The power consumption of core networks is bound to grow considerably due to increasing traffic volumes. Network reconfiguration adapting resources to the load is a promising countermeasure. However, the benefit of this approach is hard to evaluate realistically since current network equipment does not support dynamic resource adaptation and power-saving features. In this paper, we derive a dynamic resource operation and power model for IP-over-WSON network devices based on static power consumption data from vendors and reasonable assumptions on the achievable scaling behavior. Our model allows to express the dynamic energy consumption as a function of active optical interfaces, line cards, chassis, and the amount of switched IP traffic. We finally apply the model in the evaluation of two network reconfiguration schemes.