Underload Motor Protection
Presentation
Underload motor protection provides additional protection for detection of motor no-load operation.
Examples of no-load operation: pump running dry, broken drive belt, broken geared motor.
Description
Underload motor protection compares the value of the phase current minimum I MIN with the setting value of the protection Iund pickup. If the current value I MIN falls below the Iund pickup, the protection tund time delay is actuated.
By default, underload motor protection is not active.
After function setting, underload protection is activated during startup and in steady state.
Operating Principle
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Diagram Ι: The phase current minimum value I MIN does not go above the protection Iund pickup before the end of the tund time delay (for example, a pump operating at no load). Underload motor protection trips:
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A: Protection activated (change to steady state)
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B: Activation of protection time delay as soon as the pickup threshold is crossed
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C: Protection tripped at the end of the time delay
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Diagram ΙΙ: The phase current minimum value I MIN goes back and stays above the pickup before the end of the tund time delay (for example, a pump temporarily running dry). The underload motor protection does not trip:
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B: Activation of protection time delay as soon as the pickup threshold is crossed
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D: Protection disabled
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Setting the Protection
The Iund pickup and the tund time delay settings can only be accessed:
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With EcoStruxure Power Commission software (password-protected)
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By sending a setting command using the communication network (password-protected)
Iund Pickup Setting Value
The Iund pickup setting value is in multiples of Ir.
The pickup setting range is 0.3–0.9 x Ir. The increment is 0.01 x Ir. The default setting is OFF: protection not active.
The accuracy range is +/-10%.
tund Time Delay Setting Value
The tund time delay setting value is in seconds.
The time delay setting range is 1–200 s. The increment is 1 s. The default setting value for the time delay is 10 s.