Phase Imbalance Protection

Overview

The phase imbalance protection is used to protect asynchronous motors against current phase imbalance conforming to the IEC 60947-4-1 and UL 60947-4-1 standards.

The phase imbalance protection can be used to protect three-phase IE1, IE2, IE3, and IE4 asynchronous motors.

Phase imbalance causes the overheating of the motor. It can occur in case of:

• Long main supply lines.

• Defective contact on the incomer switch.

• Imbalanced network.

Operation

The overload relay calculates the imbalance current ratio in each phase as given below:

• Ii1 = (| I1 - Iavg | x 100) / Iavg
• Ii2 = (| I2 - Iavg | x 100) / Iavg
• Ii3 = (| I3 - Iavg | x 100) / Iavg

Where Iavg = (I1 + I2 + I3) / 3, and I1, I2 ,I3 are the current values in L1, L2, L3 phases.

The network imbalance ratio Iimb is the maximum imbalance current ratio calculated: Iimb = Max (Ii1, Ii2, Ii3).

When the imbalance ratio limb exceeds 40%, the overload relay triggers a trip in 5 +/- 1 s.

Settings

The table below indicates the position of the rotary switch used to enable or disable the phase imbalance protection.

Manual Reset

The phase imbalance protection can be reset manually only. For more information, refer to Trip Reset.