With the rapid development of electric vehicle and renewable energy generation, efficient and reliable motors have become the key power core. However, even in the most advanced technology system, the problem of motor phase loss still occurs frequently, which can lead to system efficiency decline, equipment burning and even safety accidents.
The so-called "phase loss" refers to the sudden loss of a phase power supply in the operation of a three-phase motor, which seems to be "one phase less", but actually causes a surge in current and magnetic field imbalance, and the motor is forced to "run with illness" under abnormal conditions.
This problem not only exists in traditional industrial motors, but also occurs frequently in driving motors of electric vehicles, pitch systems of wind turbines, photovoltaic water pumps and other scenarios. If we do not pay attention to it, the lack of phase will become the "invisible killer" of the sudden downtime of high-value equipment. Today, we will deeply analyze the principles, phenomena and coping strategies behind the lack of motor phase, so as to help you prevent trouble in daily operation and maintenance.
Warning: Phase loss operation of the motor is a serious problem, and the motor will burn out soon. Below we will help you understand why it burns the motor and what to do in an easy-to-understand way.
When the phase of the motor is missing, the current and heat will change dramatically:
- Current surge: Three-phase motor relies on three-phase alternating current to form a rotating magnetic field to drive the rotor to rotate. In the absence of a phase of electricity, the magnetic field will not rotate evenly, the torque of the motor will decrease, and the speed will slow down. However, if the load is not changed, the current of the remaining two phases will increase significantly in order to drive the load, usually up to 1.4 to 1.732 times the normal current.
- A sharp increase in heat generation: the amount of heat generated by a conductor is proportional to the square of the current (Q = I²Rt). If the current is doubled, the heat will increase by four times. In case of phase loss, the heating value of the winding can reach 15-50 times of the normal value. This makes the temperature of the motor rise sharply, which will damage the insulation in a short time and eventually burn the motor.
The burnout phenomenon is different due to different motor wiring modes:
- Delta (△) connection: The absence of one phase of power supply usually causes one phase winding to burn out due to overcurrent.
- Wye (Y) connection: When one phase of power supply is missing, the neutral point potential shifts, which often causes the two phase windings to burn out at the same time.
Why phase loss occurs:
The main causes of phase loss of the motor are as follows, and you can check them one by one:
- Power supply problems: phase loss of the power supply line itself (for example, one phase of the fuse is fused), power distribution failure, etc.
- Connection problem: the terminal in the motor junction box is loose, the outgoing line is disconnected, and the connection between the power line and the motor is loose or oxidized.
- Control circuit problems: the contactor, relay and other components in the control circuit contact oxidation, poor contact or burning.
- Problems of the motor itself: the internal winding joints of the motor are poorly soldered or loosened, and the insulation is aged, resulting in the burning of the winding.
How to judge whether the motor is in phase loss:
When the motor is in phase loss operation, some abnormal phenomena usually occur:
- Abnormal sound: The motor makes a low buzzing sound.
- Increased vibration: the vibration is greater than usual when the motor is running.
- Speed drop: the motor speed is obviously slow and weak.
- Overheating: The motor housing is hot and may even smell burnt.
What to do in case of phase loss:
If the phase loss of the motor is suspected or confirmed, stop the motor immediately for inspection:
- Power off check: ensure safety and cut off the power completely.
- Check the power supply: use a multimeter to check whether the three-phase voltage from the power supply to the motor terminal is normal.
- Check connections: Carefully check all wiring terminals and connection points for signs of looseness, oxidation, or burning.
- Check the components: check whether the fuse is in good condition and whether the contactor contact is in good condition.
- Measure the winding: if necessary, measure the winding resistance of the motor to check whether there is an open circuit or serious imbalance.
How to prevent motor burning due to phase loss:
Prevention is far more important than maintenance after the event, and the most effective way is to install a phase loss protection device:
Thermal relay
Ordinary thermal relay has a certain phase protection function, but sometimes the sensitivity is not ideal.
Special phase loss protector
Voltage detection type: It is relatively cheap to monitor whether the three-phase voltage is balanced, but it may not be sensitive to the internal phase loss of the motor.
Current detection type: judge by detecting whether the three-phase current is balanced, which can protect the motor more comprehensively and is a better choice.
Intelligent motor protector
It integrates multiple protection functions such as overload, phase loss, locked-rotor, unbalance, etc., and the protection is more accurate and reliable.
Although motor phase loss is common, it is by no means an unsolvable problem. Especially in the field of electric vehicle, the reliability of motor is closely related to the energy efficiency and operation safety of the whole system.
By installing professional phase loss protector (such as current detection type or intelligent motor protector), combined with regular inspection, fastening connection, condition monitoring and other operation and maintenance means, the risk of phase loss burning can be greatly reduced.
It is worth noting that with the development of Internet of Things and predictive maintenance technology, real-time monitoring of motor current, temperature and vibration has become possible, which also provides a more forward-looking solution for phase loss protection.
In the future, the dual strategy of fusion algorithm early warning and hardware protection will further improve the stability and life of motor operation. Remember, prevention is always more economical and safer than repair.