The Steps Of Selecting Simo Synchronous Motor

 

3. Simo Synchronous Motor

 

In addition to being able to compensate for reactive power in an overexcited state, the advantages of synchronous motors also include:

1) The speed of the synchronous motor strictly complies with n=60f/p, and the speed can be accurately controlled;

2) High operating stability. When the grid voltage drops suddenly, the excitation system will generally force excitation to ensure stable motor operation, while the asynchronous motor torque (proportional to the square of the voltage) will drop significantly;

3) The overload capacity is greater than that of the corresponding asynchronous motor;

4) High operating efficiency, especially for low-speed synchronous motors.

 

 

Synchronous motors cannot be started directly, and require asynchronous starting or variable frequency starting. Asynchronous starting means that the synchronous motor is equipped with a starting winding similar to the cage winding of the asynchronous motor on the rotor, and an additional resistor about 10 times the resistance of the excitation winding is connected in series in the excitation circuit to form a closed circuit. The stator of the synchronous motor is directly connected to the power grid to start it as an asynchronous motor. When the speed reaches the subsynchronous speed (95%), the additional resistor is cut off. Variable frequency starting is not described in detail. Therefore, one of the disadvantages of synchronous motors is that additional equipment is required for starting.

 

Synchronous motor is operated by excitation current. If there is no excitation, the motor is asynchronous. Excitation is a DC system added to the rotor. Its rotation speed and polarity are consistent with the stator. If there is a problem with the excitation, the motor will lose step and cannot adjust, triggering the protection "excitation fault" motor trip.

 

Therefore, the second disadvantage of synchronous motor is the need to add excitation devices. In the past, it was directly supplied by DC machines, but now it is mostly supplied by thyristor rectifiers. As the old saying goes, the more complex the structure and the more equipment and devices there are, the more fault points there are and the higher the failure rate.According to the performance characteristics of synchronous motors, they are mainly used in loads such as elevators, mills, fans, compressors, rolling mills, and water pumps.

 

 

In summary, the principle of selecting Xi'an Simo motor is to give priority to motors with simple structure, low price, reliable operation and convenient maintenance, provided that the motor performance meets the requirements of production machinery. In this respect, AC motors are better than DC motors, AC asynchronous motors are better than AC synchronous motors, and squirrel cage asynchronous motors are better than winding asynchronous motors.

 

For continuously running production machinery with stable load and no special requirements for starting and braking, ordinary squirrel cage asynchronous motors should be used as a priority. They are widely used in machinery, water pumps, fans, etc. Production machinery that starts and brakes frequently and requires larger starting and braking torques, such as bridge cranes, mine hoists, air compressors, irreversible steel rolling mills, etc., should use wound asynchronous motors.

 

Synchronous motors should be used in situations where there is no requirement for speed regulation, constant speed or improved power factor is required, such as medium and large capacity water pumps, air compressors, elevators, grinders, etc. For production machinery that requires a speed regulation range of more than 1:3 and requires continuous, stable and smooth speed regulation, it is advisable to use separately excited DC motors or squirrel cage asynchronous motors or synchronous motors with variable frequency speed regulation, such as large precision machine tools, gantry planers, rolling mills, elevators, etc. Production machinery that requires large starting torque and soft mechanical characteristics uses series-excited or compound-excited DC motors, such as trams, electric locomotives, heavy cranes, etc.

 

2. Rated power of the motor

 

The rated power of Xi'an Simo motor refers to the output power, that is, the shaft power, also known as the capacity, which is the characteristic parameter of the motor. People often ask how big the motor is, which generally does not refer to the size of the motor, but the rated power. It is the most important indicator to quantify the load capacity of the motor, and it is also a parameter requirement that must be provided when selecting the motor.

(Rated power, is rated voltage, is rated current, cosθ is power factor, η is efficiency)

 

The principle of correctly selecting the motor capacity should be to determine the motor power in the most economical and reasonable way, under the premise that the motor can meet the load requirements of the production machinery. If the power is selected too large, the equipment investment will increase, resulting in waste, and the motor will often run underloaded, and the efficiency and power factor of the AC motor will be low; on the contrary, if the power is selected too small, the motor will run overloaded, causing premature damage to the motor.