Before
Above shown is a transfer system control panel where the pump is started by auto-transformer. Our customer is experiencing problems with the auto-transformer as there is rapid cut-in and cut-out of the pumps. The auto-transformer had to be regularly replaced and serviced to keep up with the system demand. In view of this, we proposed our customer to change their design for the pumps to be started by a Soft-starter. Hopefully this would help our customer solve the root of the problem.
After
With the new system installed, we observe that the pump starts and stops smoother and there is no back hammering of water. For this application we chose to use torque ramp instead of voltage ramp to ramp down and ramp up the pump. Using a torque ramping method greatly improves the stability of the system.
For the acceleration and deceleration we set as 10 seconds and 20 seconds respectively. Usually for a transfer system, the deceleration has to be longer than acceleration, because the water will come back down and cause back hammering.