Phase Unbalance Protection (ANSI 46)
Phase unbalance protection detects unbalances of the motor phase currents. Phase loss detection is an extreme case of phase unbalance detection.
|
Unbalances of the motor phase currents lead to significant heat rise and braking torques that can cause premature deterioration of the motor. These effects are amplified during startup: protection must be almost immediate. |
Phase unbalance protection:
oCalculates the current unbalance for each phase, compared to the average current, expressed as a percentage:
oCompares the value of the maximum current unbalance with the Iunbal protection pickup.
The following diagram shows a maximum positive unbalance on phase 2:
If the maximum current unbalance value is higher than the phase unbalance protection Iunbal pickup, the tunbal time delay is actuated.
Phase unbalance protection cannot be deactivated.
Phase unbalance protection is activated during startup and in steady state.
oThe current unbalance does not fall below the Iunbal pickup before the end of the tunbal time delay: the phase unbalance protection trips. The behavior of the protection differs according to the motor operating conditions:
|
During startup: oA: Activation of startup phase. oB: Activation of protection time delay as soon as the pickup is crossed. oC: Protection tripped at the end of the fixed time delay of 0.7 s. |
|
1M Motor current 1D Maximum unbalance of the motor phase currents 2A Monitoring by phase unbalance protection during startup White: Not active Green: Active |
|
|
In steady state: oA: Activation of steady state phase. oB: Activation of protection time delay as soon as the pickup is crossed. oC: Protection tripped at the end of the adjustable time delay. |
|
1M Motor current 1D Maximum unbalance of the motor phase currents 2B Monitoring by phase unbalance protection in steady state White: Not active Green: Active |
|
oThe current unbalance falls below the Iunbal pickup before the end of the tunbal time delay: the phase unbalance protection does not trip.
|
In steady state: oA: Activation of steady state phase. oB: Activation of protection time delay as soon as the pickup is crossed. oD: Time delay is reset. |
|
1M Motor current 1D Maximum unbalance of the motor phase currents 2B Monitoring by phase unbalance protection in steady state White: Not active Green: Active |
|
NOTE: The SDx module (set on SDTAM early tripping protection function) can be used to open the contactor instead of tripping the device.
Set the Iunbal pickup and the tunbal time delay:
oWith the EcoStruxure Power Device app.
oWith the EcoStruxure Power Commission software.
The Iunbal pickup setting value is expressed as a percentage of the average current.
The pickup setting range is 10–40%. The increment is 1%. The default pickup setting value is 30%.
The accuracy range is +/-20%.
tunbal Time Delay Setting Value
The tunbal time delay setting value is in seconds.
The tunbal time delay setting depends on the operating conditions:
oDuring startup, the value of the time delay cannot be adjusted and equals 0.7 s.
oIn steady state, the setting range is 1–10 s. The increment is 1 s.
The default time delay setting value is 4 s.
