What is motor unbalance current protection?

The motor unbalance current protection is an important motor protection mechanism
designed to monitor and prevent unbalanced current conditions in motor
operation. Motor unbalanced current refers to the difference between the
three-phase currents of the motor and usually indicates a possible fault or
problem with the motor. The following is a detailed introduction to motor
unbalance current protection:

Reason for unbalanced current

Unbalanced current flow can be caused by a variety of reasons, including:

Faulty Windings: Faults, short circuits, or damage in the motor windings can cause
unbalanced current flow. For example, if the insulation of one winding is damaged, the current may bypass that winding, causing an imbalance.
Power supply problems: Problems in the power supply system, such as uneven
three-phase voltage supply or unstable power supply can also cause unbalanced
current flow in the motor.
Mechanical Problems: Mechanical problems, such as damaged motor bearings or uneven mechanical loading, can also cause unbalanced current flow in the motor.
Starting and stopping: During the starting and stopping process of the motor, an
unbalanced current in the motor may be caused due to various reasons (such as
power supply voltage fluctuation, improper starting time, etc.).

The principle of motor unbalance current protection

The main principle of motor unbalance current protection is to monitor the three-phase current of the motor and take measures to protect the motor when an imbalance is detected. Its working principle is usually based on the following steps:

Current Measurement: Motor unbalance current protection systems use current sensors to measure the current in each phase. These sensors convert current signals into
voltage signals for further processing.
Current comparison: The protection system compares the measured currents of the three phases to determine the differences between them. Usually, the degree of
imbalance is determined by calculating the percentage difference between the
three-phase currents.
Unbalance determination: If the system detects that the current imbalance exceeds the
preset threshold, it will determine that there is an unbalanced current in the
motor and think that a problem may occur.
Protective action of the current unbalance protection: Once an unbalanced current is
detected, the motor protection system triggers a protective action, such as cutting off the power supply or sending an alarm signal. This helps prevent the motor from continuing to run to avoid damage or reduce safety risks.

Applications of motor unbalance current protection

Motor unbalance current protection is widely used in industrial environments that
require motors to operate for long periods of time, especially those applications that require high motor performance and reliability. Here are some
application areas:

Pump and fan systems: Industrial pumps and fans often require continuous operation, and motor unbalanced current protection ensures that they remain balanced during normal operation, improving efficiency and extending motor life.
Manufacturing industry: Various production equipment in the manufacturing industry use motors. Motor unbalance current protection can ensure the reliable operation of the
equipment and reduce downtime.
Transmission and Distribution Systems: In power systems, motor unbalance current protection
prevents motors from operating under unstable or unbalanced power supply
conditions, thereby improving the stability of the grid.
Lifting equipment and transport machinery: Equipment such as elevators, cranes, and conveyor belts often use motors as the driving force source, and unbalanced
current protection ensures that they remain balanced during operation, providing safe and efficient operation.

Recommended motor unbalance current protection relay

Our PR260 unbalance current protection relay for the motor has the function of current unbalance protection. PR260 Current unbalance protection function:

I_im > Threshold set value

Current imbalance protection based on the maximum phase current imbalance to determine whether to
start phase unbalance protection function. Current unbalance is calculated as
follows:

I_max	Maximum phase current in the real-time measurement of three-phase
I_min	Minimum phase current in the real-time measurement of three-phase
I_avg	Three-phase average current

Parameters:

Protect action	OFF / Alarm / Trip DO
Threshold	5 ~ 60%
Action delay	0.1~ 50.0 s

Note:

When the three-phase average current (I_avg) is less than the motor-rated current (Ie), in the formula I_avg = Ie

In summary, motor unbalance current protection is a key motor protection mechanism that can detect and prevent unbalanced currents in motor operation, thereby protecting the motor from damage and improving motor reliability and performance. This is critical in both industrial automation and power systems to ensure the normal operation of equipment and reduce maintenance costs.