Issues regarding the measurement of the ST571 motor comprehensive protector
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The control room is planned to be able to monitor the motor operating current. The ST571 motor comprehensive protector is currently installed in the drawer cabinets of the power distribution room; it has two analog terminals for outputting analog current signals. Is the maximum output value of 20 mA the corresponding rated current value for the analog signal? Does the operating current of a motor generally exceed its rated current? If so, generally the motor operates at full scale within the DCS system; isn’t it then unnecessary to display it? What is the operating pressure for ordinary centrifugal pumps? Are there any good methods?
The 20mA output from the integrated protector should correspond to the current value set for your protector
I asked the manufacturer, and it’s the rated current value
Can it be changed? If it’s changed, will protection no longer work?
It can be changed, but only within the rated current of its protector
MCCBs have a rated current, such as 16, 25, 50, 100A, etc. When used in conjunction with motors, it is necessary to select a MCB whose rated current is higher than that of the motor. For example, for a 11kW motor with a rated current of around 18A, a 25A MCB would be suitable. A value of 20mA corresponds to an input current of 25A, which is the rated current of the MCB; therefore, setting the maximum value on the DCS screen to 25A will suffice (typically, MCCBs output signals in the range of 4-20mA, with 4mA corresponding to 0A in the DCS system). According to the design, there should be at least a 20% margin; under normal conditions it will not operate under overload, which is related to the choice and settings of the comprehensive protection system. A clamp meter can be used to measure the actual operating current of the motor, allowing for a comparison.
The range usually set is twice the rated value; otherwise, how can over-time be displayed?