El manejo de la discapacidad en las escuelas

This paper introduces a technique to estimate the flow of GIC in HV transformer based on its reactive power absorption that can be computed from available measurements of power flows at the terminals of the transformer. While previous work [12] has, through simulation, noted a correlation between reactive power absorption and GIC, this paper not only defines that relationship, but proposes its application to measure GIC using existing infrastructure in place to measure reactive power.

Reactive power flow is monitored in real time on most modern EMS/SCADA systems by the power system controlling authority. Therefore, in principle, the GIC flows on every transformer in the system due to an SMD event can be determined in real time without additional GIC monitoring equipment and

without direct knowledge of the electric field or ground characteristics of the HV transmission network.

This proposed technique is consistent with simulations carried out with commercially available EMTDC/PSCAD software. Field measurements retrieved from historical records of the May 2005 SMD event show a very good correlation between calculated GIC and measured values on a transformer with a dedicated GIC monitor. This level of agreement is very encouraging considering the relatively low GIC currents measured during the event and the relatively low time resolution of historical records.

While the example presented in this paper is for an autotransformer and is therefore complicated by the multiterminal flow of GIC, it should be noted that in the case of two winding transformers, there is only a single GIC flow path in each winding. In this case the calculation of GIC is very simple. Even in the case of autotransformers the net DC flux is easily computed with the presented technique. It is ultimately the net DC flux that causes undesired effects in the electrical grid.

If the GIC flowing through every transformer are known, it is relatively simple to estimate the flows in transmission lines. This would in turn allow the estimation of the induced electric field spatially as well as temporally. This information would be valuable in the validation and improvement of traditional field-based GIC estimation techniques.

Validation of the proposed technique with measurements of a relatively mild SMD event could be considered as a good starting point. As more measurements become available during the maximum period of solar cycle

refine this technique for broader application outside the Hydro One HV transmission network.

References

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