NUCLEAR O&M 2. Controlled start-up. This chart shows the start-up characteristics of the reactor recirculation pump before and after the ASD retrofit. Note the significant decrease in inrush current experienced with the ASD. Source: Exelon Nuclear Before amps 1000 900 800 700 600 500 400 300 200 100 5 Depress start 10 15 After amps Pump DP Indicated pump speed Min speed = 32 2.5%/sec 5%/sec 70 60 50 40 30 20 10 20 Time (sec) 25 30 35 40 system used to adjust the MG fluid coupler and the generator voltage regulator. This old electromechanical system would not always respond to small speed demand changes and would occasionally move erratically. The ASD, in contrast, is electrostatic and has no moving parts associated with the drive output controlling the pump speed. As a result, the observed speed changes are crisp, accurate, and very stable. As shown in Figure 2, it takes about 6 to 8 seconds after depressing the start pushbutton to achieve motor magnetization. Once breakaway torque is achieved, the motor speed ramps at a specified 5%/sec up to 20% speed, and then it changes to 2.5%/ sec up to the minimum operating speed of 32%. At this speed, the operator will open the pump discharge valve and then demand speed increases as required. Quad Cities uses a digital reactor recirculation control system to control the drives. This system provides a continuous speed demand-a digital signal equivalent to the analog 4-20 ma-to the drive. This signal range corresponds to a 20% to 102.5% pump speed range. The system is programmed to allow slow and fast changes in the raise speed and lower speed diFor more information please visit www.maps.platts.com November 2010 | POWER www.powermag.com 67 Amps % speed/DP (psid) NEW! U.S. Coal Activity Map and CDhttp://www.maps.platts.com http://www.powermag.com