The consensus protocol of cyber-physical power systems is proposed based on fractional-order multi-agent systems with communication constraints. It aims to enable each generator to reach a time-varying common rotor angle and rotor speed. Communication constraints including event-triggered sampling and partial information transmission are considered to render the consensus protocol more realistic. The Zeno behavior is excluded during the system sampling process. A sufficient condition is derived to solve the consensus problem. The effectiveness of the proposed consensus protocol is demonstrated by a numerical example.