 node radial test feeder chosen for the study.
With the ever increasing number and capacities of the distributed generations (DGs)penetrating the conventional radial electrical power distribution networks, there is need for a detailed assessment on the impacts the DGs have on the distribution network's sequence impedances during fault conditions. The conventional distribution networks are designed to extract power from the transmission network and distribute it to the loads. The distribution networks were not designed to have DGs directly connected into them hence their power flow is unidirectional from the main utility grid to the loads. When balanced, un-faulted and in normal operating state, the power system's voltages and currents can be evaluated and determined with utmost simplicity. When the power systems is balanced and un-faulted, the line and phase for both the voltages and the currents are of equal magnitudes and displaced by 120º from each other, however, when the power system network is unbalanced and faulted, the magnitudes of the phase voltages and currents are not equal and are displaced by angles more or less than 120º, hence evaluating and determining the network quantities can be difficult under the unbalanced and faulted operating conditions.
The ever increasing global demand on the electrical energy has lead to the integration of Distributed Generators (DGs) onto the distribution power systems networks to supplement on the deficiencies on the electrical energy generation capacities. The high penetration levels of DGs on the electrical distribution networks experienced over the past decade calls for the grid operators to periodically and critically asses the impacts brought by the DGs on the distribution network operations. The assessment on the impacts brought by the DGs on the distribution network operations is done by simulating the dynamic response of the network to major disturbances occurring on the network like the faults once the DGs have been connected into it. Connection of Wind Turbine Generators (WTGs) into a conventional electrical energy distribution network has great impacts on the short circuit current levels experienced during a fault and also on the protective devices used in protecting the distribution network equipment namely; the transformers, the overhead distribution lines, the underground cables and the line compensators and the shunt capacitors commonly used/found on the relatively long rural distribution feeders. The main factors which contribute to the impacts brought by the WTGs integration onto a conventional distribution network are: The location of interconnecting the WTG/s into the distribution feeder; The size/s of the WTG/s in terms of their electrical wattage penetrating the distribution network; And the type of the WTG interfacing technology used labeled/classified as, Type I, Type II, Type III and Type IV WTGs. Even though transformers are the simplest and the most reliable devices in an electrical power system, transformer failures can occur due to internal or external conditions that make the transformer incapable of performing its proper functions. Appropriate transformer protection should be used with the objectives of protecting the electrical power system in case of a transformer failure and also to protect the transformer itself from the power system disturbances like the faults. This paper was to investigate the effects of integrating WTGs on a distribution transformer Fuse-Fuse conventional protection coordination scheme. The radial distribution feeder studied was the IEEE 13 node radial test feeder and it was simulated using the Electrical Transient Analysis Program (ETAP) software for distribution transformer Fuse-Fuse protection coordination analysis. The IEEE 13 Node radial test feeder In-line transformer studied is a three-phase step down transformer having a star solidly grounded primary winding supplied at and a star solidly grounded secondary winding feeding power at a voltage of . The increase on the short circuit currents at the In-line transformer nodes due to the WTG integration continuously reduces the time coordination margins between the upstream fuse F633 and the downstream fuse F634 used to protect the transformer.
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