Online Transient Measurements of EHV Cable System and Model Validation

The increasing utilization of HVAC underground power cables gives rise to technical challenges related to the occurrence of electromagnetic transients. This paper discusses measurements with sensors based on open air capacitances sensing the electric fields from the line having a wide frequency bandwidth and excellent electromagnetic compatibility performance. However, since the sensors are open air capacitors, they also intercept field lines from other phases and measurement decoupling is necessary. Results from measurements, using the differentiating/Integrating technique, at a 380 kV mixed overhead line underground power cable connection obtained at a transition point and at a substation are presented and compared with PSCAD/EMTDC simulations. The measurement system gives accurate results for low and high frequency transients, while the effect of uncertainties in the decoupling is minor. For switching transients, the simulation model was validated in terms of measured and simulated voltage waveforms resulting in similar maximum overvoltage and frequency content.

I. Introduction

In Recent years an increasing number of EHV underground power cables (UGC) is incorporated at the Extra-High Voltage transmission grid due to increased urbanization as well as political and environmental developments [1]. However, UGCs display different behavior compared to overhead lines (OHLs). This can give rise to operational and grid planning challenges with respect to the steady state and transient behavior of mixed OHL-UGC grids [2]. In order to investigate the impact of new UGC installations in the existing EHV transmission system, formulation of accurate simulation models validated with measurements is of high importance.