ABB 变频器.ppt

? ABB Group * | Slide * * * The pump is usually connected to some kind of system with pipes, tanks, valves etc. How the pump and the system work together is usually presented by pump and system curves. Pump curve:Usually has its highest point Hmax at zero flow and from there the pump curve runs down. This curve can be estimated as a parabolic curve. Pumps rated operating point PN is normally selected around the best efficiency of the pump. The rated flow and head are marked as QN and HN. System curve:The system curve normally runs in opposite direction to the pump curve. At zero flow its head value equals to the static head of the system Hst The static head can equal to zero in closed loop systems like circulating pumps. * The energy efficiency of centrifugal pumps is based on these equations: 1. If we reduce the pump speed down to 80%, the Flow is reduced down to 80% 2. If we reduce the pump speed down to 80%, the Head is reduced down to 64% 3. If we reduce the pump speed down to 80%, the Power is reduced down to 48% In other words: We get 80% liquid flow with less than 50% of electric power. * These curves show the reason for using the AC drive for flow control of the centrifugal pump. The lowest curve is the actual power required to run the pump. The different control methods need more power from the line: The lowest power requirement has the AC drive, which has the best efficiency. The highest power is required for recirculation, which has the lowest efficiency. The most usual control method in the existing systems is the throttling by a valve. Its power requirement is quite high also, which means that the efficiency is poor especially in the lower flow range. * These curves show the reason for using the AC drive for flow control of the centrifugal pump. The lowest curve is the actual power required to run the pump. The different control methods need more power from the line: The lowest power requirement has the AC drive, which has the best effici