Centrifugal pump trips due to overcurrent
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I have a question and would like to thank everyone in advance :) There is a centrifugal pump in the factory, model ISG50-250B, with a head of 68 meters, a flow rate of 14 m3/h, and a motor power of 7.5 KW. It is currently used to boost the pressure of circulating water; the inlet pressure of this water is 4 kilograms per square meter, while the outlet pressure needs to be maintained at 5 kilograms per square meter. When the pump is turned on, it experiences overcurrent – around 28 A – which causes the thermal relay to trip. Is this a problem related to the selection of the water pump? And how to calculate the current head and flow rate? Thank you all
Thank you to the brother above for the reply; the outlet valve closes when the pump starts, and once it starts running it opens a little, which causes the current on both sides to exceed the limit
The selection is not appropriate. The current head is roughly 5 kilograms minus 4 kilograms, minus the losses due to resistance; in reality, the required head is less than 1 kilogram, that is, less than 10 meters. Using a pump with a head of 68 meters will result in overpressure. By opening valves to reduce the pressure, current levels will inevitably increase.
Regarding the operational control issue, a pressure gauge should be installed in front of the pump’s outlet valve. When the valve is opened, it is essential that the current level remain within acceptable limits; with such a large pressure drop, the flow rate will definitely increase significantly. In other words, your current flow rate must not exceed “14 m3/h”; only at this flow rate can a head of 68 meters be maintained before the pump outlet valve. The compressibility coefficient of water is extremely low; therefore, even though a pressure of 4 kilograms needs to be achieved after the pump’s outlet valve, the flow rate will not exceed 14 m3/h by much. Your problem lies in focusing only on traffic and not on pressure. It is necessary to ensure the outlet pressure of the pump, taking into account how the corresponding flow rate will be utilized. For reference.
To put it simply, the valve is still open too wide. With a head of 68m and a required pressure increase of 1 Bar, it’s sufficient to open the valve just a little bit; at that point the pressure will be around 10 Bar. Opening the valve any further would result in overload, which must be prevented as it can easily damage the motor
Incorrect selection – some media sticking to the impeller can also cause current overload