Star-delta starting is a widely used reduced-voltage starting method for three-phase asynchronous motors, aiming to lower starting current and protect power grids and equipment. However, unexpected motor tripping during this process is a common industrial fault, usually triggered by electrical, mechanical or wiring issues.

The most frequent cause is unreasonable parameter setting.

If the star-delta conversion time is too short, the motor fails to reach enough speed before switching to delta operation, generating a huge impulse current that triggers the circuit breaker or overload relay instantly. Meanwhile, improper overload protection current setting or damaged thermal relays will also lead to false tripping.

Wiring faults are another main trigger.

Reverse phase sequence, loose wiring contacts, damaged contactors or wrong star-delta connection modes cause phase loss, resulting in unbalanced three-phase current and immediate tripping. In addition, aged cables with short circuits or leakage can activate leakage protectors.

Mechanical failures cannot be ignored either.

Motor bearing damage, rotor blockage, excessive mechanical load or stuck transmission equipment make the motor unable to start normally, with sharp current rise and tripping. External factors like unstable grid voltage, low input voltage and excessive voltage drop during starting will also aggravate the fault.

To solve the tripping problem, technicians should first check conversion time, protection parameters and wiring connections, then inspect mechanical load and power supply voltage. Timely troubleshooting ensures stable motor starting and long-term safe operation of the equipment.