Abstract
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.
Highlights
The ever increasing global demand on the electrical energy has led to the integration of Distributed Generators (DGs) onto the distribution power systems networks to supplement on the deficiencies on the electrical energy generation capacities
There is no increase in the three phase fault currents at the secondary side of the in-line transformer when 1MW and 3MW Type I/II/III Wind Turbine Generators (WTGs) are connected at NODE634
There is a gradual and linear increase in the single-line-to-ground fault currents at the secondary side of the in-line transformer when 1MW and 3MW Type I/II/III WTGs are connected at NODE634
Summary
In order to effectively protect a power systems distribution network transformer and implement the fusefuse protection scheme, transformer protective devices must be set within the NEC 450.3 requirements for transformer overload protection to allow for the normal magnetizing inrush currents to flow [1]. Transformers having percentage impedances less than 10% on the primary/source side of the transformer, the primary side protection must have an upstream fuse rated at 300% of the transformer full load currents. The FLA mark is located on the transformer TCC log-log graph at the top decade at the 1000 seconds mark as seen from Fig 1. The thermal damage curve is shown located at the 3rd and 4th decade of the TCC coordination curve starting from the 2seconds mark to the 1000 seconds mark as shown in Fig. 1 [6]
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