Abstract: The evolutionary process of WLAN system from taking fat access point(AP) to taking “access controller(AC)+thin AP” is introduced.The traditional real-time power supervisory control and data acquisition (SCADA )system and nonrealtime Web SCADA system are discussed.To be applied in realtime SCADA system of main stations,a thin SCADA system based on centralized cloud control is proposed, with reference to the concept “AC+thin AP”. The system realizes the hierarchy simplifying of layered distributed power SCADA system.Combined with cloud system and big data technologies,the system can set up a safer and more stable largescale Electric Internet of Things, which can support more advanced power applications.

Key words: layered distributed structure, SCADA, AC, fat AP, thin AP, cloud system, centralized control