User manual 09/2009 - Schneider Electric

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User manual 09/2009 - Schneider Electric

The Protection FunctionPhase Unbalance ProtectionPresentationUnbalances of the motor phase currents lead to significant heat rise and braking torques that can causepremature deterioration of the motor. These effects are amplified during startup: protection must bealmost immediate.DescriptionPhase unbalance protection:• calculates the current unbalance for each phase, compared to the average current, expressed as a %:• Compares the value of the maximum current unbalance with the Iunbal protection pick-upThe diagram below shows a maximum positive unbalance on phase 2:I1- Iavg I2 - Iavg I3 - Iavg< 0 > 0 < 0I1 I2 I3IavgIf the maximum current unbalance value is higher than the phase unbalance protection Iunbal pick-up,the tunbal time delay is actuated.Phase unbalance protection cannot be deactivated.Phase unbalance protection is activated during startup and in steady state.66 LV434104 09/2009

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