Full-voltage starting, also known as direct starting, is the most commonly used starting method. It involves directly connecting the stator windings of the motor to the power supply and starting the motor at the rated voltage. It features high starting torque and short starting time, and is also the simplest, most economical, and most reliable starting method.
When starting an AC motor, the voltage on the distribution bus should meet the following requirements:
1. Under normal circumstances, when the motor is frequently started, the voltage should not be lower than 90% of the rated voltage; when the motor is not frequently started, the voltage should not be lower than 85% of the rated voltage.
2. When no other electrical equipment is connected to the distribution bus, the starting torque of the motor can be determined according to the condition of ensuring the motor's starting torque; for low-voltage motors, the voltage of the contactor coil should also be ensured to be no lower than the release voltage.
3. When there are no lighting or other loads sensitive to voltage fluctuations connected to the distribution bus, and the motor does not start frequently, the voltage should not be lower than 80% of the rated voltage.
The selection of starting methods for squirrel-cage motors and synchronous motors shall comply with the following provisions:
1. The motor should be started at full voltage when the following conditions are met.
When the motor starts, the voltage of the distribution bus should comply with the provisions of the "General Electrical Equipment Power Distribution Design Code".
The machine can withstand the impact torque during full-pressure starting. The manufacturer does not specify the starting method for the electric motor.
2. When the conditions for full-voltage starting are not met, the motor should be started with reduced voltage, or other appropriate starting methods should be selected.
3. When speed regulation is required, the starting method of the motor should be matched with the speed regulation method.
Advantages and disadvantages of full-voltage starting of electric motor
Full-voltage starting is a commonly used starting method, also known as direct starting. It involves directly connecting the stator windings of the motor to the power supply, starting the motor at its rated voltage. It features high starting torque and short starting time, and is a simple, economical, and reliable starting method. Currently, low-voltage squirrel-cage motors are designed and manufactured with the impact torque and heating conditions of full-voltage starting in mind, considering their mechanical strength and thermal stability. Therefore, as long as the driven equipment can withstand the impact torque of full-voltage starting and the voltage drop caused by starting does not exceed the allowable value, full-voltage starting should be selected.
The disadvantage of full-voltage starting is that the starting current is large, which can be 5 to 8 times the rated current. When the motor power is large and the power supply capacity is small, the starting current of the motor will cause a significant drop in the voltage of the power distribution system, thereby reducing the power supply quality, especially for equipment that is sensitive to voltage fluctuations.
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