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Starting Current


JONY

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Hello JONY

 

In order to calculate the starting current of the pumps, you need to know a number of parameters.

 

Firstly, the minimum start current is determined by the minimum start torque of the pumps and the ability of the motor to develop that torque, plus the start method employed.

 

If you start the motors on Full Voltage, they will always draw Locked Rotor Current, Independent of connected load, and will have a starting current typically in the range of 600% - 900% of the rated current of the motor.

 

If you use a reduced voltage starter, the current will be reduced by the voltage reduction and the torque will be reduced by the voltage reduction squared.

If you reduce the start voltage too much, you will not produce sufficient torque to start the pump.

 

By drawing out the speed torque curve of the pump, and overlaying the speed torque curve of the motor at different start settings, you can determine the minimum starting current of the pump and motor.

NB each motor has different starting characteristics, so the calculations need to be done for each motor.

Best regards,

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  • 2 months later...
Hello JONY

 

In order to calculate the starting current of the pumps, you need to know a number of parameters.

 

Firstly, the minimum start current is determined by the minimum start torque of the pumps and the ability of the motor to develop that torque, plus the start method employed.

 

If you start the motors on Full Voltage, they will always draw Locked Rotor Current, Independent of connected load, and will have a starting current typically in the range of 600% - 900% of the rated current of the motor.

 

If you use a reduced voltage starter, the current will be reduced by the voltage reduction and the torque will be reduced by the voltage reduction squared.

If you reduce the start voltage too much, you will not produce sufficient torque to start the pump.

 

By drawing out the speed torque curve of the pump, and overlaying the speed torque curve of the motor at different start settings, you can determine the minimum starting current of the pump and motor.

NB each motor has different starting characteristics, so the calculations need to be done for each motor.

Best regards,

 

very good

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