The starting current of the submersible pump reached a maximum of 227A, which caused the thermal-magnetic protection of the upstream switch to activate and trigger a trip?

The instantaneous value of the starting current is independent of the load; even if the pump impeller gets stuck, it should not cause any change in the maximum value of the starting current’s instantaneous value. If the pump impeller indeed gets stuck, it will only cause the starting current to last longer and not decrease (which could potentially trigger the thermal-magnetic protection of the upstream switch to trip). If the insulation of the motor windings with respect to ground is normal, the high maximum starting current is likely due to a decrease in the insulation resistance between the winding phases or between individual turns. It is relatively easy to check for a decrease in inter-phase insulation, but it is very difficult to check for a decrease in inter-turn insulation. Another possible reason for the high maximum starting current is a partial break in one of the three-phase windings (if the windings are wound in double strands). A double-arm bridge can be used to measure the DC resistance of three-phase windings; if a large deviation is detected, it should be suspected that there is a partial open circuit in one of the phases (the phase with the higher resistance value). In addition, it is also necessary to check whether capacitors for improving the power factor are connected in parallel to the motor; if the performance of these capacitors deteriorates, it can also lead to an increased starting current.

A submersible pump with a rated current of 12A had a starting current as high as 227A; it should have burned out long ago, rather than just tripping. The starting time is generally very short, so high currents for a brief period do not cause damage to the motor. In the case of motor stall, theoretically the actual power of the motor approaches infinity, and the stall current also approaches infinity. However, due to the internal resistance of the motor windings, the stall current is slightly higher than the starting current. Specific numerical values in this regard have not been noted, as stall can lead to motor damage; therefore, protective circuits must be added to the circuit to prevent the motor from remaining under power during a stall condition. The maximum current is the current at which the motor can operate for an extended period of time, and it is usually around 1.2 times the rated current. Often, improper calculation of the design power results in a motor that is too small for the required requirements. Yet the motor can still operate continuously when the power exceeds its rated value, with the operating current at this time being the maximum current. The rated current, on the other hand, is the current at which the motor operates under its rated power, and generally, the operating current during normal operation is less than the rated current. The starting current of a motor is generally 5 to 7 times its rated current. This post was last edited by lbp on 2009-4-7 14:46.]

I’ve been looking for a reasonable explanation for the issue of starting current, as people from the client side keep asking about it. Thank you for the answer above! Support

No specific research has been done on submersible pumps. However, the starting current of a typical motor is 5 to 7 times the rated current. A factor of 10 is considered quite high. Like 20 times this much – I’m not sure if what the original poster is referring to is a normal phenomenon. There are established guidelines for selecting general power distribution protection products. To start a regular motor directly, an instantaneous trip setting based on 10 to 12 times the rated current and a D-type curve is generally used. But for some fans. Pumps (such as submersible pumps) operate under high load when started, which is why the startup time is longer. Unless starting and stopping occur frequently, this is acceptable for mechanical equipment; in such cases, electrical engineers need to use special protective devices capable of withstanding the high currents associated with long startup times, for example by employing electronic components! ~!