© 2018 European Control Association (EUCA). The problem of decentralized frequency control in power networks has received an increasing attention in recent years due to its significance in modern power systems and smart grids. Nevertheless, generation dynamics often involve turbine/governor dynamics, which, in conjunction with non-linearities associated with generation and power flow, increase significantly the complexity in the analysis, and are not adequately addressed in the literature. In this paper we show how incremental secant gain conditions can be used in this context to reduce the conservatism in the analysis. The stability conditions derived are decentralized and are demonstrated throughout the paper with various examples.