Climate agreement goals set by the Dutch government increase the urge to reduce our greenhouse gases. To fulfil these goals on a residential level a reduction of the emission of carbon which is produced during household demand and transportation (commute) is required. On a residential level, the amount of photovoltaic systems (PV) and electric vehicles (EV) is increasing rapidly to meet these requirements. All these individual changes in the low voltage (LV) grid will have an impact on the aggregated load profile in the medium voltage (MV) network.
The MV network consists of underground cable connections, which play a vital role in the transmission and distribution of electrical power. Currently, the distribution network operator (DNO) uses a fixed ampacity which is based on fixed site conditions to rate their MV cables. The current methodology only considers the current peak of the load profile, but the ampacity of a cable connection is governed by its temperature.
Ampacity ratings for MV cables are specified for a continuous load applied on the specific underground MV cable in certain ambient conditions. When a cyclic load profile is applied the temperature of the cable will not remain constant over a 24 hour load cycle. Since this introduces moments of lesser loading the underground cable has moments during its load cycle to be able to cool down. If this method is applied the whole load profile which is applied on the MV cable could be raised by a factor so that the peak of the profile safely exceeds the nominal ampacity, but stay within the specified thermal limits.
The area in which the DNO operates is quite expansive, the material surrounding the underground MV cable connection will differ for each area. There is a big uncertainty in terms of ground conditions for the majority of the MV cables. The effect that this has on the ampacity of the cable connection will be examined. By running multiple simulations with different ambient conditions, the impact that this uncertainty has on the ampacity can be concluded.
The simulations will be done with an analytical- and a finite element model (FEM). With these models, the effects of uncertain ground conditions and the possibility to use an cyclic rating factor for specific load profiles can be calculated. This will be used to study the impact of the changing cyclic load profile due to the increase of PV and EV in the network. The interplay between these factors is interesting since the uncertain ground conditions have a negative impact on the overall ampacity while the cyclic rating factor can (partly) compensate for this loss.