Different diagnostic techniques are currently available for on-line insulation condition assessment of power transformers. Amongst these techniques a relatively new technique for detecting partial discharges (PD) in the Ultra High Frequency range of the spectrum is also introduced. The UHF technique has been recently presented in the field of transformer diagnostics, and although it is under development it shows great potential for on-line detection, recognition and location of PD activity. This paper describes the practical application of the UHF technique on two new identical 90 MVA, 150 kV power transformers. Both transformers are equipped with four external UHF sensors. Initially, injection measurements were performed to investigate the effects experienced by UHF signals when propagating through the transformer. Moreover, software developed to model the propagation of UHF signals inside the transformer tank was tested in its application to these specific transformers. The results obtained during the both the induced voltage test, as well as during the PD acceptance test in the factory are described. The practical experiences related in this paper provide further insight into the application of UHF PD monitoring techniques to power transformers.@en

This brief investigates the robust model predictive control (MPC) for train regulation in underground railway transportation. By considering the uncertain passenger arrival flow, a constrained state-space model for the train traffic of a metro loop line is developed. The goal of this brief is to design a state feedback control law at each decision step to optimize a metro system cost function subject to safety constraints on the control input. Based on Lyapunov function theory, the problem of optimizing an upper bound on the system cost function subject to input constraints is reduced to a convex optimization problem involving linear matrix inequalities. Moreover, for the inevitable disturbances leading to the delays, the robust MPC strategy of train regulation is designed for a metro loop line such that it ensures the minimization of an upper bound on metro system cost function, and meanwhile guarantees a disturbance attenuation level with respect to the disturbances. Numerical examples are given to illustrate the effectiveness of the proposed methods.@en