Large Induction Motors and Voltage Sag: How Do They Affect Each Other?

Large induction motors are widely used in industrial applications such as metallurgy, petrochemicals, mining, and cement production. They drive critical equipment including pumps, fans, compressors, and mills, making stable motor operation essential to production continuity.

At the same time, large induction motors and voltage sag can affect each other: motor starting may cause voltage sag, while voltage sag can also affect motor stability.

Why Can Large Motors Cause Voltage Sag?

During startup, a large induction motor draws significantly higher current from the power system than during normal operation.

If the grid capacity is limited or the system impedance is relatively high, the increased starting current can produce a larger voltage drop across transformers, cables, and other parts of the power system, resulting in a temporary voltage sag.

Motor starting also requires significant reactive power to establish the magnetic field. If the power system has insufficient reactive power support, the resulting voltage drop may further increase the impact on the distribution system.

Therefore, for industrial facilities with large motors, motor starting should be evaluated not only from the perspective of motor performance, but also in terms of its impact on the overall power system.

How Does Voltage Sag Affect Large Induction Motors?

When voltage sag occurs, the electromagnetic torque of an induction motor decreases as the supply voltage drops. Since motor torque is approximately proportional to the square of voltage, a significant voltage reduction can substantially reduce the motor's ability to maintain its operating condition.

If the voltage sag lasts long enough, the motor speed may decrease and the motor may eventually stall or shut down. For motors driving critical equipment such as mills, compressors, fans, and pumps, such interruptions may affect the operation of the entire production process.

Voltage sag can also affect motor control systems, contactors, protection devices, and other voltage-sensitive equipment, potentially causing unexpected trips or shutdowns.

Therefore, for industrial applications involving large induction motors, voltage sag is not only a power quality issue but also a potential production risk.

How Can the Impact Be Reduced?

A comprehensive approach can be adopted through motor starting optimization, power system improvement, and protection of critical loads.

Soft starters and variable frequency drives can be used for large motors where appropriate to limit starting current and reduce the impact of motor starting on the power system.

For existing voltage sag risks, dynamic voltage compensation can be applied to critical loads. When a voltage sag occurs, the system detects the voltage deviation and rapidly provides compensation to maintain a stable supply for protected equipment.

INPAVC for Voltage-Sensitive Industrial Loads

INPAVC Dynamic Voltage Restorer is connected in series between the power supply and the protected load and continuously monitors the input voltage.

When a voltage sag is detected, INPAVC rapidly injects the required compensating voltage through power electronic conversion technology, helping maintain a stable power supply for critical loads.

For industrial applications such as metallurgy, mining, petrochemicals, and cement production, INPAVC can provide voltage sag protection for large motors and other critical loads, helping reduce the risk of equipment shutdowns and production interruptions.